Research On The Equalization Technologies In Wireless Mimo Relaying Systems

Orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) are two commonly used key techniques in next generation wireless mobile communication systems. Orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) are defined as the downlink and uplink multiple access methods respectively in long time evolution (LTE) standard. By employing multiple transmitting and receiving antennas at the transmitter and the receiver, multiple input multiple output (MIMO) can increase the channel capacity significantly, and also becomes a required technique in LTE standard. MIMO technique can be used more efficiently combined with OFDM/SC-FDE in multipath frequency selective fading channel. Relay technology can expand coverage, eliminate blind spots, improve the quality of received signal, and becomes an alternative in the next generation mobile communication technology. By sharing and collaborating information with the source, relay technique can exploit spatial diversity gain using the independence between spatial channels, and provides an effective means of implementation for the practical application of MIMO technique.OFDM/SC-FDE can combat the multipath interference effectively by using cyclic prefix (CP) transmission, and compensate the influence of channel distortion with frequency domain equalization technique. However, SC-FDE requires more sophisticated equalization technique to exploit the multipath diversity gain. In this paper, Turbo frequency domain equalization algorithm based on soft interference cancellation is analyzed. The soft estimates information of inter-symbol interference (ISI) is reconstructed and soft interference cancellation is conducted, followed by minimum mean squared error (MMSE) based frequency domain equalization. Iterative processing between the equalizer and the decoder is utilized to suppress the multipath interference effectively. The effect of traditional equalization algorithm mainly depends on the effect of channel estimation with few information interaction between each other. In this paper, the influence of channel estimation error in the equalization is considered. The output of the equalizer is fed back to the channel estimator to refine the channel estimation and further improve the effect of equalization. The potential system performance can be exploited when both the channel estimation and equalization reach convergence.Distributed relay based cooperative SFBC/STBC schemes are studied for single antenna terminals when the configuration of multiple antennas is restricted. The following algorithms are studied, including the signal transmission protocol model, the multiplexing structure of pilot and data symbols, relaying signal processing, channel estimation, diagonalized SFBC/STBC decoding, turbo frequency domain equalization and so on. In view of the cooperative SFBC/STBC require additional relaying time slots compared with conventional SFBC/STBC, which is inefficient in the sense of spectrum efficiency, a CP-less transmission is considered and the reconstruction and recovery of CP is studied. The relay require DFT/IDFT processing to collaborate with the source to complete distributed SFBC/STBC coding. An effective time domain signal processing according to the property of DFT is considered, which reduces the complexity and processing delay.The diversity performance of conventional ARQ is limited by the effect of slow fading channel. A relay-assisted cooperative ARQ and equalization scheme is studied. The signal transmission protocol using DF and AF relays are considered respectively. The multiple retransmission signals are regarded as virtual antenna array in order to fully exploit the spatial diversity gain. Turbo frequency domain equalization in MIMO system is used to suppress inter-antenna interference (IAI) and inter-symbol interference (ISI). The implementation of the equalizer is also optimized for the colored noise introduced in AF mode. A single tone based frequency domain equalization is further studied. Considering that the memory of the received signal and the channel frequency response (CFR) increases linearly with the number of retransmission in virtual antenna based signal processing, a recursive frequency domain equalization is presented which reduces the complexity.