无线协作通信系统中的物理层网络编码理论与关键技术研究
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摘要
网络编码在信息论领域的重要突破激励了其在无线通信中的应用,而最具代表性的研究场景就是基于物理层网络编码(Physical-layer Network Coding, PNC)的协作无线双向中继网络。相比传统单向中继传输方法,基于物理层网络编码的无线双向中继方案,能够有效降低双向信息流在无线中继网络中传输时间的开销,进而提高网络吞吐量。目前,物理层网络编码已经受到了国际学术界及产业界的广泛关注。本文以无线双向中继网络作为主要研究对象,着重研究了结合多输入多输出(Multiple Input Multiple Output, MIMO)技术的物理层网络编码传输方案,并拓展研究了MIMO-Y信道中提升物理层网络编码传输可靠性的方法,以及超宽带(Ultra-Wideband, UWB)网络中具有复杂度低的抗符号间干扰技术及物理层网络编码传输技术。本文的主要研究内容和创新点归纳如下：
第一,本文研究了适用于物理网络编码的基本MIMO传输方法。针对单天线源节点和多天线中继节点的双向中继网络,本文指出了目前基于虚拟MIMO观点设计的中继接收机的缺陷,提出了针对二元物理层网络编码符号的专属中继接收机——似最大比合并(Maximal Ratio Combining Like, MRC-L)接收机。该接收机强调了对物理层网络编码的适度检测,其判决仅基于接收信号与信道响应“加和”、“差异”的最大比合并项,以及信道响应之间的“相关”项。因此,该接收机具有明晰的物理意义及较低的实现复杂度。通过分析和仿真,证明了该接收机能够在双向中继传输的多址阶段获得全分集增益。基于此接收机设计,进一步明确了该网络中“需要通过两阶段分集传输以获得端到端分集”的正确观点,纠正了传统上基于虚拟MIMO设计传输方案的一些认识误区。基于以上观点,本文又提出了在双向中继多址阶段采用MRC-L中继接收机而在广播阶段采用空时编码(Space Time Coding, STC)或者中继天线选择(Relay Antenna Selection, RAS)的两阶段分集传输方案,并通理论分析和仿真实验说明了所提两阶段分集传输方案能够获得端到端的系统分集增益。另外,针对源节点和中继节点均配置相同天线数目的MIMO双向中继网络,本文提出了一种源节点采用迫零(Zero Forcing,ZF)收发器的简单MIMO物理层网络编码传输方案。该方案利用源节点发端掌握的信道状态信息,将MIMO双向中继信道进行解耦,获得了多个等效的单输入单输出(Single Input Single Output, SISO)双向中继信道,而在每一个SISO双向中继信道中,均可利用所提的MRC-L方案进行检测。因此,所提方案以较低的复杂度获得了MIMO双向中继系统的空分复用增益。
第二,本文研究了MIMO双向中继网络中的中继天线选择方法。首先,针对单天线源节点和多天线中继节点的双向中继网络,本文提出了一种适用于二元物理层网络编码的多址-广播阶段公共天线选择方法。不同于所提的其它两阶段分集传输方案,该天线选择方法只需要中继端配置一个射频单元,并且只需要一次天线选择就可以为系统获得端到端的分集增益,具有较低的实现复杂度。另外,考虑源节点和多天线中继节点均配置多天线的MIMO双向中继网络(其中,,中继节点天线数目大于源节点天线数),本文重点针对基于ZF的MIMO物理层网络编码传输方案,提出了两种中继天线选择方法,即多址-广播阶段的分别中继天线选择(Respective Relay Antenna Selection, R-RAS)和公共中继天线选择(Common Relay Antenna Selection, C-RAS)方法,以消除基于ZF的MIMO物理层网编码传输方案受到系统天线数目配置的约束,同时获得了端到端的分集增益。特别地,本文详尽分析了该方案可达的分集增益并获得了精确的解析表达,并且通过仿真验证了理论分析的结果。
第三,本文研究了MIMO-Y信道中的用户选择及中继天线选择方法。首先,本文注意到一些基于空间分集技术来增强MIMO-Y信道传输性能的方法通常需要增加源节点的天线数目,而这在实际系统应用中具有较大局限性。本文同样注意到,无线网络中的源节点数目及中继天线数目相对容易增加。基于以上观点,本文提出了MIMO-Y信道中以获取多用户分集和多天线中继接收/发送分集增益为目标的用户选择方法和中继天线选择方法。特别地,MIMO-Y信道中的用户选择模型对应了一种有中继辅助的三方组群信息交互模型,在很多实际场景中具有潜在的应用价值；本文提出群内代表元素的优选方法,提高了MIMO-Y信道的传输可靠性。此外,本文提出了适用于MIMO-Y信道的中继天线选择方法,消除了已有基于ZF的传输方案受系统天线配置的约束,同时提高了整个系统的传输可靠性。本文通过大量仿真研究了所提方案的性能,其中一些有趣的现象将为后续的深入研究带来有益启发。
第四,作为以上基本理论研究的拓展应用,本文对UWB网络中的低复杂度抗符号间干扰技术也进行了研究。该研究为后续UWB网络中的物理层网络编码传输方案设计奠定了基础。注意到抗符号间干扰的传输方案设计是提高UWB网络传输效率的关键,本文提出了一种针对码字匹配-信号聚合(Codeword Matching and Signal Aggregation, CMS A)新型非相干UWB传输系统的低复杂度干扰预消除方案,实现该方案仅需要对传输码字(信号格式)进行优化设计。本文给出了一种具有特殊性质的正交码字：该码字除了具备传统正交码的基本性质之外,还具有移位正交性和移位重复性。基于该码字的UWB信号在经过符号间干扰信道后,依然可以和CMSA接收机完美匹配,从而能够对抗甚至部分利用符号间干扰,显著地提升了系统性能。特别地,该方案实现过程中联合接收机设计和信号格式优化的思路启发了本文针对UWB物理层网络编码传输方案的设计,因为物理层网络编码的关键同样在于对符号间干扰的有效管理。
第五,本文在上述所有工作的基础上,研究了UWB双向中继网络中的物理层网络编码传输关键技术。注意到多径信道和单输入多输出(Single Input Multiple Output, SIMO)信道的等价性,本文从基本检测理论角度出发并参照MIMO物理层网络编码的研究成果,提出了适用于UWB二元物理层网络编码符号检测的中继接收机统一结构。在此基础上,本文结合相干UWB通信特点,提出了中继端采用全Rake (All Rake, ARake)、选择Rake (Selective Rake, SRake)或部分Rake (Partial Rake, PRake)的相干UWB网络编码接收器设计。另外,注意到实际UWB系统低复杂度的需求,本文提出一种基于非相干传输参考(Transmit Reference, TR)UWB技术的物理层网络编码传输方案,该方案避免了接收机复杂的信道估计运算。特别地,该方案对TR-UWB的发送信号格式进行了优化,并提出了基于自相关接收器(Auto-correlation Receiver,AcR)结构的中继端接收机,从而以较低的复杂度实现了物理层网络编码传输。不仅如此,本文通过理论分析获得了影响该接收方案性能的主要参数,并基于此分析,讨论了源节点总发射功率受限条件下的功率分配问题和中继选址问题。最后,通过仿真验证了所提方案的优良性能。
As a major breakthrough in information theory, Network Coding has found its applications in wireless communication systems, and the most rep-resentative application scenario is the Physical-layer Network Coding (PNC) aided cooperative wireless two-way relay network. Compared to the tradition-al one-way relay transmission scheme, PNC aided wireless two-way relay can effectively reduce the exchange time of bidirectional information flows in the wireless relay network, thus improving network throughput. Recently, PNC has attracted widespread attention from both academics and industry practitioner-s. The dissertation mainly focuses on the wireless two-way relay model and the relevant advanced transmission schemes which combine PNC and Multiple Input Multiple Output (MIMO) technology. Moreover, the dissertation extend-s the study to the more complicated MIMO-Y channel, and proposes several practical schemes to improve the transmission reliability. Finally, armed with the theoretical insights, the dissertation considers the application of PNC in UWB (Ultra-Wideband) network. The major work and contributions are sum-marized as follows.
To begin with, the dissertation studies the basic MIMO transmission schemes for PNC. For two-way relay network consisting of two single-antenna source nodes and one multi-antenna relay node, the dissertation first points out the defects of some existing virtual-MIMO based schemes. Then a Maximal Ratio Combining like (MRC-L) relay receiver is proposed, which is tailored for binary PNC and achieves near optimal performance with low implementa-tion complexity. The MRC-L receiver also has a clear physical interpretation; the receiver makes decision according to three correlations, the correlations be-tween the received signal and the sum and difference of two channel responses, respectively, and the correlation between the channel responses. Analysis and simulation show that the proposed MRC-L receiver achieves full diversity ad-vantage in the multiple access (MA) phase of PNC transmission. Based on this receiver design, the dissertation further clarifies the idea of two-phase diversity transmission scheme for PNC, in which MRC-L receiver is used for MA phase and Space Time Coding (STC) or Relay Antenna Selection (RAS) is used for broadcasting (BC) phase. Analysis and simulation show that an end-to-end di-versity advantage is achieved with the two-phase diversity designs. In addition, for MIMO two-way relay network where two source nodes and one relay n-ode are all equip with the same number of antenna, a simple Zero Forcing (ZF) based MIMO-PNC transmission scheme is proposed. To be specific, the source nodes use ZF pre-coding and detection in MA and BC phases, respectively, to decouple the MIMO two-way relay channel into multiple Single Input Single Output (SISO) two-way relay channels in which the proposed MRC-L receiver is used at the relay. Therefore, the proposed ZF based MIMO-PNC scheme achieves spatial multiplexing gains at relatively low cost.
Second, the dissertation studies the RAS methods in MIMO two-way relay network. For network consisting of two single-antenna source nodes and one multi-antenna relay node, we propose a simple common relay antenna selection (C-RAS) scheme for binary PNC. Unlike other two-phase diversity transmis-sion schemes, the proposed C-RAS scheme requires only one Radio Frequency (RF) unit at the relay, and chooses only one common antenna for both MA and BC transmissions. Therefore, the proposed C-RAS scheme also achieves end-to-end diversity advantage at low-cost. In addition, for MIMO two-way relay network where the two sources nodes are equipped with the same number of antenna which is less than that of the relay node, we propose two practically RAS schemes, namely, the Respective Relay Antenna Selection (R-RAS) and C-RAS, to bypass the size constraints of ZF based MIMO-PNC while gaining end-to-end diversity advantage. Moreover, the end-to-end diversity orders of the proposed schemes are carefully analyzed while explicit results are present-ed. Simulation results validate the theoretical analysis and show the advantage of the proposed schemes.
Third, this dissertation studies user selection and RAS of MMO-Y chan-nel. The existing spatial diversity-oriented scheme for MIMO-Y channel may require additional antennas at the source nodes, which is a limitation for prac-tical application. On the other hand, the number of source nodes and the an-tenna of a dedicated relay node are relatively easy to increase. Based on the observations, two alternative spatial diversity-oriented schemes are proposed for MIMO Y channel, namely, user selection and RAS. In particular, a new application scenario for MIMO-Y channel is proposed where three groups ex-change information with the help of a relay while only one group representa-tive is selected to carry out communication. By judiciously selecting the group representative, the system performance of MIMO-Y channel is improved. Fur-thermore, following the similar line of C-RAS scheme in MIMO two-way relay channel, a practical C-RAS scheme is proposed for MIMO-Y channel, which not only bypasses the size constraints of ZF based transmission scheme for MIMO-Y channel but also improves the end-to-end diversity advantages. Ex-tensive simulation results are presented to show the advantages of the proposed scheme while some interesting observations will inspire future work.
Fourth, this dissertation extends the previous theoretical study to UW-B network and focuses on the low-complexity transmission that is robust in the presence inter-symbol interference (ISI). The insights obtained from this scheme are the foundation of the design for UWB PNC transmission. By not-ing that the ISI-robust transmission is the key to improve UWB network's throughput, a novel code optimization based ISI pre-mitigation scheme is pro-posed for the Codeword Matching and Signal Aggregation (CMSA) noncoher-ent UWB system. In particular, an interesting orthogonal block code is con-structed which enjoys two special properties, namely Shifted-Orthogonality and Shifted-Repetition, that distinguishes the proposed block code from the ordinary orthogonal block code. It is observed that, when the optimal code occurs, the leaked signal energy or the interference can be partially used to enhance the detection performance of CMS A in the presence of IFI/ISI. There-fore, the system performance is greatly improved. Moreover, the optimized transmit signal structure and receiver design in the presence of ISI for high data-rate all inspire the later design for UWB PNC transmission, since PNC itself emphasizes effective management of ISI in the MA phase.
Finally, the dissertation studies the application of PNC in the cooperative UWB two-way relay network. By noting the equivalent relation between SIMO (Single Input Multiple Output, SIMO) channel and UWB multipath channel, the dissertation starts from the basic detection principle and proposes a unified UWB receiver structure that is specific to binary PNC. Under the framework, several practical relay receivers are developed to facilitate UWB-PNC trans-mission, including the Rake-based UWB PNC coherent receivers, such as All Rake (ARake), Selective Rake (SRake) and Partial Rake (PRake) receivers. Moreover, a Transmit Reference (TR) based non-coherent UWB PNC schemes is proposed to address the low-complexity and practical design for UWB net-work, where the complicated channel estimation overhead is bypassed at the receiver. To be specific, the signal structures of the two end nodes are careful-ly designed while a novel noncoherent UWB-PNC detector is developed with the simple Auto-correlation Receiver (AcR) structure. The combination of the signal structure and receiver designs achieves a low-complexity transmission scheme for UWB PNC. Furthermore, we analyse the key influencing factors for the proposed schemes. Based on the analytical results, the power allocation between source nodes under the sum power constraint and the relay placement are also discussed. Simulation results show the effectiveness and advantages of the proposed UWB PNC schemes.
第一,本文研究了适用于物理网络编码的基本MIMO传输方法。针对单天线源节点和多天线中继节点的双向中继网络,本文指出了目前基于虚拟MIMO观点设计的中继接收机的缺陷,提出了针对二元物理层网络编码符号的专属中继接收机——似最大比合并(Maximal Ratio Combining Like, MRC-L)接收机。该接收机强调了对物理层网络编码的适度检测,其判决仅基于接收信号与信道响应“加和”、“差异”的最大比合并项,以及信道响应之间的“相关”项。因此,该接收机具有明晰的物理意义及较低的实现复杂度。通过分析和仿真,证明了该接收机能够在双向中继传输的多址阶段获得全分集增益。基于此接收机设计,进一步明确了该网络中“需要通过两阶段分集传输以获得端到端分集”的正确观点,纠正了传统上基于虚拟MIMO设计传输方案的一些认识误区。基于以上观点,本文又提出了在双向中继多址阶段采用MRC-L中继接收机而在广播阶段采用空时编码(Space Time Coding, STC)或者中继天线选择(Relay Antenna Selection, RAS)的两阶段分集传输方案,并通理论分析和仿真实验说明了所提两阶段分集传输方案能够获得端到端的系统分集增益。另外,针对源节点和中继节点均配置相同天线数目的MIMO双向中继网络,本文提出了一种源节点采用迫零(Zero Forcing,ZF)收发器的简单MIMO物理层网络编码传输方案。该方案利用源节点发端掌握的信道状态信息,将MIMO双向中继信道进行解耦,获得了多个等效的单输入单输出(Single Input Single Output, SISO)双向中继信道,而在每一个SISO双向中继信道中,均可利用所提的MRC-L方案进行检测。因此,所提方案以较低的复杂度获得了MIMO双向中继系统的空分复用增益。
第二,本文研究了MIMO双向中继网络中的中继天线选择方法。首先,针对单天线源节点和多天线中继节点的双向中继网络,本文提出了一种适用于二元物理层网络编码的多址-广播阶段公共天线选择方法。不同于所提的其它两阶段分集传输方案,该天线选择方法只需要中继端配置一个射频单元,并且只需要一次天线选择就可以为系统获得端到端的分集增益,具有较低的实现复杂度。另外,考虑源节点和多天线中继节点均配置多天线的MIMO双向中继网络(其中,,中继节点天线数目大于源节点天线数),本文重点针对基于ZF的MIMO物理层网络编码传输方案,提出了两种中继天线选择方法,即多址-广播阶段的分别中继天线选择(Respective Relay Antenna Selection, R-RAS)和公共中继天线选择(Common Relay Antenna Selection, C-RAS)方法,以消除基于ZF的MIMO物理层网编码传输方案受到系统天线数目配置的约束,同时获得了端到端的分集增益。特别地,本文详尽分析了该方案可达的分集增益并获得了精确的解析表达,并且通过仿真验证了理论分析的结果。
第三,本文研究了MIMO-Y信道中的用户选择及中继天线选择方法。首先,本文注意到一些基于空间分集技术来增强MIMO-Y信道传输性能的方法通常需要增加源节点的天线数目,而这在实际系统应用中具有较大局限性。本文同样注意到,无线网络中的源节点数目及中继天线数目相对容易增加。基于以上观点,本文提出了MIMO-Y信道中以获取多用户分集和多天线中继接收/发送分集增益为目标的用户选择方法和中继天线选择方法。特别地,MIMO-Y信道中的用户选择模型对应了一种有中继辅助的三方组群信息交互模型,在很多实际场景中具有潜在的应用价值；本文提出群内代表元素的优选方法,提高了MIMO-Y信道的传输可靠性。此外,本文提出了适用于MIMO-Y信道的中继天线选择方法,消除了已有基于ZF的传输方案受系统天线配置的约束,同时提高了整个系统的传输可靠性。本文通过大量仿真研究了所提方案的性能,其中一些有趣的现象将为后续的深入研究带来有益启发。
第四,作为以上基本理论研究的拓展应用,本文对UWB网络中的低复杂度抗符号间干扰技术也进行了研究。该研究为后续UWB网络中的物理层网络编码传输方案设计奠定了基础。注意到抗符号间干扰的传输方案设计是提高UWB网络传输效率的关键,本文提出了一种针对码字匹配-信号聚合(Codeword Matching and Signal Aggregation, CMS A)新型非相干UWB传输系统的低复杂度干扰预消除方案,实现该方案仅需要对传输码字(信号格式)进行优化设计。本文给出了一种具有特殊性质的正交码字：该码字除了具备传统正交码的基本性质之外,还具有移位正交性和移位重复性。基于该码字的UWB信号在经过符号间干扰信道后,依然可以和CMSA接收机完美匹配,从而能够对抗甚至部分利用符号间干扰,显著地提升了系统性能。特别地,该方案实现过程中联合接收机设计和信号格式优化的思路启发了本文针对UWB物理层网络编码传输方案的设计,因为物理层网络编码的关键同样在于对符号间干扰的有效管理。
第五,本文在上述所有工作的基础上,研究了UWB双向中继网络中的物理层网络编码传输关键技术。注意到多径信道和单输入多输出(Single Input Multiple Output, SIMO)信道的等价性,本文从基本检测理论角度出发并参照MIMO物理层网络编码的研究成果,提出了适用于UWB二元物理层网络编码符号检测的中继接收机统一结构。在此基础上,本文结合相干UWB通信特点,提出了中继端采用全Rake (All Rake, ARake)、选择Rake (Selective Rake, SRake)或部分Rake (Partial Rake, PRake)的相干UWB网络编码接收器设计。另外,注意到实际UWB系统低复杂度的需求,本文提出一种基于非相干传输参考(Transmit Reference, TR)UWB技术的物理层网络编码传输方案,该方案避免了接收机复杂的信道估计运算。特别地,该方案对TR-UWB的发送信号格式进行了优化,并提出了基于自相关接收器(Auto-correlation Receiver,AcR)结构的中继端接收机,从而以较低的复杂度实现了物理层网络编码传输。不仅如此,本文通过理论分析获得了影响该接收方案性能的主要参数,并基于此分析,讨论了源节点总发射功率受限条件下的功率分配问题和中继选址问题。最后,通过仿真验证了所提方案的优良性能。
As a major breakthrough in information theory, Network Coding has found its applications in wireless communication systems, and the most rep-resentative application scenario is the Physical-layer Network Coding (PNC) aided cooperative wireless two-way relay network. Compared to the tradition-al one-way relay transmission scheme, PNC aided wireless two-way relay can effectively reduce the exchange time of bidirectional information flows in the wireless relay network, thus improving network throughput. Recently, PNC has attracted widespread attention from both academics and industry practitioner-s. The dissertation mainly focuses on the wireless two-way relay model and the relevant advanced transmission schemes which combine PNC and Multiple Input Multiple Output (MIMO) technology. Moreover, the dissertation extend-s the study to the more complicated MIMO-Y channel, and proposes several practical schemes to improve the transmission reliability. Finally, armed with the theoretical insights, the dissertation considers the application of PNC in UWB (Ultra-Wideband) network. The major work and contributions are sum-marized as follows.
To begin with, the dissertation studies the basic MIMO transmission schemes for PNC. For two-way relay network consisting of two single-antenna source nodes and one multi-antenna relay node, the dissertation first points out the defects of some existing virtual-MIMO based schemes. Then a Maximal Ratio Combining like (MRC-L) relay receiver is proposed, which is tailored for binary PNC and achieves near optimal performance with low implementa-tion complexity. The MRC-L receiver also has a clear physical interpretation; the receiver makes decision according to three correlations, the correlations be-tween the received signal and the sum and difference of two channel responses, respectively, and the correlation between the channel responses. Analysis and simulation show that the proposed MRC-L receiver achieves full diversity ad-vantage in the multiple access (MA) phase of PNC transmission. Based on this receiver design, the dissertation further clarifies the idea of two-phase diversity transmission scheme for PNC, in which MRC-L receiver is used for MA phase and Space Time Coding (STC) or Relay Antenna Selection (RAS) is used for broadcasting (BC) phase. Analysis and simulation show that an end-to-end di-versity advantage is achieved with the two-phase diversity designs. In addition, for MIMO two-way relay network where two source nodes and one relay n-ode are all equip with the same number of antenna, a simple Zero Forcing (ZF) based MIMO-PNC transmission scheme is proposed. To be specific, the source nodes use ZF pre-coding and detection in MA and BC phases, respectively, to decouple the MIMO two-way relay channel into multiple Single Input Single Output (SISO) two-way relay channels in which the proposed MRC-L receiver is used at the relay. Therefore, the proposed ZF based MIMO-PNC scheme achieves spatial multiplexing gains at relatively low cost.
Second, the dissertation studies the RAS methods in MIMO two-way relay network. For network consisting of two single-antenna source nodes and one multi-antenna relay node, we propose a simple common relay antenna selection (C-RAS) scheme for binary PNC. Unlike other two-phase diversity transmis-sion schemes, the proposed C-RAS scheme requires only one Radio Frequency (RF) unit at the relay, and chooses only one common antenna for both MA and BC transmissions. Therefore, the proposed C-RAS scheme also achieves end-to-end diversity advantage at low-cost. In addition, for MIMO two-way relay network where the two sources nodes are equipped with the same number of antenna which is less than that of the relay node, we propose two practically RAS schemes, namely, the Respective Relay Antenna Selection (R-RAS) and C-RAS, to bypass the size constraints of ZF based MIMO-PNC while gaining end-to-end diversity advantage. Moreover, the end-to-end diversity orders of the proposed schemes are carefully analyzed while explicit results are present-ed. Simulation results validate the theoretical analysis and show the advantage of the proposed schemes.
Third, this dissertation studies user selection and RAS of MMO-Y chan-nel. The existing spatial diversity-oriented scheme for MIMO-Y channel may require additional antennas at the source nodes, which is a limitation for prac-tical application. On the other hand, the number of source nodes and the an-tenna of a dedicated relay node are relatively easy to increase. Based on the observations, two alternative spatial diversity-oriented schemes are proposed for MIMO Y channel, namely, user selection and RAS. In particular, a new application scenario for MIMO-Y channel is proposed where three groups ex-change information with the help of a relay while only one group representa-tive is selected to carry out communication. By judiciously selecting the group representative, the system performance of MIMO-Y channel is improved. Fur-thermore, following the similar line of C-RAS scheme in MIMO two-way relay channel, a practical C-RAS scheme is proposed for MIMO-Y channel, which not only bypasses the size constraints of ZF based transmission scheme for MIMO-Y channel but also improves the end-to-end diversity advantages. Ex-tensive simulation results are presented to show the advantages of the proposed scheme while some interesting observations will inspire future work.
Fourth, this dissertation extends the previous theoretical study to UW-B network and focuses on the low-complexity transmission that is robust in the presence inter-symbol interference (ISI). The insights obtained from this scheme are the foundation of the design for UWB PNC transmission. By not-ing that the ISI-robust transmission is the key to improve UWB network's throughput, a novel code optimization based ISI pre-mitigation scheme is pro-posed for the Codeword Matching and Signal Aggregation (CMSA) noncoher-ent UWB system. In particular, an interesting orthogonal block code is con-structed which enjoys two special properties, namely Shifted-Orthogonality and Shifted-Repetition, that distinguishes the proposed block code from the ordinary orthogonal block code. It is observed that, when the optimal code occurs, the leaked signal energy or the interference can be partially used to enhance the detection performance of CMS A in the presence of IFI/ISI. There-fore, the system performance is greatly improved. Moreover, the optimized transmit signal structure and receiver design in the presence of ISI for high data-rate all inspire the later design for UWB PNC transmission, since PNC itself emphasizes effective management of ISI in the MA phase.
Finally, the dissertation studies the application of PNC in the cooperative UWB two-way relay network. By noting the equivalent relation between SIMO (Single Input Multiple Output, SIMO) channel and UWB multipath channel, the dissertation starts from the basic detection principle and proposes a unified UWB receiver structure that is specific to binary PNC. Under the framework, several practical relay receivers are developed to facilitate UWB-PNC trans-mission, including the Rake-based UWB PNC coherent receivers, such as All Rake (ARake), Selective Rake (SRake) and Partial Rake (PRake) receivers. Moreover, a Transmit Reference (TR) based non-coherent UWB PNC schemes is proposed to address the low-complexity and practical design for UWB net-work, where the complicated channel estimation overhead is bypassed at the receiver. To be specific, the signal structures of the two end nodes are careful-ly designed while a novel noncoherent UWB-PNC detector is developed with the simple Auto-correlation Receiver (AcR) structure. The combination of the signal structure and receiver designs achieves a low-complexity transmission scheme for UWB PNC. Furthermore, we analyse the key influencing factors for the proposed schemes. Based on the analytical results, the power allocation between source nodes under the sum power constraint and the relay placement are also discussed. Simulation results show the effectiveness and advantages of the proposed UWB PNC schemes.
引文
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