Romano Fantacci

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. >

Multiple access protocol for integration of variable bit rate multimedia traffic in UMTS/IMT-2000 based on wideband CDMA

The UMTS terrestrial radio access (UTRA), based on a wideband DS-CDMA technique, fully supports the UMTS requirements and has flexible support for real-time, variable-bit-rate services, as well as an efficient packet mode. This paper presents a description and a performance evaluation of a medium access protocol which may be used in the UTRA system to provide constant-bit-rate (voice), variable bit-rate (video), and low priority data services. The performance evaluation of voice and data services has been carried out by a suitable analytical approach. Simulation results are also shown in order to validate analytical predictions.

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.

Multiuser interference cancellation receivers for OFDMA uplink communications with carrier frequency offset

In multiple access OFDM systems (OFDMA) the separation of different users is achieved by exploiting the orthogonality of the subcarriers. However, a well-known problem in OFDM-based systems is the vulnerability to synchronization errors which leads to a loss of orthogonality. In this paper, a method is proposed to counteract the effect of different frequency offsets among users in an OFDMA uplink system with a frequency selective Rayleigh fading channel. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. This is performed by means of a successive or selective cancellation method. In particular, the performance of these cancellation schemes is analyzed by assuming either an ideal or estimated frequency offset. Simulation results show that it is possible to achieve, with the interference cancellation, a performance close to the ideal case, i.e., without frequency offset among users.

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.

Queuing analysis of the selective repeat automatic repeat request protocol wireless packet networks

This paper presents an analytical approach for analyzing the mean packet delay and mean queue length at the transmitting terminal in wireless packet networks using the selective repeat (SR) automatic repeat request (ARQ) scheme to control the errors introduced by the nonstationary transmission channel. Each transmitting terminal is modeled as a discrete time queue with an infinite buffer. The nonstationary transmission channel is modeled as a two-state Markov chain. Comparisons of numerical predictions and simulation results are presented to highlight the accuracy of the proposed analytical approach.

Using wireless sensor networks to support intelligent transportation systems

In this paper we propose a system architecture for enabling mobile nodes to query a largely deployed wireless sensor network in an intelligent transportation system scenario. We identify three different types of nodes in the network: mobile sinks (i.e. the nodes moving and querying the WSN), vice-sinks (i.e. nodes able to communicate directly with mobile sinks) and ordinary sensor nodes (i.e. nodes sensing a phenomenon and communicating in a multihop fashion). We present protocols and algorithms specifically tailored to such a scenario, in particular at the MAC and network layers. Such a reference architecture well covers situations in which WSNs deployed in a parking place or along a road, provide to cars information on the conditions of the surrounding environment. We introduce and analyse a simple geographic routing protocol and two different load balancing techniques. The performance of the proposed solutions is evaluated through extensive simulations. The simple geographic routing is compared to load balancing techniques. Results support the capability of the proposed solutions to enable the introduction of novel intelligent transportation system applications.

Adaptive subcarrier allocation schemes for wireless ofdma systems in wimax networks

WiMax is one of the most important technologies for providing a broadband wireless access (BWA) in a metropolitan area. The use of OFDM transmissions has been proposed to reduce the effect of multipath fading in wireless communications. Moreover, multiple access is achieved by resorting to the OFDMA scheme. Adaptive subcarrier allocation techniques have been selected to exploit the multiuser diversity, leading to an improvement of performance by assigning subchannels to the users accordingly with their channel conditions. A method to allocate subcarriers is to assign almost an equal bandwidth to all users (fair allocation). However, it is well known that this method limits the bandwidth efficiency of the system. In order to lower this drawback, in this paper, two different adaptive subcarrier allocation algorithms are proposed and analyzed. Their aim is to share the network bandwidth among users on the basis of specific channel conditions without loosing bandwidth efficiency and fairness. Performance comparisons with the static and the fair allocation approaches are presented in terms of bit error rate and throughput to highlight the better behavior of the proposed schemes in particular when users have different distances from the BS.

Performance evaluation of prioritized handoff schemes in mobile cellular networks

This paper deals with the performance analysis of two prioritized handoff schemes for mobile cellular networks in which handoff attempts finding all channels busy are queued for a maximum time. Fixed channel assignment is assumed. In the first prioritized handoff scheme considered, handoff attempts are queued according to the first-in-first-out (FIFO) policy. Conversely, the second scheme resorts to an ideal nonpreemptive priority queueing policy to enhance system performance. Differently from previous works, in this paper the performance analysis is carried out on the basis of a model which takes into account the event that a call may terminate when the mobile user is waiting for a handoff. Comparisons with simulation results and analytical predictions derived by means of alternative approaches highlight a better estimation accuracy for the proposed method. Moreover, it is also demonstrated here that the FIFO policy allows performance very close to that of the ideal prioritized handoff scheme and, hence, that it is a solution suitable for applications in mobile cellular networks where a high service quality is required.