干扰受限的两跳多接入信道的中断概率分析

在频谱资源重复利用的背景下,干扰受限的两跳多接入信道的中断性能是亟待解决的难题之一.针对目的端干扰受限的情形,本文给出了该信道在放大转发模式下的中断概率闭式解.根据中断事件的定义将中断概率分解为两部分:一部分是中继节点发生中断的概率,另一部分是中继节点未发生中断,但中继节点到目的节点的传输发生了中断的概率.通过对第二部分中断概率进行合理的近似,推导出整个系统中断概率的闭式解,为系统的实际设计提供了理论基础.仿真结果表明,所给出的估计闭式解与蒙特卡洛仿真结果相吻合,验证了此估计解的精确性.     

Outage performance of amplify-and-forward two-way relaying with asymmetric traffics

This letter conducts the outage analysis for an amplify-and-forward (AF) based two-way relaying by jointly considering outage events at the two senders with asymmetric traffics. Unlike the current research activities, our goal is to explore the impact of traffic asymmetry on the system outage probability. We first derive the exact expressions of outage probability for the AF scenario over Rayleigh fading channels. To gain more insight, approximated expressions are developed at high signal-to-noise ratio (SNR) region. After that we interestingly find that the asymmetry of system traffics has significant impact on the system outage probability and the outage probability in the system is determined only by the one-way channel or related simultaneously to the two-way links, depending on the level of asymmetry between the two senders’ information rates. Simulation experiments are done. The simulation results verify our propositions and validate the accuracy of our derived expressions.     

On outage minimization in RF energy harvesting relay assisted bidirectional communication

This paper explores an end-to-end outage probability experienced in a bidirectional relay assisted communication where the relay is assumed to be equipped with an RF energy harvesting circuit. First, the closed-form expression for the outage of the system is derived. This is followed by the formulation of an unconstrained optimization problem to achieve minimum outage probability with respect to the relay placement and consequent time allocation for energy harvesting. The system model is further extended in an underlay cognitive radio framework to study the impact of a primary user outage constraint on the end-to-end outage performance of the two-way communications. The accuracy of analytical results is validated through simulation results. The impact of various system parameters like relay position, time allocation factor, target rate of transmission on the outage probability is also observed. In addition, it is also shown that spectral efficiency of the communication system using hybrid power-time switching relaying protocol is much superior to similar one-way and two-way relay assisted communication system with power splitting relaying protocol.

     

Service outage based power and rate allocation for parallel fading channels

The service outage based allocation problem explores variable-rate transmission schemes and combines the concepts of ergodic capacity and outage capacity for fading channels. A service outage occurs when the transmission rate is below a given basic rate r/sub o/. The allocation problem is to maximize the expected rate subject to the average power constraint and the constraint that the outage probability is less than /spl epsi/. A general class of probabilistic power allocation schemes is considered for an M-parallel fading channel model. The optimum power allocation scheme is derived and shown to be deterministic except at channel states of a boundary set. The resulting service outage achievable rate ranges from 1-/spl epsi/ of the outage capacity up to the ergodic capacity with increasing average power. Two near-optimum schemes are also derived by exploiting the fact that the outage probability is usually small. The second near-optimum scheme significantly reduces the computational complexity of the optimum solution; moreover, it has a simple structure for the implementation of transmission of mixed real-time and non-real-time services.     

硬件损伤下能量采集双向中继网络系统中断性能分析

在硬件损伤条件下分析了能量采集双向中继网络的系统中断性能,该网络的终端节点对直达链路信号和中继链路信号分别进行选择合并（Selection Combining, SC）和最大比合并（Maximum Ratio Combining,MRC）。首先,推导了该网络在SC方案下的系统中断概率,并在此基础上得到了由硬件损伤而引起的两种效应,即中继协作效应和系统协作效应。然后,推导了该网络在MRC方案下的系统中断概率。最后,通过仿真分析了硬件损伤及系统参数对系统中断性能的影响,并比较了该网络在SC方案和MRC方案下的系统中断性能。仿真结果表明:在硬件损伤条件下,MRC方案仅引起系统协作效应;相比于MRC方案,SC方案对硬件损伤更加敏感;当数据传输速率低于系统协作门限时,采用MRC能够实现更好的系统中断性能。      

Diversity–Multiplexing Tradeoff and Outage Performance for Rician MIMO Channels

In this paper, we analyze the diversity–multiplexing tradeoff (DMT), originally introduced by Zheng and Tse, and outage performance for Rician multiple-input–multiple-output (MIMO) channels. The DMT characteristics of Rayleigh and Rician channels are shown to be identical. In a high signal-to-noise ratio (SNR) regime, the log–log plot of outage probability versus SNR curve for a Rician channel is a shifted version of that for the corresponding Rayleigh channel. The SNR gap between the outage curves of the Rayleigh and Rician channels is derived. The DMT and outage performance are also analyzed for Rician multiple-input–single-output (MISO)/single-input–multiple-output (SIMO) channels over a finite SNR regime. A closed-form expression for the outage probability is derived and the finite SNR DMT characteristic is analyzed. It is observed that the maximum diversity gain can be achieved at some finite SNR–the maximum gain tends to increase linearly with the Rician factor. The finite SNR diversity gain is shown to be a linear function of the finite SNR multiplexing gain. The consistency between the DMTs for finite and infinite SNRs is also shown.      

An Analytical Approach to Outage Analysis and Critical Cooperation Ratio in Coded Cooperation

In this paper, we analyze the performance of a coded cooperation based communication system using independent flat Nakagami-m fading channels. We examine the outage behavior of the cooperative system constrained on instantaneous received power which follows the Gamma distribution. The expression for outage probability of the coded cooperative communication system is derived which is applicable for arbitrary value of parameter m and contains single integral terms only. Finally, we present an analytical approach to evaluate the critical cooperation ratio that minimizes the total outage probability of the cooperative system.     

Performance of Quadrature Amplitude Modulation for Indoor Radio Communications

The performance ofM-QAM for indoor radio communications is evaluated via a realistic model for indoor multipath propagation [1]. It is found that the outage (BER < 10^-4) is about 0.3 percent at 1 Mbit/s and 20 percent at 4 Mbits/s. Two-antenna predetection diversity reduces the outage from 1.2 to 0.04 percent at 2 Mbits/s. Increasing the signaling pulse rolloff factor from 0.5 to 1.0 reduces the outage by not more than 35 percent.     

Minimum Duration Outage for CDMA Cellular Systems: A Level Crossing Analysis

Traditionally, outage for CDMA cellular systems has been defined as the signal level (or, more precisely, the signal-to-interference ratio (SIR)) falling below a required threshold. In real cellular environments, it is not the instantaneous drop of the signal strength below the threshold that determines outage. It is, in fact, the duration of time below a threshold that determines outage for cellular systems. Moreover, the static analysis of outage precludes the time correlation in the signals which is important in real systems owing to mobility, fading and power control. In this paper, we analyze minimum duration outages for such systems, where outage is defined as an excursion of the SIR below a level for a certain minimum duration. We formulate the outage condition as a level crossing problem and extend asymptotic results from the theory of level crossings to derive analytical results for the probability of outage. This method enables us to include the time correlation of signals in the analysis as well. The validity of the asymptotic results is verified using some exact results as well as simulations. These minimum duration outages have implications in redefining user capacity and handoff performance.     

Outage capacities and optimal power allocation for fading multiple-access channels

We derive the outage capacity region of an M-user fading multiple-access channel (MAC) under the assumption that both the transmitters and the receiver have perfect channel side information (CSI). The outage capacity region is implicitly obtained by deriving the outage probability region for a given rate vector. Given a required rate and average power constraint for each user, we find a successive decoding strategy and a power allocation policy that achieves points on the boundary of the outage probability region. We discuss the scenario where an outage must be declared simultaneously for all users (common outage) and when outages can be declared individually (individual outage) for each user.     

Outage Probability of Decode‐and‐Forward Relaying Systems with Efficient Partial Relay Selection in Nakagami Fading Channels

Recently, efficient partial relay selection (e‐PRS) was proposed as an enhanced version of PRS. In comparing e‐PRS, PRS, and the best relay selection (BRS), there is a tradeoff between complexity and performance; that is, the complexity for PRS, e‐PRS, and BRS is low to high, respectively, but vice versa for performance. In this paper, we study the outage probability for e‐PRS in decode‐and‐forward (DF) relaying systems over non‐identical Nakagami‐m fading channels, where the fading parameter m is an integer. In particular, we provide closed‐form expressions of the exact outage probability and asymptotic outage probability for e‐PRS in DF relaying systems. Numerical results show that e‐PRS achieves similar outage performance to that of BRS for a low or medium signal‐to‐noise ratio, a high fading parameter, a small number of relays, and a large difference between the average channel powers for the first and the second hops.     

Cell-coverage estimation based on duration outage criterion for CDMA cellular systems

Previous papers addressing coverage analysis for code-division multiple-access (CDMA) cellular networks have focused on cell expansion from soft handoff or estimation of cell coverage based on an instantaneous outage criterion. Instantaneous outage estimates of cell coverage are a worst case assessment in that the predicted coverage as a function of the number of users is necessarily smaller than the actual coverage. We present the theoretical framework for estimating reverse-link cell coverage based on a duration outage criterion. Our results show that coverage estimates based on duration outage are typically 15%-30% larger than coverage estimates based on instantaneous outage when the correlation distance of the large-scale shadowing environment is small. We compare our theoretical duration outage results of cell coverage with simulated results that considered various large-scale shadowing conditions as well as Rayleigh small-scale fading. The theoretical and simulated coverage results are found to be in very good agreement. The simulations confirm that the presented theoretical duration outage analyses provide accurate and realistic estimates of reverse-link CDMA cell coverage.     

A Simplified Method for the Laboratory Determination of Multipath Outage of Digital Radios in the Presence of Thermal Noise

Multipath fading at microwave frequencies causes highspeed digital radio systems on line-of-sight paths to experience outage, where outage is defined here as the number of seconds in a month that the bit-error rate (BER) on an unprotected hop exceeds a threshold. The expected or predicted outage of a radio system may be calculated using a statistical model of fading in conjunction with characteristics of the radio determined by stressing it with a multipath fading simulator in the laboratory. To determine the effects of transmitted power levels (or nominal received carrier-to-noise ratio) on outage may require the simulation of 500-1000 channel conditions to characterize the radio completely. This paper describes a method of generating the complete characterization from a reduced set of simulation measurements; the method reduces the required number of measurements by a factor of about 20. Over a wide range of operating conditions, the outage calculated with this simplified method differs by less than 25 percent from that obtained with the complete characterization.     

Investigation on outage capacity of spectrum sharing system using CSI and SSI under received power constraints

In this paper, we have investigated the outage capacity of secondary user for opportunistic spectrum sharing under the joint peak and average received power constraints for Rayleigh fading environment. Under this communication scenario, on detecting the licensed primary user inactive, the secondary unlicensed users transmit data/information in the licensed frequency band such that no or minimum interference may be experienced by the primary user. The soft sensing information (SSI) and secondary user’s channel state information is used to obtain the closed form expressions for the ergodic and outage capacity using truncated channel inversion with fixed rate technique under the joint peak and average received power constraints. Numerically simulated results are provided to demonstrate the improvement in outage capacity of secondary user under the proposed spectrum sharing scheme. Moreover, the proposed scheme is also compared with other conventional spectrum sharing schemes to illustrate the benefits of SSI and received power constraints on the outage capacity of secondary user.

     

空时协作系统的中断概率分析和功率分配研究

提出了选择中继协议下最小化系统中断概率的最优功率分配方案,并给出了最佳功率分配的闭式解。根据协作节点间是否存在交互信息,分别通过对系统中断概率的分析,推出了高信噪比下中断概率的理论界。基于理论界,在功率受限情况下,通过拉格朗日乘数法,得到最优功率分配的闭合解。仿真结果表明,所推理论界在高信噪比下与仿真值近似相等,最优功率分配点的系统性能也要优于其它功率分配点。     

具有功率分配因子的不可信中继系统的中断性能和遍历保密容量

基于不存在直接链路的具有不可信中继的三节点系统,本文在协作干扰模型中引入功率分配因子,对两种放大转发因子下系统的中断概率和遍历保密容量进行了计算及对比分析。首先,系统采用平均放大因子,推导出其保密中断概率;然后,在引入同样功率分配因子的基础上,系统改用自适应瞬时放大因子,得出保密中断概率的下界;为了对比,本文接着给出了系统两种情况下的遍历保密容量;最后,仿真验证了中断概率和遍历保密容量计算的准确性,数值仿真表明引入功率分配因子可减小系统的中断概率和提高系统的遍历保密容量,瞬时放大因子下系统性能较平均放大因子下更好。      

Data on, and Investigation of, The Relation between 345 kV Transmission Line Length and Outage Rate

This paper presents the results of an analysis of outage data recorded over a 12-year period on 112 345-kV transmission lines of the Commonwealth Edison Company in Illinois; the lengths range from 3.5 to 188 miles. A linear relationship is developed between outage rate and line length; it does not pass through the origin but above it, indicating a residual outage rate corresponding to zero line length. This residual outage rate is attributed to terminal conditions and equipment, and is viewed quantitatively by equating it to a fixed number of miles of line length. Because of the wide scatter of data points, the data were grouped by line-length in 10-mile increments. The outage and years in service for each group were combined, and then analyzed by groups. The Gaussian method of least squares is used to fit a line to these points. The important value, is the outages/year due to the terminal conditions and equipment (ie, where the length of the transmission line equals zero and outages are still indicated). For accurate representation of this relation, only the values representing the largest number of data points, are included in the calculations. These show an annual failure rate of 0.7 which compares most favorably with the 0.6 found with the Markov Model (ie, by developing a failure and repair rate matrix due to the dependent outage combined with its probability matrix. A graphic method for determining the effects of terminal conditions and equipment has also been introduced.     

Choosing from redundant designs of power systems using system outage rate and cost

The push for high availability is on. As customers keep telling computer manufacturers, any outage to their operations is unacceptable. For those involved at the design stage, this usually means that functions within a computer's subsystems, like power, must be made fault-tolerant, or redundant. In its simplest form, redundancy replaces one component with two, so that the first failure will have no impact on the customer. More generally, a K-out-of-N design calls for N components to do the job of N − K + 1, so that the first K − 1 failures can be tolerated but the K-th failure causes a system outage. In this paper, we relate our own experience with power subsystems: how we chose from among different shades of redundancy by concentrating on outage rate and cost. To further simulate real life, we also considered the service strategy, i.e. whether (and when) to preventively replace a component whose failure did not cause the system to go down. A key result of the paper shows that a redundant design coupled with a well-chosen service strategy yields advantages beyond what either one alone would provide. The combination not only decreases the design's already low system outage rate, it makes the outage rate essentially constant—so that ease of predictability is ensured. Three power subsystem designs are outlined, as are the reliability and outage rate functions associated with them. Cost and service strategy are then considered, to help decide which is the optimal design based on total program cost projections and reliability objectives.     

First-order PMD outage for the hinge model

System outage due to first-order polarization-mode dispersion of links obeying the hinge model is analyzed using outage maps. We find that some fraction of the wavelength-division-multiplexed fiber capacity does not meet any outage specification.     

Distributed measurements for estimating and updating cellular system performance

We investigate the use of distributed measurements for estimating and updating the performance of a cellular system. Specifically, we discuss the number and placement of sensors in a given cell for estimating its signal coverage. Here, an "outage" is said to occur at a location if a mobile receiver there has inadequate signal-to-noise ratio (SNR -based outage) or, using another criterion, inadequate signal-to-interference ratio (SIR- based outage); and the "outage probability" is the fraction of the cell area over which outage occurs. A design goal is to improve measurement efficiency (i.e., minimizing the required number of measurement sensors) while accurately estimating the outage probability and mapping the coverage holes. The investigation uses a generic path loss model incorporating distance effects and spatially correlated shadow fading. Our emphasis is on the performance prediction accuracy of the sensor network, rather than on cellular system analysis per se. Through analysis and simulation, we assess several approaches to estimating the outage probability. Applying the principle of importance sampling to the sensor placement, we show that a cell outage probability of P_o can be accurately estimated using ~ 10/P_o power-measuring sensors distributed in a random uniform way over the area with base-sensor distances from 50% to 100% of the cell radius. This result applies to both SNR-based and SIR-based outage estimation for both indoor and outdoor environments.