Real-time rate-adaptable coding for fading channels

Abstract

In this paper, a new adaptive-rate convolutional coding system for maximizing the throughput over slowly fading channels is presented. The scheme is capable of adapting on the fly to fading conditions without the delay inherent in ARQ-based adaptive-rate strategies. The system employs a bank of encoders, and the current encoder is selected as a function of the channel state information obtained through a periodically transmitted feedback training sequence. This scheme does not require rate compatibility in the code bank, and can therefore make use of the best-known codes of any rates with arbitrary constraint lengths. At the receiver, an innovative decoding method based on the well-known Viterbi algorithm is employed. Knowledge of the encoder choices is not required at the decoder due to its ability to seamlessly track encoder transitions through an expanded Viterbi trellis. The system provides a hassle-free solution to achieving high-rate communications over fading channels.