Bi-directional OFDM Transmission using Adaptive Modulation that spreads Data Symbols

An adaptive modulation in OFDM transmission is an effective scheme in order to increase transmission rate. In performing adaptive modulation, the transmitter must transmit allocation information of modulation scheme as packet header in order for receiver to demodulate symbols exactly. When different modulation scheme is allocated to each sub-carrier according to its channel state, transmission of huge allocation information of modulation scheme is required. This leads to degradation of transmission performance. Therefore, we propose an adaptive modulation scheme in OFDM that makes less allocation information transmission. In this paper, the proposed scheme is applied to bi-directional communication and detailed performance is analyzed