A Comprehensive Framework for Performance Analysis of Dual?Hop Cooperative Wireless Systems with Fixed?Gain Relays over Generalized Fading Channels

In the present contribution, we propose a comprehensive framework for the analysis of cooperative dual-hop wireless systems over generalized fading channels, which use an amplify and forward (AF) relaying mechanism with blind and semi-blind relays. In particular, the proposed framework provides either exact results or very accurate bounds for computing the moment generating function (MGF) of the end-to-end signal-to-noise ratio (SNR) for various fading channel models typically encountered in real propagation environments. Furthermore, with the help of the MGF-based approach for performance analysis of wireless systems over fading channels, we will show that important performance indexes can be easily derived from the MGF. With respect to previous published articles on the matter, the main contribution of the paper is twofold: i) by relying on the properties of the Meijer-G function, either exact expressions or accurate bounds for the MGF of the end-to-end SNR are provided, and ii) the analysis encompasses the vast majority of fading channel models. Numerical and simulation results will be compared to substantiate the analytical derivation.     

Outage Probability Analysis of Selection and Switch-and-Stay Combining Diversity Receivers Over the α−μ Fading Channel with Co-Channel Interference

In this paper, we evaluate the performance of two dual-branch diversity techniques operating over the α?μ fading channel in presence of a dominant co-channel interferer with a minimum desired signal power constraint. These two diversity schemes are selection combining and switch-and-stay combining. We derive expressions for the outage probability in both cases, which are very simple to calculate numerically using the commercially available mathematical packages. The obtained expressions are valid for integer values of the parameter μ and, in many special cases, they reduce to either a closed form or to expressions with finite-limit integrals that can also be easily evaluated. Also, our expressions reduce to previously published well-known results for the Rayleigh as well as the Weibull fading channels as special cases. We present a set of numerical results which show the effect of fading severity of both the desired signal and the interferer on the performance.     

A New Method for the Computation of the Error Probability of Differentially Detected Modulation Formats in Mobile Radio Channels – The Case of Minimum Shift Keying

We show a new approach to analytically compute the error probability BER in mobile radio channels. The method is applicable to a variety of differentially detected modulation formats; here we use minimum shift keying (MSK) as an example. We include the following effects: (i) fading and (ii) time dispersion of the mobile radio channel (iii) noise, and (iv) filtering both of the data sequence and the received signal. Sampling is at a fixed but arbitrary instant. We develop a new mathematical formalism, which we call the two-path equivalent-matrix (TPEM) method. In this method, we reduce the general channel (including noise) exactly to a two-path fading channel without noise, whose BER can be easily computed. With this method, we can find analytically the BER for both filtered and unfiltered (G)MSK if the BER is small; for large BER a single well-behaved integral must be solved numerically. Asymptotic equations for unfiltered MSK and small BERs are also given. To a first approximation, the BER is 0.5· [(S/T)²+1/SNR] for pure MSK, where S/T is the delay spread normalized to the bit duration and SNR is the signal-to-noise ratio. The BER is increased by less than 50% for Gaussian filtering of the data sequence and receiver filtering with a time-bandwidth product larger than 0.3.     

High-Speed Downlink Access in 3G Systems: A Portent for the Evolution of 4G Systems?

Due to the need of operators to protect the high levels of investment inthird generation (3G) wireless systems, it seems likely that the path tofourth generation (4G) wireless systems will be evolutionary rather thanrevolutionary. Currently there are a number of proposals beforestandardisation bodies such as 3GPP and 3GPP2 for extending the relevant3G systems to handle asymmetrical, packet-orientatedservices with very high downlink capacities. These proposals, whichinclude HDR and 1XTREME, may pave the way towards 4G systems.This paper outlines some of the salient features of HDR and 1XTREME:adaptive modulation, advanced hybrid ARQ, new fast access controlschemes, etc. On the basis of the trends inherent in theseproposals, some possible directions for the development of 4G systems arediscussed.     

An Outage Analysis of Multibranch Diversity Receivers with Cochannel Interference in α-μ, κ-μ, and η-μ Fading Scenarios

Wireless communications systems in a frequency reuse environment are subject to cochannel interference. In order to improve the system performance, diversity techniques are deployed. Among the practical diversity schemes used, Equal-Gain Combining (EGC) appears as a reasonably simple and effective one. Unfortunately, the exact analysis of the outage probability of EGC receivers is rather intricate for it involves the evaluation of multifold nested integrals. It becomes mathematically intractable with the increase of the number of diversity branches and/or interferers. For example, for N _B diversity branches and N _I arbitrary independent cochannel interferers, the exact formulation using the convolutional approach requires 2 + N _B  + (N _B × N _I ) nested integrals, which, very quickly, and for any practical system, turns out to be mathematically intractable. In this paper, we propose accurate approximate formulations for this problem, whose results are practically indistinguishable from the exact solution. In our model, the system is composed by N _B branches and N _I interferers so that the desired signals are coherently summed, whereas the interfering signals are incoherently summed at the EGC receiver. Three sets of fading scenarios, namely α-μ , κ-μ, and η-μ, are investigated. The proposed approach is indeed flexible and accommodates a variety of mixed fading scenarios for desired and interfering signals.     

A New Method for the Estimation of Mass Functions in?the?Dempster�CShafer��s Evidence Theory: Application to Colour Image Segmentation

In this paper, the problem of colour image segmentation is addressed using the Dempster–Shafer (DS) theory. Examples are provided showing that this theory is able to take into account a large variety of special situations that occur and which are not well solved using classical approaches. Modelling both uncertainty and imprecision, and computing the conflict between images and introducing a priori information are the main features of this theory. Consequently, the performance of such a segmentation scheme is largely conditioned by the appropriate estimation of mass functions in the DS evidence theory. In this paper, a new method of automatically determining the mass function for colour-image segmentation problems is presented. The mass function of each pixel is determined by applying possibilistic c-means (PCM) clustering to the grey levels of the three primitive colours. A reliability criterion, associated with each pixel and the mass functions of its neighbouring pixels, is used into a fuzzy based reasoning system in order to decide on the appropriate segmentation. Experimental segmentation results on medical and textured colour images highlight the effectiveness of the proposed method.     

Optical transitions in Cd x Hg1 ? x Te-based quantum wells and their analysis with account for the actual band structure of the material

Quantum-confinement levels in a Cd _x Hg_{1 ? x} Te-based rectangular quantum well are calculated in the framework of the four-band Kane model taking into account mixing between the states of electrons and three types of holes (heavy, light, and spin-split holes). Comparison of the calculation results with experimental data on the photoluminescence of Cd _x Hg_{1 ? x} Te-based quantum wells suggests that optical transitions involving the conduction and light-hole bands are possibly observed in the spectra.