Centralized and distributed power control algorithms for multimedia CDMA networks

We study in this paper both centralized and distributed transmitter power control algorithms for multimedia CDMA networks. In our study, users can have different data rates as well as different quality of service (QoS) requirements characterized by bit energy‐to‐interference ratios. For centralized power control, we derive an optimum power assignment which can be obtained by solving a set of linear equations. For distributed power control (DPC), we study the fully distributed power control (FDPC) algorithm. We modify the FDPC algorithm so that it can be used in a multi‐service environment. We prove that, as long as there are solutions of power levels for all users to meet their QoS requirements, the FDPC algorithm can always find one. A quasi‐centralized power control algorithm with partial link gain measurements is proposed to speed up the process in finding a feasible power set. In the algorithm, a base station measures the link gains for all mobiles connected to it. Numerical results show that quasi‐centralized power control can find a feasible power set much faster than distributed power control. Copyright © 2005 John Wiley & Sons, Ltd.     

Uplink capacity optimization by power allocation for multimedia CDMA networks with imperfect power control

A closed-form capacity quasi-optimal power allocation scheme is presented for the uplink of multimedia code-division multiple-access (CDMA) systems with randomized received signal-to-interference ratio (SIR) resulted from the errors of power control. The optimality in capacity comes from that this scheme provides class-dependent SIR margins subject to the constraint of differentiated outage requirements. The statistics of signal under imperfect power control is modeled as lognormal random variable. The objective of capacity maximization is formulated as the minimization of total average received powers since the capacity of a CDMA system is interference limited. Under this model, we first derive the necessary conditions that a capacity-optimal power allocation should satisfy. By using conservative bounds, we provide a closed-form approximate solution to this optimization problem. This approximate solution provides nearly the same admissible region for multimedia traffic under imperfect power control as the accurate solution (the optimal one) does. The closed-form quasi-optimal power allocation scheme proposed in this paper is just based on this approximate solution. By numerical example we verify our analysis and show that great capacity gain (e.g., 92% as a maximum in the example) can be achieved by our scheme over its counterpart.     

Nonlinear power assignment in multimedia CDMA wireless networks

In this letter, we propose a new technique for power assignment in outdoor code-division multiple access cell supporting bursty multimedia traffic. The proposed scheme takes into consideration both average signal-to-interference ratios and outage probability required by multimedia traffic     

CDMA网络中多媒体业务的接入控制

从码分多址(CDMA)系统的特点出发，采用多维马尔可夫过程来分析多媒体业务共存时基于干扰水平的接入控制策略，得到在小区容量可变情况下的系统性能。文中考虑到切换用户的优先级以及不同类型用户的不同QoS要求，还在系统中设置了多级接入门限，从而实现在扩大系统容量的同时，又力求保证系统已有的链路质量，实现接入控制的目的。     

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.     

Ratioed power and rate control for CDMA wireless networks

We propose in this paper the ratioed power and rate control (RPRC) algorithm to satisfy the requirements of both the data rate and the signal quality. During the execution of the RPRC algorithm, only the representative user in each cell adjusts its power level according to certain distributed power control algorithm, and the ratio of the power level for the non‐representative user to that for the representative user is kept constant. When the RPRC algorithm is finished, the power levels for all users remain unchanged and the transmission rate is determined by the available rate. We show that the RPRC algorithm can be used for allocating the bandwidth of each cell and achieving the required rate of each user. Furthermore, simulation results reveal that the RPRC algorithm results in larger throughput and finds a feasible power set faster than the other algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

Instantaneous and local-mean power control for direct-sequence CDMA cellular networks

Proposed and existing power-control systems for direct-sequence CDMA cellular networks measure instantaneous power, whereas theoretical analyzes almost always assume long-term-average or local-mean power control. In this paper, the distinction between the two types of power control is clarified. The outage probability for direct-sequence CDMA systems using instantaneous power control is derived. The results of the analysis of local-mean power control are shown to be similar to those provided by a far more elaborate theoretical analysis.     

Performance evaluation of wireless multimedia CDMA networks usingadaptive transmission control

When multimedia information including speech, image, data etc. are transmitted, the difference in information rates, required quality, and traffic performance should be taken into account. A wireless spread spectrum system can achieve a flexible balance of these differences because of inherent asynchronous code-division multiple-access (CDMA) capability. In order to accomplish wireless multimedia communication, three parameters are investigated: the transmission power, packet length, and time slot. We propose and investigate two methods to accomplish wireless multimedia communication by using these parameters: (1) a method based on control of both transmission power and transmission packet length and (2) a method based on control of both transmission power and adaptive time slot. We derive the optimal transmission packet length and transmission power in (1) and derive optimal adaptive time slot and transmission power in (2) by using traffic of measurement and nonlinear programming. By the comparison, the two proposed methods are compared to the minislotted alternating priority (MSAP). Numerical results demonstrate that the proposed methods, when the priority of each medium is graded, show better performance than other systems in terms of average throughput and delay time of all media     

宽带CDMA网络非理想功率控制下的CAC策略

针对多媒体业务的CAC(call admission control)策略,给出了宽带CDMA(code division multiple access)网络中非理想功率控制下和外小区干扰因子对系统容量的影响分析.针对语音、视频和数据等多媒体业务的QoS(quality of service)要求,给出了一种基于QoS保证的CAC策略.仿真结果表明,非理想功率控制对系统容量有显著的影响,该策略能有效地保证不同业务的QoS需求,并明显地提高系统资源利用率.     

Scheduling in multimedia CDMA wireless networks

Wireless systems in the future will have to provide multimedia services where different users have different physical-layer quality of service (QoS) requirements (e.g., bit energy per interference power density, E/sub b//N/sub 0/, or bit error rate and power constraints) and network-layer QoS requirements (e.g., delay bound, delay-jitter, throughput, and loss). We investigate the use of power control, processing gain and/or multiple codes, and scheduling in CDMA systems to accommodate these diverse service requirements. We first show that the instantaneous capacity region, given in terms of the set of user bit rates that can be supported simultaneously subject to peak power and E/sub b//N/sub 0/ constraints, is nonconvex. This suggests that by time-sharing the channel, one may be able to get better system throughput. We define the capacity region as the convex hull of the instantaneous capacity region and we show that it may be obtained by time sharing between operating points, where each user either uses full power or is silent (bang-bang control). We then consider the problem of scheduling so as to meet prespecified delay bounds or minimum service curve requirements for traffic streams, which are specified in terms of a traffic profile such as a sigma-rho constraint (enforced by a leaky bucket) and a guarantee that the system is stable.     

A noncooperative power control game for multirate CDMA data networks

The authors consider a multirate code-division multiple acess system, in which all users have the same chip rate and vary their data rate by adjusting the processing gain. The receivers are assumed to be implemented using conventional matched filters, whose performance is sensitive to the received power levels. The authors' goal is to maximize the total system throughput by means of power control. A game theoretic approach is adopted. It is shown that for a certain type of pricing function, a unique Nash equilibrium solution exists and it possesses nice global properties. For example, it can be shown that for the optimal solution a high-rate connection should maintain a higher energy per bit than low-rate ones. The asymptotic spectral efficiency is also derived.     

Power control for wireless multimedia CDMA systems

In a wireless multimedia communication system where different types of traffic such as speech, data, and video have different data rates, good power control for individual traffic can ensure quality of service (QoS) and achieve a better throughput at the same time. The authors propose a closed-form power control function based on a parameter called the traffic exponent that simplifies the power control processing and improves the overall CDMA system performance     

宽带多媒体CDMA系统中的反向SRA功率控制算法

第三代移动通信系统设计要求支持多媒体通信。由于各种业务在接收端所要求的业务质量不同,这就要求系统应根据业务种类进行功率控制。文章通过功率等价概念的引入,研究了应用于宽带CDMA系统的SRA(Stepwise Removal Algorithm)功率控制算法,并通过算法仿真验证了该算法能在确保各种业务的业务质量的同时提高系统容量。     

Rate-regulated power control for supporting flexible transmissionin future CDMA mobile networks

In code division multiple access (CDMA) mobile networks, transmitted power is controlled to provide each user an acceptable connection by limiting the interference seen by other users. Previous work has focused on finding a power assignment that maximizes the minimum carrier-to-interference ratio where the transmission rate of each user is known and fixed. In future mobile networks, however, fluctuations in mobiles' transmission rate should be considered in designing power control algorithms. In this work, we present an algorithm for controlling mobiles' transmitter power levels while explicitly handling their time-varying transmission rates. During the whole power control process, the required signal quality is always maintained. The traffic-carrying performance of the algorithm is evaluated by simulation where different types of users are sending burst data     

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。     

SINR threshold lower bound for SINR-based call admission control in CDMA networks with imperfect power control

Signal to interference plus noise ratio (SINR)-based call admission control schemes admit calls as long as SINR is higher than a threshold value (SINR/sub th/). Setting a relatively low SINR/sub th/ results in more users admitted into the system and this in turn yields an increased outage probability (P/sub out/). Hence, determining the lower bound of SINR/sub th/ (SINR/sub th/spl I.bar/lb/) is vital to keep P/sub out/ below a maximum value, P/sub out/spl I.bar/max/x. In this letter, we derive SINR/sub th/spl I.bar/lb/ in the reverse link of CDMA systems with imperfect power control by finding the relationship between P/sub out/ (due to power control infeasibility and SINR fluctuation) and SINR/sub th/. Then, SINR/sub th/spl I.bar/lb/ is determined as the lowest SINR/sub th/ that keeps P/sub out/ below a certain P/sub out/spl I.bar/max/.     

Medium access protocol design for delay-guaranteed multicode CDMA multimedia networks

To enable multimedia real-time applications over next-generation wireless code-division multiple access (CDMA) packet-switching networks, previous efforts show a proper scheduling policy is the key to provide delay-guaranteed access services to various traffic types with different bit error rate (BER) requirements. Considering the support of the prevailing Internet protocol (IP) with variable-length packets in future mobile networks, we develop a mathematically delay-optimal medium access control (MAC) protocol over multicode CDMA (MC-CDMA) environments under the continuous-time assumption. From our investigations, we suggest that a good MAC protocol should be designed by using a proper single-server scheduling policy to guarantee packet-delay, and controlling the maximal number of simultaneous spreading-code transmissions to maintain the required BER. We further evaluate the performance of some MC-CDMA MAC protocols supporting QoS on BER and packet-delay, and show that MAC schemes conforming to our design rules give better performance on packet-delay when maintaining acceptable BER of various traffic types.     

Jointly optimal power and admission control for delay sensitive traffic in CDMA networks with LMMSE receivers

Quality-of-service (QoS) guarantees for multiclass code division multiple access networks are provided by means of cross-layer optimization across the physical and network layers. At the physical layer, the QoS requirements are specified in terms of a target signal-to-interference ratio (SIR) requirement, and optimal target powers are dynamically adjusted according to the current number of users in the system. At the network layer, the QoS requirements are the blocking probabilities and the call connection delays. The network layer guarantees that both physical layer and network layer QoS are met by employing admission control. An optimal admission control policy is proposed based on a semi-Markov decision process formulation. The tradeoff between blocking and delay is discussed for various buffer configurations. The advantage of advanced signal processing receivers is established using a comparative capacity analysis and simulation with the classical scenario in which the system uses matched filter receivers.     

Real-time multimedia broadcasting via direct-detection fiber-opticsynchronous CDMA networks

A new coding architecture for M-ary fiber-optic synchronous code division multiple access (CDMA) network is proposed to provide real-time multimedia broadcasting. In contrast with variable bit rate (VBR) transmission, the constant bit rate (CBR; i.e. isochronous) transport is more preferable in view of the networking simplicity. We apply a bit-stuffed unipolar m-sequence and maximum a posteriori (MAP) receiver in the proposed network. The system performance is determined by the following parameters: (1) number of simultaneous access broadcasting hosts K, (2) received laser power, (3) input bit rate, and (4) the dimension of M. Furthermore, the adverse impact (thermal noise, APD noise) in the photodetection process is carefully analyzed. Numerical results reveals that for the binary case, the aggregate capacity can achieve 10.2 Gbps     

Capacity and power control for CDMA microcells

Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading. The effects of fading on the desired and interfering signals, variations in the shadow standard deviation, imperfect power control, and the requiredE _b /N _o for satisfactory link operation are investigated. It is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations. Power control error is shown to significantly degrade reverse channel capacity. Twobiased forward channel power control strategies are introduced to enhance existing unbiasedbalancing forward channel power control algorithms.This research has been supported by BNR Inc.