Methods and systems for choosing cyclic delays in multiple antenna OFDM systems

Method and system for selecting cyclic delay in multi-antenna OFDM system

Priority claim

The claim in this case is entitled to the U.S. Provisional Patent Application S/N, entitled ``Method and apparatus for transmitting pilots from multiple antennas'' and filed on March 14, 2008. 61/036,895 priority rights, the application is essentially fully incorporated here by reference.

Certain embodiments of the present disclosure generally relate to wireless communication, and more particularly, to a method for selecting an appropriate cyclic delay value for multi-antenna transmission in order to accurately estimate the channel gain.

There seems to be some shortcomings in the prior art.

Some embodiments provide a method for transmitting pilots in a wireless communication system. The method generally includes generating a first pilot frequency for the first transmitting antenna based on a first cyclic delay, and generating a second pilot frequency for the second transmitting antenna based on a second cyclic delay that is at least one cyclic prefix length greater than the first cyclic delay frequency.

Some embodiments provide a method for performing channel estimation in a wireless communication system. The method generally includes obtaining a first input sample containing a first and a second pilot frequency, where the first pilot frequency is generated based on a first cyclic delay and sent from the first transmitting antenna, and the second pilot frequency is based on a second cyclic delay Generated and sent from the second transmitting antenna, the second cyclic delay is greater than the first cyclic delay by at least the cyclic prefix length, and the first input samples are from the first receiving antenna; and the first input samples are processed to obtain information about the first The first channel estimation for one transmitting antenna and the second channel estimation for the second transmitting antenna.

Some embodiments provide an apparatus for transmitting pilot frequency in a wireless communication system. The device generally includes logic for generating a first pilot frequency for the first transmitting antenna based on a first cyclic delay, and logic for generating a first pilot frequency for the second transmitting antenna based on a second cyclic delay greater than the first cyclic delay by at least the cyclic prefix length. The logic of the second pilot frequency of the antenna.

Some embodiments provide an apparatus for performing channel estimation in a wireless communication system. The device generally includes logic for obtaining first input samples containing first and second pilot frequencies, where the first pilot frequency is generated based on the first cyclic delay and sent from the first transmitting antenna, and the second pilot frequency is based on The second cyclic delay is generated and sent from the second transmitting antenna, the second cyclic delay is greater than the first cyclic delay by at least the cyclic prefix length, and these first input samples are from the first receiving antenna; and used to process these first Input samples to obtain the logic of the first channel estimate for the first transmit antenna and the second channel estimate for the second transmit antenna.

Some embodiments provide an apparatus for transmitting pilot frequency in a wireless communication system. The device generally includes a device for generating a first pilot frequency for the first transmitting antenna based on a first cyclic delay, and a device for generating a first pilot frequency for the second transmitting antenna based on a second cyclic delay greater than the first cyclic delay by at least the cyclic prefix length. The device for the second pilot frequency of the antenna.

Some embodiments provide an apparatus for performing channel estimation in a wireless communication system. The device generally includes a device for obtaining a first input sample containing a first and a second pilot frequency, wherein the first pilot frequency is generated based on the first cyclic delay and sent from the first transmitting antenna, and the second pilot frequency is based on The second cyclic delay is generated and sent from the second transmitting antenna, the second cyclic delay is greater than the first cyclic delay by at least the cyclic prefix length, and these first input samples are from the first receiving antenna; and used to process these first An apparatus for inputting samples to obtain a first channel estimation for a first transmitting antenna and a second channel estimation for a second transmitting antenna.

Some embodiments provide a computer program product for transmitting a boot frequency in a wireless communication system, including a computer readable medium on which instructions are stored, and these instructions can be executed by one or more processors. These instructions generally include instructions for generating the first pilot frequency for the first transmitting antenna based on the first cycle delay, and instructions for generating the first pilot frequency for the second transmission based on the second cycle delay that is greater than the first cycle delay by at least the cycle prefix length. The command of the second pilot frequency of the antenna.

Some embodiments provide a computer program product for performing channel estimation in a wireless communication system, including a computer readable medium having instructions stored thereon, and these instructions can be executed by one or more processors. These instructions generally include instructions for obtaining first input samples containing first and second pilot frequencies, where the first pilot frequency is generated based on the first cycle delay and sent from the first transmitting antenna, and the second pilot frequency is based on The second cyclic delay is generated and sent from the second transmitting antenna, the second cyclic delay is greater than the first cyclic delay by at least the cyclic prefix length, and these first input samples are from the first receiving antenna; and used to process these first Input samples to obtain instructions for the first channel estimate for the first transmit antenna and the second channel estimate for the second transmit antenna.

The word "exemplary" is used in this article to mean "serve as an example, instance, or illustration." Any embodiment described herein as "exemplary" need not be construed as being superior or superior to other embodiments.

The cyclic delay diversity (CDD) scheme can be applied to multi-antenna orthogonal frequency division multiplexing (OFDM) transmission to provide higher frequency diversity and improve error rate performance. Multiple artificial channel paths can be generated by transmitting cyclically delayed data from multiple antennas. The estimation of the channel gains associated with the multiple transmit antennas can be performed on the receiver side using known pilot frequencies or training sequences. However, in some cases, if the cyclically delayed pilot frequency sequences match the path delays in the channel profile, the time domain channel paths cannot be completely separated at the receiver.

<u style="single">Exemplary wireless communication system</u>

The technology described in this article can be used in various broadband wireless communication systems, including communication systems based on orthogonal multiplexing schemes. Examples of such communication systems include Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, and so on. The OFDMA system uses Orthogonal Frequency Division Multiplexing (OFDM), which is a modulation technique that divides the bandwidth of the entire system into multiple orthogonal subcarriers. These subcarriers can also be called tones, frequency slots, and so on. With OFDM, each subcarrier can be independently modulated with data. The SC-FDMA system can use interleaved FDMA (IFDMA) to transmit on sub-carriers distributed across the system bandwidth, local FDMA (LFDMA) to transmit on blocks composed of adjacent sub-carriers, or use enhanced FDMA (EFDMA) Transmit on multiple blocks composed of adjacent subcarriers. Generally speaking, modulation symbols are sent in the frequency domain under OFDM, and in the time domain under SC-FDMA.

A specific example of a communication system based on an orthogonal multiplexing scheme is the WiMAX system. WiMAX, which represents the global interoperability of microwave access, is a standard-based bandwidth-frequency wireless technology that provides high-throughput bandwidth-frequency connections over long distances. There are two main WiMAX applications today: fixed WiMAX and mobile WiMAX. Fixed WiMAX applications are point-to-multipoint, which enables broadband access such as households and businesses. Mobile WiMAX provides full mobility of cellular networks at bandwidth speeds.

IEEE 802.16 is an emerging standards organization that defines the air interface for fixed and mobile broadband wireless access (BWA) systems. These standards define at least four different physical layers (PHY) and one medium access control (MAC) layer. Among the four physical layers, the OFDM and OFDMA physical layers are the most popular in the fixed and mobile BWA fields, respectively.

FIG. 1 illustrates an example of a wireless communication system 100 in which embodiments of the present disclosure can be adopted. The wireless communication system 100 may be a broadband wireless communication system. The wireless communication system 100 can provide communication for several cellular service areas 102 served by each free radical platform 104. The base station 104 may be a fixed station that communicates with the user terminal 106. The base station 104 may alternatively be referred to as an access point, a node B, or some other terminology.

FIG. 1 depicts various user terminals 106 throughout the system 100. The user terminal 106 may be fixed (i.e., stationary) or mobile. The user terminal 106 may alternatively be referred to as a remote station, an access terminal, a terminal, a user unit, a mobile station, a station, a user equipment, a user station, etc. The user terminal 106 may be a wireless device such as a cellular phone, a personal digital assistant (PDA), a palm-type device, a wireless modem, a laptop computer, a personal computer, and the like.

Various algorithms and methods can be used for the transmission between the base station 104 and the user terminal 106 in the wireless communication system 100. For example, it is possible to transmit and receive signals between the base station 104 and the user terminal 106 according to the OFDM/OFDMA technology. If this is the case, the wireless communication system 100 may be referred to as an OFDM/OFDMA system.

The communication link that assists in the transmission from the base station 104 to the user terminal 106 may be referred to as the downlink (DL) 108, and the communication link that assists in the transmission from the user terminal 106 to the base station 104 may be referred to as the uplink. Link (UL)110. Alternatively, the downlink 108 may be referred to as the forward link or forward path, and the uplink 110 may be referred to as the reverse link or reverse path.

The honeycomb cell service area 102 may be divided into a plurality of sectors 112. The sector 112 is a physical coverage area within the cellular service area 102. The base station 104 in the wireless communication system 100 can utilize an antenna that concentrates the power flow in a specific sector 112 of the cellular service area 102. Such an antenna may be called a directional antenna.

FIG. 2 shows an example frame structure 200 for time division duplex (TDD) mode in IEEE 802.16. The transmission isochronous line can be divided into frame-based units. Each frame can span a predetermined duration, such as 5 milliseconds (ms), and can be divided into downlink sub-frames and uplink sub-frames. Generally speaking, the downlink and uplink subframes can cover any segment of the frame. The downlink and uplink subframes can be separated by a transmit transmission gap (TTG) and a receive transmission gap (RTG).

Several physical sub-channels can be defined. Each physical subchannel can include a set of subcarriers that can be contiguous or distributed across the system bandwidth. It is also possible to define several logical sub-channels and map them to physical sub-channels based on a known mapping. Logical sub-channels can simplify the allocation of resources.

As shown in Figure 2, the downlink sub-frame may include preamble, frame control header (FCH), downlink mapping (DL-MAP), uplink mapping (UL-MAP), And downlink (DL) burst. The preamble can carry a known transmission that can be used by the user station for frame detection and synchronization. The FCH can carry parameters for receiving DL-MAP, UL-MAP, and downlink bursts. The DL-MAP may carry a DL-MAP message, which may include information elements (IE) for various types of control information (for example, resource allocation or assignment) used for downlink access. The UL-MAP may carry a UL-MAP message, which may include IEs for various types of control information for uplink access. Downlink bursts can carry data to the subscriber stations being served. Uplink subframes may include uplink bursts, which may carry data transmitted by subscriber stations scheduled for uplink transmission.

The pilot frequency transmission technology described in this article can be used for multiple input multiple output (MIMO) transmission or multiple input single output (MISO) transmission. These technologies can also be used for pilot frequency transmission on the downlink and uplink. For clarity, some aspects of these techniques are described below for pilot frequency transmission on the downlink in a MIMO scenario.

FIG. 3 shows a block diagram of the design of the base station 104 and the user station 106 as one of the base stations and one of the user stations in FIG. 1. The base station 104 is equipped with multiple (<i>M</i>A) Antennas 334a to 334m. The user station 106 is equipped with multiple (<i>R</i>A) Antennas 352a to 352r.

At the base station 104, a transmit (TX) data processor 320 may receive data from a data source 312, process (e.g., encode and symbol map) the data based on one or more modulation and coding schemes, and provide data symbols. As used herein, the data symbol is a symbol corresponding to the data, the pilot frequency symbol is a symbol corresponding to the pilot frequency, and the symbol can be a real number or a complex value. The data symbols and pilot frequency symbols can be modulation symbols derived from modulation schemes such as PSK or QAM. The pilot frequency may include information known a priori for both the base station and the user station. The TX MIMO processor 330 can process these data and pilot frequency symbols and combine<i>M</i>The output symbol stream is provided to<i>M</i>Modulators (MOD) 332a to 332m. Each modulator 332 can process its output symbol stream (e.g., for implementing OFDM) to obtain an output sample stream. Each modulator 332 can further condition (eg, convert to analog, filter, amplify, and up-convert) its output sample stream and generate a downlink signal. From modulators 332a to 332m<i>M</i>The two downlink signals may be transmitted via antennas 334a to 334m, respectively.

At the user station 106, R antennas 352a to 352r can receive the M downlink signals from the base station 104, and each antenna 352 can provide the received signal to an associated demodulator (DEMOD) 354 . Each demodulator 354 can condition (e.g., filter, amplify, down-convert, and digitize) its received signal to obtain input samples and can further process these input samples (e.g., for implementing OFDM) to obtain input samples. To the symbol. Each demodulator 354 can provide the received data symbols to the MIMO detector 360 and the received pilot frequency symbols to the channel processor 394. The channel processor 394 may estimate the response of the MIMO channel from the base station 104 to the user station 120 based on the received pilot frequency symbols and provide the MIMO channel estimate to the MIMO detector 360. The MIMO detector 360 may perform MIMO detection of the received symbols based on this MIMO channel estimation and provide the detected symbols, which is an estimate of the transmitted data symbols. The receive (RX) data processor 370 can process (for example, symbol demapping and decoding) the detected symbols and provide the decoded data to the data slot 372.

The user station 106 can evaluate the channel status and generate feedback information that can include various types of information. The feedback information and data from the data source 378 can be processed by the TX data processor 380 (for example, encoding and symbol mapping), spatially processed by the TX MIMO processor 382, and further processed by the modulators 354a to 354r to generate R uplinks These signals can be transmitted via antennas 352a to 352r. At the base station 104, the R uplink signals from the user station 106 can be received by the antennas 334a to 334m, processed by the demodulators 332a to 332m, spatially processed by the MIMO detector 336, and by the RX data processor 338 Further processing (for example, symbol demapping and decoding) is performed to recover the feedback information and data sent by the user station 106. The controller/processor 340 can control the data transmission to the user station 106 based on the feedback information.

The controller/processors 340 and 390 can direct the operations at the base station 104 and the user station 106, respectively. The memories 342 and 392 can store data and program codes for the base station 104 and the user station 106, respectively. The scheduler 344 may schedule the user station 106 and/or other user stations for data transmission on the downlink and/or uplink based on the feedback information received from all the user stations.

IEEE 802.16 utilizes Orthogonal Frequency Division Multiplexing (OFDM) for downlink and uplink. OFDM divides the system bandwidth into multiple (<i>N</i>_<i>FFT</i>(A) Orthogonal subcarriers, they can also be called tones, frequency slots, etc. Each subcarrier can be modulated with data or pilot frequency. The number of subcarriers can depend on the system bandwidth and the frequency separation between adjacent subcarriers. E.g,<i>N</i>_<i>FFT</i>Can be equal to 128, 256, 512, 1024, or 2048. This total<i>N</i>_<i>FFT</i>Only a subset of each subcarrier may be used for data and pilot frequency transmission, while the remaining subcarriers can be used as protection subcarriers that allow the system to meet the spectrum envelope requirements. In the following description, the data subcarrier is the subcarrier used for the data, and the pilot frequency subcarrier is the subcarrier used for the pilot frequency. OFDM symbols can be transmitted in each OFDM symbol period (or symbol period for short). Each OFDM symbol may include data subcarriers used to transmit data, pilot frequency subcarriers used to transmit pilot frequencies, and/or guard subcarriers not used for data or pilot frequencies.

FIG. 4 shows a block diagram of the design of the OFDM modulator 400 that may be included in each of the modulators 332a to 332m and the modulators 354a to 354r in FIG. 3. In the OFDM modulator 400, the symbol-subcarrier mapper 410 receives the output symbols and maps them to the total<i>N</i>_<i>FFT</i>Subcarriers. In each OFDM symbol period, unit 412 uses<i>N</i>_<i>FFT</i>The points inverse discrete Fourier transform (IDFT) will correspond to the total<i>N</i>_<i>FFT</i>Subcarrier<i>N</i>_<i>FFT</i>The output symbols are transformed into the time domain and provided with<i>N</i>_<i>FFT</i>Useful part of a time domain sample. Each sample is a complex value to be transmitted in a chip period. Parallel-serial (P/S) converter 414 converts this<i>N</i>_<i>FFT</i>Serialization of samples. The loop prefix generator 416 copies the end of the useful part<i>N</i>_<i>CP</i>Samples and put this<i>N</i>_<i>CP</i>Samples are appended to the front of the useful part to form the inclusion<i>N</i>_<i>FFT</i>+<i>N</i>_<i>CP</i>Samples of OFDM symbols. Each OFDM symbol thus contains<i>N</i>_<i>FFT</i>Useful part of the sample and there are<i>N</i>_<i>CP</i>The loop prefix of each sample. The cyclic prefix is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) caused by delay spread in the wireless channel.

Returning to Figure 3, on the downlink, the MIMO channel is set by the base station 104<i>M</i>Transmitting antennas and this at the user station 106<i>R</i>Formed by a receiving antenna. The MIMO channel is composed of<i>MR</i>One single input single output (SISO) channel or one SISO channel for every possible transmit and receive antenna. The channel response of each SISO channel can be characterized by either the time domain channel impulse response or the corresponding frequency domain channel frequency response. The channel frequency response is the discrete Fourier transform (DFT) of the channel impulse response.

The channel impulse response of each SISO channel can be determined by<i>L</i>Time domain channel taps (channel taps) to characterize, where<i>L</i>Is typically better than<i>N</i>_<i>FFT</i>Much smaller. That is, if a pulse is applied at the transmitting antenna, the sampling rate obtained by the pulse excitation at the receiving antenna<i>L</i>A time domain sample will be sufficient to characterize the response of the SISO channel. The number of channel taps required by the channel pulse response (<i>L)</i>Depending on the delay spread of the system, the latter is the time difference between the earliest and latest signal instances that arrive at the receiving antenna with sufficient energy.

Each SISO channel may include one or more propagation paths between the transmitting antenna and the receiving antenna corresponding to the SISO channel, where these propagation paths are determined by the wireless environment. Each path can be associated with a specific complex gain and a specific delay. For each SISO channel, this<i>L</i>The complex gain of each channel tap is determined by the complex gains of the paths of the SISO channel. Each SISO channel therefore has a path<i>d</i>₀arrive<i>d</i>_<i>L</i>_-1Channel perspective, where each path<i>d</i>_<i>l</i>The complex gain of can be zero or non-zero.

Cyclic Delay Diversity (CDD) can be used in MIMO transmission to establish frequency diversity, which can improve error rate performance. With cyclic delay diversity, the OFDM symbols for each transmit antenna can be cyclically delayed by different amounts as described below. M different cyclically delayed signals can be transmitted from the M transmitting antennas. However, cyclic delay diversity may adversely affect MIMO channel estimation in some situations. In particular, if the cyclically delayed signal matches the path delay in channel perspective, it may not be possible to separate the paths. For example, for a given receiving antenna, it may not be possible to determine that the complex gain corresponding to a 2-sample delay is derived from (i) the downlink signal received from the transmitting antenna 0 with no cyclic delay and via a path with a 2-sample delay , Or (ii) the downlink signal from transmit antenna 1 with 1 sample cyclic delay and received via the path with 1 sample delay, or (iii) from the transmit antenna 2 with 2 sample cyclic delay and via no delay Downlink signal received by the path.

If the channel perspective has a path<i>d</i>₀arrive<i>d</i>_<i>L</i>_-1And if it comes from here<i>M</i>Transmitting antenna<i>M</i>Downlink signals have<i>t</i>₀arrive<i>t</i>_<i>M</i>_-1Cyclic delay, then in (<i>d</i>_<i>l</i>+<i>t</i>_<i>m</i>)<i>mod</i><i>T</i>_<i>S</i>Pair index<i>l</i>and<i>m</i>When all the values of are different, the value of each SISO channel<i>L</i>Channel taps can be unambiguously determined, where<i>l</i>=0,...,<i>L</i>-1，<i>m</i>=0,...,<i>M</i>-1，<i>T</i>_<i>S</i>Is the duration of the useful part and is equal to<i>N</i>_<i>FFT</i>Samples, and "mod" indicates the modulo operation. This condition also applies to full frequency repeated use.

For some embodiments, the cyclic delay of each transmit antenna (except the transmit antenna with 0 cyclic delay)<i>t</i>_<i>m</i>Can be selected to be equal to or greater than the maximum expected delay opening in the system. Loop prefix length<i>N</i>_<i>CP</i>Can be selected so that it is equal to or greater than the maximum expected delay opening in the system, so that<img file="TW201014234A_D0001.tif" />. Therefore, for some embodiments, the cyclic delay for each transmit antenna can be selected as follows:

<maths><img file="TW201014234A_D0002.tif" /></maths>

<maths><img file="TW201014234A_D0003.tif" /></maths>

Figure 5 shows that equation (1) is<i>N</i>_<i>C</i>_,0=0 and for<i>i</i>=1,...,<i>M</i>-1 Yes<i>N</i>_<i>C</i>_,_<i>i</i>=<i>N</i>_<i>CP</i>Cyclic delay diversity in an exemplary situation at time, where<i>M</i>= 4 transmitting antennas. Transmit antenna 0 has a cyclic delay of 0, and for this transmit antenna, the useful part is cyclically shifted/delayed by 0 samples. The transmitting antenna 1 has<i>N</i>_<i>CP</i>Cyclic delay, and for the transmitting antenna, the useful part is cyclically shifted<i>N</i>_<i>CP</i>Samples. The transmitting antenna 2 has 2<i>N</i>_<i>CP</i>ofcyclic delay, and for the transmitting antenna, the useful part is cyclically shifted by element 2<i>N</i>_<i>CP</i>Samples. The transmitting antenna 3 has 3<i>N</i>_<i>CP</i>ofcyclic delay, and for the transmitting antenna, the useful part is cyclically shifted by element 3<i>N</i>_<i>CP</i>Samples.

According to equation (1), the cyclic delay for these M transmit antennas can be selected as:

<maths><img file="TW201014234A_D0004.tif" /></maths>

<maths><img file="TW201014234A_D0005.tif" /></maths>

This design in equation (2) ensures<i>d</i>_<i>l</i>+<i>t</i>_<i>m</i>Correct<i>l</i>and<i>m</i>All values of are different. From all<i>M</i>All of the transmitting antennas<i>L</i>Unambiguous channel estimation (which is called complete channel estimation) of paths will become possible. If used for this<i>M</i>If the cyclic delays of each transmitting antenna are standardized or known a priori, there is no need to explicitly send signals for these cyclic delays.

The base station 104 can use this method to help the user station 106 perform complete channel estimation.<i>M</i>Two transmitting antennas transmit pilot frequency symbols. The pilot frequency symbol can be in<i>S</i>Subcarriers<i>k</i>₀arrive<i>k</i>_<i>S</i>_-1Send on, where general<img file="TW201014234A_D0006.tif" />. This<i>S</i>The number of pilot frequency subcarriers can be determined as described below.

Can be defined as<img file="TW201014234A_D0007.tif" />The set of coefficients is as follows:

<maths><img file="TW201014234A_D0008.tif" /></maths>

in<i>m</i>=0<i>,</i>...<i>,M</i>-1,<i>l</i>=0<i>,</i>...<i>,N</i>_<i>C,m</i>-1, and<img file="TW201014234A_D0009.tif" />，<i>q</i>=<i>l</i>‧<i>M</i>+<i>m</i>=0<i>,</i>...<i>,Q</i>-1' and<i>b</i>_<i>q</i>Is the first in the set<i>q</i>Coefficients. due to<img file="TW201014234A_D0010.tif" />, May be less than<i>N</i>_<i>CP</i>Channel taps. Thresholding can be used to zero out non-existent channel taps.

Can do this<i>S</i>Pilot frequency subcarrier definition<i>S</i>×<i>Q</i>Matrix B is as follows:

<maths><img file="TW201014234A_D0011.tif" /></maths>

in<img file="TW201014234A_D0012.tif" />Is the first of matrix B<i>i</i>Line<i>q</i>Elements in the column, where<i>i</i>=0<i>,</i>...<i>,S</i>-1 and<i>q</i>=0<i>,</i>...<i>,Q</i>-1。

The sufficient condition for complete channel estimation is that the rank of matrix B is equal to<i>L</i>‧<i>M</i>. This export wants<i>b</i>_<i>q</i>Different requirements, which means<i>d</i>_<i>l</i>+<i>t</i>_<i>m</i>Right<i>T</i>_<i>s</i>The case of modulo should be different.

The system can be operated with full frequency reuse, and each honeycomb cell service area can be used in all total<i>N</i>_<i>FFT</i>It is transmitted on two subcarriers (except the protection subcarriers). For full frequency reuse, pilot frequency symbols can be sent on each subcarrier that can be used for transmission, or<i>S</i>=<i>N</i>_<i>FFT</i>, And matrix B can have the following form<i>S</i>×<i>S</i>Vandermonde matrix V:

<maths><img file="TW201014234A_D0013.tif" /></maths>

For full frequency reuse, it is necessary to<i>b</i>_<i>q</i>The requirement of being different is sufficient to allow complete channel estimation. Even though some subcarriers are reserved for protection, all other subcarriers are used and there are more than<i>Q</i>Such subcarriers, so the matrix V will be full rank.

The system can be operated with partial frequency reuse, and each honeycomb cell service area can be used in total<i>N</i>_<i>FFT</i>Transmit on a subset of subcarriers. For example, in the case of a partial frequency reuse factor of 3, each honeycomb cell service area can be<i>N</i>_<i>FFT</i>It is transmitted on about one-third of each subcarrier. For partial frequency reuse, the pilot frequency symbol can be used in the total<i>N</i>_<i>FFT</i>The matrix B can be a sub-matrix of the Vandermonde matrix, and it needs to be<i>b</i>_<i>q</i>The necessary condition of being different may not be sufficient. However, this<i>S</i>Pilot frequency subcarrier<i>k</i>₀arrive<i>k</i>_<i>S</i>_-1It can be selected so that this necessary condition is sufficient to achieve full channel estimation.

For some embodiments, this<i>S</i>Pilot frequency subcarriers can be separated<i>p</i>Subcarriers, where<i>p</i>Can't be<i>N</i>_<i>FFT</i>Divided prime number. These pilot frequency subcarriers can be selected as follows:

<i>k</i>_<i>i</i>=<i>i</i>．<i>p</i>，<i>i</i>=0<i>,</i>...<i>,S</i>-1,　(6)

in<i>k</i>_<i>i</i>Is the first<i>i</i>The index of the pilot frequency subcarrier,<img file="TW201014234A_D0014.tif" />and<img file="TW201014234A_D0015.tif" />Mark the floor operator.

Fig. 6 shows an example pilot frequency subcarrier structure for one OFDM symbol corresponding to the design shown in equation (6). In this example,<i>p</i>=3 and each pilot frequency subcarrier is separated by three subcarriers. Pilot frequency symbols can be sent on subcarriers 0, 3, 6, etc. Can do this<i>M</i>Each of the two transmitting antennas uses the same set of pilot frequency subcarriers, as shown in FIG. 6. The OFDM symbols with these pilot frequency subcarriers can be used for the preamble shown in FIG. 2 or some other OFDM symbols.

For the design shown in equation (6), matrix B is<i>S</i>×<i>S</i>Vandermonde matrix<i>Q</i>Listed by<i>q</i>=0<i>,</i>...<i>,Q</i>-1 element<img file="TW201014234A_D0016.tif" />Constitute, and the first<i>Q</i>Ranked<i>S</i>The elements of the column are all different from these<img file="TW201014234A_D0017.tif" />Any element in each of the elements is made up the same. Therefore, complete channel estimation becomes possible under the following conditions:

1.<i>p</i>．(<i>d</i>_<i>l</i>+<i>t</i>_<i>m</i>)mod <i>N</i>_<i>FFT</i>Correct<i>l</i>and<i>m</i>All values of should be different, and

2. Number of rows in matrix B<i>S</i>Should be equal to or greater than the number of columns in matrix B<i>Q</i>, Or namely<img file="TW201014234A_D0018.tif" />。

if<i>p</i>Inexhaustible<i>N</i>_<i>FFT</i>Prime number and<img file="TW201014234A_D0019.tif" />, The above two conditions can be met, regardless of the length of the loop prefix<i>L</i>No matter how it is. However,<i>N</i>_<i>CP</i>The maximum value of (<i>N</i>_<i>CP</i>_,_<i>max</i>) May be affected by the total number of subcarriers (<i>N</i>_<i>FFT</i>), the number of transmitting antennas (<i>M</i>), and pilot frequency subcarrier spacing (<i>p</i>) The restrictions are as follows:

<maths><img file="TW201014234A_D0020.tif" /></maths>

For example, for<i>M</i>=2、<i>N</i>_<i>FFT</i>=1024 and<i>p</i>=3,<i>N</i>_<i>CP</i>_,_<i>max</i>= 170. For this example, the length of the cyclic prefix is 128. As another example, for<i>M</i>=2、<i>N</i>_<i>FFT</i>=1024, and<i>p</i>=3,<i>N</i>_<i>CP</i>_,_<i>max</i>=85. For this example, the cyclic prefix length can be selected to be 64. As yet another example, for<i>M</i>=2、<i>N</i>_<i>FFT</i>=1024 and<i>p</i>=5,<i>N</i>_<i>CP</i>_,_<i>max</i>=102. For this example, the cyclic prefix length can be selected to be 64.

The pilot frequency subcarrier spacing can be based on<i>M</i>The length of the cyclic delay applied on each transmitting antenna and the total number of subcarriers<i>N</i>_<i>FFT</i>To choose as follows:

<maths><img file="TW201014234A_D0021.tif" /></maths>

FIG. 7 shows a block diagram of the design of modulators 332a to 332m at the base station 104 in FIG. 3. For the sake of simplicity, FIG. 7 only shows the process of generating pilot frequencies for the M transmitting antennas. In the modulator 332a for transmit antenna 0, the symbol-subcarrier mapper 710a maps pilot frequency symbols to pilot frequency subcarriers (for example, determined as shown in equation (6)) and maps zero symbols to The remaining subcarriers. IDFT unit 712a<i>N</i>_<i>FFT</i>Pilot frequency and zero symbol execution<i>N</i>_<i>FFT</i>Click IDFT and provide<i>N</i>_<i>FFT</i>Time domain samples. P/S converter 714a converts this<i>N</i>_<i>FFT</i>Serialization of samples. For some embodiments, the cyclic delay unit 716a divides this<i>N</i>_<i>FFT</i>Samples are the transmit antenna 0 cyclic shift element<i>N</i>_<i>C,</i>₀Samples. The cyclic prefix generator 718a appends the cyclic prefix and provides an OFDM symbol including the first pilot frequency for transmitting antenna 0.

The modulator 332b can similarly generate an OFDM symbol including the second pilot frequency for the transmitting antenna 1. However, the cyclic delay unit 716b converts this<i>N</i>_<i>FFT</i>Each sample is the cyclic shift element of the transmitting antenna 1<img file="TW201014234A_D0022.tif" />Samples. Each of the remaining modulators 332 can similarly generate OFDM symbols including the pilot frequency for its transmit antenna, but can combine this<i>N</i>_<i>FFT</i>Samples are transmitting antennas<i>m</i>Cyclic shift element<img file="TW201014234A_D0023.tif" />Samples, of which<i>m</i>=0<i>,</i>1<i>,</i>...<i>,M</i>-1。

Figure 8 shows the design of a process 800 for generating pilot frequencies for MISO or MIMO systems. The process 800 may be executed by the base station 104 for pilot frequency transmission on the downlink, by the user station 106 for pilot frequency transmission on the uplink, or executed by some other entity.

At 810, the first pilot frequency for the first transmit antenna may be generated based on the first cyclic delay, such as a cyclic delay of zero samples. At 820, it can be based on that the length is greater than the (m-1)th cyclic delay length by at least the cyclic prefix length<i>N</i>_<i>CP</i>M-th cyclic delay to generate the m-th pilot frequency sequence for the m-th transmitting antenna, where<i>m</i>&gt;1. For some embodiments, the cyclic delay for each transmit antenna is given by equation (1), where<i>N</i>_<i>C</i>_<i>,</i>₀=0 and for<img file="TW201014234A_D0024.tif" />,have<i>N</i>_<i>C,m</i>=<i>m</i>‧<i>N</i>_<i>CP</i>More pilot frequencies for more transmit antennas can be generated based on a suitable cyclic delay.

At 810, a first sequence of samples including the first pilot frequency may be generated and cyclically delayed by the first cyclic delay. The first OFDM symbol including the first pilot frequency and having the first cyclic delay may be generated based on the cyclically delayed first sample sequence. At 820, it is possible to generate<i>m</i>Guide frequency<i>m</i>Sample sequence and cyclically delay the first<i>m</i>Cyclic delay, where<i>m</i>&gt;1. Including the first<i>m</i>Pilot frequency and has the first<i>m</i>Cyclic delay<i>m</i>OFDM symbols can be based on the cyclically delayed<i>m</i>Sample sequence to generate, where<i>m</i>&gt;1. For the first OFDM symbol, the pilot frequency symbol can be mapped to spaced apart<i>p</i>Subcarriers, where<i>p</i>Can be indivisible<i>N</i>_<i>FFT</i>The prime number. For the first<i>m</i> OFDM symbols, pilot frequency symbols can be mapped to separate<i>p</i>Subcarriers, where<i>m</i>&gt;1. The same pilot frequency subcarrier set can be used for all OFDM symbols. Number of pilot frequency subcarriers (<i>S</i>) Can be equal to or greater than<i>MN</i>_<i>CP</i>. The pilot frequency subcarrier interval (p) can be selected as shown in equation (8).

The user station 106 can deduce the difference in the MIMO channel between the base station 104 and the user station 106.<i>MR</i>Channel estimates for each of the SISO channels. For each receiving antenna, the user station 106 can obtain information from<i>S</i>Pilot frequency subcarrier<i>S</i>Received pilot frequency symbols, and the pilot frequency modulation can be removed to obtain the<i>S</i>Pilot frequency subcarrier<i>S</i>Observations. Each receiving antenna<i>j</i>of<i>S</i>An observation can be expressed as:

<b>y</b>_<i>j</i>=<b>Bh</b>_<i>j</i>+<b>n'</b>　(9)

in<b>y</b>_<i>j</i>Is on the receiving antenna j<i>S</i>Pilot frequency subcarrier<i>S</i>×1 observation vector, B is defined in formula (4)<i>S</i>×<i>Q</i>matrix,<b>h</b>_<i>j</i>It's about this<i>M</i>Transmitting antenna<i>Q</i>×1 channel gain vector, and<b>n</b>Yes<i>S</i>×1 noise vector.

vector<b>h</b>_<i>j</i>Includes elements<i>h</i>_<i>j,</i>₀arrive<i>h</i>_<i>j,Q</i>_-1. forward<img file="TW201014234A_D0025.tif" />Elements<i>h</i>_<i>j,</i>₀arrive<img file="TW201014234A_D0026.tif" />Is about the channel gain of transmitting antenna 0, next<img file="TW201014234A_D0027.tif" />Elements<img file="TW201014234A_D0028.tif" />arrive<img file="TW201014234A_D0029.tif" />Is about the channel gain of transmit antenna 1, and so on, and finally<img file="TW201014234A_D0030.tif" />Elements<img file="TW201014234A_D0031.tif" />arrive<i>h</i>_<i>j</i>_,Q-1It's about the transmitting antenna<i>M</i>-1 channel gain.<b>h</b>_<i>j</i>The estimation can be based on various techniques from<b>y</b>_<i>j</i>get. In a design,<b>h</b>_<i>j</i>The estimation of can be based on techniques such as minimum mean square error (MMSE)<b>y</b>_<i>j</i>Obtained as follows:

<maths><img file="TW201014234A_D0032.tif" /></maths>

in<img file="TW201014234A_D0033.tif" />,and<img file="TW201014234A_D0034.tif" />Yes<b>h</b>_<i>j</i>Estimate.

The same processing can be performed on each receiving antenna to obtain<i>M</i>Between the transmitting antenna and the receiving antenna<i>M</i>SISO channel<i>M</i>Channel estimates.

FIG. 9 shows a block diagram of the design of the channel estimator 900. In the channel estimator 900,<i>R</i>Units 910a to 910r are from<i>R</i>Receiving antenna 0 to<i>R</i>-1 gets corresponding to this<i>S</i>Pilot frequency subcarrier<i>S</i>A pilot frequency symbol is received. Each unit 910 removes this from its receiving antenna<i>S</i>Receive the pilot frequency modulation on the pilot frequency symbol and provide<i>S</i>Observations. Pilot frequency modulation removal can be achieved by multiplying each received pilot frequency symbol by the complex conjugate of the transmitted pilot frequency symbol.<i>R</i>Channel estimators 912a to 912r receive the data from units 910a to 910r, respectively<i>S</i>Observations. Each channel estimator 912, for example, as shown in equation (10), derives a pair of information about its receiving antenna<i>j</i>of<b>h</b>_<i>j</i>Estimate and provide<img file="TW201014234A_D0035.tif" />。<i>R</i>Demultiplexers (Demux) 914a to 914r receive from channel estimators 912a to 912r, respectively<img file="TW201014234A_D0036.tif" />. Each demultiplexer 914 demultiplexes<img file="TW201014234A_D0037.tif" />Channel gain and provide<i>M</i>Transmitting antenna<i>M</i>Channel estimates.

Figure 10 shows the design of a process 1000 for performing channel estimation for a MISO or MIMO system. The process 1000 may be performed by the subscriber station 106 for downlink channel estimation, by the base station 104 for uplink channel estimation, or by some other entity. At 1010,<i>M</i>A cyclically delayed pilot frequency sequence can be obtained from<i>M</i>Two transmitting antennas are transmitted, of which the first<i>m</i>The pilot frequency sequence is based on the length ratio (<i>m</i>-1) The cyclic delay length is at least the length of the cyclic prefix<i>N</i>_<i>CP</i>First<i>m</i>Cycle delay (<i>m</i>=1<i>,</i>...<i>,M</i>) To cycle the delay.

In 1020, the total<i>R</i>Receiving antennas to process the received samples to obtain<i>M</i>Estimated channel gain of each used transmitting antenna. In general, received samples can be obtained from any number of receiving antennas and processed to obtain channel estimates for any number of transmitting antennas for each receiving antenna. At 1020, the received samples can be processed to obtain observations of pilot frequency subcarriers, for example, by (1) performing OFDM demodulation on the received samples to obtain received pilot frequency symbols corresponding to these pilot frequency subcarriers and (ii) Remove pilot frequency modulation from these received pilot frequency symbols to obtain observations of these pilot frequency subcarriers for this process. These observations can be processed (for example, based on the MMSE technique as shown in equation (10)) to obtain channel estimates for all utilized transmit antennas.

The various operations of the method described above can be executed by various hardware and/or software components and/or modules corresponding to the device plus functional blocks illustrated in the drawings. For example, the blocks 810-820 illustrated in FIG. 8 correspond to the device plus function blocks 810A-820A shown in FIG. 8A. Similarly, the blocks 1010-1020 illustrated in FIG. 10 correspond to the device plus function blocks 1010A-1020A illustrated in FIG. 10A. More generally, when the method illustrated in the figure has a corresponding pairing device plus function drawing, the operation box corresponds to a device plus function box having a similar number.

The various illustrative logic blocks, modules, and circuits described in conjunction with the present disclosure may use general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), or other Program logic devices (PLD), individual gates or transistor logic, individual hardware components, or any combination thereof designed to perform the functions described herein are implemented or executed. The general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in cooperation with a DSP core, or any other such configuration.

The steps of the method or algorithm described in conjunction with the present disclosure can be directly implemented in hardware, in a software module executed by a processor, or in a combination of the two. The software module can reside in any form of storage medium known in the art. Some examples of storage media that can be used include random access memory (RAM), read-only memory (ROM), flash memory, EPROM memory, EEPROM memory, scratchpad, hard disk, and removable disk , CD-ROM, etc. The software module may include a single instruction or many instructions, and may be distributed on several different code segments, distributed among different programs, and distributed across multiple storage media. A storage medium can be coupled to the processor such that the processor can read and write information from and to the storage medium. In the alternative, the storage medium may be integrated into the processor.

The methods disclosed herein include one or more steps or actions for achieving the described method. These method steps and/or actions can be interchanged without departing from the scope of the claim. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions can be modified without departing from the scope of the claim.

The described functions can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, each function can be stored as one or more instructions on a computer readable medium. The storage medium can be any available medium that can be accessed by a computer. By way of example and not limitation, such computer readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, floppy disk storage or other disk storage devices, or can be used to carry or store instructions or data Any other media that can be accessed by a computer in a structured form of desired code. Disks and optical discs as used in this article include compact discs (CD), laser discs, optical discs, digital versatile discs (DVD), floppy discs, and Blu-ray<img file="TW201014234A_D0038.tif" />Optical discs, in which magnetic disks are often used to reproduce data, while optical discs use lasers to reproduce data optically.

Software or commands can also be sent on the transmission medium. For example, if the software is transmitted from a web site, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology such as infrared, radio, and microwave In the future, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission media.

In addition, it should be appreciated that the modules and/or other appropriate devices used to implement the methods and technologies described in this article can be downloaded and/or obtained in other ways by the user and/or the base station as applicable. For example, such a device can be coupled to a server to help forward devices for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (for example, RAM, ROM, physical storage media such as compact discs (CD) or floppy disks, etc.) so that once the storage device is coupled to Or provide it to the user terminal and/or base station, and the device can obtain various methods. In addition, any other suitable technique for providing the methods and techniques described herein to the device may be utilized.

It should be understood that the claimed items are not limited to the precise configurations and elements exemplified above. Various modifications, replacements and deformations can be made in the layout, operation and details of the method and device described above without departing from the scope of the requirements.

<p>100. . . Wireless communication system</p><p>102. . . Honeycomb Cell Service Area</p><p>104. . . Base station</p><p>106. . . User terminal</p><p>108. . . Downlink</p><p>110. . . Uplink</p><p>112. . . Sector</p><p>312. . . Data source</p><p>320. . . TX data processor</p><p>330. . . TX MIMO processor</p><p>340. . . Controller/Processor</p><p>342. . . Memory</p><p>344. . . Scheduler</p><p>339. . . Data slot</p><p>338. . . RX data processor</p><p>336. . . MIMO detector</p><p>360. . . MIMO detector</p><p>370. . . RX data processor</p><p>372. . . Data slot</p><p>378. . . Data source</p><p>380. . . TX data processor</p><p>382. . . TX MIMO processor</p><p>390. . . Controller/Processor</p><p>392. . . Memory</p><p>394. . . Channel processor</p><p>410. . . Symbol-subcarrier mapper</p><p>412. . . NFFT-point IDFT</p><p>414. . . Parallel-serial (P/S) converter</p><p>416. . . Cyclic prefix generator</p><p>710a. . . Symbol-subcarrier mapper</p><p>712a. . . NFFT-point IDFT</p><p>714a. . . P/S converter</p><p>716a. . . Cycle delay N_C,0Samples</p><p>718a. . . Cyclic prefix generator</p><p>718a. . . RF unit</p><p>710b. . . Symbol-subcarrier mapper</p><p>714b. . . NFFT-point IDFT712b P/S converter</p><p>716b. . . Cycle delay N_C,0+N_C,1Samples</p><p>718b. . . Cyclic prefix generator</p><p>718b. . . RF unit</p><p>710m. . . Symbol-subcarrier mapper</p><p>712m. . . NFFT-point IDFT</p><p>714m. . . P/S converter</p><p>716m. . . Cycle delay<img file="TW201014234A_D0039.tif" />Samples</p><p>718m. . . Cyclic prefix generator</p><p>718m. . . RF unit</p><p>910a. . . Remove pilot tone modulation</p><p>912a. . . Channel estimator (for example, MMSE)</p><p>914a. . . Demultiplexer</p><p>910b. . . Remove pilot tone modulation</p><p>912b. . . Channel estimator (for example, MMSE)</p><p>914b. . . Demultiplexer</p><p>910r. . . Remove pilot tone modulation</p><p>912r. . . Channel estimator (for example, MMSE)</p><p>914r. . . Demultiplexer</p>

In order to understand in detail the manner in which the above-stated features of the present disclosure are used, the above briefly summarized description may be described in more detail with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the drawings only illustrate certain typical embodiments of the present disclosure, and should not be considered as limiting its scope, as the description may be admitted to other equally effective embodiments.

Figure 1 illustrates an example wireless communication system according to certain embodiments of the present disclosure.

Figure 2 illustrates an example Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) frame for Time Division Duplex (TDD) according to certain embodiments of the present disclosure.

Figure 3 illustrates an example transmitter and an example receiver that may be used in a wireless communication system according to certain embodiments of the present disclosure.

Figure 4 illustrates a block diagram of the design of an OFDM modulator according to certain embodiments of the present disclosure.

Figure 5 illustrates an example of cyclic delay diversity according to certain embodiments of the present disclosure.

Figure 6 illustrates an example pilot frequency subcarrier structure for one OFDM symbol according to certain embodiments of the present disclosure.

FIG. 7 illustrates a block diagram of the design of the modulator at the base station in FIG. 3 according to some embodiments of the present disclosure.

Figure 8 illustrates a process for generating pilot frequencies for a multiple input single output (MISO) or multiple input multiple output (MIMO) system according to certain embodiments of the present disclosure.

FIG. 8A illustrates example elements capable of performing the operations illustrated in FIG. 8.

Figure 9 illustrates a block diagram of the design of a channel estimator according to certain embodiments of the present disclosure.

FIG. 10 illustrates a process for performing channel estimation in a MISO or MIMO system according to certain embodiments of the present disclosure.

FIG. 10A illustrates example elements capable of performing the operations illustrated in FIG. 10.