WO2015099805A1 - Procédés et agencements pour déterminer des affectations de stations à des fenêtres d'accès limité dans des réseaux sans fil - Google Patents

Procédés et agencements pour déterminer des affectations de stations à des fenêtres d'accès limité dans des réseaux sans fil Download PDF

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Publication number
WO2015099805A1
WO2015099805A1 PCT/US2013/078162 US2013078162W WO2015099805A1 WO 2015099805 A1 WO2015099805 A1 WO 2015099805A1 US 2013078162 W US2013078162 W US 2013078162W WO 2015099805 A1 WO2015099805 A1 WO 2015099805A1
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WO
WIPO (PCT)
Prior art keywords
pilot
symbols
subcarriers
tones
pilot tones
Prior art date
Application number
PCT/US2013/078162
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English (en)
Inventor
Shahrnaz Azizi
Thomas J. Kenney
Eldad Perahia
Original Assignee
Intel Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Intel Corporation filed Critical Intel Corporation
Priority to PCT/US2013/078162 priority Critical patent/WO2015099805A1/fr
Publication of WO2015099805A1 publication Critical patent/WO2015099805A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0204—Channel estimation of multiple channels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0226—Channel estimation using sounding signals sounding signals per se
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
    • H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
    • H04L2025/03375—Passband transmission
    • H04L2025/03414—Multicarrier

Definitions

  • 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.
  • 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.
  • 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.
  • 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. ID depict embodiments of a simulation comparing performance for transmitting pilot tones in every symbol as compared to transmitting pilot tones every two symbols;
  • FIG. IE depict embodiments of a simulation comparing performance for transmitting pilot tones in every symbol as compared to transmitting pilot tones every two symbols for two different modulation and coding schemes;
  • FIG. 2 depicts an embodiment of an apparatus with pilot logic to transmit and process skipped and shifting pilot tones
  • FIGs. 3A-B depict embodiments of flowcharts to transmit and process skipped and shifting pilot tones
  • FIGs. 4A-B depict embodiments of flowcharts to generate, transmit, receive, decode, and interpret communications with frames as illustrated in FIGs. 1-2.
  • the Doppler effect in a channel may be addressed in embodiments such as 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 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.
  • CSI channel state information
  • 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.
  • 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, and 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.
  • embodiments may dynamically track the channel state. While some of the embodiments described herein may refer to IEEE 802.1 lah 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 reduction of overhead in communications that include pilot tones in symbols in various scenarios such as, e.g., in Doppler scenarios.
  • logic may reduce overhead in such communications by establishing a predefined pattern of subcarriers on which the pilot tones are transmitted and pilot skipping by inserting the pilot tones only in L out of every N orthogonal frequency division multiplexing (OFDM) symbols in the communications.
  • OFDM orthogonal frequency division multiplexing
  • pilot subcarriers to carry data or other information increases the useable bandwidth for the data tones during OFDM symbol packet transmissions while obtaining benefit from implementation of the shifted pilots.
  • MHz MegaHertz
  • FFT Fast Fourier Transform
  • This pilot design has an overhead of 2/26, which is almost 8% of each OFDM symbol capacity.
  • Some embodiments comprise transmitters with pilot logic to implement pilot shifting. For instance, embodiments may shift pilot tones, or pilot signals, through the predefined pattern of pilot subcarriers for OFDM symbols in a packet transmission.
  • the pilot logic may insert pilot tones on pilot subcarriers of OFDM symbols according to the predefined pattern of pilot subcarriers for OFDM symbols and the pilot logic may achieve the pattern of L out of every N OFDM symbols by inserting OFDM symbols without pilot tones into the sequence, between the OFDM symbols that include the pilot tones in the packet transmission. For example, if L equals one and N equals two, then one OFDM symbol that does not include pilot tones may be inserted between each OFDM symbol that includes pilot tones.
  • the pilot logic may implement a different, known sequence of OFDM symbols with pilot tones and OFDM symbols without pilot tones to achieve the combination of L symbols with pilot tones and N minus L symbols without pilot tones out of every N symbols in the packet transmission.
  • the pilot logic may implement communications in accordance with the predefined pattern of pilot subcarriers by inserting tones other than pilot tones on subcarriers in N minus L out of every N symbols.
  • the pilot logic may insert tones other than pilot tones on pilot subcarriers in N minus L (N-L) out of every N symbols.
  • pilot logic in receivers that know the predefined pattern of pilot subcarriers and that determine channel estimates for the skipped pilot tones. For example, in addition to determining channel estimates for the L out of every N symbols that include pilot tones, the pilot logic may determine channel estimates for one or more of the N-L symbols that do not include the pilot tones. In several embodiments, the pilot logic may calculate the channel estimates for the symbols that do not include the pilot tones from previously estimated channel state information of adjacent subcarriers and/or previously estimated channel state information of the pilot subcarrier(s). In some embodiments, the pilot logic may average channel estimates from pilot tones in one or more previous symbols for the subcarriers that are adjacent to the pilot subcarrier in a current symbol.
  • the pilot logic may average channel estimates from adjacent subcarriers with channel estimates of the pilot subcarrier calculated for a previously received symbol. In still further embodiments, the pilot logic may use channel estimates of the pilot subcarrier calculated for a previously received symbol or average channel estimates of the pilot subcarrier calculated for previously received symbols.
  • the pilot logic may determine channel estimates for symbols that are inserted between symbols that include pilot tones. Further embodiments may not determine channel estimates for such symbols.
  • Several embodiments may include pilot logic to assign a logical pilot subcarrier to symbols without defined pilot subcarriers. For instance, some embodiments may select one or more subcarriers for which to determine channel estimates for symbols that do not include pilot tones.
  • the logical pilot subcarrier is assigned based upon an offset from the current symbol number within a predefined pattern of pilot subcarriers. In further embodiments, the logical pilot subcarrier is assigned based upon a formula for an offset from the current symbol number within a predefined pattern of pilot subcarriers.
  • the pilot logic may implement a known sequence for the pilot subcarriers to assign to symbols that do not include pilot tones. For instance, if the predefined pattern of subcarriers comprises a total number of 13 pairs of subcarriers for 13 symbols, some embodiments may comprise a function to determine the symbol number in the predefined pattern of subcarriers that comprise the subcarriers to update.
  • the pilot logic may choose to either update channel estimates for the pilot subcarriers associated with symbol 8 or symbol 7 in the predefined pattern of subcarriers, which doubles the frequency of channel updates for the subcarriers during the transmission of the packet.
  • int(half total number symbols in predefined pattern) may equal the Offset within the predefined pattern of pilot subcarriers and can be used to find the logical pilot subcarriers for a symbol.
  • Various embodiments may be designed to address different technical problems associated with system overhead associated with inclusion of pilot tones in communications. For instance, some embodiments may be designed to address one or more technical problems such as transmitting pilot tones on a predefined pattern of on subcarriers for symbols in a packet transmission. Further embodiments may comprise determining channel estimates and phase rotations from pilot tones included in symbols. And still further embodiments may comprise determining channel estimates for symbols that do not include pilot tones based upon previously estimated channel state information of subcarriers adjacent to pilot subcarriers and/or a previously estimated channel state information for the pilot subcarriers.
  • pilot tones in communications may do so by one or more different technical means such as skipping the inclusion of pilot tones in N - L out of N symbols and including additional data tones in the symbols on pilot subcarriers.
  • Several embodiments may detect the predefined pattern of pilot tones in L out of N symbols and determine channel estimates for symbols that do not include pilot tones based upon previously estimated channel state information of subcarriers adjacent to pilot subcarriers and/or a previously estimated channel state information for the pilot subcarriers.
  • 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
  • APs access points
  • STAs stations
  • Some embodiments may provide, e.g., indoor and/or outdoor "smart" grid and sensor services.
  • 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 .
  • Embodiments 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.
  • WLANs wireless local area networks
  • WMANs wireless metropolitan area networks
  • WPAN wireless personal area networks
  • cellular networks communications in networks, messaging systems, and smart-devices to facilitate interaction between such devices.
  • 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.
  • MIMO 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.
  • 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.
  • 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.
  • communications devices may be mobile or fixed.
  • the communications device 1010 may comprise a metering substation for water consumption within a neighborhood of homes.
  • 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.
  • 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 within the symbol indices or symbol numbers.
  • 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.
  • the predefined pattern of pilot subcarriers may be a fixed pattern that is known to devices 1010, 1030, 1050, and 1055.
  • 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 pilot logic 1023 may insert OFDM symbols that do not include pilot tones between symbols generated to implement the predefined pattern of pilot subcarriers 1012.
  • the pilot logic 1023 may generate symbols to implement the predefined pattern of pilot subcarriers 1012 and insert data tones or other information on the subcarriers in the symbols that are defined as pilot subcarriers according to the predefined pattern of pilot subcarriers 1012.
  • the communications device 1010 may transmit the OFDM packet one symbol after the other sequentially and every N 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).
  • 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.
  • 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.
  • 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.
  • the pattern of pilot subcarrier locations will repeat after every 13 symbol numbers.
  • the predefined pattern is cyclic.
  • the pattern begins again with symbol number 1.
  • the pattern may begin with a different symbol number and/or may traverse the symbol numbers in a different order.
  • 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).
  • 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.
  • the predefined pattern of pilot subcarriers can be established by a formula or algorithm known to pilot logic in transmitters and receivers.
  • the pilot logic 1023 includes pilot tones in L out of every N symbols.
  • the pilot logic 1043 may transmit N minus L symbols out of every N symbols without pilot tones.
  • the pilot logic 1023 may disperse the N minus L symbols throughout the N symbols such that the number of sequential symbols transmitted that do not include pilot tones is minimized.
  • the pilot logic 1023 may generate a transmission with pilot tones in L out of every N symbols the symbols with pilot carriers defined in accordance with the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100 by inserting data tones or other information on pilot subcarriers of N minus L of every N symbols.
  • the pilot logic 1023 may generate a transmission with a first symbol corresponding to symbol number 1 , which has two pilot tones, one located at the subcarrier index -7 and one located at the subcarrier index 7.
  • the second symbol transmitted may then be symbol number 2 with pilot carriers at the subcarrier indices (-2,12) but the pilot logic 1023 may insert data tones on the subcarriers at indices (-2,12).
  • the third symbol and fourth symbol may also include data tones at subcarrier indices (-10,4) and (-5,9).
  • the fifth symbol transmitted may then be symbol number 5 with pilot tones at the subcarrier indices (-13,1).
  • These pilot subcarrier shifts may continue through symbol 13 and then repeat by moving to symbol number 1 after symbol number 13 until all symbols in the transmission are generated.
  • the pilot logic 1023 may generate a transmission with pilot tones in L out of every N symbols by inserting N minus L symbols in every N symbols without pilot tones.
  • the symbols with pilot tones may be defined in accordance with the predefined pattern of pilot subcarriers 1012 as illustrated in table 1100 and the symbols without pilot tones may be added to the sequence of symbols generated in accordance with the predefined pattern of pilot subcarriers 1012.
  • L out of every N symbols in these embodiments will follow the predefined pattern of pilot subcarriers 1012 and the N minus L symbols may be dispersed amongst the L out of every N symbols.
  • the pilot logic 1023 may generate a transmission with a first symbol corresponding to symbol number 1, which has two pilot tones, one located at the subcarrier index -7 and one located at the subcarrier index 7.
  • the second symbol may be inserted without pilot tones and may not follow the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100 so the second symbol may have two additional data tones or tone with other information.
  • the third symbol transmitted may then be symbol number 2 as defined in the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100 with pilot tones at the subcarrier indices -2 and 12.
  • the third symbol may be inserted without pilot tones and may not follow the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100.
  • the fourth symbol in the transmission may be symbol number 3 as defined in the predefined pattern of pilot subcarriers 1012 defined as illustrated in table 1100 with pilot tones at the subcarrier indices -10 and 4. These pilot subcarriers shifts may continue through symbol 13 and then repeat by moving to symbol number 1 after symbol number 13 until all symbols in the transmission are generated.
  • 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.
  • MCSs modulation and coding schemes
  • Other embodiments may include more than one predefined patterns of pilot subcarriers 1012.
  • 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.
  • 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 L out of every N symbols.
  • the communications device 1030 may either skip updating the channel estimates or determine channel estimates based upon previously determined channel estimates. In many embodiments, the communication device 1030 may update the channel estimates based upon previously determined channel estimates.
  • 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. The pilot logic 1043 may also store the channel estimates and phase rotations determined by processing the pilot tones for use in determining channel estimates for symbols that do not include pilot tones. For example, in some embodiments, the pilot logic 1043 may determine the channel estimates for the symbols that do not include the pilot tones based on previously estimated channel state information of adjacent subcarriers and/or previously estimated channel state information of the pilot subcarrier(s).
  • 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.
  • 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 802.1 lah system with OFDM symbols 1200 for a 1
  • the OFDM symbols 1200 comprises 32 tones, also referred to as subcarriers, indexed from -16 to 15.
  • the 32 tones 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.
  • the DC is selected to be one of the two subcarriers closest to the middle of the frequency band.
  • 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.
  • 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.
  • the OFDM symbols may be encoded in other manners with different numbers of data tones, pilot tones, and guard tones.
  • the OFDM packet 1200 comprises OFDM symbols 1210, 1220, 1230, through 1240 and the OFDM symbols correspond to the pilot tone pattern illustrated in table 1100.
  • the OFDM symbols 1210-1240 illustrate a dot for each of the guard tones, which are also referred to as edge tones.
  • the pilot logic 1043 may determine channel estimates for symbols that do not include pilot tones.
  • 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.
  • 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 subcarriers in the current symbol 1210 do not comprise pilot tones but instead include data tones.
  • the pilot logic 1043 may determine channel estimates for the subcarriers at subcarrier indices (-7,7) by using previously determined channel estimates for adjacent subcarriers and/or one or more previously determined channel estimates for the pilot subcarriers of the current symbol.
  • the pilot logic 1043 may determine channel estimates based upon previous channel estimates of adjacent subcarriers by identifying channel estimates for adjacent subcarriers such as the channel estimates for the subcarrier indices -8 and -6 of symbols 1220 and 1230 as well as the channel estimates for the subcarrier indices 6 and 8 of symbols 1220 and 1230. In several embodiments, the pilot logic 1043 may interpolate the previously determined channel estimates for adjacent subcarriers to determine the channel estimates for the current symbol 1210.
  • the pilot logic 1043 may determine channel estimates based upon previous channel estimates of the same subcarriers by identifying channel estimates for subcarriers such as the channel estimates for the subcarrier indices -7 and 7 of symbol 1240. In several embodiments, the pilot logic 1043 may use the previously determined channel estimates as the channel estimates for the current symbol 1210.
  • the pilot logic 1043 may determine channel estimates based upon previous channel estimates of the adjacent subcarriers and same subcarriers. After determining the channel estimates, the pilot logic 1043 may average the channel estimates to determine the channel estimates for the current symbol 1210.
  • the pilot logic 1043 may comprise predictive logic to predict phase corrections or rotations for phase tracking and, in some embodiments, predicted channel estimates for updating weight coefficients for equalization. [0040] Referring now to FIG. 1 and FIG. 1C, FIG. 1C illustrates an embodiment of an
  • the symbol numbers range from symbol number 1 on the left side to symbol number 26 on the right side. Time progresses from left to right in the OFDM packet transmission 1300 so the symbol number one is generated and transmitted first and the symbol number 26 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.
  • the higher the bandwidth the more number of pilot tones that are used. For example, in 2MHz 802.1 lah, or 20 MHz 802.1 la/g/n/ac, there are four pilot tones.
  • this application does not define any pattern for four pilot tone case, the idea of shifting and skipping can easily be extended by those of ordinary skill in art to define a pattern for it to utilize the teachings herein.
  • the shifted pilot tones are inserted only in every other OFDM symbol.
  • 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 does not include pilot tones.
  • Symbol number 3 includes pilot tones defined at subcarrier indices (-10,4).
  • Symbol number 4 does not include pilot tones.
  • Symbol number 5 includes pilot tones defined at subcarrier indices (-13,1).
  • Symbol number 6 does not include pilot tones.
  • Symbol number 7 includes pilot tones defined at subcarrier indices (-3,13).
  • 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. Based upon the pilot subcarrier assignments in the table 1100 and the locations of the pilot tones in the OFDM packet transmission 1300, it can be seen that the pilot logic of the transmitter has inserted pilot tones in odd numbered symbols in the table 1100 such as symbol numbers 1 , 3, 5, 7, 9, 11 , and etc. Furthermore, the pilot logic of the transmitter has included data tones or other information on the subcarriers that are defined as pilot subcarriers in the table 1100 in the even numbered symbols such as in symbol numbers 2, 4, 6, 8, 10, 12, and etc.
  • the OFDM packet transmission 1300, the pilot tone pattern can follow the predefined pattern of pilot subcarriers in table 1100 but with "an OFDM symbol without any pilot tones" inserted in between each of the "OFDM symbols with pilot tones".
  • the pilot tones depicted in symbol number 1 would remain the same
  • the pilot tones in symbol number 3 would match the subcarrier indices of symbol number 2 in the predefined pattern of pilot subcarriers in table 1100
  • the pilot tones in symbol number 5 would match the subcarrier indices of symbol number 3 in the predefined pattern of pilot subcarriers in table 1100, and so on through symbol number 26.
  • pilot logic may process the pilot tones in the in OFDM symbols that carry pilot tones (such as symbol number 1 , 3 and etc., as shown) to determine pilot information including channel estimates and phase tracking information. As the pilot information is determined for each of the symbols that carry pilot tones, the corresponding taps for an equalizer of the receiver for the pilot subcarriers are updated and, in many embodiments, the pilot logic may use the new pilot information for tracking and estimation of the carrier frequency. [0046] However, for symbols (such as for symbol number 2, 4, and etc.
  • the pilot logic of the receiver may skip updates to the channel state information or may calculate channel estimates based upon previously estimated channel state information of adjacent subcarriers and/or previously estimated channel state information of logical pilot subcarriers.
  • the logical pilot subcarriers may be the pilot subcarriers that were predefined in the table 1100 as pilot subcarriers but used for data tones or other information or may be pilot subcarriers selected by another method. For example, OFDM symbol number 14 would have carried pilot tones on subcarrier indices (-7,7), if they had not been skipped.
  • the pilot logic at the receiver may calculate new channel estimates from currently stored channel estimates for the adjacent subcarrier indices (-8,-6) 1320 and (6,8) 1310 and/or the pilot logic at the receiver may use previously estimated values for subcarrier indices (- 7,7) in OFDM symbol number 1. Note that the channel estimates for subcarrier indices (-6,8) were updated in response to receipt of the OFDM symbol number 9, while for subcarrier indices (-8,6), no pilot tones are calculated based upon receipt of the symbols 1 through 13.
  • the pilot logic may determine channel estimates for all usable subcarriers based upon receipt of a preamble, which is prior to receipt of symbol number 1 by the receiver so the pilot logic may use the previously determined channel estimates from receipt of the preamble for subcarrier indices (-8,6).
  • the pilot logic of the receiver may determine the new channel estimates for the subcarrier indices (-7,7) by interpolating a value based upon the channel estimates calculated for adjacent subcarrier indices (-8,-6) and (6,8) from symbol number 9 and the preamble.
  • FIG. ID illustrates embodiments of a simulation 1400 comparing packet error rate
  • pilot logic may calculate channel estimates for skipped pilots, for example subcarrier indices (-7,7), by one of three methods (a), (b), or (c). According to the method (a) the pilot logic may average the channel estimates of adjacent subcarrier indices (-8,-6) and (6,8) based upon a formula:
  • Channel Estimates for subcarrier index -7 (channel estimates for adjacent subcarrier index -6 plus channel estimates for adjacent subcarrier index -8) divided by 2.
  • Channel Estimates for subcarrier index 7 (channel estimates for adjacent subcarrier index 6 plus channel estimates for adjacent subcarrier index 8) divided by 2.
  • the pilot logic may average channel estimates of adjacent subcarriers and previously obtained estimates for subcarrier indices (-7,7) based upon a formula:
  • Channel Estimates for subcarrier index 7 (channel estimates for adjacent subcarrier index 8 plus channel estimates for adjacent subcarrier index 6 plus the previous channel estimates of the subcarrier index 7) divided by 3.
  • Channel Estimates for subcarrier index -7 (channel estimates for adjacent subcarrier index 6 plus channel estimates for adjacent subcarrier index -8 plus the previous channel estimates of the subcarrier index -7) divided by 3.
  • the pilot logic may reuse of the previously determined estimates for subcarrier indices (-7,7).
  • methods (a), (b), and (c) may each outperform or underperform each other depending on the Doppler, frequency channel selectivity, and other system parameters.
  • embodiments of pilot logic may implement advanced interpolation and/or prediction algorithms to interpolate/predict the information for skipped pilots.
  • the simulation 1400 shows that when pilot positions are shifted in Doppler scenarios (outdoor channel), including pilot tones in a predefined a pattern of pilot subcarriers only in every other symbol has 0.5dB to 2dB performance degradation depending on how pilot logic may calculate channel estimates for the skipped pilots.
  • the result of method (c) provides the least performance degradation for an outdoor channel model.
  • This simulation 1400 is for an IEEE 802.1 lah, lMHz system using MCSl , and having a 1000 byte packet where all simulation impairments and a carrier offset of - 13.675 parts per million (ppm) are considered.
  • FIG. IE illustrates embodiments of a simulation 1500 comparing packet error rate (PER) performance versus signal-to-noise ratio (SNR) for transmitting pilot tones in every symbol as compared to transmitting pilot tones every two symbols for two different modulation and coding schemes (MCSs).
  • the simulation 1500 compares performance of modulation and coding scheme one (MCSl) and modulation and coding scheme two (MCS2) with pilot tones in every symbol against MCSl and MCS2 with pilot tones every 2 symbols.
  • MCSl modulation and coding scheme one
  • MCS2 modulation and coding scheme two
  • the simulation 1500 implementing MCS2 rather than MCSl realizes a 50% rate improvement relative to MCSl and degrades little more than 3dB while skipping pilot tones in MCSl realizes an 8% rate improvement in MCSl with only 0.5dB degradation. Note that using advanced interpolation algorithms for the skipped pilot tones may even bring this 0.5dB degradation lower to, e.g., 0.1 dB degradation. Effectively, in some embodiments, skipping pilot tones in some symbols of a transmission can offer an advantage of a greater number of feasible MCS selections in a communications system.
  • This simulation 1500 is for an IEEE 802.1 lah, 1MHz system using MCSl , and having a 1000 byte packet where all simulation impairments and a carrier offset of - 13.675 parts per million (ppm) are considered.
  • the communications device 1010 may facilitate data offloading.
  • 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, the network 1005, 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.
  • 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.
  • 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 memory 1011 and 1031 may comprise an offset or, in other embodiments, an offset formula.
  • the offset may indicate a symbol number offset to determine logical pilot subcarriers for which to determine channel estimates for the symbols without pilot tones.
  • 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.
  • PPDUs physical layer protocol data units
  • 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.
  • RX/TX receive/transmit chains
  • the communications devices 1010, 1030, 1050, and 1055 may each comprise a transceiver (RX/TX) such as transceivers (RX/TX) 1020 and 1040.
  • 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.
  • each subcarrier may be modulated with a modulation scheme at, e.g., a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
  • 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.
  • 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.
  • 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.
  • STF short training field
  • LTF long training field
  • 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.
  • 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
  • MIMO Multiple-Output
  • FIG. 1 may depict transceivers that include multiple antennas and that may be capable of multiple-user MIMO (MU-MIMO) operation. Note that in this case, shifting pilots patterns will be defined for each spatially transmitted stream.
  • MU-MIMO multiple-user MIMO
  • 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.
  • 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 to generate, transmit, receive, and interpret or decode frames with pilot logic to transmit and process skipped and shifting pilot tones.
  • 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.
  • MPDUs MAC protocol data units
  • 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.
  • 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.
  • IFFT Inverse Fast Fourier Transform module
  • 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).
  • 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.
  • 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.
  • 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 pilot logic 280 may skip pilot tones in some symbols by either inserting a tone other than a pilot tone on pilot subcarriers in a symbol or by inserting a symbol that does not have a predefined pilot subcarrier to generate a symbol transmission that includes pilot tones in L out of every N symbols. For instance, in many embodiments, the pilot logic 280 may generate symbols in which the pilot tones shift locations along the symbol numbers sequentially in accordance with the predefined pattern of pilot subcarriers. In several embodiments, the pilot tones may shift locations every symbol. For instance, when the communications device 1030 in FIG.
  • the RX/TX 1040 may respond with OFDM packets in which the location of the pilot subcarriers shift every symbol and the pilot logic 1043 may transmit data tones instead of pilot tones in the location (on the subcarriers) of the predefined pattern of pilot subcarriers in every other symbol.
  • 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.
  • the IDFT may comprise the IFFT 215, to perform an inverse Fast Fourier Transform (FFT) on the data.
  • 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.
  • PA power amplifier
  • 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.
  • 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
  • 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.
  • 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.
  • LNA low noise amplifier
  • 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 included in L out of every N symbols that shift locations every X symbols.
  • 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
  • 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.
  • 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.
  • the pilot tones are separated by some number of data subcarriers so that estimation of slope and intercept for subcarrier tracking could be maintained.
  • 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.
  • the channel estimator 252 may also determine channel estimates for symbols in the transmission that do not include pilot tones. For example, a symbol that does not include pilot tones may be associated via a predefined pattern of pilot subcarriers and/or an offset with one or more pilot subcarriers (logical pilot subcarriers) for which to determine channel estimates.
  • the channel estimator 252 may determine the channel estimates for the symbol by interpolating previously determined channel estimates for adjacent subcarriers, averaging the previously determined channel estimates for adjacent subcarriers and a previously determined estimate for the logical pilot subcarrier(s), or using a previously determined estimate for the logical pilot subcarrier(s).
  • the channel estimator 252 may also use and average with the previous channel estimation obtained from the LTF part of preamble. Further embodiments may include advanced interpolation or prediction algorithms 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., inter-symbol interference).
  • 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 weight coefficients applied to the equalizer 258.
  • the phase tracker 254 regularly updates the weight coefficients based on the magnitude and phase of the pilot tones.
  • 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.
  • LMS modified least mean square
  • the pilot logic 250 also comprises the buffer 256 to store pilot information such as phase correction information from the phase tracker 254. In some embodiments, the pilot logic 250 may store previously determined phase correction information determined from pilot tones of the OFDM symbols.
  • the buffer 260 may also be used to store channel information such as channel estimates information used in the equalizer 258. 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
  • the received signals are fed from the equalizer to the DBF module 220 transforms N antenna signals into L information signals.
  • the STBC module 221 may transform the data streams from the space-time streams to spatial streams.
  • the demodulation is performed in parallel on the output data of the FFT.
  • 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.
  • 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.
  • 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.
  • DRAM Dynamic Random Access Memory
  • filtering circuitry filtering circuitry
  • synchronization circuitry possibly multiple frequency conversion stages and multiple amplification stages, etc.
  • some of the functions shown in FIG. 2 may be integrated.
  • 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).
  • FIGs. 3A-B depict embodiments of flowcharts to process skipped and shifting pilot tones and to generate, transmit, receive, parse, and interpret communications.
  • the flowchart 300 may begin with receiving an OFDM packet with pilot tones in L out of every N symbols that shift locations of across the bandwidth of the packet in accordance with a predefined pattern of pilot subcarriers (element 302).
  • 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.
  • 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.
  • distributed amongst the symbols with pilot tones are N minus L symbols out of every N symbols that do not comprise pilot tones.
  • N may be two and L may be one so that every other symbol in the OFDM packet does not include pilot tones.
  • the receiver may begin to process at least some of the pilot tones to determine pilot tone phase rotations (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.
  • the receiver may store one or more of the determined channel estimates and, in some embodiments, phase rotations in memory (element 310).
  • the receiver may access the buffer and retrieve the previously determined channel estimates to calculate at least one new channel estimate for the logical pilot subcarriers associated with the symbols (element 315).
  • the pilot logic may determine, based upon a predefined pattern of pilot subcarriers, one or more pilot subcarriers associated with the symbols that do not include pilot tones.
  • the pilot logic may determine channel estimates for the symbols without pilot tones by using a previously determined channel estimate for each subcarrier, averaging channel estimates for adjacent subcarriers, or averaging channel estimates for adjacent subcarriers with a previously determined channel estimate for each subcarrier.
  • the receiver may use the predicted phase rotation to update the phase of the channel (element 320).
  • the flowchart 350 begins with a transmitter of a station such as the transmitter 206 in FIG. 2 determining a predefined pattern of pilot subcarriers assigned to transmit pilot tones (element 355).
  • pilot logic of the transmitter may access memory with or include a predefined pattern of pilot subcarriers for transmitting packets.
  • the pilot logic may comprise or have access to more than one predefined pattern of pilot subcarriers that are selectable by, e.g., the modulation and coding scheme, bandwidth, carrier frequency, communications protocol, and/or other criteria.
  • the predefined pattern of pilot subcarriers may provide a sequence of symbols associated with subcarrier indices on which to insert pilot tones during the transmission of a packet of symbols.
  • the pilot logic may generate symbols for transmission that include pilot tones in L out of every N symbols in the packet (element 360).
  • the pilot logic may generate symbols for transmission that include pilot tones in L out of every N symbols in the packet by skipping pilot tones on pilot subcarriers in N minus L out of every N symbols (element 370).
  • the pilot logic may, in lieu of inserting a pilot tone on a pilot subcarrier defined in the pattern of pilot subcarriers for a symbol, the pilot logic may insert a data tone or other information on the subcarrier.
  • the pilot logic may generate symbols for transmission that include pilot tones in L out of every N symbols in the packet by inserting N minus L symbols without pilot tones for every N symbols generated based upon the predefined pattern of pilot subcarriers (element 375).
  • the pilot logic may generate symbols with pilot tones on each of the pilot subcarriers in the predefined pattern of subcarriers but also generate symbols that do not include pilot tones and insert those symbols into the sequence of symbols defined by the predefined pattern of subcarriers.
  • the transmitter may then transmit the communication signal via one or more antenna(s) such as an antenna element of antenna array 218 in FIG. 2.
  • FIGs. 4A-B depict embodiments of flowcharts 400 and 450 to transmit, receive, and interpret or decode communications with pilot logic to transmit and process skipped and shifting pilot tones as illustrated in FIGs. 1A-C.
  • the flowchart 400 may begin with receiving a frame from the MAC sublayer logic of a communications device such as a data packet.
  • the MAC sublayer logic of the communications device may generate the frame as a data frame to transmit to stations associated with the communications device and may pass the frame as an MPDU to a PHY logic that transforms the MPDU into a packet that can be transmitted to a station.
  • the PHY logic may generate a preamble to prepend one or more of the MPDUs from the MAC sublayer logic to form a PPDU for transmission (element 405).
  • the PPDU may then be transmitted via a physical layer device such as the transmitter 206 in FIG. 2 or the transceiver 1020, 1040 in FIG. 1 so the PPDU may be converted to a communication signal (element 410).
  • the PPDU may be converted into symbols for transmission and L out of every N symbols may include pilot tones generated in accord with a predefined pattern of pilot subcarriers.
  • the transmitter may then transmit the communication signal via the antenna (element 415).
  • 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 use in phase tacking unit and to update channel estimates.
  • 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.
  • the demodulator such as the demodulator 224 demodulates the signal information via, e.g., BPSK, 16-QAM, 64-QAM, 256-QAM, QPSK, or SQPSK.
  • 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 frame in the MPDUs (element 470).
  • the following examples pertain to further embodiments.
  • One example comprises an apparatus.
  • the apparatus may generate symbols for transmission in wireless communications.
  • the apparatus may comprise memory; and pilot logic coupled with the memory to determine a predefined pattern of pilot subcarriers assigned to pilot tones; to generate the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N.
  • pilot logic comprises logic to insert tones other than pilot tones in subcarriers identified as pilot subcarriers in the predefined pattern of pilot subcarriers for N minus L symbols out of every N symbols.
  • every other symbol generated by the pilot logic does not comprise pilot tones.
  • the pilot logic comprises logic to generate L out of every N symbols with pilot tones in pilot subcarriers according to the predefined pattern of pilot subcarriers and to generate N minus L out of every N symbols that do not comprise pilot tones to transmit.
  • Another embodiment comprises a program product to generate symbols for transmission 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 determining a predefined pattern of pilot subcarriers assigned to pilot tones; and generating the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N.
  • generating the symbols comprises inserting tones other than pilot tones in subcarriers identified as pilot subcarriers in the predefined pattern of pilot subcarriers for N minus L symbols out of every N symbols. In some embodiments, generating the symbols comprises generating L out of every N symbols with pilot tones in pilot subcarriers according to the predefined pattern of pilot subcarriers and generating N minus L out of every N symbols that do not comprise pilot tones to transmit. In some embodiments, generating the symbols comprises generating every other symbol without pilot tones. [0099] Another embodiment comprises a method to generate symbols for transmission in wireless communications.
  • the method may involve determining a predefined pattern of pilot subcarriers assigned to pilot tones; and generating the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N.
  • generating the symbols comprises inserting tones other than pilot tones in subcarriers identified as pilot subcarriers in the predefined pattern of pilot subcarriers for N minus L symbols out of every N symbols. In some embodiments, generating the symbols comprises generating L out of every N symbols with pilot tones in pilot subcarriers according to the predefined pattern of pilot subcarriers and generating N minus L out of every N symbols that do not comprise pilot tones to transmit. In some embodiments, generating the symbols comprises generating every other symbol without pilot tones.
  • Another embodiment comprises a system to generate symbols for transmission in wireless communications.
  • the system may comprise pilot logic coupled with the memory to determine a predefined pattern of pilot subcarriers assigned to pilot tones; to generate the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N; and a radio coupled with the pilot logic to transmit the symbols.
  • the pilot logic comprises logic to insert tones other than pilot tones in subcarriers identified as pilot subcarriers in the predefined pattern of pilot subcarriers for N minus L symbols out of every N symbols. In some embodiments, the pilot logic comprises logic to generate L out of every N symbols with pilot tones in pilot subcarriers according to the predefined pattern of pilot subcarriers and to generate N minus L out of every N symbols that do not comprise pilot tones to transmit. In some embodiments, every other symbol generated by the pilot logic does not comprise pilot tones. [00103] Another embodiment 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 determine a predefined pattern of pilot subcarriers assigned to pilot tones; to receive the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N; and to determine channel state information in response to receipt of one or more of the N minus L symbols out of every N symbols that do not include pilot tones.
  • the pilot logic comprises logic to average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols. In some embodiments, the pilot logic comprises logic to average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols with previous channel state information estimates for the pilot subcarriers. In some embodiments, the pilot logic comprises logic use previous channel state information estimates to determine channel state information for the pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols.
  • 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 determining a predefined pattern of pilot subcarriers assigned to pilot tones; receiving the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N; and determining channel state information in response to receipt of one or more of the N minus L symbols out of every N symbols that do not include pilot tones.
  • determining channel state information comprises averaging channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols.
  • determining channel state information comprises averaging channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols with previous channel state information estimates for the pilot subcarriers. In some embodiments, determining channel state information comprises accessing memory to use previous channel state information estimates to determine channel state information for the pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols. [00107] 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 logic coupled with the memory to determine a predefined pattern of pilot subcarriers assigned to pilot tones; to generate the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N.
  • the logic comprises logic to average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols. In some embodiments, the logic comprises logic to average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols with previous channel state information estimates for the pilot subcarriers. In some embodiments, the logic comprises logic to access memory to use previous channel state information estimates to determine channel state information for the pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols.
  • Another embodiment comprises a method to determine channel state information from pilot tones in wireless communications.
  • the method may comprise determining a predefined pattern of pilot subcarriers assigned to pilot tones; receiving the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N; and determining channel state information in response to receipt of one or more of the N minus L symbols out of every N symbols that do not include pilot tones.
  • determining channel state information comprises average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols. In some embodiments, determining channel state information comprises average channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols with previous channel state information estimates for the pilot subcarriers. In some embodiments, determining channel state information comprises accessing memory to use previous channel state information estimates to determine channel state information for the pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols.
  • Another embodiment comprises an apparatus to generate symbols for transmission in wireless communications.
  • the apparatus may comprise a means for determining a predefined pattern of pilot subcarriers assigned to pilot tones; and a means for generating the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N.
  • the means for generating the symbols comprises a means for inserting tones other than pilot tones in subcarriers identified as pilot subcarriers in the predefined pattern of pilot subcarriers for N minus L symbols out of every N symbols.
  • the means for generating the symbols comprises a means for generating L out of every N symbols with pilot tones in pilot subcarriers according to the predefined pattern of pilot subcarriers and generating N minus L out of every N symbols that do not comprise pilot tones to transmit.
  • the means for generating the symbols comprises a means for generating every other symbol without pilot tones.
  • Another embodiment comprises an apparatus to determine channel state information from pilot tones in wireless communications.
  • the apparatus may comprise a means for determining a predefined pattern of pilot subcarriers assigned to pilot tones; a means for receiving the symbols with pilot tones in L out of every N symbols on pilot subcarriers in accordance with the predefined pattern of pilot subcarriers, wherein the predefined pattern of pilot subcarriers assign the pilot tones to different subcarriers during transmission of the symbols and L has a value that is less than N; and a means for determining channel state information in response to receipt of one or more of the N minus L symbols out of every N symbols that do not include pilot tones.
  • the means for determining channel state information comprises a means for averaging channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols. In some embodiments, the means for determining channel state information comprises a means for averaging channel state information estimates of subcarriers adjacent to pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols with previous channel state information estimates for the pilot subcarriers. In some embodiments, the means for determining channel state information comprises a means for accessing memory to use previous channel state information estimates to determine channel state information for the pilot subcarriers that do not include pilot tones for one or more of N minus L symbols out of every N symbols.
  • some or all of the features described above and in the claims may be implemented in one embodiment.
  • 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.
  • 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 dipswitch 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.
  • a number of embodiments may have one or more advantageous effects. For instance, some embodiments may offer reduced overhead with respect to standard overhead of transmission of pilot tones in each and every symbol. Further embodiments may include one or more advantageous effects such as smaller packet sizes for more efficient transmission, lower power consumption due to less data traffic on both the transmitter and receiver sides of communications, less traffic conflicts, less latency awaiting transmission or receipt of packets, and the like.
  • 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.
  • 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.
  • 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.
  • 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.
  • DRAM dynamic random access memory
  • I/O devices 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, BluetoothTM , Ethernet, Wi-Fi, and WiDi adapter cards are just a few of the currently available types of network adapters.

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

Une logique permet de réduire la surcharge dans des communications qui comportent des ondes pilotes dans des symboles par établissement d'une configuration prédéfinie de sous-porteuses sur lesquelles les ondes pilotes sont transmises et comprenant les ondes pilotes dans L tous les N symboles dans les communications. Une logique peut mettre en œuvre des communications conformément à la configuration prédéfinie de sous-porteuses par insertion des symboles N moins L entre des symboles avec des ondes pilotes sur chacune des sous-porteuses de la configuration prédéfinie de sous-porteuses ou par insertion d'ondes autres que des ondes pilotes sur des sous-porteuses pilotes dans N moins L tous les N symboles. Une logique peut déterminer l'information CSI ainsi que des informations de fréquence porteuse et de suivi de phase à partir d'pilotes dans les symboles. Une logique peut déterminer l'information CSI ainsi qu'une fréquence porteuse et des informations de suivi de phase à partir d'ondes pilotes dans les symboles. Et une logique peut déterminer l'information CSI pour des symboles qui ne comprennent pas d'ondes pilotes par calcul d'estimations de canal sur la base d'estimations de canal de sous-porteuses adjacentes et/ou par estimations de canal antérieures de sous-porteuses pilotes.
PCT/US2013/078162 2013-12-28 2013-12-28 Procédés et agencements pour déterminer des affectations de stations à des fenêtres d'accès limité dans des réseaux sans fil WO2015099805A1 (fr)

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Citations (5)

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US20100027717A1 (en) * 2007-07-31 2010-02-04 Reddot Wireless, Inc. Equalization of OFDM Signals Based on Time and Then Frequency Interpolation
US20100040159A1 (en) * 2006-12-27 2010-02-18 Posdata Co., Ltd Method and apparatus for generating pilot tone in orthogonal frequency division multiplexing access system, and method and apparatus for estimating channel using it
US20110249773A1 (en) * 2010-04-07 2011-10-13 Samsung Electronics Co. Ltd. Apparatus and method for estimating channel in wireless communication system
US20120082253A1 (en) * 2010-07-12 2012-04-05 Texas Instruments Incorporated Pilot Structure for Coherent Modulation
US20130083831A1 (en) * 2011-10-03 2013-04-04 Broadcom Corporation Wireless communication system with improved automatic gain control

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100040159A1 (en) * 2006-12-27 2010-02-18 Posdata Co., Ltd Method and apparatus for generating pilot tone in orthogonal frequency division multiplexing access system, and method and apparatus for estimating channel using it
US20100027717A1 (en) * 2007-07-31 2010-02-04 Reddot Wireless, Inc. Equalization of OFDM Signals Based on Time and Then Frequency Interpolation
US20110249773A1 (en) * 2010-04-07 2011-10-13 Samsung Electronics Co. Ltd. Apparatus and method for estimating channel in wireless communication system
US20120082253A1 (en) * 2010-07-12 2012-04-05 Texas Instruments Incorporated Pilot Structure for Coherent Modulation
US20130083831A1 (en) * 2011-10-03 2013-04-04 Broadcom Corporation Wireless communication system with improved automatic gain control

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