WO2012159410A1

WO2012159410A1 - Method and apparatus for beamforming

Info

Publication number: WO2012159410A1
Application number: PCT/CN2011/081054
Authority: WO
Inventors: 杨芸霞
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-05-26
Filing date: 2011-10-20
Publication date: 2012-11-29
Also published as: CN102801454A; CN102801454B

Abstract

Disclosed are a method and apparatus for beamforming. The method comprises: acquiring a channel response of a Sounding signal in-bandwidth frequency point; using the correlation between the Sounding signal in-bandwidth frequency point and the frequency point where the downlink data are located to determine a weight value for the channel response of the Sounding signal in-bandwidth frequency point to interpolate; using the interpolated weight value to determine a weight for beamforming, and using the weight for beamforming to perform beamforming of the uplink data. The present invention enables the accuracy rate of beamforming to be improved.

Description

TECHNICAL FIELD The present invention relates to the field of communications, and in particular to a beamforming method and apparatus. BACKGROUND OF THE INVENTION Wireless channels introduce what is known as fading due to electromagnetic wave multipath reflection and scattering effects. The effect of channel fading on communication quality is manifested by an increase in the probability of signal detection errors at the receiving end. In order to combat fading, techniques such as channel coding and interleaving are widely used in wireless communication to reduce the error probability of receiver signal detection. At the same time, multi-antenna technology using Multiple Input Multiple Output (SIMO) or Multiple Input Single Output (MISO), combined with spatial diversity and channel coding, can also effectively resist the channel. Decline. Beamforming is a downlink multi-antenna transmit diversity (Transmit Diversity) MISO technology based on the adaptive antenna principle. It combines the advantages of adaptive antenna technology. By using the antenna array to control the convergence and pointing of the beam, it can adaptively adjust its pattern to track the change of the terminal signal. Beamforming is characterized by improved performance in terms of antenna coverage, system capacity, spectrum utilization, and service quality at a lower cost. It is incomparable in eliminating interference, expanding cell coverage radius, reducing system cost, and increasing system capacity. The superiority. The channel Sounding is a mechanism for the terminal to send a sounding signal to the base station, and the terminal sends a Channel Sounding waveform to the base station. Through the channel reciprocity of Time Division Duplex (TDD) system, the base station can know the channel response of the base station side to the terminal side channel. This mechanism enables the base station to know the quality of the channel response within the bandwidth of the Sounding signal in the OFDMA system. The base station can select the frequency band with good channel quality as the communication band according to the quality of the channel response in the bandwidth of the sounding signal of different terminals. This mechanism enables the base station to measure the upstream channel response. When the transmitting and receiving hardware is just calibrated, the base station can estimate the downlink channel response based on the measured upstream channel response. The Sounding technology that provides channel response information (or channel state information CSI) from the SS to the BS combines with the Beamforming technology to obtain the Beamforming shaping weight and greatly improve the wireless link performance of the Beamforming technology. The following describes the principle of Beamforming: Let M be the number of transmitter transmit antennas in the MISO system. The receiver's receive signal can be expressed as:

M

y = _J h _j x _j +n

(1) where is the channel fading of the transmitting antenna j to the receiving antenna, and ^ is the symbol transmitted by the antenna j. Under the assumption that the channel of each transmitting antenna to the receiving antenna is fading independent, the transmitting signal on each transmitting antenna is: xw j = 1, 2, ···,

(2)

(3) The above limitation is to ensure that the total transmitted power at the time of multi-antenna transmission is not increased. Substituting equation (2) into equation (1),

Μ You can get ^ (4) From the above equation, the SNR under the channel condition is:

By the above formula,

Get the maximum SNR, set (6)

Then the maximum value of SNR is:

(7) According to the same derivation of the MRC, the error probability of the receiver at this time can be obtained as:

SNR

1 +

(8) Using the best weight in equation (6) to weight each transmit antenna modulation symbol as shown in (2) is Transmit Beamforming, which is also the Maximum Rate Transmit (MRT). However, the channel state information (Channel State Information (CSI) must be clarified for the transmit beamforming. For the TDD system, the Sounding technology can be used to obtain the CSI. The Sounding, that is, the UL Channel Sounding, utilizes the TDD system for uplink and downlink channel reciprocity. A means for providing channel response information (or channel state information CSI) to a base station by a terminal, and is mainly applied to a TDD system. The combination of Sounding and Beamforming in Fig. 1 will be described below. Taking the combination of Sounding and Beamforming in the IEEE 802.16e protocol as an example: The process includes the following steps: Step 1: The BS allocates a Sounding Zone resource to the uplink subframe through the PAPR/Safety_Zone/Sounding_Zone_IE of the UL-MAP; Step 2: The BS passes the UL- MAP's UL_Sounding_Command_IE specifies the Sounding implementation for each Sounding symbol in the Sounding Zone and the SS in each Soundng symbol; Step 3: SS in the uplink subframe according to UL-MAP's PAPR/Safety_Zone/Sounding_Zone_IE and UL Sounding Command lE Corresponding to the resource location corresponding to the Sounding signal of the mode; Step 4: The BS receives the UL Sounding signal, acquires uplink channel response information (or channel state information CSI) according to the user Sounding signal, and utilizes the uplink and downlink channel reciprocity of the TDD system according to the Sounding signal. The channel response estimation is performed, the Beamforming weight is calculated, and the downlink data of the user is Beamforming. In the related art, in the data transmission process combining sounding and Beamforming, since the frequency band occupied by the sounding signal and the downlink transmission data are inconsistent, the shaping weight of Beamforming is inaccurate, and the performance of uplink Beamforming is relatively poor. SUMMARY OF THE INVENTION A main object of the present invention is to provide a beamforming method and apparatus for solving at least the above-mentioned related art in the process of combining sounding and Beamforming data transmission, because the frequency band occupied by the sounding signal band and the downlink transmission data is inconsistent, The shaping weight of Beamforming is inaccurate, which leads to poor performance of downlink Beamforming. According to an aspect of the present invention, a beamforming method is provided, including: acquiring a channel response of a frequency point within a bandwidth of a Sounding signal; and using a correspondence between a frequency point of the Sounding signal bandwidth and a frequency point of the downlink data Determining the weight of the channel response of the frequency band of the Sounding signal to perform interpolation processing; determining the weight of the beamforming using the weight of the interpolation process, and beamforming the uplink data using the weight of the beamforming. Preferably, determining a weight of the Sounding signal bandwidth processing by using a correspondence between a frequency point of the Sounding signal bandwidth and a frequency point of the downlink data includes: determining a weight of the interpolation process by using the following formula:

, where is the channel response correlation matrix of the frequency band of the _Sound i _n g signal and the frequency point of the downlink data, ^Rpp is the correlation matrix between the frequency points of the Sounding signal bandwidth, which is noise, is a Sounding signal sequence, ^^ is A non-singular matrix of sounding signal sequence matrices. Preferably, acquiring the channel frequency of the Sounding signal bandwidth response comprises: using the following formula to determine the channel frequency in the Sounding signal bandwidth in response ^ ^: ^&, wherein R is a base station signal received by the terminal Sounding frequency emitted, S It is the terminal transmitting waveform. Preferably, determining the weight of the beamforming using the weight of the interpolation process comprises: determining the weight of the beamforming using the following formula: ^^ where is the channel response of the frequency within the Sounding signal bandwidth. Preferably, the interpolation process is a minimum mean square error (MMSE) interpolation process. According to another aspect of the present invention, a beamforming apparatus is provided, comprising: an obtaining module configured to acquire a channel response of a frequency point of a Sounding signal bandwidth; and a processing module configured to use a Sounding signal bandwidth inner frequency point and downlink data The correspondence between the frequency points determines the weight of the channel response of the frequency band of the Sounding signal to perform interpolation processing; the determining module is configured to determine the weight of the beamforming using the weight of the interpolation process; the beamforming module is set to use The weight of the beamforming beamforms the uplink data. Preferably, the processing module is arranged to determine the weight of the interpolation process using the following formula:

^W= ^ ^ ^y) where ^R h _P is the channel response correlation matrix of the frequency band of the Sounding signal bandwidth and the frequency point of the downlink data, which is the correlation matrix between the frequency points of the Sounding signal bandwidth, which is noise, and X is Sounding The signal sequence, ^^ is a nonsingular matrix of the Sounding signal sequence matrix. Preferably, the acquisition module is configured to determine a channel response of the frequency within the bandwidth of the Sounding signal using the following formula, H

H . ^b ~S , where R is the signal transmitted by the terminal received by the base station at the Sounding frequency, and S is the terminal transmitting waveform. Preferably, the beamforming module is arranged to determine the weight of the beamforming = ^fa using the following formula, where is the channel response of the frequency within the Sounding signal bandwidth. Preferably, the interpolation process is a minimum mean square error (MMSE) interpolation process. According to the present invention, the weight of the channel response of the frequency band of the Sounding signal bandwidth is determined according to the correspondence between the frequency point of the Sounding signal bandwidth and the frequency point of the downlink data, and the weight of the beam shaping weight is determined by using the weight. The beamforming of the uplink data solves the problem that the frequency band occupied by the sounding signal band and the downlink transmission data is inconsistent in the related art, and the shaping weight of the Beamforming is inaccurate, and the performance of the uplink Beamforming performance is relatively poor, thereby achieving an improvement. The effect of upstream data Beamforming performance. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are set to illustrate,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, In the drawings: FIG. 1 is a schematic diagram of sounding combined with Beamforming according to the related art; FIG. 2 is a flowchart of a beamforming method according to an embodiment of the present invention; and FIG. 3 is a beam shaping device according to an embodiment of the present invention. Block diagram of the structure. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. This embodiment provides a beamforming method. FIG. 2 is a flowchart of a method for beamforming according to an embodiment of the present invention. As shown in FIG. 2, the method includes: Step S202: Acquire a frequency bandwidth of a Sounding signal bandwidth Channel response Step S204: determining, by using a correspondence between a frequency point of the Sounding signal bandwidth and a frequency point of the downlink data, determining a weight of the channel response of the frequency band of the Sounding signal to perform interpolation processing; Step S206: determining a beamforming using the weight of the interpolation process Weights, and beamforming of the uplink data using the weight of the beamforming. Through the above steps, the channel response of the frequency band of the Sounding signal bandwidth is first obtained, and then the weight of the internal frequency point of the Sounding signal bandwidth and the frequency point of the downlink data is used to determine the weight of the channel response of the frequency band of the Sounding signal bandwidth. The weight is used to determine the weight of the beamforming, and the uplink data is beamformed. The problem that the shaping of the sounding signal band and the downlink transmission data is inconsistent in the related art, the inaccurate weighting of the Beamforming, and the poor performance of the uplink Beamforming performance are overcome, thereby improving the performance of the uplink data performance. Preferably, the weighting of the frequency response point of the Sounding signal bandwidth and the frequency point of the downlink data may be determined in different manners to determine the weight of the channel response of the frequency band of the Sounding signal bandwidth for interpolation, as long as the Sounding prefers the bandwidth internal frequency point. The difference from the frequency point of the downlink signal is reflected in the channel response of the frequency band within the Sounding signal bandwidth, which can overcome the problem that the frequency band of the sounding signal is inconsistent with the frequency band occupied by the downlink transmission data, resulting in inaccurate weighting of Beamforming. A preferred embodiment is provided in this embodiment: The weight of the interpolation process is determined by the following formula: ^w = ^R _hP ( ^R _PP + ^ ( ^xxH y ^l y ^l , where ^R _hP is

The channel response correlation matrix of the frequency band of the Sounding signal and the frequency of the downlink data is the correlation matrix between the frequency points of the Sounding signal bandwidth, which is noise, which is the Sounding signal sequence, and X ^H is the non-singular matrix of the Sounding signal sequence matrix. . With the preferred embodiment, the accuracy of the interpolation process weight determination is improved. Preferably, a preferred embodiment of step S202 is described below. A channel frequency response of the signal bandwidth Sounding ^& determined by the following equation, wherein R is a base station signal received at the terminal Sounding emission frequency, S is the transmitted waveform terminal. With the preferred embodiment, the channel response of the internal frequency point of the Sounding signal bandwidth is determined by the prior art, which reduces the development cost. Preferably, the following uses the weights of the interpolation process in step S206 to determine the weight of the beamforming. There may be various implementations. Only one of the preferred embodiments will be described below, and the weight of the beamforming is determined using the following formula. = , where is the channel response of the internal frequency point of the Sounding signal bandwidth. With the preferred embodiment, the channel estimation of the frequency-internal frequency point signal of the Sounding signal is interpolated, so that the accurate beamforming weight is obtained when the sounding signal band is different from the frequency band of the downlink data, and the beam is improved. The accuracy of the weighting of the weight. Preferably, the interpolation process is a minimum mean square error (MMSE) interpolation process. With the preferred embodiment, the interpolation process is performed in the manner of the prior art, which reduces the development cost, and the MMSE mode can improve the accuracy of the interpolation. The present embodiment provides a beamforming device, which can be used to implement the beamforming method described above. FIG. 3 is a structural block diagram of a beamforming device according to an embodiment of the present invention. As shown in FIG. 3, the device includes: The acquisition module 32, the processing module 34, the determination module 36, and the beam shaping module 38 are described in detail below. The obtaining module 32 is configured to obtain a channel response of the intra-frequency point of the Sounding signal bandwidth. The processing module 34 is connected to the obtaining module 32, and is configured to determine, by using the corresponding relationship between the frequency-internal frequency point of the Sounding signal and the frequency point of the downlink data, the obtaining module 32 obtains The channel response of the frequency band of the Sounding signal to the interpolation process is performed; the determining module 36 is connected to the processing module 34, and is configured to determine the weight of the beamforming using the weight of the interpolation process processed by the processing module 34; The beamforming module 38, coupled to the determining module 36, is configured to beamform the uplink data using the weight of the beamforming determined by the determining module 36. Preferably, the processing module 34 is set using the following formula to determine the interpolation _{_{weights: W = R hp (R pp}} + a n 2 (XX H r 1) - 1 ^ wherein, R _hp within _Soundin g signal bandwidth frequency The channel response correlation matrix with the frequency point of the downlink data is the correlation matrix between the frequency points of the Sounding signal bandwidth, which is noise, which is a Sounding signal sequence, and ^^ is a non-singular matrix of the Sounding signal sequence matrix. Preferably, the acquisition module 32 is set to determine the channel of the internal frequency point of the Sounding signal bandwidth using the following formula, H

The response is ^ls ~S, where R is a signal transmitted by the terminal received by the base station at the Sounding frequency point, and S is a terminal transmitting waveform. Preferably, the beamforming module 38 is arranged to determine the weight of the beamforming = the volume using the following formula, where is the channel response of the frequency within the Sounding signal bandwidth. Preferably, the interpolation process is a minimum mean square error MMSE interpolation process. The following describes a preferred embodiment of the present invention. The preferred embodiment provides a beamforming method. The preferred embodiment combines the foregoing embodiments with preferred embodiments thereof. In this embodiment, a minimum mean square error (Minimum) is used. Mean Square Error, referred to as MMSE) filtering the Sounding signal channel estimation response interpolation to obtain the MRT shaping weight of the Beamforming, the method comprising the following steps: Step 1: Acquiring the channel response estimate of the frequency point of the terminal within the Sounding signal bandwidth by using the LS channel estimation, where R is the signal transmitted by the base station at the Sounding frequency, S is the terminal transmitting waveform _t Step 2: Solving the correlation matrix, Step 2 includes the following

A. Derivation of frequency domain correlation coefficients Assuming that multipath power attenuation obeys a negative exponential distribution, the power delay distribution can be approximated by the equation (9):

— exp( ) 0<τ

0 0>τ

(9) Where is the mean square delay. By performing Fourier transform on W, the channel frequency domain correlation function can be obtained:

1 T

3⁄4(Δ )=— I exp(—1)Qxp(-j2nAf )d

(10) By arranging the above results, you can get:

1

R _H (¥)

1 + j2 Af σ.

(11)

R _H (M) =

Then the correlation coefficient of the Δ/frequency points is: 1 + 2πΔ/σ^ (12) where, the above is the frequency interval of adjacent frequency points.

Β, Frequency Domain Correlation Coefficient Estimation The channel response of the terminal within the frequency of the Sounding signal bandwidth can be obtained by LS channel estimation. Using the values obtained from these estimates, the channel frequency domain correlation coefficient can be calculated by: R _H (M) = E _tk {H _t (k)H _t (k + M)}

(13) where ^ is the average for each frequency point of each OFDMA symbol. Taking the 802.16e Sounding signal (signal waveform 1) as an example, the results of the LS channel estimation can be expressed as follows:

H(k) = H(k) + N(k) ₍₁₄₎ where, (for the estimated channel response, the true channel response is noise. The channel response and noise are independent of each other, then (6) The resulting channel frequency domain correlation coefficient can be expressed as:

R _H (M) = R _H (M) + R _Z (M) _{( 15)} where ( ^Δ ) is the channel frequency domain correlation coefficient obtained by LS channel estimation, ( ^{Δ /} ) is the true channel frequency domain correlation coefficient , ^{(Δ /)} as the correlation coefficient between the noise. If the noise estimated by the different carrier channels is uncorrelated, then ( ^Δ/ ) can be obtained as a function. Therefore _{, the} formula ( ₁₃₎ can be expressed as follows:

R _H m = \ 1 ^R R ^H( °A ⁾ / ⁺ ) ° ² . Δ ^Δ / ^/ ≠ ⁼ 0 ° _{( 16)} where ^σ2 is the system receiver noise. C. Frequency domain correlation coefficient calculation The mean square delay can be obtained according to the relationship between (12) and (16). According to the formula (12), the correlation coefficient between any two frequency points can be obtained. Step 3: According to (2), obtain the correlation matrix needed for solving in (1), and use (1) to perform MMSE interpolation to obtain the shaping weight of Beamforming of the downlink non-Sounding frequency. In this embodiment, the weight of the beamforming is determined using the following formula:

, H _b is the _LS channel estimation in the terminal obtained Sounding signal bandwidth frequency channel response. The downlink non-Sounding frequency used by the terminal and a sounding of the terminal The channel response correlation matrix between the frequency points is the correlation matrix between the Sounding frequency point and the Sounding frequency point. For noise, for the Sounding sequence sent. It should be noted that the processing in step 3 is based on the MMSE criterion. The preferred embodiment overcomes the fact that in the actual system, the frequency band of the Sounding signal band and the downlink transmission data occupied by the terminal in the OFDMA system may be inconsistent, then the MRT weighting weight of Beamforming is performed according to the Sounding signal. It is necessary to perform interpolation according to the channel response estimation of the frequency signal of the Sounding signal bandwidth. In this embodiment, an MMSE filter is added to perform interpolation, which can improve the interpolation fitting degree and obtain a more accurate MRT shaping. Weights to improve system downstream Beamforming performance. According to the foregoing embodiment, a beamforming method and device are provided. The weighting of the channel response of the inner frequency point of the Sounding signal bandwidth is determined according to the correspondence between the inner frequency point of the sounding signal bandwidth and the frequency point of the downlink data. The weight is used to determine the beamforming weight, and the uplink data is beamformed, which solves the limitation that the terminal sounding bandwidth must be consistent with the downlink transmission bandwidth when using the MMT's Beamforming downlink transmission, and the full frequency band can be realized. The point channel response estimation, at the same time, improves the interpolation fitting accuracy compared with the currently used linear interpolation, and greatly improves the performance of the MRT Beamforming downlink transmission technology. Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general-purpose computing device, which can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device so that they may be stored in the storage device by the computing device, or they may be separately fabricated into individual integrated circuit modules, or Multiple modules or steps are made into a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software. The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Claim

A beamforming method, comprising:

Obtaining the channel response of the intra-frequency point of the Sounding signal bandwidth;

Determining, by using a correspondence between a frequency point of the sounding signal bandwidth and a frequency point of the downlink data, a weight of the channel response of the inner frequency point of the sounding signal to perform interpolation processing;

The weight of the interpolation process is used to determine the weight of the beamforming, and the weight of the beamforming is used to beamform the uplink data.

The method according to claim 1, wherein determining, by using a correspondence between a frequency point of the sounding signal bandwidth and a frequency point of the downlink data, determining a channel response of the frequency channel of the Sounding signal bandwidth, and performing interpolation processing includes: : determining, by using the following formula, the weight of the interpolation process, W = R _hp (R _pp + a _n ² (XX ^H yY, where R^ is the frequency of the sounding signal bandwidth and the frequency of the downlink data) in response to the channel correlation matrix, R ^ is a correlation matrix between the Sounding signal bandwidth frequency, σ ^"2 is the noise, the signal sequence for the Sounding, X ^H is a nonsingular matrix Sounding signal sequence matrix.

3. The method according to claim 1, wherein obtaining a channel response of a frequency point within a bandwidth of the Sounding signal comprises: determining a channel response A _fa : k ~S of a frequency point within a bandwidth of the Sounding signal using the following formula, where R is a base station receiving The signal that the terminal is transmitting at the Sounding frequency, and S is the terminal transmitting waveform.

The method according to claim 2 or 3, wherein determining the weight of the beamforming using the weight of the interpolation process comprises: determining a weight of the beamforming _∞ = ^ using the following formula, wherein A _fa is The channel response of the inner frequency point of the Sounding signal bandwidth.

The method according to any one of claims 1 to 3, wherein the interpolation processing is a minimum mean square error MMSE interpolation process.

6. A beam shaping device comprising: Obtaining a module, configured to obtain a channel response of an internal frequency point of the Sounding signal bandwidth;

The processing module is configured to determine, by using a correspondence between the intra-frequency point of the sounding signal bandwidth and the frequency point of the downlink data, the weight of the channel response of the inner frequency point of the sounding signal to perform interpolation processing;

a determining module, configured to determine a weight of the beamforming using the weight of the interpolation process; and a beamforming module configured to beamform the uplink data using the weight of the beamforming. The apparatus according to claim 6, wherein said processing module is configured to determine a weight of said interpolation process using the following formula _: W = R _hp (R _pp + a _n ² (XX ^H yY , where R is The channel response correlation matrix of the frequency band of the Sounding signal and the frequency point of the downlink data, ^R pp is the correlation matrix between the frequency bands of the Sounding signal bandwidth, σ „ ² is noise, is a Sounding signal sequence, and X ^H is A non-singular matrix of a sounding signal sequence matrix. The apparatus according to claim 6, wherein the acquisition module is configured to determine using the following formula

The channel response of the inner frequency point of the sounding signal bandwidth is ^ : ^k , where R is the signal transmitted by the terminal received by the base station at the Sounding frequency point, and S is the terminal transmitting waveform. The apparatus according to claim 7 or 8, wherein the beamforming module is arranged to determine a weight of the beamforming _∞ = ^ using the following formula, wherein A _fa is a channel response of a frequency point within the bandwidth of the Sounding signal. The apparatus according to any one of claims 6 to 8, wherein the interpolation processing is a minimum mean square error MMSE interpolation processing.