Error probability of multicell CDMA over frequency selective fadingchannels with power control error

It is well known that power control is critical in CDMA mobile systems. In this paper, the error probability of a multicell CDMA system, operating with imperfect power control over a frequency selective multipath fading channel, is derived. Asymptotic expressions (for high signal-to-interference-plus-noise ratios) of the error probability show that the use of diversity combining exacerbates the effect of the power control error (PCE), since the power control is identical on each diversity channel; also, the error probability increases exponentially with PCE, while (asymptotically) increasing linearly with the number of users and decreasing inverse linearly with the processing gain. In addition to the asymptotic results mentioned above, both Chernoff bounds on, and approximations to, the error probability are found. Numerical results reveal the tightness of the Chernoff bounds, and show that the approximations are actually much tighter than the bounds, at least for PCE standard deviations of 1.5 dB or less     

Throughput and packet error probability of cellularfrequency-hopped spread-spectrum radio networks

The authors characterize multiple-access interference for cellular mobile networks, in which users are assumed to be Poisson-distributed in the plane and use frequency-hopped spread-spectrum signaling with a transmitter-oriented assignment of frequency-hopping patterns. Exact expressions for the bit error probabilities are derived for binary coherently demodulated systems without coding. Approximations for the packet-error probability are derived for coherent and noncoherent systems and these approximations are applied when forward-error-control coding is used. In all cases, the effects of varying interference power are accurately taken into account according to some propagation law. Numerical results are given in terms of bit-error probability for the exact case and throughput for the approximate analyses. Comparisons are made with previously derived bounds, and it is shown that these tend to be very pessimistic     

基于STBC的无线认知NOMA系统物理层安全性能研究

基于非正交多址接入（NOMA,Non-Orthogonal Multiple Access）的认知无线电（CR,Cognitive Radio）网络物理层传输面临主用户干扰和第三方窃听双重干扰威胁.本文提出利用空时编码（STBC,Space Time Block Coding）技术提高认知用户物理层安全性能,推导了任意认知用户的安全中断概率闭合表达式.通过蒙特卡洛仿真进行验证,结果表明,所提STBC-CR-NOMA相比未采用STBC编码方案的CR-NOMA可以明显提高用户的安全中断概率,且随着认知发射功率的增大,近端用户安全中断性能提高越大,而远端用户安全中断性能提升受认知基站发射功率的影响较小.仿真结果还表明,通过调整功率分配系数对远端用户和近端用户的安全中断性能影响不同.     

Novel Finite Summation Expressions for Total Interference Power due to Carrier Frequency Offset in Uplink Multiuser OFDM Systems

Carrier Frequency Offset which poses adverse threats in uplink Multiuser OFDM systems induces Inter-Carrier Interference (ICI) and Multiuser Interference (MUI). It is very essential that the power of ICI and MUI is calculated precisely. In previous work, the total interference power was presented in an indefinite integral form or as an infinite series. Further, an ideal channel was the scenario under consideration in earlier work. In this paper, novel finite summation expressions for power of ICI and MUI are derived over slowly fading channels which make the calculation of total interference simpler for any number of users by just specifying the total number of users and the number of subcarriers allotted for each user. Based on the mean of the dominant signal and the total interference power experienced in the system, closed-form expressions for mean and variance of the desired signal in uplink multiuser OFDM system are obtained which provide an idea of the strength of the desired signal. Finite-sum expressions for the total interference power, and closed-form expressions for mean and variance of the desired signal under Rayleigh, Weibull and Nakagami fading channels are derived and plotted from which the response of the system can be understood perfectly.     

Performance analysis of multiuser selection diversity in SIMO spectrum sharing systems

In this paper, a performance analysis is presented for user selection schemes in a single‐input multiple‐output spectrum sharing system. In the considered system, multiple secondary users try to use the licensed spectrum of a primary user in an opportunistic manner, in which an interference constraint for the primary user is satisfied. In this paper, we first use 2 conventional user selection schemes for single‐input multiple‐output spectrum sharing system and analyze the system performance for each scheme. We then propose a new user selection scheme that can overcome the limitations of those 2 conventional user selection schemes. As for the performance analysis, the average channel capacity, the outage probability, and the bit error rate performances of the system using the presented user selection schemes are analyzed and mathematical closed‐form expressions for the outage probability are derived. The performances of the system are evaluated using the derived mathematical formulas in different cases. In addition, Monte Carlo simulation results are also provided to show the accuracy and correctness of the performed analysis.     

Optimal power control for Rayleigh-faded multiuser systems with outage constraints

How can we achieve the conflicting goals of reduced transmission power and increased capacity in a wireless network, without attempting to follow the instantaneous state of a fading channel? In this paper, we address this problem by jointly considering power control and multiuser detection (MUD) with outage-probability constraints in a Rayleigh fast-fading environment. The resulting power-control algorithms (PCAs) utilize the statistics of the channel and operate on a much slower timescale than traditional schemes. We propose an optimal iterative solution that is conceptually simple and finds the minimum sum power of all users while meeting their outage targets. Using a derived bound on outage probability, we introduce a mapping from outage to average signal-to-interference ratio (SIR) constraints. This allows us to propose a suboptimal iterative scheme that is a variation of an existing solution to a joint power control and MUD problem involving SIR constraints. We further use a recent result that transforms complex SIR expressions into a compact and decoupled form, to develop a noniterative and computationally inexpensive PCA for large systems of users. Simulation results are presented showing the closeness of the optimal and mapped schemes, speed of convergence, and performance comparisons.     

Multi-User Opportunistic Scheduling using Power Controlled Hierarchical Constellations

In this letter, we study an application of hierarchical constellations (known also as embedded, multi-resolution, or asymmetrical constellations) for multi-user opportunistic scheduling. The key idea is to rely on hierarchical constellations to transmit information to two or more best users simultaneously in each transmission. The transmit power as well as the constellation parameter is changed according to the link qualities of the selected users in a way that a given target bit error rate (BER) is satisfied. The expressions for the average transmit power, and the outage probability with truncated channel inversion power control are presented. We also analyze and compare buffer distribution, average buffer occupancy, and packet loss probability of different; schemes via queuing analysis. We finally compare the hierarchical scheme for multi-user scheduling with a uniform constellation-based time-slotted scheme     

Average block error probability of multicell CDMA packet networks with fast power control under multipath fading

We derive the average block error probability of multicell code-division multiple access (CDMA) packet networks with fast power control under multipath fading. Unlike many previous works, we consider that users are connected to a base station on a minimum attenuation basis. An analytical approach for the calculation of the intracell and intercell statistics is presented. By making use of these expressions, the mean block error probability is analyzed as a function of the number of resolvable paths and the number of base stations to which mobiles can connect.     

Exploiting decentralized channel state information for random access

We study the use of channel state information (CSI) for random access in fading channels. Traditionally, random access protocols have been designed by assuming simple models for the physical layer where all users are symmetric, and there is no notion of channel state. We introduce a reception model that takes into account the channel states of various users. Under the assumption that each user has access to its CSI, we propose a variant of Slotted ALOHA protocol for medium access control, where the transmission probability is allowed to be a function of the CSI. The function is called the transmission control. Assuming the finite user infinite buffer model we derive expressions for the maximum stable throughput of the system. We introduce the notion of asymptotic stable throughput (AST) that is the maximum stable throughput as the number of users goes to infinity. We consider two types of transmission control, namely, population-independent transmission control (PITC), where the transmission control is not a function of the size of the network and population-dependent transmission control (PDTC), where the transmission control is a function of the size of the network. We obtain expressions for the AST achievable with PITC. For PDTC, we introduce a particular transmission control that can potentially lead to significant gains in AST. For both PITC and PDTC, we show that the effect of transmission control is equivalent to changing the probability distribution of the channel state. The theory is then applied to code-division multiple-access (CDMA) networks with linear minimum mean-square error (LMMSE) receivers and matched filters (MF) to illustrate the effectiveness of using channel state. It is shown that through the use of channel state, with arbitrarily small power, it is possible to achieve an AST that is lower-bounded by the spreading gain of the network. This result has implications for the reachback problem in large sensor networks.     

Joint drift analysis for multigroup slotted ALOHA: stability withmaximum utilization

In this paper, a slotted ALOHA system is considered where the users in the system are divided into two power groups. At the mobile base station, members of one group are received at a higher power level than those in the second group. This power division can be used to increase the overall throughput of the ALOHA system from 0.368 to 0.53. The two-group ALOHA system is stabilized by extending the idea of joint drift analysis, originally devised for a single group to the two-group case and the paper proposes a criterion for choosing a set of control parameters. The control parameter selection criterion guarantees one stable equilibrium point for each group, which enables the system to operate at the maximum throughput point. Combinations of the "optimal" control parameters are used to update the estimated number of users in the backlog, which is required in calculating the retransmission probability for users in each group. Simulation results demonstrate the superiority of the proposed control strategy over existing stability schemes     

Exact Outage Probability Analysis for a Multiuser MIMO Wireless Communication System With Space–Time Block Coding

A multiuser multiple-input-multiple-output (MIMO) system with orthogonal space-time block coding (OSTBC) is analyzed for the uplink of a wireless communication system in a Rayleigh fading environment. In the first part of this paper, a simple and exact closed-form expression for the outage probability of the signal-to-interference-and-noise ratio (SINR) is derived at the input of the base station (BS) receiver by making the following two assumptions: 1) All the users transmit their data by using the same OSTBC; and 2) the users are power controlled by the same BS so that the interfering users are requested to transmit with the same power. In the second part of this contribution, the outage probability of the signal-to-interference ratio (SIR) is calculated at the output of the BS receiver, which, in our case, is a spatial matched filter. To be able to analytically solve the latter problem, the presented analysis is restricted to the case of a single interferer and a 2 2 MIMO system with Alamouti coding. Monte Carlo simulations are carried out to verify the proposed analytical expressions for the outage probability.     

Distribution of a random walk with an application to a truncated nonparametric sequential test

Explicit expressions for the probability of reaching a given position at each stage of a random walk are derived for the case of absorbing boundaries. Utilizing these results, exact expressions for the power function and the average sample number function of a truncated nonparametric sequential test are obtained. Some numerical examples are also given.     

分数阶功控时的Ad Hoc网络传输容量

Ad Hoc网络是干扰受限系统,为了获得较高的网络传输容量,需要引入合适的功率控制策略,降低网络中的干扰。分数阶功率控制是一种新型的功率控制策略,是对信道反转功率控制的改进。这里推导分数阶功率控制时的中断概率和传输容量的n阶近似表达式,研究了n阶近似表达式的准确度,讨论了分数阶功率控制相对于信道反转功率控制对网络性能的改进。通过研究表明,适当的选择合适的分数阶功率控制系数可以使得中断概率最小,传输容量最大。     

A joint performance measure for the decorrelating multiuser detector

We analyze the performance of the decorrelating multiuser detector for a wireless communication system. Instead of looking at the error probability for each user, we focus on the probability distribution of the number of correctly decoded users at the receiver and the average number of correctly decoded users under the conditions of equicorrelated signatures and perfect power control. The approach is motivated by the fact that the error events for different users are not independent. Numerical results show that when the number of users is large, instead of using a set of long signatures with a very low negative cross-correlation, we can use a set of shorter signatures with a reasonably high positive correlation without sacrificing the performance. It is also found that the average number of correctly decoded users increases with increase in signal-to-noise ratio and decreases when the cross-correlation between users becomes more negative or more positive.     

Precise Outage Analysis of Selection Diversity and Switched Diversity in Bandlimited Microcellular Systems With Cochannel Interference

Precise outage probability performance analysis of a microcellular system with selection and switched diversities is considered. The microcellular system is assumed to follow a flat, slow Nakagami/Rayleigh fading model wherein the fading channels from the desired transmitter to all the receiver antennas are independent and identically distributed Nakagami channels, and all the fading channels for the interfering signals are independent, identically distributed Rayleigh channels. Three selection and switching criteria, namely, desired signal power, signal-to-interference power ratio, and total output power are considered. Unlike previous results, the system model under investigation takes into account the pulse shaping, the random delays, and the phase offsets of the interfering users. Two Nyquist pulse shapes, spectrum-raised-cosine and Beaulieu-Tan-Damen pulse shapes, are considered. Analytical outage probability expressions are derived for an arbitrary number of interferers, arbitrary diversity order, and arbitrary value of desired user fading parameter. The outage performances of the selection criteria are compared. The optimum switching thresholds for different switching criteria are formulated.     

多蜂窝上行链路通信系统性能分析

考虑存在来自其他蜂窝的不同功率同信道干扰的多用户上行链路,分析了多天线基站采用多用户调度和最大比合并接收时的系统性能。在期望信号和干扰信号分别经历Nakgami-m和Rayleigh衰落时,运用基于概率密度函数的性能分析法推导了系统中断概率的闭合表达式。仿真结论显示,系统中断概率的解析曲线与数值仿真结果一致,系统性能随着天线数和用户数的增大而提升,多天线和多用户分集增益明显,干扰功率有较大差异时系统中断概率性能有所下降。     

混合衰落信道下选择中继译码转发的性能分析

蜂窝中继通信中基站到中继以及中继到移动台可以建模成混合衰落信道,即基站到中继的信道通常经历莱斯衰落,中继到移动台的信道通常经历瑞利衰落。该文研究混合衰落信道下协同通信系统中两跳译码转发方式的性能,首先通过分析推导了基于选择最佳中继的中断概率、误符号率以及误符号率的渐近线的闭式表达式,然后基于误符号率的渐近线给出了一种功率优化方法。蒙特卡洛仿真验证了理论公式,仿真结果显示优化功率分配的性能优于平均功率分配的性能。     

Signal Detection in Cognitive Radio Networks over AWGN and Fading Channels

In this paper, we consider the problem of spectrum sensing based on energy detection method in cognitive radio over wireless communication channels when users experiences fading and nonfading effects. The closed-form analytical expressions for the detection probability are derived over nonfading additive white Gaussian noise channel, Rayleigh, Rician and Nakagami-m fading channels. The detection probability involving Marcum-Q function is replaced by closed-form expression. The probability distribution function of fading channels is used to obtain the expressions for detection probability. The new derived numerical results are simulated under various parameters.     

Performance analysis of an opportunistic multi‐user cognitive network with multiple primary users

Consider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd.     

协作NOMA系统中的一种新型节能功率分配方案

在传统的协作非正交多址（CNOMA, Cooperative Non Orthogonal Multiple Access)系统中,通常需要向弱用户分配更多的功率,分配给强用户的功率不超过总功率的一半。同时,强用户还需在协作阶段承担中继通信的任务。上述功率分配方式必将给强用户带来一定的负担。为了在满足弱用户服务质量的情况下,进一步提高强用户的中断性能,本文提出一种基于中继和无线携能通信（SWIPT, Simultaneous Wireless Information and Power Transfer）的新型功率分配方案。该方案使用能量收集设备收集能量,通过最大化系统和速率寻求无线携能通信的最优功率分割因子,从而获得系统中断概率的闭式表达。考虑到优化问题的性质,本文提出了一种在功率分配固定的情况下,通过单调优化求解无线携能通信功率分割因子的算法。仿真结果表明,与CNOMA系统的传统功率分配方案相比,本文所提方案能够在不损失弱用户中断性能的前提下,有效提升强用户的中断概率,系统和速率总体提高了近 20%。