Adaptive code-rate and modulation for multi-user OFDM system in wireless communications

An adaptive code-rate and modulation allocation algorithm is considered for a multi-user OFDM system depending on transmission power and the transfer function of a frequency selective channel. The purpose of the presented adaptive code-rate and modulation OFDM system, using punctured convolutional code and various constellation sizes, is to maximize total capacity and to adapt the proper service for each user according to channel conditions and the transmit power, while maintaining the transmission´s quality of service (QoS) at the receiver. Computer simulation results show that the capacity of the adaptive code-rate and modulation OFDM system can be adaptively changed for various services. The performance of the system in a multipath fading channel with different delay spread is also analyzed.