KR20090053599A - Method and appratus selecting transmit antenna and estimating uplink multiple-input multiple-output channels in time-division multiplexing wireless communication systems - Google Patents

Abstract

The present invention provides a new method of selecting an uplink transmission antenna for maximizing uplink traffic transmission performance in a time division duplexing (TDD) multiple-input multiple-output (MIMO) system using an access terminal (AT) using a single transmission chain. And devices. It also provides new methods and apparatuses for estimating uplink MIMO channel by effectively transmitting reverse link sounding RS through the transmit antenna selected for traffic transmission. In a TDD MIMO system using a single transmission chain in the AT, a transmission antenna that instantaneously maximizes the reverse channel gain is selected through the downlink channel estimation of the AT, and RF switching of the single transmission chain of the AT to the selected antenna is performed. ) do. The AT transmits uplink traffic and uplink channel status through the selected transmit antenna. To maximize the performance of transmitting uplink channel state, the uplink channel state of other non-selected transmit antennas is transmitted in each reverse link time slot through a transmit antenna selected by the AT to actually transmit uplink traffic. The reference signal is transmitted to a base transceiver station (BTS). An embodiment proposed by the present invention to inform the channel state BTS of other transmission antennas not selected is as follows. In the first embodiment, the predistorted sounding RS transmission method multiplexes the predistorted sounding RS through downlink channel estimation of the AT, and estimates uplink channel information for each receiving antenna of the BTS. In the second embodiment, the channel-weighted sounding RS method multiplexes a sounding RS and a channel-weighted sounding RS that are not multiplied in a single reverse link time slot and simultaneously transmits the received signal. Estimate the information.

High speed packet communication, mobile communication system, time division multiplexing system, multiple input / output antenna system, MIMO, channel estimation, transmission antenna selection, sounding RS

Description

METHOD AND APPRATUS SELECTING TRANSMIT ANTENNA AND ESTIMATING UPLINK MULTIPLE-INPUT MULTIPLE- OUTPUT CHANNELS IN TIME-DIVISION MULTIPLEXING WIRELESS COMMUNICATION SYSTEMS}

The present invention selects a transmit antenna for uplink data transmission in a time division multiplexing wireless communication system using a transmit / receive multiple antenna, and estimates an uplink multiple-input multiple-output (MIMO) channel through the selected transmit antenna. A data transmission / reception apparatus and method are disclosed.

In order to provide high-speed and high-quality data service in wireless communication, a multiple-input / output antenna system (MIMO) using multiple antennas at a transmitting end and a receiving end has been proposed. Spatial multiplexing (SM), one of the MIMO technologies, forms multiple spatial sub-channels simultaneously between a transmitter and a receiver to independently generate data for each spatial subchannel. By transmitting, it is possible to increase the data transmission capacity on each link. In addition, space division multiple access (SDMA) technology can increase the transmission capacity of a system by sending data streams to multiple receivers simultaneously. The spatial multiplexing and spatial division multiple access require spatial processing at the transmitter and the receiver, and for this purpose, the transmitter and the receiver must have MIMO channel state information (CSI) between the transmitter and the receiver. .

In time division multiplexing (TDD) systems, the downlink from the transmitter of a base transceiver station to the receiver of an access terminal (AT) and the uplink from the transmitter of an AT to the receiver of a BTS share the same frequency band. Therefore, the downlink channel can be estimated from the uplink channel estimation using the reciprocity between the uplink and the downlink channel. Therefore, when a calibration is performed to compensate for the difference between the transmitting RF chains and the receiving RF chains at each of the transmitter and the receiver, it may be assumed that the channel responses of the downlink and the uplink are correlated with each other. . That is, when represent the uplink channel response calculated in the TDD MIMO system using n _T of transmit / receive antennas in n _T of transmit / receive antennas and the AT from the BTS to the H _U n _T xn _R matrix, the calculation The matrix H _D representing the downlink channel response is expressed as Equation 1 below.

In Equation 1, A ^T represents a transpose matrix of A and h _{u, m} is a channel vector received from the m th transmit antenna of AT to the n _T receive antennas of the BTS. In order to operate MIMO techniques such as spatial multiplexing and spatial division multiple access in the downlink, a transmitter of a BTS needs to know a downlink channel matrix H _D having an size of n _T xn _R. Accordingly, in a TDD system in which uplink and downlink channels are correlated with each other, the uplink channel matrix H _U is estimated in the BTS using a sounding RS (reference signal) transmitted from the transmitter of the AT, and the transpose matrix is calculated. The downlink channel matrix H _D can be estimated.

AT is a portable communication device that must maximize the performance of the battery. Therefore, AT cannot use many RF transmission chains that consume a lot of power. After all, AT is received when there n _R of transmission / received signals from the receive antenna processing through n _R of receive RF chain and sent during a single-transmitted RF chain for one song the n _R a processed signal over / receiving One of the antennas is selected and transmitted. When the AT uses the single transmission chain, the sounding RS processed through the single transmission chain of the AT is transmitted through only one of the n _R transmit antennas. In this case, an uplink channel matrix H _U having a size of n _T xn _R , which is a channel matrix between AT and BTS, cannot be estimated, and only a channel vector having a size of n _T x 1 of a receiving antenna of BTS and a single transmit antenna of the AT is selected. It can be estimated. That is, only one column vector of the n _R column vectors constituting the uplink channel matrix H _U can be estimated. Therefore, under the constraint that AT uses only a single transmission chain, an effective sounding RS transmission technique for reverse link MIMO channel estimation is required.

In addition, since the AT uses a single transmission chain, when the AT transmits data in the uplink, data processed through the single transmission chain of the AT is transmitted through the d * th antennas selected among the n _R transmit antennas. Here, d * may be selected by a certain rule in the range from 1 to n _R. Since the propagation environment from each transmit antenna of the AT to the BTS receive antennas in the uplink MIMO channel is very different, the channel gain from each transmit antenna to the BTS receive antennas is very different. Therefore, a technique for selecting and transmitting a transmission antenna that provides the highest uplink channel gain instantaneously among the n _R transmission antennas is required.

In conclusion, in a TDD MIMO system using a single transmission chain in AT, a sounding RS transmission technique for uplink channel estimation that is effectively combined with an AT transmission antenna selection technique for uplink data transmission is required.

Accordingly, the present invention provides a novel data transmission / reception apparatus and method for improving the transmission rate and error of traffic and sounding RS data transmitted on the reverse link in a TDD MIMO system using a single transmission chain in the AT.

In addition, in the TDD MIMO system using a single transmission chain in the AT, the present invention selects a transmission antenna that maximizes the reverse channel gain instantaneously through downlink channel estimation in the AT, and converts the single transmission chain of the AT into the selected antenna. RF switching. The AT provides an apparatus and method for transmitting uplink traffic and uplink channel state through a selected transmit antenna.

The present invention also provides new methods and apparatuses for estimating an uplink MIMO channel by effectively transmitting a reverse link sounding RS over a transmit antenna selected for traffic transmission.

In addition, the present invention is to maximize the performance of transmitting the uplink channel state, through the transmit antenna selected in the AT, the uplink traffic is actually transmitted, through the uplink channel state of the other transmit antennas that are not selected every reverse link time slot It provides a method and apparatus for transmitting to the BTS by using the sounding RS for each.

In the present invention, the predistorted sounding RS transmission method multiplexes the predistorted sounding RS through downlink channel estimation of the AT, and estimates uplink channel information for each receiving antenna of the BTS. As described above, the channel-weighted sounding RS system simultaneously transmits a sounding RS that is not multiplied by a weight and a channel-weighted sounding RS in one reverse link time slot, and the BTS processes the received signal to estimate uplink channel information. Provide a method.

In the present invention, a method of RF switching a single transmission chain of AT to one antenna having the maximum channel gain among n _R transmission antennas provides the best reverse link performance in the structure of an AT using only one transmission chain. can do.

In the transmission antenna selection method for uplink data transmission proposed in the present invention, since the AT independently determines the uplink transmission antenna through downlink channel estimation, no additional signaling with the BTS is needed, and a diversity gain and an average SNR gain are obtained. By providing, it is possible to considerably improve the transmission rate and error rate of the data transmitted through the antenna selected by the proposed method and the sounding RS.

The sounding RS transmission scheme for reverse link MIMO channel estimation proposed by the present invention transmits the uplink channel state of other unselected transmit antennas of the AT to the BTS through the transmit antenna providing the maximum gain in the reverse link. Diversity gain by average antenna selection and average SNR gain significantly improve the estimation performance of uplink channel state information included in the sounding RS. In addition, the "predistorted sounding RS transmission scheme" and "channel weighted sounding RS transmission scheme" proposed by the present invention may be applied by selecting a suitable scheme according to the number of reception antennas of the base station.

According to the present invention, in a TDD MIMO system using a single transmission chain in the AT, it is possible to transmit a sounding RS for uplink channel estimation effectively combined with the AT transmission antenna selection technique for uplink traffic data transmission.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention proposes a sounding RS transmission method for uplink channel estimation that is effectively combined with a transmission antenna selection technique for uplink data transmission in a TDD MIMO system.

The structure of the TDD MIMO system proposed by the present invention will be described with reference to FIG.

<Structure of Proposed TDD MIMO System>

1 illustrates a TDD MIMO system in which the AT 100 proposed by the present invention uses a single transmission chain. A structure for transmitting a single transmission chain 124 by switching to one antenna selected from n _R transmit antennas 102 to 106 for each uplink slot is proposed. In the present invention, the uplink traffic generator 122 that forms data and the RF unit that up-converts and transmits the data to the RF band are referred to as a transmission chain 124. The transmission chain generally refers to an RF unit excluding a transmission antenna. Traffic generated from the uplink traffic generator 122 is up-converted through the transmission chain 124, and the up-converted traffic is selected among n _R transmit antennas 102 to 106 through the RF switch 128. It is transmitted through a single antenna. A detailed method of selecting a transmission antenna for transmitting the uplink traffic will now be described in detail.

(1) AT Uplink Transmit Antenna Selection for Uplink Traffic Transmission

In the present invention, when the AT uses a single transmission chain in the uplink of the TDD MIMO system, the method for selecting an uplink transmission antenna of the AT maximizes the uplink channel gain through the downlink channel estimation of the AT.

를 추정한다.The signals received from the n _R receive antennas 102-106 in FIG. 1 during the t _D- th downlink time slot are treated as baseband signals by n _R receive chains 108-112, respectively. By using downlink sounding RSs transmitted in n _T transmission chains in a BTS, the downlink channel estimator 114 of the AT has a downlink channel matrix of size n _T xn _R as shown in Equation 2 below.

Estimate

은 상기 BTS의 n_T개의 송신 안테나로부터 AT의 m번째 수신 안테나로의 채널 벡터를 나타낸다. here,

Denotes a channel vector from the n _T transmit antennas of the BTS to the m th receive antenna of the AT.

를 이용하여, 송신 안테나 선택기(116)에서는 t_U번째 상향 링크 시간 슬롯에서의 트래픽 전송을 위해, 총 n_R개의 송신 안테나들 중에서 최대 이득을 제공하는

번째 송신 안테나를 다음 <수학식 3>에 따라 선택하여 RF 스위치(128)에게 전달한다.The downlink channel matrix estimated by downlink channel estimator 114

Is used, the transmit antenna selector 116 provides the maximum gain among the total of n _R transmit antennas for traffic transmission in the t _U th uplink time slot.

The first transmit antenna is selected according to the following Equation 3 and transmitted to the RF switch 128.

를 구성하는 n_R개의 행벡터(row vector)

중에서 최대 채널 이득을 갖는 안테나를 선택하 는 동작을 나타낸 것이다. 상기 <수학식 1>과 같이 TDD 시스템의 상향 링크와 하향 링크 채널간의 상호 연관성에 의해, 하향 링크 타임 슬롯과 상향 링크 타임 슬롯간의 시간 차이, 즉 t_U - t_D가 채널의 상관 시간(coherence time) 이내 라면,

가 성립하기 때문에, 상기 추정된 하향 링크 채널 행렬을 이용하여 선택된 AT에서의 d(t_U) 번째 송신 안테나는 n_R개의 송신 안테나들 중에서 상향 링크 채널 이득을 최대화 한다. 본 발명에서 제시한 상기 방법과 같이 순시적으로 채널 이득을 최대로 하는 송신 안테나를 선택하는 방식은 고정된 하나의 송신 안테나를 사용하는 경우보다 공간 다이버시티 효과가 n_R배 증가하여 다이버시티 이득이 증가하고, 평균 신호 대 잡음비 (signal to noise ratio, SNR)가 약 0.75n_R배 정도 개선되는 효과가 있다. 즉 본 발명의 송신 안테나 선택 방법은 다이버시티 이득과 평균 SNR 이득을 제공함으로써 역방향 링크 트래픽 데이터 전송률과 에러율을 상당히 향상 시킬 수 있다.Equation 3 is a downlink channel matrix

N _R row vectors that constitute

It shows the operation of selecting the antenna having the maximum channel gain among them. As shown in Equation 1, the time difference between the downlink time slot and the uplink time slot, that is, t _U -t _D is the correlation time of the channel due to the correlation between the uplink and downlink channels of the TDD system. ), Within

Since the d (t _U ) th transmit antenna at the AT selected using the estimated downlink channel matrix maximizes the uplink channel gain among the n _R transmit antennas. As in the method of the present invention, a method of selecting a transmission antenna that maximizes channel gains instantaneously increases the spatial diversity effect by n _R times compared to the case of using a fixed transmission antenna, thereby increasing the diversity gain. In addition, the average signal-to-noise ratio (SNR) is improved by about 0.75n _R times. That is, the transmission antenna selection method of the present invention can significantly improve reverse link traffic data rate and error rate by providing diversity gain and average SNR gain.

Upon receiving the selected antenna index information from the transmit antenna selector 116, the uplink RF switch 128 switches the transmit chain 124 to a transmit antenna selected from the n _R transmit antennas 102 to 106, and uplink traffic. Data generated by the generator 122 and the uplink channel information generator 120 using the sounding RS are transmitted.

(2) AT sounding RS transmission method for uplink MIMO channel estimation

The d (t _U ) th transmit antennas selected by the above-described "AT uplink transmit antenna selection for reverse link traffic transmission" method are used for the n _R transmit antennas of the AT during the t _U th uplink time slot. Provide the maximum channel gain to the BTS. In the present invention, by transmitting the uplink sounding RS through the selected d (t _U ) th transmit antenna, it is possible to considerably improve the estimation performance of the uplink sounding RS by the spatial diversity gain and the average SNR gain by the transmission antenna selection. have. That is, uplink sounding RS is transmitted through the d (t _U ) th transmit antenna selected for uplink data transmission.

However, in this case, the channel information of the selected single antenna is transmitted to the BTS, and the BTS does not know the sounding RS values of the remaining channels. In order to solve the above problem, there is a need for a method of transmitting sounding RS of all downlink channels through a single antenna selected for the present uplink transmission.

That is, in this case, the BTS estimates a sounding RS transmitted from the selected d (t _U ) th transmit antenna of the AT every uplink time slot, thereby providing an n _T x1 sized channel from the d (t _U ) th transmit antenna to the BTS. Only vectors can be estimated. In order to estimate the uplink channel matrix H _U in the BTS, an estimate of the n _R row vectors of H _U representing the channel state from each of the n _R transmit antennas of the AT to the BTS is required. Using the d (t _U ) th transmit antenna, the uplink channel state from the other transmit antennas of the unselected AT to the BTS must be sequentially transmitted to the BTS.

The present invention proposes a sounding RS transmission scheme for transmitting, to the BTS, an uplink channel state from other non-selected transmit antennas to the BTS through a transmit antenna selected by the AT to transmit uplink traffic. That is, assuming that the actual antenna index to transmit traffic in the uplink is d, and the index of the transmit antenna to transmit the uplink channel state is c, from the c-th transmit antenna using the d-th transmit antenna of AT We propose a sounding RS transmission scheme for transmitting uplink channel status to BTS. Since the selected transmit antenna d and the antenna c to transmit the uplink channel state are different from each other, d ≠ c. The present invention proposes the following two embodiments according to the type and type of sounding RS transmitted.

<First embodiment>

(A) Predistorted sounding RS transmission method

가 성립하기 때문에, AT는 c번째 송신 안테나로부터 BTS까지의 상향 채널 벡터 h_{U ,c}(r_U) 와 d번째 송신 안테나로부터 BTS까지의 상향 채널 벡터 h_U,d(t_U)를 알 수 있으며, 이 벡터들은 다음 <수학식 4>와 같이 표현된다.During the t _D- th downlink time slot, the downlink channel estimator 114 of the AT of FIG. 1 uses the downlink sounding RS transmitted from each transmit antenna of the BTS, where n _T xn _R as shown in Equation 2 above. Estimate the downlink channel matrix H _D (t _D ) of magnitude. By the correlation between the uplink and downlink channels of the TDD system,

Since AT is known, the upstream channel vectors h _{U , c} (r _U ) from the c th transmit antenna to the BTS and the up channel vectors h _{U, d} (t _U ) from the d th transmit antenna to the BTS can be known. , These vectors are expressed as Equation 4 below.

Here, the time slot index t _D is omitted for convenience of description. h _{U, c, k} and h _{U, d, k} (k = 1, L, n _T ) denote the kth element of the h _{U, c} and h _{U, d} vectors _, respectively. Therefore, in order to transmit the uplink channel vectors h _{U, c} from the c th transmit antenna to the BTS to the BTS, a total of n _T complex symbols must be transmitted through the d th transmit antenna.

Using the channel information estimated from the downlink channel estimator 114, the transmit antenna selector 116 selects and transmits a specific antenna index having the best downlink channel state to the RF switch 128. In addition, by using the channel information estimated from the downlink channel estimator 114, the predistorter 118 of the AT multiplies the complex weight a _k to be multiplied by the sounding RS transmitted from the d th transmission antenna. Calculate as

는 sounding RS에 곱해져, 상향 링크 타임 슬롯 내의 n_T개의 시간 구간

에 나누어져서 TDM( Time Division Multiplexing ) 방식으로 전송되거나, 직교하는 n_T개의 코드가 곱해져서 CDM(Code Division Multiplexing ) 방식으로, 또는 서로 다른 n_T개의 주파수 대역에 나뉘어져서 FDM(Frequency Division Multiplexing) 방식으로 전송될 수 있다. 후술될 본 발명의 실시 예는 n_T개의 복소 심볼 a_k가 TDM 방식으로 전송되는 경우를 설명할 것이다. 그러나 제안된 기술은 CDM과 FDM 방식으로 전송되는 시스템에도 적용 가능하다. 상기 수식에 의해 전치 왜곡기(118)에서 구한 복소 가중치 a_k값은 Sounding RS를 이용한 상향 링크 채널 정보 발생기(120)로 입력된다. Sounding RS를 이용한 상향 링크 채널 정보 발생기(120)는 상기 입력 받은 복소 가중치 값을 사용하여 상기 d번째 송신 안테나에서 전송되는 sounding RS에 곱하여 상향 링크 채널 정보를 발생하고, 이 값을 송신 chain(124)로 전달한다. 송신 chain(124)는 상향링크 트래픽 발생기(122)와 상기 상향링크 채널 정보 값을 조합하여 상승 변환한다. RF스위치(128)는 n_R개의 송신 안테나(102~106)들 중에 송신안테나 선택기(116)에 의해 선택된 단일 송신 안테나로 스위칭 하고, 상기 송신 chain(124)에서 출력된 신호를 송신한다. 상향 링크 타임 슬롯 내의 k 번째 시간 구간 T_P,k에서 전송되는 복소 심 볼은 sounding RS에 복소 가중치 a_k가 곱해진 심볼로, AT의 d번째 송신 안테나를 통해 전송되어 다음 <수학식 6>과 같이 신호 벡터 Y_k가 BTS에 수신된다.That is, the complex weight a _k is obtained by dividing the k th element of h _{U, c by} the k th element of h _{U, d} . Obtained n _T Complex Weights

Is multiplied by the sounding RS to provide n _T time intervals in the uplink time slot.

N is divided into and transmitted in a time division multiplexing (TDM) method, or is multiplied by orthogonal n _T codes, and then divided into different coder bands by CDM (Code Division Multiplexing) method, or divided into different n _T frequency bands. Can be sent to. An embodiment of the present invention to be described below will describe a case in which n _T complex symbols a _k are transmitted in a TDM scheme. However, the proposed technique is also applicable to the CDM and FDM transmission systems. The complex weight a _k value obtained by the predistorter 118 by the above equation is input to the uplink channel information generator 120 using the sounding RS. The uplink channel information generator 120 using the sounding RS generates uplink channel information by multiplying the sounding RS transmitted from the d-th transmit antenna using the received complex weight value, and transmits the uplink channel information to the transmission chain 124. To pass. The transmission chain 124 combines the uplink traffic generator 122 and the uplink channel information value to up-convert. The RF switch 128 switches to a single transmit antenna selected by the transmit antenna selector 116 among the n _R transmit antennas 102 to 106 and transmits the signal output from the transmit chain 124. The complex symbol transmitted in the k th time interval T _{P, k} in the uplink time slot is a symbol obtained by multiplying the sounding RS by the complex weight a _{k, and} is transmitted through the d th transmit antenna of AT. Similarly, the signal vector Y _k is received at the BTS.

동안, 해당 수신 안테나에서 수신된 심볼을 복구함으로써 h_{U ,c}를 추정할 수 있다. 도 2는 상기 제 1 실시 예에 의해 AT(202)에서 전송되는 UL(uplink) 타임 슬롯(time slot)과 BTS(200)에서 수신되는 신호를 도시한 것이다. 각 안테나(1,2, …, n_T)의 sounding RS값에 상기 <수학식 5>에 의해 구해진 복소 가중치

가 곱해진 형태의 전치 왜곡된 sounding RS(204)가 역방향 링크 타임 슬롯에서 T_{p ,1} T_p,2, …, T_p,nT의 n_T시간 구간으로 나누어져서 TDM 방식으로 전송된다. 상기 BTS(200)의 각 안테나(1,2, …n_T)에서는 상기 <수학식 6>과 같이 신호성분이 수신되고, 이를 통해 h_U,c의 원소들을 추정할 수 있다.The complex weight a _K is multiplied by each element of the h _{U, d} vector while passing through the uplink channel. In particular, the signal received at the k-th antenna of the BTS, that is, the k-th element of the received signal vector Y _K is the k-th element of the uplink channel vector h _{U, c} from the C-th transmit antenna to the BTS, h _{U, c, k} Is received. Therefore, the BTS can estimate h _{U, c, 1} by recovering the symbol received at the first receiving antenna in the T _{P, 1} time interval of the reverse link time slot _, and at the k th receiving antenna in the T _{P, k} time interval. By recovering the received symbols, h _{U, c, k} can be estimated. Thus, n _T time intervals in the reverse link time slot

In the meantime, h _{U , c} can be estimated by recovering the symbols received at the corresponding receive antenna. 2 illustrates an uplink (UL) time slot (UL) transmitted by the AT 202 and a signal received by the BTS 200 according to the first embodiment. Complex weights obtained by Equation 5 above to the sounding RS values of the antennas 1, 2, ..., n _T

The predistorted sounding RS 204 multiplied by T _{p , 1} T _{p, 2} ,... In the reverse link time slot. It is divided into n _T time intervals of T _{p and} n _T and transmitted in a TDM scheme. Each antenna 1, 2, ... n _T of the BTS 200 receives a signal component as shown in Equation 6, through which elements of h _{U and c} may be estimated.

Second Embodiment

(B) Channel weighted sounding RS transmission method

가 곱해진 sounding RS를 d번째 송신 안테나를 통해 TDM, CDM, 또는 FDM 방식으로 전송한다.In the channel-weighted sounding RS transmission method according to the second embodiment of the present invention, n _T complex elements of the sounding RS and h _{U, c that} are not multiplied by the weight in the reverse link time slot of the AT are used.

Transmits the sounding RS multiplied by TDM, CDM, or FDM scheme through the d-th transmit antenna.

가 곱해진 sounding RS가 TDM 방식으로 전송되는 경우를 설명할 것이다. 따라서, 상향 링크 타임 슬롯은 가중치가 곱해지지 않은 sounding RS가 전송되는 시간 구간 T_NW과 채널 가중치가 곱해진 sounding RS가 전송되는 시간 구간 T_W로 나뉘어 진다. 또한 T_W는 n_T개의 시간 구간

으로 나뉘어져 h_{U ,c}의 n_T개 복소 원소

가 곱해진 sounding RS가 전송된다.An embodiment of the present invention to be described below is n _T complex elements of the sounding RS and h _{U, c} not multiplied by the weight

The case where the multiplied sounding RS is transmitted in the TDM method will be described. Accordingly, the uplink time slot is divided into a time interval T _{NW in} which the sounding RS is not multiplied by the weight and a time interval T _W in which the sounding RS is multiplied by the channel weight. Also, T _W is n _T time intervals

N _T complex elements of h _{U , c} divided by

Is multiplied by a sounding RS.

The AT transmits an unweighted sounding RS, and the BTS estimates an uplink channel vector h _{U, d} from the d th transmit antenna to the BTS using the unweighted sounding RS during T _NW of the reverse link time slot. do. In the k-th time interval T _{W, k} of T _{W in} the uplink time slot _{, a} symbol multiplied by a complex weight h _{U, c, k} is transmitted to the sounding RS, and is transmitted through the d-th transmit antenna of AT. 7> the signal vector Y _K is received at the BTS.

The BTS receiver uses the uplink channel vectors h _{U, d} estimated by the non-weighted sounding RS to convert the received signal vector y _k into a received signal such as MRC (maximum ratio combining) or minimum-mean square error (MMSE). Do the processing. In the embodiment of the present invention, assuming the case of MRC reception signal processing, if the received signal vector Y _k is MRC reception signal processing _, the k th element h _U of h _{U, c} weighted to the sounding RS as shown in Equation (8) We can estimate _{, c, k} .

Accordingly, the BTS can estimate h _{U, c, 1} by recovering a symbol received at T _{W, 1} of a reverse link time slot, _and recover h _{U, c, k} by recovering a symbol received at T _{W , k} . It can be estimated. Therefore, it is possible to estimate h _{U, c} by recovering the symbols received during T _W.

3 illustrates an uplink (UL) time slot transmitted by the AT 300 transmitted by the second embodiment and a signal received by the BTS 306. Unweighted sounding RS 302 and T _{W, 1} , T _{W, 2} ,... During the T _{W, N} interval in one reverse link time slot. The channel weighted sounding RS 304 is transmitted in a TDM manner during, T _{W, n} T time. The transmitted signal is transmitted to antenna 1, antenna 2,... In BTS 306. , And received by the antenna n _T, wherein the signal is processed by signal MRC (Maximum Ration Combining) scheme, such as reference numeral _{308 T W, 1, T W} , 2, ... If the weighted sounding RS is output as shown by reference numeral 310 during the T, _{W and nT} intervals, the reverse link channel is estimated.

4 and 5 are flowcharts illustrating an operation of a transmitter / receiver.

4 is an operation flowchart of a terminal for transmitting channel estimation information to a BTS. In step 401, the AT informs the BTS of the number of transmit / receive antennas used by the AT during initial call setup. The proposed sounding RS transmission method for uplink MIMO channel estimation transmits uplink channel information of one AT transmitting antenna during one reverse link time slot. Therefore, in order to transmit the uplink channel information of the n _R transmit antennas of the AT, the BTS and the AT must promise a rule for determining the index C of the channel state transmit antenna for each reverse link time slot. For example, if the index C of the channel state transmitting antenna is sequentially changed as 1,2, L, n _R , 1,2, L, c = 1 in the first reverse link time slot, and n _R th C = n _R in the time slot, and c = 1 in the n _R +1 th time slot.

In the operation example of the proposed invention, it is assumed that the downlink time slot index t _D and the uplink time slot index t _D sequentially increase from 1.

In step 402, the AT estimates the downlink channel matrix H _D (t _D ) by using the downlink sounding RS transmitted from each transmit antenna of the BTS for each downlink time slot. By using the estimated downlink channel matrix H _D (t _D ), the following uplink time slot is performed in step 403 through the " method of selecting an uplink transmit antenna of the AT maximizing the uplink channel gain " proposed in the present invention. traffic from t _U transfer selects the transmission antennas d (t _U) of aT.

In step 404, the transmit antenna index c (t _U ) of the AT to transmit uplink channel information through the transmit antenna d (t _U ) selected in step 403 is determined. For example, when c (t _U ) is sequentially changed such as 1,2, L, n _R , 1,2, L, c (t _U ) = rem (t _U , n _R ). Here, rem (a, b) is a function for finding the remainder of a divided by b.

In step 405, AT uses the d (t _U ) th and c (t _U ) th vectors of the estimated downlink channel matrix H _D (t _D ) to propose a “predistorted sounding RS”. Calculate the predistortion weight of the sounding RS required for the "transmission scheme" or calculate the channel weight of the sounding RS required for the "channel weighted sounding RS transmission scheme". In operation 406 using the calculated weight, the sounding RS is multiplied and transmitted according to each reverse link time slot structure described in FIGS. 2 and 3 for each transmission scheme.

 The operation flowchart for channel estimation in the BTS is shown in FIG. First, the BTS acquires information on the number of transmit / receive antennas of the AT fed back from the AT in step 501, and in step 502, the sounding RS transmitted in the corresponding reverse link time slot is the reverse direction of the several transmit antennas of the AT. Determines whether to carry link channel information.

로 구성된

를 추정한다. 또한, 이를 transpose하여 505 과정에서는 하향 링크 MIMO processing에서 요구되는 하향 링크 채널 행렬 H_D(n_R)를 구한다. 마지막으로 506 과정을 통해 BTS는 t_U ? n_R 1인 역방향 링크 타임 슬롯에서 추정된 채널 벡터들은 H_U(n_R)의 rem(t_U,n_R) 번째 행 벡터를 업데이트 한다. 본 발명에서는 TDD MIMO 시스템의 상향 링크 채널 이득을 최대로 하는 AT의 송신 안테나 선택 방법을 제안하였다. 제안하는 방식은 AT의 하향 링크 채널 추정을 통해, 순시적으로 채널 이득을 최대로 하는 AT의 송신 안테나를 선택함으로써, 고정된 하나의 송신 안테나를 사용하는 경우보다 공간 다이버시티 order가 n_R배 증가하여 다이버시티 이득이 증가하고, 평균 신호 대 잡음비(signal to noise ratio : SNR)가 약 0.75n_R배 정도 개선된다. 제안하는 송신 안테나를 선택하는 방식은 AT가 하향 링크 채널 추정을 통해 상향 링크 송신 안테나를 독자적으로 결정하기 때문에, BTS와의 추가적인 signaling이 필요 없으며, 다이버시티 이득과 평균 SNR 이득을 제공함으로써 역방향 링크에서 전송되는 트래픽 데이터와 sounding RS의 전송률과 에러율을 상당히 향상 시킬 수 있다.In step 503, the BTS estimates an uplink channel vector of the c (t _U ) th transmit antenna according to the reverse link time slot structures described in FIGS. 2 and 3 according to a reverse link sounding RS transmission scheme. 504. The process of the n _R of consecutive reverse link time slot, the reverse link channel estimate with n _R of the estimated estimation vector in a process for the

Consisting of

Estimate In addition, by transposing this process, a downlink channel matrix H _D (n _R ) required in downlink MIMO processing is obtained. Finally, through the process 506, BTS t _u ? The channel vectors estimated in the reverse link time slot of n _R 1 update the rem (t _U , n _R ) th row vector of H _U (n _R ). The present invention proposes a method of selecting an AT antenna for maximizing the uplink channel gain of a TDD MIMO system. The proposed scheme selects the transmit antenna of the AT that maximizes the channel gain instantaneously through the downlink channel estimation of the AT, thereby increasing the spatial diversity order by n _R times than using a fixed transmit antenna. The diversity gain is thus increased, and the average signal to noise ratio (SNR) is improved by about 0.75 n _R times. Since the AT selects the uplink transmit antenna independently through downlink channel estimation, no additional signaling with the BTS is required, and the transmit antenna is selected by providing the diversity gain and the average SNR gain. It can significantly improve the transmission rate and error rate of the traffic data and the sounding RS.

In the present invention, two sounding RS transmission schemes are proposed for transmitting uplink channel states of other non-selected transmit antennas to a BTS through a transmit antenna selected by the AT and transmitting uplink traffic. The "channel weighted sounding RS transmission method" transmits a sounding RS not multiplied by a weight and a sounding RS multiplied by n _T channel weights during one reverse link time slot, thereby transmitting a sounding RS multiplied by the channel weight. The time interval is reduced than the "predistorted sounding RS transmission scheme". The decrease in the time interval for transmitting the sounding RS multiplied by the channel weight causes a decrease in the signal energy for the weighted sounding RS estimation, thereby degrading the channel estimation performance, but as shown in Equation 8, the &quot; channel weighted sounding &quot; RS transmission scheme "may compensate for this by additionally obtaining MRC gains by the n _T receive antennas of the BTS. Diversity order is increased by n _T times by the receiving MRC of the BTS, thereby obtaining diversity gain and increasing the average SNR by n _T times.

On the other hand, the "predistorted sounding RS transmission method" does not need to transmit a sounding RS that is not multiplied by weight by predistorting and transmitting the sounding RS through downlink channel estimation. Therefore, since the time interval for transmitting the predistorted sounding RS becomes larger than the "channel weighted sounding RS transmission scheme", the signal energy for predistorted sounding RS estimation is increased to improve the estimation performance.

Therefore, when the number of base station receiving antennas n _T is large, the "channel weighted sounding RS transmission scheme" in which the gain by MRC reception signal processing increases is suitable, and when the number of base station receiving antennas n _T is small, the predistorted sounding RS is small. The "predistorted sounding RS transmission method" having a relatively large time interval for transmitting the C is suitable.

1 is a diagram illustrating an example of a transmitter structure in which an AT switches a single transmission chain of an AT to one antenna selected from among Tx transmission antennas in every uplink slot in a TDD MIMO system using a single transmission chain.

FIG. 2 is a diagram illustrating an example in which a predistorted sounding RS is divided into two time intervals in a reverse link time slot, transmitted in a TDM scheme, and received and estimated by being divided in each receiving antenna of a BTS.

FIG. 3 illustrates an example in which a weighted sounding RS and a channel weighted sounding RS, which are not multiplied in a weight in one reverse link time slot, are transmitted by the TDM scheme in the channel weighted sounding RS transmission scheme, and the MRC received signal is processed and restored in the BTS. Drawing

4 is an operation flowchart of a terminal for transmitting channel estimation information to a BTS;

5 is an operation flowchart in a BTS for downlink channel estimation

Claims (7)

In a mobile communication system using a multiple antenna (MIMO), the terminal selects an uplink transmission antenna using a single transmission chain (Chain) and transmits channel information, Estimating a downlink channel matrix of the multiple antennas; Determining a single transmit antenna index d of a terminal having a best channel state from the estimated channel matrix; Determining a transmit antenna index c corresponding to channel information to be transmitted through the single transmit antenna; Calculating weights of the channel information transmission antenna indexes to be transmitted; Generating uplink channel information by using the weight, and transmitting the generated uplink channel information and uplink traffic together. The method of claim 1, The calculating of the weights of the indices of the channel information transmitting antennas to be transmitted comprises calculating weights using a predistortion weighting method. The method of claim 1, The calculating of the weights of the indices of the channel information transmitting antennas to be transmitted comprises calculating a weight using a channel weighting method. In a mobile communication system using a multiple antenna (MIMO), when the terminal transmits a signal through a single antenna using a single transmission chain (Chain), in the method for obtaining channel information in the base station, Receiving the number of transmit / receive antennas of the terminal; Obtaining a transmission antenna index based on the number of antennas of the received terminal; Estimating an uplink channel matrix of the transmit antenna index to estimate an uplink channel matrix; Obtaining a downlink channel matrix using the estimated uplink channel matrix; And updating the row vector of the downlink channel matrix with the downlink channel matrix value. In a mobile communication system using a multiple antenna (MIMO), when the terminal uses a single transmission chain (chain), in a method for transmitting uplink channel information, Estimating a downlink channel to select a single transmit antenna; Calculating a complex weight as a ratio between channel values of the selected single transmit antenna and channel values of the remaining unselected transmit antennas; And multiplying the complex weight by a sounding RS transmitted from a selected antenna and dividing the complex weight into time intervals in one uplink time slot and transmitting the same by a TDM, CDM, or FDM scheme. . In a mobile communication system using a multiple antenna (MIMO), when the terminal uses a single transmission chain (chain), in a method for transmitting uplink channel information, Generating a sounding RS that is not multiplied by its weight, n _T complex elements of h _{U , c}

Multiplying to generate a sounding RS multiplied by the channel weight, Assigning a sounding RS not multiplied by the weight to some time interval T _NW in one uplink time slot, and assigning a sounding RS multiplied by the channel weight to the remaining slot time interval T _W ; And transmitting the uplink time slot through a single transmit antenna. In a mobile communication system using a multiple antenna (MIMO), the terminal selects an uplink transmission antenna using a single transmission chain (Chain), the apparatus for transmitting channel information, The transmitter is A downlink channel estimator for receiving a downlink channel signal, a downlink channel estimator for estimating a downlink channel using the received downlink channel signal, A transmit antenna selector for selecting a transmit antenna using an output value of the downlink channel estimator; A predistorter for calculating a predistortion value using the downlink channel estimate value, The transmitter is An uplink channel information generator using sounding RS for receiving the predistorter value and generating uplink channel information; And a transmission chain for selecting a single transmission antenna for transmitting the uplink channel information and uplink traffic, and an RF switch for connecting the transmission chain and the transmission antenna. .

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