Showing papers in "IEEE Communications Magazine in 1995"

The software radio architecture

Abstract: As communications technology continues its rapid transition from analog to digital, more functions of contemporary radio systems are implemented in software, leading toward the software radio. This article provides a tutorial review of software radio architectures and technology, highlighting benefits, pitfalls, and lessons learned. This includes a closer look at the canonical functional partitioning of channel coding into antenna, RF, IF, baseband, and bitstream segments. A more detailed look at the estimation of demand for critical resources is key. This leads to a discussion of affordable hardware configurations, the mapping of functions to component hardware, and related software tools. This article then concludes with a brief treatment of the economics and likely future directions of software radio technology. >

Transmission techniques for digital terrestrial TV broadcasting

Abstract: The authors discuss the potential of OFDM signaling, with its limitations and inherent problems, as well as another potential technique that has so far been overlooked: single-carrier transmission with frequency-domain equalization. The carrier synchronisation issue is dealt with before the authors introduce coded-OFDM (COFDM), which makes use of channel coding and frequency-domain interleaving. >

Propagation measurements and models for wireless communications channels

Abstract: The authors describe the type of signals that occur in various environments and the modeling of the propagation parameters. Models are essentially of two classes. The first class consists of parametric statistical models that on average describe the phenomenon within a given error. They are simple to use, but relatively coarse. In the last few years a second class of environment-specific models has been introduced. These models are of a more deterministic nature, characterizing a specific street, building, etc. They are necessarily more time consuming to use, but are also more revealing concerning physical details and hopefully more accurate. Some key parameters and the measurement of them are discussed and then the different wireless environments are treated. The latter topic is divided into outdoor environments, indoor environments, and radio penetration from outdoor to indoor environments. >

Spread spectrum access methods for wireless communications

Abstract: The authors present an overview of the characteristics of code division multiple access (CDMA) as it is currently being envisioned for use in wireless communications. There are many considerations in the design of such systems, and there are multiple designs being discussed. CDMA has been proposed for both terrestrial links and satellite links. However, there are key differences in the characteristics of the two types of links relative to the way they affect a CDMA system. The authors show how the ideas presented affect both terrestrial and satellite-based systems. >

Overview of wireless personal communications

Abstract: This article presents an overview of the current state of wireless communications, including relevant ongoing activities in technology development, standards, and spectrum allocation. The authors discuss cellular radio, cordless telephony, and wireless data systems. Ongoing and planned future developments are summarized. The presentation is oriented toward broad coverage rather than technical depth. However, brief discussions of the air interfaces for existing digital cellular and digital cordless systems are provided, because the air interface bears heavily on system capacity and the environments in which the system can be used, as well as on the cost and complexity of the equipment. >

Time division multiple access methods for wireless personal communications

Abstract: Time division multiple access (TDMA) is a classic approach to multiple access in digital cellular wireless communications systems. The authors summarize a number of frequency and time slot allocation techniques for enhancing the capacity and flexibility of TDMA-based systems. They also describe how the problems of fading, delay spread, time variability and interference affect TDMA systems, and how they may he countered and even exploited by appropriate techniques of detection, diversity, coding, adaptive equalization and slow frequency hopping (FH). It is worth emphasizing that the use of one of these techniques, slow random FH, results in a system that is in effect a hybrid of TDMA and code division multiple access (CDMA). >

Speakeasy: the military software radio

Abstract: The Speakeasy Phase II radio will use programmable processing to emulate more than 15 existing military radios. Speakeasy is a challenge, even with recent advancements in DSP technologies. The benefits, however, make the challenge highly worthwhile. >

Analog-to-digital converters and their applications in radio receivers

Abstract: Rapid advances in hardware development of analog-to-digital converters (ADCs) have paved the way for development of radio receivers using digitization at the IF, and in some cases, at the RF. The constraints placed on these receivers due to hardware limitations of these devices are discussed and some examples of high-speed, state-of-the-art ADCs are given. >

The DSP bottleneck

Abstract: The stumbling blocks in development of a commercially usable software radio have been the availability of hardware, in particular the fast DSP required. As high performance ADCs have become available commercially, with the sample rates and spurious free dynamic ranges required, hybrid techniques using specialized digital hardware, operating under software control, have become more common. >

Emerging technologies for fiber network survivability

Abstract: Reducing network protection costs, while maintaining an acceptable level of survivability, has become an important challenge for network planners and engineers. This article will review technology and architectures that may be used to implement cost effective survivable fiber networks for each transport layer, and discuss the interworking system between survivability mechanisms across different layers and associated open issues. Standards development, product availability and the current status of deployment will also be reviewed. The first section reviews a class of survivable fiber network architectures that has been deployed or is scheduled to be deployed. Next is a review of emerging technologies for these survivable architecture implementations. These emerging technologies include SONET, ATM, and passive optical technology. Finally the issue of multiple layer interworking on SONET/ATM networks is discussed. >

Direction finding and "smart antennas" using software radio architectures

Abstract: Operational tests and demonstrations of systems based on software radios are currently being performed in the 800 MHz mobile cellular radio band. These field trials are for mobile unit geolocation systems and adaptive phased array "smart antenna" applications. The geolocation system trials are in response to the demand for high confidence geolocation of mobile units for enhanced emergency 911 service and for use in the US Department of Transportation's Intelligent Vehicle Highway System (NHS) initiative. The smart antenna array application addresses the cellular service providers' need for more user channel capacity and/or geographic coverage from existing base station installations. Software radio architectures were selected because of their ability to provide superior performance at low life cycle cost. These systems use 4 to 8 wideband coherent channels and fully characterize the arriving RF energy to either geolocate the emitter or to maximize the carrier-to-interference ratio. >

Network issues for wireless communications

Abstract: This article specifically focuses on wireless personal communications, i.e., wireless access, that provides either terminal or personal mobility. In particular, we discuss some important issues in networking, traffic, and performance. Although within radio and networking aspects there are significant commonalities between traditional cellular mobile communications and wireless personal communications, there exist distinct differences due to radio propagation and fading effects, interference environment, smaller cell sizes, type and pattern of mobility, and call delivery. Indeed, with respect to networking issues, a large set of system choices, characteristics of traffic to be carried, and important parameters have to be considered. These include the problems involved in selecting an appropriate multiaccess technology to efficiently handle the required subscriber service profile across a multiplicity of systems to complete a call. To present a meaningful discussion of these issues, we address in some detail radio resource assignment, mobility management, call control, and traffic aspect, which have significant impact on the network performance. >

ADSL: a new twisted-pair access to the information highway

Abstract: The asymmetric digital subscriber line (ADSL) takes advantage of the existing twisted-pair copper loop that currently provides customer access to the telephone network. An ADSL modem is placed at each end of the loop to create a high speed access link above the existing telephone service. Since ADSL makes use of the existing copper telephone line, its application in the telephone network can conceivably be nearly as ubiquitous as the public telephone network itself. With ADSL, it is possible to connect small numbers of customers to broadband services in areas where full upgrade to hybrid fiber coaxial or fiber facilities is not economical in the near term. ADSL systems offer a means to introduce broadband services using the embedded base of metallic loops in areas where optic fiber-based, hybrid fiber-coaxial radio systems or other broadband transport systems may not be scheduled for deployment in time to meet business needs and customer demand. The article concentrates on ADSL systems capable of at least a nominal 6 Mb/s payload transport toward the customer, in addition to associated upstream channels and symmetrical "telephony" services via nonloaded loops that comply with carrier serving area design guidelines. >

Trends in local wireless networks

Abstract: Pahlavan (1985) published an article entitled "Wireless office information networks". That article examined spread spectrum, standard radio and infrared (IR) technologies for intra-office wireless networking. In May of that year the FCC released the ISM (industrial, scientific, and medical) bands for spread spectrum local communications. Although ISM bands are not restricted to any specific application, wireless local area networks (LANs) were one of the most prominent applications that were envisioned by the rule makers in the FCC. Since 1985, many small start-up companies, as well as small groups in larger companies, have started to develop wireless LANs. The present paper provides a sequel to Pahlavan by providing an overview of the past and present of the wireless LAN industry, as well as a perspective of the future directions that encompass a vision for a ubiquitous local wireless computing environment that leads to a fusion of communications and computation. >

Dispersion compensation for optical fiber systems

Abstract: Much of the currently embedded optical fiber was originally designed for light with a wavelength of 1.3 microns. If this fiber is to be used with tomorrow's optically amplified, high-speed, long span-length lightwave system operating at 1.5 microns, the chromatic dispersion in the fiber must be compensated. Dispersion compensation will be required in long-haul l0 Gb/s systems using conventional fiber. Many compensation techniques have been demonstrated and they exhibit a variety of different and often complimentary properties. Transmitter compensation techniques are the most easily implemented but provide a limited amount of compensation. The most commercially advanced technique is negative dispersion fiber. Chirped Bragg gratings are advancing rapidly, but will always be hampered by their narrow bandwidth. The adoption of any particular technique for use in a high-speed network will depend on the constraints imposed by the, as yet, undefined network architecture. >

Emerging mobile and personal communication systems

Abstract: The market demand for wireless communications has been demonstrated by the rapid growth of different second-generation wireless technologies that are optimized for particular applications and environments. Obvious examples include: digital cellular systems like GSM, ADC, PDC,and DCS1800 for widespread vehicular and pedestrian services, and cordless telecommunication systems based on CT2, DECT, and PHS standards for residential, business, and public cordless access applications. Efforts are also underway to consolidate the various radio environments and applications under a single standard for third generation wireless, i.e., FPLMTS. In the area of personal mobility, with the recent availability of "personal" numbers in various countries (e.g., 500 numbers in the United States), many fixed network operators are starting to offer such personal mobility services as "personal number service" and "number portability". These services represent initial stages of full personal mobility that will be provided by UPT in both wireline as well as wireless environments. The expected heavy demand for PCS in the United States and the underlying market/regulatory forces are driving the standardization and business activity. A number of air interface standards for the 1900 MHZ PCS band are being considered, which are based on TDMA, CDMA, and FDMA technologies singly or in combination. Many are variations of existing digital cellular and cordless telecommunications technologies. PCS networking standards are also being developed; both for standalone systems and for systems that will utilize public switched network capabilities. >

Taking the next step beyond spectrum auctions: open spectrum access

Abstract: The author presents the case for a better to approach to spectrum use involving a pragmatic and searching fashion rather than with an ideological mind set that equates the free market with one and only one particular allocation technique Spectrum auctions are considered as an application for present times The author goes on to look at the future

The TINA consortium: toward networking telecommunications information services

Abstract: The Telecommunications Information Networking Architecture (TINA) Consortium is a multinational worldwide consortium, which aims at defining and validating an "open" architecture for telecommunications services in the emerging broadband, multimedia and "information super-highway" era. The architecture is based on distributed computing, object orientation, and other concepts and standards from the telecommunications as well as the computer industry, e.g., ODP, IN, TMN, and CORBA. It is applicable to various networks, broadband (e.g., ATM) or narrowband. A large part of the TINA consortium's activity is devoted to validating the TINA architecture's current specifications through auxiliary projects, collaborative worldwide demonstrations, and implementations carried out by the consortium's core team. >

End-to-end survivable broadband networks

Abstract: Within the EC-sponsored RACE program, the IMMUNE project was established to analyze and specify appropriate strategies for introducing end-to-end survivability into corporate and public broadband networks to support these strategies by proper techniques and evaluation tools, and to demonstrate distributed restoration on PSN (public switched networks) and CPN (customer premises networks) laboratory models. The first objective was to define a set of survivability requirements and metrics to be used in the rest of the project. This has led to the identification of a range of survivability strategy options ann how they can be mapped onto user, service provider and operator requirements. The next step on the road to integral survivability is designing and planning survivable networks, and the evaluation of the restoration and protection mechanisms that will be applied in these networks. An overview is given of this part of the project. Most protection and restoration mechanisms operate within a single network layer and network part, autonomous from network management. The interaction of mechanisms in different network layers or in different network parts, and the role of network management, are discussed. For the demonstration lab models, two techniques have been selected for implementation: a distributed restoration mechanism for a meshed ATM PSN, and a CPN ATM ring protection switching mechanism. These techniques are described and an overview is given of the ongoing activities within the IMMUNE project, with a summary of the status of the demo models. >

CATV return path characterization for reliable communications

Abstract: The authors have examined the basic characteristics of hybrid-fiber coax (HFC) return systems to evaluate their ability to support bidirectional communications. The ability to support bidirectional communications on cable plants will allow deployment of two-way video applications as well as telecommunications services over the HFC plant. The results of the studies indicate that ingress in the cable return path is primarily due to broadcast signals which accumulate due to the noise-funneling effect of the cable return. Although this ingress can manifest itself in strong narrowband interferers which will prevent the use of large bandwidth channels, a reduction of node size to nodes on the order of 500 homes or lower will reduce the amount of interference. Filtering, in which a portion of the spectrum is blocked from the subscriber residence may also result in a significant reduction of ingress. Other phenomena on the return path can be dealt with by means of sound communication system design, including forward error correction to deal with impulse noise, and adaptive equalizers to deal with reflections in high data rate designs. TDMA, FDMA, and CDMA can all be utilized on the cable return path, but the capacities which result when less than perfectly synchronized CDMA is utilized are substantially lower than for TDMA and FDMA. A single carrier TDMA approach will be highly susceptible to narrowband interferers, and is unlikely to be successful. For these reasons a TDMA/FDMA or pure FDMA approach with narrow channels is likely to be the most robust multiple access technique for the cable return path. >

LAN emulation on an ATM network

Abstract: The authors evaluate architecture alternatives relating to the provision of a LAN emulation service over a connection-oriented ATM network, and present the LAN emulation architecture as actually adopted by the ATM Forum LANE SWG. The role of servers is discussed as is the provision of broadcast/multicast services. >

Self-healing virtual path architecture in ATM networks

Abstract: ATM network techniques have been actively researched and developed with the goal of realizing B-ISDN. ATM networks can transport signals of various services efficiently and economically, and offer the benefit of enhanced flexibility if the virtual path (VP) concept is adopted. Therefore, the ATM network will provide the infrastructure for B-ISDN. One of the most important themes in B-ISDN is the increased level of network reliability required to to match the high volume of data transmission that will be incurred by the information society and the "mission critical" nature of such data. The authors summarize self-healing network (SHN) schemes they have developed, and discuss problems that must be solved to realize SHN. >

Signaling traffic volume generated by mobile and personal communications

Abstract: The authors develop a framework for evaluating the signaling load in a wireless network. Using bounds and approximations, we find that the key parameter to estimate is the number of location updates between two calls. The results are dependent upon the choice of protocols, but are independent of the traffic parameters relating user calling behavior and mobility. We use the framework to draw general conclusions about signaling load, as well as to compare the signaling loads for the European and North American systems and demonstrate the impact of architectural tradeoffs. We also describe the message flows for the major contributors to the signaling load that are defined in the GSM system. >

Digital network synchronization

Abstract: With respect to network timing, the introduction of SONET equipment into the public network offers both problems and opportunities. Wide-scale deployment of SONET equipment and the use of SONET line timing for reference distribution will eventually provide improved timing performance in terms of both wander and jitter. One of the main motivations for developing the SONET architecture was to establish standards for interconnecting optical transmission equipment from different suppliers. In the process of establishing the SONET standard other (e.g. synchronization) technical issues were addressed. The article compares the existing (asynchronous) network architecture with the new (synchronous) architecture in terms of their respective performance in transporting the clock rates of tributary digital signals. Of primary interest is the timing quality of a first level digital signal such as the North American DS1 signal or the ITU-T (formerly CCITT) El signal. Although the new architecture offers eventual promise in solving numerous timing and interfacing problems for such tributary signals, the new equipment must necessarily co-exist and inter-operate with the existing facilities. Thus, another major topic of the article concerns the performance of interim networks with mixtures of asynchronous and synchronous multiplexing. >

Broadband access: comparing alternatives

Abstract: Capital investments by network providers to develop broadband access for the information superhighway have inherent risks. Nevertheless, potential rewards to telephone companies, cable TV companies, and others for serving the end consumer in an expanding information economy make such investments a business imperative. This article focuses on the incumbent terrestrial access providers, the telephone local exchange carriers (LECs) and cable multiple system operators (MSOs). First, it cites the business environment and the information highway services that are driving local telephone and cable companies to invest in broadband access, as evolving technology and relaxing regulation enable the convergence of these two industries. Broadband access technologies are then reviewed and evolutionary paths from the respective embedded bases are considered, with respect to both today's choices and the long-term vision. The two choices for broadband access are loosely termed hybrid fiber-coax (HFC) and switched digital video (SDV). The thrust of this article is to explain why these two alternatives overshadow all others and to highlight the decision factors facing network providers in choosing between them. >

P/sup 2/ codes: pragmatic trellis codes utilizing punctured convolutional codes

Abstract: A single convolutional code of fixed rate can be punctured to form a class of higher rate convolutional codes. The authors extend this pragmatic approach to the case where the core of the trellis decoder is a Viterbi decoder for a punctured version of the de facto standard, rate 1/2 convolutional code. >

Forecasting long-term demand for services in the residential market

Abstract: The TITAN tool makes possible the examination of alternative implementation strategies for advanced services in the access network, relying on component cost trends and forecasts of demand for services to evaluate the overall economic viability of new networks for advanced service delivery. >

System aspects of cellular radio

Abstract: The greatest single factor in enhancing spectral efficiency of a network is the mass deployment of microcells. By this simple technique we can repeatedly and efficiently reuse the precious spectrum. The number of users a network can support is fundamentally dependent on the common air interface (CAI) over which users communicate. User capacity is dependent on many factors, but the cardinal ones are the amount of spectrum the regulators allocate, the size of the radio coverage area from a base station (BS), and the amount of interference a particular radio link can tolerate. In this article we are primarily concerned with the system aspects associated with the CAI. We focus on the critical importance of BS siting. Starting with existing large cells, we deliberate on the problems that might arise in siting BSs in three dimensional microcells, in order to consider suitable multiple access methods for future cellular environments. >

Applications of neural networks in high-speed communication networks

Abstract: Modern communication networks are expected to have hundreds or thousands of network nodes to which thousands of users are connected. Neural networks can contribute to this emerging new telecommunication infrastructure by providing fast, flexible, adaptive, and intelligent control. This article discusses the neural networks used for solving various control problems in high-speed communication networks. >

A high-capacity ATM switch based on advanced electronic and optical technologies

Abstract: As the number of ATM broadband subscribers grows, the construction of an efficient access and tandem network will require very large ATM switches. The authors propose an architectural approach based on a concept of satellite switches of moderate capacity, loosely coupled over very high-speed links through a cross-connect core. >