KR20050106658A - A smart antenna system for forming an eigenbeam of downlink for base station in ofdm/tdd systems, and a method thereof - Google Patents

Abstract

The present invention relates to an OFDM system having a spatial covariance and a TDD system having channel reversibility, and a smart antenna system and a method for forming a downlink unique beam of the OFDM / TDD scheme. According to the present invention, the complexity of the communication system can be reduced by using the fact that all subcarriers of the OFDM system have the same spatial covariance and that the TDD system has channel reciprocity. In addition, according to the present invention, a spatial covariance matrix for eigenbeam formation can be directly obtained without feedback using pilots of all subcarriers of the uplink allocated for a user. In addition, according to the present invention, necessary instantaneous spatial covariance of downlink can be obtained by using interpolation of instantaneous spatial covariance of uplink subcarriers. In addition, according to the present invention, an error that occurs randomly due to incorrect selection of an optimal eigenbeam can be mostly recovered by a channel decoder at the rear of the receiver.

Description

Smart antenna system and method for forming an eigenbeam of downlink for base station in OFDM / TDD systems, and a method

The present invention relates to a smart antenna system and a method for forming a downlink unique beam of the OFDM / TDD scheme, more specifically, an orthogonal frequency division multiplexing (OFDM) system in which all subcarriers have a spatial covariance In a time division multiplexing (TDD) system having over-channel reciprocity, the present invention relates to a smart antenna system and a method for forming a downlink unique beam for OFDM / TDD scheme.

To fully implement a mobile communication system that allows any type of data to send and receive with the desired party anytime, anywhere, operates under a single, globally standardized standard, and is a much higher level of service than current mobile communication systems. Next generation (3rd Generation) mobile communication systems that provide a commercially available.

The next generation mobile communication system transmits and receives images and other data with high reliability as well as voice signals currently in service. In addition, as services are diversified, the bandwidth of transmission and reception data occupies a much wider band than the present, and the demand of the mobile communication network itself is expected to increase further.

Therefore, the most important technical challenge of the next generation mobile communication system should be to present a technique for transmitting more data reliably using the narrowest bandwidth possible.

However, the reduction of bandwidth used and the increase of reliability cannot be achieved at the same time, so the existing technologies proposed to date cannot solve the capacity and reliability problems that will arise in the next generation of mobile communication.

In recent years, new technologies are being actively researched to adjust the beam pattern of the antenna to suppress interference and noise, thereby simultaneously increasing capacity and improving reliability in a communication system. The so-called smart antenna technology is emerging as a core technology of the next generation mobile communication system.

Such a smart antenna technology can be said that the base station sets the optimal beam to the subscribers of the wireless communication terminal, thereby reducing the radio interference to increase the communication capacity and improve the communication quality.

For example, a smart antenna system installed in a base station may adapt to the speed of each of 1) fixed targets such as offices, 2) slow moving targets such as personal and satellite, and 3) fast moving targets such as vehicles and trains. In this way, the optimum beam pattern is continuously provided to provide maximum gain in the direction of the target, and relatively much smaller gain in the other direction, thereby suppressing interference. That is, such a smart antenna system increases the capacity of the mobile communication system and improves the reliability of communication.

Therefore, such smart antenna technology is the latest technology to be applied to W-CDMA and CDMA2000, which is a next-generation communication method that must reliably transmit a lot of data.

Until now, most transmission smart antennas have been mostly researched for downlink. In general, in order to apply a closed-loop downlink beamforming technique, the base station must know the downlink instantaneous channel in advance.

However, in the frequency division duplex (FDD) mode, since the frequency bands of the upstream and downstream channels are different from each other, the mobile terminal must feed back the instantaneous channel information to the base station. In this case, a large amount of feedback information required may be an obstacle to the closed loop beamforming technique.

The conventional blind beam forming technique is a technique for adaptively forming a downlink beam by measuring an uplink channel under the assumption that spatial propagation environments of uplink and downlink are similar to spatial statistical characteristics. This blind beamforming technique uses the reversibility of the channel and thus does not require feedback information, whereas the beamforming vector loses diversity gain because the beamforming vector does not follow the instantaneous channel variation.

In order to obtain the spatial diversity gain, the instantaneous channel information of downlink must be fed back. As the number of transmitting antennas increases, the amount of feedback information increases, and in order to track the instantaneous channel variation, the number of transmitting antennas increases. In the case where the moving speed of the moving object is high, there is considerable difficulty in applying the aforementioned beam forming technique. Recently, various techniques have been proposed to alleviate this problem.

On the other hand, as a prior art, Korean Patent Application No. 1999-43679 (October 09, 1999 application) discloses "A transmission antenna diversity control apparatus and method in a mobile communication system", which is a closed loop transmission antenna diversity A control device and method for adaptively calculating weights to perform transmit antenna diversity.

Specifically, the invention of Korean Patent Application No. 1999-43679 continuously tracks an optimal weight vector for a certain period of time, that is, obtains a weight vector by detecting a state of an initial downlink channel, and detects a state of a next downlink channel. In this case, a more accurate weight vector is obtained by using the weight vector already obtained, and then a weight variable that is applied to each antenna used for transmit antenna diversity according to the channel state is applied, and the current weight is used by using the previous weight. Adaptive weight calculation is performed.

On the other hand, as a prior art, Korean Patent Application No. 2000-11617 (filed Mar. 08, 2000) entitled "Blind transmission method and method for transmitting antenna array using feedback information in a mobile communication system" The present invention discloses an apparatus and method for transmitting antenna array system for increasing subscriber capacity by forming an appropriate transmission beam to a specific terminal station desired by using at least two antenna elements and corresponding weight vectors. will be.

Specifically, the base station apparatus according to the invention of Korean Patent Application No. 2000-11617, the reverse processor for processing the reverse signal received through the antenna array; A forward fading information acceptor for extracting forward fading information from the received reverse signal; A beamforming controller for generating a weight vector for transmitting beamforming using forward fading information and the received reverse signal; And a forward processor configured to form a transmission message as a transmission beam based on the weight vector, and output the transmission message to the antenna array. In addition, the terminal station apparatus includes a forward processor for receiving and processing the forward signal; A forward fading estimator for estimating forward fading information for each path of the received forward signal; A forward fading encoder for combining and encoding the estimated forward fading information for each path; And a reverse processor for multiplexing the encoded forward fading information with the transmission message and feeding back to the base station.

Accordingly, the invention of Korean Patent Application No. 2000-11617 uses a basic (predictive) beam forming method and a blind forward beam forming method according to the moving speed of a terminal when the feedback delay time is small or large in a mobile communication system having a multipath. By using the selected mixed forward beamforming method, the forward fading information is fed back from the terminal to form a more reliable transmission beam, thereby increasing capacity and saving transmission power of the terminal.

On the other hand, as a prior art, European Trans. Published in 2001. In pages 12 to 378 of Vol. 12 of Telecomm., A paper entitled "Exploiting the Short-term and Long-term Channel Properties in Space and Time: Eigenbeam forming Concepts for the BS in WCDMA" is published.

This prior paper discloses the structure of a space-time transceiver of a CDMA system having an adaptive antenna at a base station by the concept of intrinsic beam shaping. The concept of intrinsic beam shaping uses a long-term channel property to provide a processing dimension. In addition to reducing the meantime, the spatial covariance matrix is averaged in the downlink, or the spatial covariance matrix of similar instantaneous taps is uniquely divided in the uplink, thereby obtaining decorrelated diversity branches in space and time.

Meanwhile, US Patent Application No. 2003-144032 (filed Jul. 31, 2003) according to the prior art discloses an invention named "BEAM FORMING METHOD". This beamforming method proposes a space-time transceiver structure of a CDMA system having an adaptive antenna in a base station based on the concept of intrinsic beamforming.

Specifically, according to the invention of US Patent Application No. 2003-144032, by combining the advantages and eliminating the disadvantages of long-term intrinsic beam formation and short-term optimal coupling, which are characteristics of the rake receiver, the computational complexity is lowered, and also unique Since the eigenrake is adaptable to various propagation environments, the feedback for short-term processing does not need to increase even if the number of antennas increases, and the diversity gain and interference mitigation effect can be achieved by using the long-term and short-term characteristics of the channel simultaneously. You can get it.

On the other hand, the recent eigenbeam smart antenna technology proposed in the 3rd Generation Partnership Project (3GPP) standard can be realized by feeding back information required for beamforming in downlink through uplink. Same as

First, a spatial channel property may be classified into a long-term channel property and a short-term channel property. Here, the long-term channel characteristic refers to a spatial channel characteristic that changes in the long term according to the correlation between the antenna elements, the feature, the location of the terminal, and the like, and the short-term channel characteristic changes rapidly in the short term depending on Rayleigh fading. Spatial channel characteristics.

In general, a short-term spatial covariance matrix of a terminal obtained by using an orthogonal pilot transmitted by a base station can be obtained as in Equation 1 below. In other words, the short-term spatial covariance matrix R _ST is

here, Is the channel vector of the nth temporal tap, Where L represents the number of transmit antennas.

In addition, a long-term spatial covariance matrix can be obtained as in Equation 2 below. That is, the long-term spatial covariance matrix R _LT is

, Where Denotes a forgetting factor.

The long-term spatial covariance matrix R _LT described above may be expressed by Equation 3 by eigen-decomposition.

here, Eigenvalues as Is a diagonal matrix with And v _L represents an eigenvector corresponding to λ _L.

Also, among the L eigenvectors, we can quickly reduce the amount of feedback or computational complexity. The eigenvectors corresponding to the large eigenvalues of the dog are defined as eigen-beams or eigen-modes. The received power of the terminal among these unique beams The intrinsic beam which makes this maximum is selected.

The 3GPP WCDMA system transmits a unique beam of one bit per frame from the terminal to the base station at a feedback rate of 1500bps over a dedicated physical control channel (DPCCH) channel. Each of which determines which of the unique modes to select, and transmits the result from the terminal to the base station.

However, when the 3GPP scheme is used, the OFDM scheme has a different beamforming vector for each subcarrier, and thus, there is a problem in that a practically efficient communication system cannot be implemented because the required feedback information is greatly increased.

An object of the present invention to solve the above-mentioned problems of the prior art is to reduce the complexity of a communication system by using the fact that all subcarriers of an OFDM system have the same spatial covariance and that the TDD system has channel reversibility. The present invention provides a smart antenna system and method for forming a downlink unique beam of the OFDM / TDD scheme.

In addition, another object of the present invention for solving the problems of the prior art, OFDM / which can directly obtain the spatial covariance matrix for the unique beam formation without feedback by using the pilots of all subcarriers of the uplink allocated for one user The present invention provides a smart antenna system and method for forming a downlink unique beam of a TDD scheme.

In addition, another object of the present invention for solving the problems of the prior art, the downlink of the OFDM / TDD scheme that can obtain the required instantaneous spatial covariance of the downlink by using interpolation of the instantaneous spatial covariance of the uplink subcarrier It is to provide a smart antenna system and a method for forming a unique beam for a link.

As a means for achieving the above object, the base station transmitting apparatus of the smart antenna system for forming a downlink unique beam for the base station of the orthogonal frequency division multiplexing (OFDM) / time division multiplexing (TDD) method according to the present invention,

Multiple antennas for transmitting each OFDM symbol to a terminal receiving end or receiving each OFDM symbol transmitted from the terminal receiving end;

Fourier transform each OFDM symbol received through the multiple antennas and output them as parallel signals, estimate a channel from the Fourier transformed parallel signal, and use the channel estimation result to perform the Fourier transformed parallel signal. A base station receiver for detecting a symbol from the base station, converting the symbol into a series of serial signals, and outputting a decoded signal; And

Convert each channel-coded symbols serially input into a predetermined number of parallel signals and generate respective beam weights from each pilot channel of each subcarrier according to the channel estimation result of the base station receiver, thereby generating the respective beams having their own beams. Base station transmitter to generate and output symbols

There is a feature configured to include.

Here, the base station transmitting end, the serial / parallel (S / P) converter for converting the serially input channel coded symbols into a predetermined number of parallel signals; A signal copier for copying the parallel signal by the number of multiple antennas; A beam weight generator for generating a unique beam weight from each pilot channel of each subcarrier according to the channel estimation result; A beam weight multiplier for multiplying and outputting beam outputs generated from the beam weight generator by the output of the signal copier; And a plurality of inverse Fourier transformers for inputting the predetermined number of parallel signals to generate and output one OFDM symbol each.

Here, the beam weight generator includes: a pilot spatial covariance matrix generator for generating a pilot spatial covariance matrix of each subcarrier by inputting a channel matrix for each pilot according to the channel estimation result; A subcarrier spatial covariance matrix generator for generating a spatial covariance matrix for each subcarrier by inputting the spatial covariance matrix for each pilot by using a predetermined number of pilots present in one subcarrier; A short-term spatial covariance matrix generator for generating a short-term spatial covariance matrix by inputting each of the subcarrier spatial covariance matrices using uplink subcarriers all having the same spatial covariance matrix; A long term spatial covariance matrix generator for inputting the short term spatial covariance matrix and outputting a long term spatial covariance matrix; An inter-subcarrier spatial covariance matrix interpolator for inputting an uplink subcarrier spatial covariance matrix obtained through the uplink and outputting a predetermined number of downlink subcarrier spatial covariance matrices; An eigendivider that inputs the long-term spatial covariance matrix and divides and outputs the eigenbeam into respective eigenbeams; And a beam weight selector for inputting the divided eigenbeam and the spatial covariance matrix for each subcarrier of the downlink and outputting beam weights for each subcarrier.

Here, the short-term spatial covariance matrix is characterized in that the same matrix as the long-term spatial covariance matrix when the length of the received packet is short.

Here, the eigenbeam of the eigendivider is defined as an eigenvector corresponding to a large eigenvalue among a predetermined number of eigenvectors, and is characterized in that the eigenbeam is divided into eigenbeams to maximize the reception power of the terminal.

The base station receiver may include: a plurality of Fourier transformers for inputting OFDM symbols respectively received through the multiple antennas, Fourier transforming the number of antennas, and outputting parallel signals; A channel estimator for estimating a channel from the Fourier transformed parallel signal; A signal detector for detecting a symbol from the Fourier-transformed parallel signal using the result of the channel estimator and outputting a predetermined number of detected parallel signals; A parallel / serial (P / S) converter converting the detected parallel signals into a series of serial signals and outputting the converted serial signals; And a channel decoder for decoding and outputting the serially converted signal.

Here, the channel estimator outputs a channel matrix of each pilot for each subcarrier to calculate a beamforming weight.

On the other hand, as another means for achieving the above object, the terminal transceiver device of the smart antenna system for forming a downlink unique beam of the OFDM / TDD scheme according to the present invention,

Multiple antennas for receiving each OFDM symbol transmitted from the base station transmitting end or transmitting each OFDM symbol to the base station receiving end;

OFDM signals transmitted by forming a unique beam from the base station transmitter are respectively input to Fourier transform and output as parallel signals. The symbols are detected from the Fourier transformed parallel signals, converted into a series of serial signals, and then decoded. Terminal receiving end for outputting; And

Each of the channel-coded symbols input in serial is converted into a predetermined number of parallel signals, respectively, and the N parallel signals are copied by the number of multiple antennas in which a plurality of user signals are input as multiplexed N parallel signals. Terminal transmitter for generating and outputting OFDM symbols

There is a feature configured to include.

The terminal receiving terminal may include: a plurality of Fourier transformers for inputting OFDM symbols respectively received through the multiple antennas, Fourier transforming each of the multiple antennas, and outputting parallel signals; A signal detector for detecting a symbol from the Fourier transformed parallel signal and outputting a predetermined number of detected parallel signals; A P / S converter converting the detected parallel signal into a series of serial signals and outputting the serial signal; And a channel decoder for decoding and outputting the serially converted signal.

In this case, the channel decoder may recover an error occurring randomly when an interpolation is incorrect because an uplink subcarrier interval exceeds a channel bandwidth or an optimal natural beam selection is inaccurate due to a fast moving speed of the terminal.

The terminal transmitting end may include: a plurality of S / P converters corresponding to a plurality of base station antennas for converting channel-coded symbols respectively inputted in series into a predetermined number of parallel signals; A signal copying machine for copying the N parallel signals by the number of base station antennas when a plurality of user signals are multiplexed and input as N parallel signals; And a plurality of inverse Fourier transformers corresponding to the number of base station antennas, respectively, for inputting the N parallel signals to generate one OFDM symbol.

On the other hand, as another means for achieving the above object, the base station transmission and reception method of the smart antenna system for forming a downlink unique beam of the OFDM / TDD scheme according to the present invention,

a) receiving each OFDM symbol transmitted from a terminal transmitter through uplink;

b) Fourier transforming each of the received OFDM symbols and outputting each of them as a parallel signal, and estimating a channel from the Fourier transformed parallel signal;

c) converting serially input channel coded symbols into a predetermined number of parallel signals;

d) generating respective beam weights from each pilot channel of each subcarrier according to the channel estimation result; And

e) forming a unique beam according to the respective beam weights, generating respective OFDM symbols, and transmitting them to the terminal receiving terminal through uplink

There is a feature consisting of.

Here, step d) includes the steps of: i) generating a spatial covariance matrix for each pilot of each subcarrier by inputting a channel matrix for each pilot according to the channel estimation result; Ii) generating a spatial covariance matrix for each subcarrier by inputting the spatial covariance matrix for each pilot using a predetermined number of pilots present in one subcarrier; Iv) generating a short-term spatial covariance matrix by inputting the spatial covariance matrix for each subcarrier, respectively, using a predetermined number of uplink subcarriers received by one user having the same spatial covariance matrix; Iii) outputting a long term spatial covariance matrix by inputting the short term spatial covariance matrix; Iii) outputting a spatial covariance matrix for each downlink subcarrier by inputting a spatial covariance matrix for each uplink subcarrier obtained through the uplink; Iii) inputting the long-term spatial covariance matrix and dividing the long-term spatial covariance matrix into respective eigenbeams; And iii) inputting the divided eigenbeam and the spatial covariance matrix for each subcarrier of the uplink, and outputting beam weights for each subcarrier.

Here, the step iii), To obtain the spatial covariance matrix of each subcarrier by pilot, where Is the c subcarrier It is characterized in that the instantaneous spatial covariance matrix obtained by the first pilot tone.

Wherein, step ii) is present in one subcarrier Using two pilots It is characterized by obtaining a spatial covariance matrix of subcarriers c defined as follows.

In step (iii), since all C subcarriers of the uplink allocated to one user have the same spatial covariance matrix, It is characterized by obtaining the short-term spatial covariance matrix R _ST .

Where step iii) is To obtain the long-term spatial covariance matrix ( R _LT ), where Is the number of frames, Is characterized in that the forgetting factor (forgetting factor).

Where step iii) is To perform unique partitioning, where Eigenvalue as Is a diagonal matrix with And v _L is an eigenvector corresponding to λ _L.

Here, the step iii), Output beam weights for each subcarrier using Is the k-th subcarrier of the downlink.

On the other hand, as another means for achieving the above object, a method of transmitting and receiving a terminal of the smart antenna system for forming a downlink unique beam of the OFDM / TDD scheme according to the present invention,

a) receiving each OFDM symbol having a unique beam transmitted from a base station transmitting end;

b) Fourier transforming each of the received OFDM symbols and outputting the parallel symbols in parallel;

c) detecting a symbol from the Fourier transformed parallel signal, converting the symbol into a series of serial signals, and outputting a decoded signal;

d) converting each of the channel-coded symbols input in series into a predetermined number of parallel signals, respectively;

e) generating the respective OFDM symbols by copying the N parallel signals by the number of terminal antennas inputted with N parallel signals multiplexed by a plurality of user signals; And

f) transmitting each OFDM symbol to a base station receiving end, respectively

There is a feature consisting of.

In the step c), when the uplink subcarrier spacing exceeds the channel bandwidth and the interpolation is inaccurate or the terminal's moving speed is inaccurate, the optimal natural beam selection becomes inaccurate. It can be included as.

Therefore, according to the present invention, the complexity of the communication system can be reduced by using the fact that all subcarriers of the OFDM / TDD system have the same spatial covariance and that the TDD system has channel reversibility, and the uplink allocated for one user can be reduced. By using the pilots of all subcarriers in the link, the spatial covariance matrix for eigenbeam formation can be obtained directly without feedback, and the necessary instantaneous spatial covariance of the downlink can be obtained by interpolation of the instantaneous spatial covariance of the uplink subcarrier. In addition, a randomly generated error due to incorrect selection of an optimal eigenbeam can be mostly recovered by a channel decoder at a rear end of the receiver.

Hereinafter, a smart antenna system and a method for forming a downlink unique beam of the OFDM / TDD scheme according to the present invention with reference to the accompanying drawings will be described in detail.

First, in an OFDM / TDD system according to an embodiment of the present invention, the number of L base station antennas and the number of M terminal antennas are considered. In general, in an OFDM (or OFDMA) system, a downlink subcarrier group and an uplink subcarrier group allocated to one user are different from each other.

In the embodiment of the present invention, it is assumed that K subcarriers are allocated to a user in downlink, and in this case, K subcarriers are arranged at regular intervals to use frequency diversity and are not continuous. A subcarrier having a subcarrier index of k means a k th subcarrier among K subcarriers assigned to a user. In addition, C subcarriers are allocated to one user as an uplink, and it is common that C subcarriers are not continuously arranged on the same principle as the downlink. In addition, a subcarrier having a subcarrier index of c means a c th subcarrier among C subcarriers assigned to a user.

First, the downlink transmission signal may be expressed as Equation 4 below.

here, For the k subcarriers Beamforming vector, ego, Is an OFDM symbol transmitted on the kth subcarrier.

Since the OFDM system according to the embodiment of the present invention uses a wide band, the transmission signal is transmitted through a frequency selective fading channel. In addition, a channel impulse response (CIR) between the transmitting antenna l and the receiving antenna m is Where P is the number of multipaths.

Therefore, the channel response in the frequency domain is as shown in Equation 5 below.

In addition, the MIMO channel matrix for the subcarrier k may be expressed by Equation 6 below.

In addition, the received signal passing through the DFT in the receiver is given by Equation 7 below.

here, Is the size Represents the noise matrix.

Assuming that there is no correlation between different paths in the channel of Equation 5, the following relationship is established.

here, Is the power delay profile of the channel impulse response (CIR),

Becomes the channel ( The spatial covariance matrix of) can be defined as in Equation 10 below.

Is given by Therefore, the channel matrix of each subcarrier ( Spatial covariance matrix () ) May be given by Equation 11 below.

In Equation 11, the channel matrix of each subcarrier ( Spatial covariance matrix of ) Shows that it is not a function on any subcarrier k. In other words, in the OFDM system, since each subcarrier undergoes different frequency selective fading, each subcarrier has different channel characteristics, but the spatial covariance matrix is the same for all subcarriers.

In conclusion, the spatial covariance matrix is the same for all subcarriers, so that an accurate estimate can be obtained by averaging all subcarriers.

Meanwhile, the frequency domain channel response between the m th antenna of the uplink c subcarrier and the l th base station antenna is Is defined as As mentioned above, due to the channel reversibility of the TDD system, this is equal to the frequency domain channel response between the m th terminal antenna at the l th antenna base station in the downlink. Based on this logic, the c subcarrier of the uplink By using the first pilot, a downlink MIMO channel matrix defined as in Equation 12 can be obtained.

here, Is the c subcarrier An instantaneous spatial covariance matrix obtained as the first pilot tone may be defined as in Equation 13 below.

Where a subcarrier exists Spatial covariance matrix of the c-th subcarrier defined as follows can be obtained using three pilots.

As described above, since all C subcarriers of the uplink allocated to one user have the same spatial covariance matrix, a short-term spatial covariance matrix can be obtained as shown in Equation 15 below.

In addition, the long-term spatial covariance matrix R _LT is obtained as in Equation 16 below, as in Equation 2 of the above-described 3GPP WCDMA system. The long-term spatial covariance matrix R _LT is

This is where, Is the number of frames, and Is It is a short-term spatial covariance matrix obtained in the first frame. If the packet is very short Can be left at 0, resulting in Becomes

In addition, the eigen mode is obtained by performing eigendivision as shown in Equation 17 below.

here, Eigenvalue as Is a diagonal matrix with And v _L is an eigenvector corresponding to λ _L. However, unlike 3GPP described above, since there is no feedback, all L eigenvectors may be defined as an eigen mode.

Meanwhile, if the subcarriers used for the downlink and the subcarriers used for the uplink are different, the k-th subcarriers for the downlink are different. Is obtained as follows.

At this time, Is obtained by using the uplink considering the coherent characteristics between subcarriers. Can be obtained by interpolation of. As a most preferred example, the downlink subcarrier k is actually the jth subcarrier, and the uplink subcarrier closest to the downlink subcarrier k. Is real The first subcarrier and the nearest uplink subcarrier thereafter. Is real Assume that the first subcarrier is Is and Can be obtained by interpolation.

So using linear linear interpolation , and Can be assumed as Equation 19 to Equation 21 below.

Thus above Each element of,

Is given by.

Therefore, the optimal downlink beam obtained in the uplink frame can be utilized in the downlink of the frame of the next frame i + 1.

If the uplink subcarrier spacing is greater than the coherent bandwidth, or the movement speed of the terminal is fast, a probability that an incorrect unique beam may be selected may occur. At this time, the error due to the wrong eigen beam selection is random, and can be mostly corrected by the channel decoder at the later stage.

Hereinafter, a smart antenna system according to an embodiment of the present invention will be described in detail with reference to the above-described principles of the present invention.

1 is a block diagram illustrating a terminal of a smart antenna system of the OFDM / TDD scheme according to an embodiment of the present invention, Figure 2 illustrates a base station of a smart antenna system of the OFDM / TDD scheme according to an embodiment of the present invention It is a block diagram for that.

1 and 2, the terminal of the smart antenna system of the OFDM / TDD scheme according to an embodiment of the present invention is provided with M antennas (140-1, 140-2, ..., 140-M), The base station includes L antennas 250-1, 250-2, ..., 250-L, and the terminal and the base station are respectively composed of a transmitting end and a receiving end.

In FIG. 1, the terminal transmitter has an inverse fast fourier transformer (IFFT) 130-1 as much as the serial-to-parallel (S / P) converter 110, the signal copier 120, and the number of transmit antennas (M). , 130-2, ..., 130-M). In addition, the terminal receiving terminal is a Fourier transformer (FFT) 160-1, 160-2, ..., 160-M as many as the number of reception antennas (M), the signal detector (170), parallel- A serial (P / S) converter 180 and a channel decoder 190. In addition, the terminal antennas 140-1, 140-2, ..., 140-M are connected to the terminal transmitter during downlink communication through the respective antenna switches 150-1, 150-2, ..., 150-M. In case of uplink communication, the terminal is connected to the terminal receiving terminal.

In FIG. 2, the base station transmitting end is a serial-to-parallel converter 210, a signal copier 220, a beam weight multiplier 230, an inverse Fourier transformer 240-1, 240-2, ..., 240 as many as the number of antennas (L). -L). In addition, the base station receiving stage is a Fourier transformer 270-1, 270-2, ..., 270-L as many as the base station antennas (L), the channel estimator 290, the signal detector 280, and the parallel serial (P / S) Converter 320 and channel decoder 330 are included. In addition, the base station antennas 250-1, 250-2, ..., 250-L are connected to the base station receiving end in downlink communication through the respective antenna switches 260-1, 260-2, ..., 260-L. In case of uplink communication, the base station is connected to the base station transmitter.

Referring back to FIG. 1, the S / P converter 110 of the terminal transmitter converts the input channel coded symbols into C parallel signals.

The signal copier 120 copies as much as the number of terminal antennas (M). In addition, each of the inverse Fourier transformers 130-1, 130-2,..., 130 -M respectively inputs the C parallel signals to generate one OFDM symbol.

Thereafter, the OFDM symbols 121-1, 121-2,..., 121 -M output from the signal copier 120 are respectively inversed Fourier transformers 130-1, 130-2,..., 130 -M. Is transmitted through the terminal antennas 140-1, 140-2, ..., 140-M.

After the above process, the signal is received through the L terminal antennas 250-1, 250-2, ..., 250-L shown in FIG. 2, and then L Fourier transformers 270-1, 270-2, ..., 270-L outputs parallel signals 271-1, 271-2, ..., 271-M.

The Fourier-transformed signal is input to the channel estimator 290 and the signal detector 280. The signal detector 280 outputs its own C detected signals using the results of the channel estimator 290. do.

The detected signal outputs a series of serial signals through the parallel-to-serial converter 320, and the serial signals output the final result signal (Decoded data) through the channel decoder 330.

Here, the channel estimator 290 outputs a channel matrix for each pilot of each subcarrier to calculate the beamforming weight. For example, the channel estimator 290 may determine the c subcarrier. Channel matrix of Equation 10 from the first pilot Will be estimated.

On the other hand, Figure 3 shows the structure of the beam weight generator 310 of the base station in the OFDM / TDD smart antenna system according to an embodiment of the present invention.

Referring to FIG. 3, the beam weight generator 310 according to an embodiment of the present invention includes a spatial covariance matrix generator 311 for each pilot, a spatial covariance matrix generator 312 for each subcarrier, a short-term spatial covariance matrix generator 313, and a long term. It consists of a spatial covariance matrix generator 314, an eigendivider 315, an intercarrier spatial covariance interpolator 316, and a beam weight selector 317.

In the beam weight generator 310 according to an embodiment of the present invention, the spatial covariance matrix of each subcarrier of Equation 13 is obtained from the channel matrix of each pilot of each subcarrier through the spatial covariance matrix generator 311 of each pilot. You will get it.

Subsequently, the spatial covariance matrix for each pilot of each subcarrier is input to the spatial covariance matrix interpolator 316 for each subcarrier to output an instantaneous spatial covariance matrix for each subcarrier according to Equation 14 described above.

In this case, the spatial covariance matrix for each subcarrier generates the short-term spatial covariance matrix by Equation 15 described above through the short-term spatial covariance matrix generator 313, and then the above-described equation through the long-term spatial covariance matrix generator 314. By 16, the long-term spatial covariance matrix is output.

If, in Equation 16 Is 0, the result is In this case, there is no need to separate the long-term spatial covariance matrix and the short-term spatial covariance matrix.

Next, the eigendivider 315 receives the long-term spatial covariance matrix and outputs L eigenbeams according to Equation 17 described above.

As described above, a subcarrier used for downlink and a subcarrier used for uplink are typically different in an OFDM system. Therefore, the spatial covariance matrix for each subcarrier of the uplink obtained using the uplink according to the frequency coherent characteristic between the subcarriers. To the subcarrier spatial covariance interpolator 316, the K downlink spatial covariance matrix for each subcarrier Outputs

In addition, the spatial covariance matrix for each unique beam and subcarrier The beam weight selector 317 and input the beam weight for each subcarrier by Equation 18 (311-1), (311-2) and Outputs (311-K).

Referring back to FIG. 2, the S / P converter 210 of the base station transmitting end converts serially input channel coded symbols into K parallel signals, and the signal copier 220 converts the K parallel signals. The signal is copied by the number of terminal antennas (L), and the beam weight multiplier 230 serves to multiply the beam weight by the output of the signal copier 220.

On the other hand, Figure 4 shows the inside of the beam weight multiplier of the base station in the OFDM / TDD smart antenna system according to an embodiment of the present invention.

Referring to FIG. 4, in the beam weight multiplier according to an embodiment of the present invention, each of the inverse Fourier transformers 240-1, 240-2,..., 240-L receives one OFDM symbol by inputting K signals. The OFDM symbols are transmitted through the base station antennas 250-1, 250-2, ..., 250-L.

The OFDM symbols transmitted through the above process are received through M base station antennas 140-1, 140-2,..., 140 -M as shown in FIG. 1, and then each M Fourier transformers 160-. 1, 160-2, ..., 160-M output the parallel signals 161-1, 161-2, ..., 161-M.

The Fourier-transformed signal is input to the signal detector 170, and the detected signal outputs a series of serial signals through the parallel-to-serial converter 180. The serial signals are then passed through the channel decoder 190. The final result signal is output.

Meanwhile, according to an embodiment of the present invention, the optimal downlink beam obtained in the uplink i frame may be utilized in the downlink of the next frame i + 1 frame. If the uplink subcarrier spacing is larger than the coherent bandwidth or the terminal moves faster, an error may be generated by the wrong unique beam selection. The error generated as described above may have randomness, but may be mostly corrected by the channel decoder 190 at a later stage.

Finally, according to an embodiment of the present invention, by using the fact that all subcarriers of the OFDM / TDD system has a spatial covariance and that the TDD system has a channel reversibility, feedback of information necessary for beamforming over the uplink The spatial covariance matrix for eigenbeam formation is obtained by using the pilots of all subcarriers of the uplink.

While the invention has been shown and described in connection with specific embodiments thereof, it will be appreciated that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

According to the present invention, the complexity of the communication system can be reduced by using the fact that all subcarriers of the OFDM system have the same spatial covariance and that the TDD system has channel reciprocity.

In addition, according to the present invention, a spatial covariance matrix for eigenbeam formation can be directly obtained without feedback using pilots of all subcarriers of the uplink allocated for a user.

In addition, according to the present invention, necessary instantaneous spatial covariance of downlink can be obtained by using interpolation of instantaneous spatial covariance of uplink subcarriers.

In addition, according to the present invention, an error that occurs randomly due to incorrect selection of an optimal eigenbeam can be mostly recovered by a channel decoder at the rear of the receiver.

1 is a block diagram of a terminal of a smart antenna system of the OFDM / TDD scheme according to an embodiment of the present invention.

2 is a block diagram of a base station of a smart antenna system of the OFDM / TDD scheme according to an embodiment of the present invention.

3 is a block diagram of a beam weight generator of a base station in an OFDM / TDD smart antenna system according to an embodiment of the present invention.

4 is a block diagram of a beam weight multiplier of a base station in an OFDM / TDD smart antenna system according to an embodiment of the present invention.

Claims (21)

A smart antenna system for forming a downlink unique beam of orthogonal frequency division multiplexing (OFDM) / time division multiplexing (TDD) scheme, Multiple antennas for transmitting each OFDM symbol to a terminal receiving end or receiving each OFDM symbol transmitted from the terminal receiving end; Fourier transform each OFDM symbol received through the multiple antennas and output them as parallel signals, estimate a channel from the Fourier transformed parallel signal, and use the channel estimation result to perform the Fourier transformed parallel signal. A base station receiver for detecting a symbol from the base station, converting the symbol into a series of serial signals, and outputting a decoded signal; And Convert each channel-coded symbols serially input into a predetermined number of parallel signals and generate respective beam weights from each pilot channel of each subcarrier according to the channel estimation result of the base station receiver, thereby generating the respective beams having their own beams. Base station transmitter to generate and output symbols Base station transmission and reception apparatus of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 1, wherein the base station transmitting end, A serial / parallel (S / P) converter for converting the serially input channel coded symbols into a predetermined number of parallel signals; A signal copier for copying the parallel signal by the number of multiple antennas; A beam weight generator for generating a unique beam weight from each pilot channel of each subcarrier according to the channel estimation result; A beam weight multiplier for multiplying and outputting beam outputs generated from the beam weight generator by the output of the signal copier; And A plurality of inverse Fourier transformers for inputting the predetermined number of parallel signals to generate and output one OFDM symbol each Base station transmission and reception apparatus of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 2, wherein the beam weight generator, A pilot spatial covariance matrix generator for generating a pilot spatial covariance matrix of each subcarrier by inputting a channel matrix of each pilot according to the channel estimation result; A subcarrier spatial covariance matrix generator for generating a spatial covariance matrix for each subcarrier by inputting the spatial covariance matrix for each pilot by using a predetermined number of pilots present in one subcarrier; A short-term spatial covariance matrix generator for generating a short-term spatial covariance matrix by inputting each of the subcarrier spatial covariance matrices using uplink subcarriers all having the same spatial covariance matrix; A long term spatial covariance matrix generator for inputting the short term spatial covariance matrix and outputting a long term spatial covariance matrix;  An inter-subcarrier spatial covariance matrix interpolator for inputting an uplink subcarrier spatial covariance matrix obtained through the uplink and outputting a predetermined number of downlink subcarrier spatial covariance matrices; An eigendivider that inputs the long-term spatial covariance matrix and divides and outputs the eigenbeam into respective eigenbeams; And A beam weight selector for inputting the divided eigenbeam and the spatial covariance matrix for each subcarrier of the downlink and outputting beam weights for each subcarrier Base station transmission and reception apparatus of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 3, And the short-term spatial covariance matrix is a matrix equal to the long-term spatial covariance matrix when the length of a received packet is short. The method of claim 3, The eigenbeam of the eigendivider is defined as an eigenvector corresponding to a large eigenvalue among a predetermined number of eigenvectors, and is divided into eigenbeams to maximize reception power of a terminal among a plurality of eigenbeams. A base station transceiver of a smart antenna system for forming a unique beam. The method of claim 1, wherein the base station receiving end, A plurality of Fourier transformers for inputting OFDM symbols respectively received through the multiple antennas, Fourier transforming the number of antennas, and outputting parallel signals; A channel estimator for estimating a channel from the Fourier transformed parallel signal; A signal detector for detecting a symbol from the Fourier-transformed parallel signal using the result of the channel estimator and outputting a predetermined number of detected parallel signals; A parallel / serial (P / S) converter converting the detected parallel signals into a series of serial signals and outputting the converted serial signals; And A channel decoder for decoding and outputting the serially converted signal Base station transmission and reception apparatus of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 6, And the channel estimator outputs a channel matrix of each pilot for each subcarrier to calculate a beamforming weight. In the smart antenna system for forming a downlink unique beam of the OFDM / TDD scheme, Multiple antennas for receiving each OFDM symbol transmitted from the base station transmitting end or transmitting each OFDM symbol to the base station receiving end; OFDM signals transmitted by forming a unique beam from the base station transmitter are respectively input to Fourier transform and output as parallel signals. The symbols are detected from the Fourier transformed parallel signals, converted into a series of serial signals, and then decoded. Terminal receiving end for outputting; And Each of the channel-coded symbols input in serial is converted into a predetermined number of parallel signals, respectively, and the N parallel signals are copied by the number of multiple antennas in which a plurality of user signals are input as multiplexed N parallel signals. Terminal transmitter for generating and outputting OFDM symbols Device for transmitting and receiving a smart antenna system for forming a downlink unique beam including a. The method of claim 8, wherein the terminal receiving end, A plurality of Fourier transformers for inputting OFDM symbols respectively received through the multiple antennas, Fourier transforming the number of multiple antennas to output parallel signals; A signal detector for detecting a symbol from the Fourier transformed parallel signal and outputting a predetermined number of detected parallel signals; A P / S converter converting the detected parallel signal into a series of serial signals and outputting the serial signal; And A channel decoder for decoding and outputting the serially converted signal Device for transmitting and receiving a smart antenna system for forming a downlink unique beam comprising a. The method of claim 9, The channel decoder recovers an error that occurs randomly when an uplink subcarrier spacing exceeds a channel bandwidth and an interpolation is inaccurate or the terminal's moving speed is inaccurate. Terminal transceiver device of a smart antenna system for forming a unique beam. The method of claim 8, wherein the terminal transmitting end, A plurality of S / P converters as many as a plurality of base station antennas for converting channel-coded symbols inputted in series into a predetermined number of parallel signals, respectively; A signal copying machine for copying the N parallel signals by the number of base station antennas when a plurality of user signals are multiplexed and input as N parallel signals; And A plurality of inverse Fourier transformers as many as the number of base station antennas, each inputting the N parallel signals to generate one OFDM symbol Device for transmitting and receiving a smart antenna system for forming a downlink unique beam comprising a. A base station transmission / reception method of a smart antenna system for forming downlink unique beam for OFDM / TDD scheme, a) receiving each OFDM symbol transmitted from a terminal transmitter through uplink; b) Fourier transforming each of the received OFDM symbols and outputting each of them as a parallel signal, and estimating a channel from the Fourier transformed parallel signal; c) converting serially input channel coded symbols into a predetermined number of parallel signals; d) generating respective beam weights from each pilot channel of each subcarrier according to the channel estimation result; And e) forming a unique beam according to the respective beam weights, generating respective OFDM symbols, and transmitting them to the terminal receiving terminal through uplink Base station transmission and reception method of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 12, wherein the d) step, Iii) generating a spatial covariance matrix for each pilot of each subcarrier by inputting a channel matrix for each pilot according to the channel estimation result; Ii) generating a spatial covariance matrix for each subcarrier by inputting the spatial covariance matrix for each pilot using a predetermined number of pilots present in one subcarrier; Iv) generating a short-term spatial covariance matrix by inputting the spatial covariance matrix for each subcarrier, respectively, using a predetermined number of uplink subcarriers received by one user having the same spatial covariance matrix; Iii) outputting a long term spatial covariance matrix by inputting the short term spatial covariance matrix; Iii) outputting a spatial covariance matrix for each downlink subcarrier by inputting a spatial covariance matrix for each uplink subcarrier obtained through the uplink; Iii) inputting the long-term spatial covariance matrix and dividing the long-term spatial covariance matrix into respective eigenbeams; And Iii) outputting the beam weight for each subcarrier by inputting the divided eigenbeam and the spatial covariance matrix for each uplink subcarrier Base station transmission and reception method of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 13, Step iii), To obtain the spatial covariance matrix of each subcarrier by pilot, where Is the c subcarrier A base station transmit / receive method of a smart antenna system for forming a downlink unique beam, characterized in that the instantaneous spatial covariance matrix obtained by the second pilot tone. The method of claim 14, Step ii) is present in one subcarrier Using two pilots A base station transmission / reception method of a smart antenna system for forming a downlink unique beam, characterized in that it obtains a spatial covariance matrix of subcarriers c defined as follows. The method of claim 15, In step iii), the C subcarriers of the uplink allocated to one user all have the same spatial covariance matrix, A base station transmission / reception method of a smart antenna system for forming a downlink unique beam, characterized in that to obtain a short-term spatial covariance matrix ( R _ST ) by using a. The method of claim 16, Step iii) is a mathematical equation To obtain the long-term spatial covariance matrix ( R _LT ), where Is the number of frames, The base station transmission and reception method of the smart antenna system for forming a downlink unique beam, characterized in that the forcing factor (forgetting factor). The method of claim 17, Step iii) is a mathematical equation To perform unique partitioning, where Eigenvalue as Is a diagonal matrix with And v _L is an eigenvector corresponding to λ _L. The base station transmit / receive method of a smart antenna system for forming a downlink eigenbeam. The method of claim 18, Step iii), Output beam weights for each subcarrier using The base station transmission and reception method of the smart antenna system for forming a downlink unique beam, characterized in that the downlink k-th subcarrier. A method for transmitting / receiving a terminal of a smart antenna system for forming an OFDM / TDD type downlink unique beam, a) receiving each OFDM symbol having a unique beam transmitted from a base station transmitting end; b) Fourier transforming each of the received OFDM symbols and outputting the parallel symbols in parallel; c) detecting a symbol from the Fourier transformed parallel signal, converting the symbol into a series of serial signals, and outputting a decoded signal; d) converting each of the channel-coded symbols input in series into a predetermined number of parallel signals, respectively; e) generating the respective OFDM symbols by copying the N parallel signals by the number of terminal antennas inputted with N parallel signals multiplexed by a plurality of user signals; And f) transmitting each OFDM symbol to a base station receiving end, respectively Terminal transmission and reception method of a smart antenna system for forming a downlink unique beam comprising a. The method of claim 20, The step c) further includes recovering an error that occurs randomly when an interpolation is incorrect because an uplink subcarrier spacing exceeds a channel bandwidth or an optimal eigenbeam selection is inaccurate due to a fast moving speed of the terminal. Terminal transmission and reception method of a smart antenna system for forming a unique beam for uplink.