Resaearch On The High Efficient Coding Technology Of MIMO-OFDM Based On Bit-Interleaved Coded Modulation

Multiple Input Multiple Output(MIMO) system can use multipath components to combat multi-path fading for its physical features, but when MIMO tranplants from narrowband system to wideband system, it is inevitable that channel will frequency-selectively fade. On the other hand, Orthogonal Frequency Division Multiplexing(OFDM) has the ability of anti-multipath interference and anti-frequency selective fading. But the raise of the spectrum efficiency limits. Therefore, the combination can not only increase the data transmission rate and spectrum efficiency, but also combat multi-path and frequency selective fading. In order to improve the performance of the whole system, it is necessary to take some measures such as increasing the transmission bandwidth or transmit power, enhance the order of the modulation or the point of the constellation, which will undoubtedly lead to the complexity of system realization and the increase of power loss. Accordingly, It is a key to reduce the complexity of system realization and power loss by the change of physical link. And the combination with high-effective coded modulation can obtain higher coding gain and lower bit error rate without increasing extra system bandwidth, which is suitable for limited bandwidth channel. If Bit-Interleaved Coded Modulation(BICM) is combined with OFDM and MIMO, namely BICM-MIMO-OFDM System,it can make effective use of multi-diversity of space, time and frequency, and realize the organic combination of channel code and spatial multiplexing, effectively raise the data rate and develop the potentiality of MIMO channel, so that make sure of reliable, high efficient wireless communication over frequency selective fading channels. In this thesis the technology of modulation and coding scheme and signal detection methods which can compromise the complexity and performance was studied based on the choice of the transmit diversity and the optimization of decoding algorithm over the receiver in the MIMO system combined with BICM-OFDM coded modulation. This thesis emphatically introduced BICM and OFDM technology, analysis the theoretical basis, main characteristics of the BICM and OFDM and the advantage of the combination of the two over the fading channels. The application of BICM together with OFDM on the MIMO system over frequency selective fading channels and the study of detection algorithm were discussed. The primary contributions included in this dissertation can be summarized as follow:1.The choice of modulation and coding scheme. BICM together with OFDM was a technology which can combat the effects of the frequency selective fading. In this thesis, the application of BICM and OFDM on the MIMO system constituted MIMO-OFDM system based on BICM coded modulation. The performance was analyzed and simulated, and the performance bound provided the basis for the choice of modulation and coding scheme.2.Performance analysis and precoding design. The influence of mapping mode, convolution code, frame length and other parameters over the system performance was discussed. A kind of sectional full-rate precoding method was introduced, and rotated constellation and mesh generation matrix methods are both used for the characteristics of this system. Simulation showed that it could maximize the coding gain to improve the transmission performance, greatly increased the system capacity, and lower system bit error rate.3.The optimization of detection algorithm. To solve the problem that transmit antenna in higher order modulation constellation optimal detection algorithm and the current suboptimal detection algorithm with higher complexity, according to the advantages of spherical algorithm, a simplified improved spherical detection algorithm was applied to this system. The spherical radius of the improved algorithm can adaptively change with the channel parameters and the size of the modulation order, which greatly simplified the system complexity. Compared with other algorithms and programs, it had good adaptability and robustness in different channel conditions, antenna configuration and modulation.4.The simplification of iterative decoding and detection. The high requirements of the spectral efficiency made it necessary to consider the higher order modulation constellation, especially when further integrates MIMO to increase data rate, some of the current iteration decoding algorithms affected its practical application due to their complexity. The thesis introduced a system model of BICM-ID iterative decoding structure united with spherical decoding algorithm.Replaced the MAP demodulation in the iterative decoding process with the improved sphere algorithm to approximate the original MAP decoding performance. And as the signal-to-noise ratio and iteration number increase, the algorithm could effectively reduce the error rate. Relative to the maximum likelihood algorithm, system complexity was significantly reduced while losing a small performance.