This paper presents a method based on a sample-decision(SD) circuit to suppress crosstalk and noise for a high-speed and high-density bus system.A method to count the number of times of SD for different length of transmission lines is presented and a bit error rates(BERs) formula is given by the SD circuit.It is shown that for long transmission line systems,multiple SD circuits can improve the BERs significantly.Circuits simulation for single SD method is also done,it is found that when the amplitude peak values of the superposed crosstalk and noise are less than half of the corresponding signal ones,they will be eliminated completely for the cases investigated.
Energy efficiency(EE) can be enhanced by retransmissions and combining in hybrid automatic repeat request(HARQ) system. However, it is difficult to optimize the transmit power of each retransmission when the accurate retransmission number and future channel state information(CSI) cannot be obtained. This paper proposes a simple energy efficient HARQ scheme for point-to-point wireless communication. In the proposed scheme, the conditional word error rate(WER) of each retransmission is fixed and the transmit power is adapted correspondingly. Three performance metrics are analyzed including average transmission number, throughput and EE. Compared with the conventional equal power HARQ scheme, the proposed scheme can significantly improve the EE and other two metrics under the same constraint of average transmit power or average energy consumption. Furthermore, it is found that, selecting a conditional WER which is slightly smaller than the optimal one is sufficient for practical implementation.
In orthogonal frequency division multiplexing(OFDM) based muitihop communications,the conventional decodeand-forward(DF) relay scheme severely suffers from the error propagation problem.This drawback is serious in muitihop 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 the significant performance improvement to the conventional DF.
