WO2002071693A2 - Systeme d'acces sans fil utilisant de multiples formats de modulation dans des trames tdd et procede de commande - Google Patents

Systeme d'acces sans fil utilisant de multiples formats de modulation dans des trames tdd et procede de commande Download PDF

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Publication number
WO2002071693A2
WO2002071693A2 PCT/IB2002/000629 IB0200629W WO02071693A2 WO 2002071693 A2 WO2002071693 A2 WO 2002071693A2 IB 0200629 W IB0200629 W IB 0200629W WO 02071693 A2 WO02071693 A2 WO 02071693A2
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WO
WIPO (PCT)
Prior art keywords
wireless access
modulation
modem
tdd
set forth
Prior art date
Application number
PCT/IB2002/000629
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English (en)
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WO2002071693A3 (fr
Inventor
Paul F. Struhsaker
Robert R. Nelson
Russell C. Mckown
Original Assignee
Raze Technologies, Inc.
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Publication date
Priority claimed from US09/839,458 external-priority patent/US7173916B2/en
Application filed by Raze Technologies, Inc. filed Critical Raze Technologies, Inc.
Publication of WO2002071693A2 publication Critical patent/WO2002071693A2/fr
Publication of WO2002071693A3 publication Critical patent/WO2002071693A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
    • H04L1/0017—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy where the mode-switching is based on Quality of Service requirement
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10—Small scale networks; Flat hierarchical networks
    • H04W84/14—WLL [Wireless Local Loop]; RLL [Radio Local Loop]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0009—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the channel coding

Definitions

  • the present invention is directed, in general, to wireless access systems and, more specifically, to a burst packet transmission media access system for use in a fixed wireless access network.
  • Telecommunications access systems provide for voice, data, and multimedia transport and control between the central office (CO) of the telecommunications service provider and the subscriber (customer) premises.
  • CO central office
  • subscriber customer
  • phone lines e.g., voice frequency (VF) pairs
  • VF voice frequency
  • DLC digital loop carrier
  • the DLC equipment provided an analog phone interface, voice CODEC, digital data multiplexing, transmission interface, and control and alarm remotely from the central office to cabinets located within business and residential locations for approximately 100 to 2000 phone line interfaces.
  • This distributed access architecture greatly reduced line lengths to the subscriber and resulted in significant savings in both wire installation and maintenance.
  • the reduced line lengths also improved communication performance on the line provided to the subscriber.
  • ISDN Integrated Services Digital Network
  • the subscriber interface is based on 64 kbps digitization of the VF pair for digital multiplexing into high speed digital transmission streams (e.g., T1/T3 lines in North America, E1/E3 lines in Europe) .
  • ISDN was a logical extension of the digital network that had evolved throughout the 1980s.
  • the rollout of ISDN in Europe was highly successful. However, the rollout in the United States was not successful, due in part to artificially high tariff costs which greatly inhibited the acceptance of ISDN.
  • DLC digital subscriber line
  • cable modems have been developed and introduced.
  • the DLC architecture was extended to provide remote distributed deployment at the neighborhood cabinet level using DSL access multiplexer (DSLAM) equipment.
  • DSL access multiplexer DSL access multiplexer
  • the increased data rates provided to the subscriber resulted in upgrade DLC/DSLAM transmission interfaces from Tl/El interfaces (1.5/2.0 Mbps) to high speed DS3 and OC3 interfaces.
  • Tl/El interfaces 1.5/2.0 Mbps
  • DS3 and OC3 interfaces high speed DS3 and OC3 interfaces.
  • the entire telecommunications network backbone has undergone and is undergoing continuous upgrade to wideband optical transmission and switching equipment.
  • wireless access systems have been developed and deployed to provide broadband access to both commercial and residential subscriber premises.
  • the market for wireless access systems was driven by rural radiotelephony deployed solely to meet the universal service requirements imposed by government (i.e., the local telephone company is required to serve all subscribers regardless of the cost to install service) .
  • the cost of providing a wired connection to a small percentage of rural subscribers was high enough to justify the development and expense of small-capacity wireless local loop (WLL) systems.
  • WLL wireless local loop
  • Wireless access systems must address a number of unique operational and technical issues including: 1) Relatively high bit error rates (BER) compared to wire line or optical systems; and
  • wireless access systems Unlike physical optical or wire systems that operate at bit error rates (BER) of 10 -11 , wireless access systems have time varying channels that typically provide bit error rates of 10 ⁇ 3 to 10 "6 .
  • the wireless physical (PHY) layer interface and the media access control (MAC) layer interface must provide modulation, error correction and ARQ
  • the base stations of a fixed wireless broadband system transmit forward channel (i.e., downstream) signals in directed beams to fixed location antennas attached to the residences or offices of subscribers.
  • the base stations also receive reverse channel (i.e., upstream) signals transmitted by the broadband access equipment of the subscriber.
  • MAC Media access control
  • the MAC layer may use a number of possible configurations to allow multiple access. These configurations include:
  • FDMA frequency division multiple access
  • subscribers use separate frequency channels on a permanent or demand access basis.
  • TDMA time division multiple access
  • CDMA code division multiple access
  • subscribers share a frequency but use a set of orthogonal codes to allow multiple access.
  • SDMA space division multiple access
  • subscribers share a frequency but one or more physical channels are formed using antenna beam forming techniques .
  • subscribers share a frequency but change polarization of the antenna.
  • Each of these MAC techniques makes use of a fundamental degree of freedom (physical property) of a communications channel. In practice, combinations of these degrees of freedom are often used.
  • cellular systems use a combination of FDMA and either TDMA or CDMA to support a number of users in a cell.
  • Duplexing techniques include frequency division duplexing (FDD) and time division duplexing (TDD) .
  • FDD frequency division duplexing
  • TDD time division duplexing
  • a single channel is used for transmission and reception and specific periods of time (i.e., slots) are allocated for transmission and other specific periods of time are allocated for reception.
  • a method of coordinating the use of bandwidth must be established.
  • distributed control subscribers have a shared capability with or without a method to establish priority.
  • An example of this is CSMA (carrier sense multiple access) used in IEEE802.3 Ethernet and IEEE 802.11 Wireless LAN.
  • CSMA carrier sense multiple access
  • centralized control subscribers are allowed access under the control of a master controller.
  • Cellular systems, such as IS-95, IS-136, and GSM are typical examples. Access is granted using forms of polling and reservation (based on polled or demand access contention) .
  • JTIDS Joint Tactical Information Distribution System
  • IEEE 802.11 Wireless LAN equipment provides for a centrally coordinated TDD system that does not have a specific frame or slotting structure. IEEE 802.11 did introduce the concept of variable modulation and spreading inherent in the structure of the transmission bursts. A significant improvement was incorporated in United States Patent No. 6,052,408, entitled “Cellular Communications System with Dynamically Modified Data Transmission Parameters.” This patent introduced specific burst packet transmission formats that provide for adaptive modulation, transmit power, and antenna beam forming and an associated method of determining the highest data rate for a defined error rate floor for the link between the base station and a plurality of subscribers assigned to that base station. With the exception of variable spreading military systems and NASA space communication systems, this was one of the first commercial patents that address variable transmission parameters to increase system throughput.
  • TDD systems are digital cordless phones, also referred to as low-tier PCS systems.
  • the Personal Access Communications (PAC) system and Digital European Cordless Telephone (DECT, as specified by ETSI document EN 300-175-3) are two examples of these systems.
  • Digital cordless phones met with limited success for their intended use as pico-cellular fixed access products.
  • the systems were subsequently modified and repackaged for wireless local loop (WLL) applications with extended range using increased transmission (TX) power and greater antenna gain.
  • WLL wireless local loop
  • TX transmission
  • TDD/TDMA systems use fixed symmetry and bandwidth between the uplink and the downlink.
  • the TDD frame consists of a fixed set of time slots for the uplink and the downlink.
  • the modulation index (or type) and the forward error correction (FEC) format for all data transmissions are fixed in these systems.
  • FEC forward error correction
  • DECT and PAC systems based on fixed frames with fixed and symmetric allocation of time slots (or bandwidth) provides excellent latency and low jitter, and can support time bounded services, such as voice and Nx64 Kbps video, these systems do not provide efficient use of the spectrum when asymmetric data services are used. This has lead to research and development of packet based TDD systems based on Internet protocol (IP) or asynchronous transfer mode
  • IP Internet protocol
  • ATM converged media access
  • TDD Time Division Duplex
  • ETSI HYPERLAN II ETSI HYPERLAN II specification based on the Dynamic Slot Assignment algorithm described in "Wireless ATM: Performance Evaluation of a DSA++ MAC Protocol with Fast Collision resolution by Probing Algorithm," D. Petras and A. Kramling, International Journal of Wireless Information Networks, Vol. 4, No. 4, 1997.
  • This system allows both contention-based and contention-free access to the physical TDD channel slots.
  • This system also introduced the broadcast of resource allocation at the start of every frame by the base station .controller.
  • Other wireless standards including IEEE 802.16 wireless metropolitan network standards, use this combination of an allocation MAP of the uplink and downlink at the start of the dynamic TDD frame to set resource use for the next TDD frame.
  • Adaptive allocation of uplink and downlink bandwidth is supported.
  • the system provided for fixed, random, and demand assignment mechanisms.
  • Priority is given to quality of service (QoS) applications with resources being removed from best efforts demand access users as required.
  • QoS quality of service
  • the above-described prior art concern the allocation of services in an individual sector of a cell.
  • a cell may consist of M sectors, wherein each sector generally covers a 360/M degree arc around the cell site.
  • United States Patent No. 6,016,311 expressly addresses one possible implementation to the TDD bandwidth allocation problem.
  • the system described continuously measures and adapts the bandwidth requirements based on the evaluation of the average bandwidth required by all the subscribers in a cell and the number of times bandwidth is denied to the subscribers. Changes to the bandwidth allocation are applied based on a set of rules described in Patent No. 6,016,311. While measurements of multiple sectors are performed and recorded at a central base station controller, no global coordination of bandwidth allocation of multiple sectors in a cell or across multiple cells is provided. Thus, the prior art does not address two very important factors in allocation of bandwidth. First, bandwidth allocation must contemplate stringent bandwidth availability requirements for specific groups of services based on planning of the network. For example, consider life-line toll quality voice service.
  • Toll quality voice requires that a system guarantee a specific maximum blocking probability for all voice users based on peak busy hour call usage.
  • a description of voice traffic planning is provided in "Digital Telephony - 2 nd Edition," by J. Bellamy, John Wiley and Sons, New York, New York, 1990.
  • the allocation protocol must be able to rapidly (i.e., less than 100 msec) reallocate bandwidth resources up to the capacity necessary to meet the call blocking requirements.
  • Another service group example is a guaranteed service level agreements (SLA) . Again, bandwidth must be rapidly restored to meet the SLA conditions.
  • G possible service groups having a set of weighted priority level and associated minimum and maximum levels. The weighted priority levels and minimum and maximum levels may be used to bound the bandwidth dynamics of the TDD bandwidth allocation. Minimum levels set a floor for bandwidth allocation and maximum levels set a ceiling. Then averaging can be applied.
  • the TDD bandwidth allocation must consider adjacent and co-channel interference from both modems and sectors within a cell and between cells.
  • Cell planning tools can be used to establish the relationships for interference. For systems that operate below 10 GHz, antennas and antenna placement at a cell site will not provide adequate signal isolation.
  • a fixed wireless access network that maximizes spectral efficiency between the base stations of the fixed wireless access network and the subscriber access devices located at the subscriber premises.
  • a fixed wireless access network that implements an air interface that minimizes uplink and downlink interference between different sectors within the same base station cell site.
  • a fixed wireless access network that implements an air interface that minimizes uplink and downlink interference between different cell sites within the fixed wireless access network.
  • a fixed wireless that efficiently allocates bandwidth to individual subscribers according to dynamically changing applications used by the individual subscribers.
  • the system uses multiple modulation groups in the air interface to transmit data to, and to receive data from, subscriber access devices in each cell site and/or each sector within a cell site.
  • Each subscriber access device is added to a modulation group according to the modulation format, FEC code, and/or antenna beam (spatial component) parameter that gives the highest data throughput to each subscriber access device within acceptable error limitations.
  • Subscriber access devices that receive a comparatively noisy signal may receive a downlink signal in BPSK format with a high level of FEC protection.
  • Subscriber access devices that receive a relatively noise-free signal may receive a downlink signal in 16 QAM format with a relatively low level of FEC protection. Subscriber access devices using .the same modulation format and FEC coding are grouped together in the same modulation groups in the uplink and the downlink. Furthermore, if two or more subscriber access devices lie in the same direction away from a base station, those subscriber access devices may also be grouped together in the same modulation group according to antenna beam forming (i.e., spatial modulation) parameters of the base station. Similar modulation groupings are used in the uplink from the subscriber access devices to the transceiver base station.
  • antenna beam forming i.e., spatial modulation
  • a radio frequency (RF) modem shelf for use in a fixed wireless access network comprising a plurality of base stations capable of bidirectional time division duplex
  • the radio frequency (RF) modem shelf comprises: a) a first RF modem capable of communicating with a plurality of the wireless access devices using TDD frames, each TDD frame having an uplink for receiving data and a downlink for transmitting data; b) a modulation controller associated with the RF modem shelf capable of determining an optimum modulation configuration for each of the plurality of wireless access devices communicating with the first RF modem, wherein the modulation controller causes the first RF modem to transmit downlink data to a first wireless access device in a first data block having a first optimum modulation configuration and to transmit downlink data to a second wireless access device in a second data block having a different second optimum modulation configuration.
  • the modulation controller determines the first and second optimum modulation configurations based on channel conditions associated with channels used to communicate with the first and second wireless access devices.
  • the first modulation configuration comprises a first modulation format and the second modulation configuration comprises a, different second modulation format .
  • the second modulation format is more complex than the first modulation format if channel conditions associated with a first channel used to communicate with the first wireless access device are noisier than channel conditions associated with a second channel used to communicate with the second wireless access device.
  • the first and second modulation formats comprise one of binary phase shift keying (BPSK) , quadrature phase shift keying (QPSK) , and 16 quadrature amplitude modulation (QAM) .
  • BPSK binary phase shift keying
  • QPSK quadrature phase shift keying
  • QAM 16 quadrature amplitude modulation
  • the first modulation configuration comprises a first forward error correction code level and the second modulation configuration comprises a different second forward error correction code level.
  • the first error correction code level is more complex than the second error correction code level if channel conditions associated with a first channel used to communicate with the first wireless access device are noisier than channel conditions associated with a second channel used to communicate with the second wireless access device .
  • the first modulation configuration comprises a first physical beam forming technique and the second modulation configuration comprises a different second physical beam forming technique.
  • FIGURE 1 illustrates an exemplary fixed wireless access network according to one embodiment of the present invention
  • FIGURE 2 illustrates in greater detail an alternate view of selected portions of the exemplary fixed wireless access network according to one embodiment of the present invention
  • FIGURE 3 illustrates an exemplary time division duplex (TDD) time division multiple access (TDMA) frame according to one embodiment of the present invention
  • FIGURE 4 illustrates the timing recovery and distribution circuitry in an exemplary RF modem shelf according to one embodiment of the present invention
  • FIGURE 5A illustrates an exemplary time division duplex (TDD) frames according to one embodiment of the present invention
  • FIGURE 5B illustrates an exemplary transmission burst containing a single FEC block according to one embodiment of the present invention
  • FIGURE 5C illustrates an exemplary transmission burst containing multiple FEC blocks according to one embodiment of the present invention
  • FIGURE 6 is a flow diagram illustrating the adaptive modification of the uplink and downlink bandwidth in the air interface in wireless access network according to one embodiment of the present invention
  • FIGURE 7 is a flow diagram illustrating the adaptive assignment of selected link parameters, such as modulation format, forward error correction (FEC) codes, and antenna beam forming, to the uplink and downlink channels used by each subscriber in the exemplary wireless access network according to one embodiment of the present invention.
  • selected link parameters such as modulation format, forward error correction (FEC) codes, and antenna beam forming
  • FIGURE 8 is a flow diagram illustrating the adaptive assignment of selected link parameters to the different service connections used by each subscriber in the wireless access network according to one embodiment of the present invention.
  • FIGURES 1 through 8, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless access system.
  • FIGURE 1 illustrates exemplary fixed wireless access network 100 according to one embodiment of the present invention.
  • Fixed wireless network 100 comprises a plurality of transceiver base stations, including exemplary transceiver base station 110, that transmit forward channel (i.e., downlink or downstream) broadband signals to a plurality of subscriber premises, including exemplary subscriber premises 121, 122 and 123, and receive reverse channel (i.e., uplink or upstream) broadband signals from the plurality of subscriber premises.
  • Subscriber premises 121-123 transmit and receive via fixed, externally-mounted antennas 131-133, respectively.
  • Subscriber premises 121-123 may comprise many different types of residential and commercial buildings, including single family homes, multi-tenant offices, small business enterprises (SBE) , medium business enterprises (MBE) , and so-called "SOHO" (small office/home office) premises.
  • SBE small business enterprises
  • MBE medium business enterprises
  • SOHO small office/home office
  • the transceiver base stations receive the forward channel (i.e., downlink) signals from external network 150 and transmit the reverse channel (i.e., uplink) signals to external network 150.
  • External network 150 may be, for example, the public switched telephone network (PSTN) or one or more data networks, including the Internet or proprietary Internet protocol (IP) wide area networks (WANs) and local area networks (LANs) .
  • Exemplary transceiver base station 110 is coupled to RF modem shelf 140, which, among other things, up-converts baseband data traffic received from external network 150 to RF signals transmitted in the forward channel to subscriber premises 121-123.
  • RF modem shelf 140 also down-converts RF signals received in the reverse channel from subscriber premises 121-123 to baseband data traffic that is transmitted to external network 150.
  • RF modem shelf 140 comprises a plurality of RF modems capable of modulating (i.e., up-converting) the baseband data traffic and demodulating (i.e., down-converting) the reverse channel RF signals.
  • each of the transceiver base stations covers a cell site area that is divided into a plurality of sectors.
  • each of the RF modems in RF modem shelf 140 may be assigned to modulate and demodulate signals in a particular sector of each cell site.
  • the cell site associated with transceiver base station 110 may be partitioned into six sectors and RF modem shelf 140 may comprise six primary RF modems (and, optionally, a seventh spare RF modem) , each of which is assigned to one of the six sectors in the cell site of transceiver base station 110.
  • each RF modem in RF modem shelf 140 comprises two or more RF modem transceivers which may be assigned to at least one of the sectors in the cell site.
  • the cell site associated with, transceiver base station 110 may be partitioned into six sectors and RF modem shelf 140 may comprise twelve RF transceivers that are assigned in pairs to each one of the six sectors. The RF modems in each RF modem pair may alternate modulating and demodulating the downlink and uplink signals in each sector.
  • RF modem shelf 140 is located proximate transceiver base station 110 in order to minimize RF losses in communication line 169.
  • RF modem shelf 140 may receive the baseband data traffic from external network 150 and transmit the baseband data traffic to external network 150 via a number of different paths .
  • RF modem shelf 140 may transmit baseband data traffic to, and receive baseband data traffic from, external network 150 through central office facility 160' via communication lines 166 and 167.
  • communication line 167 may be a link in a publicly owned or privately owned backhaul network.
  • RF modem shelf 140 may transmit baseband data traffic to, and receive baseband data traffic from, external network 150 directly via communication line 168 thereby bypassing central office facility 160.
  • Central office facility 160 comprises access processor shelf 165.
  • Access processor shelf 165 provides a termination of data traffic for one or more RF modem shelves, such as RF modem shelf 140.
  • Access processor shelf 165 also provides termination to the network switched circuit interfaces and/or data packet interfaces of external network 150.
  • One of the principal functions of access processor shelf 165 is to concentrate data traffic as the data traffic is received from external network 150 and is transferred to RF modem shelf 140.
  • Access processor shelf 165 provides data and traffic processing of the physical layer interfaces, protocol conversion, protocol management, and programmable voice and data compression.
  • FIGURE 2 illustrates in greater detail an alternate view of selected portions of exemplary fixed wireless access network 100 according to one embodiment of the present invention.
  • FIGURE 2 depicts additional transceiver base stations, including exemplary transceiver base stations 110A through 110F, central office facilities 160A and 160B, and remote RF modem shelves 140A through 140D.
  • Central office facilities 160A and 160B comprise internal RF modems similar to RF modem shelves 140A through 140D.
  • Transceiver base stations 110A, HOB, and HOC are disposed in cells sites 201, 202, and 203, respectively.
  • cell sites 201-203 are partitioned into four sectors each.
  • sites 201, 202, and 203 may be partitioned into a different number of sectors, such as six sectors, for example.
  • RF modem shelves 140A-140D and the internal RF modems of central office facilities 160A and 160B transmit baseband data traffic to, and receive baseband data traffic from, access processors in central office facilities 160A and 160B of the PSTN.
  • RF modem shelves 140A-140D and the internal RF modems of central office facilities 160A and 160B also up-convert incoming baseband data traffic to RF signals transmitted in the forward (downlink) channel to the subscriber premises and down-convert incoming RF signals received in the reverse (uplink) channel to baseband data traffic that is transmitted via a backhaul network to external network 150.
  • Baseband data traffic may be transmitted from remote
  • RF modem shelves 140A-140D to central office facilities 160A and 160B by a wireless backhaul network or by a wireline backhaul network, or both.
  • baseband data traffic is carried between central office facility 160A and remote RF modem 140A by a wireline backhaul network, namely wireline 161, which may be, for example, a DS3 line or one to N TI lines.
  • a local multipoint distribution service (LMDS) wireless backhaul network carries baseband data traffic between central office facilities 160A and 160B and remote RF modem shelves 140B, 140C, and 140D.
  • LMDS local multipoint distribution service
  • baseband data traffic being sent to remote RF modem shelves 140B, 140C, and 140D is transmitted by microwave from microwave antennas mounted on transceiver base stations 110A, HOC, and 110F to microwave antennas mounted on transceiver base stations HOB, HOD, and HOE.
  • Baseband data traffic being sent from remote RF modem shelves 140B, 140C, and 140D is transmitted by microwave in the reverse direction (i.e., from transceiver base stations HOB, HOD, and HOE to transceiver base stations HOA, HOC, and HOF) .
  • downlink data traffic from central office facilities 160A and 160B is down-converted from microwave frequencies to baseband signals before being up-converted again for transmission to subscriber premises within each cell site.
  • Uplink data traffic received from the subscriber premises is down-converted to baseband signals before being up-converted to microwave frequencies for transmission back to central office facilities 160A and 160B.
  • an advantageous embodiment of the present invention adopts a flexible approach in which the physical (PHY) layer and the media access (MAC) layer are based on the use of time division duplex (TDD) time division multiple access (TDMA) .
  • TDD operations share a single RF channel between a transceiver base station and a subscriber premises and use a series of frames to allocate resources between each user uplink and downlink.
  • a great advantage of TDD operation is the ability to dynamically allocate the portions of a frame allocated between the downlink and the uplink.
  • TDD operations typically may achieve a forty to sixty percent advantage in spectral efficiency over FDD operations under typical conditions. Given the short duration of the transmit and receive time slots relative to changes in the channel, TDD operations also permit open loop power control, switched diversity techniques, and feedforward and cyclo-stationary equalization techniques that reduce system cost and increase system throughput.
  • FDD frequency division duplex
  • FIGURE 3 illustrates an exemplary time division duplex (TDD) time division multiple access (TDMA) framing hierarchy according to one embodiment of the present invention.
  • the TDD-TDMA framing hierarchy comprises hyperframe 310, which is X milliseconds (msec.) in length (e.g., 250 msec. ⁇ X ⁇ 1000 msec).
  • Hyperframe 310 comprises N superframes, including exemplary superframes 311-316. Each of superframes 311-316 is 20 milliseconds in duration.
  • Superframe 313 is illustrated in greater detail.
  • Superframe 313 comprises ten (10) TDD frames, including exemplary TDD frames 321-324, which are labeled TDD Frame 0, TDD Frame 1, TDD Frame 2, and TDD Frame 9, respectively.
  • each TDD frame is 2 milliseconds in duration.
  • a TDD transmission frame is based on a fixed period of time during which access to the channel is controlled by the transceiver base station.
  • TDD frame 321 comprises a downlink portion (i.e, base station to subscriber transmission) and an uplink portion (i.e., subscriber to base station transmission).
  • TDD frame 321 comprises:
  • Frame header 330 - Frame header 330 is a broadcast message that synchronizes the start of frame and contains access control information on how the remainder of TDD frame 321 is configured.
  • the modulation format of frame header 330 is chosen so that all subscribers in a sector of the transceiver base station can receive frame header 330.
  • frame header 330 is transmitted in a very low complexity modulation format, such as binary phase shift keying (BPSK or 2-BPSK) , or perhaps quadrature phase shift keying (QPSK or 4-BPSK) .
  • BPSK binary phase shift keying
  • QPSK quadrature phase shift keying
  • the D downlink slots contain transceiver base station-to-subscriber transmissions of user traffic and/or control signals.
  • the modulation format of each slot is optimized for maximum possible data transmission rates.
  • Downlink slots may be grouped in blocks to form modulation groups as shown in FIGURE 5A. Subscribers who receive data using the same modulation format (or modulation index) and the same forward error correction (FEC) codes are grouped together in the same modulation group. In some embodiment of the present invention, two or more modulation groups may have the same modulation format and FEC codes. In alternate embodiments of the present invention, downlink slots may be grouped in blocks based on physical beam forming, rather than on modulation format and FEC codes.
  • a transceiver base station may transmit data to several subscribers that are directionally along the same antenna beam in consecutive bursts.
  • downlink slots may be grouped in blocks based on any combination of two or more of: 1) physical beam forming, 2) modulation format, and 3) FEC codes.
  • modulation group shall be used hereafter to refer to a group of downlink slots that are transmitted to one or more subscribers using a common scheme consisting of one or more of modulation format, FEC codes, and physical beam forming.
  • U uplink slots contain subscriber-to- transceiver base station transmissions of user traffic and/or control signals.
  • the modulation format (modulation index) is optimized for maximum possible data transmission rates.
  • the modulation format and FEC codes in the uplink slots are less complex than in the downlink slots. This moves complexity to the receivers in the base stations and lowers the cost and complexity of the subscriber access device.
  • Uplink slots may be grouped in blocks to form sub-burst groups as shown in FIGURE 5A. Subscribers who transmit data using the same modulation format (or modulation index) and the same forward error correction (FEC) codes are grouped together in the same sub-burst group.
  • two or more sub-burst groups may have the same modulation format and FEC codes.
  • uplink slots may be grouped in blocks based on physical beam forming, rather than on modulation format and FEC codes.
  • uplink slots may be grouped in blocks based on any combination of two or more of: 1) physical beam forming, 2) modulation format, and 3) FEC codes.
  • sub-burst group shall be used hereafter to refer to a group of uplink slots that are transmitted to one or more subscribers using a common scheme consisting of one or more of modulation format, FEC codes, and physical beam forming.
  • Contention slots 360 - Contention slots 360 precede the U uplink slots and comprise a small number of subscriber-to-base transmissions that handle initial requests for service.
  • a fixed format length and a single modulation format suitable for all subscriber access devices are used during contention slots 360.
  • contention slots 360 are transmitted in a very low complexity modulation format, such as binary phase shift keying (BPSK or 2-BPSK) , or perhaps quadrature phase shift keying (QPSK or 4-BPSK) .
  • BPSK or 2-BPSK binary phase shift keying
  • QPSK quadrature phase shift keying
  • Collisions (more than one user on a time slot) result in the use of back-off procedures similar to CSMA/CD ' (Ethernet) in order to reschedule a request.
  • TDD transition period 350 - TDD transition period 350 separates the uplink portion and the downlink portion and allows for transmitter (TX) to receiver (RX) propagation delays for the maximum range of the cell link and for delay associated with switching hardware operations from TX to RX or from RX to TX.
  • the position of TDD transition period 350 may be adjusted, thereby modifying the relative sizes of the uplink portion and the downlink portion to accommodate the asymmetry between data traffic in the uplink and the downlink.
  • a key aspect of the present invention is that the timing of the downlink and uplink portions of each TDD frame must be precisely aligned in order to avoid interference between sectors within the same cell and/or to avoid interference between cells. It is recalled from above that each sector of a cell site is served by an individual RF modem in RF modem shelves 140A-140D and the internal RF modem shelves of central office facilities 160A and 160B. Each RF modem uses an individual antenna to transmit and to receive in its assigned sector. The antennas for different sectors in the same cell site are mounted on the same tower and are located only a few feet apart.
  • the present invention uses a highly accurate distributed timing architecture to align the start points of the downlink transmissions.
  • the present invention also determines the length of the longest downlink transmission and ensures that none of the uplink transmissions begin, and none of the base station receivers begin to receive, until after the longest downlink is completed.
  • the present invention also uses the highly accurate distributed timing architecture to align the start points of the downlink transmissions between cell sites.
  • the present invention also determines the length of the longest downlink transmission among two or more cell sites and ensures that none of the base station receivers in any of the cells begins to receive in the uplink until after the longest downlink transmission is completed.
  • a master interface control processor (ICP), as described below in FIGURE 4, may be used to align and allocate the uplink and downlink portions of the TDD frames for all of the RF modems in an RF modem shelf.
  • the access processor may communicate with several master ICPs to determine the longest downlink.
  • the access processor may then allocated the uplinks and downlinks across several cell sites in order to minimize interference between cell sites and may designate on master ICP to control the timing of all of the master ICPs .
  • FIGURE 4 illustrates the timing recovery and distribution circuitry in exemplary RF modem shelf 140 according to one embodiment of the present invention.
  • RF modem shelf 140 comprises front panel interface 410 having connectors 411-414 for receiving input clock references and transmitting clock references.
  • Exemplary connector 411 receives a first clock signal from a first external source (External Source A) and exemplary connector 414 receives a second clock signal from a second external source (External Source B) .
  • Connector 412 outputs an internally generated clock signal (Master Source Out) and connector 413 receives an external one second system clock signal (External 1 Second Clock) .
  • RF modem shelf 140 also comprises a plurality of interface control processor (ICP) cards, including exemplary ICP cards 450, 460, 470 and 480.
  • ICP interface control processor
  • ISP card 450 is designated as a master ICP card and ICP card 480 is designated as a spare ICP card in case of a failure of master ICP card 450.
  • the ICP cards provide for control functions, timing recovery and distribution, network interface, backhaul network interface, protocol conversion, resource queue management, and a proxy manager for EMS for the shelf.
  • the ICP cards are based on network processor (s) that allow software upgrade of network interface protocols.
  • the ICP cards may be reused for control and routing functions and provide both timing and critical TDD coordinated burst timing for all the RF modems in RF modem shelf 140 and for shelf-to- shelf timing for stacked frequency high density cell configurations .
  • the timing and distribution architecture in RF modem shelf 140 allows for three reference options:
  • BITS Building Integrated Timing Supply
  • Secondary - A secondary reference may be derived from any designated input port in RF modem shelf 140. For remote RF modem shelf 140, this is one of the backhaul I/O ports.
  • An ICP card is configured to recover a timing source and that source is placed on a backplane as a reference (i.e., Network Reference (A/B) ) to master ICP card 450.
  • PLL phase locked loop
  • the active master ICP card distributes timing for all of RF modem shelf 140.
  • the timing distribution architecture of RF modem shelf 140 meets Stratum 3- levels of performance, namely a free-run accuracy of +/- 4.6 PPM (parts per million), a pull-in capability of 4.6 PPM, and a holdover stability of less than 255 slips during the first day.
  • Timing masters ICP cards 450 and 480.
  • Timing slaves ICP cards 460 and 470.
  • the timing masters are capable of sourcing all clocks and framing signals necessary for the remaining cards within the AP backplane.
  • ICP cards 450 and 480 there are two timing masters (ICP cards 450 and 480), which are constrained to the slots allocated as the primary and secondary controllers.
  • the timing masters utilize the redundant timing references (External Source A, External Source B, External 1 Second Clock) found on the backplane to maintain network-qualified synchronization.
  • ISP card 450 (and ISP card 480) comprises backhaul network input/output (I/O) port 451, multiplexer 452 and PLL-clock generator 453.
  • MUX 452 selects anyone of External Source A, External Source B, Network Reference (A/B) , and the signal from I/O port 451 to be applied to PLL-clock generator 453.
  • the timing master has missing clock detection logic that allows it to switch from one timing reference to another in the event of a failure.
  • Timing is distributed across a redundant set of clock and framing signals, designated Master Clock Bus in FIGURE 4.
  • Each timing master i.e., ICP cards 450 and 480
  • ICP cards 450 and 480 is capable under software control of driving either of the two sets of clock and framing buses on the backplane. Both sets of timing buses are edge-synchronous such that timing slaves can interoperate while using either set of clocks.
  • the timing supplied by the timing master e.g., ICP card 450
  • There is a primary and secondary version of each reference To generate these references, the primary and secondary timing masters are provisioned to recover the timing from one of the following sources : Source Frequency
  • EXT REF A External BITS 64K, 1544K, 2048K
  • Timing slaves receive the timing provided by redundant sets of clock and framing buses. Under software control, timing slaves choose a default set of clocks from either the A-side or B-side timing buses. They also contain failure detection logic such that clock and framing signal failures can be detected. Once a clock or framing failure is detected, the timing slave automatically switches to the alternate set of timing buses. ICP cards 460 and 470 contain backhaul I/O ports 461 and 471, respectively, which may be used to bring in external timing signals from other RF modem shelves in the network. The timing masters (i.e., ICP cards 450 and 480) also contain the timing slave function insofar as they also utilize the timing provided on the backplane clock and framing buses.
  • a qualified timing reference is required for the timing master to derive backplane timing and to maintain synchronization within network 100 and with any outside network.
  • an access processor card can be assigned to derive this timing and to drive one of the two timing reference buses.
  • a second, physically separate card will contain a second qualified timing source and drive the second backplane timing reference.
  • the access processor backplane has connections which allow external reference timing (e.g., a GPS-derived clock) from the interface tray to be applied to the backplane.
  • external reference timing e.g., a GPS-derived clock
  • a one pulse-per-second (1PPS) signal is distributed to all system cards for time stamping of system events and errors.
  • Installations involving multiple access processor shelves require the timing reference to be distributed between all access processor backplanes.
  • the timing reference for a given backplane is cabled to the remaining backplanes through external cabling.
  • Multiple remote modem shelves are utilized to distribute high-capacity backhaul traffic to one or more additional co-located modem shelves. Traffic is distributed among the shelves through TI, T3, OC3 and/or other broadband telecommunication circuits.
  • FIGURE 5A illustrates exemplary time division duplex (TDD) frame 500 according to one embodiment of the present invention.
  • FIGURE 5B illustrates exemplary transmission burst 520 containing a single FEC block according to one embodiment of the present invention.
  • FIGURE 5C illustrates exemplary transmission burst 530 containing multiple FEC blocks according to one embodiment of the present invention.
  • TDD time division duplex
  • TDD frame 500 comprises a downlink portion containing preamble field 501, management field 502, and N modulation groups, including modulation group 503 (labeled Modulation Group 1) , modulation group 504 (labeled Modulation Group 2), and modulation group 505 (labeled Modulation Group N) .
  • a modulation group is a group of downlink slots transmitted to one or more subscribers using a common scheme of one or more of: 1) modulation format, 2) FEC codes, and 3) physical beam forming.
  • TDD frame 500 also comprises an uplink portion containing transmitter-transmitter guard (TTG) slot 506, 0 to N registration (REG) minislots 506, 1 to N contention (CON) request minislots 508, N sub-burst groups, including sub-burst group 509 (labeled Sub-Burst 1) and sub-burst group 510 (labeled Sub-Burst N) , and receiver-transmitter guard (RTG) slot 511.
  • a sub-burst group is a group of uplink slots transmitted to one or more subscribers using a common scheme of one or more of: 1) modulation format, 2) FEC codes, and 3) physical beam forming.
  • Each modulation group and each sub-burst group comprises one or more transmission bursts.
  • Exemplary transmission burst 520 may be used within a single modulation group in the downlink and covers one or more downlink slots.
  • Transmission burst 520 also may be used within a single sub-burst group in the downlink and covers one or more uplink slots.
  • Transmission burst 520 comprises physical media dependent (PMD) preamble field 521, MAC header field 522, data packet data unit (PDU) field 523, and block character redundancy check (CRC) field 524.
  • Transmission burst 530 comprises physical media dependent (PMD) preamble field 531, MAC header field 532, data PDU field 533, block CRC field 534, data PDU field 535, block CRC field 536.
  • the start of every frame includes a Start-Of-Frame (SOF) field and a PHY, Media Dependent Convergence (PMD) field.
  • PMD preambles are used to assist in synchronization and time-frequency recovery at the receiver.
  • the SOF field allows subscribers using fixed diversity to test reception conditions of the two diversity antennas.
  • the SOF PMD field is 2 N symbols long (typically 16, 32, 64 symbols long) and consists of pseudo-random noise (PN) code sequences, Frank sequences, CAZAC sequences, or other low cross-correlation sequences, that are transmitted using BPSK or QPSK modulation.
  • the SOF field is followed by downlink management messages broadcast from the base station to all subscribers using the lowest modulation or FEC index and orthogonal expansion. Management messages are transmitted both periodically (N times per hyperframe) and as required to change parameters or allocate parameters. Management messages include: 1. DownLink Map indicating the physical slot (PS) where downstream modulation changes (transmitted every frame) ;
  • UpLink MAP indicating uplink subscriber access grants and associated physical slot start of the grant (transmitted when changed and at a minimum of one second hyperframe periods (shorter periods are optional) ) ;
  • TDD frame and physical layer attributes (periodic at a minimum of one second hyperframe period) ;
  • the downlink management messages are followed by multi-cast and uni-cast bursts arranged in increasing modulation complexity order.
  • the present invention introduces the term "modulation group" to define a set of downstream bursts with the same modulation and FEC protection. A subscriber continuously receives all the downstream data in the TDD frame downlink until the last symbol of the highest modulation group supported by the link is received. This allows a subscriber maximum time to perform receive demodulation updates.
  • the downlink-to-uplink transition provides a guard time (TTG) to allow for propagation delays for all the subscribers.
  • TTG position and duration is fully programmable and set by management physical layer attribute messages.
  • the TTG is followed by a set of allocated contention slots that are subdivided between acquisition uplink ranging mini-slots and demand access request mini- slots.
  • the Uplink MAP message establishes the number and location of each type of slot. Ranging slots are used for both initial uplink synchronization of subscribers performing net entry and for periodic update of synchronization of active subscribers.
  • Contention slots provide a demand access request mechanism to establish subscriber service for a single traffic service flow.
  • the subscriber uses random backoff, in integer TDD frame periods and retries based on a time out for request of service.
  • Contention slots use the lowest possible modulation, FEC, and orthogonal expansion supported by the base station.
  • the contention slots are followed by individual subscriber transmissions (sub-bursts) that have been scheduled and allocated by the base station in the uplink MAP. Each subscriber transmission burst is performed at the maximum modulation, FEC, and orthogonal expansion supported by the subscriber.
  • the subscriber transmissions are followed by the uplink-to-downlink transition which provides a guard time (RTG) to allow for propagation delays for all the subscribers.
  • RTG duration is fully programmable and set by management physical layer attribute messages.
  • the Physical Media Dependent (PMD) burst synchronization is not used.
  • the transmission burst begins with the MAC header and is followed by the packet data unit (PDU) and the associated block CRC field that protects both the PDU and the header.
  • PDU packet data unit
  • the PDU may be a complete packet transmission or a fragment of a much larger message.
  • the PDU may be broken into segments that are protected by separate FEC CRC fields. This avoids wasting bandwidth with additional MAC headers.
  • the PMD preamble length and pattern can be programmed by transceiver base station 110. Like the SOF field at the beginning of the TDD Frame, the preamble provides a synchronization method for the base station receiver. Uplink registration and ranging packet bursts use longer PMD preambles.
  • the medium access control (MAC) layer protocol is connection oriented and provides multiple connections of different quality of service (QoS) to each subscriber.
  • QoS quality of service
  • the connections are established when a subscriber is installed and enters operation fixed wireless access network 100. Additional connections can be established and terminated with the base station transceivers as subscriber requirements changes.
  • a subscriber access device supports two voice channels and a data channel.
  • the quality of service (QoS) on both of the voice channels and data can set based on the service structure set by the wireless service provider.
  • QoS quality of service
  • a subscriber may start with two service connections: a toll quality voice channel and a medium data rate broadband data connection.
  • the subscriber may order and upgrade service to two toll quality voice channels and high speed data connection (a total of three connections) .
  • connection The maintenance of connections varies based on the type of connection established. TI or fractional TI service requires almost no maintenance due to the periodic nature of transmissions.
  • a TCP/IP connection often experiences bursty on-demand communication that may be idle for long periods of time. During those idle periods, periodic ranging and synchronization of the subscriber is required.
  • each subscriber maintains a 64-bit EUI for globally unique addressing purposes. This address uniquely defines the subscriber from within the set of all possible vendors and equipment types. This address is used during the registration process to establish the appropriate connections for a subscriber. It is also used as part of the authentication process by which the transceiver base station and the subscriber each verify the identity of the other.
  • a connection may be identified by a 16-bit connection identifier (CID) in MAC header 522 or MAC header 532. Every subscriber must establish at least two connections in each direction (upstream and downstream) to enable communication with the base station.
  • the basic CIDs assigned to a subscriber at registration, are used by the base station MAC layer and the subscriber MAC layer to exchange MAC control messages, provisioning and management information.
  • the connection ID can be considered a connection identifier even for nominally connectionless traffic like IP, since it serves as a pointer to destination and context information.
  • the use of a 16-bit CID permits a total of 64K connections within the sector. In an exemplary embodiment of fixed wireless access network 100, the CID may be divided into 2 fields.
  • Bits [16:x] may be used to uniquely identify a subscriber. In a cyclo-stationary receiver processing at a base station, this would set the antenna, equalizer, and other receiver parameters. Bits [x:l] may be used to indicate a connection to a type of service.
  • Each subscriber service can have individual modulation format, FEC, and ARQ.
  • FEC modulation format
  • ARQ ARQ-based modulation format
  • the voice data may use one type of modulation format, FEC, and ARQ
  • the broadband internet service may use a different modulation format, FEC, and ARQ.
  • the voice data may use one type of modulation format, FEC, and ARQ
  • the broadband internet service may use a different modulation format, FEC, and ARQ.
  • An apartment building could be given a set of subscriber ports [16:9] so that bits [9:7] allow 2 ⁇ 8 connections or 256 connections.
  • Requests for transmission are based on these connection IDs, since the allowable bandwidth may differ for different connections, even within the same service type. For example, a subscriber unit serving multiple tenants in an office building would make requests on behalf of all of them, though the contractual service limits and other connection parameters may be different for each of them. Many higher-layer sessions may operate over the same wireless connection ID. For example, many users within a company may be communicating with TCP/IP to different destinations, but since they all operate within the same overall service parameters, all of their traffic is pooled for request/grant purposes. Since the original LAN source and destination addresses are encapsulated in the payload portion of the transmission, there is no problem in identifying different user sessions.
  • Fragmentation is the process by which a portion of a subscriber payload (uplink or downlink) is divided into two or more PDUs . Fragmentation allows efficient use of available bandwidth while maintaining the QoS requirements of one or more of services used by the subscriber. Fragmentation may be initiated by a base station for a downlink connection or the subscriber access device for the uplink connection. A connection may be in only one fragmentation state at any given time. The authority to fragment data traffic on a connection is defined when the connection is created.
  • the MAC layer protocol in wireless access network 100 also supports concatenation of multiple PDUs in a single transmission in both the uplink and the downlink, as shown in FIGURE 5C.
  • each PDU contains a MAC header with the CID
  • the receiving MAC layer can determine routing and processing by higher layer protocols.
  • a base station MAC layer creates concatenated PDUs in the uplink MAP. Management, traffic data, and bandwidth may all be concatenated. This process occurs naturally in the downlink. In the uplink, concatenation has the added benefit of eliminating additional PMD preambles.
  • FIGURE 6 depicts flow diagram 600, which illustrates the adaptive modification of the uplink and downlink bandwidth in the air interface in wireless access network 100 according to one embodiment of the present invention.
  • an RF modem shelf such as RF modem shelf 140A, receives new access requests from subscriber access devices in fixed wireless access network 100 and determines traffic requirements for each new and existing subscriber in each sector of a single cell site (process step 605) .
  • the traffic requirements of each subscriber may be established in a number of ways, including minimum QoS requirements, service level agreements, past usage, and current physical layer parameters, such as modulation index, FEC codes, antenna beam forming, and the like.
  • the RF modem shelf determines from the subscriber traffic requirements the longest downlink portion of any TDD frame in each sector of a single cell site (process step 610) .
  • the access processor for the RF modem shelf determines the appropriate allocation of downlink and uplink portions of TDD frames for a single cell site in order to minimize or eliminate interference within the cell site (process step 615) .
  • Bandwidth is allocated, and TDD transition period 350 is positioned, such that the longest downlink transmission is complete before any receiver in the cell site starts to listen for the uplink transmission.
  • the access processor determines the longest downlink portion of any TDD frame across several closely located cell sites stations (process step 620) .
  • the access processor determines the allocation of uplink and downlink bandwidth for all TDD frames across several closely located cell sites in order to minimize or eliminate cell-to-cell interference (process step 625) .
  • bandwidth is allocated, and TDD transition period 350 is positioned, such that the longest downlink transmission is complete before any receiver in any of the closely located cell sites starts to listen for uplink transmissions.
  • the downlink portions of the TDD frames are launched simultaneously using the highly accurate clock from the distributed timing architecture (process step 630) .
  • the dynamic application of TDD bandwidth allocation is bounded by set minimum and maximum boundaries set by the service provider, based on traffic and network analysis. Further, the bandwidth bounds may be allocated in sub- groupings based on established quality of service (QoS) requirements (e.g., voice data) and Service Level Agreements (SLA) (e.g., broadband data rate) as the primary consideration and with best efforts, non-QoS data, and IP traffic as secondary considerations.
  • QoS quality of service
  • SLA Service Level Agreements
  • the bandwidth bounds may be allocated based on the fact that a subscriber may support more that one interface and thus more than one modulation format in order to achieve required error rates for one or more services provided to the subscriber.
  • FIGURE 7 depicts flow diagram 700, which illustrates the adaptive assignment of selected link parameters, such as modulation format, forward error correction (FEC) codes, and antenna beam forming, to the uplink and downlink channels used by each subscriber in wireless access network 100 according to one embodiment of the present invention.
  • the RF modem shelf monitors data traffic between subscribers and base station and determines for each subscriber the most efficient combination of modulation format, FEC code, and/or antenna beam forming for the uplink and downlink.
  • the selected combination is based at least in part on the error rates detected by the RF modem shelf when monitoring the data traffic. If the error rate for a particular subscriber is too high in either the uplink or the downlink, the RF modem shelf can decrease the modulation format complexity and use a higher level of FEC code protection in either the uplink or the downlink in order to reduce the error rate. Conversely, if the error rate for a particular subscriber is very low in either the uplink or the downlink, the RF modem shelf can increase the modulation format complexity and use a lower level of FEC code protection in either the uplink or the downlink in order to increase the spectral efficiency, provided the error rate remains acceptably low.
  • Different modulation formats and FEC codes may be used for different services (e.g., voice, data) used by a subscriber (process step 705) .
  • the RF modem shelf assigns subscribers to modulation groups in the downlink and to sub-burst groups in the uplink (process step 710) .
  • the base station transceiver then transmits media access fields (e.g., signaling, ACK & NACK) using the lowest modulation format/FEC code complexity.
  • the base station transceiver then transmits the remaining modulation groups in the downlink to the subscribers in increasing order of modulation format/FEC code complexity (process step 715).
  • the base station transceiver When the downlink is complete, the base station transceiver receives registration & contention minislots transmitted by the subscriber access devices using the lowest modulation format/FEC code complexity. The base station transceiver then receives the remaining sub-burst groups transmitted by the subscribers in increasing order of modulation format/FEC code complexity (process step 720) .
  • the use of adaptive link parameters improves the link throughput and correspondingly affects the bandwidth allocation described above in FIGURE 6.
  • Link parameters apply not only to the transmitter but to the receiver as well.
  • the present invention uses a bounded (finite) set of modulation formats to maximize bandwidth utilization to each subscriber in a channel or sector.
  • modulation formats used for media access fields are binary phase shift keying (BSPK or 2-PSK) and quadrature phase shift keying (QPSK or 4-PSK) .
  • the present invention may also use multiple-code orthogonal expansion codes in conjunction with the low complexity modulation formats for extremely robust communication.
  • the higher complexity (higher efficiency) modulation formats used for the modulation groups and the sub-burst groups may be 8-PSK, 16 quadrature amplitude modulation (QAM) , 32 QAM, 64 QAM, 128 QAM, and the like.
  • the present invention also uses bounded set of FEC codes to maximize bandwidth utilization to each subscriber in a channel or sector.
  • the level of FEC code protection is based on the services provided. Each subscriber may support multiple services.
  • the RF modem shelf may use packet fragmentation to transport data in either the uplink or the downlink. Fragmentation is the division of larger packets into smaller packets (fragments) combined with an ARQ (automatic request for retransmission) mechanism to retransmit and recover erroneous fragments.
  • the RF modem shelf automatically reduces fragment size for high error rate channels. Fragmentation is applied for guaranteed error- free sources.
  • the degree of fragmentation and ARQ is based on the service provided, since each subscriber may support multiple services.
  • FIGURE 8 depicts flow diagram 800, which illustrates the adaptive assignment of selected link parameters to the different service connections used by each subscriber in wireless access network 100 according to one embodiment of the present invention.
  • the RF modem shelf assigns connection identification (CID) values to the uplink and to the uplink connections used by a subscriber. If a subscriber uses more than one service (e.g., two voice, One data) , the RF modem shelf assigns separate CID values to each uplink connection and separate CID values to each downlink connection (process step 805) .
  • the CID comprises a bit field with the uppermost bits identifying the subscriber and the lowermost bits identifying a specific connection to the subscriber.
  • the RF modem shelf monitors data traffic between subscriber and base station and determines for each connection the most efficient combination of modulation format, FEC code, and/or antenna beam forming for the uplink and downlink (process step 810) .
  • the RF modem shelf then assigns each subscriber connection to a modulation group in the downlink and to a sub-burst group in the uplink (process step 815) .
  • the base station transmits media access fields (e.g., signaling, ACK & NACK) using the lowest modulation format/FEC code complexity. Then base station then transmits modulation groups to subscribers in increasing order of modulation format/FEC code complexity
  • process step 820 the base station receives registration & contention minislots using the lowest modulation format/FEC code complexity. Then base station then receives sub-burst groups from subscribers in increasing order of modulation format/FEC code complexity (process step 825) .
  • Physical layer usage codes are bound to subscriber CID values by a service establishment protocol. If there is a degradation or improvement in the channel between a subscriber and the base station, a protocol exists so the subscriber access device and the base station may revise the physical layer usage code and subscriber CID code. The codes and bindings can be added and deleted based on services requirements of the subscriber.

Abstract

L'invention concerne un châssis (140) de modem radiofréquence (RF) s'utilisant dans un réseau (100) d'accès sans fil fixe qui comporte une pluralité de stations (110) de base capables de mettre en oeuvre des transmissions bidirectionnelles en mode duplex à répartition temporelle (TDD) avec des dispositifs d'accès sans fil situés dans une pluralité de locaux d'abonnés. Le châssis (140) de modem radiofréquence (RF) comporte : a) un premier modem RF pour communiquer avec une pluralité de dispositifs d'accès sans fil à l'aide de trames TDD, chaque trame TDD comportant une liaison montante pour recevoir des données et une liaison descendante pour transmettre des données ; et b) un organe de commande (140) de modulation associé au châssis (140) de modem RF pour déterminer une configuration de modulation optimale pour chacun des dispositifs d'accès sans fil communiquant avec le premier modem RF. L'organe de commande (140) de modulation fait transmettre, par le premier modem RF, des données de liaison descendante vers un premier dispositif d'accès sans fil, dans un premier bloc de données présentant une première configuration de modulation optimale ; et des données de liaison descendante vers un deuxième dispositif d'accès sans fil, dans un deuxième bloc de données présentant une deuxième configuration de modulation optimale, différente de la première.
PCT/IB2002/000629 2001-03-05 2002-03-05 Systeme d'acces sans fil utilisant de multiples formats de modulation dans des trames tdd et procede de commande WO2002071693A2 (fr)

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