Francesco Vatalaro

Performance of low-complexity RAKE reception in a realistic UWB channel

We evaluate the link performance of an ultra-wide band (UWB) system using reduced-complexity RAKE receivers, which are based on either partial combining (called PRAKE) or selective combining (called SRAKE). The first is suboptimum and combines the first arriving multipath components, while the second combines the strongest multipath components. We use a statistical tapped-delay-line channel model that is based on extensive measurement campaigns, and reflects both small-scale and large-scale variations of the channel. Through semi-analytical evaluations of the bit error probability, we show that the simpler PRAKE receiver is almost as good as the SRAKE even for a small number of fingers. We show how this behavior can be related to the channel characteristics.

Low Complexity Rake Receivers in Ultra-Wideband Channels

One of the major issues for the design of ultra-wideband (UWB) receivers is the need to recover the signal energy dispersed over many multipath components, while keeping the receiver complexity low. To this aim we consider two schemes for reduced-complexity UWB Rake receivers, both of which combine a subset of the available resolved multipath components. The first method, called partial Rake (PRake), combines theirs/ arriving multipath components. The second is known as selective Rake (SRake) and combines the instantaneously strongest multipath components. We evaluate and compare the link performance of these Rake receivers in different UWB channels, whose models are based on extensive propagation measurements. We quantify the effect of the channel characteristics on the receiver performance, analyzing in particular the influence of small-scale fading statistics. We find that for dense channels the performance of the simpler PRake receiver is almost as good as that of the SRake receiver, even for a small number of fingers. In sparse channels, however, the SRake outperforms the PRake significantly. We also show that for a fixed transmitted energy there is an optimum transmission bandwidth

Analysis of LEO, MEO, and GEO global mobile satellite systems in the presence of interference and fading

Several multisatellite and multispot systems have been recently proposed for provision of mobile and personal services with global coverage, adopting GEO or non-GEO (i.e., MEO, LEO) satellite constellations. The paper addresses an in-depth analysis of these constellations, evaluating both geometrical performance measures and cochannel interference levels caused by extensive frequency reuse. The geometrical analysis yields the statistics for coverage, frequency of satellite hand-overs, and link absence periods. The interference analysis is based on a general model valid for all access techniques, which is here applied to the case of FDMA. The outage probability as a function of the specification on carrier-to-interference power ratio is evaluated for four selected constellations. Several techniques are introduced for interference reduction in non-GEO systems, in which the satellites coverage areas may intersect: spot turnoff, intraorbital plane frequency division, and interorbital plane frequency division. The effects of Rice fading have also been analyzed by means of an analytic approximated method. The overall analysis allows a fair comparison between LEO, MEO, and GEO constellations. >

CDMA cellular systems performance with fading, shadowing, and imperfect power control

This paper addresses capacity estimation for cellular code-division multiple-access (CDMA) systems, assuming the IS-95 standard as a reference. Extending a previous analytical method (Viterbi et al., 1994), we obtain a sequence of bounds on capacity, and then we introduce an accurate approximation to reduce computation complexity. The analysis accounts for interference internal and external to the reference cell, fading, shadowing, and imperfect power control. Outage probability is expressed in terms of the characteristic functions (cfs) of the interference and imperfect power control random variables (RVs). The interference contributions are computed on the basis of a Poisson distribution for the number of users in a lognormally shadowed channel. Results are provided for different channel conditions and are validated against Monte Carlo simulations. A comparison against previously published CDMA capacity estimates is carried out, aimed at clarifying some controversial issues. It is also confirmed that large system capacity is achievable under tight power control.

Services, technologies, and systems at Ka band and beyond-a survey

This paper discusses system and technology aspects crucial to the development of satellite communications at Ka band (20-30 GHz) and beyond. It surveys the evolution of Ka band geostationary Earth orbit (GEO) satellite communications until the present stage of development of systems for direct-to-user (DTU) provision of interactive multimedia services worldwide. Then it discusses the attenuation problem and main technical issues of this new technology. Finally, it provides a view on experiments and technological developments at extremely high-frequency (EHF) bands.

A spectrum- and power-efficient EHF mobile satellite system to be integrated with terrestrial cellular systems

An EHF satellite system for land-mobile applications to be integrated with a terrestrial cellular system is described. An approach to evaluate the carrier-to-cochannel interference occurring in multispot satellite coverage adopting frequency reuse is introduced, and results from the analysis are shown. Criteria for spectrum efficiency evaluation are also outlined along with traffic and link budget estimates. Possible options for payload implementation and mobile terminal design are presented. >

Performance Evaluation of Detect and Avoid Procedures for Improving UWB Coexistence with UMTS and WiMAX systems

Detect and avoid procedures (DAA) aim at improving ultra-wideband (UWB) coexistence with existing narrowband-wideband systems operating at the same time and in the same area. We assess the interference caused by UWB devices implementing DAA on UMTS, as well as on WiMAX systems, by estimating the time percentage where UWBs interferer with these systems. Both UMTS and WiMAX are supposed to provide primary services with respect to UWB. As a consequence, UWB is not allowed to influence their operations, i.e. no cooperation is assumed between UWB and UMTS, WiMAX devices. In this paper we present and discuss the performances of two DAA techniques, analyzing their dependence on some key UWB transmission parameters, such as the bit rate and emitted power. The proposed DAA procedures are simple to be implemented and their parameters can be selected so to arbitrarily reduce the average percentage of time the UWB interferes with the two considered victim systems

Effects of spreading bandwidth on the performance of UWB RAKE receivers

We consider an ultra-wide bandwidth system using reduced-complexity RAKE receivers, which are based on either selective (called SRake) or partial (called PRake) combining of a subset of the available resolved multipath components. We investigate the influence of the spreading bandwidth on the system performance using the two considered types of RAKE receivers. We show that, for a fix number of RAKE fingers and a fix transmit power, there is an optimum bandwidth. This optimal bandwidth increases with the number of RAKE fingers, and is higher for an SRake than for a Prake. We also investigate the effects of the fading statistics (Rayleigh or Nakagami) on the optimal spreading bandwidth. We find that the optimal spreading bandwidth is approximately the same for both types of fading, but that the actual performance of an SRake can be better or worse in Rayleigh fading (compared to Nakagami), depending on the spreading bandwidth and the number of fingers.

Probability of error and outage in a Rice-lognormal channel for terrestrial and satellite personal communications

This letter addresses performance evaluation in a nonselective fading channel modeled by a combination of Rice and lognormal (RLN) statistics. The RLN model is valid under widely different environmental conditions, both for terrestrial cellular and for satellite personal communication systems. The letter provides semianalytical expressions for the average error probability in the RLN channel for coherent M-ary phase shift keying (PSK) and noncoherent M-ary orthogonal transmissions, then it highlights the relationship between outage probability and cell coverage for macro and microcellular systems, and finally it provides some error probability results for nongeostationary (non-GEO) satellite systems.

Algorithms for dynamic frequency selection for femto-cells of different operators

The self-installation nature of femtocells sharing the same frequency band can lead to harmful femto-to-femto interference levels. The possibility for operators to share its licensed spectrum allows femtocells of one operator to exploit the frequency resources of other operators. In this paper we propose and analyze the performance of two dynamic frequency selection algorithms that permit to the generic femtocell the smart selection of its operating band, among those available from every operator, starting from the measurements of local interference. The performance of the proposed techniques are analyzed by simulation in terms of outage probability and the achievable Signal-to-Interference Ratio (SIR). It is observed that, in a multi-operator scenario this approach offers significant improvement in terms of achievable network capacity and quality of service to customers.