WO2015099807A1

WO2015099807A1 - Methods and arrangements for channel updates in wireless networks

Info

Publication number: WO2015099807A1
Application number: PCT/US2013/078165
Authority: WO
Inventors: Shahrnaz Azizi; Thomas J. Kenney; Eldad Perahia
Original assignee: Intel Corporation
Priority date: 2013-12-28
Filing date: 2013-12-28
Publication date: 2015-07-02

Abstract

Logic may determine channel estimates for subcarriers adjacent to a pilot tone in response to receiving the pilot tone in a symbol of a communication. Logic may determine whether or not to perform interpolation based upon an interpolation setting or a dynamic determination of a Doppler estimate. Logic may determine targeted subcarriers that are adjacent to the pilot tone in the symbol. Logic may determine adjacent subcarriers that are adjacent to the targeted subcarriers. Logic may determine channel state estimates for the adjacent subcarriers. Logic may determine channel state estimates for the targeted subcarriers based upon the channel estimates for the adjacent subcarriers. Logic may determine channel state estimates for the targeted subcarriers by interpolation of the channel estimates of the adjacent subcarriers with the channel estimates for the pilot tones to determine interpolated estimates. And logic may average the interpolated estimates with previously determined channel state estimates.

Description

METHODS AND ARRANGEMENTS FOR CHANNEL UPDATES IN WIRELESS

NETWORKS

TECHNICAL FIELD

Embodiments are in the field of wireless communications. More particularly, the present disclosure relates to channel updates to track a channel state during an evolution of a packet to attenuate degradation from frequency error and phase noise including in the presence of Doppler.

BACKGROUND

In the existing Wireless Fidelity (Wi-Fi) orthogonal frequency division multiplexing (OFDM) systems such as Institute of Electrical and Electronic Engineers (IEEE) 802.1 la/n/ac systems, initial channel state information along with other receiver parameters, such as frequency and timing offset, are estimated and applied upon receipt of preambles. Since the system parameters are estimated, there is always some residual error. In the case of frequency estimation, the residual frequency error causes constellation rotation. To prevent performance degradation due to this residual frequency error and phase noise, a Wi-Fi OFDM receiver tracks the carrier phase in the OFDM symbols as they are received. To enable this phase tracking, Wi-Fi OFDM systems predefine a certain number of subcarriers among data subcarriers, called pilot subcarriers or "pilots", at fixed subcarriers within each ODFM symbol. Pilot tones, also referred to as pilot signals, are transmitted in each OFDM symbol on the pilot subcarriers to provide the receivers with a known reference for determining corrections. Pilot signals and training symbols (preambles) may also be used for time synchronization to attenuate intersymbol interference, ISI and frequency synchronization to attenuate inter-carrier interference, ICI, caused by Doppler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a wireless network comprising a plurality of communications devices;

FIG. 1A depicts an embodiment of a table illustrating an embodiment of a predefined pattern of pilot subcarriers; FIG. IB depicts embodiments of orthogonal frequency division multiplexing (OFDM) symbols in an OFDM packet transmission with shifting pilot tones;

FIG. 1C depicts an embodiment of an OFDM packet transmission with shifting pilot tones with targeted subcarriers and adjacent subcarriers;

FIG. ID depicts embodiments of a simulation comparing performance for transmitting pilot tones with interpolation and without interpolation for two different Doppler environments;

FIG. 2 depicts an embodiment of an apparatus with pilot logic to process pilot shifting tones and determine channel estimates for targeted subcarriers;

FIG. 3 depicts an embodiment of a flowchart to process shifting pilot tones and determine channel estimates for targeted subcarriers; and

FIG. 4 depicts an embodiment of a flowchart to receive, decode, and interpret communications with frames shifting pilot tones and determination of channel estimates for targeted subcarriers as illustrated in FIGs. 1-2. DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of novel embodiments depicted in the accompanying drawings. However, the amount of detail offered is not intended to limit anticipated variations of the described embodiments; on the contrary, the claims and detailed description are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present teachings as defined by the appended claims. The detailed descriptions below are designed to make such embodiments understandable to a person having ordinary skill in the art.

With the growing applications of Wi-Fi outdoor use cases, the Doppler effect in a channel may be addressed in embodiments such as the Institute of Electrical and Electronic Engineers (IEEE) 802.11 ah systems by a method of shifting pilot subcarriers across the useable subcarriers for data and/or other information in the bandwidth of a packet transmission to allow such embodiments to track the channel state during the evolution of the packet. The Doppler effect can significantly impact the performance of systems that are sensitive the interference caused at the receivers such as IEEE 802.11 ah systems that may have significantly lower data rates than its predecessors, have relatively small amounts of data to send infrequently, and an outdoor use case that introduces channels which are likely to contain significant Doppler components since the environment may have, e.g., moving vehicles present.

With the inclusion of low data rates in IEEE 802.11 ah, using moderate to large pay load sizes a packet can be lO's of milliseconds long. The previous versions of Wi-Fi (IEEE 802.1 la b/g/n/ac) systems were largely designed for indoor use, and thus the channel was assumed stationary over the entire packet. With aspects such as lower data rates and an outdoor use case (and therefore the greater potential of Doppler), the assumption of channel stationarity may no longer be valid. It has been shown in simulations that even for modest Doppler, the IEEE 802.11 ah system performance may be degraded without additional training during the packet.

The approach to allow the system to track the channel state during the evolution of the packet is to have the known pilot signals shift to different carrier positions over the useful portion of the band during the packet, also referred to as shifting pilots or traveling pilots. The useful portion of the band may be all subcarriers that would be used for data and pilot subcarriers and omitting guard subcarriers, or other nulled subcarriers. Thus, the pilot tone, or pilot signal, can be used to compute new channel state information for those subcarriers.

The channel state is typically tracked by estimating channel state information (CSI). Determining or estimating channel state information produces channel state information estimates, commonly referred to as channel estimates or channel state estimates.

Embodiments may shift pilots by shifting known pilot subcarriers across the band during a packet transmission and transmitting known tones on the known pilot subcarriers. In other words, embodiments of transmitters and receivers may know the positions of the shifting pilot subcarriers within symbols of a packet transmission as well as the pilot tones transmitted on the shifting pilot subcarriers. Embodiments may measure information from pilot tones on pilot subcarriers about the magnitude & phase of the received tone, carrier frequency, phase error, and phase noise, referred to herein as pilot information. Several embodiments may use the pilot information to compute new channel state information for those tones and, in many embodiments, phase correction information to track channel phase with different tones and carrier frequency information. As the pilots shift through data tone locations, embodiments may dynamically track the channel state. While some of the embodiments described herein may refer to IEEE 802.11 ah systems, embodiments generally include all communications technologies that can implement pilot subcarriers including IEEE 802 systems and wireless communication technologies in general.

Embodiments may enable attenuation of the Doppler effect for applications in which Doppler components may be high such as scenarios in which an outdoor sensor or access point is located near a highway. In many embodiments, logic may attenuate the Doppler effect by determining pilot information for shifting pilots and also determining channel state estimates for targeted subcarriers. Results of simulation studies included herein show that use of interpolation to update channel estimates for subcarriers that are adjacent to pilot tones received in a symbol of a communication can improve communication performance for high Doppler effect scenarios.

Some embodiments employ pilot logic in receivers that know the predefined pattern of pilot subcarriers and to determine pilot information for the shifting pilot tones. Other embodiments may comprise pilot logic to coordinate shifting pilot tone sequences with a transmitter dynamically and to determine pilot information for the shifting pilot tones.

Several embodiments employ pilot logic to enable the attenuation of Doppler components upon deployment. Further embodiments employ pilot logic to enable the attenuation of Doppler components as a software or firmware configuration. And some embodiments employ pilot logic to enable the attenuation of Doppler components dynamically based upon estimates of Doppler components by pilot logic in a receiver.

When the attenuation of Doppler components is enabled, some embodiments comprise pilot logic to determine targeted subcarriers. For example, the pilot logic may determine targeted subcarriers as subcarriers that would benefit from updated channel state estimates. In many embodiments, the targeted subcarriers may be in proximity to the pilot tones received in the most recent symbol received in a packet transmission, which is referred to as the current symbol. In several embodiments, the targeted subcarriers may be the subcarriers that are adjacent to the pilot tones. For instance, if the pilot tones in the current symbol are at subcarrier indices -7 and 7, then the targeted subcarriers may be at subcarrier indices -6, -8, 6, and 8.

After determining targeted subcarriers, many embodiments may employ pilot logic to determine subcarriers that are adjacent to the targeted subcarriers, which are referred to herein as adjacent subcarriers. For example, adjacent subcarriers of the subcarrier indices -6, -8, 6, and 8 include the subcarrier indices -5, -9, 5, and 9. In several embodiments, the pilot logic may determine channel state estimates for the adjacent subcarriers such as the subcarrier indices -5, -9, 5, and 9. In some embodiments, the channel state estimates for the adjacent subcarriers may include previously determined channel state estimates from pilot tones. Several embodiments may buffer channel estimates determined from previously received pilot tones. Some embodiments may only comprise a small buffer and may only store one, two, or three previous channel estimates. Some embodiments may only buffer channel estimates from the last three symbols. Further embodiments may use channel estimates from a long training field (LTF) determined upon receipt of the LTF in a preamble for the communication.

In many embodiments, the pilot logic may interpolate the channel estimates of the adjacent subcarriers via, e.g. a linear interpolation function, to determine channel state estimates for the targeted subcarriers, referred to as interpolated estimates. In further embodiments, the pilot logic may also average the interpolated estimates with channel estimates for the targeted subcarrier. In some embodiments the pilot logic may also average the interpolated estimates with previously determined estimates for the targeted subcarrier such as previously determined channel estimates from pilot tones and/or previously determined channel estimates from an LTF in the preamble.

Various embodiments may be designed to address different technical problems associated with attenuating the Doppler effect in communications. For instance, some embodiments may be designed to address one or more technical problems such as determining whether or not to interpolate channel estimates. Further embodiments may comprise determining targeted subcarriers for which to determine channel estimates. And still further embodiments may comprise determining adjacent subcarriers for determining channel estimates for the targeted subcarriers, determining channel estimates for the adjacent subcarriers, and determining channel estimates for the targeted subcarriers.

Different technical problems such as those discussed above may be addressed by one or more different embodiments. For instance, some embodiments that address attenuating the Doppler effect in communications may do so by one or more different technical means such as determining whether the environment for deployment of the receiver is in an area likely to experience high interference via Doppler components. Several embodiments may determine or locate subcarriers in proximity to or adjacent to a pilot tone in a current symbol, determine or locate subcarriers that are in proximity to or adjacent to the targeted subcarrier, and determine channel estimates for the targeted subcarriers based upon channel estimates from the pilot tone, channel estimates from the adjacent subcarriers, and, in some embodiments, channel estimates for the targeted subcarriers.

Some embodiments implement Institute of Electrical and Electronic Engineers (IEEE)

802.11 systems such as IEEE 802.11 ah systems and other systems that operate in accordance with standards such as the IEEE 802.11-2012, IEEE Standard for Information technology— Telecommunications and information exchange between systems— Local and metropolitan area networks— Specific requirements— Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (http://standards.ieee.org/getieee802/download/802.l l- 2012.pdf).

Several embodiments comprise access points (APs) for and/or client devices of APs or stations (STAs) such as routers, switches, servers, workstations, netbooks, mobile devices (Laptop, Smart Phone, Tablet, and the like), as well as sensors, meters, controls, instruments, monitors, appliances, and the like. Some embodiments may provide, e.g., indoor and/or outdoor "smart" grid and sensor services. For example, some embodiments may provide a metering station to collect data from sensors that meter the usage of electricity, water, gas, and/or other utilities for a home or homes within a particular area and wirelessly transmit the usage of these services to a meter substation. Further embodiments may perform high efficiency wireless communications.

Logic, modules, devices, and interfaces herein described may perform functions that may be implemented in hardware and/or code. Hardware and/or code may comprise software, firmware, microcode, processors, state machines, chipsets, or combinations thereof designed to accomplish the functionality.

Embodiments may facilitate wireless communications. Some embodiments may comprise wireless communications like Bluetooth®, wireless local area networks (WLANs), wireless metropolitan area networks (WMANs), wireless personal area networks (WPAN), cellular networks, communications in networks, messaging systems, and smart-devices to facilitate interaction between such devices. Furthermore, some wireless embodiments may incorporate a single antenna while other embodiments may employ multiple antennas. The one or more antennas may couple with a processor and a radio to transmit and/or receive radio waves. For instance, multiple-input and multiple-output (MIMO) is the use of radio channels carrying signals via multiple antennas at both the transmitter and receiver to improve communication performance.

While some of the specific embodiments described below will reference the embodiments with specific configurations, those of skill in the art will realize that embodiments of the present disclosure may advantageously be implemented with other configurations with similar issues or problems.

Turning now to FIG. 1 , there is shown an embodiment of a wireless communication system 1000. The wireless communication system 1000 comprises a communications device 1010 that may be wire line and wirelessly connected to a network 1005. The communications device 1010 may communicate wirelessly with a plurality of communication devices 1030, 1050, and 1055 via the network 1005. The communications device 1010 may comprise an access point in some embodiments and another type of wireless-capable device in other embodiments. The communications device 1030 may comprise a low power communications device such as a sensor, a consumer electronics device, a personal mobile device, or the like. And communications devices 1050 and 1055 may comprise sensors, stations, access points, hubs, switches, routers, computers, laptops, netbooks, cellular phones, smart phones, PDAs (Personal Digital Assistants), or other wireless-capable devices. Thus, communications devices may be mobile or fixed. For example, the communications device 1010 may comprise a metering substation for water consumption within a neighborhood of homes. The communications device 1010 and/or one or more of the homes in the neighborhood may be located near a Farm to Market Road and Ranch to Market Road with a speed limit of 60 mile per hour (mph) or about 97 kilometers per hour (kph). Each of the homes within the neighborhood may comprise a sensor such as the communications device 1030 and the communications device 1030 may be integrated with or coupled to a water usage meter.

When the communications device 1010 transmits a packet to the communications device 1030 to notify the communications device 1030 that, e.g., the communications device 1010 is buffering data for the communications device 1030, the communications device 1010 may transmit an orthogonal frequency division multiplexing (OFDM) packet with a frame 1014. The OFDM 1022 of the transceiver (RX/TX) 1020 may generate the transmission with pilot tones shifting locations. In several embodiments, the symbol numbers of the shifting pilot tones may conform to a predefined pattern of pilot subcarriers 1012 in memory 1011 or in pilot logic 1023 of the transceiver (RX/TX) 1020. In many embodiments, the predefined pattern of pilot subcarriers may be a fixed pattern that is known to devices 1010, 1030, 1050, and 1055. In some embodiments, the communications device 1010 may transmit pilot tones in L out of every N OFDM symbols based upon the predefined pattern of pilot subcarriers 1012.

The communications device 1010 may transmit the OFDM packet one symbol after the other sequentially and every X symbols, the location of the pilot tones within the OFDM packet may change in accordance with the predefined pattern of pilot subcarriers 1012. Pilot tone shifting is a process where the pilot tones are assigned to different subcarriers in a symbol as a function of time. In many embodiments, only a subset of subcarriers may be defined as pilot subcarriers or data subcarriers (usable subcarriers). For example, in some embodiments, the pilot subcarriers may be defined only on subcarriers designated as data subcarriers, may not be defined on nulled subcarriers (e.g., DC subcarriers and guard subcarriers), and/or may not be defined on data subcarriers that are adjacent to guard or DC subcarriers. In further embodiments, the pilot subcarriers may not be defined on a subset of data subcarriers such as, for example, all even numbered subcarriers, all odd numbered subcarriers, or the like.

FIG. 1A depicts an embodiment of a table 1100 illustrating an embodiment of a predefined pattern of pilot subcarriers on which pilot tones are transmitted. In the present embodiment, the symbol numbers 1 through 13 define a pattern of pilot subcarriers for 13 different symbols and the pilot subcarriers are identified by the subcarrier indices defined by the pattern as pilot subcarriers. In this embodiment, there are 26 data and pilot subcarriers represented by subcarrier indices -13 through 13 in the predefined pattern of pilot subcarriers and each symbol includes two pilot subcarriers. This includes DC for the total of 27 subcarriers. The pattern of pilot subcarrier locations will repeat after every 13 symbol numbers. In other words, the predefined pattern may be cyclic and, after 13 symbols are transmitted in accordance with the predefined pattern of pilot subcarriers beginning with symbol number 1 and ending with symbol number 13, the pattern begins again with symbol number 1. In other embodiments, the pattern may begin with a different symbol number and/or may traverse the symbol numbers in a different order. In further embodiments, the pattern may be dynamically determined between the communications device 1010 and the communications device 1030 by another protocol. The table 1100 illustrates two pilot tones for each symbol number. The symbol number 1 indicates pilot subcarriers at the subcarrier index -7 and the subcarrier index 7, also referred to as (-7,7). The pilot subcarriers in symbols corresponding to symbol number 2 have pilot subcarriers at subcarrier indices (-2,12), to symbol number 3 have pilot subcarriers at subcarrier indices (-10, 4), and so on to symbol number 13, which has pilot subcarriers at subcarrier indices (-12,2). Notice that in the present embodiment, one pilot tone travels between the negative subcarrier indices, skipping five indices between each shift and the second pilot tone travels between the positive subcarrier indices, skipping five indices between each shift. In some embodiments, the predefined pattern of pilot subcarriers can be established by a formula or algorithm known to pilot logic in transmitters and receivers. In further embodiments, this may be extended to higher bandwidths and MIMO cases in which there are more than one of these spatial streams and each spatial stream has shifting pilot patterns.

Note that, in some embodiments, the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100 may only apply to one or more of modulation and coding schemes (MCSs), communications protocols, or the like associated with the transmission. Other embodiments may include more than one predefined patterns of pilot subcarriers 1012. In further embodiments, the pilot logic 1023 may generate more than one symbols sequentially for each symbol number in the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100. For example, the pilot logic 1023 may generate X symbols in accordance with symbol number 1 prior to generating X symbols in accordance with symbol number 2, prior to generating X symbols in accordance with symbol number 3, and so on through symbol number 13.

The communications device 1030 may receive the transmission from the communications device 1010 and may comprise pilot logic 1043 to determine pilot information for updating the taps of an equalizer with channel estimates and to track the phase of the pilot subcarriers. The pilot logic 1043 may utilize a predefined pattern of pilot subcarriers 1032 to determine channel state information by processing the pilot tones on the pilot subcarriers to update the channel state information with pilot information. In particular, the pilot logic 1043 may know, based upon the predefined pattern of pilot subcarriers 1032 in the memory 1031 , the location of the pilot tones in each of the symbols. The pilot logic 1043 may receive and process the pilot tones to determine pilot information and to use the channel estimates of the pilot information to update processing of the data signals received for the OFDM packet. In many embodiments, the pilot logic 1043 may also store the channel estimates determined by processing the pilot tones for use in determining channel estimates for targeted symbols. For example, in some embodiments, the pilot logic 1043 may determine the channel estimates for the pilot tones in the current symbol. The pilot logic 1043 may locate targeted subcarriers for which to determine channel estimates based upon the proximity of the targeted subcarriers to the pilot tones in the current symbol, locate adjacent subcarriers that are adjacent to the targeted subcarriers, and determine the channel estimates for the targeted subcarriers based upon previously estimated channel state information of adjacent subcarriers and/or previously estimated channel state information of the pilot subcarrier(s) and/or LTFs.

In some embodiments, the pilot logic 1043 may determine the targeted subcarriers to be the subcarriers that are adjacent to the pilot tones, i.e., the next subcarrier closer to the edge of the bandwidth of the communication and the next subcarriers closer to the center of the bandwidth of the communication. After determining which subcarriers to target for interpolating channel estimates, the pilot logic 1043 may determine which subcarriers are adjacent to the targeted subcarriers other than the pilot tones. In such embodiments, the adjacent subcarriers would be the next subcarriers in each direction from the pilot tones. For instance, if a pilot tone is located at a subcarrier index -3, the targeted subcarriers may include subcarrier indices -2 and - 4 and the adjacent subcarriers may include subcarrier indices -1 and -5.

Once the pilot logic 1043 identifies the targeted subcarriers and the adjacent subcarriers, the pilot logic 1043 may determine channel state estimates for the adjacent subcarriers. In some embodiments, the pilot logic 1043 may determine the channel state estimates for the adjacent subcarriers by determining previously determined channel state estimates from the most recent pilot tones received on those subcarriers. In further embodiments, the pilot logic 1043 may determine the channel state estimates for the adjacent subcarriers by determining previously determined channel state estimates from the long training field(s) (LTFs) received in the preamble of the communication for the adjacent subcarriers. In many embodiments, the pilot logic 1043 may retrieve the previously determined channel estimates from a buffer within or coupled with the pilot logic 1043. In some embodiments, the pilot logic 1043 may make efficient use of the buffer by only buffering, e.g., up to a few symbols of channel estimates at a time.

In some embodiments, the pilot logic 1043 may interpolate the channel estimates of the adjacent subcarriers with the channel estimates from the pilot tones in the current symbol to determine channel state estimates for the targeted subcarriers, the results of which being referred to as interpolated estimates herein. In several embodiments, the pilot logic 1043 may average the interpolated estimates with channel estimates for the targeted subcarrier prior to updating the channel estimates for the targeted subcarrier. In some embodiments, the pilot logic 1043 may average the interpolated estimates with previously determined estimates for the targeted subcarrier from pilot tones in prior symbols. In other situations, the pilot logic 1043 may average the interpolated estimates with previously determined channel estimates from an LTF in the preamble.

Referring now to FIG. 1 and FIG. IB, FIG. IB illustrates an embodiment of OFDM symbols 1200 transmitted from the communications device 1010 to the communications device 1030. FIG. IB provides an illustration of the guard tones, data and pilot tones, and the direct current (DC) tone. Note that the OFDM module 1022 may generate different OFDM symbols for different wireless communications protocols and, in many embodiments, for different bandwidths. FIG. IB illustrates a single wireless communication protocol and bandwidth for illustration purposes. Embodiments are not limited to a particular protocol or bandwidth.

FIG. IB illustrates an IEEE 802.11 ah system with OFDM symbols 1200 for a 1 MHz bandwidth channel, for transceivers such as the transceivers of FIG. 1 , corresponding to a 32- point, inverse Fourier transform. The OFDM symbols 1200 comprises 32 tones, also referred to as subcarriers, indexed from -16 to 15. The 32 tones, in this embodiment, include 24 data tones, five guard tones, two pilot tones, and one direct current (DC) tone. The four lowest frequency tones are guard tones provided for filter ramp up and filter ramp down. The index zero frequency tone is the DC tone and is nulled, at least in part, to better enable the receivers to employ direct-conversion receivers to reduce complexity. As per a common practice, the DC is selected to be one of the two subcarriers closest to the middle of the frequency band. And the data and pilot tones are provided between indices -13 through -1 and indices 1 through 13.

The RF receiver comprises an OFDM module 1042, which receives electromagnetic energy at an RF frequency and extracts the digital data therefrom. For 1 MHZ operation, OFDM 1042 may extract OFDM symbols comprising 24 data tones, five guard tones, and one DC tone such as the OFDM symbol 1210 illustrated in FIG. IB. In other embodiments, the OFDM symbols may be encoded in other manners with different numbers of data tones, pilot tones, and guard tones.

Note that the OFDM packet 1200 comprises OFDM symbols 1210, 1220, 1230, through

1260 and the OFDM symbols conform to the pilot tone pattern illustrated in table 1100. In particular, the OFDM symbols 1210-1260 illustrate a dot for each of the guard tones, which are also referred to as edge tones. There is one dot in the center of the symbols 1210-1260 illustrating the position of the DC tone as symbol index 0, and the DATA/PILOT TONES are demarked with numbers that start at the subcarrier index -13 on the left side through the -1 index next to the DC tone at the 0 index, and continue with index 1 adjacent to the DC index 0 through the index 13 adjacent to the guard tones on the right side.

As indicated in with respect to table 1100, in the present embodiment, the pilot logic 1043 may determine channel estimates for targeted subcarriers in environments with high Doppler components. For the purposes of this illustration, the symbol being processed by the pilot logic 1043 is the current symbol 1210. The current symbol 1210 illustrates emboldened and dashed arrows for the pilot subcarriers predefined in the predefined pattern of pilot subcarriers 1032 of the communications device 1030. In this example, the current symbol 1210 corresponds to symbol number 1 in the table 1100 of FIG. 1A and the pilot subcarriers are located at subcarrier indices (-7,7). The pilot logic 1043 may determine targeted subcarriers (-6,- 8) and (6,8) by determining subcarriers that are adjacent to the pilot tones in the current symbol 1210 as well as channel estimates from previously determined channel estimates such as channel estimates determined from pilot tones in symbols 1220 and 1230. And the pilot logic 1043 may also determine adjacent subcarriers (-9,-5) and (5,9) of the targeted subcarriers (-6,-8) and (6,8) and determine channel estimates for the adjacent subcarriers such as the previously determined channel estimates from symbols 1240 and 1250.

After determining the channel estimates for the targeted subcarriers (-6,-8) and (6,8) the pilot logic 1043 may interpolate those channel estimates with the channel estimates from the adjacent subcarriers in symbols 1240 and 1250 and average the interpolated results with the channel estimates from the pilot tones (-7,7) in the current symbol 1210 to determine channel estimates for the targeted subcarriers (-6,-8) and (6,8). For instance, for the case of simple linear interpolation scheme, the pilot logic 1043 may add the channel estimates from symbol index -7 from the current symbol 1210 to the channel estimates from the symbol index -9 in symbol 1250 and divide the result by two to determine the interpolated estimates for symbol index -8.

In many embodiments, the pilot logic 1043 may further average the interpolated estimates for symbol index -8 with the previously determined channel estimates for symbol index -8 to determine the channel estimates for the targeted subcarrier at symbol index -8. The pilot logic 1043 may save the channel estimates for the targeted subcarrier at symbol index -8 in a buffer and update weight coefficients for equalization and phase tracking of the pilot logic with the channel estimates and phase information for the targeted subcarrier at symbol index -8.

Referring now to FIG. 1 and FIG. 1C, FIG. 1C illustrates an embodiment of an OFDM packet transmission 1300 with shifting pilot tones with targeted subcarriers and adjacent subcarriers. In the OFDM packet transmission 1300, the symbol numbers range from symbol number 1 on the left side to symbol number 13 on the right side. Time progresses from left to right in the OFDM packet transmission 1300 so the symbol number 1 is generated and transmitted first and the symbol number 13 is generated and transmitted last.

The bandwidth of the OFDM packet transmission 1300 centers about a carrier frequency at, e.g., the subcarrier index zero, and ranges from the subcarrier index -13 to the subcarrier index 13. Note that this bandwidth is for illustration purposes and that there is no limit to the bandwidths of embodiments.

In the OFDM packet transmission 1300, the shifted pilot tones are shifted every OFDM symbol and are inserted in every OFDM symbol. In other embodiments, the shifted pilot tones may be shifted every X symbols and may be include in L out of every N symbols. For example, symbol number 1 has pilot subcarriers defined at subcarrier indices (-7,7) indicated by the inclusion of pilot tones depicted by the squares, one with a 7 in the center and one with a -7 in the center. The symbol number 2 includes pilot tones defined at subcarrier indices (-2,12). Symbol number 3 includes pilot tones defined at subcarrier indices (-10,4). Symbol number 4 includes pilot tones defined at subcarrier indices (-5,9). Symbol number 5 includes pilot tones defined at subcarrier indices (-13,1). Symbol number 6 includes pilot tones defined at subcarrier indices (-8,6). Symbol number 7 includes pilot tones defined at subcarrier indices (-3,11). And so on to symbol number 13 that includes pilot tones defined at subcarrier indices (-12,2). In the present embodiment, the OFDM packet transmission 1300 locates pilot subcarriers in accordance with the predefined pattern of pilot subcarriers in table 1100 in FIG. 1A that span the entire bandwidth and all useable subcarriers. For the time period during which the current symbol is symbol number 6, the channel estimates for pilots on subcarriers (-8,6) will be updated and will replace the original estimates obtained from LTFs in the preamble. In the present embodiment, the pilot logic 1043 has determined that the interpolation setting is on or the pilot logic 1043 has determined a Doppler estimate and, based upon the Doppler estimate, the pilot logic 1043 may update channel estimates for (-8,6) and obtain a new estimates for neighboring subcarriers (-9,5) and (-7,7). Furthermore, the pilot logic 1043 has determined to use interpolation techniques combined with averaging with the original estimates from LTFs in the preamble (not shown) of the OFDM packet transmission 1300.

Note that, in many embodiments, Wi-Fi devices such as the communication devices 1030, 1050, and 1055 may be implemented considering factors of cost and speed of operation, and may not have a lot of buffering capabilities to store received information of a few OFDM symbols for further processing. In several embodiments, interpolation functions may be implemented in a way that is performed on the currently received data in an OFDM symbol in addition to using the last saved channel estimates. While a typical cellular receiver may be capable of processing data over a region such as the circles shown in FIG. 1C, a Wi-Fi receiver may not be capable of buffering received data over a frequency and time region. In some embodiments, a Wi-Fi device may process one OFDM symbol at a time, which highlights an advantage of some embodiments described herein over an existing solution of a cellular receiver. Results of comprehensive simulations for the outdoor channel model have shown that since the channel is very frequency selective for the considered subcarrier spacing, in many embodiments, it is advantageous to interpolate over three subcarriers or less in each OFDM symbol. In such embodiments, the pilot logic 1043 may perform interpolation using the last stored channel estimation from an LTF in the preamble of the OFDM transmission 1300 and/or previous OFDM symbol, as well as the channel estimates determined from the current OFDM symbol.

In the present embodiment, prior to the data symbols illustrated FIG. 1C, the transceiver 1040 receives a preamble prepending a MAC frame and pilot logic 1043 may determine channel estimation data from LTFs for each subcarrier (-13 through 13). As an illustration, consider that the pilot logic 1043 is processing OFDM symbol number 6 in which pilot tones have traveled on subcarrier indices -8 and 6. The pilot logic 1043 may determine new channel estimates for the subcarriers (-8,6). Subcarrier 5 is next to the pilot tone at subcarrier 6. Also, note that channel estimate for subcarrier 4 was recently updated in OFDM symbol number 3, while subcarrier 5 will not be assigned any pilot tone until OFDM symbol number 11 is received in future. Hence, the pilot logic 1043 may determine interpolated estimates for subcarrier 5 in OFDM symbol number 6 using linear interpolation of channel estimates of subcarrier 4 and subcarrier 6. To take advantage of SNR averaging of the LTF structure (LTF may be made of up to multiple repeated long training sequences such as four), the pilot logic 1043 may also average the interpolated estimates with the original estimates of subcarrier 5 from the LTFs.

In many embodiments, the pilot logic 1043 may:

1. For the current OFDM symbol, process the traveled pilot(s), obtain a new channel estimate for the pilot subcarrier on which pilot has traveled, and update the stored channel estimate in a buffer.

2. Locate the subcarriers that are adjacent to the traveled pilot and target these subcarriers for updating their channel estimates (targeted subcarriers).

3. Locate the subcarriers that are adjacent to the targeted subcarriers and retrieve their channel estimation data.

4. Interpolate the channel estimates from process 3 and process 1 to obtain a channel estimate for the targeted subcarriers in process 2, average this interpolated estimate with the previously stored channel estimate for the targeted subcarriers, and save this averaged value as the targeted subcarrier channel estimates to update channel estimates for the targeted subcarriers.

FIG. ID illustrates embodiments of a simulation 1400 comparing packet error rate (PER) performance versus signal-to-noise ratio (SNR) for transmitting pilot tones with interpolation and without interpolation for two different Doppler environments. The simulation 1400 shows that when pilot tone positions are shifted in Doppler scenarios (outdoor channel), including pilot tones in a predefined a pattern of pilot subcarriers and when interpolation is performed for very high Doppler scenarios with speeds around 120 kilometers per hour (Km/h), there is a 2 decibel (dB) SNR gain compared to no interpolation. However, for smaller Doppler components on a 4th path of the channel model with speeds around 30km/h, which may represent, e.g., sensors installed in a residential area where vehicles pass at low speed occasionally, the pilot logic 1043 may follow the frequency selectivity of the channel and continue using the channel estimates from pilot tones rather than performing interpolation at high SNRs. In some embodiments, the pilot logic 1043 may dynamically estimate Doppler to determine if the impact of Doppler is sufficiently high to warrant interpolation to estimate the channel states of subcarriers adjacent to pilot tones. This simulation 1400 is for an IEEE 802.11 ah, lMHz system using MCS1 , and having a 1000 byte packet where all simulation impairments and a carrier offset of - 13.675 parts per million (ppm) are considered.

Based on results obtained from the simulation 1400, the present embodiment may use interpolation in two ways:

a) The communications device may be configured through software/firmware of the device upon installation. For example, utility meters that are installed in the apartment complexes or commercial buildings that are in vicinity of highways may enable interpolation while utility meters installed in residential area far from highways may have interpolation disabled.

b) The communications device may be configured dynamically upon detecting the presence of high Doppler in the environment. In such embodiments, the pilot logic 1043 may estimate Doppler, access other logic within the communications device that estimates Doppler, or receive the Doppler information through a network such as network 1005.

In further embodiments, the communications device 1010 may facilitate data offloading. For example, communications devices that are low power smart phones may include a data offloading scheme to, e.g., communicate via Wi-Fi, another communications device, a cellular network, or the like for the purposes of reducing power consumption consumed in waiting for access to, e.g., a station and/or increasing availability of bandwidth. Communications devices that receive data from smart phones may include a data offloading scheme to, e.g., communicate via Wi-Fi, another communications device, or the like for the purposes of reducing congestion of a cellular network..

The network 1005 may represent an interconnection of a number of networks. For instance, the network 1005 may couple with a wide area network such as the Internet or an intranet and may interconnect local devices wired or wirelessly interconnected via one or more hubs, routers, or switches. In the present embodiment, network 1005 communicatively couples communications devices 1010, 1030, 1050, and 1055.

The communication devices 1010 and 1030 comprise memory 1011 and 1031 , medium access control (MAC) sublayer logic 1018 and 1038, and physical layer (PHY) logic 1019 and 1039, respectively. The memory 1011 and 1031 may comprise a storage medium such as dynamic random access memory (DRAM), read only memory (ROM), buffers, registers, cache, flash memory, hard disk drives, solid-state drives, or the like. The memory 1011 and 1031 may store frames and/or frame structures, or portions thereof such as structures for an association request frame, an association response frame, a probe frame, and the like. The memory 1011 and 1031 may also store one or more predefined patterns of pilot subcarriers such as the predefined pattern in table 1100 of FIG. 1A.

The MAC sublayer logic 1018, 1038 may comprise logic to implement functionality of the MAC sublayer of the data link layer of the communications device 1010, 1030. The MAC sublayer logic 1018, 1038 may generate the frames and the physical layer logic 1019, 1039 may generate physical layer protocol data units (PPDUs) based upon the frames. For example, the frame builder may generate frames 1014, 1034. The physical layer logic 1019, 1039 may prepend the frames with preambles to generate PPDUs for transmission via a physical layer device such as the transceivers represented by receive/transmit chains (RX/TX) 1020 and 1040.

The communications devices 1010, 1030, 1050, and 1055 may each comprise a transceiver (RX/TX) such as transceivers (RX/TX) 1020 and 1040. In many embodiments, transceivers 1020 and 1040 implement orthogonal frequency-division multiplexing (OFDM). OFDM is a method of encoding digital data on multiple carrier frequencies. OFDM is a frequency-division multiplexing scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal subcarrier signals are used to carry data as OFDM symbols. The OFDM symbols are divided into several parallel data streams or channels, one for each subcarrier and encoded with the subcarriers by which the OFDM symbols will be transmitted to a receiving device such as twenty-four data subcarriers, five guard subcarriers, two pilot subcarriers, and one DC subcarrier.

An OFDM system uses several carriers, or "tones," for functions including data, pilot, guard, and nulling. Data tones are used to transfer information between the transmitter and receiver via one of the channels. Pilot tones are used to maintain the channels, and may provide information about time/frequency and channel tracking. And guard tones may help the signal conform to a spectral mask. The nulling of the direct component (DC) may be used to simplify direct conversion receiver designs. And guard intervals may be inserted between symbols such as between every OFDM symbol as well as between the short training field (STF) and long training field (LTF) symbols by the front-end of the transmitter during transmission to avoid inter-symbol interference (ISI), which might result from multi-path distortion.

Each transceiver 1020, 1040 comprises an RF transmitter and an RF receiver. The RF transmitter comprises an OFDM module 1022, which impresses digital data, OFDM symbols encoded with tones, onto RF frequencies, also referred to as subcarriers, for transmission of the data by electromagnetic radiation. In the present embodiment, the OFDM module 1022 may impress the digital data as OFDM symbols encoded with tones onto the subcarriers to for transmission.

FIG. 1 may depict a number of different embodiments including a Multiple-Input, Multiple-Output (MIMO) system with, e.g., four spatial streams, and may depict degenerate systems in which one or more of the communications devices 1010, 1030, 1050, and 1055 comprise a receiver and/or a transmitter with a single antenna including a Single-Input, Single Output (SISO) system, a Single-Input, Multiple Output (SIMO) system, and a Multiple-Input, Single Output (MISO) system. In the alternative, FIG. 1 may depict transceivers that include multiple antennas and that may be capable of multiple-user MIMO (MU-MIMO) operation.

The antenna array 1024 is an array of individual, separately excitable antenna elements.

The signals applied to the elements of the antenna array 1024 cause the antenna array 1024 to radiate one to four spatial channels. Each spatial channel so formed may carry information to one or more of the communications devices 1030, 1050, and 1055. Similarly, the communications device 1030 comprises a transceiver 1040 to receive and transmit signals from and to the communications device 1010. The transceiver 1040 may comprise an antenna array 1044.

FIG. 2 depicts an embodiment of an apparatus with pilot logic to process pilot shifting tones and determine channel estimates for targeted subcarriers. The apparatus comprises a transceiver 200 coupled with Medium Access Control (MAC) sublayer logic 201 and a physical layer (PHY) logic 202. The MAC sublayer logic 201 may determine a frame and the physical layer (PHY) logic 202 may determine the PPDU by prepending the frame or multiple frames, MAC protocol data units (MPDUs), with a preamble to transmit via transceiver 200.

In many embodiments, the MAC sublayer logic 201 may comprise a frame builder to generate frames. The PHY logic 202 may comprise a data unit builder. The data unit builder may determine a preamble to prepend the MPDU or more than one MPDUs to generate a PPDU. In many embodiments, the data unit builder may create the preamble based upon communications parameters chosen through interaction with a destination communications device.

The transceiver 200 comprises a receiver 204 and a transmitter 206. The transmitter 206 may comprise one or more of an encoder 208, a modulator 210, an OFDM 212, and an Inverse Fast Fourier Transform module (IFFT) 215. The encoder 208 of transmitter 206 receives and encodes data destined for transmission from the MAC sublayer logic 202 with, e.g., a binary convolutional coding (BCC), a low density parity check coding (LDPC), and/or the like. The modulator 210 may receive data from encoder 208 and may impress the received data blocks onto a sinusoid of a selected frequency via, e.g., mapping the data blocks into a corresponding set of discrete amplitudes of the sinusoid, or a set of discrete phases of the sinusoid, or a set of discrete frequency shifts relative to the frequency of the sinusoid.

The output of modulator 209 is fed to an orthogonal frequency division multiplexing (OFDM) module 212. The OFDM module 212 may comprise a space-time block coding (STBC) module 211 , a digital beamforming (DBF) module 214, and a pilot logic 280. The STBC module 211 may receive constellation points from the modulator 209 corresponding to one or more spatial streams and may spread the spatial streams to a greater number of space-time streams (also generally referred to as data streams). In some embodiments, the STBC 211 may be controlled to pass through the spatial streams for situations in which, e.g., the number of spatial streams is the maximum number of space-time streams. Further embodiments may omit the STBC.

In some embodiments, the OFDM symbols are fed to the Digital Beam Forming (DBF) module 214. Digital beam forming techniques may be employed to increase the efficiency and capacity of a wireless system. Generally, digital beam forming uses digital signal processing algorithms that operate on the signals received by, and transmitted from, an array of antenna elements. For example, a plurality of spatial channels may be formed and each spatial channel may be steered independently to maximize the signal power transmitted to and received from each of a plurality of user terminals. Further, digital beam forming may be applied to minimize multi-path fading and to reject co-channel interference.

The OFDM module 212 impresses or maps the modulated data formed as OFDM symbols onto a plurality of orthogonal subcarriers. The OFDM module 212 may comprise the pilot logic 280 to generate symbols in which the pilot tones change location within the data/pilot subcarriers in accordance with a predefined pattern of pilot subcarriers every X symbols.

The OFDM module 212 may output to an inverse Fourier transform module that performs an inverse discrete Fourier transform (ID FT) on the OFDM symbols. In the present embodiment, the IDFT may comprise the IFFT 215, to perform an inverse Fast Fourier Transform (FFT) on the data. As an illustration, for 1 MHz bandwidth operation, the IFFT 215 may perform a 32-point, inverse FFT on the data streams.

The output of the IFFT module 215 may enter the transmitter front end 282. The transmitter front end 282 may comprise a radio 284 with a power amplifier (PA) 286 to amplify the signal and prepare the signal for transmission via the antenna array 218. The signal may be up-converted to a higher carrying frequency or may be performed integrally with up-con vers ion. Shifting the signal to a much higher frequency before transmission enables use of an antenna array of practical dimensions. That is, the higher the transmission frequency, the smaller the antenna can be. Thus, an up-con verier multiplies the modulated waveform by a sinusoid to obtain a signal with a carrier frequency that is the sum of the central frequency of the waveform and the frequency of the sinusoid.

The transceiver 200 may also comprise duplexers 216 connected to antenna array 218. Thus, in this embodiment, a single antenna array is used for both transmission and reception. When transmitting, the signal passes through duplexers 216 and drives the antenna with the up- converted information-bearing signal. During transmission, the duplexers 216 prevent the signals to be transmitted from entering receiver 204. When receiving, information bearing signals received by the antenna array pass through duplexers 216 to deliver the signal from the antenna array to receiver 204. The duplexers 216 then prevent the received signals from entering transmitter 206. Thus, duplexers 216 operate as switches to alternately connect the antenna array elements to the receiver 204 and the transmitter 206. The antenna array 218 radiates the information bearing signals into a time- varying, spatial distribution of electromagnetic energy that can be received by an antenna of a receiver. The receiver can then extract the information of the received signal. In other embodiments, the transceiver 200 may comprise one or more antennas rather than antenna arrays and, in several embodiments, the receiver 204 and the transmitter 206 may comprise their own antennas or antenna arrays.

The transceiver 200 may comprise a receiver 204 for receiving, demodulating, and decoding information bearing communication signals. The receiver 204 may comprise a receiver front-end 292 to detect the signal, detect the start of the packet, remove the carrier frequency, and amplify the subcarriers via a radio 294 with a low noise amplifier (LNA) 296.

The transceiver 200 may comprise a receiver 204 for receiving, demodulating, and decoding information bearing communication signals. The communication signals may comprise a packet with pilot tones in, e.g., every symbol that shift locations every symbol. The receiver 204 may comprise a fast Fourier transform (FFT) module 219. The FFT module 219 may transform the communication signals from the time domain to the frequency domain.

The receiver 204 may comprise a pilot logic 250 comprising a channel estimator 252, a phase tracker 254, a buffer 256, an equalizer 258, and, in some embodiments, a predictive logic 260. The pilot logic 250 may be configured for processing shifting pilot tones in accordance with a predefined pattern of pilot subcarriers as well as data tones. The receiver 204 may comprise an equalizer 258 with hard-coded logic or running an equalizer application or instructions, a channel estimator 252, and a phase tracker 254.

The pilot logic 250 may comprise filters, delay elements, and taps or other logic to apply weighting functions to the input signal based upon weight values determined and updated from processing the pilot tones in the incoming signal. The weight coefficients for the weighting functions are weight values which may be adjusted based on the pilot tones to achieve a specific level of performance, and to, e.g., optimize signal quality at the receiver. In some embodiments, the pilot logic 250 is able to track channel changes over time (i.e., using the pilot tones to update the equalizer weight coefficients) because of the rotation of the pilot tones through each of the OFDM subcarriers over the OFDM packet through time. As noted above, the pilot tones are separated by some number of data subcarriers so that estimation of slope and intercept for subcarrier tracking could be maintained. As the pilot tones are shifted through symbol index locations across the band of the OFDM packet, the weight coefficients for the equalizer for the subcarriers that the pilot tones currently populate may be updated as well.

The receiver 204 may receive and convert the pilot tones to a baseband representation. The received pilot tones may then be input into the channel estimator 252 that uses the received sequences to determine updated channel estimates for the wireless channel (using, for example, a least squares approach). The channel estimator 252 may have a priori knowledge of the transmitted pilot tones, which it compares to the received signals to determine the channel estimates. The channel estimates may then be delivered to the equalizer 258.

In many embodiments, the channel estimator 252 may also determine channel estimates for targeted subcarriers in the current symbol that do targeted subcarriers do not co-locate with pilot tones. For example, the pilot logic 250 may determine a targeted subcarrier that is adjacent to a pilot tone in the current symbol and determine adjacent subcarriers to the targeted subcarriers. The channel estimator 252 may determine the channel estimates for the symbol by interpolating previously determined channel estimates of adjacent subcarriers, and averaging the interpolated estimates of adjacent subcarriers and a previously determined estimate for the targeted subcarrier. Further embodiments may include advanced interpolation or prediction functions in predict logic 260.

The baseband representation of the received data signals may be delivered to the input of the equalizer 258, which filters the signals in a manner dictated by the weighting function in accordance with the weight coefficients currently being applied to the equalizer 258. The equalizer 258 may include any type of equalizer structure (including, for example, a transversal filter, a maximum likelihood sequence estimator (MLSE), and others). When properly configured, the equalizer 258 may reduce or eliminate undesirable channel effects within the received signals (e.g., compensate the fast fading).

The received data signals with pilot tones 210 are also delivered to the input of the phase tracker 254, which uses the received signals to track the phase and to update weight coefficients applied to the equalizer 258. During system operation, the phase tracker 254 regularly updates the weight coefficients based on the magnitude and phase of the pilot tones. In addition to the receive data, the phase tracker 254 also receives data from an output of the equalizer 258 as feedback for use in the phase tracking or phase correction process. The phase tracker 254 uses the initial channel estimates determined by the channel estimator 252 to determine the weight coefficients covariance matrix (C). The phase tracker 254 may then determine the value of the constant b (related to the channel changing rate) and calculate the weight coefficients changing covariance matrix (b*C). The square root of the weight coefficients changing covariance matrix may then be determined and used within a modified least mean square (LMS) algorithm to determine the updated channel weight coefficients, which are then applied to the equalizer 258.

The pilot logic 250 also comprises the buffer 256. In some embodiments, the pilot logic 250 may store previously determined channel estimate information determined from pilot tones of the OFDM symbols.

The receiver 204 may also comprise an OFDM module 222, a demodulator 224, a deinterleaver 225, and a decoder 226, and the equalizer 258 may output the weighted data signals for the OFDM packet to the OFDM module 222. The OFDM 222 extracts signal information as OFDM symbols from the plurality of subcarriers onto which information-bearing communication signals are modulated.

The OFDM module 222 may comprise a DBF module 220, and an STBC module 221. The received signals are fed from the equalizer to the DBF module 220 transforms M antenna signals into L information signals. And the STBC module 221 may transform the data streams from the space-time streams to spatial streams. In one embodiment, the demodulation is performed in parallel on the output data of the FFT. In another embodiment, a separate demodulator 224 performs demodulation separately.

The demodulator 224 demodulates the spatial streams. Demodulation is the process of extracting data from the spatial streams to produce demodulated spatial streams. The deinterleaver 225 may deinterleave the sequence of bits of information. For instance, the deinterleaver 225 may store the sequence of bits in columns in memory and remove or output the bits from the memory in rows to deinterleave the bits of information. The decoder 226 decodes the deinterleaved data from the demodulator 224 and transmits the decoded information, the MPDU, to the MAC sublayer logic 202.

Persons of skill in the art will recognize that a transceiver may comprise numerous additional functions not shown in FIG. 2 and that the receiver 204 and transmitter 206 can be distinct devices rather than being packaged as one transceiver. For instance, embodiments of a transceiver may comprise a Dynamic Random Access Memory (DRAM), a reference oscillator, filtering circuitry, synchronization circuitry, an interleaver and a deinterleaver, possibly multiple frequency conversion stages and multiple amplification stages, etc. Further, some of the functions shown in FIG. 2 may be integrated. For example, digital beam forming may be integrated with orthogonal frequency division multiplexing.

The MAC sublayer logic 201 may decode or parse the MPDU or MPDUs to determine the particular type of frame or frames included in the MPDU(s).

FIG. 3 depicts an embodiment of a flowchart 300 to process shifting pilot tones and determine channel estimates for targeted subcarriers. The flowchart 300 may begin with receiving an OFDM packet with pilot tones that shift locations of across the bandwidth of the packet in accordance with a known, predefined pattern of pilot subcarriers (element 302). In many embodiments, the OFDM packet may be received one symbol at a time and the pilot tones may shift to a new location every X symbols, where X may be a settable, calculated or fixed value such as one. Thus, the pilot tones' locations may remain constant for X symbols before shifting to the next location and the pilot tones shift in accordance with a sequence that is known to both the transmitter and the receiver, which is referred to herein as the predefined pattern of pilot subcarriers.

After the receiver begins to receive the OFDM packet, the receiver may begin to process at least some of the pilot tones to determine pilot tone phase rotations and channel estimates (element 305). For instance, in some embodiments, the receiver may skip processing pilot tones that are at locations that are adjacent to the DC tone or the edge tones, that are affected by fading, or that are skipped for other reasons. In other embodiments, the receiver may process all the pilot tones but not use the phase rotations determined by processing selected pilot tones. And while processing pilot tones, the receiver may store one or more of the determined channel estimates and, in some embodiments, phase rotations in memory (element 310).

When the receiver receives OFDM symbols, the receiver may determine that interpolation should be implemented based upon input from, e.g., a network, and may locate targeted subcarriers (element 315) by determining subcarriers adjacent to the pilot tone(s) as well as determining adjacent subcarriers by determining subcarriers that are adjacent to the targeted subcarriers (element 320). In many embodiments, the receiver may access the buffer and retrieve the previously determined channel estimates to calculate at least one new channel estimate for the targeted subcarriers (element 325). For instance, in some embodiments, the pilot logic may determine channel estimates for the targeted subcarrier by interpolating channel estimates for adjacent subcarriers and the pilot tone, and, in some embodiments averaging channel estimates for adjacent subcarriers with a previously determined channel estimate for each subcarrier. And the pilot logic may store the channel estimates for the targeted subcarriers in a buffer as well as update the channel estimates for the targeted subcarriers in the equalizer and phase tracker (element 330).

FIG. 4 depicts an embodiment of a flowchart to receive, decode, and interpret communications with frames shifting pilot tones and determination of channel estimates for targeted subcarriers as illustrated in FIGs. 1-2. The flowchart 450 begins with a receiver of a station such as the receiver 204 in FIG. 2 receiving a communication signal via one or more antenna(s) such as an antenna element of antenna array 218 (element 455). The receiver may convert the communication signal into one or more MPDUs in accordance with the process described in the preamble (element 460). More specifically, the received signal is fed from the one or more antennas to a pilot logic such as the pilot logic 250 in FIG. 2. The pilot logic may determine pilot information from the signal to update channel estimates. In many embodiments, the pilot logic may also determine channel estimates for targeted subcarriers such as subcarriers that are adjacent to the pilot tones. The pilot logic may determine the channel estimates for the targeted subcarriers by locating adjacent subcarriers to the targeted subcarriers, determining channel estimates for the adjacent subcarriers and interpolating the channel estimates of the adjacent subcarriers with the channel estimates for the pilot tones. And in some embodiments, the interpolated estimates may be averages with the channel estimates from the LTFs in the preamble of the OFDM transmission.

The output of the pilot logic is fed to OFDM such as the OFDM 222. The OFDM extracts signal information from the plurality of data subcarriers onto which information-bearing signals are modulated. Then, the demodulator such as the demodulator 224 demodulates the signal information via, e.g., BPSK, 16-QAM, 64-QAM, 256-QAM, QPSK, or SQPSK. And the decoder such as the decoder 226 decodes the signal information from the demodulator via, e.g., BCC or LDPC, to extract the one or more MPDUs (element 460) and transmits the one or more MPDUs to MAC sublayer logic such as MAC sublayer logic 202 (element 465). The MAC sublayer logic may then decode a data or management frame in the MPDUs (element 470).

The following examples pertain to further embodiments. One example comprises an apparatus to determine channel state information from pilot tones in wireless communications. The apparatus may comprise memory; and pilot logic coupled with the memory to receive a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone; to determine a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol; to determine channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and to determine channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

In some embodiments, the apparatus may further comprise a radio coupled with an antenna array to receive the current symbol with the pilot tone. In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier. In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate. In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of an interpolation setting. In some embodiments, the pilot logic comprises logic to determine channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

Another embodiment comprises a program product to determine channel state information from pilot tones in wireless communications. The program product may comprise a storage medium comprising instructions to be executed by a processor-based device, wherein the instructions, when executed by the processor-based device, perform operations. The operations may comprise receiving a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone; determining a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol; determining channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and determining channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

In some embodiments, the operations further comprise determining whether or not to perform interpolation for the targeted subcarrier. In some embodiments, determining whether or not to perform interpolation for the targeted subcarrier comprises determining a Doppler estimate. In some embodiments, determining whether or not to perform interpolation for the targeted subcarrier comprises determining an interpolation setting. In some embodiments, determining channel state estimates for the targeted subcarrier comprises determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

Another embodiment comprises a system to determine channel state information from pilot tones in wireless communications. The system may comprise a radio to receive symbols; and pilot logic coupled with the memory to receive a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone; to determine a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol; to determine channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and to determine channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier. In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate. In some embodiments, the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of an interpolation setting. In some embodiments, the pilot logic comprises logic to determine channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

Another embodiment comprises a method to determine channel state information from pilot tones in wireless communications. The method may comprise receiving a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone; determining a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol; determining channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and determining channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

In some embodiments, the method may further comprise determining whether or not to perform interpolation for the targeted subcarrier. In some embodiments, determining whether or not to perform interpolation for the targeted subcarrier comprises determining a Doppler estimate. In some embodiments, determining channel state estimates for the targeted subcarrier comprises determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

Another embodiment comprises an apparatus to determine channel state information from pilot tones in wireless communications. The apparatus may comprise a means for receiving a current symbol with a pilot tone; a means for determining channel state estimates based upon the pilot tone; a means for determining a targeted subcarrier, wherein the targeted subcarrier is adjacent to the pilot tone in the current symbol; a means for determining channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and a means for determining channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

In some embodiments, the apparatus may further comprise a means for determining whether or not to perform interpolation for the targeted subcarrier. In some embodiments, the means for determining whether or not to perform interpolation for the targeted subcarrier comprises a means for determining whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate. In some embodiments, the means for determining channel state estimates for the targeted subcarrier comprises a means for determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate. In some embodiments, some or all of the features described above and in the claims may be implemented in one embodiment. For instance, alternative features may be implemented as alternatives in an embodiment along with logic or selectable preference to determine which alternative to implement. Some embodiments with features that are not mutually exclusive may also include logic or a selectable preference to activate or deactivate one or more of the features. For instance, some features may be selected at the time of manufacture by including or removing a circuit pathway or transistor. Further features may be selected at the time of deployment or after deployment via logic or a selectable preference such as a dips witch or the like. A user after via a selectable preference such as a software preference, an e-fuse, or the like may select still further features.

Another embodiment is implemented as a program product for implementing systems, apparatuses, and methods described with reference to FIGs. 1-4. Embodiments can take the form of an entirely hardware embodiment, a software embodiment implemented via general purpose hardware such as one or more processors and memory, or an embodiment containing both specific-purpose hardware and software elements. One embodiment is implemented in software or code, which includes but is not limited to firmware, resident software, microcode, or other types of executable instructions.

Furthermore, embodiments can take the form of a computer program product accessible from a machine-accessible, computer-usable, or computer-readable medium providing program code for use by or in connection with a computer, mobile device, or any other instruction execution system. For the purposes of this description, a machine-accessible, computer-usable, or computer-readable medium is any apparatus or article of manufacture that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system or apparatus.

The medium may comprise an electronic, magnetic, optical, electromagnetic, or semiconductor system medium. Examples of a machine-accessible, computer-usable, or computer-readable medium include memory such as volatile memory and non- volatile memory. Memory may comprise, e.g., a semiconductor or solid-state memory like flash memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and/or an optical disk. Current examples of optical disks include compact disk - read only memory (CD-ROM), compact disk - read/write memory (CD- R/W), digital video disk (DVD)-read only memory (DVD-ROM), DVD-random access memory (DVD-RAM), DVD-Recordable memory (DVD-R), and DVD- read/write memory (DVD-R/W).

An instruction execution system suitable for storing and/or executing program code may comprise at least one processor coupled directly or indirectly to memory through a system bus. The memory may comprise local memory employed during actual execution of the code, bulk storage such as dynamic random access memory (DRAM), and cache memories which provide temporary storage of at least some code in order to reduce the number of times code must be retrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the instruction execution system either directly or through intervening I/O controllers. Network adapters may also be coupled to the instruction execution system to enable the instruction execution system to become coupled to other instruction execution systems or remote printers or storage devices through intervening private or public networks. Modem, Bluetooth™ , Ethernet, Wi-Fi, and WiDi adapter cards are just a few of the currently available types of network adapters.

Claims

WHAT IS CLAIMED IS:

1. An apparatus to determine channel state information from pilot tones in wireless communications, the apparatus comprising:

memory; and

pilot logic coupled with the memory to receive a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone; to determine a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol; to determine channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and to determine channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

2. The apparatus of claim 1 , further comprising a radio coupled with an antenna array to receive the current symbol with the pilot tone.

3. The apparatus of claim 1 , wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier.

4. The apparatus of claim 3, wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate.

5. The apparatus of claim 3, wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of an interpolation setting.

6. The apparatus of claim 1 , wherein the pilot logic comprises logic to determine channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

A program product to determine channel state information from pilot tones in wireless communications , the program product comprising:

a storage medium comprising instructions to be executed by a processor-based device, wherein the instructions, when executed by the processor-based device, perform operations, the operations comprising:

receiving a current symbol with a pilot tone; to determine channel state estimates based upon the pilot tone;

determining a targeted subcarrier, wherein the targeted subcarrier in adjacent to the pilot tone in the current symbol;

determining channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and

determining channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

The program product of claim 7, wherein the operations further comprise determining whether or not to perform interpolation for the targeted subcarrier.

The program product of claim 8, wherein determining whether or not to perform interpolation for the targeted subcarrier comprises determining a Doppler estimate.

The program product of claim 8, wherein determining whether or not to perform interpolation for the targeted subcarrier comprises determining an interpolation setting.

The program product of claim 7, wherein determining channel state estimates for the targeted subcarrier comprises determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

12. A system to determine channel state information from pilot tones in wireless communications comprising:

a processor;

memory;

at least one antenna

a radio coupled with the at least one antenna to receive symbols; and

13. The system of claim 12, wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier.

14. The system of claim 13, wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate or reception of Doppler information.

15. The system of claim 13, wherein the pilot logic comprises logic to determine whether or not to perform interpolation for the targeted subcarrier by determination of an interpolation setting.

16. The system of claim 12, wherein the pilot logic comprises logic to determine channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate. A method to determine channel state information from pilot tones in wireless communications, the method comprising:

The method of claim 17, further comprising determining whether or not to perform interpolation for the targeted subcarrier.

The method of claim 18, wherein determining whether or not to perform interpolation for the targeted subcarrier comprises determining a Doppler estimate or reception of Doppler information.

The method of claim 17, wherein determining channel state estimates for the targeted subcarrier comprises determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.

An apparatus to determine channel state information from pilot tones in wireless communications, the apparatus comprising:

a means for receiving a current symbol with a pilot tone;

a means for determining channel state estimates based upon the pilot tone;

a means for determining a targeted subcarrier, wherein the targeted subcarrier is adjacent to the pilot tone in the current symbol;

a means for determining channel state estimates for an adjacent subcarrier, wherein the adjacent subcarrier is adjacent to the targeted subcarrier; and

a means for determining channel state estimates for the targeted subcarrier based upon the channel state estimates for the adjacent subcarrier and the channel state estimates based upon the pilot tone.

The apparatus of claim 21 , further comprising a means for determining whether or not to perform interpolation for the targeted subcarrier.

The apparatus of claim 22, wherein the means for determining whether or not to perform interpolation for the targeted subcarrier comprises a means for determining whether or not to perform interpolation for the targeted subcarrier by determination of a Doppler estimate or reception of Doppler information.

The apparatus of claim 21 , wherein the means for determining channel state estimates for the targeted subcarrier comprises a means for determining channel state information for the targeted subcarrier by interpolation of the channel state estimates for the adjacent subcarrier and channel state estimates for the pilot tone to determine an interpolated estimate and calculation of an average of the interpolated estimate and a previously determined channel state estimate.