Showing papers by "Romano Fantacci published in 2000"

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

Abstract: 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.

Performance evaluation of prioritized handoff schemes in mobile cellular networks

Abstract: 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.

Characterization of user mobility in low earth orbit mobile satellite systems

Abstract: Future mobile communication networks will provide a global coverage by means of constellations with nongeosynchronous satellites. Multidspotdbeam antennas on satellites will allow a cellular coverage all over the Earth. Due to the unstationarity of satellites a call may require many cell changes during its lifetime. These passages will be managed by interdbeam handover procedures. This paper deals with the modeling of the user cell change process during call lifetime in Low Earth OrbitdMobile Satellite Systems lLEOdMSSsr. The analytical derivations presented in this study can be also applied to different mobility models provided that basic assumptions are fulfilled. This paper evaluates the impact of user mobility on the blocking performance of channel allocation techniques. Moreover, the handover arrival process towards a cell has been characterized by using a usual statistical parameter for stationary point processes. Finally, a performance analysis has been carried out on the basis of the classic teletraffic theory for telephone systems.

Performance evaluation of a CDMA protocol for voice and data integration in personal communication networks

Abstract: Future wireless personal communication networks (PCN's) will require voice and data service integration on the radio link. The multiaccess capability of the code-division multiple-access (CDMA) technique has been widely investigated in the recent literature. The aim of this paper is to propose a CDMA-based protocol for joint voice and data transmissions in PCN's. The performance of such a protocol has been derived by means of an analytical approach both in terms of voice packet dropping probability and mean data packet delay. Voice traffic has been modeled as having alternated talkspurts and silences, with generation of voice packets at constant rate during talkspurts and no packet generation during silence gaps. A general arrival process is assumed for the data traffic. However, numerical results are derived in the case of a Poisson process. Simulation results are given to validate our analytical predictions. The main result derived here is that the proposed CDMA-based protocol efficiently handles both voice and data traffic. In particular, it is shown that the performance of the voice subsystem is independent of the data traffic.

Performance evaluation of polling systems for wireless local communication networks

Abstract: This paper evaluates the performance of different polling systems used in wireless local networks where the transmission channel exhibits a nonstationary behavior. Many spatially dispersed data user terminals have been assumed to share a common short-range radio uplink channel to access a hub station. We have specifically considered cyclic polling systems with M queues (terminals), having the same general packet arrival process and general switchover period. The gated and exhaustive disciplines have been considered in ordering the transmission of the packets buffered at each terminal. By appropriately modeling the uplink channel, we propose analytical approaches to derive the average packet waiting time and the average cycle length for gated polling systems, combined with stop-and-wait (SW) and go-back-N (GBN) automatic repeat request (ARQ) techniques to control errors. A gated cyclic polling scheme combined with the selective-repeated (SR) stutter ARQ technique as well as an exhaustive cyclic polling scheme combined with SW, GBN, or SR stutter ARQ techniques, respectively, have also been considered In order to give an in-depth knowledge of the behavior of suitable polling alternatives for applications in wireless local communication networks.

Performance evaluation of a reservation TDMA protocol for voice/data transmission in microcellular systems

Abstract: This paper deals with a random reservation TDMA protocol able to support constant bit rate services as well as variable bit rate services. In particular, voice communications and data transmissions are considered. Voice terminals have a higher priority assigned than data terminals in accessing the shared channel. A suitable analytical approach is proposed in order to evaluate the data and voice subsystem performance. Comparisons to the well known PRMA scheme are also given in order to highlight the superior performance of the proposed approach in terms of maximum data load and overall throughput.

Voice and data transmissions with a PRMA-like protocol in high propagation delay cellular systems

Abstract: Future mobile communication systems will require new medium access control protocols to attain an efficient multiplexing of different traffic sources while guaranteeing their requirements on quality of service. This paper investigates the performance of a modified packet reservation multiple access (PRMA) protocol, called PRMA with hindering states (PRMA-HS), for supporting voice and data transmissions in mobile cellular systems with high propagation delays. A scenario based on low Earth orbit mobile satellite systems (LEO-MSSs) has been considered, but the analytical approach is general. We have obtained that PRMA-HS achieves a high capacity of voice sources in LEO-MSSs also in the presence of data traffic. A performance analysis has been carried out showing good agreement with simulation results. Finally, the PRMA-HS performance has been evaluated in the presence of different data traffic sources.

Performance evaluation of a reservation TDMA protocol for voice/data transmission in personal communication networks with nonindependent channel errors

Abstract: This paper deals with a random reservation TDMA protocol able to support constant bit-rate services as well as variable bit-rate services. In particular, we consider here the case of voice communications and data transmissions in a fading channel environment with nonindependent errors. Voice terminals are assumed to have higher priority than data terminals, in accessing the shared channel. A suitable analytical approach is proposed in order to evaluate the data and voice subsystem performance. Computer simulations are also shown in order to validate the obtained analytical predictions. The results shown here highlight that the proposed protocol permits an efficient integration of voice and data transmissions in the same wireless network even in the presence of a nonideal transmission channel.

A modified PRMA protocol for voice and data transmissions in low Earth orbit mobile satellite systems

Abstract: Future mobile communication systems will provide multimedia services to users in every environment through uniform access procedures. In this scenario, it is essential to define efficient medium access control (IMAC) protocols that are suitable for both terrestrial and satellite systems (integrated networks). This paper envisages packet reservation multiple access (PRMA) for supporting voice and data transmissions in low Earth orbit (LEO) mobile satellite systems. In particular, a modified PRMA (MPRMA) protocol is proposed and analyzed. Simulation results are also presented in order to validate the analytical approach. A parameter optimization has been carried out to improve the protocol performance. Finally, a comparison with PRMA has permitted to highlight the advantages of the new MPRMA scheme.

Adaptive MMSE receivers for communications in non-stationary multipath fading channel

Abstract: This paper deals with two adaptive minimum mean square error (MMSE) receivers for direct sequence code division multiple access (DS/CDMA) wireless communication systems: in particular, the two different schemes, named postcombining and precombining are considered with two adaptive algorithms, the least mean squares (LMS) and the recursive least squares (RLS). The proposed adaptive MMSE receivers do not need knowledge of the desired user's signature waveform, only requiring the use of training sequences (TS) at start up, since a decision directed mode is adopted after the TS first transmission. The detectors performance is expressed in terms of the bit error rate (BER), which has been derived by simulations under the assumption of a frequency-selective Rayleigh fading channel. The reported simulation results shown highlight the adaptive MMSE receivers good behaviour and remarkable near-far resistance, even in worst fading environments.

Performance analysis and optimisation of a space-time selective PIC in CDMA wireless communication system

Abstract: This paper deals with a parallel interference cancellation (PIC) detector for DS-CDMA wireless communication systems with adaptive antenna arrays. The proposed detector's main feature lies in the utilization of PIC techniques for the adaptive antenna arrays receiver since optimum beamforming and one-shot interference cancellation are supposed to be used together. The proposed receiver is utilised at the end of up-link wireless DS/CDMA communication system in which BPSK modulation scheme is used in transmission so that asynchronous users and multipath fading phenomena are introduced. The proposed receiver basic assumption is to divide signals in reliable and unreliable ones after space-time combining. The reliable signals are directly detected and cancelled from each signal received by each sensor; afterwards processed signals are once again combined and detected in order to improve decision on unreliable signals. A suitable analytical approach is proposed in order to evaluate the error probability (P/sub e/) and optimum threshold value of the receiver under consideration. Simulation results are also presented to validate obtained analytical predictions. It is shown here that proposed receiver shows a very good performance and, thanks to inherent low complexity of cancelling techniques, allows real-time operation. The performance is expressed in terms of the bit error rate (BER), which has been derived by simulations under the assumption of a frequency-selective Rayleigh fading channel.

Orthogonal Direct Sequence Code Division Multiple Access For Broadcast Communications on Power Lines

Abstract: This paper deals with a Direct Sequence Code Division Multiple Access (DSICDM) system for Power Lines Communications (PLC): it relies on utilisation of Orthogonal Variable Spreading Factor (OVSF) sequences together with scrambling codes in order to minimise MultipIe Access Interfrence ( M I ) impairments and to provide flexible multicode allocation. Proposed scheme is particularly suitable for high bit rate broadcast communications on low voltage grid in order to guarantee "last mile" access network. System performance is expressed in terms of bit error rate (BER), which has been derived by computer simulations under the assumptions of frequency-selective multipath fading channel and additive coloured gaussian noise according to the model defined for in building networks [I].

Selective partial parallel interference cancellation for personal CDMA communications

Abstract: This paper deals with a cancellation multiuser detector for CDMA communication systems. Proposed receiver is supposed to be used at the end of up-link channel, leading to consider multipath fading phenomena. Proposed receiver approach consists in performing a weighted selective cancellation of the co-channel interfering signals, divided in two different groups according to the received power level: signals exceeding a suitable threshold are considered more reliable and, therefore, cancelled with a higher weight. In comparison with previously proposed cancellation receivers described detector shows remarkable improvement of the resistance to multiple access interference and low computational complexity, linear in the number of users.

Pre-combining advanced blind multiuser detector for time and frequency selective wireless channel

Abstract: This paper deals with an adaptive multiuser detector for DS-CDMA (Direct Sequence Code Division Multiple Access) wireless communication systems, whose main features are low complexity and joint utilization of the time diversity and blind adaptive processing techniques. The proposed multiuser detector, defined as Pre-combining Advanced Blind Adaptive Multiuser Detector (PABA-MUD), a window reprocessing technique together with an original adaptation rule is used in order to improve performance for time varying environment. In particular, pre-combining of different replicas allows deriving a unique adaptive sequence even for multipath signals. The proposed detector shows remarkable near-far resistance and requires knowledge of the desired user's signature waveform, timing and phase. No training sequence is needed. Receiver performance is expressed in terms of bit error rate (BER), which has been derived by simulations under the assumption of a time and frequency-selective Rayleigh fading channel.