Linear Dispersion Codes For MIMO Communication Systems

Linear Dispersion Codes (LDCs) is a novel space-time coding sheme proposed in recently years. This thesis focuses on the enhanced techniques of LDCs and its application in MIMO communication systems. The thesis first describes a novel mode for LDCs with limited feedback. Based on this new model, this thesis discusses the above topic in three different system models: single-user MIMO, multi-user MIMO and novel MIMO cell architecture systems.First, LDCs system with finite-rate error-free feedback is proposed in the thesis. The optimal transmission codeword is selected at the receiver and the codeword index is sent to the transmitter. A simple random search algorithm is introduced for codebook generation. Moreover, the max-min singular value criterion is adopted for codeword selection. Simulation results showed that, with only 3-4 feedback bits, the low complexity Zero-Forcing receiver can approach the Maximum Likelihood (ML) performance.A new method to design codebook is also proposed for Linear Dispersion Codes (LDCs) systems with limited feedback in single MIMO systems. The extended codebook design method is introduced based on Grassmannian subspace packing and a mapping function, which is derived from the. relationship between SVDs of the classical multiplexing systems and the LDCs systems. Our proposed codebook can guarantee the maximum min-distance of the finite set. Simulation results show that, for 2×2 MIMO systems, if the feedback bit number is 4, the proposed codebook shows the similar performance to the optimal precoding codebook and has substantial performance advantage against the random search codebook.Furthermore, in single-user MIMO systems, we propose transmit antenna selection for linear dispersion codes (LDC-TAS). We present three criteria: maximum channel gain, maximum capacity and max-min post-SNR, to select the optimal transmit antennas when linear, coherent receiver is used over a slowly varying channel. Simulation results suggest that the max-min post-SNR criterion outperforms the other selection methods in a variety of modulation modes, such as QPSK, 8PSK and 16QAM. Compared with BLAST-TAS, under the same spectral efficiency, LDC-TAS shows significant diversity advantage. In low SNR environment, LDC-TAS is still better than STBC-TAS. For multi-user MIMO systems, a novel Linear-Dispersion Division Multiple-Access (LDDMA) for multi-user uplink MIMO systems is proposed in this paper. In the new multiplexing scheme, each user's information symbol is dispersed by a user-specific matrix (USM) both in space and time domain and linearly combined at base-station side. And a simple random search algorithm, based on capacity maximization criteria, is developed to generate a bank of user-specific matrices. Simulation results are presented to demonstrate the advantages of LDDMA, compared with traditional BLAST scheme and Time-Division Linear Dispersion Codes (TD-LDCs) scheme.Based on LDDMA systems, scheduling algorithms exploiting the multiuser selection diversity for LDDMA systems with zero-force receiver is studied in this thesis. For LDDMA systems, a user subset rather than optimal user is selected for simultaneously transmitting on uplink of wireless MIMO networks. Considering the heavy computation burden on exhaust search for optimal user subset, we present three greedy selection criteria: maximum channel gain, maximum capacity and max-min post-SNR, to select the suboptimal user subset. In addition, we generalize the scheduling algorithms: one user can be allocated several or no USMs according to its channel fading matrix. Simulations demonstrate that max-min post-SNR algorithm offers the best BER performance when zero-force, coherent receiver is used over a slowly varying channel.Finally, this thesis discusses the performance of 3 space-time coding schemes used in a new wireless communication cell structure. Equilateral triangle cell structure with the cooperation of base-stations is introduced and 3 space-time coding schemes: OSTBC, VBLAST and LDCs are analyzed based on this cell structure. Because of ISI in BLAST and low spectrum efficiency in OSTBC, neither of them is suitable for equilateral triangle cell structure. Simulation results suggest that, in equilateral triangle cell structure, the performance of LDCs is obviously better than OSTBC and VBLAST in a variety of spectrum efficiency and decoding algorithms. Specially, compared with OSTBC, LDCs has a 3-4dB gain.