System level performance evaluation of MIMO and SISO OFDM-based WLANs

In this paper we investigate the system level performance of an Orthogonal Frequency Division Multiplexing (OFDM) Wireless LAN network enhanced through Multiple-Input Multiple-Output (MIMO) techniques and compare it to the performance of the conventional Single-Input Single-Output (SISO) network. The MIMO scheme we apply is closed loop power allocation based on Singular Value Decomposition (SVD). The above investigations are carried out by means of a software based simulation platform. In order to characterize the system level performance accurately, a suitable link-to-system interface based on channel capacity has been developed. The performance evaluation is achieved by monitoring the average system throughput and the percentage of satisfied users. Extensive system level simulations have been carried out that prove the superiority of MIMO techniques especially for heavy traffic load conditions.     

Error rate performance analysis of dual-hop relaying transmissions over generalized-K fading channels

In this paper we present analytical expressions for the lower bounds of the error performance of dual-hop amplify-and-forward transmissions over independent and not necessarily identical Generalized-K fading channels. Using a tight upper bound for the end-to-end SNR, a novel expression for the probability density function is derived. Based on the abovementioned formula, tight lower bounds for the average bit error probability for a variety of modulation schemes are derived. In order to validate the accuracy of the proposed mathematical analysis, various numerical and computer simulation results are presented.     

Error Performance of Digital Modulation Schemes with MRC Diversity Reception over η-μ Fading Channels

This paper provides exact-form expressions for the average symbol error probability (ASEP) of various digital modulation schemes with maximal ratio combining (MRC) diversity over L independent, not necessarily identically distributed (n.i.d.) eta-mu fading channels. The derived expressions are given in terms of the Lauricella and Appell hypergeometric functions and include several others available in the literature such as those for Nakagami-m and Hoyt. General asymptotic ASEP expressions are also derived for all the considered modulation schemes which provide useful insights regarding the factors affecting the performance of the considered system.     

Evaluation of Interoperability Criteria and Mechanisms for Seamless Inter-Working Between UMTS-HSDPA and WLAN Networks Enhanced with MIMO Techniques

This article proposes criteria and mechanisms that achieve seamless inter-working between the multi-radio access technologies that will compose the fourth-generation (4G) wireless mobile environment. We address the problem of incorporating system interoperability in order to provide the user with seamless mobility across different radio access technologies; namely we focus on inter-working UMTS-High Speed Downlink Packet Access (HSDPA) and WLAN networks, as these two networks are believed to be major components of the 4G wireless network. Interoperability results in providing the user with a rich range of services across a wide range of propagation environment and mobility conditions, using a single terminal. Specifically, the article aims at defining the criteria and mechanisms for interoperability between the two networks. Our approach considers the use of Cost functions to monitor the essential parameters at the system level in order to trigger an interoperability procedure. Initial user assignment and inter-system handover are considered the incidents that initiate the interoperability algorithm execution. The overall objective of this work is to assess the performance of our developed interoperability platform and to optimize system performance by guarantying a minimum QoS requirement and maximizing network capacity.     

Cascaded generalised-K fading channel

A versatile fading distribution that generalises many commonly used models for multi-path and shadow fading is the so-called generalised-K (KG) distribution. By considering the product of N independent but not necessarily identically distributed (n.i.d.) squared KG random variables (RVs), we derive exact closed-form expressions for the moment generating function, probability density function, cumulative distribution function and the moments of the cascaded KG fading channel. Expressions for the ergodic capacity and the error performance of different digital modulation schemes are also obtained. Based on the above mentioned formulas, we analyse the performance of orthogonal space-time block codes over multiple-input multipleoutput keyhole KG fading channels. Various performance evaluation results demonstrate the proposed mathematical analysis.     

A method of accurate determination of azimuthal distribution of received RF power

In this paper, we introduce a method for the determination of directional distribution of received RF power, with angular resolution independent of receiving antenna radiation pattern. The proposed method is based on a series of measurements taken while rotating, at fixed predefined steps, a usual directional antenna of known radiation pattern on the azimuthal plain. It is proved that the resolution accuracy of the measurement method depends only on the angular step of the antenna rotation and it is independent of the antenna beamwidth. As a result of this feature, the proposed method allows the determination of the RF power angular distribution with fine resolution using a directional antenna of much wider beamwidth for the measurements. Copyright © 2001 John Wiley & Sons, Ltd.     

Higher Order Capacity Statistics of Diversity Receivers

A statistical analysis for the channel capacity (CC) for several diversity receivers under optimal rate adaptation with constant transmit power is provided. Independent but not necessarily identically distributed Nakagami-m fading channels are considered. Specifically, the moments of the CC at the output of selection combining, maximal-ratio combining, and switched and stay combining are obtained, assuming integer-order fading parameters, while for the Rayleigh model the moments of the CC at the output of equal-gain combining and generalized-selection combining are derived in closed form. Using these formulas, a new performance criterion, namely as fading figure (FF) as well as the variance, skewness, and kurtosis, are studied. Our findings show that the FF improves with an increase of the signal-to-noise ratio (SNR), the fading parameters, and/or the diversity order. Also, unlike to the variance of the error probability, the variance of the CC is a monotonic function of the average input SNR.     

Services in interworking 3G and WLAN environments

Interworking WLANs and 3G mobile networks are expected to provide ubiquitous wireless communications at high data rates and a large variety of services with variable bandwidth and QoS requirements, across a wide range of propagation environments and mobility conditions, using dual mode terminals. The interworking of the two networks is a major step toward a new generation of wireless networks in which other radio technologies are also be integrated. In this article we present possible architectures that enable the interworking of 3G and WLAN networks. We then address the capabilities of various terminal types and describe future services in the interworking environment. Finally, we present market forecasts on terminal and service demand growth.     

Channel capacity evaluation for a multiple-inputmultiple-output terminal in the presence of user?s hand

The impact of the user's hand holding a multiple-input-multiple-output (MIMO) terminal on system performance and specifically on channel capacity is investigated. A 4 times 4 MIMO system is considered with a personal digital assistant terminal equipped with a compact array of 4 patch elements. The proposed methodology is based on the use of radiation patterns of the antenna elements in the presence of the other elements and in the presence of a user's hand. Radiation patterns are obtained by means of simulations as well as of measurements conducted in an anechoic chamber. Two MIMO channel models are considered, namely a correlation-based model and a geometry-based model, where the antenna patterns are incorporated. The evaluation of MIMO channel capacity demonstrates the impact of the specific terminal antenna array. Moreover, significant degradation of channel capacity is proved because of the presence of the user's hand.     

Normalization of propagation measurements with respect to terrain effect

In this paper, we introduce a method for the reliable modelling of propagation loss using measurements data. Using point to point effective height calculation, we apply a methodology for the normalization of signal propagation loss measurements with respect to terrain effect. Moreover, by applying the proposed normalization methodology on two different measurement data sets, taken in the same urban environment (Athens, Greece), it is experimentally proved that the effective height is accurately expressing the influence of terrain morphology in the vicinity of mobile unit on signal variability. Copyright © 2001 John Wiley & Sons, Ltd.