Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/022—Site diversity; Macro-diversity
  • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0452—Multi-user MIMO systems
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy

Definitions

• DIDO Distributed-Input-Distributed-Output
• Prior art multi-user wireless systems add complexity and introduce limitations to wireless networks which result in a situation where a given user's experience (e.g. available bandwidth, latency, predictability, reliability) is impacted by the utilization of the spectrum by other users in the area.
• a given user's experience e.g. available bandwidth, latency, predictability, reliability
• the increasing demands for aggregate bandwidth within wireless spectrum shared by multiple users and the increasing growth of applications that can rely upon multi-user wireless network reliability, predictability and low latency for a given user
• prior art multi-user wireless technology suffers from many limitations. Indeed, with the limited availability of spectrum suitable for particular types of wireless communications (e.g. at wavelengths that are efficient in penetrating building walls), prior art wireless techniques will be insufficient to meet the increasing demands for bandwidth that is reliable, predictable and low-latency.
• FIG. 1 illustrates one embodiment of the MU-MAS consists of a centralized processor 101, a network 102 and M transceiver stations 103 communicating wirelessly to N client devices UE1-UE4;
• FIG. 2 illustrates one embodiment consisting of multiple routers or gateways 202 and high-speed wired links 205 that interconnect the centralized processor 201 to 202 as well as routers or gateways 202 among themselves;
• FIG. 3 illustrates one embodiment of the BTS-AP 408 retransmits the streams of bits to multiple BTS-RPs 409 and 410 over point-to-multipoint wireless links;
• FIG. 4 illustrates one embodiment of the BTS-AP 408 retransmits the streams of bits to multiple BTS-RPs 409 and 410 over point-to-multipoint wireless links;
• FIG. 5 illustrates one embodiment of a DIDO system utilized the mesh network
• FIG. 6 illustrates one example of BSN deployment in downtown San Francisco, CA
• FIG. 7 illustrates one embodiment shows two stations downtown San Francisco with point-to-multipoint links. Note that any BTS- P can repeat the signal to other BTS-NPs as well as shown on the left side of that figure;
• FIG. 8 illustrates an exemplary mesh network deployment with nodes distributed around downtown San Francisco
• FIG. 9 illustrates one embodiment of solar panels 901 are connected to the charge controller 902 (the image of a meter is for illustration purposes only, and not a requirement for a charge controller) that charges the battery;
• FIG. 10 illustrates one embodiment of the invention utilizes the rectenna
• FIG. 11 illustrates one embodiment of the rectenna 1001 is combined with the antenna 1007 used for the point-to-point multipoint wireless link to form the receiver;
• FIG. 12 illustrates one embodiment of a typical DIDO network consisting of active BTSs 1201 transmitting streams of bits to the UEs 1203 and inactive BTSs;
• FIG. 13 illustrates one embodiment of all UEs may be moving to the same area
• FIG. 14 illustrates one embodiment of power consumption is not an issue and there are no inactive BTSs in the neighborhood of the UEs that can be turned on, another solution is to increase the transmit power at the BTSs far away from the UE cluster
• DIDO Distributed-Input Distributed-Output
• DIDO Distributed-Input Distributed-Output
• DIDO Distributed-Input-Distributed-Output
• the MU-MAS consists of a centralized processor 101, a network 102 and M transceiver stations 103 communicating wirelessly to N client devices UE1-UE4, as depicted in Figure 1.
• the centralized processor unit 101 receives N streams of information with different network contents (e.g., videos, web-pages, video games, text, voice, etc., streamed from Web servers or other network sources C1-C5) intended for different client devices.
• N streams of information with different network contents (e.g., videos, web-pages, video games, text, voice, etc., streamed from Web servers or other network sources C1-C5) intended for different client devices.
• stream of information to refer to any stream of data sent over the network containing information that can be demodulated or decoded as a standalone stream, according to certain modulation/coding scheme or protocol, to produce certain voice, data or video content.
• the stream of information is a sequence of bits carrying network content that can be demodulated or decoded as a standalone stream.
• the centralized processor 101 utilizes precoding transformation to combine (according to certain algorithm) the N streams of information from the network content C1-C5 into M streams of bits.
• the precoding transformation can be linear (e.g., zero-forcing [22], block-diagonalization [20-21], matrix inversion, etc.) or non-linear (e.g., dirty-paper coding [11- 13] or Tomlinson-Harashima precoding [14-15], lattice techniques or trellis precoding [16-17], vector perturbation techniques [18-19]).
• the stream of bits is the complex baseband signal produced by the centralized processor and quantized over given number of bits to be sent to one of the M transceiver stations 103.
• the MAS is a distributed-input distributed-output (DIDO) system as described in our previous patent applications [0002-0018].
• DIDO system consists of:
• UE User Equipment
• An RF transceiver for fixed or mobile clients 104 receiving data streams over the downlink (DL) channel from the DIDO backhaul and transmitting data to the DIDO backhaul via the uplink (UL) channel
• BTS Base Transceiver Station
• the BTSs 103 interface the DIDO backhaul with the wireless channel.
• BTSs of one embodiment are access points 103 consisting of DAC/ADC and radio frequency (RF) chain to convert the baseband signal to RF.
• RF radio frequency
• the BTS is a simple RF transceiver equipped with power amplifier/antenna and the RF signal is carried to the BTS via RF-over-fiber technology as described in our previous patent applications.
• a CTR is one particular type of BTS 103 designed for certain specialized features such as transmitting training signals for time/frequency synchronization of the BTSs and/or the UEs, receiving transmitting control information from/to the UEs, receiving the channel state information (CSI) or channel quality information from the UEs.
• One or multiple CTR stations can be included in any DIDO system. When multiple CTRs are available, the information to or from those stations are combined to increase diversity and improve link quality.
• the CSI is received from multiple CTRs via maximum ratio combining (MRC) techniques to improve CSI demodulation.
• the control information is sent from multiple CTRs via maximum ratio transmission (MRT) to improve SNR at the receiver side.
• the scope of the invention is not limited to MRC or MRT, and any other diversity technique (such as antenna selection, etc.) can be employed to improve wireless links between CTRs and UEs.
• the CP is a DIDO server 101 interfacing the Internet or other types of external networks with the DIDO backhaul.
• the CP computes the DIDO baseband processing and sends the waveforms to the distributed BTSs for DL transmission
• the BSN is the network 102 connecting the CP 101 to the distributed BTSs 103 carrying information for either the DL or the UL channel.
• the BSN is a wireline or a wireless network or a combination of the two.
• the BSN is a DSL, cable, optical fiber network, or line-of-sight or non-Iine-of-sight wireless link.
• the BSN is a proprietary network, or a local area network, or the Internet. 2.
• the BSN is the wireline network in Figure 2 consisting of multiple routers or gateways 202 and high-speed wired links 205 that interconnect the centralized processor 201 to 202 as well as routers or gateways 202 among themselves.
• the wired links 205 carry the streams of bits to be sent to all the BTSs 204 connected to the same DIDO BSN.
• Routers and gateways are connected to switches or hubs 203 via wired links 206.
• the wired links 206 carry only the streams of bits intended to the BTSs 204 connected to the same switch or hub 203.
• the BTSs 204 send the streams of bits received from the centralized processor 201 simultaneously over the DIDO wireless link in a way that every UE recovers and demodulates its own stream of information.
• the wired links 205 and 206 are comprised of various network technologies including, but not limited to, digital subscriber lines (DSL), cable modems, fiber rings, Tl lines, hybrid fiber coaxial (HFC) networks.
• DSL digital subscriber lines
• cable modems fiber rings
• Tl lines hybrid fiber coaxial
• HyFC hybrid fiber coaxial
• Dedicated fiber typically has very large bandwidth and low latency, potentially less than a millisecond in a local region, but it is less widely deployed than DSL and cable modems.
• Today, DSL and cable modem connections typically have between 10- 25ms in last-mile latency in the United States, but they are very widely deployed.
• the streams of bits sent over the BSN consist of baseband signals from the CP to the BTSs. Assuming each complex sample of the baseband signal is quantized over 32 bits (i.e., 16 for real and 16 for imaginary parts) the total bandwidth requirement for the BSN to operate the BTSs at lOMSample sec (i.e., a 10MHz bandwidth) over the wireless DIDO links is 320Mbps. Typically, only 16 or fewer bits of quantization are enough to represent the baseband signal with negligible error (especially if compression techniques are utilized to reduce the bandwidth requirements), thereby reducing the BSN throughput requirement to 160Mbps or less. In one embodiment of the invention, the DIDO systems use compression techniques to reduce the amount of throughput required over the BSN backhaul.
• DIDO technology has been proven to provide an order of magnitude increase in spectral efficiency over any existing wireless technology. Therefore, it is possible to relax the baseband throughput requirement at the BTS from lOMSample/sec down to 5 Sample/sec or 1 Sample/sec, while providing comparable or higher per-user throughput over the wireless link than any conventional wireless communications systems. Hence, in practical DIDO deployments, the throughput requirement at the BSN can be as low as 16Mbps to every BTS.
• BTS-AP access point
• BTS-RP repeater
• wireless links used for the BSN backhaul are commercially available WiFi bridges operating in the ISM 2.4, 5.8 or 24 GHz bands [1-5], or wireless optics communications such as laser light transmission [6], or any other radio frequency (RF) or optics proprietary system that can provide high-throughput low-latency wireless network connections.
• RF radio frequency
• the BTS-AP 408 retransmits the streams of bits to multiple BTS-RPs 409 and 410 over point-to-multipoint wireless links, as shown in Figure 4.
• the BTS- AP employs the same wireless resource (i.e., same time and same frequency band) for all links to the BTS-RPs, and avoids interference between links by creating very narrow beams (via highly directional antennas or antenna arrays using beamforming techniques). Narrow beams can also be used at the BTS-RPs to improve link quality and reduce interference from other neighbor locations.
• the same wireless resource can be shared between those BTS-RPs via different multiple access techniques such as TDMA, FDMA, OFDMA or CDMA.
• the present invention employs point-to-point or point-to-muitipoint line-of-sight (LOS) links.
• LOS line-of-sight
• the LOS may not be available and the link employs beamforming, MRT, MIMO or other diversity techniques to improve link quality in non-LOS (NLOS) links.
• mesh networks [5,7-9] A practical mesh network in downtown San Francisco, CA has been deployed by Webpass [8] using Wi-Fi transceivers operating in the ISM band that can achieve speeds from 45Mbps up to 200Mbps. As described above, these speeds would be sufficient for carrying the streams of bits from the CP to the BTSs in a practical BSN deployment.
• a DIDO system utilized the mesh network [5,7-8] in Figure 5 to extend coverage to multiple BTSs distributed across a wide area. Every loop of the mesh network comprises of one or multiple BTS-APs to guarantee continuous connection to other BTS-RPs, even in the occurrence of temporary or permanent network failures.
• FIG. 6 One example of BSN deployment in downtown San Francisco, CA, is depicted in Figure 6.
• the circles indicate locations that have access to fiber or other types of high-speed wireline network connections. Some of those locations may be equipped with BTS-APs, or routers and switches using antennas 307 for point-to-point wireless transmission of the streams of bits to other BTSs.
• the solid dots denote BTS-RPs 309, or routers and switches employing antennas 307 to receive the streams of bits and retransmit them over the DIDO wireless links.
• the BTS-AP can also retransmit its own stream of bits wirelessly over the DIDO link, thereby acting as a repeater too.
• one or more of the highest BTS-APs in the BSN broadcast control information to all other DIDO BTSs.
• Control information consists of training sequences or known pilots at given frequency used to recover time and frequency offsets at the BTSs.
• the main BTS-AP sends one training sequence known by all other BTSs, such that those BTSs can estimate time and frequency offsets, and use them for time and frequency synchronization.
• the BTSs do not need any global positioning system (GPS) receiver to keep time and frequency synchronization among each other.
• GPS global positioning system
• the BTS-AP sends streams of bits to the BTS-RPs as opposed to streams of information in cellular systems. Streams of bits are sent over the BSN backhaul in our invention, whereas the streams of information are sent from the tower to the subscribers (i.e., last part of the communications link, following the backhaul) in a cellular system.
• the links from the BTS-AP to every BTS-RP are fixed point-to-point, meaning they use high directional antennas such that interference to other BTS-RPs is removed and the link quality is improved.
• cellular systems transmit energy over the entire cell or sector or part of sector (via beamforming) and avoids interference across clients by using different multiple access techniques (e.g., TDMA, FDMA, OFDMA, CDMA, SDMA).
• BTS-AP When only one BTS-AP is insufficient to serve multiple BTS-RPs spread across a wide area, additional BTS-APs can be used to establish other point-to-point multipoint links to the BTS-RPs.
• Figure 7 shows two stations downtown San Francisco with point- to- multipoint links. Note that any BTS-RP can repeat the signal to other BTS-NPs as well as shown on the left side of that figure.
• FIG. 8 depicts an exemplary mesh network deployment with nodes distributed around downtown San Francisco.
• a few key advantages of the mesh type of architecture are: • Serendipitous deployment: The BTSs can be placed anywhere it is convenient. For the BTS-AP the only requirements are connection to power source and to high-speed wired network. The BTS-RP has no need for network connection, since that can be established wirelessly, and it can be placed anywhere there is roof access available. In contrast, in prior art wireless systems, such as cellular, BTSs are restricted in their physical placement relative to one another and physical obstacles, often resulting in expensive, inconvenient or unsightly placement, or if a required placement is not available resulting in loss of coverage.
• the BTSs can be installed in a serendipitous fashion, it is realistic to assume that from almost any location around the service area it is possible to find at least one BTS connected to the mesh network. Hence, when installing a new BTS-RP there is good chances to find other BTS-RPs or BTS-APs in that neighborhood to access the mesh network. Likewise, any UE at a give location can see at least one or more BTSs to deliver its stream of information.
• the BSN is a serendipitous network where its nodes (e.g., BTS, BTS-AP or BTS-RP) are installed wherever it is convenient.
• nodes e.g., BTS, BTS-AP or BTS-RP
• the convenience of installation of the BTSs in the network is evaluated based on:
• BTSs • whether it is feasible to obtain authorization to install BTSs in certain special locations (e.g., rooftops, power poles, light poles, monuments) or there is any restriction imposed by FCC emission limits;
• Some embodiments discussed herein and in the related patents and applications require: i) access to a wireline network connection; ii) a power outlet. Removing these two requirements can significantly simplify the installation and maintenance of BTSs making the DIDO network more serendipitous. As discussed above, it is possible to remove the first requirement by utilizing BTS-AP and BTS-RP to create point-to-point multipoint wireless links. To eliminate the second requirement, embodiments of the invention provide two solutions: i) exploiting solar power; ii) employing wireless power transfer.
• solar panels 901 are connected to the charge controller 902 (the image of a meter is for illustration purposes only, and not a requirement for a charge controller) that charges the battery 903, as shown in Figure 9.
• the battery provides DC current to the BTS 905 via the inverter 904, that converts the battery voltage to the voltage defined by the specs of the BTS. For example, if the BTS accepts input voltage of 6V and the battery provides 12V, the inverter converts 12V into 6V.
• the BTS is equipped with the antenna 906 to transmit and receive radio waves to/from the UEs via the wireless DIDO link.
• the BTS is connected to another antenna 907 that provides network connectivity via the point-to- point multipoint wireless link.
• the antennas 906 and 907 can be tuned at the same frequency or different frequencies, depending on the part of the spectrum used for the two different types of links.
• the DIDO link to antenna 906 can be designed to operate at VHF or UHF
• the point-to-point multipoint link to antenna 907 may use the ISM band at microwaves (i.e., 5.8GHz for WiFi).
• those links are not limited to any particular frequency of operation.
• the BTS draws 3 Amps (A) of current at 6VDC input voltage to transmit 1W over the wireless link, with less that 10% efficiency (i.e., accounting for power loss in the circuitry and use of class A linear power amplifiers, which are typically very inefficient).
• the battery is rated for 60Ah, the presently preferred embodiment would discharge it only down to 50% (or 30Ah) to preserve its lifespan. Then, it would take approximately 10 hours to discharge the battery down to 50%, when the BTS is continuously powered on and operating at 1W of radiated power.
• Typical commercially available solar panels operate with efficiency of about 20% to produce about 12W/ft 2 .
• the total power produced by the solar panel 901 is 60W, Since the battery voltage is typically 12VDC, the solar panel 901 provides 5 A of current to the battery through the charge controller. Hence it would take approximately 6 hours to recharge the battery from 50% to a 100% full charge with that solar panel.
• This is a typical example of a self-sustained system, where the charging rate is faster than the discharging rate. Note that a short charging rate and long discharging rate is particularly convenient for night operation, when the solar panel is inactive due to the lack of sunlight.
• multiple batteries and a switch are used to switch across different batteries, allowing independent charging/discharging cycles throughout the day and maintaining consistent power supply during the night hours.
• wireless power transfer Another embodiment of the invention utilizes the rectenna 1001 in Figure 10 to provide DC current to the battery 1003 through the charge controller 1002.
• the wireless power is transmitted to the rectenna 1001 via a highly directional antenna at a different location.
• the wireless power transmitter is one or more BTS-APs with highly directional antennas to form a very narrow beam aimed to the location of the rectenna 1001.
• the rectenna 1001 itself is equipped with a highly directional antenna to increase the amount of received power.
• the rectenna 1001 is combined with the antenna 1007 used for the point-to-point/multipoint wireless link to form the receiver 1107 shown in Figure 11.
• This is a compact design where the same antenna 1107 is used to demodulate digital content coming from the wireless network as well as storing power to feed the battery and so the BTS.
• FIG. 12 shows a typical DIDO network consisting of active BTSs 1201 transmitting streams of bits to the UEs 1203 and inactive BTSs 1202 that are connected to the BSN but are not transmitting any data over the wireless link.
• the circle around the active BTSs indicate their coverage area.
• the UEs are uniformly distributed around the given area and the CP has activated all BTSs in the proximity of the UEs to guarantee good coverage.
• the distribution of the UEs may change.
• the CP recognizes the change in UE d stributions and activates the BTSs in closer proximity to the UEs, while setting the others in standby.
• the CP determines the pathloss from every BTSs to every UE base on the CSI feedback or any training or other control information sent from the UEs to the BTSs via the uplink wireless channel. Note that the number of active BTSs is kept constant as the UE configuration changes over time to guarantee there are enough degrees of freedom over the wireless link to create parallel non-interfering channels to all UEs.
• the active BTSs are not set to standby as the UE distribution changes, thereby guaranteeing better coverage at the expense of more power consumption and higher computational complexity at the CP.
• This invention relates generally to the field of communication systems. More particularly, the invention relates to a system and method for distributed input-distributed output wireless communications using space-time coding techniques.
• MIMO Multiple Access
• Input Multiple Output because several antennas are used on each end. By using multiple antennas to send and receive, multiple independent radio waves may be transmitted at the same time within the same frequency range.
• MIMO technology is based on the use of spatially distributed antennas for creating parallel spatial data streams within a common frequency band.
• the radio waves are transmitted in such a way that the individual signals can be separated at the receiver and demodulated, even though they are transmitted within the same frequency band, which can result in multiple statistically independent (i.e. effectively separate) communications channels.
• ⁇ can rely on uncorrected or weakly-correlated multi-path signals to achieve a higher throughput and improved signal-to-noise ratio within a given frequency band.
• Airgo Networks was recently able to achieve 108 Mbps in the same spectrum where a conventional 802.11 g system can achieve only 54 Mbps (this is described on Airgo' website, currently at http://www.airgonetworks.com).
• MIMO systems typically face a practical limitation of fewer than 10 antennas per device (and therefore less than 10X throughput improvement in the network) for several reasons:
• MIMO antennas on a given device must have sufficient separation between them so that each receives a statistically independent signal.
• MIMO bandwidth improvements can be seen with antenna spacing of even one-sixth wavelength ( ⁇ /6), the efficiency rapidly deteriorates as the antennas get closer, resulting in lower MIMO bandwidth multipliers.
• the antennas typically must be made smaller, which can impact bandwidth efficiency as well.
• the physical size of a single ⁇ device can become unmanageable.
• An extreme example is in the HF band, where MEMO device antennas may have to be separated from each other by 10 meters or more.
• MIMO-type technology is a virtual antenna array.
• Such a system is proposed in a research paper presented at European Cooperation in the field of Scientific and Technical Research, EURO-COST, Barcelona, Spain, Jan 15-17, 2003: Center for
• Virtual antenna arrays are systems of cooperative wireless devices (such as cell phones), which communicate amongst each other (if and when they are near enough to each other) on a separate communications channel than their primary communications channel to the their base station so as to operate cooperatively (e.g. if they are GSM cellular phones in the UHF band, this might be a 5 GHz Industrial Scientific and Medical (ISM) wireless band).
• This allows single antenna devices, for example, to potentially achieve MIMO-like increases in bandwidth by relaying information among several devices in range of each other (in addition to being in range of the base station) to operate as if they are physically one device with multiple antennas.
• a method comprising: transmitting a training signal from each antenna of a base station to each of a plurality of client devices utilizing tropospheric scatter, each of the client devices analyzing each training signal to generate channel characterization data, and transmitting the channel characterization data back to the base station utilizing tropospheric scatter; storing the channel characterization data for each of the plurality of client devices; receiving data to be transmitted to each of the client devices; and precoding the data using the channel characterization data associated with each respective client device to generate precoded data signals for each antenna of the base station; and transmitting the precoded data signals through each antenna of the base station to each respective client device.
• FIG. 1 illustrates a prior art MIMO system.
• FIG. 2 illustrates an N-antenna Base Station communicating with a plurality of Single- antenna Client Devices.
• FIG. 3 illustrates a three Antenna Base Station communicating with three Single- Antenna Client Devices
• FIG. 4 illustrates training signal techniques employed in one embodiment of the invention.
• FIG. 5 illustrates channel characterization data transmitted from a client device to a base station according to one embodiment of the invention.
• FIG. 6 illustrates a Multiple-Input Distributed-Output ("MIDO") downstream transmission according to one embodiment of the invention.
• MISO Multiple-Input Distributed-Output
• FIG.7 illustrates a Multiple-Input Multiple Output (“MIMO") upstream transmission according to one embodiment of the invention.
• MIMO Multiple-Input Multiple Output
• FIG. 8 illustrates a base station cycling through different client groups to allocate bandwidth according to one embodiment of the invention.
• FIG. 9 illustrates a grouping of clients based on proximity according to one embodiment of the invention.
• FIG. 10 illustrates an embodiment of the invention employed within an NVIS system.
• FIG. 11 illustrates an embodiment of the invention employing the use of troposphenc scatter.
• FIG. 12 illustrates a prior art tropospheric scatter transmission system.
• FIG. 13 illustrates an embodiment of the invention employing the use of a tropospheric scatter transmission system over a coverage area.
• FIG. 14 illustrates a Direct Broadcast Satellite dish and RF signal paths in an embodiment of the invention.
• FIG. 15 illustrates an embodiment of the invention employing the use of conventional MIMO with tropospheric scatter.
• Figure 16 illustrates an overhead view of a coverage area surrounded by 12 clusters of 3 antennas.
• Figures 17a-c illustrates 3 client antennas in a coverage area from different elevation views.
• Figure 1 shows a prior art ⁇ ⁇ system with transmit antennas 104 and receive antennas 105.
• Such a system can achieve up to 3X the throughput that would normally be achievable in the available channel.
• There are a number of different approaches in which to implement the details of such a MIMO system which are described in published literature on the subject, and the following explanation describes one such approach.
• each of the transmit antennas 104 receives each training signal and converts it to baseband.
• the baseband signal is converted to digital by a D/A converter (not shown), and the signal processing subsystem 107 characterizes the training signal.
• Each signal's characterization may include many factors including, for example, phase and amplitude relative to a reference internal to the receiver, an absolute reference, a relative reference, characteristic noise, or other factors.
• Each signal's characterization is typically defined as a vector that characterizes phase and amplitude changes of several aspects of the signal when it is transmitted across the channel. For example, in a quadrature amplitude modulation ("QAM”)-modulated signal the QAM signal-modulated signal.
• QAM quadrature amplitude modulation
• OFDM orthogonal frequency division multiplexing
• the signal processing subsystem 107 stores the channel characterization received by each receiving antenna 105 and corresponding receiver 106. After all three transmit antennas 104 have completed their training signal transmissions, then the signal processing subsystem 107 will have stored three channel characterizations for each of three receiving antennas 105, resulting in a 3x3 matrix 108, designated as the channel characterization matrix, "H.” Each individual matrix element 3 ⁇ 4 is the channel characterization (which is typically a vector, as described above) of the training signal transmission of transmit antenna 104 i as received by the receive antenna 105 j.
• the signal processing subsystem 107 inverts the matrix H 108, to produce H "1 , and awaits transmission of actual data from transmit antennas 104. Note that various prior art MIMO techniques described in available literature, can be utilized to ensure that the H matrix 108 can be inverted.
• a payload of data to be transmitted is presented to the data Input subsystem 100. It is then divided up into three parts by splitter 101 prior to being presented to coding and modulation subsystem 102. For example, if the payload is the ASCII bits for "abcdef,” it might be divided up into three sub-payloads of ASCII bits for "ad,” “be,” and “cf" by Splitter 101. Then, each of these sub-payloads is presented individually to the coding and modulation subsystem 102.
• Each of the sub-payloads is individually coded by using a coding system suitable for both statistical independence of each signal and error correction capability. These include, but are not limited to Reed-Solomon coding, Viterbi coding, and Turbo Codes. Finally, each of the
• each of the receiving antennas 105 will receive a different combination of the three transmitted signals from antennas 104.
• Each signal is received and converted down to baseband by each RF receiver 106, and digitized by an A/D converter (not shown). If y n is the signal received by the nth receive antenna 105, and jc n is the signal transmitted by nth transmit antenna 104, and N is noise, this can be described by the following three equations.
• V3 Xl Hi3 + J3 ⁇ 4 H 23 + ⁇ 3 ⁇ 4 H 33 + N
• FIG. 2 illustrates one embodiment of the invention in which a Base Station 200 is configured with a Wide Area Network, interface (e.g. to the Internet through a Tl or other high speed connection) 201 and is provisioned with a number (n) of antennas 202.
• a Base Station 200 is configured with a Wide Area Network, interface (e.g. to the Internet through a Tl or other high speed connection) 201 and is provisioned with a number (n) of antennas 202.
• Client Devices 203-207 each with a single antenna, which are served wirelessly from the Base Station 200.
• Client Devices 203- 207 that are wireless- network equipped personal computers
• this architecture will apply to a large number of applications, both indoor and outdoor, where a Base Station is serving wireless clients.
• the Base Station could be based at a cellular phone tower, or on a television broadcast tower.
• the Base Station 200 is positioned on the ground and is configured to transmit upward at HF frequencies (e.g., frequencies up to 24MHz) to bounce signals off the ionosphere as described in co-pending application entitled SYSTEM AND
• the Base Station 200 is positioned on the ground and is configured to transmit at angle into the troposphere using tropospheric scatter
• the Base Station 200 and Client Devices 203-207 set forth above are for the purpose of illustration only and are not required for complying with the underlying principles of the invention.
• the Base Station may be connected to a variety of different types of wide area networks via WAN interface 201 including application- specific wide area networks such as those used for digital video distribution.
• the Client Devices may be any variety of wireless data processing and/or communication devices including, but not limited to cellular phones, personal digital assistants ("PDAs”), receivers, and wireless cameras.
• PDAs personal digital assistants
• the Base Station's n Antennas 202 are separated spatially such that each is transmitting and receiving signals which are not spatially correlated, just as if the Base Station was a prior art MEMO transceiver.
• ⁇ /6 i.e. 1/6 wavelength
• ⁇ /2 the further apart these Base Station antennas are placed, the better the system performance, and ⁇ /2 is a desirable minimum.
• the underlying principles of the invention are not limited to any particular separation between antennas.
• a single Base Station 200 may very well have its antennas located very far apart.
• the antennas may be 10 meters apart or more (e.g., in an
• one embodiment of the invention polarizes the signal in order to increase the effective bandwidth of the system.
• Increasing channel bandwidth through polarization is a well known technique which has been employed by satellite television providers for years.
• Using polarization it is possible to have multiple (e.g., three) Base Station antennas very close to each other, and still be not spatially correlated.
• conventional RF systems usually will only benefit from the diversity of two dimensions (e,g. jc and y) of polarization, the architecture descried herein may further benefit from the diversity of three dimensions of polarization (x, y and z).
• FIG 3 provides additional detail of one embodiment of the Base Station 200 and Client Devices 203-207 shown in Figure 2.
• the Base Station 300 is shown with only three antennas 305 and only three Client Devices 306-308. It will be noted, however, that the embodiments of the invention described herein may be implemented with a virtually unlimited number of antennas 305 (i.e., limited only by available space and noise) and Client Devices 306-308.
• Figure 3 is similar to the prior art ⁇ architecture shown in Figure 1 in that both have three antennas on each sides of a communication channel.
• a notable difference is that in the prior art MIMO system the three antennas 105 on the right side of Figure 1 are all a fixed distance from one another (e.g., integrated on a single device), and the received signals from each of the antennas 105 are processed together in the Signal Processing subsystem 107.
• the three antennas 309 on the right side of the diagram are each coupled to a different Client Device 306-308, each of which may be distributed anywhere within range of the Base Station 305. As such, the signal that each Client Device receives is processed
• FIG. 29 06181.P514X independently from the other two received signals in its Coding, Modulation, Signal Processing subsystem 311.
• Figure 3 illustrates a Multiple Input (i.e. antennas 309) Distributed Output (i.e. antennas 305) system, referred to hereinafter as a "MIDO" system.
• each MIDO Client Device 306-308 requires only a single receiving antenna, whereas with MIMO, each Client Device requires as least as many receiving antennas as the bandwidth multiple that is hoped to be achieved. Given that there is usually a practical limit to how many antennas can be placed on a Client Device (as explained in the B ckground), this typically limits MEMO systems to between four to ten antennas (and 4X to 10X bandwidth multiple).
• each antenna is equipped with a transceiver 304 and a portion of the processing power of a Coding, Modulation, and Signal Processing section 303.
• each Client Device 306-308 no matter how much Base Station 300 is expanded, each Client Device 306-308 only will require one antenna 309, so the cost for an individual user Client Device 306-308 will be low, and the cost of Base Station 300 can be shared among a large base of users.
• the channel is characterized.
• a training signal is transmitted (in the embodiment herein described), one-by-one, by each of the antennas 405.
• Figure 4 illustrates only the first training signal transmission, but with three antennas 405 there are three separate transmissions in total.
• Each training signal is generated by the Coding, Modulation, and Signal Processing subsystem 403, converted to analog through a D/A converter, and transmitted as RF through each RF Transceiver 404.
• Various different coding, modulation and signal processing techniques may be employed including, but not limited to, those described above (e.g., Reed Solomon, Viterbi coding; QAM, DPSK, QPSK modulation, . . , etc).
• Each Client Device 406-408 receives a training signal through its antenna 409 and converts the training signal to baseband by Transceiver 410.
• An A/D converter (not shown) converts the signal to digital where is it processed by each Coding, Modulation, and Signal Processing subsystem 411.
• Signal characterization logic 320 then characterizes the resulting signal (e.g., identifying phase and amplitude distortions as described above) and stores the characterization in memory. This characterization process is similar to that of prior art ⁇ systems, with a notable difference being that the each client device only computes the characterization vector for its one antenna, rather than for n antennas.
• the Coding Modulation and Signal Processing subsystem 420 of client device 406 is initialized with a known pattern of the training signal (either at the time of manufacturing, by receiving it in a transmitted message, or through another initialization process).
• Coding Modulation and Signal Processing subsystem 420 uses correlation methods to find the strongest received pattern of the training signal, it stores the phase and amplitude offset, then it subtracts this pattern from the received signal.
• it finds then second strongest received pattern that correlates to the training signal it stores the phase and amplitude offset, then it subtracts this second strongest pattern from the received signal. This process continues until either some fixed number of phase and amplitude offsets are stored (e.g.
• Coding Modulation and Signal Processing subsystems for Client Devices 407 and 408 implement the same processing to produce their vector elements 3 ⁇ 4i and 3 ⁇ 4i.
• the memory in which the characterization is stored may be a non-volatile memory such as a Flash memory or a hard drive and/or a volatile memory such as a random access memory (e.g., SDRAM, RDAM).
• a non-volatile memory such as a Flash memory or a hard drive
• a volatile memory such as a random access memory (e.g., SDRAM, RDAM).
• different Client Devices may concurrently employ different types of memories to store the characterization information (e.g., PDA's may use Flash memory whereas notebook computers may use a hard drive).
• PDA's may use Flash memory whereas notebook computers may use a hard drive).
• the underlying principles of the invention are not limited to any particular type of storage mechanism on the various Client Devices or the Base Station.
• each Client Device 406- 408 since each Client Device 406- 408 has only one antenna, each only stores a 1x3 column 413-415 of the H matrix.
• Figure 4 illustrates the stage after the first training signal transmission where the first row of 1x3 columns 413-415 has been stored with channel characterization information for the first of the three Base Station antennas 405. The remaining two columns are stored following the channel
• the three training signals are transmitted at separate times. If the three training signal patterns are chosen such as not to be correlated to one another, they may be transmitted simultaneously, thereby reducing training time.
• each Client Device 506-508 transmits back to the Base Station 500 the 1x3 column 513-515 of matrix H that it has stored. To the sake of simplicity, only one Client Device 506 is illustrated transmitting its characterization information in Figure 5.
• An appropriate modulation scheme e.g. DPSK,
• P5I4X 64QAM, OFDM for the channel combined with adequate error correction coding (e.g. Reed Solomon, Viterbi, and/or Turbo codes) may be employed to make sure that the Base Station 500 receives the data in the columns 513-515 accurately.
• error correction coding e.g. Reed Solomon, Viterbi, and/or Turbo codes
• the Coding, Modulation and Signal Processing subsystem 503 of Base Station 500 receives the 1x3 column 513- 15, from each Client Device 507-508, it stores it in a 3x3 H matrix 516.
• the Base Station may employ various different storage technologies including, but not limited to non-volatile mass storage memories (e.g., hard drives) and/or volatile memories (e.g., SDRAM) to store the matrix 516.
• Figure 5 illustrates a stage at which the Base Station 500 has received and stored the 1x3 column 513 from Client Device 509.
• the 1 3 columns 514 and 515 may be transmitted and stored in H matrix 516 as they are received from the remaining Client Devices, until the entire H matrix 516 is stored.
• a MIDO transmission from a Base Station 600 to Client Devices 606-608 will now be described with reference to Figure 6. Because each Client Device 606-608 is an independent device, typically each device is receiving a different data transmission. As such, one embodiment of a Base Station 600 includes a Router 602 communicatively positioned between the WAN Interface 601 and the Coding, Modulation and Signal Processing subsystem 603 that sources multiple data streams (formatted into bit streams) from the WAN interface 601
• the three bit streams, u ⁇ - u 3 , shown in Figure 6 are then routed into the Coding, Modulation and Signal Processing subsystem 603 and coded into statistically distinct, error correcting streams (e.g. using Reed Solomon, Viterbi, or Turbo Codes) and modulated using an appropriate modulation scheme for the channel (such as DPSK, 64QAM or OFDM).
• error correcting streams e.g. using Reed Solomon, Viterbi, or Turbo Codes
• an appropriate modulation scheme for the channel such as DPSK, 64QAM or OFDM.
• the embodiment illustrated in Figure 6 includes signal precoding logic 630 for uniquely coding the signals transmitted from each of the antennas 605 based on the signal characterization matrix 616.
• the precoding logic 630 multiplies the three bit streams « t - u 3 in Figure 6 by the inverse of the H matrix 616, producing three new bit streams, w u ' 3 .
• the three preceded bit streams are then converted to analog by D/A converters (not shown) and transmitted as RF by Transceivers 604 and antennas 605.
• each u contains the data from one of the three bit streams routed by the Router 602, and each such bit stream is intended for one of the three Client Devices 606-608.
• each «i is received at each Client Device antenna 609 (plus whatever noise N there is in the channel).
• the output of each of the three antennas 605 is a
• each i is calculated by the precoding logic 630 within the Coding, Modulation and Signal Processing subsystem 603 by implementing the following formulas:
• V 3 UiH ⁇ i + U 2 H " ' 3 2 + 3 H " '33
• each j 3 ⁇ 4 is calculated at the receiver after the signals have been transformed by the channel
• the embodiments of the invention described herein solve for each Vj at the transmitter before the signals have been transformed by the channel.
• Each antenna 609 receives u ⁇ already separated from the other bit streams intended for the other antennas 609.
• Each Transceiver 610 converts each received signal to baseband, where it is digitized by an A/D converter (now shown), and each Coding, Modulation and Signal Processing subsystem 611 , demodulates and decodes the j3 ⁇ 4 bit stream intended for it, and sends its bit stream to a Data Interface 612 to be used by the Client Device (e.g., by an application on the client device).
• the embodiments of the invention described herein may be implemented using a variety of different coding and modulation schemes. For example, in an OFDM implementation, where the frequency spectrum is separated into a plurality of sub-bands, the techniques described herein may be employed to characterize each individual sub-band. As mentioned above, however, the underlying principles of the invention are not limited to any particular modulation scheme.
• the Channel characterization matrix 616 at the Base Station is continually updated.
• the Base Station 600 periodically (e.g., every 250 milliseconds) sends out a new training signal to each Client Device, and each Client Device
• 35 06181.P514X continually transmits its channel characterization vector back to the Base Station 600 to ensure that the channel characterization remains accurate (e.g. if the environment changes so as to affect the channel or if a Client Device moves).
• the training signal is interleaved within the actual data signal sent to each client device.
• the training signals are much lower bandwidth than the data signals, so this would have little impact on the overall throughput of the system.
• the channel characterization matrix 616 may be updated continuously as the Base Station actively communicates with each Client Device, thereby maintaining an accurate channel characterization as the Client Devices move from one location to the next or if the environment changes so as to affect the channel.
• One embodiment of the invention illustrated in Figure 7 employs MHvlO techniques to improve the upstream communication channel (i.e., the channel from the Client Devices 706-708 to the Base Station 700).
• the channel from each of the Client Devices is continually analyzed and characterized by upstream channel characterization logic 741 within the Base Station. More specifically, each of the Client Devices 706-708 transmits a training signal to the Base Station 700 which the channel characterization logic 741 analyzes (e.g., as in a typical MLMO system) to generate an JV x channel characterization matrix 741, where N is the number of Client Devices and M is the number of antennas employed by the Base Station.
• the embodiment illustrated in Figure 7 employs three antennas 705 at the Base Station and three Client Devices 706-608, resulting in a 3x3 channel characterization matrix 741 stored at the Base Station 700.
• the MIMO upstream transmission illustrated in Figure 7 may be used by the Client Devices both for transmitting data back to the Base Station 700, and for transmitting channel characterization vectors back to the Base Station 700 as illustrated in Figure 5. But unlike the embodiment illustrated in Figure 5 in which each Client Device's channel characterization vector is transmitted at a separate time, the method shown in Figure 7 allows for the
• each signal's characterization may include many factors including, for example, phase and amplitude relative to a reference internal to the receiver, an absolute reference, a relative reference, characteristic noise, or other factors.
• the characterization might be a vector of the phase and amplitude offsets of several multipath images of the signal.
• QAM quadrature amplitude modulation
• OFDM orthogonal frequency division multiplexing
• the training signal may be generated by each Client Device's coding and modulation subsystem 711, converted to analog by a D/A converter (not shown), and then converted from baseband to RF by each Client Device's transmitter 709. hi one embodiment, in order to ensure that the training signals are synchronized, Client Devices only transmit training signals when requested by the Base Station (e.g., in a round robin manner). In addition, training signals may be interleaved within or transmitted concurrently with the actual data signal sent from each client device. Thus, even if the Client Devices 706-708 are mobile, the training signals may be continuously transmitted and analyzed by the upstream channel characterization logic 741, thereby ensuring that the channel characterization matrix 741 remains up-to-date.
• the total channel bandwidth supported by the foregoing embodiments of the invention may be defined as tnin (N, M) where N is the number of Client Devices and M is the number of Base Station antennas. That is, the capacity is limited by the number of antennas on either the Base Station side or the Client side.
• one embodiment of the invention employs synchronization techniques to ensure that no more than min (N, M) antennas are transmitting receiving at a given time.
• the number of antennas 705 on the Base Station 700 will be less than the number of Client Devices 706-708.
• An exemplary scenario is illustrated in Figure 8 which shows five Client Devices 804-808 communicating with a base station having three antennas 802.
• the Base Station 800 selects the two Client Devices 807, 808 which were not included in the first group. In addition, because an extra antenna is available, the Base Station 800 selects an additional client device 806 included in the first group. In one embodiment, the Base Station 800 cycles between groups of clients in this manner such that each client is effectively allocated the same amount of bandwidth over time. For example, to allocate bandwidth evenly, the Base Station may subsequently select any combination of three Client Devices which excludes Client Device 806 (i.e., because Client Device 806 was engaged in communication with the Base Station for the first two cycles).
• the Base Station may employ the foregoing techniques to transmit training signals to each of the Client Devices and receive training signals and signal characterization data from each of the Client Devices.
• Client Devices or groups of client devices may be allocated different levels of bandwidth. For example, Client Devices may be prioritized such that relatively higher priority Client Devices may be guaranteed more communication cycles (i.e., more bandwidth) than relatively lower priority client devices.
• the "priority" of a Client Device may be selected based on a number of variables including, for example, the designated level of a
• the Base Station dynamically allocates bandwidth based on the Current Load required by each Client Device. For example, if Client Device 804 is streaming live video and the other devices 805-808 are performing non-real time functions such as email, then the Base Station 800 may allocate relatively more bandwidth to this client 804. It should be noted, however, that the underlying principles of the invention are not limited to any particular bandwidth allocation technique.
• the Base Station will receive and store effectively equivalent channel characterization vectors for the two Client Devices 907, 908 and therefore will not be able to create unique, spatially distributed signals for each Client Device. Accordingly, in one embodiment, the Base Station will ensure that any two or more Client Devices which are in close proximity to one another are allocated to different groups.
• the Base Station 900 first communicates with a first group 910 of Client Devices 904, 905 and 908; and then with a second group 911 of Client Devices 905, 906, 907, ensuring that Client Devices 907 and 908 are in different groups.
• the Base Station 900 communicates with both Client Devices 907 and 908 concurrently, but multiplexes the communication channel using known channel multiplexing techniques.
• the Base Station may employ time division multiplexing ('TDM”), frequency division multiplexing (“FDM”) or code division multiplexing
• CDMA Code Division Multiple Access
• each Client Device described above is equipped with a single antenna
• the underlying principles of the invention may be employed using Client Devices with multiple antennas to increase throughput.
• a client with 2 antennas will realize a 2x increase in throughput
• a client with 3 antennas will realize a 3x increase in throughput, and so on (i.e., assuming that the spatial and angular separation between the antennas is sufficient).
• the Base Station may apply the same general rules when cycling through Client Devices with multiple antennas. For example, it may treat each antenna as a separate client and allocate bandwidth to that "client" as it would any other client (e.g., ensuring that each client is provided with an adequate or equivalent period of communication).
• one embodiment of the invention employs the MIDO and/or M1MO signal transmission techniques described above to increase the signal-to-noise ratio and transmission bandwidth within a Near Vertical Incidence Skywave (“NVIS") system.
• NVIS Near Vertical Incidence Skywave
• a first NVIS station 1001 equipped with a matrix of N antennas 1002 is configured to communicate with client devices 1004.
• the NVIS antennas 1002 and antennas of the various client devices 1004 transmit signals upward to within about 15 degrees of vertical in order to achieve the desired NVIS and minimize ground wave interference effects.
• the antennas 1002 and client devices 1004 support multiple independent data streams 1006 using the various MIDO and MEMO techniques described above at a designated frequency within the NVIS spectrum (e.g., at a carrier frequency at or below 23 MHz, but typically below 10 MHz), thereby significantly increasing the bandwidth at the designated frequency (i.e., by a factor proportional to the number of statistically independent data streams).
• the NVIS antennas serving a given station may be physically very far apart from each other. Given the long wavelengths below 10 MHz and the long distance traveled for the signals (as much as 300 miles round trip), physical separation of the antennas by 100s of yards, and even miles, can provide advantages in diversity. In such situations, the individual antenna signals may be brought back to a centralized location to be processed using conventional wired or wireless communications systems. Alternatively, each antenna can have a local facility to process its signals, then use conventional wired or wireless communications systems to communicate the data back to a centralized location. In one embodiment of the invention, NVIS Station 1001 has a broadband link 1015 to the Internet 1010 (or other wide area network), thereby providing the client devices 1003 with remote, high speed, wireless network access.
• the Internet 1010 or other wide area network
• one embodiment of the invention employs the MIDO and/or MIMO signal transmission techniques described above (collective referred to heretofore as "DIDO") to increase the signal-to-noise ratio and transmission bandwidth within a tropospheric scatter (“troposcatter”) system.
• DIDO tropospheric scatter
• a first troposcatter station 1101 equipped with a matrix of N antennas 1102 is configured to communicate with M client devices 1104.
• the upward angle of transmission is exaggerated for illustration purposes in Figure 11. A more typical low angle for troposcatter transmission is shown in prior art Figure 12.
• the antennas of the various client devices 1104 transmit signals back through tropospheric scatter, and they are received by base station antennas 1102.
• the troposcatter base station antennas 1102 are aimed at an upward angle so that part of the transmission scatters and reflects off the troposphere so as to hit the target area where the M client devices 1 104 are located.
• Calculating specific antenna elevation angles and optimizing antennas for troposcatter is well understood to those skilled in the art, and several online calculators exist for making such calculations. As an example, one such calculator can be downloaded at htt :/ home.planet.n l/ ⁇ alphe078/propagat 1.htm . This particular troposcatter
• P514X calculator's input parameters include distance between the transmit and receive antennas, transmission frequency, antenna heights, output power, station noise characteristics, obstacle distance/heights, antenna gain, and bandwidth.
• An exemplary prior art troposcatter radio terminal i.e. transceiver and antenna
• the system has a nominal transmission range of 100 miles. Such a system typically transmits less than 1 Mbps.
• Newer troposcatter modems such as the General Dynamics and Radyne Corporation TM-20 modem can achieve up to 20 Mbps. But, both systems only can achieve such data rates with a single data stream in a given channel,
• the antennas 1102 and client devices 1104 support multiple independent data streams 1106 using the various DIDO techniques described herein at a designated frequency within the troposcatter spectrum (e.g., at a carrier frequency from below 50 MHz to above 10 GHz).
• DIDO techniques include, but are not limited to, the transmission of training signals, the characterization of the channel vectors, and the transmission back to the troposcatter base station 1101 of the channel vectors so as to form a channel matrix,
• the troposcatter antennas served by a given troposcatter base station 1101 may be close (e.g. as close as ⁇ /6) or physically very far apart (10s or 100s of miles) from each other and/or they may be clustered in groups.
• the term "troposcatter base station 1101" as used herein refers to a common channel matrix computation system, similar to Figure 2's Base Station 200, but one in which the transmitting antennas 1102 may in fact be distributed very far from a given site.
• the specific configuration will depend on the desired coverage area, the need to avoid obstacles in the terrain, and if necessary, the need to achieve more diversity and or a wider angle between transmit antennas.
• a DIDO base station by utilizing channel state information feedback from the client devices after sending training signals, will produce a
• troposcatter Station 1101 has a broadband link
• the troposcatter base station antennas 1102 and the client device antennas 1104 will work best if they each have a line-of-sight (LOS) view of the troposphere to the common volume 1121.
• the common volume 1121 is an area of the troposphere where tropospheric scattering will cause some of the transmitted signal to reflect back to the ground. Typically, most of the transmitted signal will pass through the troposphere as indicated by 1120. Perfect LOS transmissions over long distances with very narrow angles between antennas may result in poor diversity. This can be mitigated by separating the base station antennas 1102 by large distances, but the scattering effect of the troposphere itself may also create diversity,
• a LOS path to the common volume 1121 can be planned for when the base station antennas 1102 are installed, it is more difficult to guarantee that a client device antenna 1104 has a LOS view of the common volume 1121.
• the common volume 1121 is often going to be at a low angle in the sky. If, for example, a consumer wishes to place a client device antenna 1104 in a window of her house, or on the roof of her house, even though the antenna may have a view of some of the sky, it may be obstructed from having a view of the particular patch of the sky which contains the common volume 1121.
• Troposcatter base station 1301 serves the same function as troposcatter base station 1101, but its antennas are deliberately distributed far apart in antenna clusters 1341-1344.
• the antenna clusters 1341-1344 are aimed such that their transmissions reflect from the troposphere to a common ground coverage area 1360.
• This coverage area may be a town, a city, a rural area, or an uninhabited area under exploration. It may also be an area on a body of water.
• Antenna cluster 1341 transmits RF transmission 1330, which scatters in common volume 1321 and then reflects back to earth as RF reflection 1331 into coverage area 1360 where it then is received in coverage area 1360 by one or more client antennas 1361-1363.
• antenna clusters 1342-1344 transmit RF that scatters in common volumes 1322-1324, respectively, and then the RF reflects back to earth in to coverage area 1360 where it is then received by one or more client antennas 1361-1363.
• one or more client antennas 1361-1363 transmit back through common volumes 1321-1324 to antenna clusters 1341-1344 as a return path.
• Some or all client antennas 1 61-1363 may not have a LOS view the sky to see all common volumes 1321-1324. But so long as each client antenna 1361-1363 can see at least one common volume 1321-1324, then it will be able to have communications with the troposcatter base station 1301. Clearly, the more antenna clusters 1341-1344 that are established around the coverage area 1360, the less chance that a client antenna 1361 will be unable to see at least one common volume 1321-1324.
• the troposcatter base station 1101 communicates to the antenna clusters 1341-1344 through communication links 1351-1354.
• These communications links 1351-1354 may be physically implemented via various means, including optical fiber, leased communications lines,
• P514X such as DS3 lines, or they may be implemented through wireless communications.
• communication links 1351-1354 may be implemented utilizing troposcatter communications.
• each of the antenna clusters 1341-1344 will have its own local RF transceivers which are directed by the troposcatter base 1301 as to precisely what RF signals are to be generated in synchrony so that all antenna clusters 1341-1344 work in a coordinated fashion as a single DIDO system.
• each antenna cluster 1341-1344 will have its own base station 1301 and will operate independently from the other antenna clusters 1341-1344.
• each antenna cluster may transmit at a different frequency so as to avoid interfering with the others, or directional antennas maybe used for client antennas 1361-1363 may so as to reject transmission from all but a signal antenna cluster 1341-1344.
• FIGS 16 and Figures 17a-c The communications links, then base station and the common volumes from Figure 13 are not shown in Figures 16 and Figures 17a-c for the sake of clarity, but such components still exist, and are implemented as previously described.
• Figure 16 shows an overhead (plan) view of a coverage area 1360 surrounded by 12 clusters 1611-1643 of 3 antennas 1651-1653 each, for a total of 36 antennas. All of these antennas are aimed such that when they scatter off of their respective common volumes, the reflected RF reaches the coverage area 1360. Coverage area 1360 has many client antennas, of which 3, 1361-1363 are illustrated. Figure 16 also indicates the north/south/east/west orientation of the illustration.
• Figures 17a-c shows the 3 client antennas 1361-1363 in the coverage area 1360 schematically as antennas 1701.
• Figure 17a shows the antennas 1701 in an elevation view from the south;
• Figure 17b shows the antennas 1701 in an elevation view from the west;
• Figure 17c shows the antennas 1701 in an overhead (plan) view from above.
• Note the schematic illustration of the antennas 1701 shows them as triangles in the elevation views and as squares in the overhead view, but they are the same antennas.
• the antennas could be any of many prior art antenna shapes.
• the 3 antennas may be located in many different positions relative to each other, including being miles apart. And finally, in one embodiment, far more than 3 antennas are deployed in a given coverage area.
• Figure 17a-c shows how the RF beams from the various antennas in Figure 16 arrive at a large variety of angles to antennas 1701.
• antenna cluster 1613's transmission arrives at angle 1713
• 1612's transmission arrives at angle 1712
• 16H's transmission arrives at angle 1711.
• antenna clusters 1613- 1615 are positioned successively further from coverage area 1360, but are all aimed to reflect down to coverage area 1360, resulting in varied angles of arrival.
• antenna clusters' 1631-1633's transmission arrive at angles 1731-1733, respectively;
• clusters 1621-1623 arrive at angles 1721-1723, respectively; and
• clusters 1641-1643 arrive at angles 1.741-1743, respectively.
• antennas 1701 transmit back to the various antenna clusters 1611-1643.
• some or all of antennas 1701 may be directional and only utilize certain transmission and reception angles. This may be used to either increase the gain off the signal (e.g. using a dish antenna), or can be used to limit the return path transmissions to certain angles to avoid interfering with other receivers using a similar frequency.
• One desirable frequency range to use for tropospheric communications is above 12 GHz.
• Some of the 12 GHz band is currently used in the US for Direct Broadcast Satellite (DBS) communications.
• DBS Direct Broadcast Satellite
• Typically, DBS radio signals are transmitted from geostationary satellites, and a consumer has a dish installed on the roof of his home (or someplace where the dish as a view of the southern sky in the direction of the desired satellite).
• the satellite signal is received at angle 1410 of Figure 14, and then is collected by dish 1401 and reflected to antenna and low- noise block (LNB) 1402.
• LNB antenna and low- noise block
• Some satellite dishes 1401 are constructed to receive satellite signals from 2 or 3 angles, and reflect them to multiple LNBs 1402.
• the 12 GHz band is largely unutilized in the US except for this purpose. Because of the high frequency 12 GHz is easily absorbed by various terrestrial objects (e.g. tree leaves) and as a result is difficult to use for other than LOS applications.
• DIDO troposcatter system described above, and illustrated in Figures 11 and 13 is used at the same frequency as DBS satellite transmission 1410, but the base station antennas (either 1102 or 1341-1344) are positioned and angled such
• the angle(s) of RF reflection from the common volume(s) 1121 or 1321-1324 are such that they will not be reflected by the satellite dishes 1401 into their LNBs 1402. This can be accomplished by placing the base station antennas 1102 or 1341-1344 at angles so that they never transmit in the same direction as the satellite signal 1410 (e.g. always transmit from the north, since all geosynchronous satellites transmit from the south), or choose an elevation angle for the transmission such that the RF reflection 1420 back to the ground bounces away from the LNBs 1402.
• the 12 GHz troposcatter approach just described not only applies to DIDO systems, but can be also used for 1-way conventional broadcast without return path or spatial multiplexing. In this case, each client receiver would receive the same signal.
• Embodiments of the invention may include various steps as set forth above.
• the steps may be embodied in machine-executable instructions which cause a general-purpose or special-purpose processor to perform certain steps.
• the various components within the Base Stations and Client Devices described above may be implemented as software executed on a general purpose or special purpose processor.
• various well known personal computer components such as computer memory, hard drive, input devices, . . . etc, have been left out of the figures.
• the various functional modules illustrated herein and the associated steps may be performed by specific hardware components that contain hardwired logic for performing the steps, such as an application-specific integrated circuit (“ASIC") or by any combination of programmed computer components and custom hardware components.
• ASIC application-specific integrated circuit
• certain modules such as the Coding, Modulation and Signal Processing Logic 603 described above may be implemented on a programmable digital signal processor ("DSP") (or group of DSPs) such as a DSP using a Texas Instruments' TMS320x architecture (e.g., a TMS320C6000, TMS320C5000, . . . etc).
• DSP programmable digital signal processor
• the DSP in this embodiment may be embedded within an add-on card to a personal computer such as, for example, a PCI
• 06181.P514X card 06181.P514X card.
• DSP architectures may be used while still complying with the underlying principles of the invention.
• Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions.
• the machine-readable medium may include, but is not limited to, flash memory, optical disks, CD-ROMs, DVD ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of machine-readable media suitable for storing electronic instructions.
• the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).
• a method comprising:
• tropospheric scatter to transmit a training signal from each antenna of a base station to each of a plurality of client devices, each of the client devices analyzing each training signal to generate channel characterization data, and transmitting the channel characterization data back to the base station;
• 06181.P514X storing the channel characterization data for each of the plurality of client devices; receiving data to be transmitted to each of the client devices; and
• tropospheric scatter uses tropospheric scatter to transmit the precoded data signals through each antenna of the base station to each respective client device.
• a method comprising: transmitting a training signal from each antenna of a base station to each of a plurality of client devices utilizing tropospheric scatter, each of the client devices analyzing each training signal to generate channel characterization data, and transmitting the channel characterization data back to the base station utilizing tropospheric scatter; storing the channel characterization data for each of the plurality of client devices; receiving data to be transmitted to each of the client devices; and precoding the data using the channel characterization data associated with each respective client device to generate precoded data signals for each antenna of the base station; and transmitting the precoded data signals through each antenna of the base station to each respective client device.
• NVIS Near Vertical Incidence Sky wave
• Prior art multi-user wireless systems may include only a single base station or several base stations.
• a single WiFi base station (e.g., utilizing 2.4 GHz 802.1 lb, g or n protocols) attached to a broadband wired Internet connection in an area where there are no other WiFi access points (e.g. a WiFi access point attached to DSL within a rural home) is an example of a relatively simple multi-user wireless system that is a single base station that is shared by one or more users that are within its transmission range. If a user is in the same room as the wireless access point, the user will typically experience a high-speed link with few transmission disruptions (e.g.
• Adding additional WiFi base stations in situations with a large number of users will only help up to a point.
• Within the 2.4GHz ISM band in the U.S. there are 3 non-interfering channels that can be used for WiFi, and if 3 WiFi base stations in the same coverage area are configured to each use a different non-interfering channel, then the aggregate throughput of the coverage area among multiple users will be increased up to a factor of 3. But, beyond that, adding more WiFi base stations in the same coverage area will not increase aggregate throughput, since they will start sharing the same available spectrum among them, effectually utilizing time-division multiplexed access (TDM A) by "taking turns" using the spectrum.
• TDM A time-division multiplexed access
• the link quality is likely good in that situation, the user would be receiving interference from neighbor WiFi adapters operating in the same frequency band, reducing the effective throughput to the user.
• ⁇ employs multiple antennas at transmit and receive sides of wireless links to improve link quality (resulting in wider coverage) or data rate (by creating multiple non-interfering spatial channels to every user). If enough data rate is available for every user (note, the terms "user” and “client” are used herein interchangeably), however, it may be desirable to exploit channel spatial diversity to create non-interfering channels to multiple users (rather than single user), according to multiuser ⁇ (MU-MIMO) techniques [20-27]. .
• MIMO multiple-input multiple-output
• 4x30Mbps l 20Mbps, which is much higher than required to deliver high definition video content (which may only require ⁇ 10Mbps).
• downlink data rate may be shared across the four users and channel spatial diversity may be exploited to create four parallel 30Mbps data links to the users.
• MU- ⁇ schemes have been proposed as part of the LTE standard [1-3], but they can provide only up to 2X improvement in DL data rate with four transmit antennas.
• Practical implementations of MU-MIMO techniques in standard and proprietary cellular systems by companies like ArrayComm [4] have yielded up to a ⁇ 3X increase (with four transmit antennas) in DL data rate via space division multiple access (SDMA).
• SDMA space division multiple access
• a key limitation of MU-MIMO schemes in cellular networks is lack of spatial diversity at the transmit side. Spatial diversity is a function of antenna spacing and multipath angular spread in the wireless links. In cellular systems employing MU-MIMO techniques, transmit antennas
• multipath angular spread is low since cell towers are typically placed high up (10 meters or more) above obstacles to yield wider coverage.
• a given sector of a given cell ends up being a shared block of DL and UL spectrum among all of the users in the cell sector, which is then shared among these users primarily in only the time domain.
• cellular systems based on Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) both share spectrum among users in the time domain.
• TDMA Time Division Multiple Access
• CDMA Code Division Multiple Access
• These methods include limiting transmission power from the base station so as to limit the range of interference, beamforrning (via synthetic or physical means) to narrow the area of interference, time-domain multiplexing of spectrum and or MU-MIMO techniques with multiple clustered antennas on the user device, the base station or both. And, in the case of advanced cellular networks in place or planned today, frequently many of these techniques are used at once.
• the coverage area must be mapped out, the available locations for placing towers or base stations must be identified, and then given these constraints, the designers of the cellular system must make do with the best they can. And, of course, if user data rate demands grow over time, then the designers of the cellular system must yet again remap the coverage area, try to find locations for towers or base stations, and once again work within the constraints of the circumstances. And, very often, there simply is no good solution, resulting in dead zones or inadequate aggregate data rate capacity in a coverage area. In other words, the rigid physical placement requirements of a cellular system to avoid interference among towers or base stations utilizing the same frequency results in significant difficulties and constraints in cellular system design, and often is unable to meet user data rate and coverage requirements.
• MANET mobile ad hoc network
• Mobile ad hoc network- is an example of a cooperative self -configuring network intended to provide peer-to-peer communications, and could be used to establish communication among radios without cellular infrastructure, and with sufficiently low-power
• routing protocols can potentially mitigate interference among simultaneous transmissions that are out of range of each other.
• a vast number of routing protocols have been proposed and implemented for MANET systems (see http://en.wikipedia.org/wiki/List of ad- hoc routing protocols for a list of dozens of routing protocols in a wide range of classes), but a common theme among them is they are all techniques for routing (e.g. repeating) transmissions in such a way to minimize transmitter interference within the available spectrum, towards the goal of particular efficiency or reliability paradigms.
• All of the prior art multi-user wireless systems seek to improve spectrum utilization within a given coverage area by utilizing techniques to allow for simultaneous spectrum utilization among base stations and multiple users.
• the techniques utilized for simultaneous spectrum utilization among base stations and multiple users achieve the simultaneous spectrum use by multiple users by mitigating interference among the waveforms to the multiple users. For example, in the case of 3 base stations each using a different frequency to transmit to one of 3 users, there interference is mitigated because the 3 transmissions are at 3 different frequencies. In the case of sectorization from a base station to 3 different users, each 180 degrees apart relative to the base station, interference is mitigated because the beamforming prevents the 3 transmissions from overlapping at any user.
• Prior art multi-user wireless systems add complexity and introduce limitations to wireless networks and frequently result in a situation where a given user's experience (e.g. available bandwidth, latency, predictability, reliability) is impacted by the utilization of the spectrum by other users in the area.
• a given user's experience e.g. available bandwidth, latency, predictability, reliability
• the increasing demands for aggregate bandwidth within wireless spectrum shared by multiple users and the increasing growth of applications that can rely upon multi-user wireless network reliability, predictability and low latency for a given user
• prior art multi-user wireless technology suffers from many limitations. Indeed, with the limited availability of spectrum suitable for particular types of wireless communications (e.g. at wavelengths that are efficient in penetrating building walls), it may be the case that prior art wireless techniques will be insufficient to meet the increasing demands for bandwidth that is reliable, predictable and low-latency.
• FIG. 1 illustrates a prior art ⁇ system.
• FIG. 2 illustrates an N-antenna Base Station communicating with a plurality of Single-antenna Client Devices.
• FIG. 3 illustrates a three Antenna Base Station communicating with three Single- Antenna Client Devices
• FIG. 4 illustrates training signal techniques employed in one embodiment of the invention.
• FIG. 5 illustrates channel characterization data transmitted from a client device to a base station according to one embodiment of the invention.
• FIG. 6 illustrates a Multiple-Input Distributed-Output ("MIDO") downstream transmission according to one embodiment of the invention.
• MISO Multiple-Input Distributed-Output
• FIG. 7 illustrates a Multiple-Input Multiple Output (" ⁇ ") upstream transmission according to one embodiment of the invention.
• FIG. 8 illustrates a base station cycling through different client groups to allocate throughput according to one embodiment of the invention.
• FIG. 9 illustrates a grouping of clients based on proximity according to one embodiment of the invention.
• FIG. 10 illustrates an embodiment of the invention employed within an NVIS system.
• FIG. 11 illustrates an embodiment of the DIDO transmitter with 1/Q compensation functional units.
• FIG. 12 a DIDO receiver with I/Q compensation functional units.
• FIG. 13 illustrates one embodiment of DIDO-OFDM systems with I Q compensation.
• FIG. 14 illustrates one embodiment of DIDO 2 x 2 performance with and without I Q compensation.
• FIG. 15 illustrates one embodiment of DIDO 2 2 performance with and without I Q compensation.
• FIG. 16 illustrates one embodiment of the SER (Symbol Error Rate) with and without I/Q compensation for different QAM constellations.
• FIG. 17 illustrates one embodiment of DIDO 2 x 2 performances with and without compensation in different user device locations.
• FIG. 18 illustrates one embodiment of the SER with and without VQ
• FIG. 19 illustrates one embodiment of a transmitter framework of adaptive DIDO systems.
• FIG. 20 illustrates one embodiment of a receiver framework of adaptive DIDO systems.
• FIG. 21 illustrates one embodiment of a method of adaptive DIDO-OFDM.
• FIG. 22 illustrates one embodiment of the antenna layout for DIDO
• FIG. 23 illustrates embodiments of array configurations for different order DIDO systems.
• FIG.24 illustrates the performance of different order DIDO systems.
• FIG.25 illustrates one embodiment of the antenna layout for DIDO
• FIG.26 illustrates one embodiment of the DIDO 2 2 performance with 4-QAM and FEC rate 1 ⁇ 2 as function of the user device location.
• FIG.27 illustrates one embodiment of the antenna layout for DIDO
• FIG.28 illustrates how, in one embodiment, DIDO 8 8 yields larger SE than DIDO 2 x 2 for lower TX power requirement.
• FIG.29 illustrates one embodiment of DIDO 2 x 2 performance with antenna selection.
• FIG.30 illustrates average bit error rate (BER) performance of different DIDO precoding schemes in i.i.d. channels.
• FIG.31 illustrates the signal to noise ratio (SNR) gain of ASel as a function of the number of extra transmit antennas in i.i.d. channels.
• SNR signal to noise ratio
• FIG.32 illustrates the SNR thresholds as a function of the number of users (A/) for block diagnalization (BD) and ASel with 1 and 2 extra antennas in i.i.d. channels.
• FIG. 33 illustrates the BER versus per-user average SNR for two users located at the same angular direction with different values of Angle Spread (AS).
• AS Angle Spread
• FIG. 34 illustrates similar results as FIG. 33, but with higher angular separation between the users.
• FIG. 35 plots the SNR thresholds as a function of the AS for different values of the mean angles of arrival (AOAs) of the users.
• AOAs mean angles of arrival
• FIG. 36 illustrates the SNR threshold for an exemplary case of five users.
• FIG. 37 provides a comparison of the SNR threshold of BD and ASel, with 1 and 2 extra antennas, for two user case.
• FIG.38 illustrates similar results as FIG. 37, but for a five user case.
• FIG.39 illustrates the SNR thresholds for a BD scheme with different values of AS.
• FIGS.43-44 illustrate the SNR thresholds as a function of the number of users (M) and angle spread (AS) for BD and ASel schemes, with 1 and 2 extra antennas, respectively.
• FIG 45 illustrates a receiver equipped with frequency offset estimator/compensator.
• FIG. 46 illustrates DIDO 2 x 2 system model according to one embodiment of the invention.
• FIG. 47 illustrates a method according to one embodiment of the invention.
• FIG, 48 illustrates SER results of DIDO 2 2 systems with and without frequency offset.
• FIG. 49 compares the performance of different DIDO schemes in terms of SNR thresholds.
• FIG. 50 compares the amount of overhead required for different embodiments of methods.
• FIG. 52 illustrates results when turning off the integer offset estimator.
• FIG. 53 illustrates downlink spectral efficiency (SE) in [bps/Hz] as a function of mutual information in [bps/Hz].
• SE downlink spectral efficiency
• FIG. 54 illustrates average per-user symbol error rare (SER) performance as a function of the mutual information in [bps/Hz].
• FIG. 55 illustrates average per-user SER performance as a function of the minimum mutual information in [bps/Hz] and the thresholds used to switch between different DIDO modes.
• FIG.56 illustrates average per-user SER vs. SNR for fixed modulation and adaptive DIDO systems.
• FIG.57 illustrates downlink SE vs. SNR for fixed modulation and adaptive DIDO systems.
• FIG.58 illustrates average per-user SER vs. SNR for adaptive DIDO systems with different thresholds.
• FIG.59 illustrates downlink SE vs. SNR for adaptive DIDO systems with different thresholds
• FIG. 60 illustrates average per-user SER performance as a function of the minimum singular value of the effective channel matrix and the CQI threshold for 4-QAM constellation.
• FIG.61 illustrates one embodiment of a circular topology of base transceiver stations (DIDO antennas)
• FIG. 62 illustrates an one embodiment of an alternate arrangement of
• FIG. 63 illustrates one embodiment in which a base station network (BSN) is used to deliver precoded baseband data from the centralized processors (CPs) to DIDO antennas.
• BSN base station network
• FIG. 64 illustrates one embodiment in which the BSN is used to carry modulated signals.
• FIG. 65 illustrates one embodiment comprised of two DIDO base stations perfectly synchronized and two users with Line Of Sight (LOS) channels
• FIG. 66 illustrates the path loss of DIDO at 85MHz and 400MHz using the
• FIG. 67 illustrates the period maximum delay between channel state information and data transmission as a function of the relative velocity between transmitter and receiver for different frequencies in the UHF band
• FIG. 68 illustrates propagation effects in DIDO systems for three different carrier frequencies.
• FIG. 69 illustrates the areas in the US territory currently covered by transceiver stations operating in the Maritime band.
• the colors identify the number of active channels (out of the 146 channels available in the Maritime band) that would cause harmful interference to DIDO-NVIS stations at any location.
• FIG.70 illustrates sunspot number from the January 1900 throughout June
• FIG. 71 illustrates the path loss of WiMAX, LTE and NVJS systems.
• FIG.72 illustrates the locations of DIDO-NVIS transmitter (TX) and receiver (RX) stations
• FIG.73 illustrates DIDO-NVIS receive antenna location, "lambda” denotes the wavelength at 3.9MHz ( ⁇ 77meters)
• FIG.74 illustrates typical 4-QAM constellations demodulated at three users' locations over DIDO-NVIS links.
• FIG. 75 illustrates SER as a function of PU-SNR for DIDO-NVIS 3x3.
• FIG.76 illustrates DIDO-NVIS cells across the territory of the 48 contiguous states of the USA.
• DIDO Distributed-Input Distributed-Output
• DIDO systems are described in the related application U.S. Patent 7,418,053, where multiple antennas of the same DIDO base station in Figure 2 work cooperatively to pre-cancel interference and create parallel non-interfering data streams to multiple users.
• These antennas, with or without local transmitters and/or receivers may be spread across a wide coverage area and be interconnected to the same DIDO base station via wired or wireless links, including networks such as the Internet.
• networks such as the Internet.
• a single base station may have its antennas located very far apart, potentially resulting in the base station's antenna array occupying several square kilometers.
• the separation of antennas from a single DIDO base station may be physically separated by 100s of yards or even miles, potentially providing diversity advantages, and the signals for each antenna installation may either processed locally at each antenna location or brought back to a centralized location for processing.
• methods for practical deployment of DIDO systems including addressing practical issues associated with processing signals with widely distributed DIDO antennas, are described in the related applications U.S. Patent No.
• Recent publications [32,33] analyzed theoretically the performance of cooperative base stations in the context of cellular systems. In practice, when those cooperative base stations are connected to one another via wireless, wired, or optical network (i.e., wide area network, WAN backbone, router) to share precoded data, control information and/or time/frequency synchronization information as described in U.S. Patent No.
• wireless, wired, or optical network i.e., wide area network, WAN backbone, router
• a significant advantage of DIDO systems over prior art systems is that DEDO systems enable the distribution of multiple cooperative distributed antennas, all using the same frequency at the same time in the same wide coverage area, without significantly restricting the physical placement of the distributed antennas.
• prior art multiuser systems which avoid interference from multiple base transmitters at a given user receiver
• the simultaneous RF waveform transmissions from multiple DEDO distributed antennas deliberately interfere with each other at each user's receiver.
• the interference is a precisely controlled constructive and destructive interference of RF waveforms incident upon each receiving antenna which, rather than impairing data reception, enhances data reception.
• multiple distributed antenna RF waveform transmission interference and user channel interference have an inverse relationship: multiple distributed antenna RF waveform interference results in simultaneous non-interfering user channels.
• DIDO opens the door to a very large increase in multi-user wireless spectrum efficiency by specifically doing exactly what prior art systems had been meticulously designed to avoid doing.
• DIDO systems consist of;
• DIDO Clients 6110 wireless devices that estimate the channel state information (CSI), feedback the CSI to the transmitters and demodulate precoded data. Typically each user would have a DIDO client device.
• CSI channel state information
• DIDO Distributed Antennas 6113 wireless devices interconnected via a network that transmit precoded data to all DIDO clients.
• a wide variety of network types can be used to interconnect the distributed antennas 6113 including, but not limited to, a local area network (LAN), a wire area network (WAN), the Internet, a commercial fiber optic loop, a
• the number of DIDO distributed antennas is at least equal to the number of clients that are served via precoding, and thereby avoids sharing channels among clients. More DIDO distributed antennas than clients can be used to improve link reliability via transmit diversity techniques, or can be used in combination with multi-antenna clients to increase data rate and/or improve link reliability.
• distributed antenna may not be merely an antenna, but refers to a device capable of transmitting and or receiving through at least one antenna.
• the device may incorporate the network interface to the DIDO BTS 6112 (described below) and a transceiver, as well as an antenna attached to the transceiver.
• the distributed antennas 6113 are the antennas that the DIDO BTS 6112, utilizes to implement the DIDO multi-user system.
• BTS Base Transceiver Station
• the BTS may be connected to the Internet, public switched telephone network (PSTN) or private networks to provide connectivity between users and such networks . For example, upon clients' requests to access web content, the CP fetches data through the Internet and transmits data to the clients via the DIDO distributed antennas.
• PSTN public switched telephone network
• DIDO Base Station Network (BSN) 6111 One embodiment of DIDO technology enables precisely controlled cooperation among multiple DEDO distributed antennas spread over wide areas and interconnected by a network.
• the network used to interconnect the DIDO distributed antennas is a metro fiber optic ring (preferabl , with the DIDO distributed antennas connecting to the metro fiber optic ring at locations where it is convenient), characterized by relatively low latency and reasonably high throughput (e.g. throughput to each DEDO antenna comparable to the wireless throughput achievable from
• the fiber optic ring is used to share control information and precoded data among different stations.
• many other communication networks can be used instead of a metro fiber optic ring, including fiber optic networks in different topologies other than a ring, fiber-to-the-home (FFTH), Digital Subscriber Lines (DSL), cable modems, wireless links, data over power line, Ethernet, etc.
• the communication network can be used instead of a metro fiber optic ring, including fiber optic networks in different topologies other than a ring, fiber-to-the-home (FFTH), Digital Subscriber Lines (DSL), cable modems, wireless links, data over power line, Ethernet, etc.
• the communication network can be used instead of a metro fiber optic ring, including fiber optic networks in different topologies other than a ring, fiber-to-the-home (FFTH), Digital Subscriber Lines (DSL), cable modems, wireless links, data over power line, Ethernet, etc.
• FFTH fiber-to-the-home
• DSL Digital Subscriber Line
• interconnecting the DIDO distributed antennas may well be made up of a combination of different network technologies.
• some DIDO distributed antennas may be connected to DSL, some to fiber, some to cable modems, some on Ethernet, etc.
• the network may be a private network, the Internet, or a combination.
• much like prior art consumer and commercial WiFi base stations are connected via a variety of network technologies, as is convenient at each location, so may be the DIDO distributed antennas.
• BSN Base Station Network
• RTT round trip time
• jitter the delay between BTS and the DIDO distributed antennas
• the BSN may be designed with dedicated fiber links.
• a combination of low and high latency BSNs can be employed.
• DIDO BTSs can be used in a given coverage area.
• a DIDO cell As the coverage area served by one DIDO BTS.
• One embodiment with circular topology is depicted in Figure 61 (the dots are the DIDO clients 6110, and crosses are the DIDO distributed antennas 6113).
• the BSN does not have circular shape as in Figure 61.
• the DIDO distributed antennas may be placed randomly
• the coverage area is one city
• multiple DIDO cells can be designed to cover the whole city. In that case, cellular planning is required to allocate different frequency channels to adjacent DIDO cells to avoid inter-cell interference.
• one DIDO cell can be designed to cover the entire city at the expense of higher computational complexity at the DIDO BTS (e.g., more CSI data from all the users in the same DIDO cell to be processed by the BTS) and larger throughput requirement over the network interconnecting the DIDO distributed antennas.
• the BSN 6111 is used to deliver precoded baseband data from the BTS 6112 to the DIDO distributed antennas 6113.
• the DIDO distributed antenna 6313 includes a radio transceiver 6330 equipped with digital-to-analog converter (DAC), analog-to-digital converter (ADC), mixer and coupled to (or including) a power amplifier 6338,
• DAC digital-to-analog converter
• ADC analog-to-digital converter
• Each DEDO distributed antenna receives the baseband precoded data 6332 over the BSN 6311 (such as fiber optic cable 6331) from the BTS 6312, modulates the signal at the carrier frequency and transmits the modulated signal to the clients over the wireless link via antenna 6339.
• a reference clock signal is provided to the radio transceiver by a reference clock generator 6333.
• the BSN is used to carry modulated signals as illustrated in Figure 64, which shows the structure of DIDO systems employing RF-over-fiber.
• Figure 64 shows the structure of DIDO systems employing RF-over-fiber.
• the BSN is a fiber optic channel 6431 with sufficient bandwidth
• RF radio frequency
• Multiple radios 6440 can be employed at the BTS 6412 to modulate the baseband
• the RF modulated signal is converted into optical signal by the radio interface unit (REJ) 6441.
• REJ radio interface unit
• One example of an RIU for UHF is the FORAX LOS 1 by Syntonics [19].
• the optical signal propagates from the BTS to the DIDO distributed antennas 6413 over the BSN 6411.
• the DIDO distributed antennas are equipped with one amplifier interface unit (AIU) 6445 that converts the optical signal to RF.
• the RF signal is amplified by amplifier 6448 and sent through the antenna 6449 over the wireless link.
• the DIDO distributed antenna consists only of one AIU 6445, power amplifier 6448 and antenna 6449. Moreover, if the fiber propagation delay is known and fixed, all the radios at the BTS can be locked to the same reference clock 6442 as in Figure 64, with an appropriate delay to compensate for the propagation delay, and no time/frequency synchronization is required at the DIDO distributed antenna, thereby simplifying further the complexity of DIDO systems.
• existing cellular towers with antennas, transceivers, and backhaul connectivity are reconfigured such that the backhauls are connected to a DIDO BTS 6112.
• the backhaul connectivity becomes functionally equivalent to the BSN 6111.
• the cellular transceivers and antennas become functionally equivalent to the DIDO distributed antennas 6113.
• the transmitters may have been configured to transmit at a low power level so as to not cause interference with a nearby cell using the same frequency.
• existing cellular towers are partially used for DIDO, as described in the preceding paragraph, and partially used as conventional cellular towers, so as to support compatibility with existing cellular devices.
• TDMA is used to alternate between DIDO use and conventional cellular use. So, at any given time, the cellular towers are used for only DIDO or for conventional cellular communications.
• DIDO distributed antennas can be located anywhere within a coverage area, and work cooperatively without channel interference, this results in larger transmit antenna spacing and multipath angular spread. Thus, far more antennas can be used, while still maintaining spatial diversity.
• DIDO distributed antennas can be placed anywhere there is a reasonably fast Internet (or other network) connection, even if it is only a few feet from the ground, indoor or outdoor.
• Reduced coverage can be compensated by larger transmit power (e.g., 100W rather than ⁇ 200mW as in typical cellular systems in urban areas or ⁇ 250mW in typical WlFi access points) because there is no concern (or far less concern than with prior art cellular systems) about higher-powered transmissions interfering with another cell or WiFi access point using the same frequency.
• Larger spatial diversity translates into a larger number of non-interfering channels that can be created to multiple users. Theoretically (e.g., due to large antenna spacing and angular spread), the number of spatial channels is equal to the number of transmit DIDO stations. That yields an nX improvement in aggregate DL data rate, where n is the number of DIDO stations. For example, whereas prior art cellular system might achieve a maximum of net 3X
• a DEDO system might achieve a 10X, 100X or even greater improvement in aggregate spectrum utilization.
• DIDO distributed antennas can be designed as inexpensive devices with single antenna transceivers (similar to WiFi access points). Moreover, they do not require costly real estate or expensive installation as cell towers because of the ability to flexibly locate them within the coverage area.
• the DIDO BTS 6112 computes the precoding weights from the CSI feedback from the entire DIDO cell. Precoded data are sent from the DIDO BTS 6112 to the DIDO distributed antennas in Figure 6 via the DIDO BSN 6111. One precoded data stream is sent to each of the DIDO distributed antennas.
• the feedback loop in Figures 19-20 consists of:
• the delay over the feedback loop should be lower than the channel coherence time.
• the feedback loop delay depends on the BTS computational resources relative to the computational complexity of the DIDO precoding as well as latency over the BSN.
• Processing at each client and DIDO distributed antenna is typically very limited (i.e., on the order of a microsecond or less with a single DSP or CPU), depending on the hardware and processor speed.
• Most of the feedback loop delay is due the latency for transmission of precoded data from the DIDO BTS 6112 to the DIDO distributed antennas 6113 over the DIDO BSN 6111 (e.g., on the order of milliseconds).
• a low latency or high latency BSN can be used in DIDO systems depending on the available network.
• the DIDO BTS 6112 switches among two or more types of BSN network infrastructure based on the each users' channel coherence time. For example, outdoor clients are typically characterized by more
• IFS-Web 6181 P515X severe Doppler effects due to the potential of fast mobility of clients or objects within the channel (i.e., resulting in low channel coherence time).
• Indoor clients have generally fixed wireless or low mobility links (e.g., high channel coherence time).
• DIDO distributed antennas connected to low latency BSN network infrastructure e.g., dedicated fiber rings
• DIDO distributed antennas connected to high latency BSN network infrastructure e.g., consumer Internet connections such as DSL or cable modems
• indoor and outdoor clients can be multiplexed via TDMA, FDMA or CDMA schemes.
• DIDO distributed antennas connected to low latency BSNs can also be used for delay-sensitive algorithms such as those used for client time and frequency synchronization.
• DIDO provides an inherently secure network when more than one DIDO distributed antenna is used to reach a user.
• the precoded streams from the BTS to the DIDO distributed antennas consist of linear combinations of data (for different clients) and DIDO precoding weights.
• the data stream sent from the BTS to the BSN generally cannot be demodulated at the DIDO distributed antenna, since the DIDO distributed antenna is unaware of the precoding weights used by the BTS.
• the precoding weights change over time as the complex gain of the wireless channels from DIDO distributed antenna-to-client varies (due to Doppler effects), adding an additional level of security.
• the data stream intended to each client can be demodulated only at the client's location, where the precoded signals from all transmit DIDO distributed antennas recombine to provide user interference-free data. At any other location, demodulation of data intended to one particular user is not possible due to high levels of inter-user interference.
• the clients send data (e.g., to request Web content to the DIDO BTS 6112 from the Internet), CSI and control information (e.g., time/frequency synchronization, channel quality information, modulation scheme, etc.).
• data e.g., to request Web content to the DIDO BTS 6112 from the Internet
• CSI and control information e.g., time/frequency synchronization, channel quality information, modulation scheme, etc.
• the UL channel there are two alternatives for the UL channel that may be used separately or in combination: i) clients communicate directly to the DIDO BTS 6112 via TDMA, FDMA or CDMA schemes; ii) clients communicate to multiple DIDO distributed antennas by creating spatial channels via MEMO techniques as in Figure 7 (in the MIMO case, however, transmission time synchronization among clients is required).
• the DIDO distributed antennas are synchronized in time and frequency. If RF-over-fiber is employed as in Figure 64, all radio transceivers at the BTS are locked to the same reference clock 6442, thereby guaranteeing perfect time and frequency synchronization. Assuming negligible jitter over the DIDO BSN 6111, artificial delays can be added to the transmit RF waveforms at the DIDO BTS 6112 side to compensate for propagation delays over the DIDO BSN 6111 to different DIDO distributed antennas.
• DIDO BSN 6111 is used to carry baseband waveforms as in Figure 63, time and frequency synchronization is required for the radio transceivers at different DIDO distributed antennas. There are various methods to achieve this synchronization, and more than one method can be used at once. i. Time and frequency synchronization via GPSDO
• time/frequency synchronization is achieved by connecting the transmitter in radio transceiver 6330 to a GPS Disciplined Oscillators (GPSDO).
• GPSDO GPS Disciplined Oscillators
• An alternate embodiment utilizes the 60Hz (in the United States, 50Hz in other regions) signal available over power lines as a common clock reference for all transmitters. Based on empirical measurements, the jitter of the 60Hz reference signal (after low pass filtering) can be on the order of 100 nanoseconds. It would be necessary, however, to compensate for deterministic offsets due to variable propagation path length along the power lines at different locations. iii. Time and frequency synchronization with free-running clocks
• An alternative embodiment is used to compensate the time and frequency offsets across different DIDO distributed antennas whose clocks are not synchronized to an external clock reference, but rather are free-running as described in the related U.S. Patent No. 7,599,420 and in Figures 45, 46 and 47.
• all DIDO distributed antennas have free-running clocks as illustrated in Figure 46 that can generate a periodic reference signal (one pulse per second (PPS) in one embodiment).
• PPS pulse per second
• the DIDO BTS 6112 sends an initial trigger signal to all DIDO distributed antennas via the DEDO BSN 6111 to trigger their transmission at the next PPS.
• the roundtrip time (RTT) over the BSN is assumed to be of the order of particular time interval (10msec in one embodiment, or ⁇ 5ms in each direction), so all DIDO distributed antennas will start transmitting with a relative time offset of at most lsec+5msec.
• Each DIDO distributed antenna sends one training signal (i.e., Zadoff-Chu
• Training signals from different DIDO distributed antennas are orthogonal or sent via TDMA/FDMA to avoid interference.
• the users estimate the relative time of arrival from every transmitter by correlating the receive signal with the known training sequence.
• the same training sequence can be sent periodically and the correlation can be averaged over a long period of time (e.g., on the order of minutes in one embodiment) to average-out multipath effects, particularly in the case of mobile users.
• time-reversal techniques [31] can be applied to pre-compensate for multipath effects at the transmitter and obtain precise time of arrival estimates. Then, the users compute the delays (i.e., deterministic time offsets) of each transmitter relative to a given time reference (e.g., one of the DIDO distributed antennas can be chosen as an absolute time reference). The relative time offset is fed back from the clients to the DIDO distributed antennas or directly to the DIDO BTS 6112. Then, each DIDO antenna averages the time offset information obtained from all the users and adjusts its PPS (and clock reference) according to that.
• a given time reference e.g., one of the DIDO distributed antennas can be chosen as an absolute time reference.
• the relative time offset is fed back from the clients to the DIDO distributed antennas or directly to the DIDO BTS 6112.
• each DIDO antenna averages the time offset information obtained from all the users and adjusts its PPS (and clock reference) according to that.
• the time offset is computed from measurements by many users to average out the difference in propagation delay across users.
• Figure 65 shows one case with two DIDO distributed antennas 6551 and 6552 perfectly synchronized (e.g., via GPSDO) and two users 6553 and 6554 with Line Of Sight (LOS) channels.
• DIDO distributed antennas can keep running the algorithm periodically to improve the offset estimates.
• the DIDO transmit stations are typically at fixed locations (e.g. transceiver DIDO distributed antennas connected to the DIDO BSN 6111).
• the algorithm should converge after a period of time. The same algorithm is rerun every time one DIDO distributed antenna changes its location or a new DIDO distributed antenna is added to the DIDO BSN 6111.
• Frequency Offset Compensation once the 1 PPS reference signals at all DIDO distributed antennas are synchronized, the DIDO distributed antennas send training to one or multiple users to estimate the relative frequency offset between stations. Then, the frequency offset compensation method described in the related U.S. Patent No. 7, 9,420 and Figure 47 is applied to transmit precoded data to all users while compensating for the offset. Note that for the best performance of this algorithm, two conditions need to be satisfied: i) good SNR between all DIDO transmitters and the user (or users) responsible for frequency offset estimation; ii) good clock stability: if the OCXOs at the DIDO distributed antennas are stable, the frequency offset estimation can be carried out only occasionally, thereby reducing the feedback information.
• the DIDO BSN 6111 is used for at least the following three purposes:
• the DIDO clients feedback the CSI wirelessly to the DIDO distributed antennas. If TDMA, FDMA or CDMA schemes are used for feedback, only one DIDO distributed antenna (the one with best SNR to all users) is selected to receive the CSI. If
• the CSI is fed back from the DIDO distributed antennas to the DIDO BTS 611 via the DIDO BSN 6111.
• the CSI can be fed back wirelessly directly from the clients (or the DIDO distributed antennas) to a DIDO BTS 6112 equipped with one antenna via TDMA or CDMA schemes.
• This second solution has the advantage of avoiding latency caused by the DIDO BSN 6111, but may not be achievable if the wireless link between each of the clients (or the DIDO distributed antennas) and the DIDO BTS 6112 is not of high enough SNR and reliability.
• the CSI may be quantized or any number of limited feedback algorithms known in the art can be applied [28-30].
• Control Information The DIDO BTS 6112 sends control information to the DIDO distributed antennas via the DIDO BSN 6111. Examples of control information are: transmit power for different DIDO distributed antennas (to enable power control algorithms); active DIDO distributed antenna IDs (to enable antenna selection algorithms); trigger signals for time synchronization and frequency offset values.
• Precoded data the DIDO BTS 6112 sends precoded data to all DIDO distributed antennas via the DIDO BSN 6111. That precoded data is then sent from the DIDO distributed antennas synchronously to all clients over wireless links.
• Time selectivity is caused by relative motion of transmitter and receiver that yields shift in the frequency domain of the received waveform, known as the Doppler effect.
• Figure 67 shows the period At as a function of the relative velocity between transmitter and receiver for different frequencies in the UHF band.
• CSI channel state information
• Frequency selectivity depends on the channel delay spread. Typical values of delay spread for indoor environments are below 300 nsec [S-10]. In urban and suburban areas the delay spread ranges between 1 and 10 usee [11,12]. In rural environments it is typically on the order of 10 to 30 usee [11-13].
• Carrier frequency 400MHz for best tradeoff between range Doppler and antenna size/spacing.
• OFDM orthogonal frequency division multiplexing
• the cyclic prefix is lOusec, based upon the maximum delay spread expected in UHF channels, corresponding to 50 channel taps at 5MHz bandwidth.
• the OFDM waveform can be designed with 1024 tones, corresponding to -5% loss in spectral efficiency.
• the total OFDM symbol length is 215usec.
• Packet Size is limited by the latency over the DIDO BSN 6111 and Doppler effects. For example, the nominal RTT of one embodiment is 10msec. Then, the time required to send precoded data from the DIDO B ST 6112 to the DIDO distributed antennas is -5msec (half RTT). Assuming maximum users' speed of 7mph at 400MHz as in Figure 68, the channel gain can be considered constant for approximately 10msec. Hence, we use the remaining 5msec to send data and define the packet size as (5e-3/215e-6) 23 OFDM
• DIDO distributed antennas can be placed on existing cell towers, as a practical matter, given limited real estate available at existing cell towers, there may be a limited number of antenna locations available. For example, if a maximum of four antennas were placed on each tower this might yield up to 3x increase in data rate as shown in [4] (due to lack of spatial diversity). In this configuration, latency across DIDO transmitters is negligible, since they are all placed on the same tower, but without additional spatial diversity, the gain in spectral utilization will be limited.
• the DIDO distributed antennas are placed in random locations throughout the coverage area all connected to the DIDO BSN 6111. Unlike a the coverage area of given cell in a prior art cellular system, which is based on
• the coverage area of a DIDO cell is based instead on the transmission range of each DIDO distributed antenna, which in accordance with the path loss model in one embodiment is approximately lKm.
• a user within lKm of at least one DIDO distributed antenna will receive service, and a user within range of several DIDO distributed antennas will get non-interfering service from the DIDO distributed antennas within range.
• NVIS near- vertical incident skywave
• the HF band is divided into several subbands dedicated to different types of services.
• the Maritime band is defined between 4MHz and 4.438MHz.
• the ionosphere consists of ionized gas or plasma.
• the plasma behaves as an electromagnetic shield for radio waves propagating from Earth upwards that are refracted and reflected back to Earth as in Figure 10.
• the ionization level depends on the intensity of solar radiations that strike the ionosphere producing plasma.
• One empirical measure of the solar activity is the simspot number (SSN) that varies on 11 -year cycles as shown in Figure 70.
• SSN simspot number
• Any wireless system is affected by thermal noise produced internally to radio receivers.
• HF links are severely affected by other external noise sources such as: atmospheric noise, man-made noise and galactic noise.
• Man- made noise is due to environmental sources such as power lines, machinery, ignition systems, and is the main source of noise in the HF band. Its typical values range between -133 and - 110 dBm/Hz depending on the environment (i.e., remote versus industrial).
• Typical values of delay spreads in NVIS channels are around 2ms corresponding, corresponding to the roundtrip propagation delay Earth-ionosphere (about
• That value may be larger ( ⁇ 5msec) in presence of multilayer refractions in the ionosphere.
• the three transmitting distributed antennas are locked to the same GPSDO that provide time and frequency reference.
• the three receiving DIDO clients have free- running clocks and synchronization algorithms are implemented to compensate for time/frequency offsets.
• the carrier frequency is 3.9MHz, bandwidth is 3.125KHz and we use OFDM modulation with 4-QAM.
• Typical 4-QAM constellations demodulated at the three DIDO client locations are depicted in Figure 74.
• Our DIDO-NVIS 3x3 testbed creates three simultaneous spatial channels over NVIS links by pre-cancelling inter-user interference at the transmit side and enabling successful demodulation at the users' side.
• SER symbol error rate
• DIDO-NVIS system design As follows:
• Bandwidth 1-3 MHz, depending on HF spectrum availability. Larger bandwidths are less practical, since they require more challenging broadband antenna designs. For example, 3MHz bandwidth at 4MHz carrier frequency corresponds to fractional antenna bandwidth of 75%.
• the HF frequencies corresponding to the plasma critical frequency of the ionosphere are between 1 and 10 MHz. Radio waves at lower frequencies ( ⁇ lMHz) are typically reflected by the ionosphere at nighttime, whereas higher frequencies (-10MHz) at daytime.
• the frequency of optimal transmission (FOT) at given time of the day varies with the SSN.
• the carrier frequency can be adjusted throughout the day depending on the FOT provided by the ionospheric maps.
• the cyclic prefix is 2msec (based upon typical delay spread expected in NVIS links) corresponding to 2000 channel taps at lMHz bandwidth.
• the OFDM waveform can be designed with 2 14 tones, corresponding to -10% loss in spectral efficiency due to cyclic prefix.
• the total OFDM symbol duration (including cyclic prefix and data) at lMHz bandwidth is 18.4msec.
• Packet Size is limited by the minimum channel coherence time expected in NVIS links.
• the minimum coherence time is approximately 1 sec and the channel gain can be considered constant over one tenth of that duration ( ⁇ 100msec) in the worst case scenario.
• the packet size is about five OFDM symbols.
• the packet size can be dynamically adjusted as the coherence time varies over time.
• DIDO-NVIS systems One practical solution to implement DIDO-NVIS systems is to place multiple DIDO distributed antennas along the circumference of a circular region of radius -100 miles as in Figure 61. These stations are connected to each other via a BSN that carries control information. At the speed of light through optical fiber, the propagation latency along the circumference of radius 100 miles is -3.4 msec. This delay is much smaller than typical channel coherence time in NVIS channels and can be tolerated without any significant performance degradation for the DIDO precoder. Note that if the optical fiber is shared across different operators, that delay may be larger (i.e., 10-30msec) due to the packet switched nature of the Internet. Multiple DIDO-NVIS cells as in Figure 76 can be distributed to provide full coverage over the USA. For example, Figure 76 shows that 109 DIDO cells of radius 125 miles are required to cover the entire territory of the 48 contiguous states in the USA.
• 3GPP "Multiple Input Multiple Output in UTRA", 3GPP TR 25.876 V7.0.0, Mar. 2007
• 3GPP "Base Physical channels and modulation", TS 36.211, V8.7.0, May 2009
• Figure 1 shows a prior art MIMO system with transmit antennas 104 and receive antennas 105. Such a system can achieve up to 3X the throughput that would normally be achievable in the available channel.
• MIMO system with transmit antennas 104 and receive antennas 105.
• Such a system can achieve up to 3X the throughput that would normally be achievable in the available channel.
• There are a number of different approaches in which to implement the details of such a MIMO system which are described in published literature on the subject, and the following explanation describes one such approach.
• each of the transmit antennas 104 transmits a "training signal" from each of the transmit antennas 104 to each of the receivers 105.
• the training signal is generated by the coding and modulation subsystem 102, converted to analog by a D/A converter (not shown), and then converted from baseband to RF by each transmitter 103, in succession.
• Each receive antenna 105 coupled to its RF Receiver 106 receives each training signal and converts it to baseband.
• the baseband signal is converted to digital by a D/A converter (not shown), and the signal processing subsystem 107 characterizes the training signal.
• Each signal's characterization may include many factors including, for example, phase and amplitude relative to a reference internal to the receiver, an absolute reference, a relative
• Each signal's characterization is typically defined as a vector that characterizes phase and amplitude changes of several aspects of the signal when it is transmitted across the channel.
• the characterization might be a vector of the phase and amplitude offsets of several multipath images of the signal.
• QAM quadrature amplitude modulation
• OFDM orthogonal frequency division multiplexing
• the signal processing subsystem 107 stores the channel characterization received by each receiving antenna 105 and corresponding receiver 106. After all three transmit antennas 104 have completed their training signal transmissions, then the signal processing subsystem 107 will have stored three channel characterizations for each of three receiving antennas 105, resulting in a 3x3 matrix 108, designated as the channel
• the signal processing subsystem 107 inverts the matrix H 108, to produce H "1 , and awaits transmission of actual data from transmit antennas 104. Note that various prior art ⁇ techniques described in available literature, can be utilized to ensure that the H matrix 108 can be inverted.
• Input subsystem 100 It is then divided up into three parts by splitter 101 prior to being presented to coding and modulation subsystem 102. For example, if the payload is the ASCII bits for "abcdef,” it might be divided up into three sub-payloads of ASCII bits for "ad,” "be,”
• Each of the sub-payloads is individually coded by using a coding system suitable for both statistical independence of each signal and error correction capability. These include, but are not limited to Reed-Solomon coding, Viterbi coding, and Turbo Codes.
• each of the three coded sub-payloads is modulated using an appropriate modulation scheme for the channel. Examples of modulation schemes are differential phase shift key (“DPSK") modulation, 64-QAM modulation and OFDM. It should be noted here that the diversity gains provided by ⁇ allow for higher-order modulation constellations that would otherwise be feasible in a SISO (Single Input-Single Output) system utilizing the same channel.
• DPSK differential phase shift key
• 64-QAM modulation 64-QAM modulation
• OFDM OFDM
• each of the receiving antennas 105 will receive a different combination of the three transmitted signals from antennas 104.
• Each signal is received and converted down to baseband by each RF receiver 106, and digitized by an A D converter (not shown). If y n is the signal received by the nth receive antenna 105, and ⁇ ⁇ is the signal transmitted by nth transmit antenna 104, and N is noise, this can be described by the following three equations:
• the three transmitted signals j n are then demodulated, decoded, and error-corrected by signal processing subsystem 107 to recover the three bit streams that were originally separated out by splitter 101. These bit streams are combined in combiner unit 108, and output as a single data stream from the data output 109. Assuming the robustness of the system is able to overcome the noise impairments, the data output 109 will produce the same bit stream that was introduced to the data Input 100.
• Figure 2 illustrates one embodiment of the invention in which a Base
• BS 200 is configured with a Wide Area Network (WAN) interface (e.g. to the Internet through a Tl or other high speed connection) 201 and is provisioned with a number (N) of antennas 202.
• WAN Wide Area Network
• N number of antennas 202.
• Base Station For the time being, we use the term "Base Station” to refer to any wireless station that communicates wirelessly with a set of clients from a fixed location. Examples of Base Stations are access points in wireless local area networks (WLANs) or
• the Base Station 200 is positioned on the ground and is configured to transmit upward at HF frequencies (e.g., frequencies up to 24MHz) to bounce signals off the ionosphere as described in co-pending application entitled SYSTEM AND METHOD FOR ENHANCING NEAR VERTICAL INCIDENCE SKYWAVE ("NVIS”)
• HF frequencies e.g., frequencies up to 24MHz
• the Base Station may be connected to a variety of different types of wide area networks via WAN interface 201 including application-specific wide area networks such as those used for digital video distribution.
• the Client Devices may be any variety of wireless data processing and/or communication devices including, but not limited to cellular phones, personal digital assistants ("PDAs”), receivers, and wireless cameras.
• the Base Station's n Antennas 202 are separated spatially such that each is transmitting and receiving signals which are not spatially correlated, just as if the Base Station was a prior art MHvlO transceiver.
• ⁇ /6 i.e. 1/6 wavelength
• a single Base Station 200 may very well have its antennas located very far apart.
• the antennas may be 10 meters apart or more (e.g., in an NVIS implementation mentioned above). If 100 such antennas are used, the Base Station's antenna array could well occupy several square kilometers.
• one embodiment of the invention polarizes the signal in order to increase the effective throughput of the system.
• Increasing channel capacity through polarization is a well known technique which has been employed by satellite television providers for years.
• Using polarization it is possible to have multiple (e.g., three) Base Station or users' antennas very close to each other, and still be not spatially correlated.
• conventional RF systems usually will only benefit from the diversity of two dimensions (e.g. x and y) of polarization, the architecture described herein may further benefit from the diversity of three dimensions of polarization (x, y and z).
• one embodiment of the invention employs antennas with near-orthogonal radiation patterns to improve link performance via pattern diversity.
• Pattern diversity can improve the capacity and error-rate performance of MIMO systems and its benefits over other antenna diversity techniques have been shown in the following papers:
• FIG. 3 provides additional detail of one embodiment of the Base Station 200 and Client Devices 203-207 shown in Figure 2.
• the Base Station 300 is shown with only three antennas 305 and only three Client Devices 306-308. It will be noted, however, that the embodiments of the invention described herein may be
• Figure 3 is similar to the prior art MIMO architecture shown in Figure 1 in that both have three antennas on each sides of a communication channel.
• the three antennas 105 on the right side of Figure 1 are all a fixed distance from one another (e.g., integrated on a single device), and the received signals from each of the antennas 105 are processed together in the Signal Processing subsystem 107.
• the three antennas 309 on the right side of the diagram are each coupled to a different Client Device 306-308, each of which may be distributed anywhere within range of the Base Station 305.
• the signal that each Client Device receives is processed independently from the other two received signals in its Coding, Modulation, Signal Processing subsystem 311.
• FIG. 3 illustrates a Multiple Input (i.e. antennas 305) Distributed Output (i.e. antennas 305) system, referred to hereinafter as a "MIDO" system.
• the MIDO architecture shown in Figure 3 achieves a similar capacity increase as ⁇ over a SISO system for a given number of transmitting antennas.
• each MEDO Client Device 306-308 requires only a single receiving antenna, whereas with MEMO, each Client Device requires as least as many receiving antennas as the capacity multiple that is hoped to be achieved. Given that there is usually a practical limit to how many antennas can be placed on a Client Device (as explained in the Background), this typically limits MEMO systems to between four to ten antennas (and 4X to 10X capacity multiple). Since the Base Station 300 is typically serving many Client Devices from a fixed and powered location, is it practical to expand it to far more antennas than ten, and to separate the antennas by a suitable distance to achieve spatial diversity. As illustrated, each
• the channel is characterized.
• a training signal is transmitted (in the embodiment herein described), one-by-one, by each of the antennas 405.
• Figure 4 illustrates only the first training signal transmission, but with three antennas 405 there are three separate transmissions in total.
• Each training signal is generated by the Coding, Modulation, and Signal Processing subsystem 403, converted to analog through a D/A converter, and transmitted as RF through each RF Transceiver 404.
• Various different coding, modulation and signal processing techniques may be employed including, but not limited to, those described above (e.g., Reed Solomon, Viterbi coding; QAM, DPSK, QPSK modulation, . . . etc) .
• Each Client Device 406-408 receives a training signal through its antenna 409 and converts the training signal to baseband by Transceiver 410.
• An A D converter (not shown) converts the signal to digital where is it processed by each Coding, Modulation, and Signal Processing subsystem 4 .
• Signal c iaracterization logic 320 then characterizes the resulting signal (e.g., identifying phase and amplitude distortions as described above) and stores the characterization in memory.
• This characterization process is similar to that of prior art MIMO systems, with a notable difference being that the each client device only computes the characterization vector for its one antenna, rather than for n antennas. For example, the
• Coding Modulation and Signal Processing subsystem 420 of client device 406 is initialized with a known pattern of the training signal (either at the time of manufacturing, by receiving it in a transmitted message, or through another initialization process).
• Coding Modulation and Signal Processing subsystem 420 uses correlation methods to find the strongest received pattern of the training signal, it stores the phase and amplitude offset, then it subtracts this pattern from the received signal.
• it finds then second strongest received pattern that correlates to the training signal it stores the phase and amplitude offset, then it subtracts this second strongest pattern from the received signal. This process continues until either some fixed number of phase and amplitude offsets are stored (e.g.
• the memory in which the characterization is stored may be a non-volatile memory such as a Flash memory or a hard drive and/or a volatile memory such as a random access memory (e.g., SDRAM, RDAM).
• a non-volatile memory such as a Flash memory or a hard drive
• a volatile memory such as a random access memory (e.g., SDRAM, RDAM).
• different Client Devices may concurrently employ different types of memories to store the characterization information (e.g., PDA's may use Flash memory whereas notebook computers may use a hard drive).
• PDA's may use Flash memory whereas notebook computers may use a hard drive.
• the underlying principles of the invention are not limited to any particular type of storage mechanism on the various Client Devices or the Base Station.
• each Client Device 406-408 since each Client Device 406-408 has only one antenna, each only stores a 1x3 row 413-415 of the H matrix.
• Figure 4 illustrates the stage after the first training signal transmission where the first column of 1x3 rows 413-415 has been stored with channel characterization information for the first of
• the three Base Station antennas 405. The remaining two columns are stored following the channel characterization of the next two training signal transmissions from the remaining two base station antennas. Note that for the sake of illustration the three training signals are transmitted at separate times. If the three training signal patterns are chosen such as not to be correlated to one another, they may be transmitted simultaneously, thereby reducing training time.
• each Client Device 506-508 transmits back to the Base Station 500 the 1x3 row 513-515 of matrix H that it has stored.
• An appropriate modulation scheme e.g. DPS , 64QAM, OFDM
• adequate error correction coding e.g. Reed Solomon, Viterbi, and/or Turbo codes
• Base Station 500 receives the 1x3 row 513-515, from each Client Device 507-508, it stores it in a 3x3 H matrix 516.
• the Base Station may employ various
• FIG. 5 illustrates a stage at which the Base Station 500 has received and stored the 1x3 row 513 from Client Device 509.
• the 1 3 rows 514 and 515 may be transmitted and stored in H matrix 516 as they are received from the remaining Client Devices, until the entire H matrix 516 is stored.
• a MIDO transmission from a Base Station 600 to Client Devices 606-608 will now be described with reference to Figure 66. Because each Client Device 606-608 is an independent device, typically each device is receiving a different data transmission. As such, one embodiment of a Base Station 600 includes a Router 602 communicatively positioned between the WAN Interface 601 and the Coding, Modulation and Signal Processing subsystem 603 that sources multiple data streams (formatted into bit streams) from the WAN interface 601 and routes them as separate bit streams «i- «3 intended for each Client Device 606-608, respectively. Various well known routing techniques may be employed by the router 602 for this purpose.
• the three bit streams, HI- «3, shown in Figure 6 are then routed into the Coding, Modulation and Signal Processing subsystem 603 and coded into statistically distinct, error correcting streams (e.g. using Reed Solomon, Viterbi, or Turbo Codes) and modulated using an appropriate modulation scheme for the channel (such as DPSK, 64QAM or OFDM).
• the embodiment illustrated in Figure 6 includes signal precoding logic 630 for uniquely coding the signals transmitted from each of the antennas 605 based on the signal characterization matrix 616. More specifically, rather than routing each of the three coded and modulated bit streams to a separate antenna (as is done in Figure 1), in one embodiment, the precoding logic 630 multiplies the three bit streams wi- «3 in Figure 6 by the
• each Hi contains the data from one of the three bit streams routed by the Router 602, and each such bit stream is intended for one of the three Client Devices 606-608.
• each u is received at each Client Device antenna 609 (plus whatever noise N there is in the channel).
• the output of each of the three antennas 605 is a function of «i and the H matrix that characterizes the channel for each Client Device.
• each j is calculated by the precoding logic 630 within the Coding, Modulation and Signal Processing subsystem 603 by implementing the following formulas:
• V2 U]H " ' 2 l + U 2 K l 22 + 3H _1 23
• Each antenna 609 receives u, already separated from the other w n- i bit streams intended for the other antennas 609.
• Each Transceiver 610 converts each received signal to baseband, where it is digitized by an A/D converter (now shown), and each Coding, Modulation and Signal Processing subsystem 611, demodulates and decodes the J:; bit stream intended for it, and sends its bit stream to a Data Interface 612 to be used by the Client Device (e.g., by an application on the client device).
• the embodiments of the invention described herein may be implemented using a variety of different coding and modulation schemes.
• the techniques described herein may be employed to characterize each individual sub-band.
• the underlying principles of the invention are not limited to any particular modulation scheme.
• the channel characterization matrix 616 at the Base Station is continually updated.
• the Base Station 600 periodically (e.g., every 250 milliseconds) sends out a new training signal to each Client Device, and each Client Device continually transmits its channel characterization vector back to the Base Station 600 to ensure that the channel characterization remains accurate (e.g. if the environment changes so as to affect the channel or if a Client Device moves).
• the training signal is interleaved within the actual data signal sent to each client device. Typically, the training signals are much lower throughput than the data signals, so this would have little impact on the overall throughput of the system. Accordingly, in this embodiment, the
• Filed Via EFS-Web 6181 P515X channel characterization matrix 616 may be updated continuously as the Base Station actively communicates with each Client Device, thereby maintaining an accurate channel characterization as the Client Devices move from one location to the next or if the environment changes so as to affect the channel.
• One embodiment of the invention illustrated in Figure 7 employs ⁇ techniques to improve the upstream communication channel (i.e., the channel from the Client Devices 706-708 to the Base Station 700).
• the channel from each of the Client Devices is continually analyzed and characterized by upstream channel
• each of the Client Devices 706-708 transmits a training signal to the Base Station 700 which the channel characterization logic 741 analyzes (e.g., as in a typical ⁇ system) to generate an N x M channel characterization matrix 741, where N is the number of Client Devices and M is the number of antennas employed by the Base Station.
• the embodiment illustrated in Figure 7 employs three antennas 705 at the Base Station and three Client Devices 706-608, resulting in a 3x3 channel characterization matrix 741 stored at the Base Station 700.
• the ⁇ upstream transmission illustrated in Figure 7 may be used by the Client Devices both for transmitting data back to the Base Station 700, and for transmitting channel characterization vectors back to the Base Station 700 as illustrated in Figure 5.
• each signal's characterization may include many factors including, for example, phase and amplitude relative to a reference internal to the receiver, an absolute reference, a relative reference, characteristic noise, or other factors.
• the characterization might be a vector of the phase and amplitude offsets of several multipath images of the signal.
• QAM quadrature amplitude modulation
• OFDM orthogonal frequency division multiplexing
• the training signal may be generated by each Client Device's coding and modulation subsystem 711, converted to analog by a D/A converter (not shown), and then converted from baseband to RF by each Client Device's transmitter 709.
• Client Devices in order to ensure that the training signals are synchronized, Client Devices only transmit training signals when requested by the Base Station (e.g., in a round robin manner).
• training signals may be interleaved within or transmitted concurrently with the actual data signal sent from each client device.
• the training signals may be continuously transmitted and analyzed by the upstream channel characterization logic 741, thereby ensuring that the channel characterization matrix 741 remains up-to-date.
• the total channel capacity supported by the foregoing embodiments of the invention may be defined as min (N, M) where M is the number of Client Devices and N is the number of Base Station antennas. That is, the capacity is limited by the number of antennas on either the Base Station side or the Client side.
• one embodiment of the invention employs synchronization techniques to ensure that no more than min (N, M) antennas are transmitting/ receiving at a given time.
• the number of antennas 705 on the Base Station 700 will be less than the number of Client Devices 706-708.
• An exemplary scenario is illustrated in Figure 8 which shows five Client Devices 804-808 communicating with a base station having three antennas 802.
• the Base Station 800 selects the two Client Devices 807, 808 which were not included in the first group. In addition, because an extra antenna is available, the Base Station 800 selects an additional client device 806 included in the first group. In one embodiment, the Base Station 800 cycles between groups of clients in this manner such that each client is effectively allocated the same amount of throughput over time. For example, to allocate throughput evenly, the Base Station may subsequently select any combination of three Client Devices which excludes Client Device 806 (i.e., because Client Device 806 was engaged in communication with the Base Station for the first two cycles).
• the Base Station may employ the foregoing techniques to transmit training signals to each of the Client Devices and receive training signals and signal characterization data from each of the Client Devices.
• certain Client Devices or groups of client devices may be allocated different levels of throughput. For example, Client Devices may be prioritized such that relatively higher priority Client Devices may be guaranteed more communication cycles
• the "priority" of a Client Device may be selected based on a number of variables including, for example, the designated level of a user's subscription to the wireless service (e.g., user's may be willing to pay more for additional throughput) and/or the type of data being communicated to/from the Client Device (e.g., real-time communication such as telephony audio and video may take priority over non-real time communication such as email).
• the Base Station dynamically allocates throughput based on the Current Load required by each Client Device. For example, if Client Device 804 is streaming live video and the other devices 805-808 are performing non-real time functions such as email, then the Base Station 800 may allocate relatively more throughput to this client 804. It should be noted, however, that the underlying principles of the invention are not limited to any particular throughput allocation technique.
• the Base Station will receive and store effectively equivalent channel characterization vectors for the two Client Devices 907, 908 and therefore will not be able to create unique, spatially distributed signals for each Client Device. Accordingly, in one embodiment, the Base Station will ensure that any two or more Client Devices which are in close proximity to one another are allocated to different groups.
• the Base Station 900 first communicates with a first group 910 of Client Devices 904, 905 and 908; and then with a second group 911 of Client Devices 905, 906, 907, ensuring that Client Devices 907 and 908 are in different groups.
• the Base Station 900 communicates with both Client Devices 907 and 908 concurrently, but multiplexes the communication channel using known channel multiplexing techniques.
• the Base Station may employ time division multiplexing ('TDM”), frequency division multiplexing (“FDM”) or code division multiple access (“CDMA”) techniques to divide the single, spatially-correlated signal between Client Devices 907 and 908.
• 'TDM time division multiplexing
• FDM frequency division multiplexing
• CDMA code division multiple access
• each Client Device described above is equipped with a single antenna
• the underlying principles of the invention may be employed using Client Devices with multiple antennas to increase throughput.
• a client with 2 antennas will realize a 2x increase in throughput
• a client with 3 antennas will realize a 3x increase in throughput, and so on (i.e., assuming that the spatial and angular separation between the antennas is sufficient).
• the Base Station may apply the same general rules when cycling through Client Devices with multiple antennas. For example, it may treat each antenna as a separate client and allocate throughput to that "client" as it would any other client (e.g., ensuring that each client is provided with an adequate or equivalent period of communication).
• one embodiment of the invention employs the MIDO and/or MIMO signal transmission techniques described above to increase the signal-to-noise ratio and throughput within a Near Vertical Incidence Skywave (“NVIS") system.
• NVIS Near Vertical Incidence Skywave
• a first NVIS station 1001 equipped with a matrix of N antennas 1002 is configured to communicate with M client devices 1004.
• the NVIS antennas 1002 and antennas of the various client devices 1004 transmit signals upward to within about 15 degrees of vertical in order to achieve the desired NVIS and minimize ground wave interference effects.
• a designated frequency within the NVIS spectrum e.g., at a carrier frequency at or below 23 MHz, but typically below 10 MHz
• the NVIS antennas serving a given station may be physically very far apart from each other. Given the long wavelengths below 10 MHz and the long distance traveled for the signals (as much as 300 miles round trip), physical separation of the antennas by 100s of yards, and even miles, can provide advantages in diversity. In such situations, the individual antenna signals may be brought back to a centralized location to be processed using conventional wired or wireless communications systems. Alternatively, each antenna can have a local facility to process its signals, then use conventional wired or wireless communications systems to communicate the data back to a centralized location. In one embodiment of the invention, NVIS Station 1001 has a broadband link 1015 to the Internet 1010 (or other wide area network), thereby providing the client devices 1003 with remote, high speed, wireless network access.
• the Internet 1010 or other wide area network
• the Base Station and/or users may exploit
• polarization/pattern diversity techniques described above to reduce the array size and/or users' distance while providing diversity and increased throughput.
• the users may be in the same location and yet their signals be uncorrelated because of polarization pattern diversity.
• pattern diversity one user may be communicating to the Base Station via groundwave whereas the other user via NVIS.
• One embodiment of the invention employs a system and method to compensate for in-phase and quadrature (I/Q) imbalance in distributed-input distributed- output (DIDO) systems with orthogonal frequency division multiplexing (OFDM).
• user devices estimate the channel and feedback this information to the Base Station; the Base Station computes the precoding matrix to cancel inter-carrier and inter-user interference caused by I/Q imbalance; and parallel data streams are transmitted to multiple user devices via DIDO precoding; the user devices demodulate data via zero-forcing (ZF), minimum mean-square error (MMSE) or maximum likelihood (ML) receiver to suppress residual interference.
• ZF zero-forcing
• MMSE minimum mean-square error
• ML maximum likelihood
• the transmit and receive signals of typical wireless communication systems consist of in-phase and quadrature (I Q) components.
• I Q in-phase and quadrature
• the inphase and quadrature components may be distorted due to imperfections in the mixing and baseband operations. These distortions manifest as I/Q phase, gain and delay mismatch.
• Phase imbalance is caused by the sine and cosine in the modulator/demodulator not being perfectly orthogonal.
• Gain imbalance is caused by different amplifications between the inphase and quadrature components.
• delay imbalance due to difference in delays between the I-and Q-rails in the analog circuitry.
• I/Q imbalance causes inter-carrier interference (ICI) from the mirror tones.
• ICI inter-carrier interference
• M. D. Benedetto and P. Mandarini "Analysis of the effect of the VQ baseband filter mismatch in an OFDM modem," Wireless personal communications, pp. 175-186, 2000; S. Schuchert and R. Hasholzner, "A novel VQ imbalance compensation scheme for the reception of OFDM signals," IEEE Transaction on Consumer Electronics, Aug. 2001; M. Valkama, M. Renfors, and V.
• DIDO systems consist of one Base Station with distributed antennas that transmits parallel data streams (via pre-coding) to multiple users to enhance downlink throughput, while exploiting the same wireless resources (i.e., same slot duration and frequency band) as conventional SISO systems.
• a detailed description of DIDO systems was presented in S. G. Perlman and T. Cotter, "System and Method for Distributed Input- Distributed Output Wireless Communications," Serial No. 10/902,978, filed July 30, 2004 ("Prior Application"), which is assigned to the assignee of the present application and which is incorporated herein by reference.
• DEDO precoders There are many ways to implement DEDO precoders.
• One solution is block diagonalization (BD) described in Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, "Zero - forcing methods for downlink spatial multiplexing in multiuser MEMO channels," IEEE Trans. Sig. Proc, vol. 52, pp. 461 ⁇ 71 , Feb. 2004. K. . Wong, R. D. Murch, and K. B. Letaief, "A joint channel diagonalization for multiuser MEMO antenna systems," EEEE Trans. Wireless Comm., vol. 2, pp. 773-786, Jul 2003; L. U. Choi and R. D.
• Murch "A transmit preprocessing technique for multiuser MEMO systems using a decomposition approach," EEEE Trans. Wireless Comm., vol. 3, pp. 20-24, Jan 2004; Z. Shen, J. G. Andrews, R. W. Heath, and B. L. Evans, "Low complexity user selection algorithms for multiuser MEMO systems with block diagonalization,” accepted for publication in EEEE Trans. Sig. Proc, Sep. 2005; Z. Shen, R. Chen, J. G. Andrews, R. W. Heath, and B. L. Evans, "Sum capacity of multiuser MEMO broadcast channels with block diagonalization," submitted to EEEE Trans. Wireless Comm., Oct. 2005; R. Chen, R. W. Heath, and J. G.
• I Q mismatch causes two effects: ICI and inter-user interference.
• the former is due to interference from the mirror tones as in SISO-OFDM systems.
• the latter is due to the fact that I/Q mismatch destroys the orthogonality of the DIDO precoder yielding interference across users. Both of these types of interference can be cancelled at the transmitter and receiver through the methods described herein.
• Three methods for I Q compensation in DEDO-OFDM systems are described and their performance is compared against systems with and without I/Q mismatch. Results are presented based both on simulations and practical measurements carried out with the DEDO-OFDM prototype.
• the training signals employed for channel estimation are used to calculate the DIDO precoder with I Q compensation at the transmitter;
• the signal characterization data accounts for distortion due to I Q imbalance and is used at the transmitter to compute the DEDO precoder according to the method proposed in this document. b. Embodiments of the Invention
• the equivalent channel is the one you would observe if there were no I Q gain and phase imbalance.
• t. o
• r is the discrete time index
• h e ,h c e C** ,s [s, ,..., s N ]
• x and L is the number of channel taps.
• the second contribution in (1) is interference from the mirror tone. It can be dealt with by constructing the following stacked matrix system (note carefully the conjugates)
• H ⁇ "' , H'" e C 2 denote the m-th row of the matrices H F and H C , respectively, and W e C jt4 is the DIDO pre-coding matrix.
• the DIDO precoding matrix W in (3) is designed to cancel these two interference terms.
• BD block diagonalization
• Q. H. Spencer, A. L. Swindlehurst, and M. Haardt "Zeroforcing methods for downlink spatial multiplexing in multiuser MIMO channels," IEEE Trans. Sig. Proc, vol. 52, pp. 461-471, Feb. 2004.
• Letaief "A joint channel diagonalization for multiuser ⁇ antenna systems," IEEE Trans. Wireless Comm., vol. 2, pp. 773-786, Jul 2003. L. U. Choi and R.
• the receiver may apply any number of other filters known to those skilled in the art.
• the receiver may perform a maximum likelihood symbol detection (or sphere decoder or iterative variation). For example, the first user might use the ML receiver and solve the following optimization
• Figure 13 illustrates one embodiment of a framework for DIDO-OFDM systems with I Q compensation including IQ-DIDO precoder 1302 within a Base Station (BS), a transmission channel 1304, channel estimation logic 1306 within a user device, and a 2F, MMSE or ML receiver 1308.
• the channel estimation logic 1306 estimates the channels //TM' and ffM via training symbols and feedbacks these estimates to the precoder 1302 within the AP.
• the BS computes the DIDO precoder weights (matrix W) to pre-cancel the interference due to I/Q gain and phase imbalance as well as inter-user interference and transmits the data to the users through the wireless channel 1304.
• User device m employs the ZF, MMSE or ML receiver 1308, by exploiting the channel estimates provided by the unit 1304, to cancel residual interference and demodulates the data.
• Method 1 - TX compensation In this embodiment, the transmitter calculates the pre-coding matrix according to the criterion in (4).
• the user devices employ a "simplified" ZF receiver, where /y ⁇ u > and 316 assumed to be diagonal matrices.
• Method 2 - RX compensation In this embodiment, the transmitter calculates the pre-coding matrix based on the conventional BD method described in R. Chen, R. W. Heath, and J. G. Andrews, 'Transmit selection diversity for unitary precoded multiuser spatial multiplexing systems with linear receivers," accepted to IEEE Trans, on Signal Processing,
• the user devices employ a ZF filter as in (8).
• this method does not pre-cancel the interference at the transmitter as in the method 1 above. Hence, it cancels the inter-carrier interference at the receiver, but it is not able to cancel the inter- user interference.
• the users only need to feedback the vector // ⁇ ⁇ "" for the transmitter to compute the DIDO precoder, as opposed to method 1 that requires feedback of both // ⁇ m > and fj ⁇ . Therefore, method 2 is particularly suitable for DIDO systems with low rate feedback channels.
• method 2 requires slightly higher computational complexity at the user device to compute the ZF receiver in (8) rather than (1 1).
• Method 3 - TX-RX compensation In one embodiment, the two methods described above are combined.
• the transmitter calculates the pre-coding matrix as in (4) and the receivers estimate the transmit symbols according to (8).
• I/Q imbalance whether phase imbalance, gain imbalance, or delay imbalance, creates a deleterious degradation in signal quality in wireless communication systems. For this reason, circuit hardware in the past was designed to have very low imbalance. As described above, however, it is possible to correct this problem using digital signal processing in the form of transmit pre-coding and/or a special receiver.
• One embodiment of the invention comprises a system with several new functional units, each of which is
• a DIDO transmitter uses pre-coding based on channel state information to cancel inter-carrier interference (ICI) from mirror tones (due to I Q mismatch) in an OFDM system.
• a DIDO transmitter includes a user selector unit 1 102, a plurality of coding modulation units 1 104, a corresponding plurality of mapping units 1 106, a DIDO IQ-aware precoding unit 1108, a plurality of RF transmitter units 11 14, a user feedback unit 11 12 and a DIDO configurator unit 1110.
• the user selector unit 1102 selects data associated with a plurality of users
• Each coding modulation unit 1 104 encodes and modulates the information bits of each user and send them to the mapping unit 1 106.
• the mapping unit 1106 maps the input bits to complex symbols and sends the results to the DIDO IQ-aware precoding unit 1 108.
• the DIDO IQ-aware precoding unit 1108 exploits the channel state information obtained by the feedback unit 1 112 from th e u s ers to compute the DIDO IQ-aware precoding weights and precoding the input symbols obtained from the mapping units 1 106.
• Each of the precoded data streams is sent by the DIDO IQ-aware precoding unit 1 108 to the OFDM unit 1 115 that computes the IFFT and adds the cyclic prefix.
• This information is sent to the D/A unit 1116 that operates the digital to analog conversion and send it to the RF unit 1 114.
• the RF unit 1 114 upconverts the baseband signal to intermediate radio frequency and send it to the transmit antenna.
• the precoder operates on the regular and mirror tones together for the purpose 0 f c ompensating for I/Q imbalance. Any number of precoder design criteria may be
• the precoder completely removes the ICI due to I/Q mismatch thus resulting in the receiver not having to perform any additional compensation.
• the precoder uses a block diagonalization criterion to compl e te l cancel inter-user interference while not completely canceling the I Q effects for each user, requiring additional receiver processing.
• the precoder uses a zero-forcing criterion to completely cancel both inter-user interference and ICI due to I/Q imbalance. This embodiment can use a conventional DIDO-OFDM processor at the receiver.
• One embodiment of the invention uses pre-coding based on channel state information to cancel inter-carrier interference (ICI) from mirror tones (due to I/Q mismatch) in a DIDO-OFDM system and each user employs an IQ-aware DIDO receive r .
• a system including the receiver 1202 includes a plurality of RF units 1208, a corresponding plurality of A/D units 1210, an IQ- aware channel estimator unit 1204 and a DIDO feedback generator unit 1206.
• the RF units 1208 receive signals transmitted from the DIDO transmitter units 11 14 downconverts the signals to baseband and provide the downconverted signals to the A D units 1210.
• the A D units 1210 then convert the signal from a naiOg to digital and send it to the OFDM units 1213.
• the OFDM units 1213 remove the cyclic prefix and operates the FFT to report the signal to the frequency domain.
• the OFDM units 1213 send the output to the IQ-aware channel estimate unit 1204 that computes the channel estimates in the frequency domain. Alternatively, the channel estimates can be c om p uted in the time domain.
• the OFDM units 1213 send the output to the IQ-aware receiver unit 1202.
• the IQ-aware receiver unit 1202 computes the IQ receiver
• the IQ-aware channel estimate unit 1204 sends the channel estimates to the DIDO feedback generator unit 1206 that may quantize the channel estimates and send it back to the transmitter via the feedback control channel 1 112.
• the receiver 1202 illustrated in Figure 12 may operate under any number of criteria known to those skilled in the art including ZF, MMSE, maximum likelihood, or MAP receiver.
• the receiver uses an MMSE filter to cancel the ICI caused by IQ imbalance on the mirror tones.
• the receiver uses a nonlinear detector like a maximum likelihood search to jointly detect the symbols on the mirror tones. This method has improved performance at the expense of higher complexity.
• an IQ-aware channel estimator 1204 is used to determine the receiver coefficients to remove ICI. Consequently we claim a DIDO-OFDM system that uses pre-coding based on channel state information to cancel inter-carrier interference (ICI) from mirror tones (due to I Q mismatch), an IQ-aware DIDO receiver, and an IQ-aware channel estimator.
• the channel estimator may use a conventional training signal or may use specially constructed training signals sent on the inphase and quadrature signals. Any number of estimation algorithms may be implemented including least squares, MMSE, or maximum likelihood.
• the IQ-aware channel estimator provides an input for the IQ-aware receiver.
• Channel state information can be provided to the station through channel reciprocity or through a feedback channel.
• One embodiment of the invention comprises a DIDO-OFDM system, with I Q-aware precoder, with an I/Q-aware feedback channel for
• the feedback channel may be a physical or logical control channel. It may be dedicated or shared, as in a random access channel.
• the feedback information may be generated using a DIDO feedback generator at the user terminal, which we also claim.
• the DIDO feedback generator takes as an input the output of the VQ aware channel estimator. It may quantize the channel coefficients or may use any number of limited feedback algorithms known in the art.
• one embodiment comprises an IQ-aware DIDO configurator that uses an IQ-aware channel estimate from one or more users to configure the DIDO IQ-aware precoder, choose the modulation rate, coding rate, subset of users allowed to transmit, and their mappings to space-time-frequency code slots.
• DIDO 2 x 2 systems will be compared:
• Figure 14 depicts the 64-QAM constellations obtained from the three systems described above. These constellations are
• the first constellation 1401 is very noisy due to interference from the mirror tones caused by I Q imbalance.
• the second constellation 1402 shows some improvements due to I Q
• the second constellation 1402 is not as clean as the ideal case shown as constellation 1403 due to possible phase noise that yields inter-carrier interference (ICI).
• ICI inter-carrier interference
• Figure 15 shows the average SER (Symbol Error Rate) 1501 and per-user goodput 1502 performance of DIDO 2x2 s stems with 64-QAM and coding rate 3/4, with and without I/Q mismatch.
• SER and goodput performance is evaluated as a function of the average per-tone transmit power (rather than total transmit power) to guarantee a fair comparison across different cases.
• we use normalized values of transmit power (expressed in decibel), since our goal here is to compare the relative (rather than absolute) performance of different schemes.
• Figure 15 shows that in presence of I Q imbalance the SER saturates, without reaching the target SER ( ⁇ 10 "2 ), consistently to the results reported in A. Tarighat and A. H. Sayed, "MIMO OFDM receivers for systems with IQ imbalances," IEEE Trans. Sig. Proc, vol. 53, pp. 3583-3596, Sep. 2005.
• This saturation effect is due to the fact that both signal and interference (from the mirror tones) power increase as the TX power increases.
• the proposed I/Q compensation method it is possible to cancel the interference and obtain better SER performance. Note that the slight increase in SER at high SNR is due to amplitude saturation effects in the DAC, due to the larger transmit power required for 64-QAM modulations.
• FIG. 16 graphs the SER performance of different QAM constellations with and without I/Q compensation.
• the proposed method is particularly beneficial for 64-QAM constellations.
• the method for I Q compensation yields worse performance than the case with I/Q mismatch, possibly because the pro po sed method requires larger power to enable both data transmission and interference cancellation from the mirror tones.
• 4-QAM and 16-QAM are not as affected by VQ mismatch as 64-QAM due to the larger minimum distance between constellation points. See A. Tarighat, R. Bagheri, and A. H. Sayed, "Compensation schemes and performance analysis of IQ imbalances in OFDM receivers," IEEE Transactions on Signal Processing, vol. 53, pp.
• Figure 17 shows that all three compensation methods always outperform the case of no compensation. Moreover, it should be noted that method 3 outperforms the other two compensation methods in any channel scenario.
• the relative performance of method 1 and 2 depends on the propagation conditions. It is observed through practical measurement campaigns that method 1 generally outperforms method 2, since it pre-cancels (at the transmitter) the inter-user interference caused by I/Q imbalance. When this inter-user interference is minimal, method 2 may outperform method 1 as illustrated in graph 1702 of Figure 17, since it does not suffer from power loss due to the I/Q compensation precoder.
• method 2 can be used to reduce the amount of feedback required for the DIDO precoder, at the expense of worse SER performance.
• DIDO distributed-input distributed-output
• This method dynamically allocates the wireless resources to different user devices, by tracking the changing channel conditions, to increase throughput while satisfying certain target error rate.
• the user devices estimate the channel quality and feedback it to the Base Station (BS); the Base Station processes the channel quality obtained from the user devices to select the best set of user devices, DIDO scheme, modulation/coding scheme (MCS) and array configuration for the next transmission; the Base Station transmits parallel data to multiple user devices via pre-coding and the signals are demodulated at the receiver.
• BS Base Station
• MCS modulation/coding scheme
• a system that efficiently allocates resources for a DIDO wireless link includes a DIDO Base Station with a DIDO configurator, which processes feedback received from the users to select the best set of users, DIDO scheme, modulation/coding scheme (MCS) and array configuration for the next transmission; a receiver in a DIDO system that measures the channel and other relevant parameters to generate a DIDO feedback signal; and a DIDO feedback control channel for conveying feedback information from users to the Base Station.
• MCS modulation/coding scheme
• DIDO transmission schemes i.e., antenna selection or multiplexing
• MCS modulation/coding scheme
• array configurations based on the channel quality information, to minimize SER or maximize per-user or downlink spectral efficiency
• DIDO transmission schemes i.e., antenna selection or multiplexing
• MCS modulation/coding scheme
• MHvlO multiple-input multiple-output
• diversity schemes such as orthogonal space-time block codes (OSTBC) (See V. Tarokh, H. Jafarkhani, and A. R. Calderbank, "Spacetime block codes from orthogonal designs,” ⁇ Trans. Info, Th., vol. 45, pp. 1456-467, Jul. 1999) or antenna selection (See R. W. Heath Jr., S. Sandhu, and A. J. Paulraj, "Antenna selection for spatial multiplexing systems with linear receivers," IEEE Trans. Comm., vol. 5, pp. 142-144, Apr. 2001) are conceived to combat channel fading, providing increased link robustness that translates in better coverage.
• OSTBC orthogonal space-time block codes
• antenna selection See R. W. Heath Jr., S. Sandhu, and A. J. Paulraj, "Antenna selection for spatial multiplexing systems with linear receivers," IEEE Trans. Comm., vol. 5, pp. 142-1
• SM spatial multiplexing
• implementation is to adaptively switch between diversity and multiplexing transmission schemes, by tracking the changing channel conditions.
• Catreux Adaptive modulation and MEMO coding for broadband wireless data networks
• OFDM orthogonal frequency division multiplexing
• a novel adaptive DIDO transmission strategy is described herein that switches between different numbers of users, numbers of transmit antennas and transmission schemes based on channel quality information as a means to improve the system performance.
• schemes that adaptively select the users in multiuser MIMO systems were already proposed in M. Sharif and B. Hassibi, "On the capacity of MIMO broadcast channel with partial side information," IEEE Trans. Info. Th., vol. 51, p. 506522, Feb. 2005; and W. Choi, A. Forenza, J. G. Andrews, and R. W. Heath Jr., "Opportunistic space division multiple access with beam selection," to appear in IEEE Trans, on Communications.
• the training symbols of the Prior Application for channel estimation can be employed by the wireless client devices to evaluate the link-quality metrics in the adaptive DIDO scheme;
• the base station receives signal characterization data from the client devices as described in the Prior Application.
• the signal characterization data is defined as link-quality metric used to enable adaptation;
• the Prior Application describes a mechanism to select the number of transmit antennas and users as well as defines throughput allocation. Moreover, different levels of throughput can be dynamically assigned to different clients as in the Prior Application.
• the current embodiment of the invention defines novel criteria related to this selection and throughput allocation.
• the goal of the proposed adaptive DIDO technique is to enhance per-user or downlink spectral efficiency by dynamically allocating the wireless resource in time, frequency and space to different users in the system.
• the general adaptation criterion is to
• the Base Station collects the channel state information (CSI) from all the users in 2102. From the received CSI, the BS computes the link quality metrics in time/frequency/space domains in 2104. These link quality metrics are used to select the users to be served in the next transmission as well as the transmission mode for each of the users in 2106. Note that the transmission modes consist of different combinations of
• the BS transmits data to the users via DEDO precoding as in 2108.
• the Base Station collects the channel state information (CSI) from all the user devices.
• the CSI is used by the Base Station to determine the instantaneous or statistical channel quality for all the user devices at 2104.
• the channel quality (or link quality metric) can be estimated in the time, frequency and space domains.
• the Base Station uses the link quality metric to determine the best subset of users and transmission mode for the current propagation conditions.
• a set of DIDO transmission modes is defined as combinations of DIDO schemes (i.e., antenna selection or multiplexing), modulation/coding schemes (MCSs) and array configuration.
• data is transmitted to user devices using the selected number of users and transmission modes.
• the mode selection is enabled by lookup tables (LUTs) pre-computed based on error rate performance of DIDO systems in different propagation
• LUTs Map channel quality information into error rate performance.
• the error rate performance of DIDO systems is evaluated in different propagation scenarios as a function of the SNR. From the error rate curves, it is possible to compute the minimum SNR required to achieve certain pre-defined target error rate. We define this SNR requirement as SNR threshold. Then, the SNR thresholds are evaluated in different propagation scenarios and for different DIDO transmission modes and stored in the LUTs. For example, the SER results in Figures 24 and 26 can be used to construct the LUTs. Then, from the LUTs, the Base Station selects the transmission modes for the active users that increase throughput while satisfying predefined target error rate. Finally, the Base Station transmits data to the selected users via DIDO pre-coding. Note that different DIDO modes can be assigned to different time slots, OFDM tones and DIDO substreams such that the adaptation may occur in time, frequency and space domains.
• configurator 1910 performs a plurality of functions including selecting the number of users, DIDO transmission schemes (i.e., antenna selection or multiplexing), modulation/coding scheme (MCS), and array configurations based on the channel quality information 1912 provided by user devices.
• DIDO transmission schemes i.e., antenna selection or multiplexing
• MCS modulation/coding scheme
• array configurations based on the channel quality information 1912 provided by user devices.
• the user selector unit 1902 selects data associated with a plurality of users
• Each coding modulation unit 1 04 encodes and modulates the information bits of each user and sends them to the mapping unit 1906.
• the mapping unit 1906 maps the input bits to complex
• Both the coding modulation units 1904 and the mapping unit 1906 exploit the information obtained from the DIDO configurator unit 1910 to choose the type of modulation coding scheme to employ for each user. This information is computed by the DIDO configurator unit 1910 by exploiting the channel quality information of each of the users as provided by the feedback unit 1912.
• the DIDO precoding unit 1908 exploits the information obtained by the DEDO configurator unit 1910 to compute the DIDO precoding weights and precoding the input symbols obtained from the mapping units 1906,
• Each of the precoded data streams are sent by the DIDO precoding unit 1908 to the OFDM unit 1915 that computes the EFFT and adds the cyclic prefix. This information is sent to the D/A unit 1916 that operates the digital to analog conversion and sends the resulting analog signal to the RF unit 1 14.
• the RF unit 1914 upconverts the baseband signal to intermediate radio frequency and send it to the transmit antenna.
• the RF units 2008 of each client device receive signals transmitted from the
• DIDO transmitter units 1914 downconverts the signals to baseband and provide the downcon verted signals to the A/D units 2010.
• the A/D units 2010 then convert the signal from analog to digital and send it to the OFDM units 2013.
• the OFDM units 2013 remove the cyclic prefix and carries out the FFT to report the signal to the frequency domain.
• the OFDM units 2013 send the output to the channel estimate unit 2004 that computes the channel estimates in the frequency domain.
• the channel estimates can be computed in the time domain.
• the OFDM units 2013 send the output to the receiver unit 2002 which demodulates/decodes the signal to obtain the data 2014.
• the channel estimate unit 2004 sends the channel estimates to the DEDO feedback
• the DIDO configurator 1 10 may use information derived at the Base
• the DIDO Feedback Generator 2006 uses the estimated channel state 2004 and/or other parameters like the estimated SNR at the receiver to generate a feedback message to be input into the DIDO Configurator 1910,
• the DIDO Feedback Generator 2006 may compress information at the receiver, may quantize information, and/or use some limited feedback strategies known in the art,
• the DIDO Configurator 1910 may use information recovered from a DIDO
• the DIDO Feedback Control Channel 1912 is a logical or physical control channel that is used to send the output of the DIDO Feedback Generator 2006 from the user to the Base Station.
• the control channel 1 12 may be implemented in any number of ways known in the art and may be a logical or a physical control channel. As a physical channel it may comprise a dedicated time/frequency slot assigned to a user. It may also be a random access channel shared by all users. The control channel may be pre- assigned or it may be created by stealing bits in a predefined way from an existing control channel.

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