Variable rate adaptive trellis coded QAM for high bandwidth efficiency applications under Rayleigh fading channel

Abstract

A high bandwidth efficiency variable rate adaptive channel coding scheme, ATCQAM, is proposed. Known pilot symbols are transmitted periodically to aid demodulation. Past channel states are fed back to the transmitter with delay. Current channel state is then predicted at the transmitter to decide on the appropriate modulation mode for the current symbol. At good channel states, high level modulation is used to boost up the average throughput. At bad channel states, low level modulation is used to increase error protection. By matching the variable modulation level with a variable rate channel coder, the physical bandwidth is maintained constant. Design issues for the ATCQAM are considered. Practical schemes to maintain transmitter-receiver synchronization, namely the quasi-closed loop control and the closed-loop control, are discussed. The effects of finite feedback delay, finite interleaving depth and mobile speed are investigated.