Research On Efficient Transmission Technique And Cooperative Communication For Next Generation Wireless Communication Systems

To improve the spectrum efficiency and keep high transmission rate of the next generation wireless communication, orthogonal frequency division multiplexing (OFDM) and Multiple input multiple output (MIMO) has already become the key physical layer transmission techniques of the next generation wireless communication. OFDM, which can resistant to frequency selective fading and impove the transmission rate, is a multi-carrier modulation technique. For multi-carrier systems, channel estimation is pivotal to the system performance. On the other hand, MIMO can exploit diversity gain and multiplex gain to improve the performance and increase the system capacity. However, it is difficult for mobile users to achieve MIMO techniques. Cooperative communication can achieve spatial diversity such as MIMO without multiple antennas equipment, which provides new idea to achieve spatial diversity for these mobile teiminals inability to equip multiple antennas due to the constraits with the size, power or the cost, which also leads to new direction for application of MIMO. Therefore, cooperative communication has already become a research hotspot.On the basis of international current research works, this thesis investigates some key theories and technologies for next generation wireless communication systems in depth, and presents some new contributions in the following topics:channel estimation for uplink multi-carrier code division multiple access (MC-CDMA), phase compensation of cooperative communication, relay selection, cooperative relay based on OFDM. On the channel estimation of multi-carrier, the thesis proposes a new channel estimation scheme with the aided of the estimated channel parameters. Compared to the conventional uplink MC-CDMA channel estimation, the proposed scheme can estimate channel paratemeters accurately, including estimating path numbers and time delays. The proposed scheme successfully resolves the robust problem when the conventional scheme determines the important taps by threshod.On the topic of distributed space-time cooperative communication, a novel distributed space-time cooperation based on phase compensation is proposed. Comparing with conventional distributed space-time cooperation schemes, the proposed scheme increases phase compensation block for each relay, which significant reduces the complexity of the destination receiver. It means the receiver can achieve the maximum likelihood performance with linear complexity. On the other hand, the proposed scheme increase the block of phase compensation. For fair comparison, the complexity of the proposed scheme includes the part of phase compensation. Through complexity analysis and computer simulation, it is shown that the proposed scheme not only has better performance, but also has lower complexity.On the topic of cooperative relay selection, we propose a more reasonable relay selection scheme based on partial link. Different from the current relay selection based on whole link, the relay selection based on partial link only needs to consider the channel information between the source node and the relay nodes. Since it does not need to wait the whole channel information, on one hand, it saves the system burden to communicate information; on the other hand, it reduces the delay sensitivity of acquisiting the whole channel information. It makes pratical operation easily, and lows down the stricts of time synchronization. The complexity will not increase with the increase of relay nodes. The proposed scheme aims at maximizing the average mutual information, which emphasizes that cooperation happens when necessary, unlike the existing scheme based on partial link considers purely cooperation. Then a joint optimization, in terms of power allocation and relay selection, is employed to guarantee a robust performance for relay selection based on partial relay link.On the topic of OFDM relay cooperation, this thesis proposes an adaptive bit and power allocation algorithm for OFDM-based regenerative relay systems though theorectical analysis, aiming at minimizing the transmit power consumption under the requirements of transmission rate and the target bit error ratio (BER). First, adaptive bit and power allocation is introduced into OFDM regenerative relay systems and the optimization problem is presented. Furthermore, adaptive bit and power algorithm with subcarrier pairing is proposed to further improve the system performance. Simulation results show that the proposed algorithms can improve the performance in terms of the transmit power efficiency comparing with equal bit allocation algorithm.