Spectral efficiency of a cellular MC/DS‐CDMA system in Rayleigh fading

The spectral efficiency of a multicarrier direct‐sequence code‐division multiple‐access (MC/DS‐CDMA) cellular system, operating in a mobile radio environment with Rayleigh fading, is investigated and evaluated in terms of channel capacity (in the Shannon sense) per user, estimated in an average sense. The analysis is based on the combination of path‐diversity reception, achieved by a conventional coherent maximal‐ratio combining (MRC) RAKE receiver and the physical frequency diversity potential provided by orthogonal frequency division multiplexing (OFDM). As shown, a closed‐form expression for the achieved spectral efficiency of the considered system's operation is derived following a recently presented general method. Copyright © 2005 John Wiley & Sons, Ltd.     

多业务CDMA蜂窝移动通信系统的功率控制

本文提出了多业务CDMA蜂窝移动通信系统的一种下行链路功率控制策略，系统的最优功率分配可以归结为求解归一化链路增益矩阵在有约束条件下的最大实特征值。在对系统的最优功率分配进行理论分析的基础上，给予了相应的仿真结果，并针对实际系统负载过重的情形，提出了按照业务优先级别逐步去除小区用户的功率控制策略。     

On the optimum processing gain for a hybrid DS/FFH‐CDMA cellular system over Rayleigh fading channels

The optimization between the processing gain and the theoretically achievable average channel capacity per user (in the Shannon sense) of a constant total system's allocated bandwidth hybrid direct sequence/fast frequency hopping code‐division multiple‐access (DS/FFH‐CDMA) cellular system, when operating in a Rayleigh fading environment, is presented. Then, the spectral efficiency, expressed in (bits/s/Hz), is estimated in terms of the achievable average channel capacity per user, during the operation over a broadcast cellular time‐varying link, and leads to a simple theoretical novel‐closed‐form expression for the optimal processing gain value based on the maximization of the achieved spectral efficiency. The final expression derived can be useful for the practical design of a DS/FFH‐CDMA cellular system and for an initial quantitative analysis since it relates to the optimal processing gain applied and all system's parameters. Finally, numerical results are presented to illustrate and prove the validity of the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimizing information efficiency in a direct-sequence mobile packet radio network

We consider a direct-sequence multihop packet radio network using slotted ALOHA in a Rayleigh fading environment. We are interested in optimally choosing the transmission range, code rate, and slotted ALOHA transmission probability to be used by each node. We use a new performance measure, information efficiency, to analyze the network and show that the information efficiency of the low-cost mobile packet radio network can be improved approximately 20 fold by using the optimum parameters. We suggest a practical trellis-coded modulation scheme which comes close to realizing the theoretic limits found.     

FDMA,TDMA与CDMA蜂窝系统频谱效率的比较

从理论上分析比较了FDMA，TDMA与CDMA蜂窝网系统的频谱效率，指出了其频谱效率的限制因素和提高方法，计算了Q-CDMA，GSM与TACS三种实用蜂窝网系统的频谱效率，得出了几点有用结论。     

Optimum processing gain for a hybrid direct sequence/slow frequency hopping code division multiple access cellular system over Rayleigh fading channels: the direct sequence/slow frequency hopping code division multiple access case

In this paper, the optimum value of the processing gain of a hybrid direct sequence/slow frequency hopping code division multiple access cellular system, when operating in a Rayleigh fading environment, is examined. The optimization is based on the maximization of the average spectral efficiency achieved, expressed in bits per second per Hertz, which is estimated in terms of the achievable average channel capacity (in the Shannon–Hartley theorem sense) per user during the operation over a broadcast cellular time‐varying link. The analysis leads to a simple theoretical novel closed‐form expression for the optimal processing gain that is related with the system's parameters but becomes independent of hopping frequencies assigned to each system's cell. Finally, the expression derived can be useful for the practical design of a direct sequence/slow frequency hopping code division multiple access cellular system and for an initial quantitative analysis. Numerical results are presented to illustrate the presented analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectral efficiency for a hybrid DS/FH code-divisionmultiple-access system in cellular mobile radio

The spectral efficiency of a hybrid cellular direct-sequence/frequency hopping code-division muItiple-access (DS/FH-CDMA) system operating in a Rayleigh-fading environment is examined. In this work, spectral efficiency is evaluated in terms of the theoretically achievable channel capacity (in the Shannon sense) per user, on the condition that this is estimated in an average sense. The analysis covers the downlink assuming a static model of operation and a direct-sequence/slow-frequency hopping (DS/SFH) as well as a direct-sequence/fast-frequency hopping (DS/FFH) scheme. As it is shown, the spectral efficiency of cellular DS/FFH-CDMA operating in a Rayleigh-fading environment is greater than that of broad-band DS- and DS/SFH-CDMA systems operating under normalized conditions. This is justified by the combination of path-diversity reception as achieved by conventional coherent RAKE receivers and the frequency diversity that is inherently present in FFH transmission     

Outage probability of cellular mobile radio systems with selective co‐channel interference cancellation receiver in overloaded array environments

This article outlines a general numerical procedure for computing the probability of outage of a cellular mobile radio system that is equipped with a smart antenna to suppress a few strongest co‐channel interferers (CCI) out of a total of N_I active interferers by adaptive null‐steering. Aside from the interference‐limited case, refined outage criterion that either treat receiver noise as CCI or consider a minimum detectable receiver signal threshold are studied. Exact closed‐form expressions for both the basic and refined outage criterion are also derived by assuming that all the CCI signals are subject to Nakagami‐m fading with a positive integer fading severity index. Selected numerical examples are provided to illustrate the application of the theory which includes the investigation into the effects of fade distribution of the CCI signals and traffic loading on the outage probability, and also the study of spectrum utilization efficiency improvement using a selective co‐channel interference nulling (cancellation) technique. Copyright © 2002 John Wiley & Sons, Ltd.     

Statistical characterization of non-WSSUS mobile radio channels

In this paper, statistical characterizations of mobile radio channels that do not satisfy the assumption of wide-sense stationary uncorrelated scattering (WSSUS) are discussed, most importantly the local scattering function. The framework presented is particularly suited for doubly underspread non-WSSUS channels. Application examples and measurement results illustrate its practical usefulness.     

Area spectral efficiency of cellular mobile radio systems

A general analytical framework quantifying the spectral efficiency of cellular systems with variable-rate transmission is introduced. This efficiency, the area spectral efficiency, defines the sum of the maximum average data rates per unit bandwidth per unit area supported by a cell's base station. Expressions for this efficiency as a function of the reuse distance for the worst and best case interference configurations are derived. Moreover, Monte Carlo simulations are developed to estimate the value of this efficiency for average interference conditions. Both fully loaded and partially loaded cellular systems are investigated. The effect of random user location is taken into account, and the impact of lognormal shadowing and Nakagami (1960) multipath fading is also studied     

New frequency management chart minimizing intermodulation products for mobile cellular systems

In this paper, a new frequency management chart for mobile cellular system is presented. By using this new chart, the system nonlinearity-induced intermodulation products in a traditional cellular system can be greatly reduced for heavy traffic and completely eliminated for light traffic.     

Optimal SIR for an hybrid cellular DS/SFH CDMA system

A hybrid direct‐sequence/slow frequency hopping code‐division multiple‐access (DS/SFH CDMA) system operating in a Rayleigh fading environment is described and its spectral efficiency is estimated in terms of the theoretically achievable average channel capacity (in the sense of information theory) per user. The analysis covers the operation over a broadcast cellular time‐varying link and leads to a simple novel closed‐form expression for the optimal average spread signal‐to‐interference power ratio (SIR) received by each user based on the maximization of the achieved spectral efficiency. Copyright © 2007 John Wiley & Sons, Ltd.     

中继蜂窝网络中动态无线资源分配方案

提出一种中继蜂窝网络中基于动态复用分割的无线资源分配方案。该方案在所设计的帧结构基础上,从时间域和频率域进行联合的资源分配。其基本思想是通过小区间的协作使频带资源可以最有效的复用来提高系统性能。仿真结果论证了该方案在小区容量方面可以获得较大的增益。     

A simple detector for trellis-coded PSK mobile radio systems

A simple detector for a trellis-coded PSK mobile radio system is proposed. A precoder is added to the regular TC-PSK modulator before convolution coding, and a simple one-bit differential detector is used in the receiver. The decision is made symbol by symbol based on the output samples. The bit error rate of this system is evaluated in fast Rayleigh fading characterizing mobile radio channels by numerical integration.     

Efficient receiver structure for GSM mobile radio

The paper describes a receiver structure for the digital GSM mobile radio which is suitable for implementation using a DSP processor. The simulation results show that proposed simplifications have minor influence on the receiver performance and drastically reduce its computational complexity.     

蜂窝移动通信中一种分级紧致的动态信道分配方案

本文提出一种分级紧致的动态信道分配（CCDCA）方案。文中首先根据信道使用情况与业务量的关系，将小区分成“冷态”和“热态”，并给出了相应的阈值，然后在对“热态”的处理过程中利用“冷态”的先验信息，对不同状态的小区给出了不同的紧致措施。该方案还能保证小区间有较小的服务偏差，提高了整个系统的服务质量。文中还根据冷、热态的特点构造了一个二维马尔科夫链模型，计算出了模型的主要参数；其思想可用于分析多种信道分配问题。仿真结果证明CCDCA方案有较小的呼阻率和较高的频谱利用率。     

多业务无线蜂窝移动通信系统的一种呼叫允许控制策略

第三代移动通信系统要求支持宽带多媒体业务,如话音、视频、数据等多种业务,不同业务有不同的QoS要求。本文提出的多业务无线蜂窝移动通信系统中一种基于QoS的呼收允许控制策略,对不同业务的切换呼叫给予不同的优先权。本文分析了两种呼叫允许控制（CAC）算法,一种是各种业务的切控呼叫无缓冲器,不进入排队系统;另一种是各种业务的切换呼叫设置有缓冲器,进入排除系统,并且话音、视频业务的切切呼叫比数据业务的切换呼叫有更高的优先权,系统的空闲信道应首先分配给话音、视频业务的切换呼叫,再分配给数据业务的切换呼叫。在分析两种CAC算法的呼叫阻塞概率、切换失败概率以及系统吞吐量的基础上,给出了计算机仿真结果。     

Analysis for spectrum efficiency in single cell trunked and cellular mobile radio

Spectrum efficiencies for single-cell trunked and cellular mobile radio systems are analyzed, taking into consideration fading circumstances and call blocking probability. Two kinds of transmit power control methods are considered. One retains area mean power at the receiver constant and the other retains local mean power constant. For single-cell trunked systems, it has been shown how spectrum efficiency is limited by the required traffic quality or permitable adjacent channel interference. A narrower channel spaced system shows superiority to wide-band systems, if an adjacent channel interference protection ratio is lower than about -40 dB and a few percent interference probability is permitted. On comparing cellular systems, superiority in spectrum efficiency is determined by the product of protection ratio and channel spacing. Call blocking probability and interference have little effect on spectrum efficiency comparison. For both systems, the two kinds of transmit power control and the two interchannel interference criteria show no significant difference between their effects on spectrum efficiency.     

Performance analysis of dynamic channel assignment algorithms in cellular mobile systems with hand‐off

In this paper, the traffic performance of dynamic channel assignment (DCA) in cellular mobile system with hand‐off is investigated. A traffic model for cellular system incorporating hand‐off is established first. Under the framework of the model, a hand‐off priority scheme is developed to reduce the forced termination of calls in progress. This paper analyses and derives the traffic performance bound for DCA strategies with hand‐off by extending the maximum packing (MP) scheme to include the hand‐off procedure. For practical implementation, a distributed DCA algorithm (DDCA) is also proposed. A non‐priority scheme and the proposed priority scheme can be combined with either MP or DDCA. It is shown that the simulation results of DDCA scheme are comparable with the analytical bounds given by MP for both the non‐prioritized case and prioritized case. A reasonable trade‐off between the new call blocking probability and forced termination probability can be achieved by using the proposed prioritized scheme in DCA. Copyright © 2002 John Wiley & Sons, Ltd.     

Analysis of hierarchical cellular networks with mobile base stations

In this paper, we develop and evaluate a hierarchical cellular architecture for totally mobile wireless networks (TMWNs). Extensive performance tests were conducted to evaluate the performance of a two‐tier system and compare its throughput, handoff blocking rate and new call success rate with those obtained by a one‐tier model. Our tests have shown that when the total number of channels is kept the same, the two‐tier system outperformed the one‐tier counterpart under all load conditions. Under the constraint of equal power consumption, the two‐tier system still achieved improvement over the one‐tier system, especially at light and medium load levels. The improvement of the two‐tier system over the one‐tier system was observed to diminish as the degree of randomness in the mobility model is reduced; scenarios where the one‐tier system outperforms the two‐tier system are given. Load balancing schemes based on the concept of reversible handoffs are introduced and their performance improvements are analyzed. Comparison results on the percentage of terminal coverage are presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. The model extends the Markov chain approach previously used in hierarchical architectures with stationary base stations and uses a corrected derivation for the handoff blocking probability. Copyright © 2002 John Wiley & Sons, Ltd.