Closed Loop Transmit Diversity Research Articles

CLTD-OSIC NONLINEAR PRECODING ALGORITHM FOR MU-MIMO TDD MULTIUSER SYSTEMS

A modification of the closed-loop transmit diversity (CLTD) precoding algorithm is considered for using in multiuser multiple input multiple output (MU-MIMO) systems with the time division duplex (TDD). The closed-loop transmit diversity (CLTD) precoding algorithm based on the reciprocity relation between the receiving and transmitting paths possesses a number of advantages as compared to the known algorithms. It is suggested to apply the procedure of ordered successive interference cancelation (OSIC) while forming up the precoding matrix that would allow a significant increase of the resistance to interference during reception. The results of modeling with the help of the MATLAB software package are provided. The results demonstrate the efficiency of the suggested CLTD algorithm modification.

Nonlinear iterative precoding algorithm for MIMO multiuser systems

A modification of the known linear precoding algorithm CLTD (closed-loop transmit diversity) intended for multiuser radio communication systems and using theMIMOtechnology has been proposed. The efficiency of the original precoding algorithm CLTD possessing a number of advantages as compared to earlier precoding methods based on complete information about the communication channel state is enhanced at the expense of introducing nonlinearity. The use of nonlinear procedure of ordered successive interference cancellation (OSIC) in forming the precoding matrix makes it possible to significantly increase the noise immunity of the entire system as a whole at the expense of a slight rise of algorithm computational complexity. In addition, the results of computer simulation are presented reflecting the efficiency of the proposed modification of the algorithm for forming a precoding matrix as compared to the original CLTD algorithm.

ECMA-392 시스템을 위한 부 반송파 그룹핑 기반 폐루프 전송 다이버시티 기법 설계

ECMA-392는 개인 휴대용 장치를 위한 최초의 CR (cognitive radio) 표준으로서, 2개까지의 전송 안테나를 지원하며 이를 위한 전송 다이버시티 기법으로는 개방루프 방식만을 지원한다. 본 논문에서는 ECMA-392 시스템을 위한 간단한 형태의 부반송파 그룹핑(sub-carrier grouping) 기반 폐루프 전송 다이버시티 기법을 설계하고자 한다. ECMA-392 시스템에 적합한 부반송파 그룹핑 방법을 제시할 것이며, 각각의 부 반송파 그룹에 대해 채널 환경에 따른 전송 안테나 선택 방법을 제안한다. 이때 피드백 정보량을 줄이기 위해, 채널 환경에 따른 전송 안테나 결정을 수신단에서 하고 결정된 전송 안테나의 인덱스 값만을 송신단에 보내주는 방식을 사용한다. ECMA-392 표준에서 제시하는 개방루프 전송 다이버시티 기법들과의 성능비교를 통해, ECMA-392 시스템에 폐루프 전송 다이버시티 기법의 도입 여부에 대한 판단 근거를 제시하고자 한다.

Closed-Loop Transmit Diversity Techniques for Small Wireless Terminals and Their Performance Assessment in a Flat Fading Channel

Closed-loop transmit diversity is considered an important technique for improving the link budget in the third generation and future wireless communication standards. This paper proposes several transmit diversity algorithms suitable for small wireless terminals and presents performance assessment in terms of average signal-to-noise ratio (SNR) and outage improvement, convergence, and complexity of operations. The algorithms presented herein are verified using data from measured indoor channels with variable antenna spacing and the results explained using measured radiation patterns for a two-element array. It is shown that for a two-element array, the best among the proposed techniques provides SNR improvement of about 3 dB in a tightly spaced array (inter-element spacing of 0.1 wavelength at 2 GHz) typical of small wireless devices. Additionally, these techniques are shown to perform significantly better than a single antenna device in an indoor channel considering realistic values of latency and propagation errors.

Closed-Loop Transmit Diversity Techniques for Small Wireless Terminals and Their Performance Assessment in a Flat Fading Channel

Closed-Loop Transmit Diversity Techniques for Small Wireless Terminals and Their Performance Assessment in a Flat Fading Channel

Closed-Loop Transmit Diversity with Imperfect Feedback

In the closed-loop transmit diversity systems, feedback delay and feedback error, as well as the sub-optimum reconstruction of the quantized feedback data, are the usual sources of deficiency. We address the efficient reconstruction of the beamforming weights in the presence of the feedback imperfections, by exploiting the residual redundancies in the feedback stream. We propose two approaches to improve the performance. One is based on using a channel predictor at the receiver to compensate for the delay. Another approach deals with the feedback imperfections in a unified reconstruction algorithm using JSCC techniques. Furthermore, we introduce the concept of Blind Antenna Verification (BAV). The closed-loop Mode 1 of the 3GPP standard is used as a benchmark, and the performance is examined within a Wideband-CDMA simulation framework. It is demonstrated that the proposed algorithms outperform the standard at all mobile speeds, and are suitable for the implementation in practice.

A Robust Closed-Loop Transmit-Diversity Scheme with Unknown CSI Reliability

In a closed-loop scenario, the performance of transmit-diversity schemes for a multiple antenna system depends on the reliability of the channel state information (CSI). However, estimating the reliability of the instantaneous CSI at the transmitter is a challenging task. In this paper, we propose a robust transmit-diversity scheme for the case when the instantaneous CSI available at the transmitter is imperfect and its reliability is unknown to the transmitter. We show by simulation that our proposed scheme is efficient when the CSI reliability varies arbitrarily in every channel realization.

Capacity of Generalized UTRA FDD Closed-Loop Transmit Diversity Modes

Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennae have been included into universal terrestrial radio access (UTRA) frequency division duplex (FDD) specification. Closed-loop modes provide larger system capacity than open-loop modes, but they need additional side information of the downlink channel in the transmitter. In FDD systems this requires a separate feedback channel. Quantization of channel state information (CSI) in closed-loop transmit diversity schemes decreases the performance when compared to a closed-loop system where the transmitter has access to complete CSI. In this paper, we analyze the effect of quantization of CSI and deduce approximate capacity formulae for closed-loop transmit diversity schemes that are generalizations of the closed-loop schemes included in UTRA FDD specification. Moreover, we calculate approximation error and show by simulations that our approximation is tight for flat Rayleigh fading environments with and without fast transmit power control.

On the Performance of Closed-Loop Transmit Diversity with Noisy Channel Estimates and Finite-Depth Interleaved Convolutional Codes

In this paper, closed-form expressions for the uncoded bit error probability of closed-loop transmit diversity (CLTD) algorithms with two transmit and one receive antennas and noisy channel state information (CSI) in time-varying Rayleigh fading channels are derived. Two CLTD algorithms considered are the phase-amplitude CLTD (PA-CLTD), where the transmit antennas may transmit with different signal energy, and the phase-only CLTD (PO-CLTD), where the transmit antennas must transmit with the same signal energy. In addition to the uncoded bit error probability, this paper also derives the pairwise error probability when finite-depth interleaved convolutional codes are used with CLTD algorithms. However, due to the complexity of the coded system, the pairwise error probabilities are not in the closed-form expressions. The results have shown that PA-CLTD performs slightly better than PO-CLTD although PA-CLTD requires significantly more feedback information and that, when the Doppler spread is large, the performance of CLTD algorithms may degrade significantly. Moreover, a comparison between PA-CLTD, the Alamouti space-time code and the SISO system indicates that PA-CLTD outperforms the other two systems when the Doppler spread is small and the pilot SNR is large. Finally, the analytical results are compared with results from Monte Carlo simulation and the comparison shows that the analytical results match well with the simulation results.

Closed-loop transmit diversity systems with hybrid antenna selection

The paper investigates closed-loop transmit diversity (CLTD) systems with antenna selection technique. The expected received signal-noise-ratio (RxSNR) of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.

Efficient Weight Vector Representation for Closed-Loop Transmit Diversity

For a closed-loop transmit (Tx) diversity, the Tx weights are calculated at a receiver, and fed back to a transmitter. As the number of Tx antennas increases, the potential gain of closed-loop Tx diversity may be significant. However, the amount of feedback information, which is the number of Tx weights that should be fed back, linearly increases, and the performance improvement of a closed-loop Tx diversity system may not be as significant as expected due to delay in the feedback process. Thus, an efficient Tx weight representation, which can reduce the amount of feedback information, is needed. In this letter, a Tx weight vector representation is presented, and its performance is analyzed. Analysis shows that this weight vector representation, referred to as basis selection, significantly reduces the amount of feedback information with little performance degradation.