Abstract The unique capabilities of new cellular systems are expected to provide users with integrated multimedia services. Since the air interface still represents the system bottleneck, this paper proposes novel scheduling techniques to integrate efficiently the support of real‐time traffic (i.e. voice and video) and data bursty traffic under quality of service (QoS) guarantees. Prioritization among traffic classes is adopted and a polling service discipline is employed within a class, where the permission rights of each traffic source are determined on the basis of token bucket regulators. Two polling‐based approaches are compared to serve the sources of a class: (i) when a source is enabled to transmit, a burst of packets is sent at once; (ii) within the time interval destined to a traffic class, a cyclic service of the sources is allowed on a packet basis. With realistic assumptions on both radio channel conditions and protocol signaling overhead, this paper compares these two different approaches and the dynamic slot assignment++ (DSA++) scheme appeared in the literature. The obtained results highlight that our second scheme (case ii) allows increasing the number of supported video traffic sources of many units with respect to DSA++. Finally, an analytical approach has been proposed for our second polling scheme. Copyright © 2004 John Wiley & Sons, Ltd.

The performance of radiolocation systems which make use of observed time difference of arrival techniques is investigated. We refer to a classical third generation WCDMA wireless system where measurements are performed in the direct connection (from base station to mobile). The system performance is evaluated by using a ray-tracing technique to characterize the behaviour of typical urban environments.

This paper compares two possible scenarios for mobile Internet surfing according to the Personalised Access to Local Information and services for tOurists (PALIO) Project (IST-1999-20656). In particular, we consider WAP phones with Short Message Service (SMS) and Personal Digital Assistants (PDA) with General Packet Radio Service (GPRS). Suitable round robin scheduling schemes are analyzed for downlink transmissions. Part of this work has been also contributed to the COST 273 Project.

Mobile satellite systems (MSSs) are expected to play a significant role in providing users with communication services worldwide. In such a context, low Earth orbit (LEO) satellite constellations seem to be a good solution to attain a global coverage and to allow the use of low-power lightweight mobile terminals. This paper analyzes the performance of a novel medium access control (MAC) scheme suitable for applications in LEO-MSSs, named packet reservation multiple access with hindering states (PRMA-HS), that has been derived by proper modifications of the well-known PRMA protocol. We envisage a mixed traffic with voice sources and data sources with different quality of service (QoS) requirements. The good behavior of the proposed PRMA-HS scheme is validated by extensive comparisons with the classical PRMA protocol. Finally, it is shown that PRMA-HS efficiently supports integrated voice and data traffic in LEO-MSSs.

This paper, based on the PALIO project, deals with an information tourist service accessible through mobile phones by means of the Wireless Application Protocol (WAP). We have considered a Global System for Mobile communications (GSM) network where the WAP traffic is transported by the Short Message Service (SMS) on a logical channel that also conveys signaling messages. Suitable models have been proposed for both WAP and signaling traffic. An analytical approach (validated by simulations) has been developed to evaluate the mean delay to browse a WAP page.

We address the radio resource management problem in high altitude platform stations (HAPS) systems. We propose a centralized resource allocation strategy, named ORA-LF, that allows maximizing the system throughput while preserving the fairness among mobile terminals carrying the same traffic type. We also describe a simplified procedure, named SRA-LF, that allows making the ORA-LF strategy compatible with real time implementations.

Abstract This paper, based on the PALIO Project within the fifth Research Framework of the European Commission, deals with an information tourist service accessible through mobile phones by means of theWireless Application Protocol(WAP). We have considered aGlobal System for Mobile communications(GSM) network where the WAP traffic is transported by theShort Message Service(SMS) on a logical channel that also conveys signaling messages. Suitable models have been considered for both WAP browsing traffic and signaling traffic. We have proposed a theoretical approach to evaluate the mean delay to browse a WAP page taking into account the impact of the signaling load. Analytical predictions have been validated through comparisons with simulation results. Moreover, we have also considered a specificQuality of Service(QoS) requirement in terms of the maximum deck transmission delay that is guaranteed in 95 per cent of cases. Consequently, it has been possible to evaluate the number of WAP users that can be supported per cell. The study carried out in this paper permits to prove the feasibility for the envisaged mobile service based on WAP and it also allows dimensioning WAP pages so that each user experiences reasonable browsing delays. Copyright © 2001 John Wiley & Sons, Ltd.

Future wireless systems will allow the mobile access to multimedia services. This paper proposes a medium access control (MAC) protocol that permits an efficient integration of real time-variable bit rate (rt-VBR) traffic and bursty available bit rate (ABR) traffic. This scheme, named minislotted-dynamic resource assignment (M-DRA), provides rt-VBR sources with a quality of service independent of the ABR traffic load. The M-DRA scheme effectiveness has been validated by comparisons with other protocols.

This paper proposes an analytical study which aims at evaluating the received power statistics in DS-CDMA cellular systems which use a closed-loop power control scheme to compensate for fast multipath fading. The effects of a limited transmission power at the mobile terminals have been also investigated. This study is based on a first order Taylor expansion of the fast fading fluctuations. The accuracy of the obtained results has been verified through computer simulations. Classical frequency-selective channel models have been taken into account which involve the use of a diversity RAKE receiver at the base station. Finally, the system capacity is evaluated under different environmental conditions.

This paper envisages data transmissions in a low-mobility wireless local area network based on a DS-CDMA air interface. A Rayleigh fading channel and suitable Internet-like traffic model have been envisaged to study the impact of the closed-loop power control on an adaptive coding scheme. The following quality of service (QoS) parameters have been considered in this study: the mean datagram transmission delay and the mean transmission energy per useful bit. We have obtained that our proposed adaptive coding scheme permits one to avoid the use of closed-loop fast power control. Such choice permits one to improve both previous QoS parameters, so allowing an efficient management of radio resources.

This paper studies the problems related to the transmission of digital data in ATM-like format over a noisy wireless channel affected by burst of errors. A cell structure more suitable for wireless application is proposed and a protocol for error control and packet re-transmission is presented that provides good throughput performances. This protocol is based on an ARQ scheme with partial re-transmission used in conjunction with a cyclic error detection code. The system parameters are tuned to provide easy conversion between the standard ATM cell and the wireless-ATM one.

A FEC coding strategy compatible with the H.263 standard is proposed, which uses unequal error protection to improve image quality for low bit rate video transmission over noisy channels. The H.263 bit stream is partitioned into classes of different sensitivity, without introducing any modification into the standard stream syntax. The experimental results show that the proposed scheme can be used either when video is transmitted over channels having high round-trip delay and limited bandwidth, or as a FEC segment of an integrated FEC-ARQ strategy.

Two edge-preserving segmentation algorithms for multiband images are proposed in this paper. In particular, when dealing with multipolarization SAR data, adaptive neighborhood structures are selected for modelling polarimetric complex amplitudes and region labels, and for achieving detail-preservation. Experimental results show that the novel schemes produce significant visual improvements for detail preservation, and exhibit equivalent or higher classification performance with respect to the classical classification schemes. These results have been obtained from multiband, polarimetric SAR SIR-C data, selected for archaeological application studies.

Digital high-definition TV (HDTV) signals are generally compressed to reduce transmission bandwidth requirements. A compression algorithm for the bit rate reduction of an HDTV image using the wavelet transform is presented. The major problems related to the transmission of a compressed HDTV signal are analyzed. Transmission is examined both on a noisy channel and an asynchronous transfer mode (ATM) network. The effects of channel noise on the reconstructed image are determined, and a solution to mitigate the degradation of the image quality is presented. A model for the output bit rate of the HDTV coder is derived and used to simulate the transmission of an ATM multiplexer so that the network's main performance parameters can be determined.>

Some new schemes for communication systems using error-detecting codes are described. These schemes use hybrid strategies for the retransmission of the codewords detected in error, and combine the advantages of the go-back-N and selective protocols. The memory, introduced at the receiver side, enhances their performance with respect to the classical schemes. The results show that the protocols described provide a net improvement with respect to other similar schemes.>

Two automatic-repeat-request (ARQ) protocols using a concatenated coding scheme are described. The structure, introduced in a codeword of a concatenated coding scheme, is used to improve the performance of ARQ protocols, especially for high error rates in the communication channel. The performance of the scheme described herein is derived through theoretical analysis. The results show that the proposed scheme outperform other similar ARQ protocols.>

Of the automatic-repeat-request (ARQ) techniques commonly used in communication systems, selective protocols, while the most efficient, have the notable drawback of requiring large buffers at the receiver side. A selective ARQ protocol with a finite-length buffer is described. If N is the number of codewords transmittable in the round-trip delay, the protocol requires a buffer length N+N/sub a/, N/sub a/>or=2 being an integer. A lower bound on the throughput of the protocol is derived. It achieves higher throughputs than similar schemes giving results comparable to those for selective protocols with infinite-length buffer for high error rates in the communication channel.>

A method for the integration of the modulation operation in an automatic-repeat-request (ARQ) scheme is described. This method uses a memory for the successive transmissions of a codeword and, through a suitable encoding operation, the Euclidean distances among the codewords are significantly increased with the number of transmissions. The application of the described method to some different modulation schemes, such as M-ary PSK with M>2 and continuous-phase frequency shift keying modulation, is described. The optimum combination of the modulation and channel coding operations for some short block codes is also presented. The results of the theoretical analysis show that the method described permits improving both the error probability and the throughput of an ARQ protocol with respect to similar schemes.>

In this paper results of investigations about the effects of channel errors in the transmission of images compressed by means of techniques based on Discrete Cosine Transform (DCT) and Vector Quantization (VQ) are presented. Since compressed images are heavily degraded by noise in the transmission channel, more seriously for what concern VQ-coded images, theoretical studies and simulations are presented in order to define and evaluate this degradation. Some channel coding schemes are proposed in order to protect information during transmission. Hamming codes (7,4), (15,11) and (31,26) have been used for DCT-compressed images; more powerful codes, such as Golay (23,12), for VQ-compressed images. Performances attainable with soft- decoding techniques are also evaluated; better quality images have been obtained than using classical hard decoding techniques. All tests have been carried out to simulate the transmission of a digital image from HDTV signal over an AWGN channel with PSK modulation.

In classical diversity techniques used in combating fading and in spread-spectrum systems, the same information is transmitted over m>or=2 channels, and the overall error probability is reduced by a suitable combination of the m received signals. Two techniques are proposed whereby the signals transmitted over the m channels corresponding to a given message can be encoded through a suitable error-correcting coding operation, thereby enhancing reductions in the receiver-side bit error probability with respect to classical diversity techniques. Gains have also been achieved by introducing a soft decoding operation at the receiver side and, in spread-spectrum systems, by adding side information. Applications to fading-affected communication systems and spread-spectrum systems are discussed.>

In this paper, the integration of the modulation operation in an automatic-repeat-request scheme, using error-detecting codes, is analyzed. A new protocol is described, in which the modulation operation facilitates the recovery of the transmitted code word. The results show a net improvement in the throughput of the automatic-repeat-request scheme, particularly for mean and high error-rate conditions. Continuous-phase-frequency shift keying modulations, which present a low bandwidth occupancy, are particularly considered.

The integration of channel coding and modulation in a communication system to increase the Euclidean distance between modulated signals is analyzed. Systems using binary continuous-phase frequency-shift keying modulation and some block codes, such as Hamming codes and shortened Hamming codes, are considered. It is shown that the minimum Euclidean distance depends on the configuration of the parity-check matrixHof the code. For the examined codes the optimum configurations ofH, which give the maximum values of the minimum Euclidean distance, are determined.

This paper describes a technique for increasing the efficiency of an ARQ communication system utilizing error detection codes. In this technique the blocks containing errors are not discarded at the receiver, as in the conventional ARQ systems. Such blocks are retained in order to make use of the information contained in them. A reliability value is associated to each demodulated symbol; this reliability value is updated every time a new retransmission is made, even if the vector received is in error. The process of updating the symbols often eliminates automatically the errors introduced by the channel. The results obtained by means of a simulation show that this method offers a considerable reduction in the average number of retransmissions, in comparison with conventional ARQ systems.

In this paper a complete communication system simulation package is described, which includes digital as well as analog operations to be performed on the signal to be transmitted. The package simulates the transmitter, the communication channel, and the receiver. The digital transmission simulation considers data communication systems with digital filtering, source and channel coding performing the operations of transmitter coding and receiver decoding. The two coding operations can be realized both separately and independently and in a strictly connected or "integrated" form. The analog transmission simulation includes the modulator, the transmitter pulse shaping filter, the communication channel, the receiving filter, and the demodulator. This section is very general, so that it allows the simulation of both analog and digital transmissions. Simulation results are presented regarding some combinations of the following techniques: predictive source coding, block codes able to correct random and burst errors, and modulation techniques such as AM,M-level PSK, FSK, and MSK. In particular, the paper presents the results of the analyses of an integrated source-channel coding applied to digital transmissions and of a system transmitting both voice and data for a VHF communication link between ground and aircraft for air traffic control applications.

In this work, a combined amplitude-phase modulation communication system is considered. Amplitude modulation is used to transmit a voice signal, and phase modulation is used for data transmission. Such a scheme was studied as a possible realization of a data channel between aircraft and ground station, which can be introduced without great modifications of the actual on-board equipment. The performance of the combined modulation system is evaluated through a computer simulation.

In this paper we present a class of burst-error-correcting binoid codes derived from Samoylenko's codes. These codes, at high code rate, seem to be very useful for a not-too-noisy transmission channel when the encoding-decoding operations are performed by means of a general purpose computer.