Pilot design for improved channel and interference estimation

(Cross-reference of related applications) This application is entitled "PILOT DESIGN FOR IMPROVED SIMPLIFIED CHANNEL AND INTERFERENCE ESTIMATION WITH DEDICATED PILOT TONES FOR OFDMA", filed January 5, 2007, transferred to the assignee of the present application and incorporated herein by reference. Claim the priority of US Provisional Application No. 60 / 883,756.

The present disclosure relates generally to communications, and more specifically to pilot designs for wireless communication systems.

A wireless multiple access communication system can support multiple users by sharing available wireless communication resources. Examples of such multiple access systems are code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal FDMA (OFDMA) systems and single carrier FDMA (SC-). Includes FDMA) system.

The wireless multiple access system may support multiple-input multiple-output (MIMO) transmission over forward and / or reverse links. In a reverse link (or uplink), one or more terminals are multiple (N) at that terminal._TFrom multiple (N) transmitting antennas, multiple (N) at the base station_RTransmissions to the receiving antennas may be transmitted. N_TTransmitting antennas and N_RThe MIMO channel formed by the receiving antennas is N_CIt may be decomposed into individual spatial channels. Where N_C min {N_T, N_R}. Improved performance (eg, higher throughput and / or greater reliability) may be achieved by utilizing a spatial channel formed by multiple transmit and receive antennas.

For MIMO transmission over a reverse link, the radio channel between each terminal and the base station is typically estimated and used to recover the data transmission transmitted by that terminal through that radio channel. Channel estimation is typically performed by transmitting a pilot from each terminal and measuring the pilot at a base station. Pilots consist of symbols that are a priori known by both terminals and base stations. Therefore, the base station can estimate the channel response for each terminal based on the pilot symbols received from that terminal and the known pilot symbols. Since pilot transmission means overhead, it is desirable to minimize pilot transmission to the extent possible. However, pilot transmission should be in a state where the base station can obtain good channel estimates for each terminal.

Therefore, there is a need in the art for transmitting pilots to obtain good channel estimates.

Techniques for transmitting pilots and for processing receiving pilots to obtain channels and interference estimates are described herein. The transmitter (eg, terminal) may generate a pilot symbol for the first cluster in the time / frequency block (or tile) based on the first sequence, or the first in the time / frequency block. Pilot symbols for two clusters may be generated based on the second sequence. The transmitter may further generate a pilot symbol for the third cluster in the time / frequency block based on the first sequence or the third sequence, and the second sequence or the fourth sequence. Pilot symbols may be generated for the fourth cluster in the time / frequency block based on. Each cluster may cover a group of pilot symbols, typically adjacent to each other, in a time / frequency block. The first, second, third and fourth sequences may contain common elements arranged in different orders or may be considered as different versions of a single sequence. For example, the elements in the second sequence may be in reverse order (or inverted) with respect to the elements in the first sequence. The transmitter may transmit the pilot symbol in each of those clusters in the time / frequency block.

The plurality of transmitters may share a time / frequency block, or may be assigned different sequences orthogonal to each other for each cluster in the time / frequency block. Each transmitter may generate a pilot symbol for each cluster based on the sequence assigned to that transmitter for that cluster.

The receiver (for example, a base station) may obtain a receive pilot symbol from a plurality of clusters in a time / frequency block. The receiver may form multiple base vectors for the transmitter, with each base vector formed by multiple versions of the sequence assigned to that transmitter. The basis vector is a vector of elements used to process the received symbol. Multiple versions of a sequence may correspond to different orders of elements in the sequence, and different sequences and ideas may be obtained. The receiver may form a plurality of basis vectors based on a particular channel model, for example, a channel model having a linearly changing time component and a linearly changing frequency component. The receiver may process the receive pilot symbol with multiple basis vectors to obtain channel estimates for the transmitter. The receiver may repeat the same process (for example, generating a basis vector and processing a received pilot symbol with the basis vector) for each transmitter sharing a time / frequency block. The receiver may also obtain noise and interference estimates based on the received pilot symbol and at least one basis vector not used for channel estimation.

Various aspects and features of the present disclosure will be described in more detail below.

<figref num="1">FIG. 1 shows a block diagram of two terminals and one base station.</figref><figref num="2">Figure 2 shows the tile structure.</figref><figref num="3A">Figures 3A to 3D show the structure of the four pilot patterns.</figref><figref num="3B">Figures 3A to 3D show the structure of the four pilot patterns.</figref><figref num="3C">Figures 3A to 3D show the structure of the four pilot patterns.</figref><figref num="3D">Figures 3A to 3D show the structure of the four pilot patterns.</figref><figref num="4">Figure 4 shows different synthesis options for the four pilot clusters.</figref><figref num="5A">5A-5D show the use of multiple versions of the scrambling sequence to obtain symmetric pilot symbols for the four pilot patterns shown in FIGS. 3A-3D.</figref><figref num="5B">5A-5D show the use of multiple versions of the scrambling sequence to obtain symmetric pilot symbols for the four pilot patterns shown in FIGS. 3A-3D.</figref><figref num="5C">5A-5D show the use of multiple versions of the scrambling sequence to obtain symmetric pilot symbols for the four pilot patterns shown in FIGS. 3A-3D.</figref><figref num="5D">5A-5D show the use of multiple versions of the scrambling sequence to obtain symmetric pilot symbols for the four pilot patterns shown in FIGS. 3A-3D.</figref><figref num="6">FIG. 6 shows the processing performed by the transmitter to transmit the pilot.</figref><figref num="7">FIG. 7 shows a device for transmitting a pilot.</figref><figref num="8">FIG. 8 shows the processing performed by the receiver to process the receiving pilot.</figref><figref num="9">FIG. 9 shows a device for processing a receiving pilot.</figref>

Detailed explanation

The techniques described herein may be used in various communication systems that support MIMO transmission and utilize frequency division multiplexing (FDM) forms. For example, these techniques may be used in systems that utilize orthogonal FDM (OFDM), single carrier FDM (SC-FDM), and the like. OFDM and SC-FDM divide the system bandwidth into multiple (K) orthogonal subcarriers. Orthogonal subcarriers are also called tones, bins, and so on. Each subcarrier may be modulated with data. In general, modulated symbols are transmitted in the frequency domain with OFDM and also in the time domain with SC-FDM. These techniques may also be used for transmission over reverse links (or uplinks) as well as forward links (or downlinks). For clarity, these techniques are described below for transmission over reverse links.

FIG. 1 shows a block diagram of the design of two terminals 110x and 110y and base station 150 in a wireless communication system. The terminal may also be referred to as a user device (UE), mobile station, access terminal, subscriber unit, station, and the like. The terminal may be a mobile phone (cellular phone), a personal digital assistant (PDA), a wireless communication device, a handheld device, a wireless modem, a laptop computer, a cordless phone, or the like. The base station may also be referred to as node B, evolved node B (eNode B), access point, and the like. In FIG. 1, the terminal 110x is equipped with a single antenna, the terminal 110y is equipped with a plurality of antennas, and the base station 150 is equipped with a plurality of antennas. Each antenna may be a physical antenna or an antenna array. For simplicity, FIG. 1 shows only the processing units for data transmission over the reverse link and signaling transmission over the forward link.

At each terminal 110, the transmit (TX) data and pilot processor 120 receives traffic data from the data source 112, processes the traffic data (eg, formatting, encoding, interleaving, and symbol mapping) and prints the data symbols. You may generate it. Further, the processor 120 may generate a pilot symbol together with the data symbol and multiplex it. As used herein, the data symbol is a symbol for the data, the pilot symbol is a symbol for the pilot, and the symbol is typically a complex number. The data symbol and pilot symbol may be modulation symbols from a modulation scheme such as PSK or QAM. Pilots are data that is a priori known by both terminals and base stations.

At terminal 110y, TX MIMO processor 122y may perform transmitter spatial processing on data and pilot symbols based on direct MIMO mapping, precoding, beamforming, and the like. Data symbols may be transmitted from one antenna for direct MIMO mapping or from multiple antennas for precoding and beamforming. Processor 122y is N_YA stream of output symbols, N_YIt may be provided to a number of modulators (MOD) 130a to 130ny. At terminal 110x, processor 120x may supply a single output symbol stream to modulator 130x. Each modulator 130 may perform modulation on the output symbol (eg, for OFDM, SC-FDM, etc.) to obtain an output chip. Each modulator 130 may further process (eg, convert to analog, filter, amplify, up-convert) its output chip to generate a reverse link signal. At terminal 110x, a single reverse link signal from modulator 130x may be transmitted from antenna 132x. In terminal 110y, N from modulators 130a ~ 130ny_YEach of the reverse link signals is N_YIt may be transmitted through the antennas 132a to 132ny.

At base station 150, N_YThe antennas 152a to 152nr may receive reverse link signals from terminals 110x and 110y and optionally other terminals. Each antenna 152 may supply a received signal to its respective demodulator (DEMOD) 154. Each demodulator 154 processes its received signal (eg, filtering, amplifying, downconverting, and digitizing) to obtain a sample, and further about the sample (eg OFDM, SC-) to obtain a received symbol. You may perform demodulation (for FDM etc.). Each demodulator 154 may supply a receive data symbol to the receive (RX) spatial processor 160 and a receive pilot symbol to the channel processor 162. The channel processor 162 may estimate the response of the radio channel from each terminal 110 to the base station 150 as well as noise and interference based on the receive pilot symbol. The RX spatial processor 160 may perform MIMO detection on received data symbols with channel estimation and noise and interference estimation from processor 162 to obtain data symbol estimation. The RX data processor 170 may process the data symbol estimation (eg, deinterleave and decode) and supply the decoded data to the data sink 172.

The base station 150 may transmit traffic data and signaling (for example, allocation of time / frequency resources) to the terminal. The signaling is processed by the TX signaling processor 174 and further N_RIt may be processed by modulators 154a-154nr to generate a number of forward link signals. N_RThe number of forward link signals is N_RIt may be transmitted through the NR antennas 152a to 152nr. At each terminal 110, the forward link signal from base station 150 is signaled received by one or more antennas 132, processed by one or more demodulators 130, and further transmitted by base station 150. May be processed by the RX signaling processor 134 to recover.

Controllers / processors 140x, 140y and 180 may control the operation of various processing units of terminals 110x and 110y and base station 150, respectively. The memories 142x, 142y and 182 may store data and program code for terminals 110x and 110y and base station 150, respectively. The scheduler 184 may schedule terminals for transmission on forward and / or reverse links.

FIG. 2 shows a tile structure 200 that may be used for forward and / or reverse links. The time / frequency resources available for a given link may be divided into tiles. The tile may be called a time / frequency block, a resource block, a hop area, or the like. Each tile may cover multiple (F) subcarriers in multiple (T) symbol periods. Here, F and T may be arbitrary integer values, respectively. The F subcarriers in a given tile may be continuous subcarriers or may be dispersed across all K subcarriers. Each tile contains FT resource units. Here, the resource unit is one subcarrier in one symbol period. The FT modulation symbols may be transmitted in the FT resource units in each tile. Each tile may be assigned to one or more terminals for data transmission.

Figure 2 also shows a frequency hopping scheme that may be used for forward and / or reverse links. Frequency hopping may provide against the effects of harmful paths and randomization of interference (against) frequency diversity. Using frequency hopping, terminals may be assigned tiles at different parts of the system bandwidth over different hop periods. The hop period is the duration of one tile and spans the T symbol period.

Data and pilots may be transmitted in various ways on the tile. In one design, data and pilot symbols are transmitted in different resource units. The pilot symbol may also be transmitted based on a pilot pattern indicating a particular resource unit used for the pilot symbol. In general, the pilot pattern may contain any number of pilot symbols, and the pilot symbols may be located anywhere in the tile. The number of pilot symbols may be chosen based on the trade-off between pilot overhead and channel estimation performance. The spacing of the cross pilot symbols may be chosen based on the expected delay spread of the radio channel. Smaller frequency separations between pilot symbols may be used to handle larger delay spreads. The spacing of the cross pilot symbols may be chosen based on the expected Doppler spread of the radio channel. Smaller time separations between pilot symbols may be used to handle larger Doppler diffusion.

Pilot symbols may also be placed to support spatial multiplexing techniques such as MIMO and / or Spatial Access Multiple Access (SDMA). Spatial multiplexing may be used to simultaneously transmit multiple data streams through multiple spatial channels or layers formed by multiple transmit and receive antennas. To support spatial multiplexing, pilot symbols may be arranged in a cluster within a tile. The number of pilot symbols (M) in each cluster may be equal to or greater than the supported spatial ranks. Spatial rank refers to the number of spatial channels and thus the number of data streams that may be transmitted in parallel. The pilot symbol group in each cluster may occupy a continuous area in time and frequency for each terminal so that the variation of the radio channel across the pilot symbol in one cluster is as small as possible.

FIG. 3A shows the design of pilot pattern 310 for 16x8 tiles covering F = 16 subcarriers during the T = 8 symbol period. In this design, the tile contains 12 pilot symbols arranged in 4 clusters at the 4 corners of the tile. As shown in Figure 3A, the four clusters may be given indexes of 1,2,3 and 4. Each cluster contains M = 3 pilot symbols transmitted over one subcarrier in three consecutive symbol periods. The three pilot symbols in each cluster may be used for channel estimation for up to three spatial channels.

Figure 3B shows the design of pilot pattern 320 for 16x8 tiles. In this design, the tile contains 12 pilot symbols arranged in 4 clusters at the 4 corners of the tile. Each cluster contains M = 3 pilot symbols transmitted over three consecutive subcarriers in one symbol period. The three pilot symbols in each cluster may be used for channel estimation for up to three spatial channels.

Figure 3C shows the design of pilot pattern 330 for 16x8 tiles. In this design, the tile contains 16 pilot symbols arranged in 4 clusters at the 4 corners of the tile. Each cluster contains a pilot symbol of M = 4 transmitted over two consecutive subcarriers in two consecutive symbol periods. The four pilot symbols in each cluster may be used for channel estimation for up to four spatial channels.

Figure 3D shows the design of pilot pattern 340 for 16x8 tiles. In this design, the tile contains 24 pilot symbols arranged in 8 clusters in 4 rows of tiles. Each cluster contains M = 3 pilot symbols transmitted over one subcarrier in three consecutive symbol periods. The three pilot symbols in each cluster may be used for channel estimation for up to three spatial channels.

Figures 3A-3D show four exemplary pilot patterns. Various other pilot patterns may be defined. In general, the pilot pattern may contain any number of clusters, and each cluster may contain any number of pilot symbols. In addition, the cluster and pilot symbols may be arranged in any way on the tile. For clarity, much of the following description assumes the use of pilot pattern 310 in Figure 3A.

In general, one or more terminals may share a given tile. If the tile has a cluster of M pilot symbols, up to M data streams may be transmitted over up to M spatial channels or layers. A terminal with a single antenna (eg, terminal 110x in FIG. 1) may transmit a single data stream over a single spatial channel. A terminal having a plurality of antennas (for example, the terminal 110y in FIG. 1) may transmit a plurality of data streams on a plurality of spatial channels.

For clarity, much of the description below assumes that Q terminals share a given tile. Here, a 1 Q M is. It is also assumed that each terminal transmits one data stream on one spatial channel. The process for this tile is described below.

The base station may obtain F / T receive symbols from the tile for Q terminals. The received symbol may be expressed as follows.<maths num="1"><img file="JP2010516111A_D0001.tif" /></maths>

In equation (1), the first F elements of each vector correspond to the F subcarriers in the first symbol period of the tile, and the next F elements correspond to the F in the second symbol period. Corresponds to F subcarriers, and so on, and the last F elements correspond to F subcarriers in the last symbol period.<maths num="2"><img file="JP2010516111A_D0002.tif" /></maths>

It may be assumed to be a complex Gaussian random variable with a zero mean and a known covariance matrix. The channel gain may be assumed to be independent among the Q terminals.<maths num="3"><img file="JP2010516111A_D0003.tif" /></maths>

The base station may estimate the channel gain for each terminal as well as noise and interference based on the received pilot symbol. The base station performs channel estimation based on the assumption that the statistical properties of the radio channel for each terminal are known and that the channel gains across the tiles for each terminal are correlated. Is also good.

The covariance matrix for each terminal q may be approximated as follows. Where q {1, ..., Q}.<maths num="4"><img file="JP2010516111A_D0004.tif" /></maths><maths num="5"><img file="JP2010516111A_D0005.tif" /></maths>

The three eigenvectors of these approximations have an F · T × 1 dimension and may be used in place of the actual eigenvectors for channel estimation for terminal q across tiles. Furthermore, for practical interests, the first eigenvalue λ_1,qIs typically the other two eigenvalues λ_{2, q}And λ_{3, q}It is at least an order of magnitude larger than that.

The three approximate eigenvectors may be expressed as follows.<maths num="6"><img file="JP2010516111A_D0006.tif" /></maths><maths num="7"><img file="JP2010516111A_D0007.tif" /></maths><maths num="8"><img file="JP2010516111A_D0008.tif" /></maths><maths num="9"><img file="JP2010516111A_D0009.tif" /></maths><maths num="10"><img file="JP2010516111A_D0010.tif" /></maths><maths num="11"><img file="JP2010516111A_D0011.tif" /></maths>

Based on the channel model shown in equation (4), the channel response of terminal q may be expressed as:<maths num="12"><img file="JP2010516111A_D0012.tif" /></maths><maths num="13"><img file="JP2010516111A_D0013.tif" /></maths>

The pilot pattern may include all P pilot symbols, which may be arranged in 4 clusters (each cluster contains M pilot symbols). As a result, P = 4M. For example, as shown in FIGS. 3A-3D, the pilot symbols may be placed symmetrically with respect to the center of the tile. If each terminal transmits one data stream on one spatial channel, the number of terminals that can share the tile is limited to M, i.e. Q M.

The Q terminals may share the cluster, and each of the Q terminals may simultaneously transmit M pilot symbols in the cluster. Each terminal may scramble or spread its M pilot symbols in a scrambling sequence assigned to that terminal.<maths num="14"><img file="JP2010516111A_D0014.tif" /></maths>

The scrambling sequence may also be referred to as a diffusion sequence, an orthogonal sequence, a pilot sequence, a sequence, and the like. The scrambling sequence may have unit modulus elements and should be of length M. In one design, M scrambled sequences (each scrambled sequence contains M elements in one column of the Fourier matrix) are based on M columns of the M × M Fourier matrix. Is defined. The elements in n rows and m columns of the M × M Fourier matrix are e for n = 0, ..., M-1 and m = 0, ..., M-1.^{-j2π n m / M}May be given as. The M scrambling sequences may also be defined in other ways. In either case, the Q scrambling sequences may be selected from among the M available scrambling sequences. In one design, each terminal is assigned one scrambling sequence and uses the same scrambling sequence for all clusters in the tile. In other designs, each terminal may use different scrambling sequences for different clusters in the tile.

The pilot symbol transmitted by the terminal q in the tile may be expressed as follows.<maths num="15"><img file="JP2010516111A_D0015.tif" /></maths><maths num="16"><img file="JP2010516111A_D0016.tif" /></maths>

The next M elements are for the pilot symbols transmitted in cluster 2 in the upper right corner of the tile, and the next M elements are for the pilot symbols transmitted in cluster 3 in the lower left corner of the tile. The next M elements are for the pilot symbols transmitted in cluster 4 in the lower right corner of the tile.<maths num="17"><img file="JP2010516111A_D0017.tif" /></maths><maths num="18"><img file="JP2010516111A_D0018.tif" /></maths>

Here, a, b, and c are three elements of the scrambling sequence, and may have any complex numerical value.<maths num="19"><img file="JP2010516111A_D0019.tif" /></maths><maths num="20"><img file="JP2010516111A_D0020.tif" /></maths><maths num="21"><img file="JP2010516111A_D0021.tif" /></maths><maths num="22"><img file="JP2010516111A_D0022.tif" /></maths><maths num="23"><img file="JP2010516111A_D0023.tif" /></maths><maths num="24"><img file="JP2010516111A_D0024.tif" /></maths><maths num="25"><img file="JP2010516111A_D0025.tif" /></maths>

A set of basis vectors may be defined for each terminal q as follows.<maths num="26"><img file="JP2010516111A_D0026.tif" /></maths><maths num="27"><img file="JP2010516111A_D0027.tif" /></maths><maths num="28"><img file="JP2010516111A_D0028.tif" /></maths>

If the number of degrees of freedom of the channel for the Q terminals sharing the tile is less than the total number of pilot symbols in the tile, the pilot symbols not used to estimate the channel parameters are the noise and noise in that tile. It may be used to estimate the power of interference. The observation space has P dimensions corresponding to all P pilot symbols in the tile. In the design described above, the channel of each terminal may be characterized by three parameters, or the 3Q dimension may be used to estimate the channel parameters for all Q terminals. The remaining P-3Q dimensions of the observation space may be used to estimate the power of noise and interference.

Noise and interference may be estimated as the power of the projection of the onto received signal onto a dimension that is not occupied by the pilot signals transmitted by the Q terminals. The received signal may be projected onto a basis vector for all M available scrambling sequences, such as:<maths num="29"><img file="JP2010516111A_D0029.tif" /></maths><maths num="30"><img file="JP2010516111A_D0030.tif" /></maths>

Equation (8) also accumulates the results of four backdiffusions for the four clusters in different ways for different basis vectors.<maths num="31"><img file="JP2010516111A_D0031.tif" /></maths><maths num="32"><img file="JP2010516111A_D0032.tif" /></maths><maths num="33"><img file="JP2010516111A_D0033.tif" /></maths><maths num="34"><img file="JP2010516111A_D0034.tif" /></maths>

The noise and interference powers may be estimated as follows.<maths num="35"><img file="JP2010516111A_D0035.tif" /></maths><maths num="36"><img file="JP2010516111A_D0036.tif" /></maths>

The first sum may be used as an estimate of the power of noise and interference, but may include channel modeling errors if the channels of each terminal do not change linearly across the tiles.<maths num="37"><img file="JP2010516111A_D0037.tif" /></maths>

The double sum exists when Q &lt;M.

Channel estimates may be obtained for each terminal q based on the minimum mean square error (MMSE) criteria, as follows:<maths num="38"><img file="JP2010516111A_D0038.tif" /></maths>

Using the channel model shown in equation (2), the channel estimation for each terminal q may be expressed as follows.<maths num="39"><img file="JP2010516111A_D0039.tif" /></maths>

θ_TAnd θ_FIdentify the center of the pilot cluster in the tile and therefore depends on the placement of the pilot symbol in the tile.<maths num="40"><img file="JP2010516111A_D0040.tif" /></maths><maths num="41"><img file="JP2010516111A_D0041.tif" /></maths><maths num="42"><img file="JP2010516111A_D0042.tif" /></maths><maths num="43"><img file="JP2010516111A_D0043.tif" /></maths>

Eigenvalue λ_{i, q}May be estimated by methods known in the art.

The assumption in deriving the channel estimates is that the channel for each terminal is constant for the M pilot symbols in each cluster. If the channels vary across M pilot symbols in each cluster, descramble / despread may have a residual error that degrades the channel estimate.

To see the effect of backdiffusing the error, equation (8) may be expanded as follows.<maths num="44"><img file="JP2010516111A_D0044.tif" /></maths>

As shown in equation (12), the result of the projection with respect to the terminal q w_{i, q}Includes components from terminal q as well as contributions from other terminals and noise. Projection result w for terminal q_{i, q}Contribution from other terminals k in_{i, q, k}May be expressed as:<maths num="45"><img file="JP2010516111A_D0045.tif" /></maths>

If despreading is perfect, n for all other terminals_{i, q, k}= 0, and the contribution from other terminals is the result of projection w with respect to terminal q._{i, q}Does not appear in. However, if those channels vary across the M pilot symbols in the cluster, the contribution from other terminals is non-zero.

Based on the channel model in equation (5), the channel response of each terminal k may be expressed as follows.<maths num="46"><img file="JP2010516111A_D0046.tif" /></maths><maths num="47"><img file="JP2010516111A_D0047.tif" /></maths><maths num="48"><img file="JP2010516111A_D0048.tif" /></maths>

Then, the contribution from the terminal k may be expressed as follows.<maths num="49"><img file="JP2010516111A_D0049.tif" /></maths><maths num="50"><img file="JP2010516111A_D0050.tif" /></maths><maths num="51"><img file="JP2010516111A_D0051.tif" /></maths><maths num="52"><img file="JP2010516111A_D0052.tif" /></maths>

Equation (20) shows that for terminal q, the time variation in the channels of other terminals k is the result of projection w for terminal q._{i, q, k}Error or bias in n_{i, q, k}Introduces.<maths num="53"><img file="JP2010516111A_D0053.tif" /></maths>

To mitigate error contributions from other terminals, the scrambling sequence for terminal q may be applied in a symmetrical manner with respect to the center of the tile.<maths num="54"><img file="JP2010516111A_D0054.tif" /></maths>

If each cluster contains a pilot symbol with M = 3, the original scrambling sequence and inverted scrambling sequence for terminal q may be given as follows:<maths num="55"><img file="JP2010516111A_D0055.tif" /></maths>

The original scrambling sequence may be used for the two clusters on the left side of the center of the tile, and the inverted scrambling sequence may be used for the two clusters on the right side of the center of the tile. .. The original scrambling sequence and the inverted scrambling sequence may also be considered as two versions of the same scrambling sequence.

FIG. 5A shows the use of the original scrambling sequence and the inverted scrambling sequence for the pilot pattern shown in FIG. 3A.<maths num="56"><img file="JP2010516111A_D0056.tif" /></maths><maths num="57"><img file="JP2010516111A_D0057.tif" /></maths>

The pilot symbol is symmetrical with respect to the center of the tile. This pilot symmetry reduces errors in channel estimation for terminal q.

FIG. 5B shows the use of the original scrambling sequence and the inverted scrambling sequence for the pilot pattern shown in FIG. 3B.<maths num="58"><img file="JP2010516111A_D0058.tif" /></maths><maths num="59"><img file="JP2010516111A_D0059.tif" /></maths>

The pilot symbol is symmetrical with respect to the center of the tile.

Figure 5C shows the use of four versions of the scrambling sequence for the pilot pattern shown in Figure 3C. In this example, each cluster contains a pilot symbol with M = 4. Also, the four versions of the scrambling sequence may be given as follows:<maths num="60"><img file="JP2010516111A_D0060.tif" /></maths><maths num="61"><img file="JP2010516111A_D0061.tif" /></maths><maths num="62"><img file="JP2010516111A_D0062.tif" /></maths><maths num="63"><img file="JP2010516111A_D0063.tif" /></maths><maths num="64"><img file="JP2010516111A_D0064.tif" /></maths>

The pilot symbol is symmetrical with respect to the center of the tile.

FIG. 5D shows the use of the original scrambling sequence and the inverted scrambling sequence for the pilot pattern shown in FIG. 3D.<maths num="65"><img file="JP2010516111A_D0065.tif" /></maths><maths num="66"><img file="JP2010516111A_D0066.tif" /></maths>

The pilot symbol is symmetrical with respect to the center of the tile.

Figures 5A-5D show four examples where multiple versions of the scrambling sequence are used to obtain pilot symbols that are symmetrical with respect to the center of the tile. In general, any version of the scrambling sequence may be used to achieve a symmetric pilot symbol, depending on how the cluster is defined. All versions of the scrambling sequence may have the same elements, but these elements may be arranged in different orders in different versions.<maths num="67"><img file="JP2010516111A_D0067.tif" /></maths><maths num="68"><img file="JP2010516111A_D0068.tif" /></maths>

Result w of projection on terminal q from other terminal k_{i, q, k}Contribution to may be expressed as follows.<maths num="69"><img file="JP2010516111A_D0069.tif" /></maths>

For i = 1,2 and 4, n due to the inversion of the scrambling sequence_{i, q, k}It can be shown that = 0. n_{3, q, k}Does not have to be equal to 0, even with flipping. This is about the time-varying components of the channel, w_{3, q}It means that there may be an error that affects. Nevertheless, the error introduced in the channel estimation is smaller with flipping due to the multiplication by the MMSE ratio corresponding to the time-varying component.<maths num="70"><img file="JP2010516111A_D0070.tif" /></maths><maths num="71"><img file="JP2010516111A_D0071.tif" /></maths>

Computer simulations show that for high signal-to-noise-and-interference ratios (SINRs), channel estimation errors for vehicular channels with the pilot pattern shown in Figure 5A. It shows that the floor can be reduced by approximately 2 decibels (dB). This can improve packet error rate and data performance.

For clarity, the technology has been described for pilot transmission over reverse links, as well as channel and interference estimation for terminals. The technique may also be used for pilot transmission over forward links and channel estimation for base stations. On forward links, different spatial channels or layers may be assigned different scrambling sequences. The processing for different layers on the forward link may be analogous to the processing for different terminals on the reverse link.

FIG. 6 shows the design of a process 600 performed by the transmitter to send a pilot to the receiver.

Process 600 may be performed by the terminal to send a pilot to the base station on the reverse link. Process 600 may also be performed by the base station to send a pilot to the terminal on the forward link. Therefore, the transmitter may be a terminal or a base station, and the receiver may be a base station or a terminal. Pilot symbols for the first cluster in the time / frequency block (or tile) may be generated based on the first sequence (block 612). The pilot symbol for the second cluster in the time / frequency block may be generated based on the second sequence (block 614). The pilot symbol for the third cluster in the time / frequency block may be generated based on the first sequence or the third sequence (block 616). The pilot symbol for the fourth cluster in the time / frequency block may be generated based on the second sequence or the fourth sequence (block 618). Pilot symbols may be transmitted in each cluster (block 620).

The first, second, third and fourth sequences may contain common elements arranged in different orders and may be considered as different versions of a single sequence. For example, the elements in the second sequence may be in reverse order (or inverted) with respect to the elements in the first sequence. Pilot symbols may be generated so that they are symmetrical with respect to the center of the time / frequency block, for example, as shown in FIGS. 5A-5D. The pilot symbols in all clusters may also be arranged in other ways, and in some cases asymmetrically. Each sequence may contain M elements used to generate M pilot symbols for a cluster. Here, M may be 3, 4, and so on. Each sequence may include elements in a Fourier matrix or sequence of elements defined in other ways.

For reverse links, the first sequence may be assigned to a terminal and is orthogonal to at least one other sequence assigned to at least one other terminal sharing the first cluster. Is also good. Similarly, the second, third and fourth sequences may be assigned to the terminal. Each sequence assigned to a terminal may be orthogonal to another sequence assigned to another terminal for the cluster in which it is used. For forward links, the first sequence may be assigned to a layer and may be orthogonal to at least one other sequence assigned to at least one other layer for the first cluster.

FIG. 7 shows the design of the device 700 that transmits the pilot. The apparatus 700 is a means for generating a pilot symbol for the first cluster in the time / frequency block based on the first sequence (module 712), in the time / frequency block based on the second sequence. Generate a pilot symbol for the third cluster in the time / frequency block based on the means for generating the pilot symbol for the second cluster (module 714), the first sequence or the third sequence. Means for (module 716), means for generating pilot symbols for the second cluster in the time / frequency block based on the second or fourth sequence (module 718), and their respective Includes means for transmitting pilot symbols in a cluster (module 720). The first, second, third and fourth sequences may contain common elements arranged in different orders. Modules 712 to 720 are processors and electronics. It may include devices), hardware devices, electronics components, logic circuits, memory, etc., or any combination thereof.

FIG. 8 shows the design of process 800 performed by the receiver to process pilots received from one or more transmitters. Process 800 may be performed by the base station to process pilots received on reverse links from one or more terminals. Process 800 may also be performed by the terminal to process pilots received on the forward link from the base station for one or more layers. Here, each layer may be considered as a separate transmitter. Therefore, the receiver may be a base station or a terminal, and the transmitter may be a terminal or a base station. The receive pilot symbol may be obtained from multiple clusters in the time / frequency block (block 812). Each of the multiple basis vectors may be formed in multiple versions of the sequence assigned to the transmitter (block 814). The sequence may contain M elements, and multiple versions of the sequence may correspond to different orders of M elements in the sequence. The plurality of basis vectors are formed and constructed based on a specific channel model, for example, a channel model having a linearly changing time component and a linearly changing frequency component, as shown in equation (7). You may. To obtain channel estimates for the transmitter, the receiving pilot symbol may be processed with multiple basis vectors, for example, as shown in equations (8) and (11) (block 816). To obtain noise and interference estimates, the received pilot symbol may also be processed with at least one other basis vector, for example, as shown in equations (8) and (9) (block 818).

For block 814, for example, each basis vector may be formed based on the original version of the sequence and the inverted version of the sequence, as shown in equation (22). Alternatively, each basis vector may be formed based on four versions of the sequence, for example, as shown in equation (23). In any case, multiple versions of the sequence may be used to generate pilot symbols for multiple clusters so that the pilot symbols are symmetrical with respect to the center of the time / frequency block.

For block 816, for example, multiple complex numbers (eg, w), as shown in equation (8)._{i, q}) May be obtained based on the inner product of the received pilot symbol with a plurality of basis vectors. The complex numbers include a first complex number indicating the average channel gain for the time / frequency block, a second complex number indicating the channel variation across frequency, and a third complex number indicating the channel variation across time. But it's okay. Channel estimates for transmitters may be obtained, for example, based on multiple complex values, as shown in equation (11).

FIG. 9 shows the design of the device 900 for processing the receiving pilot. Device 900 is a means for obtaining received pilot symbols from multiple clusters in a time / frequency block (module 912), for forming each of a plurality of base vectors with multiple versions of a sequence assigned to a transmitter. Means (module 914), means for processing received pilot symbols with multiple base vectors to obtain channel estimates for transmitters (module 916), and at least one to obtain noise and interference estimates. Other base vectors include means for processing received pilot symbols (module 918). Multiple versions of a sequence may correspond to different orders of elements in the sequence. Modules 912 to 918 may include processors, electronic devices, hardware devices, electronic components, logic circuits, memory, etc., or any combination thereof.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented by hardware, firmware, software, or a combination thereof. For hardware implementation, the processing unit of an entity (eg, terminal or base station) is one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processors (DSPDs), programmable. Logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, and other electronic devices designed to perform the functions described herein. It may be implemented in a unit, a computer, or a combination thereof.

For firmware and / or software implementation, the technology may be implemented in modules (eg, procedures, functions, etc.) that perform the functions described herein. Firmware and / or software instructions may be stored in memory (eg, memory 142x, 142y or 182 in FIG. 1) and executed by a processor (eg, processor 140x, 140y or 180). The memory may be mounted inside the processor or may be outside the processor. Firmware and / or software instructions also include, for example, random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), programmable read-only memory (PROM), electrically erasable PROM (EEPROM). ), FLASH memory, compact disk (CD), magnetic or optical data storage, etc., may be stored in other processor readable media.

The previous description of the disclosure is provided to allow one of ordinary skill in the art to manufacture or use the disclosure. Various variations to the present disclosure will be readily apparent to those skilled in the art. Also, the general principles defined herein may be applied to other modifications without departing from the spirit or scope of the present disclosure. Therefore, this disclosure is not intended to be limited to the examples described herein, but is intended to be given the broadest scope consistent with the principles and novel features disclosed herein. Has been done.