Research And Implementation Of Adaptive Modulation And Coding Algorithm Based On OFDM Baseband

OFDM has been one of the core technique in the fourth generation mobile communication system (4G) due to its high data rate transmission capacity with high spectrum utilization and robustness to multi-path delay. With variable modulation mode and variable coding method, adaptive modulation and coding can provide high spectrum utilization under the bit error rate constraint. To guarantee the transmission quality and enhance the transmission rate, it is an inevitable tendency to apply adaptive modulation and coding to OFDM system.In this thesis,the development of adaptive modulation and coding and the basic principles are presented firstly. Then Hughes-Hartogs algorithm, Chow algorithm, Fischer algorithm and SBLA algorithm are studied. Among the algorithms, The SBLA algorithm can be best applied to OFDM syetem due to its high performance and low complexity. What's more, the SBLA algorithm is improved to implement the adaptive modulation and coding in OFDM baseband.The most important technology of adaptive modulation and coding is SNR estimation algorithm. The traditional SNR estimation algorithms often perform well in additive white Gaussian noise (AWGN) channel. However, their performance may degrade dramatically in a multi-path channel. To deal with it, a novel SNR estimation algorithm based on the subcarriers of OFDM syetem is choosed. The empty subcarriers are used for SNR estimation in this work. Then, the received data subcarriers is used to estimate the energy of the transmitted data and noise. Simulation results show that the proposed method is not sensitive to Doppler shift and multi-path delay spread. The proposed method has lower complexity compared with the existing algorithms.Finally, the hardware implementation of the adaptive modulation and coding syetem based on OFDM baseband algorithms is investigated. The synthesized results show that the adaptive modulation and coding syetem accounts for 9.9 percent of the entire OFDM baseband hardware resources and 4.4 percent of power consumption, which indicates that our design has the characteristics of small area and low power consumption.