Research On Adaptive Power And Bit Allocation In MIMO-OFDM System

OFDM has been regarded as an efficient approach to combat the adverse effects of multi-path spread by changing frequency selective channels into flat ones in frequency domain. MIMO(Multiple Input Multiple Output) can be equivalent to parallel and independent channels in space and transmit multiple data streams. Spectrum efficiency can be improved dramatically under the constraint of constant bandwidth. Therefore, the combination of MIMO and OFDM has been the important technique of wideband wireless communication system.In MIMO-OFDM systems, we use a method to adaptively allocate data and power according to instantaneous channel state information. This method can fully utilize wireless resources when compared with static multiplexing schemes, so it can meet the requirements of high-rate and high-efficiency in the mobile communication.In this thesis,we firstly introduce the knowledge and key techniques about OFDM and MIMO simply,According to the basic theory of the OFDM technology, a OFDM system basing on the FFT algorithm is designed and simulated. The part of system design introduces the basic theory of the models of the system. The system performance between different modulation modes and different channels is analyzed. Then a MIMO-OFDM system based on SVD is introduced. The development of adaptive modulation and the basic principles are presented. Water-filling algorithm, greedy algorithm, and Chow algorithm are studied. What's more, a new algorithm based on multi-carriers adaptive bit allocation is presented by improving the greedy algorithm. It is conclude from the simulation results that the new algorithm has approximate performance with the former greedy algorithm in system performance, but has small algorithmic complexity and high efficiency, which is easy to implement when compared with original ones.