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高频谱效率协作中继技术研究
中文摘要

随着无线数据流量的爆炸性增长以及新业务和应用场景的不断出现,如何提高频谱效率,利用有限的频谱资源支持更高的数据速率和海量的设备连接成为未来无线通信面临的核心问题。协作中继技术在扩大无线通信覆盖范围和提高系统可靠性等方面拥有巨大优势,但与直接传输相比,传统的半双工(Half-Duplex, HD)协作通信带来了频谱效率的损失。因此,一些先进的高频谱效率协作中继技术成为当前无线通信领域的研究热点,主要包括双路中继(Two-Path Relaying, TPR)、全双工(Full-Duplex, FD)中继和双向中继(Two-Way Relaying, TWR)。大多数现有的高频效协作中继方法采用相干检测,需要瞬时信道状态信息(Channel State Information, CSI)。然而,在信道环境变化迅速或传输时延较大等情况下,很难获得准确的瞬时CSI。本文基于差分调制和非相干检测,提出了一系列不需要瞬时CSI的高频谱效率协作中继方法。本文的主要创新点有以下三点。 1.提出了一种去噪转发(Denoise-and-Forward,DNF) TPR (DNF-TPR)方法,并进行理论分析。两个HD中继交替接收和发送以形成虚拟FD中继,在瞬时CSI未知的情况下,中继通过一个非相干最大似然(Maximum Likelihood, ML)译码器将接收到的来自源节点和另一个中继的叠加信号映射成一个去噪符号,目的节点利用上一个时隙收到的去噪符号来消除当前时隙接收信号中的中继间干扰。推导了 DNF-TPR的端到端误比特率(Bit Error Rate,BER)的闭合表达式和分集增益。仿真结果验证了理论分析的结论,并表明,DNF-TPR的BER性能和频谱效率都优于残余自干扰(Residual Self-Interference, RSI)超过特定值(将近8dB)的FD中继。与HD中继选择方法相比, DNF-TPR方法显著提高了系统的频谱效率。 2.提出了一种FD分布式天线译码转发中继(Full-Duplex Distributed Antenna Relaying, FDDAR)方法,并进行理论分析。该方法在瞬时CSI未知的情况下,根据ML准则为采用分布式天线的中继设计了一个非相干译码器,从接收到的叠加了自干扰的源节点信号中得到源节点的发送信息,避免了经典FD中继系统性能依赖于RSI等级的问题。推导了 FDDAR的端到端BER的闭合表达式。仿真结果验证了理论分析的结论,并表明,FDDAR的BER性能和频谱效率都优于RSI超过特定值(将近6dB)的FD中继。与HD中继方法相比,FDDAR方法显著提高了系统的频谱效率。 3.提出了FD模式下基于DNF方式的TWR (FD-DNF-TWR)方法和二时隙FD模式分布式天线(Full-Duplex Distributed Antenna, FDDA)译码转发 TWR (FDDA-TWR)方法,并进行理论分析。FD-DNF-TWR方法中,两个源节点向中继发送信息,在瞬时CSI未知的情况下,中继通过一个非相干ML译码器从存在RSI的两个源节点的叠加信号中产生共同信息,同时中继将上一个时隙产生的共同信息转发给两个源节点,两个源节点能够根据该共同信息和自己的信息得到另一个源节点的发送信息。FDDA-TWR方法中,一个源节点在奇数时隙与中继交换信息,另一个源节点在偶数时隙与中继交换信息,在瞬时CSI未知的情况下,釆用分布式天线的源节点和中继分别通过非相干ML译码器从有用信息与自干扰的叠加信号中提取有用信息,避免了 FD-DNF-TWR中存在回传自干扰和RSI的问题。推导了 FD-DNF-TWR和FDDA-TWR的端到端BER的闭合表达式。仿真结果验证了理论分析的结论,并表明,与HD模式下基于DNF的TWR (DNF-TWR)方法相比,FD-DNF-TWR获得了相近的BER性能,并进一步提高了系统的频谱效率。FDDA-TWR的BER性能和频谱效率都优于RSI超过特定值(将近6dB)的二时隙FD译码转发TWR (FD-TWR)方法。 关键词:双路中继,全双工中继,双向中继,频谱效率,误比特率

英文摘要

With the explosive growth of wireless data traffic and the emergence of new business and application scenarios, how to improve the spectral efficiency to support higher data rate and massive equipment connection with limited spectrum resources becomes a key problem of future wireless communication. Cooperative relaying has shown huge advantages in expanding the coverage of wireless communication and improving the reliability of the system, but conventional cooperative communication based on half-duplex (HD) induces the loss of spectral efficiency compared with direct transmission. Therefore, a series of advanced cooperative relaying technologies with high spectral efficiency become the hot topics, including two-path relaying (TPR), full-duplex (FD) relaying and two-way relaying (TWR). Most of these cooperative relaying schemes apply coherent detection, in which instantaneous channel state information (CSI) is required. However, accurate instantaneous CSI is hard to obtain when the channel environment changes rapidly or the propagation delay is high. Based on differential modulation with non-coherent detection, this dissertation proposes a series of cooperative relaying schemes with high spectral efficiency in which instantaneous CSI is not required. The contributions in the dissertation can be summarized as follows. 1.A denoise-and-forward (DNF) TPR (DNF-TPR) scheme is proposed, and the theoretical analysis is given. Two HD relays send and receive in turn to form a virtual FD relay. The superimposed signals received by the relay from the source and another relay are mapped into a denoised symbol through non-coherent maximum likelihood (ML) decoder without instantaneous CSI, and the destination utilizes the denoised symbol received in the previous timeslot to cancel the inter-relay interference in the current timeslot. The closed-form end-to-end bit error rate (BER) and the diversity gain are derived. The simulation results validate the theoretical analysis, and show that the BER and the spectral efficiency of DNF-TPR outperform that of FD relaying with residual self-interference (RSI) exceeding a certain level (almost 8dB). Compared with HD relay selection scheme, the spectral efficiency is significantly improved by DNF-TPR. 2.A FD relaying scheme with distributed antenna based on decode-and-forward (FDDAR) is proposed, and the theoretical analysis is given. The non-coherent ML decoder designed for the relay with distributed antenna could obtain the source information from the received superimposed signals of the source signal and the self-interference without instantaneous CSI, which avoids the problem in classical FD relaying that the performance depends on the level of RSI. The closed-form end-to-end BER of FDDAR is derived. The simulation results validate the theoretical analysis, and show that the BER and the spectral efficiency of FDDAR outperform that of the FD relaying with RSI exceeding a certain level (almost 6dB). Compared with the HD relaying, FDDAR improves the spectral efficiency significantly. 3.A FD mode TWR scheme based on DNF (FD-DNF-TWR) and a two-timeslot FD mode distributed antenna (FDDA) TWR scheme based on decode-and-forward (FDDA-TWR) are proposed, and the theoretical analysis is given. In FD-DNF-TWR, two sources send messages to the relay, and the relay generates common information according to the superimposed signals from the two sources and the RSI through a non-coherent ML decoder without instantaneous CSI. At the same time, the relay forwards the common information generated in the previous timeslot to the two sources, and the source could obtain the information from another source according to the common information and its own information. In FDDA-TWR. a source exchanges information with the relay in the odd timeslots, and another source exchanges information with the relay in the even timeslots. Two sources and the relay with distributed antenna extract the useful information from the superimposed signals of the useful information and the self-interference by the non-coherent ML decoder without instantaneous CSI, respectively. Thus, the back-propagating self-interference and the RSI in FD-DNF-TWR are avoided. The closed-form end-to-end BER of the two schemes are derived. The simulation results validate the theoretical analysis, and show that compared with the HD mode TWR scheme based on DNF (DNF-TWR), FD-DNF-TWR achieves similar BER performance and improves the spectral efficiency further. The BER and the spectral efficiency of FDDA-TWR outperform that of two-timeslot FD mode TWR scheme based on decode-and-forward (FD-TWR) with RSI exceeding a certain level (almost 6dB). Key words: Two-path relaying; Full-duplex relaying; Two-way relaying; Spectral efficiency; Bit error rate

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