Bit error rate performance analysis in amplify-and-forward relay networks

Wireless Networks - Two methods are proposed in this paper to estimate asymptotic and exact bit error rate (BER) in two-hop amplify-and-forward (AF) relay networks . Rayleigh-fading channels are...     

Semi-blind amplify-and-forward with partial relay selection

The performance of the dual-hop semi-blind amplify-and-forward relay channel, where the intermediate relay node is selected depending on the instantaneous and partial channel knowledge, is investigated. Using closed-form expressions for the cumulative distribution function of the end-to-end signal-to-noise ratio (SNR), outage probability, SNR moments and average bit error rate are derived.     

Improving amplify-and-forward relay selection algorithm based on partial relay link

This article addresses the design problem of selecting an appropriate relay in amplify-and-forward(AF) cooperative diversity systems.In this regard,this article focuses on relay selection based on partial channel knowledge only across the source and relay links.In particular,the two fundamental questions will be answered,that is,whether to cooperate and whom to cooperate with.Through answering these two questions,an improved relay selection strategy based on partial relay link,which emphasizes that cooperat...     

认知无线电选择中继放大转发协议性能分析

研究了基于完全信道信息和部分信道信息的最佳中继选择策略认知中继网络中断概率,详细推导了这两种策略中断概率的封闭表达式,然后分析了它们的平均误码率。仿真结果表明,基于完全信道信息的中断概率和平均误码率性能要优于部分信道信息,并且两种策略的性能随中继节点数目、干扰温度增加而提高。     

Adaptive protocol for cooperative communication systems with a single semi-blind amplify-and-forward relay

In this paper, a basic cooperative system with a single semi-blind amplify-and-forward (AF) relay is considered. We present a novel protocol which can adaptively determine the transmission mode according to channel conditions. The spectral efficiency of the protocol is analyzed and its average symbol error probability (ASEP) is derived. Both analytical analysis and simulation results demonstrate the validity of our design. Compared to the conventional AF protocol, a significant increase of spectral efficiency is achieved, and the ASEP performance can also be obviously improved.     

放大转发OFDM协同中继系统多业务资源分配机制

提出了点到点多载波协同中继系统多业务资源分配框架,并给出了一种最优化自适应功率、载波和比特分配算法;为了降低算法复杂度,又提出了一种次优搜索算法,该算法依据信道特性,在满足业务QoS基础上使业务占用资源最小.仿真结果表明:提出的最优算法在保障多媒体业务QoS的基础上能够有效改善频谱效率,对比于传统算法有1～2bit/(s·Hz)的性能提升;而提出的次优搜索能够取得接近最优算法的性能(差别在0.6 bit/(s·Hz)左右),并且实现复杂度由指数级别降至线性.     

基于比例速率保证的信道误差OFDMA中继系统资源分配

针对存在有信道估计误差的正交频分多址( OFDMA)中继系统,在考虑用户传输中断概率的同时,提出了满足不同用户最小服务质量( QoS)需求和比例公平性约束条件下的中继选择、子载波分配和功率分配的联合优化问题,建立了以最大化系统总容量为目标的优化模型。在此基础上以速率最大化为目标进行最佳中继选择,并通过动态子载波分配来满足用户的最小QoS需求和比例公平性,最后采用拉格朗日乘子法来得到最优功率分配方案。仿真结果表明,此算法在降低用户中断概率的同时,提高了系统吞吐量并保证了用户速率的比例公平性。     

Performance of transmit diversity assisted amplify-and-forward relay system with partial relay selection in mixed Rayleigh and Rician fading channels

The performance of transmit diversity(TD)assisted amplify-and-forward(AF)relay system with partial relay selection,which experiences mixed Rayleigh and Rician fading channels,is investigated.We first investigate the closed-form expression of the cumulative distribution function for the end-to-end equivalent signal-to-noise ratio(SNR),and then the exact expressions of outage probability and average symbol error probability(SEP)are derived.The theoretical observations are verified by the Monte Carlo simulatio...     

Cooperative spectrum sensing using amplify-and-forward relaying with partial relay selection in cognitive radio networks

Cooperative spectrum sensing has been shown to be an effective approach to improve the detection performance by exploiting the spatial diversity among multiple cognitive nodes. By using the amplify-and-forward relaying with partial relay selection, this paper proposes a novel cooperative spectrum sensing scheme, which provides higher detection performance and is interesting in distributed cognitive radio networks. In the proposed sensing scheme, the “best” cognitive relay by means of partial relay selection technique amplifies and forwards the signals transmitted from the primary user (PU) to the cognitive user (CU). Then the CU detects PU’s states (i.e., presence or absence) via an energy detector. Moreover, the average missed-detection probability of proposed sensing scheme is studied over Nakagami-m fading channels, where m is a positive integer. In particular, the tight closed-form lower bounds of the average missed-detection probability are presented for the convenience of performance evaluation in practice. Finally, numerical results are provided to validate the derived closed-form lower bounds and the influence of the number of cognitive relays on the detection performance is also discussed.     

Diversity order for amplify-and-forward dual-hop systems with fixed-gain relay under Nakagami fading channels

Dual-hop transmission systems employing fixed-gain amplify-and-forward (AF) relaying have been studied recently over Nakagami fading channels. These analyses, however, either have imposed certain constraints on the fading parameters or have not been totally accurate when evaluating the diversity order of the systems. In this letter, we will develop a methodology for evaluating the diversity order of such systems. The methodology can be easily extended to analyze fixed-gain AF relaying with multiple relays.     

Optimal precoder for amplify-and-forward half-duplex relay system

In this paper, an optimal unitary precoder is designed for an amplify-and-forward (AF) half-duplex relay system to obtain the maximum coding gain while the original ergodic channel capacity for the relay system is kept unchanged. A closed-form design is derived for Quadrature Amplitude Modulation (QAM) signals by employing the properties of Farey sequence in number theory. Simulation results indicate that the proposed design greatly improves the bit error rate (BER) performance for the relay system     

Symbol error rate on fading self-interference channel in full-duplex

In-band full-duplex (FD) is being considered as a promising technology for the next generation wireless communication systems. In this paper, the performance of orthogonal frequency division multiplexing (OFDM) modulation system with different symbol duration and the code spreading system with different spreading sequence lengths under time-varying self-interference (SI) channel in FD mode is investigated respectively. Typically, the SI channel is estimated during the SI cancellation duration and used for SI suppression in the whole data transmission duration. First, the expressions of the residual SI power during the data transmission duration are derived under the classical, the uniform, and the two-way Doppler SI channels. Second, the signal-to-interference-and-noise-ratio after the SI mitigation is obtained. Third, the symbol error rates for the OFDM modulation and the code spreading systems are given. Simulation results show that OFDM symbol length should be selected longer when the symbol duration is significantly lower than the SI coherent time while the length of the coding spreading system should be chosen shorter.     

Mobile-to-mobile fading channels in amplify-and-forward relay systems under line-of-sight conditions: statistical modeling and analysis

This paper deals with the modeling and analysis of narrowband mobile-to-mobile (M2M) fading channels for amplify-and-forward relay links under line-of-sight (LOS) conditions. It is assumed that a LOS component exists in the direct link between the source mobile station (SMS) and the destination mobile station (DMS), as well as in the links via the mobile relay (MR). The proposed channel model is referred to as the multiple-LOS second-order scattering (MLSS) channel model. The MLSS channel model is derived from a second-order scattering process, where the received signal is modeled in the complex baseband as the sum of a single and a double scattered component. Analytical expressions are derived for the mean value, variance, probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the received envelope of MLSS channels. The PDF of the channel phase is also investigated. It is observed that the LOS components and the relay gain have a significant influence on the statistics of MLSS channels. It is also shown that MLSS channels include various other channel models as special cases, e.g., double Rayleigh channels, double Rice channels, single-LOS double-scattering (SLDS) channels, non-line-of-sight (NLOS) second-order scattering (NLSS) channels, and single-LOS second-order scattering (SLSS) channels. The correctness of all analytical results is confirmed by simulations using a high performance channel simulator. Our novel MLSS channel model is of significant importance for the system level performance evaluation of M2M communication systems in different M2M propagation scenarios. Furthermore, our studies pertaining to the fading behavior of MLSS channels are useful for the design and development of relay-based cooperative wireless networks.     

Subcarrier pairing for amplify-and-forward and decode-and-forward OFDM relay links

We consider a two-hop relay link in which orthogonal frequency division multiplexing (OFDM) is used on both hops. Under a joint sum-power constraint, our aim is to allocate power over subcarriers on the two hops such that the instantaneous rate of the relay link is maximized. Ordered subcarrier pairing (OSP) has been proposed in the literature to further improve the relay link rate; however, the optimality of OSP has been proven only for equal power allocation and the proof of its optimality under optimal power allocation has not been available yet. In this letter, we will provide our proof which verifies that OSP is optimal for both amplify-and-forward (AF) and decode-and-forward (DF) relay links when optimal power allocation is applied.     

MF中继选择系统的物理层安全性能

针对合谋窃听场景下单天线多中继修改转发（MF）协作无线系统的安全性能较差问题,提出一种合谋窃听场景下联合源节点发送天线选择（TAS）和多中继选择的MF协作物理层安全系统,考虑最优的最大化主信道信噪比（SNR）和次优的最大化源节点-中继节点链路 SNR 两种中继选择方案,推导其安全中断概率（SOP）和遍历安全容量（ESC）的解析表达式。最优或次优中继选择的MF安全中继系统的SOP和ESC的数值计算结果与仿真结果相吻合,验证了上述理论分析的正确性;同时也表明源节点发射天线数和中继节点数越多、窃听节点数越少,最优或次优中继选择的MF安全中继系统的物理层安全性能越好。     

Variable‐rate adaptive modulation with optimum switching thresholds for cooperative systems with relay selection

In this paper, the performance of variable‐rate adaptive modulation schemes in the amplify‐and‐forward cooperative systems with relay selection is analyzed over Rayleigh fading channels. We consider constant power and discrete‐rate adaptive multi‐level modulation techniques. The switching levels required for discrete‐rate adaptive modulation have been determined for two schemes, namely fixed switching levels and optimum switching levels, both respecting a target bit error rate requirements, where in the later scheme, the switching levels are optimally determined in a way that the average spectral efficiency of the system is maximized. Two M‐ary modulation schemes, namely quadrature amplitude modulation and phase shift keying, are considered. Closed‐form expressions are derived for three performance metrics, namely average spectral efficiency, outage probability, and average bit error rate, for two cases: independent and identically distributed fading relay links and independent and non‐identically distributed links. It is shown that, compared with using fixed switching levels, employing optimum switching levels provides a slight improvement in the spectral efficiency and moderate improvements in the signal‐to‐noise ratio gain and in the outage probability of the system. It is also shown that compared with the independent and identically distributed links, independent and non‐identically distributed relay links yield a slight increase in the signal‐to‐noise ratio gain and a slight decrease in the diversity order of the system. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamic joint resource allocation and relay selection for 5G multi-hop relay systems

LTE/LTE-A networks have become widely exploited to address the increasing demands of mobile traffic. Relay technologies have recently been introduced to fulfill such requirements. Currently, the LTE-A relay standard is restricted to two-hop relaying. This architecture minimizes system complexity, but multi-hop relay architecture could potentially provide greater capacity and coverage in the future. However, many complexities of the multi-hop relaying paradigm must be resolved. In this work, we focus on downlink resource allocation and relay selection, by which a user may be connected to a base station through a multi-hop relay and have several relay stations from which to choose within his range. To overcome the additional challenges introduced by multi-hop relay nodes, we propose a dynamic joint resource allocation and relay selection scheme. Numerical results are presented to demonstrate the validity of the proposed algorithm.     

A closed-form sum-rate lower bound for amplify-and-forward multi-way relay networks

In this letter, we investigate the sum-rate performance of the multi-way relay network (MWRN) with amplify-and-forward (AF) relaying, where multiple users exchange information with the help of a relay node. We consider a full exchange scenario where each user has to decode messages form all the other users. We analyze the sum-rate lower and upper bounds of the AF MWRN, and derive a closed-form expression for the average sum-rate low bound when the number of users is sufficient large. Numerical results show that the derived bound is tight.     

Symbol rate processing for the downlink of DS-CDMA systems

Many services of third-generation (3G) mobile radio systems will have higher data rates in the downlink than in the uplink. We propose to utilize adaptive antennas at the base stations because spatial interference suppression is able to reduce the near-far effect in the downlink of single-user detection direct-sequence (DS) code division multiple access (CDMA) systems. Besides the channel parameters in terms of directions of arrival, delays, and medium-term average path attenuations which are estimated in the uplink, we also take into account the correlation properties of the spreading and scrambling codes. In DS-CDMA the users are distinguished by different spreading codes, which change over time due to scrambling. In Brunner et al. (see Proc. EPMCC, p.375-80, 1999), the beamforming vectors at the base station were computed slotwise, whereas in this paper, we favor a symbol-rate beamforming at the base station. The new approach optimizes the actual values of the decision variables of the RAKE demodulators at the receivers. The superiority of the symbol rate beamforming algorithm compared to slotwise beamforming is shown by bit error rate (BER) simulations     

Symbol error rate of the dm-mpsk under the influence of jamming signals

Focusing on the performance of the chirp spread spectrum (CSS) communication system under the influence of jamming, we analytically derive the symbol error rate (SER) for the direct modulation CSS system withM-ary phase shift keying in the presence of broadband and tone jamming signals. From numerical results, it is confirmed that the analytic result agrees closely with the empirical SER.