共查询到19条相似文献,搜索用时 140 毫秒
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为了考察使用多中继选择与多用户选择的放大转发(AF)中继系统的物理层安全性能,推导了其在瑞利衰落信道上和联合发送天线选择/接收最大比合并天线分集下的非零安全容量概率和安全中断概率的精确表达式以及在高信噪比下的渐近安全中断概率解析表达式。AF中继系统的非零安全容量概率和安全中断概率的数值计算和仿真结果相吻合,验证了以上理论分析的正确性;分析结果表明,其安全分集增益为源节点发射天线数、最优中继节点接收天线数、中继节点数的三者乘积与最优中继节点发射天线数、最优用户接收天线数、用户数三者乘积之间的最小值,且与窃听信道无关。 相似文献
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在Nakagami-m衰落信道下,分析了两跳固定增益放大转发中继通信系统的性能.首先采用基于概率密度函数(PDF)的性能分析法推导了无协作分集时系统的中断概率和平均误符号率(ASER)的闭合表达式,然后采用基于矩生成函数(MGF)的方法推导了有协作分集时系统的中断概率和ASER表达式以及接收信噪比的n阶矩的闭合表达式.仿真结果显示,所推导的闭合表达式与数值仿真结果吻合良好,协作分集和较大的m值可提升系统性能,中继前后两跳的信道质量对系统性能的影响并不相同. 相似文献
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在 Nakagami m衰落信道下,目的端和窃听者采用最大比合并策略,本文研究了在机会式自适应解码转发中继选择安全协作系统中的安全性能。由于实际信道中的反馈延迟,最优的合法中继选择基于合法信道反馈的过时信道状态信息。为了评价机会式中继选择在改善安全性能上的表现,分别推导了准确的正安全容量概率和准确的安全中断概率闭合表达式。此外,针对两种不同情况, 推导了形式简单的渐近表达式,并明确给出安全分集阶数和安全阵列增益。理论分析和数值仿真表明,增加中继个数和目的节点的天线数能够改善安全中断概率的性能表现,且在信道状态信息过时的条件下,系统的安全分集阶数与中继数无关。 相似文献
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利用高斯Q函数的高阶次幂在最大比合并(MRC)分集接收瑞利衰落信道上统计平均的结果,推导了Nakagami 衰落信道上采用组合发射选择合并(SC)/接收 MRC 天线分集的相干检测差分编码四相相移键控(DE-QPSK)的平均误符号率(ASER)精确表达式。利用高斯Q函数的近似表达式和矩生成函数(MGF)方法,推导了Nakagami衰落信道上采用组合SC/MRC天线分集的相干检测DE-QPSK 的ASER近似表达式。通过数值计算和仿真,验证了DE-QPSK的ASER精确表达式的正确性以及近似表达式的准确性。利用精确表达式和近似表达式可研究收发天线数目和衰落参数对DE-QPSK的ASER性能的影响,为实际SC/MRC天线分集方案的设计提供了理论指导。 相似文献
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在协同自适应解码转发中继系统中,该文针对Nakagami-m衰落信道,研究了基于多天线低复杂度的机会式传输策略的物理层安全性能。为充分利用天线分集增益提升系统安全性能,发送节点均采用发送天线选择策略,接收节点均采用最大比合并策略。推导了系统安全中断概率的闭合表达式,并进一步提供了渐近性能分析,得到了系统的安全分集阶数。仿真结果验证了理论分析的正确性,并揭示了各系统参数对机会式传输方案的安全性能的影响。结果表明,通过增加合法节点的天线数和增大合法信道的Nakagami衰落信道参数可显著提升系统安全性能。 相似文献
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机会中继能够在多中继节点的情况下灵活方便地实现协同分集,与采用分布式空时编码(DSTC)实现协同分集相比大大简化了物理层的复杂度,并且能够获得相同的分集增益。鉴于OFDM技术可以有效地抗频率选择性衰落,在机会中继的基础上结合OFDM技术,研究多用户协同分集系统性能。提出了机会OFDMA中继的方法,理论上推导了此方法能够带来完全分集增益,并仿真验证了结论。 相似文献
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基于跨层机制的最佳协作中继选择及其系统实现 总被引:5,自引:0,他引:5
为了获得最佳的协作中继用户,通过推导协作中继传输系统的误符号率,提出了基于放大重传和解码重传下最佳协作中继的选择准则,并结合跨层协作的思想给出了基于MAC层来实现最佳协作中继选择的分布式协议.与此同时,提出了协作分集系统的物理层传输方案,分析了瑞利衰落信道环境下所提方案的系统性能,得到了系统误比特率的闭式解.此外,针对协作中继选择准则和协作分集传输方案的误码性能进行了系统仿真和性能比较,结果表明,所提出的协作中继选择准则明显优于传统中继选择准则,且协作传输方案可以获得明显的分集增益,系统平均误比特率显著下降. 相似文献
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传统协同分集通过使网络中各单天线用户共享彼此天线,形成虚拟多天线阵列来实现空间分集,使得体积和功耗受限的网络终端也能获得分集增益,然而这并没有将信道编码和空时编码结合起来以使系统得到编码增益。为了能够获得编码增益来进一步改善系统性能,本文提出了一种基于信道编码和分布式空时分组码级联方式下的两用户协同分集方案,并且在准静态的瑞利衰落信道下对系统误码性能进行了理论推导和系统仿真,给出了误比特率的上限解析表达式。在协同用户间信道存在噪声的情况下,我们分别对CRC-DSTBC和CC-DSTBC级联下的发射方案进行了性能分析和系统仿真。仿真结果表明:即使协同用户间的信道存在噪声,本文所提出的协同分集方案与传统协同分集相比,不但获得了分集增益,同时也得到了编码增益,系统误比特率大大降低,从而显著提高了系统性能,并且这也和理论分析相吻合。 相似文献
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The performance of wireless communication systems is improved over flat fading channel by using Alamouti coding scheme, which provides the quality of diversity gain. In this paper, performance analysis of symbol error rate (SER) and particle swarm optimization (PSO)–based power allocation (PA) for Alamouti amplify and forward (AF) relaying protocol using maximum ratio combining (MRC) technique is presented. Analytical expression of SER upper bound and SER approximation is derived for Alamouti AF relaying protocol with quadrature phase shift keying (QPSK) modulation over Rayleigh fading channel and Rician fading channel. In addition, PSO‐based optimum PA factor is calculated on the basis of the minimum SER of proposed method. PSO‐based optimum PA gives 0.5 dB of improved signal‐to‐noise ratio (SNR) compared with the equal power allocation (EPA). The theoretical approximate SER result is compared with the simulated SER. The proposed protocol provides full diversity gain and reduces SER compared with the existing AF and decode and forward (DF) relaying protocols over Rayleigh fading channel and Rician fading channel. 相似文献
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在多中继协作网络中,机会中继编码协作已然成为一种高效且被广泛研究的协作策略,然而现有工作存在着资源浪费或者系统复杂度高的问题。为此,针对如何在资源利用率与系统复杂度之间获得良好折中的问题,该文提出一种新型的机会中继编码协作策略,在不增加额外开销的情况下,使源节点能够自适应地向目的节点发送校验信息。并在Nakagami信道模型下,给出了系统中断概率的解析表达和误比特率上界的闭式表达。仿真结果表明,与已有机会中继编码协作策略相比,在获得性能提升的同时,所提策略对系统复杂度和资源利用率均有所改善。 相似文献
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本文基于机会中继协作通信系统的优良特性,改进了传统的多中继ARQ(Automatic Repeat Request)协作分集机制,联合物理层与数据链路层优化了无线频谱与能量的利用率,并且首次提出了采用Markov(马尔可夫)吸收链方法的端到端性能分析模型.在此分析模型的基础上,对本文改进的机会协作重传协议进行了端到端成功传输概率、丢包率、时延、吞吐量等性能参数的数值分析,最后用仿真实验对此模型进行了验证,详细讨论了最大重传次数、信道衰落参数、总发送功率等对性能的影响.结果表明,本文改进的机会协作重传协议在节能、抗信道衰落方面,表现出了比直接重传协议和传统的多中继协作重传协议具有更优越的性能. 相似文献
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Yongxu Hu Kwok Hung Li Kah Chan Teh 《Wireless Communications and Mobile Computing》2011,11(6):742-749
In this paper, we derive the upper bound of bit‐error rate (BER) performance and diversity gain for a decode‐and‐forward (DF) cooperative system. Either maximal‐ratio combining (MRC) or cooperative MRC (C‐MRC) is employed at the receiver in the presence of independent, non‐identical Nakagami‐m fading. Both analytical and simulation results show that C‐MRC takes advantage of spatial diversity more efficiently and thus achieves the same or better performance and diversity order as compared to MRC. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Bletsas A. Dimitriou A.G. Sahalos J.N. 《Wireless Communications, IEEE Transactions on》2010,9(1):14-20
This work evaluates opportunistic relaying in the presence of thermal noise as well as interference, when channel sensing is conducted reactively, in slow fading environments. The studied scenario employs a single gateway that provides access towards several destinations with weak links and exploits a network of intermediate relays. In sharp contrast to prior art, no inter-relay channel state information or communication is assumed, no network coding is needed, while low-complexity receivers at each destination are employed. It is shown that information can be relayed without delay, while harvesting benefits of cooperative diversity, even at the presence of interference. The participating relays are required to offer strong paths towards source and destination, while at the same time they are as "isolated" as possible from each other. From that perspective, the notion of relay "usefulness" is redefined in both noise and interference-limited environments, under opportunistic relaying. 相似文献
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Exact integral expressions are derived for calculating the symbol-error rate (SER) of multilevel quadrature amplitude modulation (MQAM) in conjunction with L-fold antenna diversity on arbitrary Nakagami fading channel. Both maximal-ratio combining (MRC) (in independent and correlated fading) and equal-gain combining (EGC) predetection (in independent fading) diversity techniques have been considered. Exact closed-form SER expressions for two restricted Nakagami fading cases (MRC reception) are also derived. An exact analysis of EGC for MQAM has not been reported previously, despite its practical interest. Remarkably, the exact SER integrals can also be replaced by a finite-series approximation formula. A useful procedure for computing the confluent hypergeometric series is also presented 相似文献
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Wireless ad-hoc networks can experience significant performance degradation under fading channels. Spatial diversity has been
shown to be an effective way of combating wireless fading with the multiple-input multiple-output (MIMO) technique by transmitting
correlated information through multiple antennas. The virtual MIMO technique, which allows multiple wireless stations with
single antenna to form a virtual transmission array, is shown to be a viable solution from several recent studies. In this
paper, we propose a complete system framework for wireless ad-hoc networks utilizing two different cooperative relaying techniques
at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control
protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer,
diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Simulations with both
constant bit rate and TCP (transmission control protocol) traffic show significant performance gains of the proposed cooperative
relaying schemes. 相似文献