A general analysis of signal strength handover algorithms withcochannel interference

In this paper, the problem of computing cochannel interference statistics in signal strength measurements in mobile radio systems is presented. In a cellular environment with cross-correlated log-normal shadowings, extensions of Wilkinson's method and Schwartz and Yeh's (1982) method are proposed for evaluating the statistics of differences between signal strengths that a mobile terminal measures on the links to any pair of base stations in the presence of cochannel interferers. The derived statistics are then used in the performance analysis of relative signal strength handover algorithms. Results provided by the two methods are compared with simulation results, in order to assess their accuracy, and computational issues are addressed. From numerical results, it is also seen that handover algorithm performance has a noticeable dependence on both cross correlation among shadow fadings and the interference level. Finally, it is seen that previous approaches to derive cochannel interference statistics in the presence of log-normal shadowing can be obtained as particular cases     

On the design of a small zone land mobile radio system in UHF band

For designing a land mobile radio system, particularly a small zone high capacity system in the UHF band, various performance degradation causes, such as signal fading, cochannel interference, intermodulation disturbance, and sensitivity suppression, should be inclusively taken into account. The magnitudes of these degradations vary with time, because of field strength variation due to multipath fading, environmental shadowing effect, and the distance of mobile station from the base. Hence the circuit performance objective given in a probablistic form must be allotted for in each one of these causes. Variabilities of these degradations are estimated in terms of desired and undesired signal field strength variations. In the estimation, path diversity effect is considered and a root square sum approximation technique is employed. Also, the process used to determine the allottment is proposed from the viewpoints of efficient frequency utilization and realizability of base and mobile radio equipment.     

Cochannel interference estimation for M-ary PSK modulated signals

Although the signal-to-interference power ratio (SIR) based criterion for diversity reception has been highlighted in the literature as the most effective method for reducing the effects of cochannel interference, it is often not clear how to measure this parameter in a practical context. This work addresses the problem of finding a way to determine the level of interference (due to frequency reuse) from neighbouring cells in a mobile telephone system, with M-ary PSK modulated signals and fast fading channel. The proposed parameter measures the quality of the received signal corrupted by additive white noise and cochannel interference, for any number of interferers. It is also suitable for high bit rate transmission, as in indoor mobile radio systems, since the proposed method requires sampling the received signal at just one sample/symbol.     

Optimal channel reuse in cellular land mobile radio systems

Origination probability for cochannel interference is introduced to the study of the influence of all cochannel interferers surrounding the base station of interest. In addition, the probability of cochannel interference, which is of importance in determining system parameters in a cellular communication scheme, is evaluated for the mobile radio environment as expressed by Rayleigh fading and shadowing. As a consequence, the optimal number of radio channels to allocate to each cell is derived through the use of a simple mathematical model. The theoretical results obtained are useful not only as a step in the maturation of the cellular land mobile radio system, but also for the development of the portable radio telephone system.     

多径衰落移动无线系统中的同频道干扰预测

同频道干扰是微蜂窝结构移动通信网所要考虑的一个核心问题，要想成功地对任何一种频率再用无线系统进行规划设计，就必须很好地了解并分析研究同频道干扰对系统性能的影响。本文对具有Ｎａｋａｇａｍｉ衰落和对数正态衰落的同频道干扰特性进行了理论分析，并提出了对微蜂窝多径衰落移动无线电系统中的同频道干扰及其影响进行预测的近似方法。     

Effect of cochannel interference on handover in microcellular mobile radio

The effect of cochannel interference on a fast handover algorithm for microcellular mobile radio systems is described. The presence of cochannel interference had only a marginal effect on the handover point when the microcell base stations were spaced by 300 m. Increasing the mobile speed increased the effective cell length.<>     

Efficient Spectrum Utilization for Mobile Radio Systems Using Space Diversity

Space diversity combining is a well-known method of smoothing amplitude fluctuations of the received signal in Rayleigh fading environments, such as mobile radio. Perhaps less well known is that space diversity combining can also be an excellent method of combating cochannel interference. In this paper, it is shown that high spectrum efficiencies in mobile radio systems can be achieved with a modest number of space diversity branches. With a large number of diversity branches it is shown that frequency reuse is possible resulting in spectrum efficiencies, as defined herein, greater than 100 percent.     

Cochannel Interference in High-Capacity Mobile Radio Systems

The probability of cochannel interference is evaluated for a mobile radio system operating in Rayleigh fading and log-normal shadowing environment. All cochannel cells surrounding the base station are taken into consideration in this evaluation. The results obtained are used to calculate the reuse distance and the cluster size (number of cells in a group). The blocking probability, the number of channels in each cell, the protection ratio, and the standard deviation are taken as parameters in this evaluation. The results show that shadowing has a severe effect on the interference level and on the channel reuse distance ratio.     

Outage possibilities in mobile radio systems suffering cochannelinterference

Mobile radio systems are usually designed on the basis of providing adequate reception quality to a specified area. The outage probability equations are used to determine the quality of radio reception when that quality is limited by a minimum required signal level, interference from a cochannel transmitter, and variability in the received signal levels. Considering Rayleigh fading and lognormal shadowing as joint causes of signal variation, average outage probability expressions are derived for mobile radio systems of a uniform nature. These expressions are used to investigate the influence of various system and propagation characteristics on reception quality     

Error rate performance of noncoherent detection of duobinary coded MSK and TFM in mobile radio communication systems

Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes, duobinary coded minimum shift keying (MSK) and tamed frequency modulation (TFM), use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environments with noncoherent detection. A closed form expression for the probability of error of duobinary coded MSK with discriminator detection has been derived and evaluated for different cases of fast and slow fading and cochannel interference. The probability of error of duobinary coded MSK and TFM with differential detection has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.     

Macroscopic Diversity in Frequency Reuse Radio Systems

Macroscopic diversity is a technique that can facilitate high quality and ubiquitous communications between low-power portable radiotelephones and data terminals, and radio base stations (ports) that are connected to the local network. It uses radio signals from several base stations to mitigate the effect of shadow fading, a variation of signal strength over space created by the presence of buildings, foliage, and terrain variations. With a path loss exponent of four and a shadow fading standard deviation of 10 dB, four-branch macroscopic diversity results in a 13 dB improvement in signal strength and a 15 dB improvement in signal to cochannel interference ratio for high user capacity interference-limited operation. (Both figures are for 99 percent statistical coverge of the service area.) The improvement in signal to cochannel interference ratio is equivalent to a factor-of-five savings of spectrum.     

Super-resolution broad null beamforming for cochannel interferencecancellation in mobile radio networks

An innovative beamforming-type approach for suppressing cochannel interference in mobile radio networks is introduced. This approach combines a super-resolution direction and power profile finding algorithm, together with a signal subspace-type broad null beamformer which can steer both sharp and controlled broad nulls in the appropriate directions. The latter property makes the beamformer ideal for mobile communication systems where the angular spread of the incoming rays from a cochannel interfering mobile station is often too large to be eliminated by a sharp null, resulting in a significant degradation in the performance of a conventional system     

Outage probabilities of cellular mobile radio systems with multipleNakagami interferers

Closed-form expressions for outage probabilities of mobile radio channels experiencing multiple, cochannel, independent Nakagami interferers are derived. This is done for the case of Nakagami fading alone with an arbitrary number of interferers. Analytical results for the case of Nakagami fading combined with log-normal shadowing are obtained for a single interferer. The case of multiple shadowed interferers is examined by simulation. The fading severity parameter in the Nakagami distribution may be varied to model different fading conditions. Interferers with similar and different Nakagami statistics are analyzed. The probability of cochannel interference is related to the reuse distance, which is one of the key parameters in the design of cellular mobile radio systems. In addition, the effects of specifying a minimum signal power requirement for satisfactory reception are investigated. A number of system examples that illustrate applications of the results are included     

Optimum combining in digital mobile radio with cochannel interference

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signal-to-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.     

Performance of antenna array systems with optimum combining in aRayleigh fading environment

The effect of cochannel interference on the performance of digital mobile radio systems in a Rayleigh fading environment is studied. The average bit error rate (BER) of an antenna array system with an optimum combining scheme that maximizes the output signal-to interference-plus-noise ratio is analyzed. BER expressions which are easy to evaluate numerically are derived for coherent binary phase-shift keying schemes in an environment with cochannel interference and noise     

Signal-to-interference calculations for corner-excited cellularcommunications systems

Signal-to-inference ratio calculations for corner-excited cellular communications systems are presented. Specifically, the ratio of median signal power to the sum of median interference powers is considered. The interference model includes cochannel interference, and immediately adjacent as well as nonimmediately adjacent channel interference. Related system parameters are cluster size, receiver, and transmitter filter characteristics, propagation exponent, tier coverage, and directional antenna front-to-back ratio. Both mobile-to-baseand base-to-mobile communications are considered. The method and model used for calculation are more complete than any previously reported in the technical literature. The calculated results show that the effect of adjacent channel interference compared to cochannel interference cannot be ignored in general. In mobile-to-base communications, the effect of immediately adjacent channel interference introduced by an interfering mobile which is very close to the receiving base antenna is serious     

Optimum Combining in Digital Mobile Radio with Cochannel Interference

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signalto-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.     

Indirect Cochannel Interference Cancelling

This paper describes a blind cochannel interference cancelling technique, indirect cochannel interference cancelling (ICIC), that cancels a constant envelope modulated interferer in cellular mobile radio communication channels. ICIC exploits the constant envelope property of the interfering signal to simplify the receiver structure. The basic concept of ICIC and the possible receiver structures are discussed. The performance of a ICIC receiver in practical channels as well as its sensitivities to the channel parameters are investigated by simulation.     

A complex baseband platform for spatial-temporal mobile radio channel simulations

Joint spatial-temporal signal processing has been recognized as the key to reducing the effects of the intersymbol and cochannel interference seen in very high bit-rate mobile radio communications systems. Developing hardware simulators that can simulate mobile radio propagation scenarios in time and space domains is essential for evaluating the real-time performance of spatial-temporal signal processing schemes. This paper outlines a complex baseband platform developed for spatial-temporal mobile radio channel simulations. The platform consists of a complex baseband fading/array response simulator, a digital signal processor (DSP) board, and a general-purpose parameter estimator that uses systolic array implementation of the recursive least square (RLS) algorithm. Results of experiments conducted using the developed platform are presented to confirm the proper operation of the system.     

Performance of generalized selection combining for mobile radiocommunications with mixed cochannel interferers

The performance of generalized selection combining (GSC) space diversity for mobile radio systems in the presence of multiple cochannel interferers is studied. Two cochannel interference models are considered: (1) L cochannel interferers consisting of L-N Nakagami-m (1960) interferers and N Rayleigh interferers and (2) L cochannel interferers in which each interferer follows Nakagami-m distribution for a fraction of time and Rayleigh distribution for the remaining of time. The fading parameters of the Nakagami-m interferers are limited to integer values only. The desired signal is assumed to be Rayleigh faded. Also, all the desired signals and the cochannel interferers received on each branch are independent of each other. Closed-form expressions are derived for the probability density functions (PDFs) of the instantaneous signal-to-interference power ratio (SIR) at the output of the GSC for the two cochannel interference models. Using these SIR PDFs, closed-form expression for evaluating the outage probability and the average bit error probability (BEP) are subsequently derived. A differential phase-shift keying scheme is considered in the derivation. Numerical results showing the influences of various system parameters on the outage probability and the average BEP are then presented