Block Codes Of The Space-time Wireless Communications

Recently, multiple input multiple output (MIMO) system which originates from the employment of multiple antennas at transmitter and receiver has many advantages such as large system capacity,high spectral efficiency. On the other hand, orthogonal frequency division multiplexing (OFDM) which bases on the orthogonal transmission of sub-carriers also has some obvious merits such as strong anti-multipath ability, high spectral efficiency .The combination of the two techniques MIMO-OFDM, has become a hotspot recently and regarded as promising technique for future next-generation mobile communication systems.Space-time block codes (STBC) based on orthogonal design has attracts enough attentions in its applications in MIMO-OFDM systems for its full diversity exploiting and low coding/decoding complexity .These applications include not only system performance improvement ,but also reduction of the peak to average power ratio in MIMO-OFDM systems.Under these backgrounds, this paper first studies space-time block codes under the single carrier, flat fading situation, discusses the encoding/decoding principle and its performance under different channels. Then, the author focused on the performance of space-time codes under time selective and frequency selective channels, uncovered the fundamental cause of how maximum Doppler shift and power delay profile influences the performance of space-time codes through deduction and simulation. Finally, the author find the feasibility of applying space-time block codes in the reduction of peak to average power ratio in OFDM systems, thus proposed a new PAPR reduction method.The method proposed in this paper mainly bases on the frequency freedom exploitation, assimilates conventional PAPR reduction thought from probability view, meanwhile,it guarantees the structure of space-time/frequency block codes in multiple carriers system. The analyses and simulation results suggest that the method not only achieves some reduction effects, but also has no performance degradation.According to the development of space-time block codes, the research on its performance approaches saturation, and more studies rely on the performance discussion of space-time codes with modified structure, therefore, the proposed method which extracts other merits other than coding gain is a favorable exploration in applying space-time block code. Due to low complexity and obvious reduction effects, this method also has some value in practical systems.