In orthogonal frequency division multiplexing （OFDM） based multihop communications, the conventional decodeand-forward （DF） relay scheme severely suffers from the error propagation problem. This drawback is seriou...In orthogonal frequency division multiplexing （OFDM） based multihop communications, the conventional decodeand-forward （DF） relay scheme severely suffers from the error propagation problem. This drawback is serious in multihop networks as errors made by any relay node may fail the decoder at the destination in great chance. In this paper, we propose a bit error rate （BER） modified DF protocol （BMDF） which can be applied to systems where error correction channel coding and M-ary modulation are used. By modeling all links except the last one as a binary symmetric channel （BSC）, we derive a log likelihood ratio （LLR） modification function relying only on the accumulated BER of all previous links to be applied to the output of the soft demapper. Furthermore, to reduce the computational complexity and signaling overhead, the modification function is simplified from its original exponential expression and less BERs are delivered between nodes by making successive subcarriers share the same BER. In addition, for situations where the channel state information （CSI） of forward link is available, the proposed BMDF can be further enhanced by combining with subcarrier pairing （SP） and power allocation （PA）, where a sorted-channel gain SP scheme and a greedy PA algorithm are proposed. The simulation results verify thesignificant performance improvement to the conventional DF.展开更多
基金The authors would like to thank National Natural Science Foundation of China （No. 61072059）.
文摘In orthogonal frequency division multiplexing （OFDM） based multihop communications, the conventional decodeand-forward （DF） relay scheme severely suffers from the error propagation problem. This drawback is serious in multihop networks as errors made by any relay node may fail the decoder at the destination in great chance. In this paper, we propose a bit error rate （BER） modified DF protocol （BMDF） which can be applied to systems where error correction channel coding and M-ary modulation are used. By modeling all links except the last one as a binary symmetric channel （BSC）, we derive a log likelihood ratio （LLR） modification function relying only on the accumulated BER of all previous links to be applied to the output of the soft demapper. Furthermore, to reduce the computational complexity and signaling overhead, the modification function is simplified from its original exponential expression and less BERs are delivered between nodes by making successive subcarriers share the same BER. In addition, for situations where the channel state information （CSI） of forward link is available, the proposed BMDF can be further enhanced by combining with subcarrier pairing （SP） and power allocation （PA）, where a sorted-channel gain SP scheme and a greedy PA algorithm are proposed. The simulation results verify thesignificant performance improvement to the conventional DF.
