This book considers the problem of Adaptive Modulation scheme selection through an OFDM based system over parallel frequency-selective fading channels. Here, an adaptive coding scheme is also proposed by using Generalized Concatenated Codes (GCC), which have simple structure and are designed in such a way that they are best suited for fading channels. GCC are based on binary cyclic codes. The criterion of study is the optimization of throughput of the system. Through a proposed adaptive algorithm,a modulation selection scheme is proposed which is based on the quality of the Sub-channels. Moreover, a code assigning method for the different sub-channels, which adapts itself to the channel conditions is also proposed. The proposed scheme combats against channel impairments better than those used in conventional systems by exploiting individual sub-channel condition. Results show better performance in terms of lower bit error rate as well as higher throughput.