Research On Turbo Iteration Techniques In Wireless Communication Systems

The demand for high-speed mobile wireless communications is rapidly growing. The next-generation wireless personal communication systems are expected to provide ubiquitous,high-quality,and high-rate mobile multimedia transmission. Turbo iteration technology promises to be a key technique for wireless communication systems of the near future.However,to achieve this objective various technical challenges must be overcome.For example,the wireless communication channels are very difficult,especially,how to improve the performance,such as spectral efficiency and throughout,and how to reduce the complexity of the system, while ensuring the quality of the service over the time-variation and frequency selective fading channels must be discussed.Focusing on the characteristics of the channels and the next-generation mobile communication systems,the key techniques of the iterative detection are investigated,based on the principle of the Turbo iterative decoding.It can be generalized to four points.1.Turbo TCM equalization and decoding system and its algorithmA novel low-complexity scheme of Turbo Trellis-coded Modulation(TCM) iterative equalization and decoding is presented,which serially concatenates a soft-input-soft-output(SISO)equalizer and symbol-by-symbol Turbo TCM(TTCM) decoder through an iterative process in order to realize iterative equalization and decoding process.This scheme can not only improve the bandwidth efficiency,but also reduce the intersymbol interference(ISI).The equalizer with maximum a posteriori(MAP)is replaced with linear one based on minimum mean-square error (MMSE)at the receiver so that the complexity of the system can be reduced greatly. Computer simulation results show that the novel low-complexity receiver on fading channel can achieve comparable performance with TTCM on Gaussian channel with coding.2.Space-time iterative equalization and decoding system and its algorithm in MIMO channelA low-complexity scheme of iterative equalization and decoding in multiple-input-multiple-output(MIMO)fading channel is presented,which serially concatenates a soft-input-soft-output(SISO)equalizer,decoder and MIMO estimator through an iterative process in order to realize iterative equalization and decoding process under the unknown channel information.The sub-optimal equalization algorithm based on minimum mean-square error(MMSE)and the decoding algorithm MAP are used.Simulation results show that the proposed scheme can decrease the bit error rate of the system effectively,and its complexity is lower than before.3.Iterative equalization and decoding method based on space time BICM in MIMO systemsA scheme of iterative equalization and decoding based on space time BICM is proposed,in which bit interleaved coded modulation(BICM)is used at the transmitter. Compared with other coding modulation method,the BICM codes are more discrete, so it can get rid of the relativities between symbol bits,and increase the coding diversity gain further in MIMO fading channels.Simulation results show that the proposed scheme can decrease the bit error rate of the system effectively,and its complexity is decreased.4.Adaptive precoding method in MIMO systemsA scheme of adaptive precoding with low-complexity is proposed,in which the precoder and the receiver based on zero forced(ZF)algorithm are placed at transmitter and receiver respectively.So the receiver transmit the channel information to the transmitter,at the same time equalization and decoding,then the transmitter can choose the number of the substreams and the precoding matrices,and complete the adaptive precoding.Simulation results show that the proposed scheme without transmit channel information decrease the bit error rate of the system effectively,and its complexity is exponential decreased.