Performance analysis of cellular CDMA networks overfrequency-selective fading channel

An effect of multipath fading on the performance of a cellular code-division multiple-access (CDMA) system is analyzed in this paper. A wide-sense stationary uncorrelated scattering (WSSUS) channel model and the coherent binary phase-shift keying (BPSK) with asynchronous direct-sequence (DS) spreading signal are assumed in the analysis. The average error probability for both the forward link and reverse link of a cellular CDMA system over a frequency-selective fading channel using a conventional correlation-type receiver and RAKE receiver are derived. The impact of imperfect power control and channel capacity of a cellular CDMA system is also investigated. The closed forms of average error probability derived in the paper can save a lot of computation time to analyze the performance and channel capacity of a cellular CDMA system. The analytical results show that the performance and maximum transmission rate of cellular CDMA systems degrade with an increase in the number of simultaneous users and the number of interfering cells. The signal-to-interface ratio (SIR) for the reverse link derived in this paper can directly describe the interrelationships among a number of paths, number of users, number of interfering cells, fading factors, and maximum variation of a received unfaded signal     

On first-order Markov modeling for the Rayleigh fading channel

Previous models for the received signal amplitude of the flat-fading channel that use first-order finite-state Markov chains are examined. The stochastic properties of a proposed first-order model based on these models are examined. The limitations of using an information theoretic metric, which is sometimes used to justify a first-order Markov chain as a sufficient model for very slowly fading channels, are discussed. A simple method of qualitatively comparing autocorrelation functions is instead proposed. The usefulness of the first-order Markov chain in representing the flat-fading channel is examined by looking at two specific problems in wireless system applications that represent two disparate cases. The first case involves analysis over a short duration of time, relative to the inverse of the normalized Doppler frequency, while the second involves analysis over a long duration of time. Contrary to previous reports, the results indicate that first-order Markov chains are not generally suitable for very slowly fading channels. Rather, first-order Markov chains can be suitable for very slowly fading applications, which require analysis over only a short duration of time     

WCDMA随机接入信道的数学建模及性能分析

文章主要讨论了宽带码分多址(WCDMA)网络中无线小区随机接入信道(RACH)的数学建模方法及性能分析.首先介绍了WCDMA的RACH及信息发送方式,然后描述了RACH随机接入过程的时隙ALOHA接入方式,并在此基础上重点分析了RACH数学建模的方法和详细过程,给出了RACH吞吐量的计算公式,最后,对RACH的性能进行了分析.     

The multi-user detection under fading channel

This paper proposes a method of blind multi-user detection algorithm based on signal sub-space estimation under the fading channels in the present of impulse noise. This algorithm adapts recursive least square (RLS) filter that can estimate the coefficients using only the signature waveform. In addition, to strengthen the ability of resisting the impulse noise, a new suppressive factor is induced, which can suppress the amplitude of the impulse, and improve the ability of convergence speed. Simulation results show that new RLS algorithm is more robust against consecutive impulse noise and have better convergence ability than conventional RLS. In addition, Compared to the least mean square (LMS) detector, the new robust RLS sub-space based method has better multi-address-inference (MAI) suppressing performance, especially, when channel degrades.     

Nakagami衰落信道下的蜂窝系统性能分析

文中考虑多小区蜂窝系统中小区边缘用户受到来自其他小区间同信道干扰,分析了在Nakagami-m衰落信道下,用户和基站均为单天线时的多小区蜂窝系统性能,以获得干扰信号衰落参数m和干扰基站发射功率对系统性能的影响。采用概率密度函数（PDF）分析法推导了系统中断概率和平均误符号率（ASER）的闭合表达式,并进一步通过数值仿真来分析同信道干扰对系统性能的影响。仿真结果表明,系统的中断概率和ASER的解析曲线均与仿真结果一致,系统性能随着干扰信号衰落参数m和干扰功率的增加而降低。     

Bit-error rate of TDMA links under cochannel interference inoverlaid cellular networks

This paper presents a series of numerical experiments conducted to investigate the error performance of a simulated digital time-division multiple-access (TDMA) radio link between a portable handset and the base station serving it, subject to interference coming from other portable handsets. The experiments take radio channel impairments such as fading, shadowing, and distance loss into account. Analytical expressions for the bit-error probability in uncoded digital radio transmission bursts under interference from nearby analog FM or digital minimum-shift keying (MSK) transmitters are reviewed. Numerical methods are used to extend analytical estimates of symbol error probability of a link with a single interferer, without channel impairments, to the case where the interference is due to a random distribution of transmitters whose signals are subject to fading, shadowing, and distance power loss. Specifically, three links, each based on one of three different modulation methods, MSK, quadrature phase-shift keying (QPSK) (proposed in the North American Digital Cellular Standard IS-54), and Gaussian MSK (GMSK) [used in the Global Standard for Mobile communications (GSM)] are simulated, and the bit-error rate (BER) results reported. The BER results generated thus indicate the sensitivity of the digital radio link to the user density for a given radio frequency (RF) bandwidth and, where applicable, to fading depth and postmodulation intersymbol interference (ISI) removal method. Possible extensions and applications of the simulation model to the problem of resource sharing between coexisting networks are suggested     

Optimal channel assignment in cellular networks

In this paper, we consider the problem of assigning frequencies to mobile terminals in a cellular network. We show that an optimal solution can be obtained by solving a sequence of alternating linear and quadratic maximization programming problems. We address co-channel constraints and adopt as an objective function the maximization of potentially established calls. Our algorithm is fairly general, and does not depend on any special network structure. This study indicates that mathematical programming can be used as an efficient technique for solving the aforementioned problem.     

Inter-cell interference modeling for cellular networks

We develop and analyze several inter-cell interference modeling methods for various fading scenarios in wireless systems. The models can analyze multiple interfering signals under different fading scenarios. Incoherent addition of multiple interfering signals is assumed. In this paper, we present two approaches, i.e., the approximate and exact analysis methods to calculate the probability density function (PDF) of the power of the interference signals. We propose the use of the generalized Gram-Charlier Series to analyze the error of the reference model. Although the computational complexity of exact analysis is high, it can be used to ensure the accuracy of the approximate analysis method. Hermite polynomials are used to simplify the integration operation into the summation operation, thus reduces the computational complexity of the exact method dramatically. The approximate method is simple although it may lead to increased errors. The methods proposed are useful in designing and analyzing practical systems.     

Effect of power control imperfections on the reverse link of cellular CDMA networks under multipath fading

In this paper, we present an analytical approach for the evaluation of the impact of power control errors on the reverse link of a multicell direct sequence code-division multiple access (CDMA) system with fast power control under multipath fading. Unlike many previous papers, the joint effect of multipath fading and fast power control on interference statistics is explicitly accounted for and mobiles are assumed to connect to a base station according to a minimum attenuation criterion. Both the average bit error rate (BER) and the outage probabilities that a user experiences are estimated. The results have been used to evaluate the system capacity from two points of view. First, the maximum capacity supported by the system in order to maintain an average BER below a prescribed level has been calculated. Second, the maximum capacity possible to ensure that the outage probability does not exceed a set limit is analyzed. Capacity is shown to be significantly affected by the imperfections of power control. Our results can be used to quantify the relative capacity loss due to fast power control errors in a cellular CDMA network affected by slow fading, multipath fading, and cochannel interference.     

Radio planning and coverage optimization of 3G cellular networks

Radio planning and coverage optimization are critical issues for service providers and vendors that are deploying third generation mobile networks and need to control coverage as well as the huge costs involved. Due to the peculiarities of the Code Division Multiple Access (CDMA) scheme used in 3G cellular systems like UMTS and CDMA2000, network planning cannot be based only on signal predictions, and the approach relying on classical set covering formulations adopted for second generation systems is not appropriate. In this paper we investigate mathematical programming models for supporting the decisions on where to install new base stations and how to select their configuration (antenna height and tilt, sector orientations, maximum emission power, pilot signal, etc.) so as to find a trade-off between maximizing coverage and minimizing costs. The overall model takes into account signal-quality constraints in both uplink and downlink directions, as well as the power control mechanism and the pilot signal. Since even small and simplified instances of this NP-hard problem are beyond the reach of state-of-the-art techniques for mixed integer programming, we propose a Tabu Search algorithm which provides good solutions within a reasonable computing time. Computational results obtained for realistic instances, generated according to classical propagation models, with different traffic scenarios (voice and data) are reported and discussed. Preliminary results have been presented in [5, 7, 8]. This work has been supported by the “Progetto Cofinanziato 2001–2003” of the Italian Ministry of Education, University and Scientific Research (MIUR), Optimization models and methods for telecommunication network design and management. Edoardo Amaldi received the “Diplome” in Mathematical Engineering from the Swiss Federal Institute of Technology at Lausanne (EPFL) in 1988. After one year in the Computational and Neural Systems program, California Institute of Technology, USA, he came back at EPFL where he earned the “Doctoratés Sciences” (PhD) in October 1994. He then joined the School of Operations Research and Industrial Engineering, Cornell University, USA, where he did research and taught graduate courses in mathematical programming. Since 1998 he is with the Dipartimento di Elettronica e Informazione (DEI), Politecnico di Milano, Italy, where he is currently an Associate Professor in Operations Research. His main research interests are in discrete optimization, the design and analysis of algorithms, and computational complexity with applications in telecommunications, image/signal processing, machine learning, and computational biology/finance. In 2005 he received an IBM Faculty Award for his work on the maximum feasible subsystem problem. He serves on the Program Committees of several international workshops and conferences (including the European Symposium on Algorithms, International Network Optimization Conference, International Workshop on Efficient and Experimental Algorithms–WEA) and since 2005 he is on the Steering Committee of WEA. Antonio Capone is an Associate Professor at the Dipartimento di Elettronica e Informazione of the Technical University of Milan (Politecnico di Milano). His expertise is on networking and main research activities include protocol design (MAC and routing) and performance evaluation of wireless access and multi-hop networks, traffic management and quality of service issues in IP networks, and network planning and optimization. He received the M.S. and Ph.D. degrees in electrical engineering from the Politecnico di Milano in 1994 and 1998, respectively. In 2000 he was a visiting professor at UCLA, Computer Science department. He currently serves as editor of the Wiley Journal of Wireless Communications and Mobile Computing. He served in the technical program committee of several international conferences and he is a regular reviewer of the main journals in the networking area. He is currently involved in the scientific and technical activities of several national and European research projects, and he leads several industrial projects. He is a Senior Member of the IEEE. Federico Malucelli (Ferrara, 7/4/62) got a Laurea in Computer Science and Ph.D. in Computer Science both from Universita’ di Pisa in 1988 and 1993 respectively. Since 2003 he is full professor of Operations Research at the Politecnico di Milano. In 1998–2002 he was associate professor of Operations Research at the Politecnico of Milano, and from 1992 to 1998 research associate at Pisa and Perugia Universities. He has visited several foreign universities and research laboratories, including HP Laboratories, Palo Alto (USA), Universite’ de Montreal (Canada) and Linkoping Universitet (Sweden). He has served as research unit coordinator for several nationwide MIUR and CNR research projects on optimization in telecommunications networks and transportation systems. His main research interests include: models and algorithms for combinatorial optimization problems, with applications in particular to telecommunications, transportations, logistics, and electronic circuit design. He has published more than 30 articles on international scietific journals.     

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.     

Cutoff rate of 16-DAPSK over a Rayleigh fading channel

The cutoff rate of 16-DAPSK modulation and differential detection over a Rayleigh fading channel is calculated, which provides the ensemble performance of coded data transmission. Given the code rate, the minimum SNR required for reliable communication is obtained with parameters such as the ring ratio and the diversity number     

Handover and channel assignment in mobile cellular networks

A taxonomy of channel assignment strategies is provided, and the complexity in each cellular component is discussed. Various handover scenarios and the roles of the base station and the mobile switching center are considered. Prioritization schemes are discussed, and the required intelligence distribution among the network components is defined     

慢变无线信道下的序列检测

本文对多径信道序列检测的VA(Viterbi Algorithm)算法进行了改进,建立了节点度量的递推方程,改进后的VA算法适用于多径信道先验信息已知的序列检测.其中信道先验信息由健壮型RLM(Recursive Least M-estimate)算法及Kalman滤波器在训练序列阶段联合估计.仿真结果显示:在训练阶段对信道进行联合估计时,对相比于传统的RLS算法,RLM算法有效地提高了抵抗大脉冲干扰的能力,加快了待估的参数的收敛速度.而在实际接收阶段,新的度量递推算法在比特误码性能上接近采用全序列比较欧氏距离的最佳算法,但是复杂度却很低.     

Signal power random fading based interference-aware routing for wireless sensor networks

Power loss and interference coexist in wireless transmissions where random uncertainty is aggravated due to the mobility of sensor nodes. A probability interference model was proposed, based on the physical model and random fading of the received signal power, to depict the uncertainty of wireless interference. In addition, an interference-aware routing metric was designed, in which interference, routing convergence and residual energies of nodes were integrated. Furthermore, an interference-aware probabilistic routing algorithm was proposed for mobile wireless sensor networks, and its correctness and time and space complexities were proved. The NS-2 simulation experiments showed that the proposed algorithm can achieve higher packet delivery ratio than Greedy Perimeter Stateless Routing in various cases like the pause time and maximum moving speed. Simultaneously, the energy consumption of a packet and average delay were taken into consideration to better meet the needs of mobile scenarios with higher reliability.     

Distributed fault-tolerant channel allocation for cellular networks

A channel allocation algorithm includes channel acquisition and channel selection algorithms. Most of the previous work concentrates on the channel selection algorithm since early channel acquisition algorithms are centralized and rely on a mobile switching center (MSC) to accomplish channel acquisition. Distributed channel acquisition algorithms have received considerable attention due to their high reliability and scalability. However, in these algorithms, a borrower needs to consult with its interference neighbors in order to borrow a channel. Thus, the borrower fails to borrow channels when it cannot communicate with any interference neighbor. In real-life networks, under heavy traffic load, a cell has a large probability to experience an intermittent network congestion or even a communication link failure. In existing distributed algorithms, since a cell has to consult with a large number of interference neighbors to borrow a channel, the failure rate will be much higher under heavy traffic load. Therefore, previous distributed channel allocation algorithms are not suitable for real-life networks. We first propose a fault-tolerant channel acquisition algorithm which tolerates communication link failures and node (MH or MSS) failures. Then, we present a channel selection algorithm and integrate it into the distributed acquisition algorithm. Detailed simulation experiments are carried out in order to evaluate our proposed methodology. Simulation results show that our algorithm significantly reduces the failure rate under network congestion, communication link failures, and node failures compared to nonfault-tolerant channel allocation algorithms. Moreover, our algorithm has low message overhead compared to known distributed channel allocation algorithms, and outperforms them in terms of failure rate under uniform as well as nonuniform traffic distribution     

蜂窝通信网络中的分布式无线信道分配方法

文中提出了一种适用于蜂窝通信网的分布式无线信道分配方法。当网络部署环境中出现干扰后,终端用户通过控制信道,发送反馈信息至基站;基站接收到反馈信息后,对可用信道进行扫频,利用广播帧通知受干扰的终端用户可用信道信息;然后终端用户收到基站发送的广播帧后,根据优先级机制,选择新的信道重新建立与基站的通信,当蜂窝通信网中终端用户受外部干扰而信道中断后,该方法可减少终端用户和基站之间信令的开销。     

Effect of channel fade rate on throughput of three GHARQ-II schemesover Rayleigh fading channel

The performance of three GHARQ-II schemes, based on punctured convolutional codes, used over a simulated Rayleigh fading channel subject to additive white Gaussian noise are compared. Various fade rates and signal to noise ratios are considered     

相关衰落下多天线 LS-CDMA信道容量

对相关多径信道下不同扩频地址码的多天线CDMA系统的信道容量进行了研究,在研究中分别采用了在多码检测和多用户检测联合检测算法.在多码检测的情况下,李道本教授发明的LS码多天线CDMA系统比Walsh码和Gold码的多天线系统有更大的系统容量,后两者在大的信噪比(20dB)时候均有平台效应;在采用多用户检测时它们的容量几乎相同.由于具有零相关窗特性,对于LS码而言这两种方法是等效的.当发射天线数目等于接收天线数目时,系统的容量和天线数目呈线性关系.     

Maximum packing channel assignment in cellular networks

We study the performance of the maximum packing channel assignment algorithm (MPA) in channelized cellular networks. MPA is a greedy algorithm, which rejects a call only when it is forced to do so, even if this involves rearrangement of channels assigned to the ongoing calls, without dropping any of them. We ignore handoffs and model the channel reuse constraints in the cellular network by a hypergraph. As the traffic and the number of channels are scaled together, we get a limiting regime where the blocking probability in the cells can be computed by solving a nonlinear optimization problem. The carried traffic in this limiting case is an upper bound on the performance of MPA for practical finite-channel systems. We show that the performance of MPA in a finite-channel cellular system can be closely approximated by considering a simple fixed-routing circuit-switched network. Thus, the finite-channel performance of MPA can be studied using methods well known in the area of circuit-switched networks. We compare the performance of MPA with other asymptotically optimal algorithms and demonstrate its optimality for low and moderate offered traffic. We envisage MPA as a practical channel assignment algorithm, for moderate size systems, and suggest approximations to reduce its complexity