Pilot design for improved channel and interference estimation

(54) Title: PILOT DESIGN FOR ESTIMATED INTERFERENCE AND ENHANCED CHANNEL (30) Unionist Priority: 26/03/2007 us 11 / 691,243, 05/01/2007 US 60 / 883,756, 05/01/2007 US 60 / 883,756 , 26/03/2007 US 11 / 691,243 (73) Holder (s): Qualcomm Incorporated (72) Inventor (s): Alexei Gorokhov, Dhananjay Ashok Gore,

Petru Cristian Budianu (74) Attorney (s): Montaury Pimenta, Machado & Lioce (86) International Request: pct us2008050136 from 03/01/2008 (57) Summary: pilot design for estimating INTERFERENCE AND PERFECTED CHANNEL. Techniques for pilot transmission and pilot processing received to obtain interference and channel estimates are described. A terminal can generate pilot symbols for a first grouping in a frequency and time block based on a first sequence and can generate pilot symbols for a second grouping in the frequency and time block based on a second sequence. The first and second sequences can include common elements arranged in different orders and can be considered different versions of a single sequence. The terminal can transmit pilot symbols in their respective groupings. A base station can obtain the pilot symbols received from multiple groupings in the frequency and time block. The base station can form each of the multiple base vectors with multiple versions of the sequence assigned to the terminal and can process the pilot symbols received with multiple base vectors to obtain a channel estimate for the terminal.

(87) International Publication: wo 2008 / 086H0 of 17/07/2008

<img file="BRPI0806279A2_D0001.tif" />

<img file="BRPI0806279A2_D0002.tif" />

ΡΙ0806279-0

PILOT DESIGN FOR INTERFERENCE ESTIMATE AND ENHANCED CHANNEL

The present invention claims the priority of provisional US application No. 60 / 883,756, entitled PILOT DESIGN FOR IMPROVED SIMPLIFIED CHANNEL AND INTERFERENCE ESTIMATION WITH DEDICATED PILOT TONES FOR OFDMA, filed on January 5, 2007, assigned to the assignee of this application and incorporated here by reference.

Foundations

Field

The present description generally refers to communication, and more specifically to a pilot design for a wireless communication system.

Foundations

A wireless multiple access communication system can support multiple users by sharing available radio resources. Examples of such multiple access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA systems (OFDMA) , and FDMA Single Carrier Systems (SC-FDMA).

A wireless multiple access system can support the transmission of multiple inputs and multiple outputs (MIMO) on the forward and / or reverse link. On the reverse link (or uplink), one or more terminals can send transmissions from multiple transmission antennas (N_T) at the terminals for multiple receiving antennas (N_R). A MIMO channel formed by the N_T transmitting antennas and N_R receiving antennas can be decomposed into N_ç space channels, where N_ç &lt;min {N_T, N_r}. Improved performance (for example, higher throughput and / or greater reliability) can be

2/35 achieved by exploring the space channels formed by multiple transmitting and receiving antennas.

For MIMO transmission on the reverse link, the wireless channel between each terminal and the base station is normally estimated and used to retrieve the data transmission sent by the terminal via the wireless channel. Channel estimation is typically performed by sending the pilot from each terminal and measuring the pilot at the base station. The pilot consists of symbols that are previously known by both the terminal and the base station. The base station can thus estimate the channel response for each terminal based on the pilot symbols received from that terminal and the known pilot symbols. Since the pilot's transmission represents overhead, it is desirable to minimize the pilot's transmission as much as possible. However, the pilot transmission must be such that the base station can obtain a good channel estimate for each terminal.

<td>There is, therefore,</td><td>an</td><td>need in</td><td>technique</td><td>per</td>

<td>techniques for shipping</td><td>in</td><td>shape pilot</td><td>that</td><td>good</td>

<td>channel estimate can</td><td>to be</td><td>derived.</td><td></td><td></td>

summary

The techniques for pilot transmission and for processing the received pilot to obtain channel and interference estimates are described here. A transmitter (for example, a terminal) can generate pilot symbols for a first cluster in a time frequency block (tile) based on a first sequence and can generate pilot symbols for a second cluster in the time frequency block based on in a second sequence. 0 transmitter can additionally generate pilot symbols for a third grouping in the frequency and time block based on the first sequence or a

3/35 third sequence and can generate pilot symbols for a fourth grouping in the time frequency block based on the second sequence or a fourth sequence. Each grouping can cover a group of pilot symbols, typically adjacent to each other, in the time frequency block. The first, second, third and fourth sequences can include common elements arranged in different orders and can be considered different versions of a single sequence. For example, the elements in the second sequence can be in an inverted order with respect to the elements in the first sequence. The transmitter can transmit the pilot symbols in their respective groupings in the time frequency block.

Multiple transmitters can share the time frequency block and can receive different strings that are orthogonal to each other for each grouping in the time frequency block, transmitter can generate pilot symbols for grouping based on the sequence assigned to that transmitter for that grouping.

A receiver (for example, a base station) can obtain pilot symbols received from multiple clusters in the time frequency block. The receiver can form multiple base vectors for a transmitter, with each base vector being formed with multiple versions of a sequence assigned to that transmitter. A base vector is a vector of elements used for processing received symbols. The multiple versions of the sequence can correspond to different ordering of the elements in the sequence and can be considered as different sequences. The receiver can form the multiple base vectors additionally based on a particular channel model, for example, a channel model with

Each each

4/35 linear variation of time component and linear variation of frequency component. The receiver can process the received pilot symbols with multiple base vectors to obtain an estimate and channel for the transmitter. The receiver can repeat the same processing (for example, generating the base vectors and processing the pilot symbols received with the base vectors) for each transmitter sharing the time frequency block. The receiver can also contain a noise and interference estimate based on the received pilot symbols and at least one unused base vector for the channel estimate.

The various aspects and characteristics of the description are described in greater detail below.

Brief Description of Drawings

Figure 1 illustrates a block diagram of two terminals and a base station.

Figure 2 illustrates a tile structure.

Figures 3a to 3d illustrate drawings of four pilot patterns.

Figure 4 illustrates different combination options for four pilot groupings.

Figures 5a to 5d illustrate the use of multiple versions of a cryptographic sequence to obtain symmetric pilot symbols for the four pilot patterns illustrated in figures 3a to 3d.

Figure 6 illustrates a process performed by a transmitter to transmit a pilot.

Figure 7 illustrates an apparatus for the pilot transmission.

Figure 8 illustrates a process performed by a receiver to process the received pilot.

5/35

Figure 9 illustrates an apparatus for processing the received pilot.

Detailed Description

The techniques described here can be used for various communication systems that support MIMO transmission and use a form of frequency division multiplexing (FDM). For example, techniques can be used for systems using Orthogonal FDM (OFDM), single-carrier FDM (SC-FDM), etc. OFDM and SC-FDM divide the system bandwidth into multiple orthogonal subcarriers (K) which are also referred to as tones, bins, etc. Each subcarrier can be a data modulator. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The techniques can also be used for transmissions on the reverse link (or uplink) in addition to the forward link (or downlink). For the sake of clarity, the techniques are described below for reverse link transmissions.

Figure 1 illustrates a block diagram of a drawing of two terminals HOx and HOy and a base station 150 in a wireless communication system. A terminal can also be referred to as a user equipment (UE), a mobile station, an access terminal, a subscriber unit, a station, etc. A terminal can be a cell phone, a personal digital assistant (PDA), a wireless communication device, a portable device, a wireless modem, a laptop computer, a cordless phone, etc. A base station can also be referred to as a Node B, an evolved Node B (eNode B), an access point, etc. In figure 1, the HOx terminal is equipped with a single antenna, the llOy terminal is equipped with multiple antennas, and the base station 150 is equipped with multiple antennas. Each antenna can be a physical antenna or a

6/35 set of antennas. For the sake of simplicity, Figure 1 illustrates only the processing units for transmitting data on the reverse link and transmitting signaling on the forward link.

At each terminal 110, a pilot and transmission data (TX) processor 120 can receive traffic data from a data source 112, process (e.g., format, encode, merge, and map to symbol) the traffic data, and generate data symbols. Processor 120 can also generate and multiplex pilot symbols with data symbols. As used here, a data symbol is a data symbol, a pilot symbol is a pilot symbol, and a symbol is typically a complex value. Data symbols and pilot symbols can be modulation symbols from a modulation scheme such as PSK or QAM. The pilot is data that is known in advance by both the terminals and the base station.

At the HOy ​​terminal, a MIMO TX 122y processor can perform spatial processing of the transmitter on the data and pilot symbols based on direct MIMO mapping, pre-coding, beam formation, etc. A data symbol can be sent from an antenna for direct MIMO mapping or from multiple antennas for pre-coding and beam formation. The 122y processor can provide N_Y modulators (MOD) 130a to 130ny. At the ΙΙΟχ terminal, the 120x processor can provide a single output symbol string for a 130x modulator. Each modulator 130 can perform modulation (for example, for OFDM, SÇFDM, etc.) on the output symbols to obtain output chips. Each modulator 130 can further process (for example, convert to analog, filter, amplify, and upwardly convert) its output chips to generate a reverse link signal. At the HOx terminal, a single signal

7/35 130x modulator reverse link can be transmitted from the 132x antenna. At the HOy ​​terminal, N_Y reverse link signals from modulators 130a to 130ny can be transmitted via N_Y antennas 132a to 132ny, respectively.

At base station 150, N_R antennas 152a to 152nr can - receive reverse link signals from llOx and HOy terminals and possibly other terminals. Each antenna 152 can provide a received signal to a respective demodulator (DEMOD) 154. Each demodulator 154 can process (for example, filter, amplify, downwardly convert and digitize) its received signal for obtaining samples and can additionally perform demodulation (for example, for OFDM, SC-FDM, etc.) on samples for obtaining symbols received. Each demodulator 154 can provide received data symbols to a space receiving (RX) processor 160 and can provide received pilot symbols to a channel processor 162. Channel processor 162 can estimate the wireless channel response from each terminal 110 to base station 150 in addition to noise and interference based on received pilot symbols. The space processor RX 160 can perform MIMO detection on received data symbols with channel estimates and noise and interference estimates from channel processor 162 to obtain data symbol estimates. An RX 170 data processor can process (e.g., deinterleave and decode) the data symbol estimates and deliver the decoded data to a 172 data store.

The base station 150 can send traffic and signaling data (e.g., frequency resource designations) to the terminals. Signaling can be processed by a TX 174 signaling processor and further processed by modulators 154a to 154nr

8/35 to generate N_R forward link signals, which can be transmitted via Nr antennas 152a to 152nr. At each terminal 110, forward link signals from base station 150 can be received by one or more antennas 132, processed by one or more demodulators 130, and further processed by an RX 134 signaling processor to retrieve signaling sent by the station base 150.

The controllers / processors 140x, 140y, and 180 can control the operation of various processing units at the HOx and HOy terminals and base station 150, respectively. The 142x, 142y and 182 memories can store data and program codes for the HOx and HOy terminals and the base station 150, respectively. A 184 programmer can program the terminals for transmission on the forward and / or reverse link.

Figure 2 illustrates a tile structure 200 that can be used for the forward and / or reverse link. The frequency and time resources available for a given link can be divided into tiles, which can also be referred to as frequency and time blocks, resource blocks, skip regions, etc. Each tile can cover multiple subcarriers (F) in multiple symbol periods (T), where F and T can each be any integer value. The F subcarriers on a given tile can be consecutive subcarriers or can be distributed across K total subcarriers. Each tile includes FT resource units, where a resource unit is a sub-carrier in a symbol period. FT modulation symbols can be sent in the FT resource units on each tile. Each tile can receive one or more terminals for data transmission.

Figure 2 also illustrates a frequency hopping scheme that can be used for the forward link

9/35 and / or reverse. The frequency jump can provide frequency diversity against harmful path effects and randomization of interference. With frequency hopping, a terminal can receive tiles in different parts of the system's bandwidth at different hopping periods. A skip period is the length of time for a tile and comprises T symbol periods.

The data and the pilot can be sent in a number of ways on a tile. In a drawing, data and pilot symbols are sent in different resource units. Pilot symbols can also be sent based on a pilot pattern that indicates the specific feature units to be used for pilot symbols. In general, a pilot pattern can include any number of pilot symbols, and pilot symbols can be located anywhere within a tile. The number of pilot symbols can be selected based on an exchange between the pilot overhead and the channel estimate performance. The spacing of the pilot symbols across the frequency can be selected based on the expected delay spread of the wireless channel. The lower frequency separation between the pilot symbols can be used to handle the longer delay spread. The spacing of the pilot symbols over time can be selected based on the expected Doppler spread of the wireless channel. The smallest time separation between the pilot symbols can be used to handle the largest Doppler spread.

Pilot symbols can also be located to support spatial multiplexing techniques such as MIMO and / or Space Division Multiple Access (SDMA). With spatial multiplexing, multiple data streams can be transmitted simultaneously through multiple spatial channels or layers formed by

10/35 multiple transmitting antennas and multiple receiving antennas. To support spatial multiplexing, pilot symbols can be arranged in groupings within a tile. The number of pilot symbols (M) in each cluster can be equal to or greater than a spatial classification to be supported. Spatial classification refers to the number of spatial channels, and thus the number of data streams that can be transmitted in parallel. The pilot symbols in each cluster can occupy a contiguous region in time and frequency so that, for each terminal, the variations of the wireless channel through the pilot symbols in a cluster are as small as possible.

Figure 3a illustrates a drawing of a pilot pattern 310 for a 16x8 tile that covers F = 16 subcarriers in T = 8 symbol periods. In this drawing, the tile includes 12 pilot symbols that are arranged in four groupings located in the four corners of the tile. The four groupings can receive indices of 1, 2, 3 and 4, as illustrated in figure 3a. Each grouping includes M = 3 pilot symbols sent on a subcarrier in three consecutive symbol periods. The three pilot symbols in each cluster can be used for channel estimation for up to three spatial channels.

Figure 3b illustrates a design of a pilot pattern 320 for a 16x8 tile. In this drawing, the tile includes 12 pilot symbols that are arranged in four groupings located in four corners of the tile. Each grouping includes M = 3 pilot symbols sent on three consecutive subcarriers in a symbol period. The three pilot symbols in each cluster can be used for channel estimation for up to three spatial channels.

11/35

Figure 3c illustrates a drawing of a pilot pattern 330 for a 16x8 tile. In this drawing, the tile includes 16 pilot symbols that are arranged in the four groupings located in four corners of the tile. Each grouping includes M = 4 pilot symbols sent on two consecutive subcarriers in two consecutive symbol periods. The four pilot symbols in each cluster can be used for channel estimation for up to four spatial channels.

Figure 3d illustrates a drawing of a pilot pattern 340 for a 16x8 tile. In this design, the tile includes 24 pilot symbols that are arranged in eight groupings located in four rows of tile. Each grouping includes M = 3 pilot symbols sent on a subcarrier in three consecutive symbol periods. The three pilot symbols in each cluster can be used for channel estimation for up to three spatial channels.

Figures 3a to 3d illustrate four pilot patterns. Several other pilot patterns can also be defined. In general, a pilot pattern can include any number of groupings, and each group can include any number of pilot symbols. Additionally, groupings and pilot symbols can be arranged in any way on a tile. For the sake of clarity, much of the description below considers the use of pilot pattern 310 in figure 3a.

In general, one or more terminals can share a given tile. If the tile has clusters of M pilot symbols, then up to M strings of data can be transmitted in up to M spatial channels or layers. A single antenna terminal (for example, HOx terminal in figure 1) can transmit a single data stream

12/35 in a single space channel. A terminal with multiple antennas (for example, the HOy ​​terminal in figure 1) can transmit multiple data streams across multiple spatial channels.

For the sake of clarity, much of the description below considers that Q terminals share a particular tile, where 1 &lt;Q &lt;M, and that each terminal transmits a sequence of data in a spatial channel. The processing for this tile is described below.

The base station can obtain FT symbols received from the tile for the Q terminals. The received symbols can be expressed as:

Q

Ζ = + “o. Eq (1) where z_q is an F · T x 1 vector of modulation symbols transmitted by the q terminal in the F · T resource units on the tile, h_q is an F · T x 1 vector of complex channel gains for the F · T resource units in the tile for the q terminal, it is a scalar for a power deviation for the q terminal, y is an F · T x 1 vector of symbols received for the F · T resource units on the tile, there is an F · T x 1 noise and interference vector for the tile, and ° denotes a multiplication of elements by elements.

In equation (1), the first F elements of each vector correspond to F subcarriers in the first tile symbol period, the next F elements correspond to F subcarriers in the second symbol period, and so on, and the last F elements correspond to to F

13/35 subcarriers in the last symbol period. H_q contains complex channel gains of frequency domain for the q terminal, which can be considered as a complex Gaussian random variable with zero mean and a known covariance matrix. The channel gains can be considered as independent between the Q terminals. For the sake of simplicity, noise and interference cannot be considered additional white Gaussian noise (AWGN) with a mean zero vector and a covariance matrix equal to σ²Ι, where σ² is the variation of noise and interference and I is the identity matrix.

The base station can estimate the channel gains for each terminal in addition to noise and interference based on the received pilot symbols. The base station can perform the channel estimate based on a consideration that the statistical properties of the wireless channel for each terminal are known and that the channel gains through the tile for each terminal are correlated.

A covariance matrix for each terminal q, where q and {1, ..., Q}, can be approximated as follows:

Eq (2) / = 1 where Ui is the approximate eigenvector i for the channel for terminal q, λ

'• 9 is the eigenvalue i for the channel for terminal q,

And {} denotes an expectation operation, and ^H denotes a Hermitian or complex transposition.

Equation (2) is based on an observation that, for cases of practical interest, the covariance matrix of a terminal has a maximum of three significant eigenvalues ​​and can be approximated with three eigenvectors u, U2 and i₃. These three approximate eigenvectors have the dimension of F · T x

14/35 and can be used instead of the real eigenvectors for the channel estimate for the q terminal through the tile. Additionally, for cases of practical interest, the / 1 first eigenvalue is typically at least an order of magnitude greater than the other two eigenvalues ​​and

The three approximate eigenvectors can be expressed as:

Ü2 = flr, o ⁰ “F, i&gt; &amp; = Ura ® Ur.o»

Fxl vector,

Eq (3) ^ F (F²1) fir.0 "

FxJ vector,

T-x'1 veil,

T χ 1 vector, fira ₃ where j ι ^ ΐ -1) ® denotes a Kronecker product.

For a vector η χ 1 a_nxi = [ai, a₂, ...,at]^T and a vector m xOsl b_mxl= [bi&gt; b₂, ..., B_m]^T, Where ^T denotes a trásnspos-i³çâó-, the product Kronecker Cmnxi = a.nxi®bmxi can be supplied as:

^Thei Umxl ^Thei Umxl - [# ià » ^αϊ ^ 2&gt; ··· ' ^TheiPm&gt; ^β2^1»^β2^2» ·» ^β2 ^ »ι» ··· » ^The, J \ ' ^βη ^ 2 '- » ^flno]^Then - mxl.

£ mnxi is an mnxl vector containing the product of each element of a_nxi with each bmxi element.

In equation (3), u_F, o is a whole vector consisting of the number one, scaled by a constant to reach the unit power for u_F,₀. Uf, i θ a vector with values

15/35 from - (Fl) to (F — 1) in steps of 2, scaled by a constant to reach unit power for Uf, i- u_{F (1}varies linearly through F tile subcarriers. u_T, o is a whole vector consisting of the number one, scaled by a constant to reach the unit power for u_T, · Ut, i is a vector with values ​​from - (T — 1) to (Tl) in steps of 2, scaled by a constant to reach the unit power for u_T, i. Ut, i varies linearly through T tile symbol periods.

Ui is an F · T x 1 vector consisting of the number one, scaled by a constant to achieve a unit power for Ui. u₂ is an F · T x 1 vector containing T sequences of F elements in u_F, i, scaled by a constant to reach the unit power for u₂. u₃ is an F · T x 1 vector containing F repetitions of each of the T elements in u_T, i, scaled by a constant to reach the unit power for u₃. ui models the DC or average component. u₂ models the channel variation in frequency. u₃ models the variation of the channel over time.

The channel response of each terminal q through the tile can be modeled as a random function of frequency and time. This function can be approximated by the first three terms of the Taylor series expansion, as follows:

ôf (Λ / ο) + (t ~ ^fO)

Õt

ΟοΛ&gt;)

Eq (4)

In equation (4), the two-dimensional function (2D) is approximated with (i) a first term for the value of at the origin, or (ii) a second term for a linear function through frequency, or fo)_faith (iii) a third term for a linear function through the

16/35 time, or ^^{T &lt;q ίθ}\ The slopes S_{F&gt; q} and S_T,_q of linear functions across frequency and time are determined by the slope of £? (/ »*) with respect to frequency and time, respectively, at the origin.

Based on the channel model illustrated in equation (4), the channel response from terminal q can be expressed as:

Ã, («/&gt;«,) -^Theg + βρ „- (ⁿf-ⁿfo) + βτ, (ⁿ, - «rt»)&gt; Eq (5) where the_q is an average channel gain that corresponds to term 4_q(f_O4th)_f Federal Police,_q is the slope of the linear function through the frequency for the terminal q, β_{Τ (&lt;3} is the slope of the linear function over time for the terminal q, eh_q(n_f, n_t). it is a two-dimensional function for the channel response of the q terminal.

As illustrated in equation (5), the channel response of the q terminal through the tile can be characterized by the three complex parameters a_q, β_{Γί (ϊ}, and β_τ, ς · The center of the tile can be provided as (n_fo, n_to), where n_f0= (F + l) / 2 and nto⁼(T + 1) / 2. The channel response for a symbol with discrete coordinates (n_f, n_t) can be obtained as illustrated in equation (5).

A pilot pattern can include P total pilot symbols that can be arranged in four groups, with each group including M pilot symbols, so that P = 4M. The pilot symbols can be located in locations that are symmetrical around the tile, for example, as illustrated in figures 3a to 3d. If each terminal transmits a sequence of data on a space channel, then the number

17/35 of terminals that can share the tile is limited to M, or Q &lt;M.

The Q terminals can share a grouping, and each of the Q terminals can simultaneously transmit M pilot symbols in that grouping. Each terminal can encrypt or spread its M pilot symbols with an encryption string assigned to that terminal. The encryption strings for the Q terminals can be denoted as s_q, with q = 1,. . ., Q, and must be orthogonal to each other. Cryptographic strings can also be referred to as scattering strings, orthogonal strings, pilot strings, strings, etc. Encryption strings can have unit module elements and must be of length equal to M. In a drawing, M cryptographic strings are defined based on M columns of a Fourier matrix Μ χ M, with each cryptographic sequence containing M elements of a Fourier matrix column. The row element ne of column m of the Fourier matrix Μ χ M can be supplied as

-jlrtn-mPM ^and , with n = em = 0, ..., Ml. M encryption strings can also be defined in other ways. In any case, the Q encryption strings can be selected from the available M encryption strings. In a drawing, each terminal receives an encryption string and uses the same encryption string for all groupings on the tile. In another design, each terminal can use different encryption strings for different groupings on the tile.

The pilot symbols transmitted by the q terminal on the tile can be expressed as:

18/35

7ρ

Έχΐ

Eq (6) where ΐ4χΐ is a 4x1 vector all made up of number one, and laughs,_q is a Pxl vector of pilot symbols transmitted by the q terminal on the tile.

The first M elements of £ i,_q are for the pilot symbols sent in cluster 1 in the top left corner of the tile, the following M elements are for the pilot symbols sent in cluster 2 in the top right, the next M elements are for pilot symbols sent in cluster 3 in the corner bottom left and the last M elements are for the pilot symbols sent in cluster 4 in the bottom right corner. The pilot vectors laugh,_q for terminals 1 to Q they are orthonormal.

Figure 3a illustrates the pilot symbols transmitted to pilot pattern 310 with the encryption sequence s_q= [a, b, c]^T, where a, b and c are three elements in the encryption string and can have any complex values. The three elements a, bec in £_q are applied to three pilot symbols from left to right in each grouping on the tile.

Figure 3b illustrates the pilot symbols transmitted to pilot pattern 320 with the encryption string £_q= [a, b, c]^T. The three elements a, b and c in s_qare applied to the three pilot symbols from top to bottom in each grouping on the tile.

Figure 3c illustrates the pilot symbols transmitted to pilot pattern 330 with the encryption string s_q= [a, b, c, d]^T. The four elements a, b, c and d are applied to the four pilot symbols in a z pattern in each grouping on the tile.

Figure 3d illustrates the pilot symbols transmitted to pilot pattern 340 with the sequence of

19/35 encryption_q= [a, b, c]^T. The three elements a, b and c in s_q are applied to the three pilot symbols from left to right in each grouping on the tile.

A set of base vectors can be defined for each terminal q, as follows:

Eq (7)

<td></td><td>f</td><td></td><td>'-í</td><td></td><td>-f</td><td></td><td>í</td>

<td></td><td> 1</td><td></td><td> -1</td><td></td><td> 1</td><td></td><td> -1</td>

<td>V, =</td><td> 1</td><td>, v₂ =</td><td> 1</td><td>, V₃ =</td><td> -1</td><td>, y₄ =</td><td> -1</td>

<td></td><td> 1</td><td></td><td> 1</td><td></td><td> 1</td><td></td><td> 1</td>

Figure 4 illustrates the vectors v_x av₄. The four vectors vi av₄ they have different combinations of signals for the four groupings on the tile and represent different combination options for the pilot symbols received in the four groupings, as described below.

Each terminal q is associated with a set of four base vectors Pxl ri,_q, r₂,_q, r₃,_q er₄,_q. laughs,_q contains the transmitted pilot symbols, r₂,_q is generated with v₂ and is used to detect channel variation through frequency. r₃,_q is generated with v₃ and is used to detect channel variation over time. r₄,_q is generated with v₄ and can be used to estimate noise and interference.

If the number of degrees of freedom of the channels for the Q terminals sharing the tile is less than the total number of pilot symbols on the tile, then the pilot symbols not used to estimate the channel parameters can be used to estimate the noise and interference power on the tile. The observation space has P dimensions corresponding to the total P pilot symbols on the tile. In the drawing described above, the channel of each terminal

20/35 can be characterized by three parameters, and 3Q dimensions can be used to estimate the channel parameters for all Q terminals. The remaining P-3Q dimensions of the observation space can be used to estimate the noise and interference power.

Noise and interference can be estimated as the projection power of a signal received in dimensions not occupied by the pilot signals transmitted by the Q terminals. The received signal can be projected onto the base vectors for all available M encryption strings, as follows:

for / sEÍ,., ^ 4 is # = 1, .. ,, M

Bi (8) where x is a vector P x 1 with P pilot symbols received on the tile, and

Wi,_q is the result of the projection of the received vector x on the base vector r_{I Q}.

For each terminal q, equation (8) effectively spreads the M pilot symbols received without each cluster with an encryption sequence s_q for that terminal q. Equation (8) additionally accumulates the four scattered results for the four groupings in different ways for different base vectors. With reference to figure 4, to laugh,_q, the de-scattering results for the four clusters are added to obtain Wi,_q, which is indicative of an average channel gain for the q terminal. Stop₂,_q, the scatter results for the two upper clusters are subtracted from the scattered results for the two lower clusters to obtain w₂,_q, which is indicative of channel variation through frequency for terminal q. Stop₃,_q, the de-scattering results for the two left clusters are subtracted from the results

21/35 bottom right to obtain w, The noise power estimated as follows:

i (Q 4 M / = 1? = Q + 1 * 2 z where is the noise power and Na eauation (9). a scattered to the two right groupings to obtain w₃,_q, which is indicative of channel variation over time for terminal q. Stop₃,_q the scatter results for the upper right and lower left clusters are subtracted from the scattered results for the upper left and qq clusters and interference can be

Eq (9) /

estimated interference, first sum captures the projection power of x in r₄,_q, which is not used for channel estimation for any terminal. The first sum can be used as an estimate of noise and interference power, but it can include channel modeling error if the channel of each terminal does not vary linearly through the tile. The double sum captures the power of the projection of x in r_i,_q generated with the encryption strings not used by any of the Q terminals. The double sum is present if Q &lt;M.

A channel estimate can be derived for each terminal q based on the MMSE criteria, as follows:

H_? = E {h_? ) (E {x /})^-1 x,

Eq (10) li where - «is a vector F -Τ χ 1 for the channel estimate for

To the terminal q. - »is an estimate of h_q in equation (1).

Using the channel model illustrated in equation (2), the channel estimate for each terminal q can be expressed as:

22/35 oode A ^ ETi * f Í^F T (F²V Ρ I ' ^THE V 3P (F²-l) 1

Eq (ll)

IF TV:

3P

T- &amp;

v¹ θτ and θρ pilot on the tile identify the center of the groupings and are, therefore, dependent on the location of the pilot symbols on the tile. The center of the upper left cluster can be provided by | X + 1 + U &lt;2 2 / __{for example}pi_Of Q_F= i _if the pilot symbols are located in the topmost row of the tile, 0_F= 3 if the pilot symbols are located in the second uppermost row, etc.

In equation (11), the channel estimate - &lt;t for terminal q can be obtained based on a sum of the three weighted vectors, where ui, u₂ and U3 are defined in equation (3). The weight for u ± is determined by the parameter

Pi, eigenvalue Xi,_q, power deviation A²q, estimate of. * 2 noise and interference^σ , and result of Wi projection,_q. The eigenvalues ​​Xi,_q can be estimated in any way known to the art.

An estimated channel consideration is that used in deriving the channel from each terminal is constant for the M pilot symbols in each cluster. If the channel varies through M pilot symbols in each cluster, then the decryption / scattering may have residual errors that can degrade the channel estimate.

23/35

To observe the effects of defrost errors, equation (8) can be expanded as follows:

Δ „Ii ,, or,„ + n₀

Eq (12) = Δ, r (h, or_M) + r J Δ, h, ° r_{1&gt; Jt} + r I_O where - * is a vector Ρ χ 1 of the complex channel gains for terminal k for pilot symbols P, and - ° is a noise and interference vector P χ 1 for pilot symbols P. È * contains P elements in h_k for the pilot symbols P, and contains P elements in n₀ for the P pilot symbols.

As illustrated in equation (12), the result of the projection w_{i &lt;q} for terminal q includes a component of terminal q in addition to contributions from other terminals and noise. The contribution ni,_q,_k another terminal k in the result of the w projection_irq for terminal q can be expressed as:

Eq (13)

If the defrost is perfect, then n_{i &lt;q},_k= 0 for all other terminals, and no contribution from other terminals appears in the w projection result_{I Q} to terminal q. However, contributions from other terminals are non-zero when their channels vary through M pilot symbols in a cluster.

Based on the channel model in equation (5), the channel response of each k terminal can be expressed as:

Ε * «α * · (ϊ₁®ΐΜχΐ) + 2Α_?&gt;*·(«_/-η_{/ ο}) · (Ν₂01_Μχ,) + 2^-^ .

Eq (14)

24/35

For the pilot pattern illustrated in figure 3a, v_Tcan be provided as:

<td></td><td></td><td> '-7'</td><td></td><td></td>

<td></td><td></td><td> -5</td><td></td><td></td>

<td></td><td></td><td></td><td></td><td> -2</td>

<td>'í</td><td></td><td> -3</td><td rowspan="2">= 5v₃ ®l_Mxl + y, ®</td><td></td>

<td> 1</td><td></td><td> 3</td><td> 0</td>

<td></td><td></td><td></td><td></td><td> 2</td>

<td></td><td></td><td> 5</td><td></td><td></td>

<td></td><td></td><td> 7</td><td></td><td></td>

Eq (15)

<td></td><td> -2’</td><td>λ</td>

<td></td><td> 0</td><td>° s *</td>

<td></td><td> 2</td><td> /</td>

Combining equations (6) and (14), the term Vp · h * ° r_1? P_Od_{what if}r expressed as:

VP · ϊ * ° Γι_&gt;5* α₄+ + ’ ^ANDq (16)

P, = 5v₃®s, + and_t , θ * = Σι® £ *&gt;. Ê * = where

The contribution of terminal k can then be expressed as:

p = Pr (L ° r_{1&gt; it}) = a_k (vf Vj) (sJ s *) + 2/7_f&gt;* · (N_f - n_/0) · (Yy₂) (ss *) Eq (17) +²&amp;, k · («, -» zo) · (yf y₃) (s ^ sj + 2β_{τ k} · (Vf ® s) Θ *.

The encryption strings for the endpoints. Q are orthogonal, so that:

s? s, = J „. Eq (18)

Equation (18) indicates that the product dot de y_q with sr is equal to 1.0 when q = ke is equal to 0.0 otherwise.

The vi vi vectors₄ they are also orthogonal, so that:

Eq (19) vf Xk = 4th_ik .

Equation (17) can then be simplified as follows:

p · · (yf ® s?) θ * = 2Λλ · (yf y,) (s ej.

Eq (20)

25/35

Equation (20) indicates that for terminal q, the time variation in the channel of another terminal k introduces an error or ni orientation,_{q (k} in the result of the Wi projection,_q,_k for _s is 0 if k / 7 is the terminal q. This error is due to the fact that **

To mitigate the error contributions from other terminals, the encryption sequence for terminal q can be applied symmetrically around the center of the tile. For the pilot pattern illustrated in the figure_s*

3a, an inverted encryption string ~^q of length equal to 3 can be defined for terminal q, as follows:

Eq (21)

If pilot, then inverted to s, = [abc \^T each grouping includes M = 3 symbols the original encryption strings and the q terminal can be provided as:

'original encryption string, es | = [cZ&gt; a]^r reverse encryption string

Eq (22)

The original encryption sequence can be used for the two groupings to the left of the tile center, and the 'inverted encryption sequence can be used for the two groupings to the right of the tile center. The original and inverted encryption strings can also be considered as two versions of the same encryption string.

Figure 5a illustrates the use of original and inverted encryption strings for the pilot pattern illustrated in figure 3a. In this example, the elements a, b and c in the original encryption sequence s__q are applied to

26/35 three pilot symbols from left to right in each cluster to the left of the tile center. The c, b and b elements in the inverted encryption sequence -? are applied to the three pilot symbols from left to right in each grouping to the right of the tile center. The pilot symbols are symmetrical around the center of the tile. This pilot symmetry reduces the error in the channel estimate for terminal q.

Figure 5b illustrates the use of original and inverted encryption strings for the pilot pattern illustrated in figure 3b. In this example, elements a, b and c in the original encryption string s_q are applied to the three pilot symbols from top to bottom in each grouping above the center of the tile. The elements c, b and b in the inverted encryption sequence - «are applied to the three pilot symbols from top to bottom in each cluster below the center of the tile. The pilot symbols are symmetrical around the center of the tile.

Figure 5c illustrates the use of four versions of the encryption sequence for the pilot pattern illustrated in figure 3c. In this example, each grouping includes M = 4 pilot symbols, and four versions of the encryption string can be provided as:

s „- [fl6cí /], first version of the encryption string,

Eq. (23)

-«² \ P adc \, _ifg_unci_The encryption string version, s, 3 = [cdab]^T, third version of the encryption string, and

27/35 ^-?4 'fourth version of the encryption string.

Elements a, b, c and d in the first £ version_qare applied to four pilot symbols in a z pattern in the upper left cluster. The elements b, a, dec in the second version s_q2 are applied to the four pilot symbols in a z pattern in the upper right cluster. Elements c, d, a and b in the third version £ 3_q3 are applied to the four pilot symbols in a z pattern in the lower left cluster. The elements d, c, b, and a in the fourth version s ^_q4 are applied to the four pilot symbols in a z pattern in the lower right cluster. The pilot symbols are symmetrical around the center of the tile.

Figure 5d illustrates the use of original and inverted encryption strings for the pilot pattern illustrated in figure 3d. In this example, elements a, b, and c in the original encryption sequence £_q are applied to the three pilot symbols from left to right in each grouping to the left of the center of the tile. The elements c, b and b in the inverted encryption sequence are applied to the three pilot symbols from left to right in each grouping to the right of the center of the tile. The pilot symbols are symmetrical around the center of the tile.

Figures 5a to 5d illustrate four examples in which the multiple versions of the encryption sequence are used to obtain pilot symbols that are symmetrical with respect to the center of the tile. In general, any number of versions of the encryption sequence can be used to achieve symmetric pilot symbols, depending on how the groupings are defined. All versions of the encryption string

28/35 can have the same elements, but these elements can be arranged in different orders in different versions.

For the pilot pattern illustrated in figure 5a, using the original and inverted encryption sequences illustrated in equation (24), the base vectors ri,_q with i = 1, ..., 4 can be expressed as:

<td> 1</td><td>V</td><td> 1</td><td>1 Ml Ml 1 1 L</td><td> 1</td><td>1 1 IM | M ►o</td><td> 1</td><td>1 -s;</td>

<td> -¹·⁹ Vp</td><td> §4</td><td> ’ ^L2·⁹~ Vp</td><td></td><td> ’ ³”Vp</td><td></td><td> ’ ~⁴·⁹~ Vp</td><td></td>

<td></td><td>s¹</td><td></td><td>s*</td><td></td><td>L &lt;</td><td></td><td>I L</td>

Eq (24)

Channel estimation and noise and interference estimation for terminal q can be performed as described above, also with base vectors r_{I Q}being defined as shown in equation (24) instead of in equation (7). The contribution of another k terminal to the result of the Wi projection,_q,_k for terminal q can be expressed as:

η ,, ^ = ά (^ ° ^) = ά θ *,

Eq (25) where

<img file="BRPI0806279A2_D0003.tif" />

It can be illustrated that ni,_q,_k= 0 with i = 1, 2, and 4 due to the inversion of the encryption sequence. n₃,_q,_k may not be equal to 0 even with the inversion, which means that there may be an error affecting w₃,_q for the time-varying component of the channel. Nevertheless, the error introduced in the channel estimate is smaller with the inversion due to. multiplication by an MMSE ratio corresponding to the time variation component.

For the pilot pattern illustrated in figure 5d, the use of four versions of the encryption sequence

29/35 illustrated in equation (23), the base vectors r_{I Q} with i =

1, ..., 4 can be expressed as:

.Ι._?

<td> 1</td><td>V 5.2</td><td> 1</td><td> ’“5,' “5,2</td><td> 1</td><td> “5, 5,2</td><td> 1</td><td> 5, “5,2</td>

<td>⁼ Vp</td><td> 5,3</td><td> ’ -²* - Jv</td><td> 5,3</td><td> ’ “³* Vp</td><td> “5,3</td><td> ’ -⁴”- Vp</td><td> “5,3</td>

<td></td><td></td><td></td><td> 5,4.</td><td></td><td> . 5,4 _</td><td></td><td> . 5,4.</td>

. Eq (26)

The computer simulations illustrate that for the signal to noise and interference ratio (SINR), the floor of the channel estimation error can be reduced by approximately 2 dB for vehicular channels with the pilot pattern illustrated in figure 5a. This can improve the packet error rate and data performance.

For reasons of clarity, the techniques have been described for pilot transmission over the reverse link and for estimating channel and interference for terminals. The techniques can also be used for pilot transmission on the forward link and for channel estimation for a base station. In the forward link, different spatial channels or layers can receive different encryption strings. Processing for different layers on the forward link can be analogous to processing for different terminals on the reverse link.

Figure 6 illustrates a drawing of a process 600 performed by a transmitter to transmit a pilot to a receiver. Process 600 can be performed by a terminal to transmit the pilot on the reverse link to a base station. Process 600 can also be performed by a base station to transmit the pilot on the forward link to the terminals. The transmitter can therefore be a terminal or base station, and the receiver can be a base station or a terminal. The pilot symbols for a first grouping in a frequency and time block (or tile)

Different 30/35 can be generated based on a first sequence (block 612). The pilot symbols for a second grouping in the frequency and time block can be generated based on a second sequence (block 614). The pilot symbols for a third grouping in the frequency and time block can be generated based on the first sequence or a third sequence (block 616). The pilot symbols for a fourth grouping in the frequency and time block can be generated based on the second sequence or a fourth sequence (block 618). The pilot symbols can be transmitted in their respective groupings (block 620).

The first, second, third and fourth strings can include common elements arranged in orders and can be considered versions of a single sequence. For example, the elements in the second sequence can be in an inverted order with respect to the elements in the first sequence. Pilot symbols can be generated so that they are symmetrical around the center of the frequency and time block, for example, as illustrated in figures 5a to 5d. The pilot symbols in all groups can also be arranged in other ways, possibly in non-symmetrical ways. Each sequence can include M elements used to generate M pilot symbols for a grouping, where M can be three, four, etc. Each sequence can include elements in a column of a Fourier matrix or elements defined in other ways.

For the reverse link, the first sequence can be assigned to one terminal and can be orthogonal to at least one other sequence assigned to at least one other terminal sharing the first cluster. Similarly, the second, third and fourth strings can be assigned to the terminal. Each sequence

31/35 assigned to the terminal can be orthogonal to other sequences assigned to other terminals for the cluster in which that sequence is used. For the forward link, the first sequence can be assigned to a layer and can be orthogonal to at least one other sequence assigned to at least one other layer for the first grouping.

Figure 7 shows a drawing of an apparatus 700 for the pilot transmission. 0 apparatus 700 includes means for generating pilot symbols for a first grouping in a frequency and time block based on a first sequence (module 712), means for generating pilot symbols for a second grouping in the frequency and time block with based on a second sequence (module 714), means for generating pilot symbols for a third grouping in the frequency and time block based on the first sequence or a third sequence (module 716), means for the generation of pilot symbols for a fourth grouping in the frequency and time block based on the second sequence or a fourth sequence (module 718), and means for the transmission of pilot symbols in their respective groupings (module 720). The first, second, third and fourth strings can include common elements arranged in different orders. Modules 712 to 720 can comprise processors, electronic devices, hardware devices, electronic components, logic circuits, memories, etc. or any combination thereof. '

Figure 8 illustrates a drawing of a process 800 performed by a receiver to process the pilot received from one or more transmitters. Process 800 can be performed by a base station to process the pilot received on the reverse link from one or more terminals. O

32/35 process 800 can also be performed by a terminal to process the pilot received on the forward link from a base station to one or more layers, where each layer can be considered as a separate transmitter. The receiver can therefore be a base station or a terminal, and the transmitter can be a terminal or a base station. The received pilot symbols can be obtained from multiple groupings in a frequency and time block (block 812). Each of the multiple base vectors can be formed with multiple versions of a sequence assigned to a transmitter (block 814). The sequence can include M elements, and multiple versions of the sequence can correspond to different orderings of the M elements in the sequence. The multiple base vectors can be further formed based on a particular channel model, for example, a channel model with a time component that varies linearly and a frequency component that varies linearly, as illustrated in the equation (7). The received pilot symbols can be processed with multiple base vectors to obtain a channel estimate for the transmitter, for example, as illustrated in equations (8) and (11) (block 816). The received pilot symbols can also be processed with at least one other base vector to obtain an estimate of noise and interference, for example, as illustrated in equations (8) and (9) (block 818).

For block 814, each base vector can be formed based on an original version and an inverted version of the sequence, for example, as illustrated in equation (22). Alternatively, each base vector can be formed based on four versions of the sequence, for example, as illustrated in equation (23). In any case, the multiple versions of the sequence can be used to

33/35 generate the pilot symbols for the multiple groupings so that the pilot symbols are symmetrical around the center of the frequency and time block.

For block 816, multiple complex values ​​(for example, Wi,_q) can be obtained based on dot products of the received pilot symbols, with multiple base vectors, for example, as illustrated in equation (8). The multiple complex values ​​may comprise a first complex value indicative of an average channel gain for the frequency and time block, a second complex value indicative of channel variation across frequency, and a third complex value indicative of channel variation across time. The channel estimate for the transmitter can be derived based on multiple complex values, for example, as illustrated in equation (11).

Figure 9 illustrates a drawing of an apparatus 900 for processing the received pilot. Apparatus 900 includes means for obtaining pilot symbols received from multiple clusters in a frequency and time block (module 912), means for forming each of the multiple base vectors with multiple versions of a sequence designated for a transmitter (module 914), means for processing pilot symbols received with multiple base vectors to obtain a channel estimate for the transmitter (module 916), and means for processing the pilot symbols received with at least one gold base vector to obtain an interference noise estimate (module 918). The multiple versions of the sequence can correspond to different ordering of the elements in the understanding of sequence devices. 912 modules, hardware devices, 918 components can electronics, electronics,

34/35 logic circuits, memories, etc. or any combination thereof.

The techniques described here can be microcontrollers, electronics, others implemented by various means. For example, techniques can be implemented in hardware, firmware, software or a combination of them. For a hardware implementation, the processing units in an entity (for example, a terminal or a base station) can be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable port sets (FPGAs), processors, controllers, microprocessors, devices electronic units designed to perform the functions described here, a computer, or a combination of them.

For a firmware and / or software implementation, the techniques can be implemented with modules (for example, procedures, functions, etc.) that perform the functions described here. Firmware and / or software instructions can be stored in memory (for example, 142x, 142y, or 182 in Figure 1) and executed by a processor (for example, the 140x, 140y or

180). The memory can be implemented inside the processor or outside the processor. Firmware and / or software instructions can also be stored in another processor-readable medium such as random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), read memory programmable only (PROM), electrically erasable PROM (EEPROM),

35/35 FLASH memory, compact disc (CD), magnetic or optical data storage device, etc.

The previous description of the description is provided to allow anyone skilled in the art to create or make use of the description. Various modifications to the description will be readily apparent to those skilled in the art, and the generic principles defined here can be applied to other variations without departing from the spirit or scope of the description. Accordingly, the description should not be limited to the examples described here, but the broader scope consistent with the principles and novelty features described here should be agreed.