By Ibrahim Habib and Franco Mazzenga, Guest Editors Wireless communications for public safety, emergency communications, and delivery of wideband services to rural communities are topics of crucial importance to the welfare of the society. Broadband wireless digital subscriber loop (WDSL) technologies offer complementary and possibly low cost solutions to providing broadband connectivity services even to low densely populated areas that otherwise would be outside the loop. At the same time the availability of broadband wireless technologies can be useful for effective information dissemination in times of natural and man-made disasters thus providing a fundamental tool helping public safety agencies in providing quick response and support to communities needing urgent assistance and relief. The topic has been largely investigated (e.g. see references 1-6 and references therein) during the last two decades. The quality of communications services offered by the actual public safety systems is in general well behind of that offered by commercial systems. At the same time, due to costs of radio coverage and trunking, the quality of services provided by existing commercial mobile systems in low densely populated areas, e.g. rural areas, is well below that offered by operators in urban and sub-urban areas. Current solutions for rural areas for example provide basic telephone services and only are rarely suitable for effective data access. Some rural areas that are close to natural woods with dry climates are prone to fires that could be disastrous. Reliable emergency communications systems should be adequately available with access to the residents in order for emergency authorities to be able to respond to such natural disasters, as quickly as possible, if they occur. The society obvious need for new and advanced communications services for supporting public safety operations has led to the evolution of current systems towards a new generation of professional mobile radio (PMR) and standard communication systems. Terrestrial Trunked Radio (TETRA) technology has gained wide acceptance (especially in Europe) and is considered one of the mature technologies for PMR and even for PAMR (Public Access Mobile Radio) markets. TETRA has been conceived in accordance to the requirements issued by public safety agencies such as ambulance services, law enforcement, civil emergency management/disaster recovery, fire services, coast guard services, search, and rescue services, government administrations and so forth. In recent years it has been observed that integration between mobile broadband technologies and TETRA can be helpful for the achievement of the advanced services envisioned for the next generation of Public Safety and Disaster Recovery (PSDR) communication systems. In fact, data rates required for advanced emergency services provisioning plus the demand for enhanced mobility improved ad hoc functionality, and international interoperability reach far beyond the scope of the current PSDR narrowband telecommunication systems and call for mobile broadband enhancements. A significant challenge faced by professionals conducting public protection and disaster relief operations is the problem of incompatible communications systems. The goal of the MESA project established between the ETSI and the TIA (www.projectmesa.org) 7 was to develop advanced mobile broadband technical specifications that could solve interoperability issues among different communication technologies and to define enhanced functionalities of the public safety communication (PSC) systems. One task of this special issue is to address the integration of current PMR systems with 3G and 4G technologies for providing enhanced communication services including real time access to (local) sensor networks (if any) as well as to databases for retrieving and distributing audio, video, and geographical information. This could be important during an emergency operation where a large amount of contextual information is generated and need to be distributed wirelessly to personnel from different emergency agencies 8, 9. In parallel, on the commercial side for civilian applications, access to broadband communication services has become an established, global commodity required by a large percentage of the population. It is widely recognized in developed countries that the setting up broadband wireless access networks is helpful to solve the “digital divide” gap. Efforts to bringing mass-market broadband services even to low densely populated areas such as the rural ones follow the initiative of the European Commission called Bridging the broadband gap which is intended to carry high-speed broadband internet to all Europeans and in particular to EU's less-developed areas. WDSL systems, even supporting mobile and nomadic users, that are based on the Worldwide Interoperability for Microwave Access (WIMAX) and other technologies such as the Rural WCDMA (which is an effective solution to rapidly extend UMTS to rural areas) can play a significant role in the broadband wireless access market. Furthermore it should be observed that rural broadband access is not limited to Europe but it represents a common global challenge. The R-WCDMA and WiMAX technologies seem to be promising solutions for the provisioning of broadband services to rural areas. They can easily incorporate all the technical solutions to improve the link budgets and, very importantly, allow the re-use of already existing wireless terminals (at least for R-WCDMA). In general, it is well known that networks for rural coverage could be constructed from the integration of more than one communication technologies such as satellite, terrestrial and high altitude platforms (HAPs) (if any). In this case, techniques for the intelligent use of the available radio technologies could help reducing deployment costs and improving spectrum usage. Alternatives for broadband access could be based on structured terrestrial networks adopting (possibly cheap) techniques for enlarging the cell coverage area of a single base station deployed for offering point-to-multipoint (PMP) services. These solutions include relay stations and/or distributed (sub)-networks organized in a mesh or ad-hoc that are connected to the base station which, in turn, provides access to the core network. This special issue includes a number of interesting papers covering different aspects of emergency and rural communications systems. Some of the topics discussed in this special issue include: hybrid network architectures comprising satellite and HAPS for covering rural areas as well as for supporting emergency situations; integration of heterogeneous communication networks; protocols for ad-hoc, mesh, and VANET networks. The problems of information dissemination during emergency and localization are also analyzed. Finally, we would like to thank the authors who presented their work, the reviewers for their meticulous reviews, and the editor-in-chief and the editorial staff of the Journal for their excellent efforts and support producing this special issue. Ibrahim Habib received the Ph.D. degree from the City University of New York, the M.Sc. degree from Polytechnic University of New York, USA, and the B.Sc. degree from Ain Shams University, Cairo, Egypt all in Electrical Engineering. In 1991 he joined the Faculty of the City University of New York where is now a Full Professor. His research interests span different areas of traffic engineering in IP, wireless, and optical networking. He has published more than 100 papers and reports in those areas. From 1998 till 2000 he was with AT&T Labs, and from 2000 till 2001 with Telcordia Technologies, Applied Research Department working on the architecture design of IP over optical networks, optical control plane and Operations Support Systems (OSS). He was a Guest Editor of the IEEE Journal on Selected Areas in Communications (JSAC), the IEEE Communications Magazine and was an Editor of the same Magazine. He was chair of many technical sessions, symposia and conferences. He is listed in many Marquis's who is who in the World and who is who in America editions. Franco Mazzenga received the Dr. Ing. degree in electronics engineering cum laude from the University of Rome Tor Vergata, Italy in 1993. From 1993 to 1994 he was with Fondazione Ugo Bordoni making research on the propagation at millimeter waves. In 1997 he obtained the Ph.D. degree in telecommunications from the University of Rome Tor Vergata. From 1998 to 2000 he was a researcher in Consorzio di Ricerca in Telecomunicazioni (CoRiTel). From 2000 to 2006 he was a researcher in the Electronic Engineering Department of the University of Rome Tor Vergata. Currently he is an associate professor of communications in the same department. Since 2001 he is the technical director of the Consorzio Università Industria Laboratori di Radiocomunicazioni (Radiolabs - http://www.radiolabs.it). He is the author and co-author of more than 90 scientific papers that have been presented on congresses or published on national and international journals. He is co-author of a book on Radar systems (in Italian) and co-author of four patents on communication technologies and applications. His research interests are on wireless access systems and networks and related technologies, GNSS systems and complex network theory applied to communication systems.

The 16 articles in this special issue report cutting-edge research achievements in the field of applications of Networks for Healthcare.

In this paper, we study the problem of maintaining fairness for TCP connections in wireless local area networks (WLANs) based upon the IEEE 802.11 standard. Current implementations of 802.11 use the so-called distributed coordination function (DCF), which provides similar medium access priority to all stations. Although this mode of operation ensures fair access to the medium at the MAC level, it does not provide any provisions for ensuring fairness among the TCP connections. TCP unfairness may result in significant degradation of performance leading to users perceiving unsatisfactory quality of service. We propose and analyze two solutions that are capable of enabling TCP fairness with minimal additional complexity. The proposed solutions are based on utilizing a rate-control mechanism in two modes: static or adaptive. They do not require modifying existing standards at the MAC or network layers. Hence, they are fully compatible with existing devices. Our performance analysis results prove the efficaciousness of our proposed solutions in achieving TCP fairness compared to existing approaches. We have, also, implemented the proposed solutions in an ad-hoc experimental test-bed, and performed measurements to demonstrate the validity of our approach and results

In this paper, we describe the design and implementation of a GMPLS software engine that is used to enable non-GMPLS switches (e.g., Ethernet switches, routers and other cross-connects) to participate in the dynamic setup and release of end-to-end bandwidth guaranteed connections. We have deployed this engine in the experimental Cheetah optical network, and hence we call it the Cheetah Virtual Label Switching Router (CVLSR). It allows users to share the network resources dynamically and makes it possible to extend the connections across the local area network to the end-users. The CVLSR engine is also equipped with a function called dynamic network clustering which is needed to enable a broad range of applications such as remote visualization, grid computing and e-learning. We have successfully demonstrated the inter-operability of the CVLSR with commercially available GMPLS enabled SONET-based cross-connect switches. The purpose of this paper is to share our experience in designing and deploying the CVLSR in the Cheetah network. We believe that these and similar efforts will result in significant progress towards enabling connection-oriented high performance networking.

In this article, we describe our experiences in implementing an experimental wide-area GMPLS network called CHEETAH (Circuit-Switched End-to-End Transport Architecture). The key concept is to add a complementary end-to-end circuit based service with dynamic call-by-call bandwidth sharing to the connectionless service already available to end hosts via the Internet. The current CHEETAH experimental network consists of off-the-shelf GMPLS-capable SONET switches (with Ethernet interfaces) deployed at three locations, Research Triangle Park, North Carolina, Atlanta, Georgia, and Oak Ridge, Tennessee. We designed and implemented a CHEETAH software package to run on Linux end hosts connected to the CHEETAH network. Among other functions, this software package includes an RSVP-TE client module to enable end users and applications to dynamically initiate requests for dedicated end-to-end circuits and receive/respond to requests for circuits. We present measurements for typical end-to-end circuit setup delays across this network. For example, end-to-end circuit setup delay from a Linux end host in NC to a host in Atlanta is 166ms.

This paper presents an adaptive filtering algorithm for the delivery of multimedia content with different quality of service (QoS) requirements, over wideband code-division multiple access (W-CDMA) networks. We assume that the service provider offers two distinct grades of service (GoS) to which users may subscribe: premium, or economy. Subscribers to the premium service receive higher quality levels measured by a set of parameters such as coding rate and format. The proposed algorithm guarantees that all users receive their contractual level of quality while maximizing the radio links' throughput, and maintaining the QoS requirements (e.g., target B.E.R, maximum transfer delay, and percentage of packets lost or delayed) for each media stream (e.g., voice, video, and data) downloaded to the users. Multimedia adaptation filters are installed at the output ports of the radio network controller. Simulation results show significant improvement in terms of increasing the number of admitted users while reducing the percentage of packets lost or delayed.

This paper proposes a novel packet scheduler for the high speed downlink packet access (HSDPA) air interface. In designing the scheduler we take in account two different user types and two distinct traffic classes. Our aim is to differentiate the quality of service and at the same time to achieve a high throughput and a fair allocation of resources among users. The performance of the proposed scheme is compared through simulations with other scheduling techniques (e.g., maximum SIR). This work is the outcome of a joint activity between the University of Siena and CUNY.

This paper investigates the efficiency of deploying distributed dynamic routing using the GMPLS control plane in optical transport networks. Our main objective is not to propose new protocols or algorithms, but rather to find the limitations of the existing GMPLS distributed dynamic routing implementation and quantify its value-added proposition. Thus, we could provide guidance to service providers to minimize the cost and maximize the savings. Some of our findings through NSFNET simulations reveal that a) for distributed dynamic routing to be effective traffic loads should be less than 0.8 Erlang/per-wavelength, the number of wavelengths in a bundled traffic engineering (TE) links should be less than 10. b) Distributed dynamic routing can save at least 15% wavelengths per link and increase the traffic loads by 20%

This paper deals with modifications to the current IEEE 802.11b distributed coordination function (DCF) protocol of the medium access control (MAC) to support service differentiation between premium and regular users. A volume-based revenue model has been integrated with our simulation tool to understand clearly the impact of different traffic classes and user types. This work has been carried out under a joint cooperation between the University of Siena and CUNY.

We address the problem of optimizing the delivery of multimedia services with different quality-of-service (QoS) requirements to mobile users. We assume that the network provides two distinct classes of service to which users may subscribe: Premium, or Economy. Subscribers to the Premium service pay more for their connections but receive a higher level of quality measured by a set of parameters such as call blocking probability, coding rate, and format of the multimedia services. By optimizing the delivery of the multimedia services, we mean that the network guarantees that all users receive their agreed-upon contractual level of quality, while maximizing the links' throughput, avoiding congestion, and maintaining the QoS requirements for each type of media (e.g., video, voice and data). Our proposed solution is based upon utilizing genetic algorithms to solve a multiobjective optimization function that adaptively selects the downloading bit-rate for each type of traffic flow subject to the constraints of the optimization function. A traffic flow is an abstract of aggregate traffic of the same type of media (e.g., voice, video, or data) that is downloaded to a group of users who share some common attribute such as the same class of service. The optimization function is adaptive in the sense that the selected downloading bit-rates are time-dependant according to the dynamics of the links' traffic-loads and users' requests. It is implemented on every output port of each node in the network. The function is used to control a filter that changes the coding rate of each media-type and, if necessary, performs transcoding of one, or more, media-types (i.e., video, voice, or data). Simulation results show significant improvement in terms of increasing the number of admitted users, while maintaining the QoS requirements, as well as target call blocking rates. An interesting result to report is that the performance improvement of the system (measured by the gain in the number of admitted users at a certain utilization factor) is not simply bounded by the maximum available link throughput. It is, rather, limited by the additional revenue gained by admitting more users. The increase in the revenue saturates at a certain offered traffic-load. Hence, it is not worth it, from a service provider perspective, to admit additional users above this traffic load despite the fact that the filtering algorithm results indicate otherwise.

It has been demonstrated that advertising the availability of wavelength and converter resources in all-optical DWDM transport networks with sparse wavelength conversion capabilities can drastically improve the blocking performance of these networks thus achieving better usage of the network resources. An important aspect with consequences in network performance is when to originate the wavelength-availability and converter-availability link state advertisements (LSAs). Frequent link-state advertisements could overwhelm the network control plane with many update messages that need to be processed. On the other hand, delaying these advertisements could result in inaccurate link-state information thus degrading the network blocking performance. In this paper, we propose two different link-state update policies to advertise the availability of wavelength and converter resource in all-optical DWDM transport networks with sparse wavelength conversion capabilities. The first one is very simple and serves as our base policy for comparison. The second policy, which is very efficient in handling the dynamic nature of all-optical DWDM networks with different degrees of wavelength conversion, reduces the number of LSAs considerably while maintaining the call blocking probability.

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 propose a novel wireless radio resource manager to control both the transmission power and the bit rate of mobile devices cooperatively, whereas previous work has focused on handling them separately. The proposed scheme is called Genetic Algorithm for Mobiles Equilibrium (GAME). Based on an evolutionary computational model, GAME assigns optimally both the transmitting power and bit rate values to every mobile device in a given cell. Optimal allocation is in the sense that every mobile unit gets only enough resources necessary for meeting or exceeding its quality of service (QoS) requirements. GAME solves an optimization function that strives to maintain the QoS requirements of the different multimedia streams subject to the physical channel characteristics. Having done that, we gain further benefits as well. In addition to maintaining the QoS requirements, GAME tends to prefer assigning lower levels of transmission power, thus extending the mobile units' battery life, minimizing interference seen by other users, and significantly decreasing the call blocking (or dropping) rates. Furthermore, GAME radio resource allocations reduce infrastructure costs by requiring fewer base stations per square kilometer. In our experiments, we have seen a 70% average expansion in the base station coverage area with 40% decrease in mobile call outage probability among other benefits.

Abstract Ultra Wide Bandwidth (UWB) techniques are getting an increased importance due to their many features such as high bit rates availability, low power consumption and location capabilities. UWB technology enables the development of advanced wireless local area networks providing integrated multimedia services to nomadic users over hot‐spot areas. The assessment of the possible interference caused by UWB devices on already existing narrowband and wideband systems is fundamental to ensure not‐conflicting coexistence and, therefore, the acceptance of UWB technology worldwide. In this paper we analyze coexistence between an indoor UWB system and an outdoor fixed wireless access (FWA) system operating in the 3.5–5.0 GHz band. We consider a realistic UWB master/slave system architecture using pulse amplitude modulated spread spectrum signals for multiple access and we evaluate the UWB system interfering power in the FWA band accounting for the UWB power spectrum shape. Both upstream and downstream communication directions are analyzed. We show through computer simulation, that in many practical cases UWB system can coexist with FWA without causing any dangerous interference. Copyright © 2004 John Wiley & Sons, Ltd.

In this paper, we present an adaptive filtering strategy for improving the delivery of multimedia services with guaranteed quality of service (QoS) on an end-to-end basis. Multimedia content is downloaded along an integrated wired/wireless network from media servers to mobile end-users. The proposed strategy assures that the network resources (e.g. capacities, buffer) are efficiently utilized and the QoS requirements (e.g. delay bandwidth) of two different classes of end-users are always respected as traffic flows in downstream. This objective is achieved by filtering, in each node of the network, the amount as well as type of content downloaded such that possible congestion episodes are avoided and the downloading speed of content is maintained. According to the proposed strategy, filters are able to select the bit-rate values required to download traffic by adaptively scaling the coding rate and, if necessary, transcoding media streams. The action performed by each filter is controlled by an optimization function that is implemented in our proposed resource manager. Simulation results demonstrate that the filtering strategy has significantly decreased the call-blocking rate while maintaining users QoS requirements and maximizing network capabilities.

We consider the combined control of mobile stations' transmitter power and bit rate in a CDMA microcellular environment. The objective is maximizing the number of QoS-satisfied mobile users in conjunction with minimizing network infrastructure cost. We first review the challenges associated with microcells and user mobility in a Manhattan-like street grid. Next, we discuss the additional aid offered by the combined scheme over the power-only method in utilizing the scarce radio resources efficiently. We demonstrate through link-level and system-level simulations the significant enhancements over the established power-only control scheme. Both coverage and spectrum efficiencies are improved for voice/data services having diverse QoS requirements.

This paper investigates and compares the performance of two generalized multiprotocol label switching (GMPLS)-based distributed control and management protocols for dynamic lightpath provisioning in future IP networks. The first protocol is a global information-based link state approach that consists of both an integrated RWA (routing and wavelength assignment) algorithm and a signaling algorithm. Two triggering mechanisms for LSA (link state advertisement) update procedures are considered; one is a periodically-based update and the other is a threshold-based update. The second protocol is a local-information based fixed alternate link routing approach where the signaling protocol is closely integrated with the RWA protocols.

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.

The purpose of this work is to show the benefits gained by dynamically provisioning low-rate traffic streams at the IP/MPLS layer in future IP-centric WDM-based optical networks. First, several low-rate data flows are statistically multiplexed (groomed) onto one wavelength at the IP/MPLS router. Then, conventional dynamic lightpath provisioning schemes at the physical WDM layer, where the bandwidth of a connection request is assumed to be a full wavelength capacity, are extended to allow the provisioning of "sub-lambda" connection flow requests at the IP/MPLS layer. In this work, provisioning a connection request implies that a flow of data is successfully routed if both an active path and another alternate link and node-disjoint backup path are setup at the same time.

We propose an algorithm for controlling mobile users transmitter power and information bit rate cooperatively in CDMA networks. The active component of this scheme is called genetic algorithm for mobiles equilibrium (GAME). Based an an evolutionary computational model, the base station tries to achieve an adequate equilibrium between its users. Thereof each mobile can send its traffic with a suitable power to support it over the different path losses and interference. In the mean time, its battery life is being preserved while limiting the interference seen by neighbors. This optimization is based on each user traffic, required signal quality, the channel characteristics and users spatial distribution. A significant enhancement in signal quality and power level has been noticed through several experiments.

We consider the combined control of mobile stations' transmitter power and bit rate in CDMA microcells. The objective is to maximize the number of QoS-satisfied mobile users. We discuss the additional aid offered by the combined scheme over the power-only method in utilizing the scarce radio resources efficiently. Next, we review the problems associated with the microcellular environment and users' mobility in a Manhattan-like street grid. We demonstrate through system level simulations the significant enhancements over the established power-only control scheme. Both spectrum efficiency and system capacity are improved for multimedia services having diverse QoS requirements.

In wireless ATM-based networks, admission control is required to reserve resources in advance for calls requiring guaranteed services. In the case of a multimedia call, each of its substreams (i.e., video, audio, and data) has its own distinct quality of service (QoS) requirements (e.g., cell loss rate, delay, jitter, etc.). The network attempts to deliver the required QoS by allocating an appropriate amount of resources (e.g., bandwidth, buffers). The negotiated QoS requirements constitute a certain QoS level that remains fixed during the call (static allocation approach). Accordingly, the corresponding allocated resources also remain unchanged. We present and analyze an adaptive allocation of resources algorithm based on genetic algorithms. In contrast to the static approach, each substream declares a preset range of acceptable QoS levels (e.g., high, medium, low) instead of just a single one. As the availability of resources in the wireless network varies, the algorithm selects the best possible QoS level that each substream can obtain. In case of congestion, the algorithm attempts to free up some resources by degrading the QoS levels of the existing calls to lesser ones. This is done, however, under the constraint of achieving maximum utilization of the resources while simultaneously distributing them fairly among the calls. The degradation is limited to a minimum value predefined in a user-defined profile (UDP). Genetic algorithms have been used to solve the optimization problem. From the user perspective, the perception of the QoS degradation is very graceful and happens only during overload periods. The network services, on the other hand, are greatly enhanced due to the fact that the call blocking probability is significantly decreased. Simulation results demonstrate that the proposed algorithm performs well in terms of increasing the number of admitted calls while utilizing the available bandwidth fairly and effectively.

ATM supports a wide range of multimedia traffic. While ATM provides increased flexibility in supporting various types of traffic the traffic control problems become more difficult to solve when trying to achieve efficient use of network resources. One of such problem is the bandwidth allocation. This paper presents a new approach to the bandwidth allocation problem for video traffic using radial basis functions neural networks (RBFNN). Estimation of an accurate amount of bandwidth to support this traffic has been a challenging task using conventional algorithmic approaches. In this paper, we show that a radial basis function neural network (RBFNN) is capable of learning the non-linear multi-dimentional mapping between different multimedia traffic patterns quality of service (QoS) requirements and the required bandwidth to support each call. Our method employs "on-line" measurements of the traffic count process over a monitoring period which is determined such that the error in estimating the bandwidth is minimized to less than 3% of the actual value. In order to simplify the design of the RBFNN, the input traffic is preprocessed through a low pass filter in order to smooth all high frequency fluctuations. A large set of training data, representing different traffic patterns with different QoS requirements, was used to ensure that RBFNN can generalize and produce accurate results when confronted with new data. The reported results prove that the neurocomputing approach is effective in achieving more accurate results than other traditional methods, based upon mathematical or simulation.

In this paper we propose a generic call admission control scheme based on genetic algorithms. The scheme is applied to a wireless network using an adaptive resource allocation framework. A multimedia connection is represented in terms of three substreams (video, audio and data) each with a pre-specified range of acceptable quality of service (QoS) requirements. This range of requirements make the application adaptive in the sense that each of its substreams specify to the network a number of acceptable QoS levels instead of just a single one. For example, MPEG-based video can be transmitted at different levels of varying qualities. As resource availability in the wireless network changes, the control scheme selects the best possible QoS level that each substream can obtain for a certain period of time. In case of congestion, the control scheme attempts to free up some wireless resources by degrading the QoS of existing calls to a lesser level in order to accommodate new calls. This is done, however, under the constraint of achieving maximum utilization of the resources; and sharing them fairly among the calls. The degradation in the QoS is limited to a minimum value for each multimedia substream defined in a user-defined profile. From the user perspective, the perception of the QoS degradation is very graceful and happens only during over-load periods. The network services, on the other hand, are greatly enhanced due to the fact that the call blocking probability is significantly decreased. Genetic algorithms have been used to solve the optimization problem. Simulation results for a wireless ATM network demonstrate that the proposed scheme performs well in terms of increasing the number of calls admitted while effectively utilizing the available bandwidth fairly among the calls.

Multimedia traffic measurements for determining spatial correlation in videoteleconference sessions over a CSMA/CD LAN are performed and the results are presented in this paper. Since packet arrival streams are both correlated and bursty, we present the analysis of the cross-correlation characteristics between the number of arriving audio and video packet batches in discrete-time slots. The results of this experimental study can be extended to WAN environments such as ATM. If cross-correlation among monomedia streams is not properly taken into account, it can severely impact network performance.

We propose a new neurocomputing call admission control (CAC) algorithm for asynchronous transfer mode (ATM) networks. The proposed algorithm employs neural networks (NNs) to calculate the bandwidth required to support multimedia traffic with multiple quality-of-service (QoS) requirements. The NN controller calculates the bandwidth required percall using on-line measurements of the traffic via its count process, instead of relying on simple parameters such as the peak, average bit rate and burst length. Furthermore, to enhance the statistical multiplexing gain, the controller calculates the gain obtained from multiplexing multiple streams of traffic supported on separate virtual paths (i.e., class multiplexing). In order to simplify the design and obtain a small reaction time, the controller is realized using a hierarchical structure of a bank of small size, parallel NN units. Each unit is a feed-forward back-propagation NN that has been trained to, learn the complex nonlinear function relating different traffic patterns and QoS, with the corresponding received capacity. The reported results prove that the neurocomputing approach is effective in achieving more accurate results than other conventional methods that are based upon mathematical or simulation analysis. This is primarily due to the unique learning and adaptive capabilities of NNs that enable them to extract and memorize rules from previous experience. Evidently such unique capabilities poise NNs to solve many of the problems encountered in the development of a coherent ATM traffic management strategy.

In the near future, high speed integrated networks, employing asynchronous transfer mode (ATM) cell switching and multiplexing technique, will be used to provide new and diverse mixture of services and applications. Multimedia teleconferencing, video-on-demand, television broadcasting, and distant learning are some examples of these emerging services. The ATM technique is based on the principle of statistical multiplexing, which is flexible enough to support different types of traffic while providing efficient utilization of the network's resources. New classes of techniques such as neural networks and fuzzy logic have many adaptive, learning and computational capabilities that can be utilized to design effective traffic management algorithms. The subject of this paper is to demonstrate how such neurocomputing techniques can be used to address ATM traffic management issues such as traffic characterization, call admission control, usage parameters control and feedback congestion control.

ATM has been recommended by the CCITT as the transport vehicle for the future B-ISDN networks. In ATM-based networks, a set of user declared parameters that describes the traffic characteristics, is required for the connection acceptance control (CAC) and traffic enforcement (policing) mechanisms. At the call set-up phase, the CAC algorithm uses those parameters to make a call acceptance decision. During the call progress, the policing mechanism uses the same parameters to control the user's traffic within its declared values in order to protect the network's resources and avoid possible congestion problems. A novel policing mechanism using neural networks (NNs) is presented. This is based upon an accurate estimation of the probability density function (pdf) of the traffic via its count process and implemented using NNs. The pdf-based policing is made possible only by NNs because pdf policing requires complex calculations, in real-time, at very high speeds. The architecture of the policing mechanism is composed of two interconnected NNs. The first one is trained to learn the pdf of "ideal nonviolating" traffic, whereas the second is trained to capture the "actual" characteristics of the "actual" offered traffic during the progress of the call. The output of both NNs is compared. Consequently, an error signal is generated whenever the pdf of the offered traffic violates its "ideal" one. The error signal is then used to shape the traffic back to its original values.>

Accurate characterization of the multimedia traffic is essential, in asynchronous transfer mode (ATM) broadband networks, in order to develop a robust set of traffic descriptors. Such a set is required, by the usage parameter control (UPC) algorithm, for traffic enforcement (policing). The authors present a novel approach to characterize and model the multimedia traffic using neural networks (NNs). A backpropagation NN is used to characterize and predict the statistical variations of the packet arrival process resulting from the superposition of N packetized video sources and M packetized voice sources. The accuracy of the results is verified by matching the index of dispersion for counts (IDC), the variance, and the autocorrelation of the arrival process to those of the NN output. The results show that the NNs can be successfully utilized to characterize the complex nonrenewal process with extreme accuracy.>

Variable bit rate (VBR) coding techniques have received great research interest as very promising tools for transmitting bursty multimedia traffic with low bandwidth requirements over a communication link. Statistically multiplexing the multimedia bursty traffic is a very efficient method of maximizing the utilization of the link capacity. The application of computer simulation techniques in analyzing a rate-based access control scheme for multimedia traffic such as voice traffic is discussed. The control scheme regulates the packetized bursty traffic at the user network interface of the link. Using a suitable congestion measure, namely, the multiplexer buffer length, the scheme dynamically controls the arrival rate by switching the coder to a different compression ratio (i.e., changing the coding rate). VBR coding methods can be adaptively adjusted to transmit at a lower rate with very little degradation in the voice quality. Reported results prove that the scheme greatly improves the link performance, in terms of reducing the probability of call blocking and enhancing the statistical multiplexing gain.>