基于过时信道状态信息的机会协作性能研究

机会中继是协作通信系统中提高频谱效率和节省功率消耗的常用方法.在通信过程中,信道估计时刻和实际中继传输信息时刻存在一定的延时,其产生的过时信道状态信息（Outdated CSI）会严重地影响协作通信系统的性能.分别从考虑直传链路和不考虑直传链路两方面,分析了过时信道状态信息对机会协作分集系统中断概率的影响.仿真结果表明,系统性能随着相关系数ρ的减小而变差,并且随着中继节点数目的增加而提高.     

Performance analysis of cellular networks with mobile relays under different modes

With the popularity of smart phones and tablets, people make intensive use of these devices on public transport. The deployment of mobile relays on public transport may increase the quality of mobile services.The objective of this paper is to study the performance of cellular networks when mobile relays are deployed in public transport vehicles. We consider two modes: in the FDD mobile relay mode, the same spectrum is reused for all links while in the TDD/FDD hybrid mode, a small part of the spectrum is dedicated to the access link between the terminals inside a transport vehicle and the mobile relay. We provide a general analytical model for the two mobile relay modes by using the stochastic geometry approach. Key metrics like the CDF of the SINR and the CDF of the end-to-end rate are computed. Furthermore, the cell total average rate and the energy efficiency in different modes are evaluated. It has been found that penetration loss is a factor that determines how much gain mobile relay can bring. Numerical results show that when the ratio of vehicular UEs in the cell is 0.4 and the penetration loss is 20 dB, the FDD mobile relay mode and the TDD/FDD hybrid mobile relay mode can achieve \(+16.3, +29.1\%\) cell rate gain respectively compared with the direct mode.     

Performance analysis of multiple-antenna cooperative networks under Weibull fading

In wireless communications, cooperative relaying is well-known to enhance the overall system performance, but implementation and cost constraints stand against its wide deployment. This paper investigates the performance of cooperative relays with and without multiple antennas under independent and identically distributed (i.i.d.) Weibull faded channels in a two-hop wireless network. We consider the Weibull fading channel model due to its flexibility in describing the radio propagation environment more than the classical Rayleigh model. Our study relies on applying selection combining (SC) along with threshold decode and forward (TDF) protocol at the cooperative relays as a good compromise between cost and performance. In addition, maximal ratio combining (MRC) is used at the destination. We derive analytical expressions for the end-to-end (E2E) error performance of the network under such scenario and provide simulation results to confirm the validity of the obtained analytical expressions.     

Optimum/sub-optimum detectors for multi-branch dual-hop amplify-and-forward cooperative diversity networks with limited CSI

We study the optimum maximum-likelihood (ML) detection and sub-optimum detection for a multi-branch dualhop cooperative diversity network with limited channel state information (CSI). Compared to the full CSI strategy, the signalling overhead at each relay involved with the limited CSI is reduced by 50%. We derive optimum ML detection with the limited CSI, which involves numerical integral evaluations. We also propose two closed-form sub-optimum detection rules of low complexity. It is shown that the first sub-optimum detection has almost identical performance to the optimum ML detection when Gaussianity in the added noise dominates, and the second sub-optimum detection has almost identical performance to the optimum ML detection when non-Gaussianity dominates. Finally, we propose a hybrid sub-optimum detection and demonstrate that its performance is almost identical to that of the optimum ML detection for general cases.     

Performance analysis of threshold digital relaying M2M cooperative networks

Exact average bit error probability (BEP) expressions for mobile-to-mobile cooperative networks employing threshold digital relaying over N-Nakagami fading channels are derived. The power allocation problem is formulated for performance optimization. The average BEP performance is evaluated via numerical simulation to verify the accuracy of the analysis with binary phase shift keying (BPSK) modulation. The simulation results showed that the fading coefficient, number of cascaded components, relative geometrical gain, and power-allocation parameter have a significant influence on the performance.     

Power allocation of cooperative amplify-and-forward communications with multiple relays

Cooperative diversity is one of the most effective ways to mitigate the fading effect of wireless channels and obtain the spatial gain in wireless networks.In this paper,an optimal power allocation(OPA)scheme for a cooperative communication system using the amplify-and-forward(AF)transmit strategy with multiple relay users is proposed by minimizing the bit-error-rate(BER)at the destination under the constraint of the total transmit power of both the source user and the relay users.Simulation results indicate that the proposed power allocation method can achieve significant BER performance improvement than using the equal power allocation(EPA)scheme,while still attains low complexity.The system performance is improved significantly with the increasing of the number of relay users at high signal-noise ratio(SNR).However,at low SNR,the system performance decreases when the relay number increases.Thus,an adaptive relay selection scheme may be used to choose the appropriate relay numbers in different transmission scenarios to provide system performance improvement and keep the power allocation scheme with low complexity.     

Performance analysis of multiuser diversity in cooperative multi-relay networks under rayleigh-fading channels

In multiuser cooperative relay networks, cooperative diversity can be obtained with the help of relays, while multiuser diversity is an inherent diversity in multiuser systems. In this letter, the performance analysis of multiuser diversity in cooperative multi-relay networks is presented. Both the case of all relay participating and the case of relay selection are considered. We first derive asymptotic expressions of outage probability and symbol error probability for amplify-and-forward (AF) and decode-and-forward (DF) protocols with joint multiuser and cooperative diversity. Then, the theoretical analysis are validated by Monte Carlo simulations. Both the theoretical analysis and simulations show that a multiuser diversity order of K and a cooperative diversity order of M+ 1 can be achieved simultaneously for both AF and DF protocols (where K is the number of accessing users and M is the number of available relays). These demonstrate that the multiuser diversity can be readily combined with the cooperative diversity in multiuser cooperative relay networks.     

非理想CSI下MIMO MRC协作通信系统的误码性能分析

协作分集和多输入多输出( MIMO)最大比合并(MRC)技术能够克服多径衰落对无线通信系统的影响和扩展覆盖范围.研究瑞利衰落信道上非理想信道状态信息下采用MIMO MRC的解码前传(DF)中继协作通信系统的误码性能.使用矩生成函数法,推导采用M进制相移键控、广义矩形M进制正交幅度调制的DF协作通信系统的平均误符号率的精...     

Performance analysis of rate-adaptive cooperative MAC based on wireless local area networks

Bi-dimensional Markov chain model based on cooperative medium access control (MAC) of wireless local area networks (WLAN) is considered to reflect system performance accurately. Two basic factors that affect the analysis results are station retry limits and non-saturated transmit probability. A uniform solution considering both factors is proposed. To prove the theoretical analysis, a cooperative MAC (CoopMAC) topology is established and the simulation model is enhanced by changing the cooperative table to the nodes' memory with more information added. Meanwhile, the three-way handshake scheme is modified and a handshake threshold is set based on the packet size. Simulation results show the performance analytical model is accurate, and the rate-adaptive cooperative MAC protocol significantly improves the network performance in terms of non-saturated system throughput and delay.     

无人机辅助空地协同无定形组网仿真评估

现有无线通信网络正在从"以基站为中心的" 蜂窝化组网向"以用户为中心的" 无定形组网演进.然而,现有的无定形组网技术其组网的灵活性受限于地面基站的部署位置.针对现有无定形组网技术灵活性受限的问题,提出了空地协同无定形组网技术.通过采用以用户的需求驱动无人机中继悬停部署实现地理空间层面无定形组网,采用"控制覆盖与业务覆盖...     

Performance of amplify-and-forward cooperative networks with differential unitary space time coding

In wireless communications, multi-input multi-output technology has been appreciated for its high transmission rate and diversity gain. These can also be exploited in cooperative networks by using network nodes as virtual antenna arrays. In this paper, we analyze the performance of cooperative networks with differential unitary space-time modulation under high signal-to-noise ratio. Relaying protocol is based on amplify-and-forward. The effect of relay location and energy allocation as well as the comparison with a conventional cooperative network is also addressed.     

Performance analysis of QAM in amplify-and-forward cooperative communication networks over Rayleigh fading channels

Performance analysis of quadrature amplitude modulation (QAM) schemes for cooperative amplify-and-forward (AF) dual-hop relaying system over independent and identically distributed (i.i.d.) Rayleigh fading channels are presented in this paper. Specifically, we derive closed-form lower-bound expressions of average symbol error rate (ASER) for general order rectangular QAM (RQAM) and cross QAM (XQAM) using well-known moment generating function (MGF) based approach with maximal ratio combining (MRC) scheme. Further, using best relay selection scheme (BRS), we also derive an ASER expression for XQAM. Numerical and simulated results are compared to validate the correctness of derived expressions. Furthermore, comparative analysis of RQAM and XQAM schemes is discussed which confirms that XQAM is better alternative over RQAM for transmission of odd number of bits per symbol for the considered system model. We also compare the ASER performance for MRC and BRS schemes in terms of SNR gain using different XQAM constellations. Moreover, the impact of system parameters on ASER is also highlighted.     

基于AF协作的多中继M2M通信系统的SER性能分析

基于移动端对移动端(M2M)信道衰落服从重叠Nakagami-m分布的假设,研究M-PSK调制下移动放大转发(AF)中继对M2M系统的性能影响。利用矩母函数(MGF)方法,推导了多AF中继辅助M2M通信(MAF-M2M)系统的误符号率(SER)性能下界表达式,并结合近似概率密度函数(PDF)方法,给出了更为逼近的近似SER表达式。结果表明,目的端采用最大比合并时,AF中继可以明显改善不同m参数信道下M2M通信系统性能。计算机仿真结果验证了性能界和近似SER的正确性。     

基于发射分集的多点中继合作通信系统性能研究

为了降低合作通信系统中的误码率和中断概率,本文研究了多点中继合作通信系统.采用矩母函数(Moment Generating Function)分析方法,通过引入超几何函数,详尽推导出Rayleigh衰落信道下的平均符号错误率和中断率的精确表达式.通过蒙特卡洛仿真,验证了表达式的正确性,其性能优于单点中继合作通信系统.     

Joint optimization of relay-precoders and decoders with partial channel side information in cooperative networks

We jointly optimize the relay-precoders and decoders with full or partial channel side information (CSI) in a cooperative network. Specifically, three different CSI assumptions are considered: 1) full CSI at the destination terminal and the relay terminals; 2) full CSI at the destination terminal and partial CSI at the relay terminals; 3) partial CSI at the destination terminal and the relay terminals. We show that, under the assumption of full CSI at the destination terminal and the relay terminals, the optimum relay-precoder is the cooperative transmission beamforming and the optimum decoder is a maximum ratio combiner. Under the two partial CSI assumptions, the optimum relay-precoders and decoders work in a fashion of channel selection. It is demonstrated that the proposed optimum relay-precoders and decoders improve the performance considerably     

Performance of phase-shift keying communication systems with partial fading channel statistical information

In this paper, a method of evaluating the performance of phase-shift keying systems over non-Rayleigh fading channels is presented. The technique is based on utilizing a quasi-moment expansion of the probability density function. The results obtained using fourth-order statistics show good agreement with those obtained using full statistical information which is not available in practice.     

Performance analysis of ZF receivers with imperfect CSI for uplink massive MIMO systems

We consider the uplink of massive multiple-input multiple-output systems in a multicell environment. Since the base station (BS) estimates the channel state information (CSI) using the pilot signals transmitted from the users, each BS will have imperfect CSI in practice. Assuming zero-forcing method to eliminate the multi-user interference, we derive the exact analytical expressions for the probability density function of the signal-to-interference-plus-noise ratio, the corresponding achievable rate, the outage probability, and the symbol error rate (SER) when the BS has imperfect CSI. An upper bound of the SER is also derived for an arbitrary number of antennas at the BS. Moreover, we derive the upper bound of the achievable rate for the case where the number of antennas at the BS goes to infinity, and the analysis is verified by presenting numerical results.     

智能窃听下协作NOMA网络的性能分析

针对下行双用户NOMA (Non-Orthogonal Multiple Access)系统模型中存在智能窃听者,该窃听者可以自适应地选择被动窃听或主动干扰工作模式,在不精确了解其干扰水平的情况下,部分NOMA用户很有可能遭遇传输质量下降乃至保密中断,这将对信息安全传输构成严重威胁。另外,由于信道衰落,用户的位置对系统整体性能有很大影响,难以保证距离源节点较远用户的传输质量。为解决上述问题,本文提出了一种新型的两阶段用户协作方案。第一阶段,远用户采用全双工(full-duplex,FD)干扰智能窃听者,第二阶段,近用户可作为一个中继协助源节点转发远用户信号信息,并在接收端采用串行干扰消除（Successive Interference Cancellation, SIC）技术进行解码。使用户间达成合作,提高通信链路安全性和用户服务质量。考虑到系统中不同用户的信息接收速率与通信需求不同之间的相关性,分别推导了遍历安全容量和遍历容量的解析表达式,同时分析了功率分配因子和用户间协作发射功率等因素对性能的影响,并通过Monte-Carlo仿真验证了其正确性。      

Performance optimization for energy harvesting cognitive cooperative networks with imperfect spectrum sensing

Wireless Networks - In this paper, considering imperfect spectrum sensing in a cognitive cooperative system, we study the performance optimization for throughput maximization of secondary user (SU)...