Telecommunications are strategic for train control system operations. The European ERTMS/ETCS system for high speed trains control utilizes dedicated GSM-R mobile network(s). The costs for deployment and maintenance of GSM-R network are not sustainable for the extension of train control to low/medium traffic lines. This paper investigates on the possibility of replacing dedicated mobile radio infrastructures with the radio network integrating one (or more) existing PLMNs and satellite as backup. A methodology for performance assessment is presented and applied to the study of network availability and operational costs. Availability can be improved by allowing train to intelligently select the public network(s) time by time. Operational costs are dictated by the satellite component which may become essential in rural areas. Looking at the European scenario, a discussion on the extension of the Euroradio protocol to operate over multi-bearer mobile network is also presented.

Social information in online social games is a relevant resource that can be exchanged as far as some obstacles are removed. The comprehension of the nature of social information in games is the first step. Categorization of practical instances and specification follow. Further we introduce a reference framework based on the concept of a Social Information Service provider that enables the exchange between different service domains that produce and consume social information. Further we discuss the communication flow based on open standards and introduce three use cases. Moreover, we document the feasibility of such an approach thanks to an implementation called PASION. Real world data have been collected and analyzed in an extensive set of trials based on social games exposed in Facebook. Results enlighten the importance of social information sharing for games and social platforms, its impact on the social architecture of the games and the correlation with the cardinality of player groups in sessions of social games.

The increasing demand of indoor broadband access encourages the diffusion of the "home base stations", known as femtocells. Their self installation nature envisages interference problems due to a possible overload of local femtocell installations in the same area. To reduce the interference among femtocells we propose and analyze the performance of a dynamic frequency selection strategy, according to which each femtocell is able to select one of the possible frequencies available from all the operators in order to experience the best Signal-to-Interference Ratio (SIR). We assume that mobile operators share their requency bands allowing femtocells subscribed to a certain operator to exploit the frequency resources of other operators. In this paper we evaluate the performance in terms of allowed number of active femtocells per operator when the channels available from operators increase. It is observed that the application of the proposed Dynamic Frequency Selection (DFS) algorithm with band sharing allows single operator to significantly improve the number of active femtocells deployed in the area with respect to the non band sharing case, i.e. a Spectrum Sharing Gain is achieved.

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.

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

Ultra wide bandwidth (UWB) spread-spectrum techniques will play a key role in short range wireless connectivity providing high bit rates, low power consumption and location capabilities. UWB can be used in the design of advanced wireless local and personal area networks providing integrated multimedia services to nomadic users within hot-spot areas. Due to the very large UWB signal bandwidth, the assessment of the possible interference caused by UWB devices on already existing narrowband systems is important to ensure not conflicting coexistence and, therefore, to guarantee acceptance of UWB technology worldwide. This paper investigates on the coexistence between an UWB-based system and WCDMA-UMTS terminals. UWB interference on the UMTS terminal is evaluated accounting for the UWB signals characteristics and the UWB network architecture. The dependence of the interference from the UWB signal parameters is analyzed through computer simulation and demonstrates that, in all practical cases, UWB system can coexist with UMTS terminals without causing any dangerous interference.

Bluetooth is a low-cost, short-range wireless technology capable of providing many communication functionalities, ranging from wire replacement to simple personal area networking. In Bluetooth local networking applications, a critical issue still under study is the evaluation of the network performance when multiple piconets are simultaneously active in the same area, thus, causing mutual interference. We provide a closed-form expression for the packet loss probability in Bluetooth dense piconet area accounting for capture effects due to propagation losses. The effectiveness of the proposed approach is assessed by comparing the analytical results with those obtained from Monte Carlo simulations. By considering different scenarios, we show the dependence of results on the geometry and on the characteristics of the environment. It is observed that packet loss probability can significantly change with the position of the reference receiver in the area, as well as with the extension of the piconets area as compared with the coverage area of the receiver. We use the packet loss probability to evaluate the upper and the lower bounds of the network aggregate throughput and the average packet transmission time. Due to propagation effects, large variations of these parameters with the position of the reference receiver in the area are evidenced.

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.

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.

We provide a closed-form expression for the packet loss probability in Bluetooth networks accounting for capture effects due to propagation losses. The effectiveness of the proposed approach is assessed comparing the analytical results with those obtained from Monte Carlo simulations. By considering different scenarios, we show the dependence of results on the geometry and on the characteristics of the environment. It is observed that packet loss probability can significantly change with the position of the reference receiver in the area, as well as with the extension of the served area as compared with the coverage area of the receiver.

For code-division multiple-access (CDMA) cellular communications synchronous operation offers significant advantages over asynchronous operation. This feature has been already included in second-generation systems, such as the CdmaOne based on the IS-95 standard. Nonetheless, synchronous operation does not seem to be assessed as a basic system option for third-generation systems. This is mainly due to the contrasted choice of having global positioning system (GPS) receivers located at any of the base transceiver stations (BTSs) to perform station synchronization. However, the existing CdmaOne interface permits time transfer between the various BTSs and a simple time difference measurement technique can provide an internal, network-based means for time synchronization of base stations clocks. This paper considers a previously proposed approach based on the pilot strength measurements message delivered by every mobile station (MS), combined with round trip delay measurements that BTSs perform on the MS transmissions. We consider some possible algorithms to reduce time misalignments, and continuously phase-lock the clocks at different BTSs. Having developed an appropriate analytical/simulation approach, in the environment of a CDMA network, the paper evaluates and compares the performance of two suitable centralized architecture configurations, i.e., master-slave synchronization (MSS) and mutual synchronization (MUS). Both network architectures turn out to be applicable and provide suitable timing performance. Finally, the paper provides a preliminary discussion on some related issues, such as GPS avoidance, synchronization of BTSs inside buildings, tunnels, and subways and hybrid MSS/MUS synchronization network architectures.

Abstract Smart antennas are a powerful means to provide the increased bandwidth efficiency needed to deliver advanced third generation (3G) interactive multimedia services anywhere and anytime. In this paper we focus on the development of smart antennas located at the base stations of a code division multiple access (CDMA) cellular system. First, we review the main characteristics of antenna array systems and highlight some issues related to the inclusion of smart antennas in a 3G CDMA system. A classification of the proposed beamforming techniques and a discussion on the advantages and drawbacks of smart antennas are provided. Then, we introduce an original smart antenna technique based on rotation and resizing of the available sectors much simpler than common smart antennas based on beamforming techniques addressing a specific user. We discuss on the impact of the proposed technique in the base station architecture. Finally, we provide simulation results in order to show the effectiveness of the proposed approach and to relate transmission performance to system parameters. It turns out that the smart sectorization technique provides significant capacity improvements under statistically uniform user distribution (up to about 80 per cent for data traffic). Copyright © 2002 John Wiley & Sons, Ltd.

At the end of 1999, the 3G Partnership Programme (3GPP) completed the first release of UMTS (Universal Mobile Telecommunications System) specifications, known as 3GPP Rel 99. Since then, several countries have started to introduce what are known as 3rd Generation (3G) wireless networks. This has been a major accomplishment within the framework of the ITU International Telecommunication Union—IMT-2000 standardization effort. In May 2001, NTT DoCoMo started in Japan their WCDMA (Wideband Code Division Multiple Access) experimental service. As is well known, WCDMA is one of the two modes of operation of the UMTS. On 4 October 2001, NTT DoCoMo launched commercial services with an initial coverage area in the Tokyo urban area with a 30 km radius. NTT DoCoMo started commercialising the FOMA N2001 and P2101V terminals, the first 3G handsets ‘i-motion-compatible’. In addition, the M-stage visual service allows streamed audio-video entertainment, the real time visual service allows video telephony and with the P2401 data module high speed data communications are possible up to 384 kbps. Download and play of network games is possible with Java. It was further announced that by November 2002 a video-clip distribution service would start: this is the i-motion service that would allow users to download files at 384 kbps directly from the official i-mode-compatible portals (FOMA 3rd Generation). Initially 28 content providers are expected to offer 37 different i-motion sites with music, news, and headlines. Then, the offer is expected to expand to include interactive multimedia channels. Having spent more than €116 billion overall on 3G licenses, network providers in Europe are running fast to develop their own networks, and most of them could have been ready to deliver to commercial UMTS services soon, if it were not for the delay in handset delivery. The shortage of dual-mode GSM/UMTS handsets is expected to last until the third quarter of 2002. This is therefore the present estimated date for the roll-out of most of the UMTS networks in Europe. In 2003 the UMTS market is expected to take-off. 3GPP Rel.04 still with separate transport and signaling control paths, but with unified ‘Media Gateways’ to jointly process circuit switched and packet switched traffic; 3GPP Rel.05 with full network integration of transport and control signal, merging into a single IP paradigm. the cost of the licenses and the cost of deployment of 3G networks indicate that, even for incumbent operators who have many more ways than the newcomers to optimise their business plans, the breakeven point for their investments will likely be after some 5–7 years from roll-out of services; the continuous trend towards integration of wireless cellular technologies with wired networks and services, as well as with other wireless short range technologies, such as those under the suite of IEEE 802.11, and Bluetooth series of standards; the expansion of the IP paradigm towards the wireless world, fuelled by the standardization of IPv6, with its expanded addressing capability, and the development of the mobile IP protocol; the user's desire to rely upon friendly technologies, accompanied by his/her unwillingness accepting changes in habits to run behind the changes of technologies, while asking technologies and services ‘to solve real problems’. All the above reasons imply the need for continuous upgrading of networks and services transparently to the user: even profound technological (r)evolutions must be hidden to the user. The most profitable networks and successful operators will be the most flexible and responsive, as competition will be based on the spectrum of delivered services rather than simply on tariffs as mostly was for the 2G era. We can therefore easily expect that a long series of ‘advances in 3G wireless networks’ will set the scene and silently but deeply shape our future. The user will be unaware of most of them so that he/she will perceive service continuity while at the same time enjoying advantages in getting a faster, more ample, more ubiquitous, and more friendly service. This is the main motivation for this special issue which intends to highlight some of the possible technologies being introduced ‘while 3G networks are running’. The special issue hosts five papers. All of them have been selected with the aim of pointing out some of the avenues in 3G that will possibly provide an expanded set of services, increased system capacity, and enlarged coverage. S. S. Soliman and C. E. Wheatley provide the first paper of our special issue, entitled ‘Geolocation technologies and applications for third generation wireless.’ Among the new services that are expected to take off with the introduction of 3G systems are precise location-oriented services. These services are among the main ingredients for the diffusion of electronic commerce in the domain of mobile communications (m-commerce). In their paper the authors first put localization technologies associated to cellular systems in their historical perspective, they then discuss the principles of main geolocation technologies both for 2G and for 3G systems. Some technologies are autonomous, and put different requirements on the network and terminals, while others rely upon usage of the GPS. The authors finally consider a method suitable for cellular base stations synchronization that can improve geolocation accuracy. The second paper by R. Giuliano et al. is entitled ‘Smart cell sectorization for third generation CDMA systems.’ It deals with the development of the intelligent (or ‘smart’) antenna technology for cellular base stations. Smart antennas can steer the beam towards the wanted user and/or null the pattern towards harmful interferers. They can aid to implement the localization function. The main driver to their inclusion in 3G networks is upgrade in system capacity without the need to dramatically increase the number of base stations. This is especially desirable in urban areas where the availability of new cell sites is more and more problematic in some countries. Finally, in the paper a technique is proposed to make sectorization ‘smart’ through rotation and resizing of sectors to adapt them to CDMA traffic conditions. In the third paper by A. Engelhart et al., entitled ‘A survey of multiuser/multisubchannel detection schemes based on recurrent neural networks,’ the authors provide a survey of new detection schemes based upon neural networks. They show that the new techniques provide better performance than conventional approaches. The authors conclude, through comparison of performance evaluation results, that specific types of recurrent neural networks such as RNN/soft are the most promising candidates to outperform classical linear detection schemes. The fourth paper by M. Vázquez-Castro et al. is entitled ‘Channel modeling for satellite and HAPS systems design’. In fact, a standardization effort is going on within regulatory bodies to supplement the IMT-2000 terrestrial component with a satellite component to expand coverage of 3G systems. The paper depicts the state of the art and current trends in the framework of satellite and High Stratospheric Platforms Stations (HAPS) technologies for IMT-2000. Stratospheric platforms can be unmanned aircrafts or helium filled balloons kept ‘almost geostationary’ at an altitude of about 25 km above the earth surface. Most of satellite and HAPS systems will use new architectures and higher frequency bands, so that to evaluate their performance new tools must be developed. The authors concentrate on several physical layer issues whose proper understanding is central to correct system design, such as channel modelling, power control, spatial diversity, and availability. The last paper is co-authored by N. Batsios and F.-N. Pavlidou, and is entitled ‘Uplink–downlink design issues for next generation satellite networks.’ It is concerned with protocols for efficient use of the satellite radio resources. Among the most important protocol design issues, the emphasis of this paper is on the Medium Access Control (MAC) protocol design, as well as in research programmes that led to their development. Then the authors propose an adaptive multiple access scheme as a candidate for next generation satellite systems. The paper is backed with an extensive set of references for further studies on the subject. The Guest Editors wish to acknowledge the efforts of many people who brought this special issue to life: the Editor-in-chief Professor Mohsen Guizani, the authors and reviewers, and last but not least the editorial staff of the Journal. We hope that the papers selected for this special issue provide an interesting excerpt of some of the potential technologies to boost 3G services and to provide continuous growth to their expansion.

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.

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.

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.>

In next generation mobile satellite systems very high spectrum efficiency will be a primary objective. High spectrum efficiency is often related to a significant amount of co-channel and/or adjacent channel interference. Therefore, system design should in general include consideration of both interference and noise effects. Interference evaluation in a mobile satellite cellular system is different from the case of a terrestrial system due to the presence of the on-board antenna which acts as a spatial filter. The paper addresses the modeling of interference in single and multi-satellite cellular system and provides some results of the analysis.>

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.>