Adaptive bits and power allocation for MIMO OFDM systems

This thesis proposes an adaptive bits and power allocation scheme for an Orthogonal Frequency Division Multiplexing (OFDM) system based on the Digital Video Broadcasting standard for digital terrestrial television broadcasting (DVB_T), using Multiple Input Multiple Output (MIMO) architecture. The goal of the adaptive modulation is to determine the optimum choice of modulation constellations and transmission power for each MIMO-OFDM subchannel to minimize the overall transmission power with a constant data rate and specified Bit-Error Rate (BER).;The adaptive modulation algorithm is based on a greedy algorithm. The greedy algorithm provides an optimal power minimum solution when the power functions are convex in every transmission antenna.;The system simulation is performed by MATLAB programs, and the results show that the proposed adaptive modulation scheme closely tracks the change of the channel, and the MIMO-OFDM system with adaptive modulation requires significantly lower transmission power than a MIMO-OFDM system with a fixed modulation constellation. The results also show that the transmission power saving increases with the number of the transmission antennas.;The proposed system uses OFDM with guard interval to split a frequency selective wireless channel into a number of frequency flat channels and decreases the complexity of the adaptive modulation algorithm. The spatial multiplexing gain of the proposed MIMO system achieves the data rate requirement of the system. The MIMO transmission scheme used in the proposed system is based on the channel Singular Value Decomposition (SVD), which decomposes the MIMO matrix channel into a set of independently parallel Single Input Single Output (SISO) subchannels with different gains.