E. Del Re

Handover and dynamic channel allocation techniques in mobile cellular networks

This paper deals with an efficient dynamic channel allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical fixed channel allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique. >

Efficient dynamic channel allocation techniques with handover queuing for mobile satellite networks

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites. >

Handover queuing strategies with dynamic and fixed channel allocation techniques in low Earth orbit mobile satellite systems

This paper deals with the performance evaluation of various resource management strategies that are suitable for low Earth orbit mobile satellite systems (LEO-MSSs). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: (a) the first input first output (FIFO) scheme and (b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines.

Performance analysis for a guaranteed handover service in an LEO constellation with a "satellite-fixed cell" system

It is anticipated that the satellite component of the future universal mobile telecommunications system (UMTS) will be based (partly or totally) on non-geostationary (nonGEO) constellations of satellites to serve mixed populations of users, each category being treated through different contracts stipulating different quality of service (QoS). In particular, we envisage a high-quality premium service which guarantees the success of each handover procedure, called guaranteed handover (GH) service, and a low-cost lower quality service called regular service, where handover failures are accepted provided that the probability of a call being unsuccessful does not exceed a given value. This paper proposes a strategy which eliminates forced call terminations due to handover failures, thus allowing the GH service. This procedure applies to low Earth orbit (LEO) constellations using the satellite-fixed cell technique. An analytical model has been derived to calculate QoS parameters for a mixed population of GH and regular users. Providing both GH service to some users and regular service to other users requires an increased satellite capacity with respect to the case where all the users are served with the regular service; this capacity increase has been evaluated as a function of the percentage of GH users, the traffic load per cell, and the considered satellite mobility environment. The GH approach has been validated through the comparison with another scheme which envisages the queuing of handover requests for privileged users.

Next-generation mobile satellite networks

Due to the increasing demands of multimedia services supporting high bit rates and mobility, ATM, TCP/IP, and satellite technology are going to be associated to form the internetwork infrastructure of future global systems. In this scenario, distinctions between terrestrial and satellite communications systems, as well as between fixed networks and 3G mobile networks, will cease to exist in a global coverage wireless system. The European Action COST252 actively participated in developing the satellite component of UMTS.

Comparison of CDMA and OFDM techniques for downstream power-line communications on low voltage grid

This paper provides a fair comparison between direct sequence code division multiple access (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) systems for broadband downstream power-line communications (PLCs). The considered schemes seem particularly suitable for high bit rate broadcast flexible communications on low voltage grid in order to guarantee local access. The performance of the considered systems is expressed in terms of bit error rate (BER), derived by simulations under the assumptions of frequency-selective multipath fading channel and additive colored Gaussian noise according to the in-building networks model, under the same overall working conditions of bandwidth occupation, transmitted power, and global data rate.

A continuously adaptive MLSE receiver for mobile communications: algorithm and performance

The paper presents a Euclidean distance maximum likelihood sequence estimation (MLSE) receiver, based on the Viterbi algorithm (VA), suitable for fading and noisy communications channels, as that specified by the Group Special Mobiles (GSM). In a mobile cellular system, the fast varying channel characteristics, due to the fading and Doppler effects, require adaptive methods to update the channel coefficients to the MLSE receiver. The proposed technique continuously estimates the channel characteristics directly within the metric calculation of the VA. At each step of the VA, the sequence associated to the path with the best metric value (minimum-survivor method) among the survivor paths is used to update the channel estimate (employing conventional adaptive algorithms) throughout the entire informative sequence. However, the detection of the transmitted data sequence is performed by the VA only at the end of each burst. The proposed technique allows simpler receiver implementation and the simulation results show a good performance of this adaptive MLSE receiver in typical GSM environments.

The GSM procedures in an integrated cellular/satellite system

In an integrated cellular/satellite system for mobile communications a satellite subsystem cooperates with a terrestrial cellular network for providing user services. The paper addresses the problems related of the reuse of the procedures of the GSM cellular standard in an integrated system. Allowing at most changes only at the mobile terminal and/or in the satellite network. The results of the study show that most of the GSM procedures can be reused in an integrated system (in a few cases with limited protocol variations) but some others would require modifications to the cellular network. The results of this study shall also be useful for the suitable definition of the protocols of an integrated satellite/terrestrial system for the next generation of mobile and personal communication services. >

A coordinated European effort for the definition of a satellite integrated environment for future mobile communications

The complete integration of a satellite network with a terrestrial cellular network is a system architecture challenge that requires solving problems at both the transmission and network levels. However, the potential advantages of the integrated system suggest careful study of the appropriate solutions. The main technical advantages are: a limited increase in the complexity of the terminal for both the satellite and terrestrial systems, making it attractive for its potential low cost; the fixed earth stations (FESs) of the satellite system are similar to cellular base stations and switching centers, this avoids expensive development of FESs, which can be adapted from the terrestrial stations and may even be collocated with some of them, saving the common parts. The main operational benefits that could be achieved are the extension of the mobile services (bearer services, teleservices, supplementary services) offered by the terrestrial system to not yet covered areas, Eastern Europe and North Africa, aeronautical and maritime mobiles, so that one integrated land/aeronautical/maritime (LAM) system could be conceived for all mobiles. The European COST 227 Integrated Space/Terrestrial Mobile Networks project is discussed.

Different queuing policies for handover requests in low Earth orbit mobile satellite systems

In this paper, a mobility model suitable for low Earth orbit mobile satellite systems (LEO-MSSs) has been presented, and its statistical parameters have been derived in order to evaluate the impact of the mobility on the performance of the fixed channel allocation (FCA) strategy. Moreover, we have foreseen that interbeam handover requests, which do not immediately find service, can be queued to reduce the handover failure rate. Two different queuing disciplines have been assumed: (1) the first-input-first-output (FIFO) scheme and (2) an idealized strategy that requires knowledge of the last useful instant (LUI) within which the handover procedure must be completed in order to rank the queued handover requests. An analytical approach has been developed to compare these queuing techniques, and its results have been validated through simulations.