Research On Adaptive MIMO-SCFDE Systems In Mobile Broadband Communication Environment

MIMO-OFDM and MIMO-SCFDE are the significant techniques for the physical layer of the wideband wireless communications. These systems exploit the spatial multiplexing of MIMO technique to increase the transmission rates. In addition, they are the block-wise transmission systems which can make the equalizer simple and combat frequency-selective fading effectively.When the transmitter obtains the knowledge of the channel state information (CSI), the communication systems can exploit the channel better by changing the transmit strategy adaptively to increase the data transmission rates and/or the system BER performance. The channel state information is usually obtained at receiver and need to be sent back to the transmitter. For MIMO-OFDM and MIMO-SCFDE systems, the amount of feedback rises rapidly with the increase of the antennas and sub- channels. This thesis reviews several adaptive algorithms of reducing the feedback in MIMO-OFDM systems. But these algorithms are applicable to static or quasi-static environment and their adaptabilities in time varying channels are still poor. In this thesis we introduce an adaptive algorithm based on frequency sub-channels selection for MIMO-SCFDE system and the corresponding algorithm is proposed in static environment. The current adaptive technology for MIMO-SCFDE has rarely been reported in mobile environment.With the rapid development of mobile broadband wireless communications, the demands of communication system performance for mobile environment are growing increasingly. Especially, in the outdoor vehicular broadband wireless environment, the amount of feedback of the MIMO system is large and needs to be conveyed to the transmitter frequently. The situation will burden the communication system severely. This thesis proposes an adaptive single-rank precoding algorithm for MIMO-SCFDE in mobile environment. This algorithm is based on the adaptive algorithm in the static environment, and considers the requirement of the adaptive algorithms in the mobile environment. Our proposed algorithm includes two sections:one is the determination criteria used for the rank and frequency sub-channel selection, and the other is the update strategies of the feedback information. Simulation results show that the algorithm can maintain low feedback and simple BER controllability. And the system has capability against feedback delay. Further, considering the simulation result that the selected rank is usually two or three in the 4×4 single-rank precoding MIMO-SCFDE system, we propose a method to increase spectral efficiency. The approach can utilize the receiver diversity gain greatly and still meet the requirements of the system performance. Finally, for the 2×2 single-rank precoding MIMO-SCFDE system, the selected rank is usually one and therefore the system has some power waste when meeting the requirements of bit error performance. According to the question, the Bit-loading algorithm is proposed in the single-rank precoding MIMO-SCFDE system in order to further utilize the capacity of the system. This algorithm adjusts the numbers of the time-domain sub-channels exploiting two different modulations to improve system performance. Thus it can increase spectral efficiency and utilize the capacity of channel greatly.