Performance analysis of a slotted CDMA ALOHA network

ALOHA is a simple and efficient way of allowing many machines with bursty data streams to communicate with a central computer. For cases where machines are equally likely to transmit to one another, CDMA ALOHA, which allows for full connectivity, may be a better multiple access protocol than slotted ALOHA through a central machine. This paper first describes a model for a fully connected, full duplex, and slotted CDMA ALOHA network where the receiver-based code access protocol is used. The stations can send data to, and receive data from, different stations simultaneously. The model is analyzed using discrete-time Markov chain, and some numerical results are presented. For a system with a large number of users where Markov analysis is impractical, equilibrium point analysis is used to predict the stability of the system and determine the throughput as well as the delay performance of the system when it is stable. It is shown that a CDMA slotted ALOHA network has a much better performance compared to simple slotted ALOHA networks.     

Calculating the outage probability in a CDMA network with spatialPoisson traffic

In this paper, we provide a spatial Poisson point pattern model of traffic in a code division multiple access (CDMA) wireless network. We show how the theory of Poisson processes can be applied to provide statistical information about interference levels in the network. In particular, we calculate approximations and a bound on the outage probability at a designated cell site in the network, utilizing high-order cumulants, which have very simple analytical forms and can easily be computed once the mean measure of the spatial Poisson point pattern is known. We consider a Poisson-Gaussian approximation and an Edgeworth approximation in which the Gaussian distribution is twisted to satisfy the required cumulants, and we provide a Chernoff bound on performance that also utilizes the cumulant information. We show that the theory can be applied to nonstationary, time nonhomogeneous systems. We provide a particular example of a M/M/∞, spatial queueing model of a CDMA wireless network     

Performance enhancement of DS-CDMA system using overlapping sectors with interference avoidance

A cellular system with overlapping sectors is proposed to enhance system performance through interference avoidance. Due to the overlapping effect, each user is allowed to select one sector out of many for operation. It is shown that the mutual interference among users in different regions within a cell can be minimized by choosing a good sector combination. The potential benefits of the proposed technique are investigated in two scenarios: orthogonal and nonorthogonal code division multiple access systems. In the former case, it is shown that when compared with the traditional nonoverlapping sectors system, one is able to reduce the number of spreading codes required to support all users by using appropriate code allocation in the proposed system. A theoretical framework based on combinatorial enumeration is developed to assess the performance of the proposed system. For the latter case, the enhancement takes the form of multiple access interference reduction. Simulation results show that its improvement is significant and can be further enhanced by increasing the number of overlapping sectors.     

Performance of ATM traffic in optical CDMA

An ATM transit switch is proposed based on direct sequence optical code division multiple access technique. No buffering is necessary to facilitate the switching. Code conversion is used instead to emulate the switching function. The switch not only provides asynchronous access to the users but also has a limited capability of dynamic bandwidth allocation. It is free from timing jitters and switching delay is significantly reduced. A look‐up table is employed in the switching and updated through network management functions. The switch provides a new approach to asynchronous cross‐connection in the ATM core network. The performance of the new switch is evaluated by a set of prime codes and modified prime codes. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance analysis of multihop cellular network with fixed channel assignment

Multihop cellular network (MCN) has been proposed to incorporate the flexibility of ad hoc networks into traditional single-hop cellular networks (SCNs). The performance analysis of MCN through analytical models is not trivial because the classic Erlang B formula no longer applies to MCN where multihop transmission is allowed. In this paper, we first propose a clustered MCN (cMCN) architecture with the use of dedicated information ports (DIPs), which are deployed wireless ports functioning as central controllers for multihop users. The proposed cMCN can be considered as a complement of the existing cellular network. Then, we study the feasibility of modeling time division multiple access (TDMA)-based cMCN with fixed channel assignment (FCA) scheme for uplink transmission. An exact multi-dimensional Markov chain model to analyze the performance of cMCN with FCA is developed. Furthermore, an approximated model which results in reduced complexity is also presented. The analytical results from both models are matched with the simulation results closely. The results show that cMCN with the proposed FCA scheme can reduce the call blocking probability significantly as compared to SCNs with either the conventional FCA or a dynamic channel assignment (DCA) scheme.     

Performance of a nonblocking space-division packet switch in a timevariant nonuniform traffic environment

The authors study the performance of a nonblocking space-division packet switch, given that the traffic intensities at the switch not only are nonuniform but also change as a function of time. A finite-state Markov chain is used as an underlying process to govern the time variation of traffic for the entire switch. The packet arrivals at each input form an independent Bernoulli process modulated by the underlying Markov chain. The output address of each packet is independently and randomly assigned with probability distributions, which are also modulated by the Markov chain. Provided that the traffic on each output is not dominated by individual inputs the service time of each output queue for sufficiently large switches can be characterized by an independent Markov modulated phase-type process. A matrix geometric solution for the resultant quasi-birth-death type queuing process is presented. The maximum throughput is obtained at the system saturation. The performance of the switch is numerically examined under various traffic conditions. A contention priority scheme to improve the switch performance is proposed     

Performance of wideband CDMA systems supporting multimedia traffic

We evaluate the performance of wideband CDMA cellular systems providing different classes of multimedia traffic and supporting user mobility. A Markovian teletraffic model of the user dynamics is developed. Constraints are imposed in the model which account for the multiple access interference among active users. Results are shown in terms of call blocking probabilities and average number of active connections. The methodology proposed is a useful tool for the design and planning of third generation cellular systems     

基于智能天线阵接收的蜂窝CDMA网络性能分析

本文分析了在频率选择性信道中基于智能天线阵接民的蜂窝CDMA网络上行链路的性能,分析基于多个小区的异步蜂窝CDMA系统,系统采用BPSK调制,并采用智能天线阵接收的RAKE合并技术,通过分析最终得到了在该环境下的闭合的CDMA系统误码率公式,结果表明基于智能天线阵接收的蜂窝CDMA性能要比不采用的好得多,并给出了误码率与系统用户数,小区数和衰落模型之间的关系,结果对于分析蜂窝CDMA系统容量具有一定的指导意义。     

Performance analysis of cache strategy for signaling traffic management in a wireless ATM network

In a wireless ATM network for mobile multimedia services, conventional signaling protocols generate heavy traffic because the signaling load must be handled in a HLR (Home Location Register). This centralized structure of the wireless ATM network causes critical connection setup delays. Thus, distributed processing based on a reduction of the connection setup delays is needed in wireless ATM networks. A cache strategy for call delivery with cache updates of registration based on ATM multicasting is introduced with a comparison of the cost of cache scheme with the cost of a conventional scheme. Results show that the cache scheme has better performance than conventional methods when portable mobility is low with large traffic density. This revised version was published online in July 2006 with corrections to the Cover Date.     

Efficient scheduling of nonuniform packet traffic in a WDM/TDMlocal lightwave network with arbitrary transceiver tuning latencies

A passive-star-based, broadcast-and-select, local lightwave network which can support a limited number of wavelength-division multiplexed (WDM) channels, but serve a much larger number of nodes, is considered. Each node is equipped with one tunable transmitter and one fixed receiver, and each WDM channel is operated in a time-division multiplexed (TDM) fashion for carrying packet traffic. Bandwidth is allocated to the node pairs when traffic flow between them is nonuniform, while also accommodating transceiver tuning latency. Our approach exploits well-known results from scheduling theory to create efficient transmission schedules. Multiprocessor task scheduling heuristics that can be applied to load balancing in a multichannel network is also examined     

Cell loss analysis and design trade-offs of nonblocking ATMswitches with nonuniform traffic

In practical ATM switch design, a proper dimensioning of buffer sizes and a cost effective selection of speed-up factor should be considered to guarantee a specified cell loss requirement for a given traffic. Although a larger speed-up factor provides better throughput for the switch, increasing the speed-up factor involves greater complexity and cost. Hence, it may not be cost effective to increase the speed-up factor for 100% throughput. Moreover, with a given buffer budget, an increase in the speed-up factor beyond a certain value only adds to the cell loss. The paper addresses design trade-offs existing between finite input/output buffer sizes and speed-up factor in a nonblocking ATM switch. Another important issue is the adverse effect on cell loss performance caused by nonuniform traffic (different traffic intensity and unevenly distributed routing). The paper analyzes cell loss performance of ATM switches with nonuniform traffic, and examines the effect of each nonuniform traffic parameter. The authors also provide an algorithm for effective buffer sharing that alleviates the performance degradation caused by traffic nonuniformity     

Performance analysis of CDMA with imperfect power control

The standard correlation receiver for code-division multiple access (CDMA) systems is susceptible to the near-far problem. Power control techniques attempt to overcome near-far effects by varying transmitted power levels to ensure that all signals are received with equal power levels. Since these algorithms cannot perfectly compensate for power fluctuations in a mobile communications channel, the capacity of the system is reduced for a given bit-error rate (BER). This paper examines the performance of a CDMA system using imperfect power control by extending analytical techniques that account for multiple access interference. Single cell capacity is compared with systems employing perfect power control     

Hot-spot traffic relief with a tilted antenna in CDMA cellularnetworks

Direct-sequence code division multiple-access (DS-CDMA) cellular networks are highly promising in terms of their potential to provide more capacity than an advanced mobile phone system (AMPS). However, heterogeneous traffic loading causes traffic congestion in a CDMA hot-spot. This paper presents a tilted antenna mechanism for sectored cells in CDMA cellular networks to relieve the congestion in a hot-spot sector. The fixed antenna-tilted mechanism, which only tilts the hot-spot antenna, can provide the merit of traffic balancing. Besides, we design a dynamic antenna-tilted mechanism in which tilting the antennas of the hot spot and its adjacent cell sectors is based on varying the signal-to-noise ratio (SNR). The dynamic mechanism can automatically tilt the antenna corresponding to the variation of traffic. Consequently, more capacity can be provided than in a fixed tilting mechanism, which only tilts the hot-spot antenna. Another benefit is the traffic-balancing effect with a tilted-antenna mechanism that reduces the transceivers of a hot-spot base station. Therefore, extra facilities are unnecessary for the hot spot than for a normal or light traffic sector     

Performance analysis of optical CDMA with prime codes

An `extended' prime code is introduced for optical code-division multiple access (CDMA). The probability distribution of the interference generated by crosscorrelation functions of the original and extended prime codes are derived analytically. The performances of both codes are then analysed using a Gaussian approximation. Finally, the extended prime code is shown to be preferable to the original code     

Performance analysis of CDMA systems with integrated services

The paper analyzes the performance of unslotted code-division multiple-access schemes with integrated services, namely real-time voice services and nonreal-time data services. In order to support integrated services using a common infrastructure, we apply dedicated mode transmission for real-time services and common channel transmission for nonreal-time services with varying processing gain. Most previous work covers the analysis of the system for fixed or exponential packet length, infinite population and infinite buffer size, where the results mainly depend on the mean values of the traffic. We remove these assumptions and analyze the behavior of the system with respect to voice and data users for the more general and realistic case of finite population, finite buffers, and variable data-packet length. Emphasis is placed on the study of the effect of system parameters and user characteristics on the system performance. Specifically, we show via analysis and simulation that even when the mean data-packet length is small, the system can have bottlenecks due to the packet-length characteristics and, therefore, dynamic adaptation and control of the system is required. Our analytical tool can be used to develop and analyze optimal resource-allocation strategies to maximize the throughput of wireless systems with integrated services. It is shown that optimum variable system parameters can be found when the system parameters and quality-of-service requirements of multimedia services are given.     

Performance analysis of an optical network employing waveband and traffic grooming

This paper analyses an optical network architecture composed by an arrangement of nodes equipped with multi-granular optical cross-connects (MG-OXCs) in addition to the usual optical cross-connects (OXCs). Then, selected network nodes can perform both waveband as well as traffic grooming operations and our goal is to assess the improvement on network performance brought by these additional capabilities. Specifically, the influence of the MG-OXC multi-granularity on the blocking probability is evaluated for 16 classes of service over a network based on the NSFNet topology. A mechanism of fairness in bandwidth capacity is also added to the connection admission control to manage the blocking probabilities of all kind of bandwidth requirements. Comprehensive computational simulation are carried out to compare eight distinct node architectures, showing that an adequate combination of waveband and single-wavelength ports of the MG-OXCs and OXCs allow a more efficient operation of a WDM optical network carrying multi-rate traffic.     

多媒体CDMA系统在功率约束条件下的业务容量分析

码分多址接入（CDMA）技术可以灵活地支持无线多媒体业务传输。该文分析了多小区环境下CDMA系统上行链路的多媒体业务容量，主要讨论了用户最大发射功率约束条件在不同用户激活因子情况下对系统容量的影响。分析和计算结果表明用户最大发射功率约束使系统的容量有所降低。     

Time-dependent analysis of mobile communication traffic in aring-shaped service area with nonuniform vehicle distribution

A method of analysis for modeling cellular telephone systems which incorporates vehicular traffic theory into the model is introduced. By obtaining position- and time-dependent vehicle density data, it is possible to investigate the behavior of communication traffic for any type of road traffic. The method allows car movement in both directions on the highway to be considered. However, situations in which one direction carries such an intense load that the other may be ignored are treated, and a simplified model with enough information to examine worst-case scenarios is developed. Simulation and analysis results are presented     

CDMA网络干扰分析与定位

分析了CDMA系统的内外部干扰,结合实际工作列出了查找,定位外部干扰源的步骤和方法,给出了几种常见外部干扰源的频谱图.