Research On ARQ Transmission Technique In MIMO Wireless Communication Systems

Practical wireless communication systems would inevitably encounter channel distortions, noise, or fading, leading to potential packet failures. The ARQ (automatic repeat request) technique is an effective means for packet error correction through incrementally retransmitting the failed packet. Meanwhile, the MIMO (multi-input multi-output) technique has gained special attentions in the next wireless communication systems for its advantages of improving the spectral efficiency and reliablity through spatial multiplexing or diversity mode. One new spatial freedom is provided by MIMO, which leads to that the advantages of MIMO ARQ systems can not been fully excavated by conventional ARQ techniques. It is therefore an important task to investigate the MIMO ARQ techniques.This thesis studies the ARQ transeciver techniques in MIMO systems. Firstly, ARQ affects the tradeoff between multiplexing and diversity due to its time diversity gain. Thus, the thesis studies the mode swithing algorithm for MIMO ARQ systems under the statitical CSIT (channel state information at transmitter). In addition, the precoding can further improve the system performance when the transmitter has prefect or partial CSIT. Therefore, this thesis further studies the ARQ precoding in conventional point-to-point MIMO systems. Furthermore, the ARQ precoding design in MIMO AF (amplify-and-forward) relay systems is proposed.Firstly, the excavations of diversity and multiplexing gains has different dependences on the channel characteristics and CSI, thus the performance analysis of diversity and multiplexing gains in different channel characteristics and CSI is the base of mode switching. However, the uncertainty of ARQ diversity gain leads to the difficulty in performance analysis. Under the statistical CSIT, the mode swithing of MIMO ARQ systems is proposed in the thesis for the first time. Multiple important practical factors are considered:transmit correlation, CEE (channel estimation error), packet loss probability constraint. The distributions of the post SINR (signal-to-interference-plus-noise ratio) for different modes are obtained by using Gamma approximations. Then the closed-form expressions of the throughput are derived when the ARQ technique is employed, based on which the throughput-based mode switching algorithm is proposed to improve the spectral efficency. Numerical results show that the proposed scheme outperforms the fixed transmission mode schemes and the considered factors affect the throughput and the mode switching point.After that, the precoding technique can further improve the performance when the transmitter has perfect or partial CSIT. Unlike the precoder design for the single transmission, the precoder design for ARQ retransmissions must take into account previous receptions but cannot go back to change precoders for previous transmissions. Therefore, the thesis further investigates how MIMO-ARQ precoders are designed under perfect CSIT and CEE.In LTE systems, the multiple codewords are employed where each codeword can be modulated and coded individually. Thus, the codeword that employs lower MCS (modulation and coding scheme) level will need lower SINR threshold to be decoded successfully, while the codeword that employs higher MCS level will need higher SINR threshold. Consequently, in the retransmissions, improving the subchannel gain of the worst codeword too much, as in conventional precoder schemes, will waste power. To solve the problem, with the novel objective of minimizing the packet error rate this thesis proposes a novel ARQ precoding structure. Then, the percoding design problem is reformulated as a joint optimization problem with power allocation (PA) and channel pairing. The optimal solution can be achieved by enumrating the channel pairings and allocating power corresponding to each channel pairing. Given a channel pairing, the thesis proposes a two-step PA algorithm. In this way, the ARQ performance of LTE systems can be improved significantly for the power waste problem is solved.Relaying has become a promising technology to extend the coverage and improve the spectral efficiency in cellular networks. Different from the typical MIMO systems, the ARQ precoder design in MIMO AF relay systems becomes more complex since more information needs to be considred. This thesis addresses the difficult ARQ precoder design problem for the first time in the academia. Firstly, with the objective of maximizing the retransmission capacity, the thesis proposes a novel progressivly optimal relay-only ARQ precoder when the perfect CSI is only available at the relay and the destination. Then the JSR (joint source and relay) ARQ precoder is considered assuming the perfect CSI known at all nodes. In the retransmissins, a novel precoder structure is proposed by introducing a channel pairing matrix in the source. Then, the JSR ARQ precoder design problem is formulated as a joint optimization problem with a non-convex PA and channel pairing. After that, a suboptimal PA algorithm and a simplified channel pairing search method are proposed. Secondly, we consider the robust JSR retransmission precoder design for MIMO AF relay systems with CEE. The effect of CEE to MSE (mean squared error) performance is derived, then we propose a novel ARQ precoder structure by employing matrix diagonalization and channel pairing. Accordingly, we formulate the precoder design as a joint optimization problem with source/relay PA and channel pairing. In order to achieve the globally optimal solution, we employ exhaustive search for the channel pairing and with each given channel pairing, we propose an optimal PA algorithm to solve the nonconvex PA problem by utilizing the necessary conditions for optimality. However, the complexity of the optimal channel pairing and PA is very high. In order to reduce the complexity, we further propose a suboptimal PA algorithm by iteratively optimizing the PA at the source and the relay, and a simplified channel pairing searching method based on the asymptotic optimal solution. Numerical results show that the proposed robust ARQ precoder shows significant performance gains. Moreover, the proposed suboptimal PA algorithm and simiplified channel pairing method have small performance degradation when comparing with the optimal ARQ precoder algorithm.In this thesis, the mode swithing is first studied for MIMO ARQ systems when the statistical CSIT is only available. Then, when the perfect or partial CSIT is available, the novel MIMO ARQ precoder is proposed to solving the waste power problem in the LTE systems. Furthermore, we propose a novel ARQ precoder for MIMO AF relay systems. All the researches in the thesis will help comprehend the effect of ARQ on MIMO systems and cast some bright light on the ARQ transceiver design of the practical MIMO systems and MIMO AF relay systems.