KR101298136B1 - Apparatus and method for beamforming in multiple antenna systems - Google Patents

Abstract

The present invention relates to a beam forming apparatus and method in a multi-antenna system, comprising: estimating channel information of each channel estimation section by dividing an entire band into a predetermined number of channel estimation sections, and The method may include obtaining a channel change amount, and generating a beam coefficient by generating a beam coefficient using the channel information of each channel estimation interval and the channel change amount, and obtaining channel information of a downlink resource allocation band. In addition, there is an advantage in that the link performance of the multi-antenna system can be improved by adaptively forming a beam according to a change of a channel.

Multiple Antenna, Resource Allocation Method, Channel Estimation, Beamforming

Description

Apparatus and method for beamforming in a multi-antenna system {APPARATUS AND METHOD FOR BEAMFORMING IN MULTIPLE ANTENNA SYSTEMS}

1 is a diagram illustrating a PUSC resource allocation unit in a multiple antenna system according to the prior art;

2 is a diagram illustrating a procedure for estimating a channel in a multi-antenna system according to an embodiment of the present invention;

3 illustrates a channel estimation table in a multi-antenna system according to the present invention;

4 is a diagram illustrating a procedure for forming a beam in a multiple antenna system according to an embodiment of the present invention;

5 is a block diagram of a transmitter in a multi-antenna system according to the present invention; and

6 is a diagram illustrating a performance change graph according to an exemplary embodiment of the present invention.

The present invention relates to a beamforming apparatus and method in a multi-antenna system, and more particularly, to an apparatus and method for forming a beam when uplink / downlink resource allocation schemes are different in the multi-antenna system.

Due to the rapid growth of the wireless mobile communication market, various multimedia services are required in a wireless environment. In order to provide the multimedia service, research on a multi-antenna system (for example, MIMO (Multiple Input Multiple Output)) capable of efficiently using a limited frequency is being conducted as the capacity of transmission data and the speed of data transmission are increased.

The multi-antenna system can increase transmission reliability and transmission rate compared to a single antenna system without additional frequency or transmission power allocation.

The multi-antenna system uses a smart antenna to maximize the efficiency of limited radio resources. The smart antenna emits a directional beam only to a specific user without forming a radiation beam in all directions to efficiently use the radio resource. That is, the smart antenna is a beam shaping system that provides a function of a spatial filter that can increase or remove a signal in a desired direction by adjusting a beam coefficient of an array antenna.

An adaptive antenna system, which is a representative technology of the smart antenna technology, is a system for adaptively forming a beam pattern in a wireless channel environment. That is, the adaptive antenna system continuously detects the cell service area and adaptively forms a beam pattern according to a change in the radio channel environment. For example, in the case of a multi-antenna system of time division duplex orthogonal frequency division multiplex access, a forward beam coefficient is calculated by estimating reverse channel information corresponding to the same frequency tone. do. Thereafter, the time-division duplex multiple antenna system forms a downlink beam using channel information of the uplink signal.

As described above, in order to adaptively form a beam in a wireless channel environment in a multi-antenna system using the time division duplex scheme, an uplink channel is estimated to form a downlink beam. However, when the uplink / downlink subchannel allocation scheme is different in the multi-antenna system, it is difficult to identify channel information of an allocated band for transmitting the downlink signal using the uplink. Furthermore, when the multi-antenna system uses a diversity scheme, since uplink subchannels are irregularly allocated, it is difficult to identify channel information of an allocated band for transmitting the downlink signal using the uplink.

Thus, the multi-antenna system is unable to adaptively form a beam in a radio channel environment. For example, a PUSC (Patial Usage of SubChannel) subchannel allocation scheme, which is a diversity scheme in an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system, is a subchannel allocation scheme of uplink / downlink as shown in FIG. This appears different.

1 illustrates a PUSC resource allocation unit in a multiple antenna system according to the prior art.

As shown in FIG. 1, when the PUSC subchannel allocation scheme is used, FIG. 1A illustrates an uplink subchannel allocation scheme and FIG. 1B illustrates a downlink subchannel allocation scheme. Indicates the allocation method.

As shown in (a) of FIG. 1, the IEEE 802.16 system allocates a subchannel in a tile structure to uplink. The tile consists of 4x3 subcarriers on the frequency-time axis. Here, the tile transmits pilot symbols to four subcarriers corresponding to the corners of the 4x3 subcarriers and transmits data to the remaining eight subcarriers.

As shown in (b) of FIG. 1, the IEEE 802.16 system allocates resources in a cluster structure to downlink. The cluster consists of 14x2 subcarriers on the frequency-time axis.

As described above, if the uplink / downlink subchannel allocation scheme is different in the time-division duplex multiple antenna system, it is difficult to identify the channel information of the downlink allocation band as the uplink beam adaptively to a wireless channel environment. There is a problem that can not form.

Accordingly, an object of the present invention is to provide an apparatus and method for estimating a channel of an allocated band for transmitting a downlink signal when a resource allocation scheme of uplink / downlink is different in a multi-antenna system.

Another object of the present invention is to provide an apparatus and method for forming a beam when resource allocation schemes of uplink and downlink are different in a multi-antenna system.

It is still another object of the present invention to provide an apparatus and method for adaptively forming a beam in response to a channel change in a multi-antenna system.

According to the first aspect of the present invention for achieving the above object, the beamforming method in a multi-antenna system, the channel information of each channel estimation interval is divided by dividing the entire band into a predetermined number of channel estimation intervals from the signal received from the receiver And estimating a channel change amount of the receiver, and generating a beam coefficient by using the channel information of the channel estimation interval and the channel change amount.

According to a second aspect of the present invention, a beamforming apparatus of a multi-antenna system includes a channel estimator for estimating channel information of each channel estimation interval by dividing a whole band into a predetermined number of channel estimation intervals, And a beam coefficient generator for generating a beam coefficient using the channel information and the channel variation amount of the receiver, and a beam former for forming a beam to the receiver using the beam coefficient.

According to a third aspect of the present invention, a method for estimating a downlink channel using an uplink signal in a time division duplex wireless communication system having different uplink / downlink resource allocation schemes includes: Dividing an entire band of an uplink signal into a predetermined number of channel estimation intervals, checking resource allocation information of each channel estimation interval, and estimating channel information of each channel estimation interval using the resource allocation information Characterized in that it comprises a process.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Hereinafter, the present invention describes a technique for forming a beam when the resource allocation scheme of uplink / downlink in a multiple antenna system is different.

In the following description, a multiple antenna system of Time Division Duplex and Orthogonal Frequency Division Multiple Access is described as an example.

When the resource allocation scheme of uplink / downlink is different in the multi-antenna system, as shown in FIG. 2, allocation for transmitting the downlink signal using the uplink channel information spread over the entire band is allocated. Obtain channel information of the band. The following description will exemplify a PUSC (Patial Usage of SubChannel) subchannel allocation scheme in which the resource allocation scheme of the uplink / downlink is different. Accordingly, the uplink is allocated a subchannel having a tile structure as shown in (a) of FIG. 1, and the downlink has a subchannel having a cluster structure as shown in (b) of FIG. 1. Assigned.

2 illustrates a procedure for estimating a channel in a multi-antenna system according to an exemplary embodiment of the present invention.

Referring to FIG. 2, first, the transmitter divides the entire uplink band into N channel estimation intervals in step 201. In this case, the number N of the channel estimation intervals has the same value as the divisor of the total number of clusters constituting the downlink full band (the total number of clusters% N = 0). For example, as shown in FIG. 3, when the PUCS symbol length is 12 and the allocated subchannel is 8, the uplink PUSC band including 210 tiles is divided into 30 channel estimation intervals. Here, one slot is composed of three symbols. Thus, the 12 PUSC symbols represent 4 slots.

After dividing the entire band into the channel estimation interval, the transmitter proceeds to step 203 and determines whether there is a tile allocated for each tile index during the uplink allocation slot. For example, as shown in FIG. 3, it is checked whether resources of a user for forming the beam are allocated for each tile index during 4 slots. Here, when a plurality of tiles are allocated to one tile index, only the first one of the tiles is used as channel information of the tile index. In another embodiment, an average of a plurality of tiles included in the tile index is used as channel information of the tile index. The channel information of the tile index is estimated using the pilot subcarriers included in the resource allocated tile.

After checking the resource allocation information for each tile index, the transmitter proceeds to step 205 to estimate channel information of each channel section using channel information for each tile index existing in each channel estimation section. For example, when tiles are allocated to a plurality of tile indexes, such as the 0 th channel estimation section and the 29 th channel section of FIG. 3, the average of the channel information of the tile indexes is the channel information of the channel estimation section. If a tile is assigned to only one tile index in the channel estimation section like the first channel estimation section, the channel information of the tile index is used as the channel information of the channel estimation section. On the other hand, if there is no tile allocated to all tile indexes, such as the second channel estimation interval, the channel information of the channel estimation interval is set to zero.

After estimating channel information of each channel estimation interval, the transmitter proceeds to step 207 to estimate channel information of the interval where the channel information is zero. In this case, the transmitter sets the K-th channel estimation section in which the channel information is 0 to have the same channel information as the channel information of the (K-1) -th channel estimation section. If the channel information of the 0 th channel estimation section is 0, the 0 th channel estimation section is set to have the same channel information as the channel information of the channel estimation section having the smallest index among the non-zero channel estimation sections. do. For example, the second channel estimation section in which the channel information is 0 in FIG. 3 has the same channel information as the channel information of the first channel estimation section.

Thereafter, the transmitter terminates the present algorithm.

As described above, when the resource allocation method of the uplink / downlink in the multi-antenna system is different, the channel information of each channel estimation section is estimated by dividing the entire uplink bandwidth into a channel estimation section of a predetermined size. Accordingly, the multi-antenna system may obtain downlink channel information for forming a beam using channel information of each channel estimation section. That is, the multi-antenna system may form a beam as shown in Equation 1 below.

Here, Y _c represents a transmission data signal having a beam, W represents a beam coefficient generated from uplink channel information, and X represents a transmission data vector. In addition, c represents a cluster index (for example, 60 in total when the size of the FFT is 1024), and D represents the number of clusters for forming a beam. For example, as shown in FIG. 3, when the entire uplink band is divided into 30 channel estimation intervals, one channel estimation interval is composed of 28 (4 × 7) subchannels. Accordingly, since one channel estimation interval represents channel information of two clusters, one beam may be formed per two clusters.

In the multi-antenna system, when a beam is formed by using a maximum resonance transmission (MRT) technique, the beam coefficient in Equation 1 is calculated as in Equation 2 below.

는 상기 채널 정보의 전력을 나타낸다.Where H denotes channel information, and

Denotes the power of the channel information.

As shown in Equation 2, a beam coefficient for normalizing power of the multi-antenna system is calculated.

When the beam is formed in the multi-antenna system as shown in Equation 1, the estimated channel information of each channel estimation section may be used to form the beam by delaying several frames according to a processing delay. If the channel change of the multi-antenna system is severe, beam formation is degraded because the beam is formed using channel information prior to several frames according to the processor delay. Accordingly, the multi-antenna system forms a downlink beam in consideration of channel change (eg, moving speed) of each user as shown in FIG. 4.

4 illustrates a procedure for forming a beam in a multiple antenna system according to an embodiment of the present invention.

Referring to FIG. 4, in step 401, the transmitter divides the entire uplink band into N channel estimation intervals. In this case, the number N of the channel estimation intervals has the same value as the divisor of the total number of clusters included in all the downlink bands (the total number of clusters% N = 0).

After dividing the entire band into channel estimation intervals, the transmitter proceeds to step 403 to estimate channel information of each channel estimation interval. In other words, the transmitter checks whether there is a tile allocated to each tile index during the uplink slot. Thereafter, the transmitter estimates channel information of each channel section using the allocated tile existing in each channel estimation section. For example, when tiles are allocated to a plurality of tile indexes in the channel estimation interval, the average of channel information of the tile indexes is used as channel information of the channel estimation interval. If a tile is assigned to only one tile index in the channel estimation section, channel information of the tile index is used as channel information of the channel estimation section. On the other hand, if there is no tile assigned to all tile indexes of the channel estimation interval, the channel information of the channel estimation interval is set to zero. Here, the channel estimation section in which the channel information is 0 has the same channel information as the channel information of the previous channel estimation section.

After estimating channel information of each channel estimation section, the transmitter proceeds to step 405 to calculate the instantaneous beam coefficients of a frame for forming a beam as shown in Equation 3 below.

Here, the _ins W (k) represents the instantaneous beam coefficient of the k-th frame, the _i h denotes the channel information of the i-th transmit antenna, the N _T denotes a number of transmit antennas of the transmitter.

After calculating the instantaneous beam coefficient, the transmitter proceeds to step 407 to generate a beam coefficient according to a channel change using the instantaneous beam coefficient and the previous beam coefficient. Here, the beam coefficients according to the channel change are generated using Equations 4 and 5 below.

Here, AvgW (k) represents a beam coefficient according to a channel change of a k-th frame, AvgW (k-1) represents a beam coefficient of a previous frame, and W _ins (k) represents an instantaneous beam of a k-th frame. Indicates coefficients. Also, α is a coefficient for determining a channel change amount in the beam coefficient, and α has a large value when the channel change is severe. That is, the beam coefficient according to the channel change gives a greater weight to the instantaneous beam coefficient than the beam coefficient of the previous frame when the channel change is large.

After generating the beam coefficient according to the channel change as shown in Equation 4, the transmitter normalizes the power of the beam coefficient as shown in Equation 5 below.

는 상기 채널 정보의 전력을 나타낸다. 여기서, 상기 다중 안테나 시스템은 상기 채널 추정 구간으로 하향링크의 채널 정보를 추정하였으므로 상기 채널 추정 구간으로 빔을 형성하기 위한 빔 계수를 생성한다.Here, W (b) represents the normalized beam coefficient, AvgW (b) represents the beam coefficient of the b-th channel estimation interval,

Denotes the power of the channel information. Here, the multi-antenna system estimates downlink channel information in the channel estimation section, and generates beam coefficients for forming a beam in the channel estimation section.

After generating the beam coefficients, the transmitter proceeds to step 409 to form a downlink beam using the generated beam coefficients.

Thereafter, the transmitter terminates the present algorithm.

5 is a block diagram of a transmitter in a multiple antenna system according to the present invention.

As shown in FIG. 5, the transmitter includes a multiple transmit / receive antenna, a duplexer 500, a receiver 510, and a transmitter 520.

First, the duplexer 500 connects the antenna and the transmitting and receiving terminals 510 and 520 according to a transmission and reception interval so that the receiving end 510 and the transmitting end 520 share the antenna. That is, the duplexer 500 connects the antenna and the transmitter 520 during the transmission interval, and connects the antenna and the receiver 510 during the reception interval. Here, the antenna is composed of an array antenna for forming a beam.

The receiving end 510 includes an RF processor 511, an OFDM demodulator 513, a channel estimator 515, and a beam coefficient generator 517.

The RF processor 511 outputs a frequency down-modulated RF signal received through the antenna to a baseband signal.

The OFDM demodulator 513 outputs a frequency domain signal by performing Fast Fourier Transform on the time domain signal provided from the RF processor 511.

The channel estimator 515 estimates channel information of each channel estimation interval by dividing the entire band of the signal provided from the OFDM demodulator 513 into N channel estimation intervals. Here, the channel estimator 515 estimates channel information of each channel estimation interval as shown in FIG. 2.

The beam coefficient generator 517 considers channel information of a channel estimation section for forming a beam and channel change amount of the user for forming the beam among channel information of each channel estimation section provided from the channel estimator 515. Generate beam coefficients. For example, the beam coefficient generator 517 generates beam coefficients according to channel changes by using Equations 4 and 5 below.

The transmitter 520 includes a beam former 521, an OFDM modulator 523, and an RF processor 525.

The beam former 521 performs beamforming by multiplying data corresponding to a downlink resource allocation band by a beam coefficient generated by the beam coefficient generator 517.

The OFDM modulator 523 converts the beamformed frequency domain signal from the beamformer 521 into a time domain signal by performing an inverse fast Fourier transform.

The RF processor 525 frequency-modulates the beam-formed time-domain signal received from the OFDM modulator 523 into an RF signal to form a beam to the corresponding user through the antenna.

6 is a graph illustrating performance change according to an embodiment of the present invention. In the following description, the horizontal axis represents a carrier to noise ratio, and the vertical axis represents a frame error ratio (FER).

Referring to FIG. 6, in the multi-antenna system, the present invention forms a beam by dividing the entire band into 30 channel allocation intervals and the performance when using a switched beamforming that applies one beam coefficient to the entire band. The change graph is shown. Here, the switched beamforming method refers to a beamforming method of applying a downlink beam by selecting only an approximate direction of a received signal.

First, as shown in (a) of FIG. 6, when the user to form a beam moves to 3 km / h in the multi-antenna system, the present invention generates an error in a frame even at a signal to noise ratio lower than that of the switched beam. The probability is low.

Next, as shown in (b) of FIG. 6, even when a user to form a beam moves in the multi-antenna system at 60 km / h, the present invention provides an error in a frame even at a signal-to-noise ratio lower than that of the switched beam. The probability of occurrence is low.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the channel information and the channel estimated by dividing uplink allocation information spread over all bands into N channel estimation intervals in a multi-antenna system using a time division duplex scheme and having different uplink / downlink subchannel allocation schemes. By forming the downlink beam according to the amount of change, channel information of the resource allocation band of the downlink can be obtained, and the beam performance can be improved by adaptively forming the beam according to the channel change to improve the link performance of the multi-antenna system. There is this.

Claims (20)

In the beamforming method in a transmitter of a multi-antenna system, When the resource allocation scheme of the uplink / downlink is different, dividing a signal received from the receiver into a predetermined number of channel estimation intervals; Estimating channel information of each channel estimation section; Checking a channel change amount of the receiver; And generating a beam coefficient by using the channel information of each channel estimation section and the channel variation amount to form a beam. The method of claim 1, The process of estimating the channel information, Checking resource allocation information of each channel estimation section; Estimating channel information of each channel estimation interval using the resource allocation information. 3. The method of claim 2, Estimating the channel information, Identifying a resource allocated to the channel estimation interval; Estimating a channel of the resources when at least two resources are allocated to the channel estimation interval; Calculating an average of channel estimates of the resources; And setting the average of the channel estimation values as channel information of the channel estimation interval. The method of claim 3, The allocated resource identifies a tile allocated to each channel estimation interval. The method of claim 3, Estimating a channel of the resource when one resource is allocated to the channel estimation interval; And setting the channel estimate value as channel information of the channel estimation interval. The method of claim 3, And if there is no tile assigned to the channel estimation interval, setting channel information of a previous channel estimation interval as channel information of the channel estimation interval. The method of claim 1, The number of channel estimation intervals, characterized in that any one of the divisor of the number of clusters (Cluster) included in the entire band of the downlink. The method of claim 1, The channel change amount of the receiver, characterized in that the movement speed of the receiver. The method of claim 1, The process of generating the beam coefficients, Checking channel information of a band for transmitting a signal among channel information of each channel estimation section; Generating an instantaneous beam coefficient using the checked channel information; Calculating a weight according to the channel change amount; And generating the beam coefficients by applying the weights to the instantaneous beam coefficients and the previous beam coefficients. The method of claim 1, The beam coefficients are generated as in Equation 6 below.

Here, AvgW (k) denotes a beam coefficient according to a channel change of a k-th frame, AvgW (k-1) denotes a beam coefficient of a previous frame, and W _ins (k) denotes an instantaneous beam coefficient of a k-th frame. In the beam forming apparatus of a multiple antenna system, A channel estimator for estimating channel information of each channel estimation interval by dividing the entire band into a predetermined number of channel estimation intervals when the resource allocation scheme of the uplink / downlink is different; A beam coefficient generator for generating a beam coefficient using the channel information and the channel change amount of the receiver; And a beam former for forming a beam to the receiver using the beam coefficients. 12. The method of claim 11, And the channel estimator estimates channel information of each channel estimation interval using resource information allocated to each channel estimation interval. 12. The method of claim 11, The beam coefficient generator, And generating a beam coefficient by applying weights according to channel variation to instantaneous beam coefficients generated using the channel information and previous beam coefficients. 12. The method of claim 11, The beam coefficient generator, characterized in that for generating a beam coefficient using the equation (7).

Here, AvgW (k) denotes a beam coefficient according to a channel change of a k-th frame, AvgW (k-1) denotes a beam coefficient of a previous frame, and W _ins (k) denotes an instantaneous beam coefficient of a k-th frame. A method for estimating a downlink channel using an uplink signal in a transmitter of a time division duplex type wireless communication system having different uplink / downlink resource allocation schemes, Dividing the entire band of the uplink signal into a predetermined number of channel estimation intervals; Checking resource allocation information of each channel estimation section; Estimating channel information of each channel estimation interval using the resource allocation information. 16. The method of claim 15, Estimating the channel information, Identifying a resource allocated to the channel estimation interval; Estimating a channel of the resources when at least two resources are allocated to the channel estimation interval; Calculating an average of channel estimates of the resources; And setting the average of the channel estimation values as channel information of the channel estimation interval. 17. The method of claim 16, The allocated resource identifies a tile allocated to each channel estimation interval. 17. The method of claim 16, Estimating a channel of the resource when one resource is allocated to the channel estimation interval; And setting the channel estimate value as channel information of the channel estimation interval. 17. The method of claim 16, And if there is no tile assigned to the channel estimation interval, setting channel information of a previous channel estimation interval as channel information of the channel estimation interval. 16. The method of claim 15, The number of channel estimation intervals, characterized in that any one of the divisor of the number of clusters (Cluster) included in the entire band of the downlink.

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