多媒体CDMA蜂窝网络上行顽健功率控制算法

研究了同时承载带宽保障业务和尽力而为业务的多媒体CDMA蜂窝网络上行链路顽健功率控制问题.考虑业务突发性、链路增益估计误差以及小区间干扰等因素,通过推导中断概率提出了一种非线性迭代算法.在给定尽力而为业务数据率分配方案的情况下,该非线性迭代算法能够判断是否可以通过功率控制有效地保证带宽保障业务和尽力而为业务的服务质量.在此基础上,分别为支持离散数据率和连续数据率的两类多媒体CDMA蜂窝网络设计了相应的上行链路功率控制算法.最后,通过仿真验证了所提出非线性迭代算法的收敛性,并通过与一种次优功率控制算法进行比较说明了所提出功率控制算法的性能优势.     

Novel multimedia traffic modeling based CAC scheme for CDMA communication systems

As the radio spectrum is a very scarce resource, the Call Admission Control （CAC） is one of the most important parts in radio resource management. The Code Division Multiple Access （CDMA） based next generation wireless communications systems will support the transmission of multimedia traffic, such as voice, video and data, thus the CAC, which can support the multimedia traffic and guarantee the Quality of Service （QoS） of different traffic, has gained broad attention. In this paper, a novel multimedia traffic modeling method and a corresponding dynamic QoS based CAC are proposed. The analysis and simulation results show that the proposed CAC scheme can guarantee the QoS to different traffic demand, and improve the system performance significantly.     

Multicarrier CDMA for cellular overlay systems

A code-division multiple access (CDMA) cellular overlay system is investigated, employing the idea of multicarrier CDMA, which has previously received significant attention as an alternative to traditional single-carrier CDMA. Overlay is pursued here as a means of long-term transition from narrowband cellular to CDMA cellular. A major result of this paper is the demonstration that the use of multicarrier CDMA in a fading channel is particularly beneficial to the narrowband system, as the CDMA users can reduce their transmitted powers as a result of diversity. Another significant conclusion is that the use of transmitter notching in the CDMA system in order to avoid active narrowband users outperforms a strategy in which a narrowband user is avoided by simply dropping the particular carrier which overlays it. Finally, results on the use of the minimum mean-squared error (MMSE) receiver in a fading channel are extended for use in the overlay scenario     

CDMA transmitter filtering for cellular overlay systems

In this paper, the overlay of a code-division multiple-access (CDMA) cellular system in a frequency band which is already providing service to a narrow-band cellular system is investigated. The motivation for this study is to demonstrate the potential of CDMA overlay as an efficient method for making a long-term transition from narrow-band cellular to CDMA cellular. For the single cell case, it was shown by Rainbolt and Miller (see IEEE J. Select. Areas Commun., vol.16, p.1756-64, 1998) that interference caused to the narrow-band system by even a lightly-loaded CDMA system is significant, a problem which can be greatly alleviated through the use of notch filtering in the CDMA transmitters to avoid active narrow-band users. Similar conclusions will be reached in this paper for the cellular case. The effects of notching on CDMA performance will be looked at in detail, and it will be shown that the notching is less of a problem than is the narrow-band interference inherent in overlay systems     

Decentralized dynamic power control for cellular CDMA systems

The control of transmit power has been recognized as an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. Indeed, power control allows for mobile users to share radio resources equitably and efficiently in a multicell environment. Much of the work on power control for CDMA systems found in the literature assumes a quasi-static channel model, i.e., the channel gains of the users are assumed to be constant over a sufficiently long period of time for the control algorithm to converge. In this paper, the design of dynamic power control algorithms for CDMA systems is considered without the quasi-static channel restriction. The design problem is posed as a tradeoff between the desire for users to maximize their individual quality of service and the need to minimize interference to other users. The dynamic nature of the wireless channel for mobile users is incorporated in the problem definition. Based on a cost minimization framework, an optimal multiuser solution is derived. The multiuser solution is shown to decouple, and effectively converge, to a single-user solution in the large system asymptote, where the number of users and the spreading factor both go to infinity with their ratio kept constant. In a numerical study, the performance of a simple threshold policy is shown to be near that of the optimal single-user policy. This offers support to the threshold decision rules that are employed in current cellular CDMA systems.     

Overview of radiolocation in CDMA cellular systems

Applications for the location of subscribers of wireless services continue to expand. Consequently, location techniques for wireless technologies are being investigated. With code-division multiple access (CDMA) being deployed by a variety of cellular and PCS providers, developing an approach for location in CDMA networks is imperative. This article discusses the applications of location technology, the methods available for its implementation in CDMA networks, and the problems that are encountered when using CDMA networks for positioning     

Distributed power control in CDMA cellular systems

In wireless cellular communication, it is essential to find effective means for power control of signals received from randomly dispersed users within one cell. Effective power control will heavily impact the system capacity. Distributed power control (DPC) is a natural choice for such purposes, because, unlike centralized power control, DPC does not require extensive computational power. Distributed power control should be able to adjust the power levels of each transmitted signal using only local measurements, so that, in a reasonable time, all users will maintain the desired signal-to-interference ratio. In this paper, we review different approaches for power control, focusing on CDMA systems. We also introduce state-space methods and linear quadratic power control (LQPC) to solve the power-control problem. A simulation environment was developed to compare LQPC with earlier approaches. The results show that LQPC is more effective, and is capable of computing the desired transmission power of each mobile station in fewer iterations, as well as being able to accommodate more users in the system     

The coverage-capacity tradeoff in cellular CDMA systems

In cellular CDMA systems that employ single-user detectors, in-cell interference limits the coverage of the cell. Thus for a given upper limit on transmit power, the coverage of a cell is inversely proportional to the number of users in it. This tradeoff between coverage and number of users is explicitly characterized here. Our analysis may be used in cellular planning to set hard limits on the number of users admitted into the cell in order to meet coverage requirements. Furthermore, our approach allows us to arrive at a precise definition for the pole capacity of a cell, which serves as an upper bound on the number of users a cell can support as the coverage shrinks to zero. We also present a technique to calculate cell coverage as a function of carried traffic, for any given admission policy     

Uplink load in CDMA cellular radio systems

Well-operating resource-management algorithms are crucial in wireless networks for ensuring the quality of service and, perhaps more importantly, for securing stability when operating at high load. These algorithms benefit from accurate feedback of the current network load. In the uplink of a code-division-multiple-access cellular network, the load is strongly related to the uplink noise rise, i.e., the ratio between total received power and background-noise power. This paper is primarily concerned with characterizing and approximating the uplink load. Two different load definitions are made. These relate to the received and transmitted carrier powers, respectively. Bounds that can be established in practice, e.g., before a resource decision is made, are used to develop a procedure for approximating the uplink load in practice. Furthermore, a stochastic approach to link budgets is used to establish the uplink load's role in the tradeoff between coverage and individual user satisfaction. Simulations indicate that the average error of the proposed load approximations is small for all load levels expected to appear in practice.     

Asynchronous fast frequency-hopping CDMA cellular systems

We address the problem of constructing frequency-hopping codes for use in a fast frequency-hopping code-division multiple-access cellular system with a K-cell frequency-reuse scheme. Different hopping codes are used in different cochannel cells to reduce the cochannel interference. The frequency-hopping patterns possess ideal auto- and cross-correlation properties for use in the intracells and ideal autocorrelation and nearly ideal cross-correlation properties in the cochannel intercells. Additionally the cardinalities (the number of patterns) of the codes for use in the intracells meets the bound and hence are optimal. The maximum number of users which can be accommodated by using the proposed scheme is 20% more than the scheme using the same frequency-hopping code in all cells under a carrier-to-interference ratio of -15 dB     

Performance evaluation for multichannel access schemes in CDMA cellular systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multichannels for a CDMA system is a requisite to satisfy the demanded capacity. In this paper, five schemes of multichannel assignment are proposed. Based on computer simulation, performance measures such as blocking probabilities, the overall capacity, the capacity of each channel and the number of retrials are obtained. Simulation results indicate that the SIR-based selection scheme is preferable to the other schemes. © 1998 John Wiley & Sons, Ltd.     

A hybrid CAC algorithm for maximizing downlink capacity of M-WiMAX systems

Due to the implementation of an Adaptive Modulation-Coding (AMC) mechanism in the 802.16e physical layer, each connection’s bandwidth requirements cannot be statically computed, but they derive as a function of the terminals’ instantaneous Signal-to-Noise Ratio (SNR). Therefore, the Connection Admission Control (CAC) mechanism fails to establish an efficient policy that would optimally exploit the system’s resources. In this respect, the present paper formulates initially an adequate method for statistically calculating the average capacity of a Mobile-WiMAX system, according to the distribution of the several attenuation factors that affect the signal along the propagation path. In parallel, based on the processing of the terminal’s SNR samples, a sophisticated algorithm for filtering out any misleading measurements is developed. This second method aims at predicting the upcoming Modulation-Coding state of every connection, so as to acquire a short-term view of its spectrum demands. Finally, all the above info collected from both the estimation methods is utilized by the CAC procedure in order to perform an as accurate as possible computation of the resource availability. As a result, this hybrid approach succeeds in maximizing the network revenue through significantly increasing the number of concurrently serviced connections while guaranteeing their Quality of Service (QoS) standards.     

Downlink power allocation and adjustment for CDMA cellular systems

This letter provides a downlink power control algorithm and its convergence for adjusting as well as allocating appropriate power levels according to the need of mobiles. The adjustment process and its property provide a distinct view for understanding existing CDMA downlink power control algorithms     

一种CDMA蜂窝定位中减小NLOS误差的算法

随着下一代移动通信研究的热潮,移动定位技术的研究也方兴未艾。在移动定位方程的解算中,测量噪声和NLOS误差是主要误差源,尤其是NLOS已经成为影响定位精度的主要因素。本文研究了CDMA系统中的NLOS误差减小问题,基于残余函数概念提出了ARWA算法,在NLOS路径不能有效识别的条件下,有效地减小了NLOS误差;仿真结果显示这种算法的定位精度明显强于一般LS估计。     

Centralised power control in CDMA cellular mobile systems

Efficient power control is of great importance in the design of high capacity cellular radio systems. Optimum power control scheme, in the sense that it minimises the outage probability, has been fully investigated for FDMA/TDMA cellular systems. The authors propose optimum power control and several centralised power control algorithms for CDMA cellular systems. Simulation results indicate that the optimum power control scheme outperforms the perfect average power control algorithm by ~1.9 dB under the IS-95 defined radio condition     

Macrodiversity power control in hierarchical CDMA cellular systems

Hierarchical code division multiple access (CDMA) cellular systems, consisting of macrocells with underlying microcells, are studied. We seek power control schemes which will allow both hierarchical layers to share the same spectrum. For the reverse link, hierarchical maximal ratio combining (HMRC) is applied where each mobile station (MSs) is received and coherently combined by base stations (BSs) in both layers. For the forward link, selective transmit diversity (STD) is applied where each BS provides multiple transmit paths for MSs to choose. We show that both HMRC and STD are effective in hierarchical CDMA architectures. We conclude that hierarchical architectures are a viable solution for improving CDMA cellular system capacity, and a significant performance gain can be achieved without assigning disjoint spectrum between the layers, by utilizing macrodiversity schemes such as HMRC and STD     

Average external interference in cellular radio CDMA systems

An analytical and numerical evaluation by Gilhoussen et. al.(see IEEE Trans. Veh. Technol, vol.40, no.2, p.303-3121, 1991) of the capacity of a cellular radio CDMA system has been proposed. This evaluation has shown the interest of using spread spectrum techniques in the area of cellular radio systems. However, considering the computations made by Gilhoussen et. al. for the reverse link, we note the following: the calculations lead at a given moment to the evaluation of the average external interference for which a quantity is claimed only intuitively to be an upper bound. We construct a sequence of approximations for the average external interference, where the average external interference is the sequence limit. The claimed upper bound of Gilhoussen is also the first element of this sequence of approximations. We show by numerical means that the sequence is decreasing which justifies the claim of Gilhoussen     

Transmit beam-tracking algorithm in FDD CDMA cellular wireless system

A beam-tracking algorithm for downlink transmit beamforming in an FDD CDMA cellular wireless system is investigated. The method takes advantage of the power-controlled system and searches for the beamformer direction corresponding to the minimum transmit power. There is no complex computation needed; thus it simplifies the downlink transmit beamforming system.     

A variable rate multipulse speech coder for CDMA cellular systems

Variable Rate (VR) speech coders are classified into: source-controlled VR coders where the rate is selected depending on the local character of the speech, and network-controlled VR coders where an external control signal selects the coding rate. The first category benefits from the variable rate channels used by Code Division Multiple Access (CDMA) mobile communications. The second category is indispensable for the right behaviour of the CDMA systems under conditions as high traffic levels. The VR speech coder presented in this communication exhibits both types of control. The source control is achieved by means of a Voice Activity Detector (VAD) and a phonetic classifier. The network control acts on the selection procedure of the multipulse excitation sequence to the synthesis filter. This is the main advantage of our VR MultiPulse speech coder because by means of an external signal the bit rate can be changed only every 4 msec, without transitions or distortions. Considering one-way communication, six different operating rates can be externally selected ranging from 4.8 to 9.1 kbps for the active frames; an average bit rate of 380 bps is required for the noise frames.This work has been partly funded by the Spanish Research National Plan under grant no. TIC92-0800-C05-02 and by Northern Telecom.     

Radio resource management for cellular CDMA systems supporting heterogeneous services

A novel radio resource management (RRM) scheme for the support of packet-switched transmission in cellular CDMA systems is proposed by jointly considering the physical, link, and network layer characteristics. The proposed resource management scheme is comprised of a combination of power distribution, rate allocation, service scheduling, and connection admission control. Power distribution allows individual connections to achieve their required signal-to-interference-plus-noise ratio, while rate allocation guarantees the required delay/jitter for real-time traffic and the minimum transmission rate requirement for non-real-time traffic. Efficient rate allocation is achieved by making use of the randomness and burstiness; of the packet generation process. At the link layer, a packet scheduling scheme is developed based on information derived from power distribution and rate allocation to achieve quality of service (QoS) guarantee. Packet scheduling efficiently utilizes the system resources in every time slot and improves the packet throughput for non-real-time traffic. At the network layer, a connection admission control (CAC) scheme based on the lower layer resource allocation information is proposed. The CAC scheme makes use of user mobility information to reduce handoff connection dropping probability (HCDP). Theoretical analysis of the grade of service performance, in terms of new connection blocking probability, HCDP, and resource utilization, is given. Numerical results show that the proposed RRM scheme can achieve both effective QoS guarantee and efficient resource utilization.