Research On Decision Feedback Equalization And Multi-user Precoding

In wireless communications, decision feedback equalization performed at the receiver and the precoding performed at the transmitter can efficiently suppress the interference and improve the transmission reliability. At the receiver, the decision feedback equalization can make use of the existing decision symbols assisting the subsequent detection. By the help of decision feedback equalizer, the inter-symbol interference caused by the multi-path channel can be mitigated. When the receivers are separated, the multi-user interference is suppressed by the precoding performed at the transmitter. In this dissertation, both of them are carefully discussed. In the first part, the focus is on the decision feedback equalization. We will consider the decision feedback equalizer design in single carrier transmission and relay transmission individually. Then the multi-user precoding design is carefully considered.In the first chapter, the existing decision feedback equalization and multi-user precoding methods are carefully reviewed. Then, the two topics are investigated in the following parts.In the second chapter, the focus is on the decision feedback equalizer design in single-input single-output (SISO) single carrier transmission. The proposed decision feedback equalizer has the following properties:(ⅰ) hard decision feedback symbols,(ⅱ) constant feedback equalizer coefficients during equalization,(ⅲ) independency between the forward equalizer and the decision feedback equalizer. The simulation result shows that the proposed decision feedback equalizer has better performance than the existing equalizer with the same equalization complexity.Then, in the third chapter, the decision feedback equalizer in single carrier time-reversal space-time transmission is introduced. The analysis shows that the proposed decision feedback equalization can be realized in the frequency domain and the equalizer coefficients can be calculated from the frequency channel response with low complexity. Then the simulation results show that the proposed equalizer has better bit error rate performance.In the fourth chapter, the decision feedback equalizer is combined with the multi-antenna precoding in multiple-input multiple-output (MIMO) single carrier transmission. The equalization process can be implemented in the frequency domain and the feedback equalizer coefficients are calculated according to the frequency channel response and the precoding matrix. In addition, the precoding performed at the transmitted needs little channel state information and it is easy to implement. The simulation results show that the proposed equalizer have better equalization performance and lower computational complexity.In the fifth chapter, the decision feedback equalizer is introduced in the relay transmission. The analysis exhibits that the relay transmission highly depends on the channel state information (CSI). In practice, the communication nodes in relay system only have imperfect channel state information. The focus is on the decision feedback equalizer design based on the imperfect CSI. In addition, the relationship between maximizing the channel capacity and optimizing the decision feedback equalizer will be given.In the sixth chapter, our focus is on the multi-user precoding design at the transmitter. In practice, the receiver may have multiple antennas. So the receiver equalizer design affects the precoding design at the transmitter. We will give a unified optimization method, which contains both the transmitter and the receiver optimization. In addition, the unified optimization method can be modified in order to accommodate multiple criterions, such as linear zero forcing, zero forcing THP, linear minimum mean squared error (MMSE) and MMSE THP.