On implementation of bit-loading algorithms for OFDM systems with multiple-input multiple-output

A new implementation scheme for bit-loading algorithms is discussed for orthogonal frequency division multiplexing (OFDM) system with multiple-input multiple-output (MIMO) over a wireless transmission channel. For M transmit and N receive antennas, subchannel precoders; and decoders jointly partition each frequency bin into a set of min(M,N) parallel eigen channels. Using a simulation technique, we study the relationship between the eigenvalue (gain of eigen channel) distribution and number (finite) of total antennas under the conditions of fixed M/N or fixed number of receive antennas in the Rayleigh fading channel environment. The study result leads to the proposed implementation scheme where all the parallel eigen channels are divided into groups and same number of bits per symbol are assigned to all the channels within each group. We further consider two additional techniques to improve the BER performance of a system with fixed number of antennas. In the numerical example, simulation results of system BER performance are shown for the proposed group bit-loading method and the conventional method (ideal) on the channel-by-channel basis. The results indicate that with the additional techniques, the BER performance of the proposed implementation scheme approaches closely to that of the ideal bit-loading method, but with a great reduction on computation complexity.