Adaptive symbol length for OFDM systems in doubly selective channels

Symbol length is an important factor that can affect the spectrum efficiency and the performance of Orthogonal Frequency Division Multiplexing OFDM system. However, the symbol length is usually fixed in conventional OFDM systems, which decreases the spectrum efficiency considerably, especially in a mobile environment. This paper introduces an adaptive OFDM system in which the delay spread and Doppler spread are estimated at the receiver and according to their estimated values, the transmitter vary the symbol length such that the Bit Error Rate BER is always around a certain predetermined value. The value of the BER is chosen according to the type of the transmitted information. Simulation has been implemented and the results show that the proposed adaptive algorithm gives an improvement in the total throughput of the system without significantly sacrificing the BER performance.