Transmission Design in Soft-Decoded-and-Forward (SDF) TCM-based Cooperative Communication Systems

Abstract

In this work, we propose a mew transmission mechanisn for TCM-based cooperative communication systems when the soft-decoded-and-forward protocol is employed. In this work, we first assume that the relay node and the destination are connected by the error-free backbond. The decoding metric in this work is based on the joint probability of the received signal at the relay node and the destination rather than the conditional probability of received signal at the destination given the decoding information of the relay node. The relay node does not need to actually decode the transmitted signal from the source. Therefore, contrast to the HDF protocol, the coding delay can be greatly reduced in this case. When the channel is not error-free, several problems such as how to truncate these results, how to select the appropriate truncation level and how to choose the quantization scheme, have to be taken into account. In this work, these problems are partly resolved. The performance of the proposed forwarding strategy is shown to be superior to the HDF or AF protocols under the same setting. Following this, two variants are proposed as well with the aim to reduce the amount of information gathered by the relay node to the destination. One is to transmit the information of the branch with minimum metric at a stage only and the other is to selectly transmit the decoding information of the relay node based on the channel condition between the source and the relay node. Both variants have the comparable performance to the original strategy.