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A new modulation scheme was proposed to deal with the error propagation（EP） existing during the successive cancellation（SUC） detection in the VBLAST（vertical Bell labs layered space-time） system.In the scheme,the former demodulated signal was designed to use the modulation with better noise suppression performance（e.g.binary phase shift keying modulation）,and the latter demodulated signal was suggested to employ the modulation with higher frequency ef-ficiency（e.g.multi-decimal modulations）.Analysis and simulation results show that system reliability for SUC detection is improved without penalty to the system availability.

A combined channel estimation method of time-frequency-selective fading channels in MIMO-OFDM systems was proposed.The time-varying channel was modeled as an autoregressive（AR） process and a low-dimensional Kalman filter based on pilots was used to estimate the AR parameters,and the LS（least square） algorithm was adopted to track the time-varying channel fading factors.The Kalman estimator explored the time-domain correlation of the channel,and a minimum mean square error（MMSE） combiner was used to modify the Kalman estimates.The proposed solution could reduce the complexity of the high-dimensional Kalman filter and track the channel both in frequency and time domains.The simulation results show that this method improves the LS estimates and has a comparable performance to the com-plex high-dimensional Kalman channel estimation method.

Considering that the orthogonality of STBC in frequency-selective fading will be destroyed by the multiple path interference（MPI）,an iterative interference cancellation based maximum likelihood sequence estimation（MLSE） decoding scheme was proposed for STBC in frequency-selective fading.Meanwhile,the maximum ratio combining（MRC） method was introduced to improve the proposed scheme,and decrease the computational complexity further.These schemes could effectively make up for the decoding deficiency of conventional STBC in frequency-selective fad-ing.They canceled not only the MPI from even terms corresponding to the orthogonality undestroyed by fading,but also the MPI from odd terms corresponding to the orthogonality destroyed by fading;they has superior performance.More-over,they have lower decoding complexity when compared with direct MLSE decoding of the long sequence signal.Thus they implement good decoding performance with low complexity.

A ratio-adjustable time-frequency training sequence was proposed.The coarse carrier frequency offset（CFO） estimation was accomplished with the aid of the training sequence in frequency domain and a predefined lookup table,while the fine one was obtained by the aid of the training sequence in time domain.Simulation results show that the per-formance of the proposed method is better than Lei’s method with almost the same overhead.However,its computational complexity is much lower than Lei’s.