Bit allocation algorithm for multi-user adaptive OFDM system with adaptive trellis coded MQAM

In this paper, a multiuser adaptive OFDM (orthogonal frequency-division multiplexing) transmission system is simulated. A bit allocation algorithm is considered in this system We propose a DCA-DBA-DCA algorithm using the adaptive trellis coded modulation (ATCM) and compare its performance with fixed OFDM and other adaptive algorithms. The simulation shows that DCA can increase system performance by 5∼6 dB and our system can greatly reduce the computational cost while maintain a fairly good QoS. By changing the interval between two DCA (dynamic channel allocations) our system can be used in various environments.