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.     

Capacity unbalance between uplink and downlink in spectrallyoverlaid narrow-band and wide-band CDMA mobile systems

In this paper, we discuss capacity unbalance between uplink (mobile-to-base) and downlink (base-to-mobile) in future code division multiple access (CDMA) radio networks where both narrow-band and wide-band CDMA systems are coexisted. Since the two links are not operated in an identical condition, their capacities are unequal and either of the links determines the whole system capacity. The purpose of this paper is to examine which link limits the system capacity and what are the limiting factors. To facilitate the examination, “transmission capacity” and “connection capacity” are defined, and simplified formulas are presented to compute those capacities, respectively for uplink and downlink. Signal quality required for each link, effectiveness of power control, spatial distribution of mobile users and other-cell as well as same-cell user interference are usually determining the limiting link. Besides, the traffic unbalance between the links imposed by specific service applications and the network evolution scenarios are also shown to be very influencing factors     

Non-cooperative uplink power control in cellular radio systems

This paper presents uplink power control in cellular radio systems from an economic point of view. A utility function is defined for each mobile user, which reflects the user's preference regarding the carrier-to-interference ratio (CIR) and the transmitter power. We observe that, on one hand, mobile users prefer to transmit at a lower power for a fixed CIR. On the other hand, for a given transmitter power, users prefer to obtain a better CIR. Based on this observation, we make two fundamental assumptions about the utility function. We formulate the uplink power control problem as a non-cooperative N-person game. Under the two assumptions that we make about the utility function, there exists a Nash equilibrium. To show the generality of the framework, we study one special case by defining the utility as a linear function. This model encompasses many of the widely studied power control problems. A more general case is also studied by defining utility as an exponential function. This paper establishes a general economic-based framework for studying resource management in wireless networks and points out new research directions.     

Non-cooperative uplink power control in cellular radio systems

This paper presents uplink power control in cellular radio systems from an economic point of view. A utility function is defined for each mobile user, which reflects the user's preference regarding the carrier-to-interference ratio (CIR) and the transmitter power. We observe that, on one hand, mobile users prefer to transmit at a lower power for a fixed CIR. On the other hand, for a given transmitter power, users prefer to obtain a better CIR. Based on this observation, we make two fundamental assumptions about the utility function. We formulate the uplink power control problem as a non-cooperative N-person game. Under the two assumptions that we make about the utility function, there exists a Nash equilibrium. To show the generality of the framework, we study one special case by defining the utility as a linear function. This model encompasses many of the widely studied power control problems. A more general case is also studied by defining utility as an exponential function. This paper establishes a general economic-based framework for studying resource management in wireless networks and points out new research directions. This revised version was published online in July 2006 with corrections to the Cover Date.     

两跳中继CDMA蜂窝系统的上行链路容量分析

首先在两跳中继CDMA蜂窝系统的基础上,提出了2种使用带外信道提高传统CDMA蜂窝系统上行链路容量的中继方法;然后通过分析传统无中继CDMA蜂窝系统的干扰功率,分别得到这2种中继方法对当前小区和邻居小区总的干扰功率;最后在一种对称小区模型的基础上,通过数值计算对两跳中继CDMA蜂窝系统的上行链路容量进行分析,并讨论了2种中继方法对系统性能所产生的影响.     

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     

码分多址测控系统的功率调节

远近效应是码分多址测控系统中影响飞行器多址接收性能的重要因素。分析了远近效应在多站测控系统中对飞行器接收性能的影响,提出了在该系统中进行功率控制的必要性,给出了地面测控站功率调节的方法和策略,可作为多站应用的码分多址测控系统功率调节的参考思路。     

基于大系统方法的上行CDMA蜂窝系统性能分析

结合大尺度和小尺度衰落,采用大系统分析方法对CDMA蜂窝系统上行链路的性能进行分析。首先分析了小区内多址干扰和小区间干扰的情况;其次推导出了通过匹配滤波器后的信干噪比值,该值只与小区负载、用户功率、信道增益有关;最后分析了系统的误码率、吞吐量和频谱效率,并通过仿真验证了分析的准确性。仿真结果发现,随着小区负载的增大,系统的误码率增大,吞吐量下降,但频谱效率有所提高。     

Effect of co-phasing diversity on CDMA downlink capacity

The impact of distributed antennas using co-phasing transmission diversity on downlink CDMA channels is examined. An expression is derived that demonstrates that uniform downlink signal-to-interference ratio across users can be achieved by appropriately weighting the distribution of transmit powers across distributed antennas. The capacity of a downlink CDMA system employing distributed antennas with optimum power allocation is then found by simulation.     

UWB设备对CDMA系统下行链路容量的影响

本文研究了超宽带(UWB)设备对CDMA系统下行链路容量的影响.文中首先建立了UWB设备的分布模型,针对已有的WCDMA系统模型,应用计算机仿真,得出CDMA系统中加入UWB设备后的系统容量与UWB设备发射功率、分布密度的关系.     

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     

A framework for uplink power control in cellular radio systems

In cellular wireless communication systems, transmitted power is regulated to provide each user an acceptable connection by limiting the interference caused by other users. Several models have been considered including: (1) fixed base station assignment where the assignment of users to base stations is fixed, (2) minimum power assignment where a user is iteratively assigned to the base station at which its signal to interference ratio is highest, and (3) diversity reception where a user's signal is combined from several or perhaps all base stations. For the above models, the uplink power control problem can be reduced to finding a vector p of users' transmitter powers satisfying p⩾I(p) where the jth constraint p_j⩾I_j(p) describes the interference that user j must overcome to achieve an acceptable connection. This work unifies results found for these systems by identifying common properties of the interference constraints. It is also shown that systems in which transmitter powers are subject to maximum power limitations share these common properties. These properties permit a general proof of the synchronous and totally asynchronous convergence of the iteration p(t+1)=I(p(t)) to a unique fixed point at which total transmitted power is minimized     

多业务CDMA系统上行链路容量分析

研究了多业务CDMA系统的上行链路容量,提出一种容量分析方法。在方法中考 虑了多业务的激活概率,分析了不同业务的掉话率,以系统掉话率为基准给出了系统容量。该 分析方法表明CDMA系统的容量受多业务的Eb/N0、传输速率和业务激活概率的影响。     

Soft handoff and uplink capacity in a two-tier CDMA system

This paper examines the effect of soft handoff on the uplink user capacity of a code division multiple access system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft-handoff scenario studied here, both macrocell and microcell base stations serve each system user, and the two received copies of a desired user's signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple approximate methods are presented for estimating soft-handoff capacity and are shown to be quite accurate.     

On the design of uplink and downlink group-orthogonal multicarrier wireless systems

Group-orthogonal multicarrier code-division multiple access (GO-MC-CDMA) has been proposed as an attractive multiplexing technique for the uplink segment of wireless systems. More recently, a variant of this scheme has also been proposed for the downlink. This paper presents a unified bit error rate (BER) performance analysis of group-orthogonal wireless systems when using maximum likelihood (ML) multiuser/multisymbol detection covering both link directions. Valuable design rules regarding the number of subcarriers per group and the selection of spreading codes are derived. Simulations results using realistic system parameters and ETSI BRAN channel models are also presented which serve to validate the analytical results.     

CDMA/TDD system for wireless multimedia services with trafficunbalance between uplink and downlink

This paper proposes a code division multiple access (CDMA) time division duplex (TDD) system for wireless multimedia services with traffic unbalance between uplink and downlink. In the proposed system, the number of uplink time slots in a TDD frame differs from that of downlink. Moreover, the difference can be reset by the network operator according to the traffic pattern. We evaluate the performance of the proposed system under multimedia environment using Markov analysis and computer simulation. The results show that the frequency utilization is maximized even when the uplink and downlink traffic volumes are unbalanced. This, in turn, reduces drastically the blocking rate of multimedia calls (connections) in the proposed system compared with that in the traditional CDMA systems where the uplink and downlink use equal bandwidth     

Open-loop power control error in cellular CDMA overlay systems

Adaptive power control has widely been used in DS/CDMA systems to overcome the so-called “near-far” problem. This paper studies the adaptive open-loop power control of a cellular CDMA system, which is overlaid in the downlink by a narrowband signal. The effects of downlink power allocation schemes to power control error in the presence of narrowband interference are analyzed. In order to get a minimum power control error in the CDMA overlay situations, an optimum downlink power allocation scheme is used, which works well for a wide range of signal to narrowband interference ratio     

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.     

UDN中基于上下行对偶性的分布式干扰协调

针对超密集网络（UDN,Ultra-Dense Networks）中的小区间干扰问题,提出一种基于上下行对偶性的分布式干扰协调方法。首先设计了新的TDD帧格式,在原有LTE标准的基础上加入了信道估计部分与上下行迭代部分;接着利用网络的对偶原理,设计了新的迭代干扰处理算法,将最大化信干噪比和最小化残留干扰相综合,实现最大全网和数据的优化目标。理论分析和仿真结果表明,基于最大信漏噪比准则选取迭代初值时,可在一次迭代后达到较好的和数据率性能;并且该方法能在较短的时间内完成干扰协调,只需要已知局部信道信息,在UDN中易于实现,性能上优于其它分布式迭代干扰处理算法。