A new rate adaptive system: Controlled soft demodulation

In this paper, we propose a novel rate-adaptive system where the receiver adjust demodulation schema to the channel condition, by using controlled soft demodulation (CSD) and rateless erasure code. In CSD, the receiver demodulates only those reliable bits which determined by log likelihood ratio (LLR) criterion and treats non-demodulated bits as deleted. Dynamic LLR threshold strategy and fix LLR threshold strategy were presented to supply some implementations of this system. We analyzed the performance of these strategies over an additive white Gaussian noise channel, and compared the results with the Adaptive Demodulation system. The adaptive solutions were also provided, by analyzing the simulation results with the Raptor codes. The analysis indicates that the CSD system could avoid some defects of traditional rate-adaptive schemes, such as feedback overhead and complexity of the system, it also has better performance than the Adaptive Demodulation system, with much more flexible approach.