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Military Microwaves Supplement
Recent Advances in Radar Technology
Using Calibration to Optimize Performance in Crucial Measurements
Europe’s Wireless Futures
European technologies and market prospects continue to play a critical role in the wider picture of the worldwide wireless and mobile scene. This special supplement to Microwave Journal provides an overview of developments in Europe’s key wireless technologies and looks at trends for the future.
Microwave Journal European Staff
It’s been one of the most intriguing technology races of this century: the European mobile community achieving the Global System for Mobile Communications (GSM), arguably the world’s leading digital cellular standard. Not only has it seen adoption in Europe (a legal obligation of the European Union), it has also achieved undeniably widespread deployment throughout the world. However, GSM’s success raises questions: What is the future outlook for GSM-derived digital cellular? How do nondigital cellular technologies fare in different markets alongside GSM?
In fact, the success of GSM outside of Europe has made it the de facto international standard (North America is the exception), and substantial growth should continue. Forecasts for total cellular populations variously suggest that, worldwide, between 250 and 500 million subscribers will be using GSM by the 2002/2003 time frame. Therefore, despite alternative cellular technologies, these figures would still place GSM well above the combined population of everything else (both analogue and digital) put together. The success of GSM has meant that it is now seen as a natural base for extension and exploitation. As far as European debate is concerned, many observers would suggest that the sheer scale of GSM deployment overwhelms other wireless platforms (for example, paging or even private radio).
However, GSM evolution itself is principally concerned with the biggest prize of all: high speed data. Data applications — originally a minor part of the GSM specification — will open the door to many easily accessed services, particularly on the Internet. Participants in the mobile community, specifically major vendors, have taken great pains to explain detailed migration strategies that would provide GSM with upgrade paths. Ultimately, these strategies will centre on the creation of the so-called third-generation (3G) mobile standards (also termed the Universal Mobile Telecommunications System (UMTS)). All of the critical parameter definitions revolve around available bandwidth. Broadly, narrowband services can be defined as 9.6 to 64 kbps, wideband as 64 kbps to 2 Mbps and broadband above 2 Mbps, as shown in Figure 1 .
The probable international 3G standard will be wideband CDMA (W-CDMA) to which the main digital cellular standards such as GSM and CDMA will migrate. Whilst UMTS will offer data transmission speeds of 2 Mbps, compared with present capability of 9.6 kbps for most GSM handsets, technologies “on the way to UMTS” such as General Packet Radio Service (GPRS) will offer 144 kbps.
However, there are difficult business questions to be resolved even with a migration path. For example, UMTS has stimulated considerable debate in the regulatory sphere. In most cases, European countries have decided to embark on a round of new mobile licences specifically for UMTS. According to telecom analysts at ABN AMRO, licence activity has already closed in Finland (some 15 bidders chased four licences). In the UK, the UMTS licence auction round will begin in January 2000 followed by activity in Denmark, France, Germany, the Netherlands and Switzerland. This time frame would put the European round ahead of the US, for example, which may not see licences until sometime around 2001.
Exactly how profitable UMTS services will be for operators and how they should be positioned in the marketplace remain subjects for considerable debate. While it is expected that UMTS or UMTS-like services will arrive in the early years of the next decade in Europe, the licence environment may be running ahead of serious intention to deploy. Operators have expressed disquiet about the prospective level of investment required for new infrastructure at the same time that they are recouping returns from their present (GSM) networks. Equally, whilst there is a great deal of enthusiasm for the potential applications that broadband mobility can offer, many in the industry see no killer application that would make UMTS a compelling proposition for either service provider or end user. In fact, the killer application may well have arrived, albeit belatedly, in the form of mobile access to Internet services. However, given the present and likely ownership structure of the mobile industry, there may well be more reason to expect technology platforms to be commonalized as far as possible with the appearance of various multimode terminals. Overall, observers such as ABN AMRO expect to see worldwide roaming based on 3G technology by 2005.
Equally, it all depends on the starting points and business environments of the individual markets. In general, European experiences will probably remain quite distinct from those of the US. Where GSM has been most successful, it has led to other possibilities. In Finland, where mobile penetration is reckoned to be well over 50 percent, nonvoice services (data) based on GSM are believed to already account for as much as 15 percent of mobile revenues accruing to operators. More typically, the present experience of most developed countries (including the US) suggests this revenue proportion is much lower, probably around one percent. In fact, messaging and narrowband data services (including two-way operation) are already well developed in the US. However, they have not been derived from a cellular platform, but rather through paging-style technologies. This has meant that even in spite of a sharp growth in the cellular market, paging in the US has reached 20 percent penetration; in Europe, because of a mix of standards and complexities concerning frequency allocations, the figure is less than five percent.
Migration through Edge
GSM operators and vendors have jointly recognized that the technology will stay competitive and cost effective with continual refinement. This refinement will ultimately engage 3G or UMTS technologies, but careful plans have been made to migrate current GSM operations to UMTS technologies via enhanced GSM technologies, particularly so-called Enhanced Date Rate for GSM Evolution (EDGE) technologies.
The background to this planning rests on expectations that the business of wireless data is expected to grow in the region of 100 to 200 percent per annum and the mobile communications industry agrees that wireless data services, in their various guises, will form the foundation for future business. The enormous success of short messaging in many countries proves that people accept the benefits of nonvoice services. We are now facing the introduction of Wireless Application Protocol as well as the higher transmission speeds of high speed circuit switched data (HSCSD), soon to be joined by the convenience of direct Internet connection with the General Packet Radio Service (GPRS).
Many wireless data applications today can be implemented with the current available GSM data rates of 9.6 kbps. However, bandwidth-hungry fixed-line applications — Web browsing, access to corporate data bases and so on — would benefit from higher transmission speeds when used over the mobile network. EDGE, a new radio interface technology with enhanced modulation, increases HSCSD and GPRS data rates by up to threefold.
The GSM standard is being developed to support mobile services with radio interface data rates even over 400 kbps. This work is being performed under the European Telecommunication Standard Institute (ETSI) EDGE work item. The major change in the GSM standard to support higher data rates is the new modulation system known as 8PSK (phase-shift keying). This modulation system will not replace but rather coexist with the existing gaussian minimum-shift keying (GMSK) modulation. With 8PSK it is possible to provide higher data rates with somewhat reduced coverage, whereas GMSK will still be used as a robust mode for wide area coverage. In mature GSM markets, cellular data penetration is forecast to increase exponentially during the early 2000s. New wireless data applications and innovative terminal types will generate completely new markets; aggressive GSM operators can expect to obtain up to 30 percent of their airtime and revenue from wireless data by 2000.
HSCSD and GPRS, introduced to GSM in 1998 and 1999, respectively, will enable cellular operators to offer higher than 9.6 kbps data rates to their subscribers for new data applications. Cellular operators that have invested in HSCSD and GPRS expect to be able to offer higher data rates without building too many new sites. The Enhanced Circuit Switched Data (ECSD) and Enhanced GPRS (EGPRS) solutions offer data services comparable to 3G levels with considerably fewer radio resources than found in standard GSM. This means that EDGE transceivers (TRX) carry more data per time slot, decreasing the need for new TRXs/frequencies. In addition, end-user response times decrease, ensuring good services levels as data usage increases.
It could be possible for EDGE Phase 2 to provide a voice service using adaptive multirate codec (AMR) solution types. EDGE TRXs would then be capable of carrying multiple speech calls per time slot, increasing voice capacity. Also, high quality codecs (for example, 32 kbps) would be feasible. EDGE as a voice solution looks especially interesting for indoor systems because of its scalable capacity.
The EDGE Phase 1 standard, scheduled to be completed in the third quarter of this year, will contain both EGPRS and ECSD services. EGPRS will be based on the footprint of GPRS, whereas ECSD will enhance the data rates of HSCSD. It is expected that packet data will dominate circuit switched data in future GSM data networks, calling for EGPRS solutions with high flexibility and spectral efficiency. Also, the high data rate real-time services provided with ECSD are seen as important for applications such as video retrieval and video telephony.
EDGE will provide significantly higher data rates on the 200 kHz GSM carrier. The data rates being specified by ETSI would bring ECSD rates up to 38.4 kbps/time slot and EGPRS rates up to 60 kbps/time slot. The data throughput per carrier increases even over 400 kbps. For ECSD, it is possible to support a 64 kbps real-time service with a low bit error ratio by allocating two time slots of 32 kbps each. The enhanced modulation will adapt to radio circumstances and, hence, offer the highest data rates in good propagation conditions whilst ensuring wider area coverage at lower data speeds per time slot.
EDGE will also allow operators without a UMTS licence to stay competitive in wireless data markets. However, UMTS operators can also use EDGE for gradual rollout of high speed data services and for wide area coverage where UMTS would be used for urban areas.
The European standards community (and ETSI in particular) has also embarked on several nondigital cellular projects. The first operational systems of a new digital wireless technology delivering voice communication and data transfer are now available. Terrestrial trunked radio (TETRA), based on a decade of standards work currently being fine-tuned by ETSI (and the only such set of standards endorsed by ETSI), is the catalyst for a new generation of digital trunked radio products and systems. These trunked systems optimise radio spectrum usage, reducing the cost to operators of this increasingly scarce resource. Effectively, TETRA represents the digital standard to public mobile radio in the ETSI environment in the same way that GSM has represented the digital cellular standard and Digital Enhanced Cordless Telephony (DECT) the digital cordless standard. The TETRA acronym originally stood for Trans-European trunked radio. As interest in TETRA grew, the wording (like the GSM acronym before it) was altered to reflect TETRA’s greater geographic scope and application.
TETRA is focused on the requirements of a particular market. Major incidents in the last 10 years, such as air and ferry disasters, necessarily involving multiple emergency services sometimes from several European countries plus the removal of many trade barriers and passport controls, have fueled the drive towards establishing a pan-European communications medium for public safety and public service organisations. Manufacturers, operators and user groups are involved in the standardisation and development process, utilizing an effort of more than 100 man years and numerous simultaneous working groups and strategic task forces. The TETRA Memorandum of Understanding (MoU) was signed in December 1994, promoting the concept of a single European-wide standard for digital mobile radio services and ensuring a multivendor market. The MoU now comprises close to 60 companies in 18 countries, including the US, Singapore, Israel and New Zealand.
The Market Potential
The market for TETRA systems is emerging in two broad areas: public safety and utility organisations and public access operators providing managed voice/data communications systems for business. Research produced for Marconi Mobile Communications by MZA estimates the global market for TETRA will be worth more than £230 M by 2001, rising to almost £1.3 B in 2003. Potential users include emergency services, construction companies, public utilities and transport networks — any group of users with demands for high performance communications. These users demand fast call setup, high quality speech capable of operating in noisy environments (both literal and electronic) and the delivery of efficient group communications between terminals.
Today, most public safety organisations, public services and, of course, the military, run their own push-to-talk systems known as private mobile radio (PMR); many other organisations rely on public access mobile radio (PAMR) systems, buying airtime from a PAMR network operator. TETRA is relevant to both network types: private and public users.
TETRA features overcome many of the shortcomings of other networks. Current GSM/PCN digital cellular telephony offers national/international coverage and public switched telephone network (PSTN) access, but its data transfer rates are low (14.4 kbps) and it lacks the instant call setup and workgroup capability provided by existing analogue mobile radio networks. However, today’s analogue mobile radio networks are limited to simplex (one way at a time) operation and offer relatively poor PSTN connectivity. Mobile packet data networks offer dedicated data-only services but coverage is limited, transmission rates are low by comparison and voice communication is not available.
A fully operational TETRA system will combine the features of digital cellular, mobile radio, wireless data and paging. It will offer national coverage, high voice quality, instant call setup and corporate virtual private networks (VPN) for workgroups. A TETRA unit can communicate directly to a local area network (LAN), for example, enabling the user to log directly into databases. With compression, the TETRA unit could be a videophone with real-time movement. In addition, TETRA will replace four discrete hardware in-vehicle pieces of equipment — mobile data terminal, PMR despatch telephone, cellular phone and pager — with a single device. Its combination of performance, features and facilities is not available in any other mobile communications standard, offering faster data speeds than anything currently available in mobile technology, including GSM.
TETRA features include high speed quality communications even under poor signal conditions and in noisy environments, high quality reception over cells up to 60 km apart at 400 MHz and rapid call setup (less than 0.3 second). Person-to-person and person-to-group calls can be set up quickly compared with, typically, 10 seconds for GSM/PCN systems. The elimination of dialing and ringing improves this speed still further. In addition, a TETRA system features easy-to-use, full-duplex (two-way) conversation with PSTN or private automatic branch exchange (PABX) interconnection, simultaneous voice and data transmission up to a combined maximum of 28.8 kbps and image transmission capability (video and Internet access has been demonstrated successfully over TETRA using the ITU H.263 compression algorithm). The system also offers high security, plus a choice of encryption methods (voice, data, signalling and user identity can be encrypted) and efficient use of the radio spectrum in addition to direct inter-terminal communication (mobile-to-mobile). Direct mode allows terminals to communicate directly with each other so that radios will still communicate with one another on a one-to-one basis where coverage exists. (Cellular mobile phone systems cannot provide this service.) TETRA also features a low cost infrastructure. Marconi Communications devices switch at 8 kbps per channel — eight-times more efficient than alternative 64 kbps switching systems — using less bandwidth to achieve the same result. This capability reflects the fact that this type of switch and terminal development is uniquely TETRA-specific, not simply an extension of existing GSM systems, which also rely on 64 kbps per channel. The system has repeater operation from standard terminals (a standard mobile terminal can be used as a repeater to extend coverage of a TETRA network) and a network broadcast facility (transmissions can be made to all users). Call-priority allocation (up to eight levels of priority can be set so that calls with high priority overrule those of lower priority if no idle channels are available) is also offered, as well as group call and group communication. Here, a number of users can share the same channel, enabling many users to coordinate on a specific task or monitor the activities of other members of the group. (Typical users will include vehicle fleets and emergency services.) Lastly, the system provides automatic call management or despatcher control.
A major advantage of TETRA is its efficient use of spectrum (always a scarce commodity). Available spectrum has been divided over the years into smaller and smaller slices, reaching a channel spacing of 12.5 kHz in the UK, for example. Users migrating to TETRA, whose capacity is greater than existing methods, should free spectrum currently tied down with analogue systems.
Four frequency bands are likely to be used for TETRA and one of them (385 to 400 MHz) is already allocated across Europe for emergency services. The other bands are 410 to 430 MHz for public networks such as Dolphin, 450 to 470 MHz and 870 to 920 MHz. Marconi has developed a complete first-generation family of products in the 380 to 400 MHz range and is developing products at 800 MHz, notably for the Middle and Far East markets and China.
TETRA is based on a 25 kHz TDMA carrier (underlying transmission path) supporting up to four simultaneous channels for voice or data transfer (7.2 kbps each or a total of 28.8 kbps). The carrier includes high level security and encryption features. Three phases of standardisation are already complete with a fourth and final phase nearing fruition. Three generic standards are currently in place: V+D for trunked voice and data, packet data optimised (PDO) for packet data and direct-mode operation, a package of features enabling one-to-one voice calls, group calls and voice calls while simultaneously monitoring a network. Depending on the user’s need, one or more of these variants can be packaged in standards-based equipment, making TETRA a flexible and powerful tool.
A new study by ETSI’s TETRA European Project on the future direction of the technology is scheduled to begin shortly. Topics for discussion will include methods of interworking with the Tetrapol alternative and with planned next-generation cellular systems such as GPRS and, eventually, UMTS.
Voice and Data
In addition to basic voice communication, approximately 30 supplementary services have so far been identified for inclusion within the TETRA feature set. Mobile communications services include priority calling and dynamic group number assignment; fixed communications services include call holding, call barring and call forwarding. PDO, the second phase of TETRA data application development, supports a wide range of applications involving a mix of packet, circuit and short messages(s) up to 2048 bits. These applications include database interrogation/update, file transfer, messaging/paging, vehicle location, telemetry, video transmission, image transfer/graphics, computer-aided despatch and mobile office functionality.
For the future, Digital Advanced Wireless Service (DAWS), a standard for broadband data, is under development in a joint ETSI/APCO (US Association of Public Communications Officers) initiative. A packet-data solution based on an air interface up to 155 Mbps, DAWS is still under development. While the access methods and modulation scheme have yet to be finalised, the aim is to provide an Internet Protocol (IP)-based, multimedia service with full mobility. The service is likely to be available for integration within commercial TETRA systems after 2002.
Why Not GSM?
In being TDMA based, TETRA is similar to GSM: TDMA is a notably efficient algorithm in its use of spectrum, using slots of time rather than slots of frequency domain multiple access (FDMA). Reflecting the needs of TETRA’s main target markets, TDMA’s operational strengths lie in areas of high capacity and high density (such as city centres), whereas FDMA is best suited to wide area, low capacity use. However, while complementary in many respects to GSM, TETRA meets a different market need. There are currently approximately one million PMR/PAMR mobile radio subscribers. TETRA technology provides significant additional benefits and a natural upgrade. It also has the potential to capture new markets where fast data transfer and workgroup functions are attractive, such as distribution, utilities and field services. Significantly, GSM operators have not been notably successful in marketing cellular phones to those commercial sectors.
In addition to TETRA’s many features that are unavailable on GSM, public safety organisations demand fast call setup and tend to make short-duration calls, often involving groups; GSM is principally concerned with person-to-person calls via the PSTN and currently involves far longer call setup times. Unlike GSM, for example, TETRA supports the provision of tailored network coverage, VPNs and, working at 400 MHz, TETRA infrastructure is also less costly an investment than GSM at 800 MHz.
The sheer number of current TETRA field trials worldwide is, by any standard, impressive. Many countries are involved, notably Scandinavia, the Netherlands and the UK, but pilot or operational systems are also either in negotiation or under construction as far afield as Hungary and New Zealand.
A look at recent contracts for one supplier, Marconi Communications, indicates clearly the potential spread of TETRA. Among turnkey TETRA projects, the organisation responsible for generating and distributing electricity throughout Croatia, Hrvatska Elektroprivreda, has chosen TETRA as its next-generation private mobile communications network for field engineers —the first TETRA contract for a utility anywhere in the world. In Italy, the Carbineri have chosen TETRA for the first phase of a nationwide mobile communications system in the Lazio region. The system, which is to be operational by mid-2000, has a very high level of resilience achieved partly through alternate routing between network switches. Saudi Aramco, a Saudi Arabian oil company, has chosen a TETRA solution as a customised, private mobile communications network. Special features include intrinsically safe hand portables suitable for oil field work. The project will also establish the first TETRA system at 800 MHz. Other examples of contracts for Marconi TETRA systems include the Portuguese police in Porto and Coimbra and the railway authority in Singapore.
In a buoyant, expanding global market for TETRA systems, a massive viable market is the US. Following presentations by, among others, the TETRA MoU Group and ETSI, proposals are being sought for a TDMA option for a future US standard. TETRA is a leading candidate, being ideally suited to the high capacity trunked systems needed in many US metropolitan areas. TETRA is also being considered in China as a national digital standard.
With the first wave of implementations well under way, TETRA is proving itself as a robust system in which the expectation of quality of service for data can be identical to that of voice, even in the harshest environments. By the end of this year, TETRA will be an operational reality in numerous countries with the confidence that the greatest challenge has already been met: a willingness within the industry to cooperate to produce advanced, fully interoperable, standards-based technology.
Wireless access to telecommunications networks has undergone revolutionary changes over the past few years due in no small part to the rapid advances of radio technology since the commercial introduction of mobile cellular technology in the 1980s. However, whilst their historical development forms common threads of technology, there is a distinction to be made between mobile telecommunications and wireless access. Wireless access is defined here as the use of radio to connect users from essentially fixed locations to networks of various kinds. The vast realm of mobile telecommunications that allows end users to move over considerable distances at considerable speed is excluded from this definition. These systems typically have switching functionality included; access-only systems do not. Also excluded from discussion are general-purpose transmission systems that may be used for access but are not exclusively designed for it.
By most accounts, fixed wireless telecommunications are headed for explosive growth. The industry can be expected to grow to US$8.5 B in 2007 according to Pioneer Consulting (New York Times, June 14, 1999). Fixed wireless access systems can coexist with mobile systems in a given area without problems if the radio spectrum needs of both are met. Indeed, some (but not all) modern digital switches now have the capability to serve simultaneously as the mobile switching center (MSC) of a cellular mobile system and as the local exchange of a wireline and/or fixed wireless system. In some currently available product configurations, an MSC can support connections to mobile base stations while simultaneously supporting V5.2 connections to wireless local loop (WLL) systems. With increasing deregulation, regulatory agencies may allow, and operators may find attractive, the offerings of both fixed and mobile service. The fact that both may be implemented simultaneously on the same switch, (and both may be wireless) makes this combined service business particularly attractive. This convergence of fixed and mobile service offerings is predicted by some analysts to be a major trend over the next few years.
Most of the wireless access systems today bring users access to a circuit switch, but the emergence of products that bring users direct access to packet switches at various data rates is now being seen. According to this definition of wireless access, the emergence of a number of different applications and classes of product is noted, based in part on the data speed they require or support. To categorize applications and products in such a rapidly evolving field is at best an instantaneous snapshot of dynamic movement. Products both exist and are emerging that arguably can fulfill more than one classification. Many of the low speed access products of today promise to evolve into high speed products tomorrow. Undoubtedly there exist, or will soon emerge, fixed wireless access products that do not fall into any of these classes. But to understand their extent and potential, it is nevertheless helpful to enumerate the basic categories of fixed wireless access systems from a user’s perspective as they exist today.
Five such categories and applications include wireless access as a means to provide WLL. This application involves the use of wireless access as a replacement for the final wired loop from a PSTN to residential and business subscribers located within a few kilometers of a telephone exchange. Typically these wireless systems support voice and low to medium speed voice band data calls today, and promise to support much higher data rates in the future. These systems operate in the 1.9 and 3.4 GHz bands, although some systems use the 800 MHz mobile and other bands. The subscriber density and coverage supported by these systems vary considerably. The most advanced WLL systems today can support the coverage, traffic and subscriber density needs of highly urbanized populations as well as those of rural areas.
Long distance wireless access as a means to provide telephone service to residential and business subscribers who are located at considerable distances (up to hundreds of kilometers from the local exchange) is another category. This application is often denoted as point-to-multipoint (PMP) because it uses radio to connect a single point (the local exchange) to many points (multiple terminal stations to which subscribers connect). Microwave radio systems for this application often operate in the 500 MHz to 2.5 GHz frequency range. Satellite systems that provide fixed wireless access are also now being deployed. Typically these are deployed in very remote areas where ground-based wireline or wireless systems cannot be economically deployed.
High speed packet data Internet access is a third category. This class of products is used to provide end users with very high speed wireless data access (circa 1 to 2 Mbps) to data networks, including intranets and the Internet. These systems use licenced frequency bands such as 1.9 and 3.4 GHz.
Another category is wireless broadband access for short range, but very high speed (tens of Mbps) data for businesses or public institutions. These systems generally operate in recently opened bands in the 10 to 42 GHz range and can provide access at distances up to approximately 25 kilometers.
The fifth category is wireless LAN (WLAN) access using radio to replace the cables of standard private LANs. These systems can use unlicenced frequency bands, such as 2.4 GHz, and are typically intended for indoor use. Some systems offer outdoor radio adjuncts in order to link nearby buildings.
The use of radio to replace the final wired loop from an exchange to subscribers’ premises has been widely deployed only over the last three years. Driven by the many advances in radio technology and manufacturing processes commonly associated with the mobile cellular industry, WLL has recently become an economically attractive alternative to traditional wired outside the plant. For operators of telephony networks, outside the plant often constitutes a major capital expense. The choice of WLL can impact more than half of their typical investment expenses. The cost advantage that WLL offers over traditional wire fixed line can thus have a major impact on a service provider’s bottom line.
Although modern WLL technology shares some aspects of the common architecture of mobile systems, for example, cellular technology, sectorization, frequency re-use and low power, the best WLL technologies and products do not share the shortcomings commonly associated with today’s mobile cellular telephony. Mobile cellular networks, by their very nature, must spend considerable processing resources on the tasks of tracking the geographic location of users and allowing their dispersion to undergo rapid dynamic change. With fixed subscribers, such tasks are not needed. The location of subscribers does not undergo dynamic change. Because the direction of a subscriber relative to a serving base station is fixed, WLL antennas may exploit the benefits of directionality. The best WLL technologies and products can therefore provide significantly higher subscriber densities, higher call capacity and better quality of service than their mobile counterparts. Mobile cellular systems generally must compromise on voice quality by sampling voice at rates such as 8 or 13 kbps. Purpose-built WLL systems often use higher sampling rates such as 32 or 64 kbps, yielding toll grade voice quality.
WLL systems are attractive as an alternative to wireline access because they generally can be deployed much more rapidly and at a lower cost, yet provide equivalent or better service. To be a true commercial substitute for wireline, WLL systems seek to provide transparency. WLL is most attractive when it behaves in a similar manner to high quality wireline telephony, but at considerably lower cost. This means that the dialing procedures, voice quality, access to and behavior of subscriber supplementary services and the call setup time closely match those provided by high quality wired lines. The best WLL technologies and products available today achieve good transparency, both for analogue as well as integrated services digital network (ISDN) telephone service. Indeed, the highest compliment that can be paid to a WLL product is for a typical end user to be unable to detect that a call is using a WLL line without visually noting the presence of an antenna.
Because WLL operates as a public outdoor radio technology, it must operate only in licenced radio bands to reduce interference. The exact frequencies under which WLL systems operate are, therefore, controlled by national, regional and international regulatory bodies. Public telephone service providers seeking to operate WLL systems generally must apply for radio spectrum in the locations in which they wish to operate. Common operating frequencies of modern WLL systems are in the 1.9 and 3.4 GHz bands. Some WLL radio technologies such as DECT offer advanced radio techniques such as dynamic channel selection (DCS) to provide a high level of coexistence and excellent spectrum efficiency.
There exist perhaps eight to 10 million WLL lines contracted in the world today. Most use their WLL connection for voice and voice band data communications. For an urban application, the price per subscriber line of WLL equipment varies considerably, but today it is often in the range of US$500 to $600. Prices have declined rapidly in the three years since the introduction of modern WLL systems, and are expected to continue to fall. Growing WLL deployments are allowing vendors to benefit from greater scales of production, which in turn permits price reductions. With the price of wired loop access often in the range of US$1000 and essentially flat (driven largely by the costs of civil works, conduit and cable), the price advantage of WLL is becoming ever more pronounced.
Industry analysts predicted an extremely rapid expansion of WLL, with estimates often exceeding 100 million lines over the first five years. In fact, these extremely optimistic estimates have not yet come to fruition. The use of WLL is indeed expanding, but at a more moderate pace than many observers initially foresaw. The reasons for this are many. The economic setback in Southeast Asia, the region that initially adopted WLL most vigorously, is one. The price difference between WLL and wireline is attractive, but not always sufficient to overcome the natural inertia to continue with the more familiar wireline access. Nevertheless, with continuing price declines and positive reports from WLL field deployments, most industry observers continue to predict rapid growth for WLL over the next few years.
With many different WLL radio technologies on the market and systems with different qualities of service and different levels of transparency, some operators are hesitant to adopt WLL. But as the industry undergoes its inevitable shakeout, it is likely that WLL systems will become more standardized and generic, just as wireline technology is commonly perceived to be. Those WLL systems that are merely mobile cellular with the mobility turned off are pressured now to improve their transparency with wireline. Purpose-built WLL systems, which already have good transparency, are being pressured now to standardize and align their operations and management systems with the rest of the network. Most significantly, the demand of operators that WLL systems support ever higher data rates requires vendors to continually evolve their systems. All these factors assure that both price declines and expansion of functionality in WLL systems are likely as they continue to be deployed in the years ahead.
In terms of markets, WLL equipment vendors have so far found their greatest successes in the teledensity application, that is, the use of WLL as a means to expand rapidly and economically the number of telephone lines in a given location, providing basic telephone service in areas that previously had little or none. It is therefore no surprise that the greatest numbers of WLL lines installed to date are in the developing nations of Asia, Africa and Latin America. With the International Telecommunications Union reporting that 962 million households worldwide lack a telephone, this market for WLL looks promising almost indefinitely. There are clear signs of a growing interest in WLL in developed nations as well, particularly where new and competitive telephone service providers are concerned.
Despite having their best success providing basic telephone service in developing nations, WLL equipment manufacturers are driven to continually update their equipment in order to provide customers with more advanced services to match those that can be provided by the newer wireline technologies. As technologies such as V.90 modems, digital subscriber lines (xDSL) and cable modems are deployed, WLL systems are pressured to match their capabilities. Arguably, only systems using the most modern digital radio technologies (such as DECT) and other TDMA and CDMA technologies are likely to maintain significant WLL market share. Even in the least developed areas (urban and rural), there is both a need and a demand for modern data services such as Internet access at ever increasing data rates.
The requirement to support continually higher data rates suggests that the introduction of packet technologies over WLL radio interfaces will become commonplace in the next few years. Instead of connecting only to traditional circuit switches, WLL systems are likely to directly interface to IP routers as well. It is the ability of packet technology to increase the sharing of radio resources (particularly useful in handling bursty data), which drives the interest in applying packet technology to WLL. With increasing deregulation, traditional as well as new operators may seek to provide both circuit switched telephony services as well as packet switching for services such as Internet access.
In the long term, many analysts predict a full transition of telecommunications networks from circuit to packet technologies such as IP and asynchronous transfer mode for all services including voice telephony. While such a transition is likely to occur over an extended period of time, it is clear that the WLL systems of today are already preparing to meet this challenge.
With the Internet as a major instigator of the requirement for high speed data access, it is interesting to note the asynchronous nature of most Internet data exchanges. Today, an Internet Web user typically sends a relatively small amount of data in the uplink (PC to Internet service provider (ISP)) direction. This transmission might consist of a few mouse clicks or the typed entry of a Web address. The response in the downlink direction (ISP to PC) to that relatively small amount of data is often a large amount of text, graphic, audio or video data, such as the display of a Web page with complex graphics. Thus, the flow of information in user access to the Internet is commonly quite asymmetric in nature. Radio technologies that can dynamically adapt to asymmetry have a distinct advantage over those that do not. In particular, if the duplexing of two-way communications is achieved by means of time division duplex, it is significantly easier to adjust to asymmetry in real time than with frequency division duplex.
On the horizon, WLL systems are likely to continually incorporate various new technological advances such as smart antenna technology, the dynamic alteration of the shape of electromagnetic propagation, to improve performance. A number of methods for this have been demonstrated. For WLL systems, greater capacity will be achieved by reduced interference and more efficient use of radiated power. Here again, products and radio technologies that can incorporate these advanced techniques are likely to find a competitive advantage over those that cannot.
Fixed Wireless over Long Distance
Another category of fixed wireless access exists that can bring subscribers service from a telephone exchange when the subscribers are located at distances considerably greater than those of a standard local loop. Systems that do this by wireless means have existed for decades and are used in both developed and developing nations.
A popular technology for this has emerged over the last decade: TDMA PMP microwave radio. As part of such systems, an interface unit is located near an exchange. From this station, there can be multiple microwave radio hops of up to 50 km using TDMA radio, commonly in the 1.5 or 2.5 GHz band, to stations that provide connection points for wired telephone sets. Systems providing such access for telephone subscribers even hundreds of kilometers away from the exchange are in use today. Under the most advanced systems, even ISDN service can be offered to these very distant subscribers. More recently, some systems have added WLL tails so that even the last connection from the final radio station to the subscriber’s premises may also be provided by wireless means.
The price of these systems varies considerably because their configurations, subscriber densities, coverage areas and services can vary widely. The price may range from a few hundred to a few thousand dollars per subscriber. As a strategy to provide service to rural and remote areas, operators may deploy these systems until the subscriber growth in a given community reaches a level where it becomes economically viable to deploy a small exchange or the remote module of a distant exchange. At such a time the WLL tails already in place may continue to be used to provide access to the new exchange.
In this category of fixed wireless access over very long distances there are also systems that use earth satellites to provide access to a network. Configurations vary considerably. Very small aperture terminal satellite technology may be applied to support voice and data services to remote communities that cannot be economically accessed by cable or ground-based microwave radio. When the traffic from such a community does not justify the leasing of a permanent satellite radio channel, demand-assigned multiple access technology may be deployed to optimize satellite usage. Thus, satellite resources are only allocated as needed, making it economically viable to provide access to a very small number of subscribers in extremely remote areas.
High Speed Packet Data Access
A third interesting application of fixed wireless access that is now emerging is very high speed Internet access using packet data technology. Some WLL products that are currently used primarily for voice and voice band data are based on technical standards that support high speed packet data. Some of today’s WLL circuit technology systems promise to evolve soon to support packet data as well. But there is also emerging a class of products that are designed from the beginning to support very high speed wireless packet technology with IP and point-to-point protocol. For these products, Internet and intranet access, and VPNs between business locations are primary applications. Voice calls may or may not be supported.
Wireless Broadband Access
At the leading edge of fixed wireless access technology today, access by broadband wireless is now emerging. These systems support very high data rates (in the range of tens of megabits per second) for voice and data applications for business customers. Monocellular, line-of-sight technology is used to relay huge amounts of data from business premises into operators’ networks. Up to 15 km distance is currently achievable in normal conditions, depending on climate and spectrum. This technology allows operators to avoid the long lead time and great expense of laying fibre-optic cable to connect their networks to business buildings in urban and suburban areas.
Wireless broadband access operates towards the high end of commercially available radio spectrum (10 to 42 GHz) with somewhat different licenced bands allocated in Europe and North America. Included in this application is local multipoint distribution service (LMDS) at particular frequency bands (generally 28 GHz) within the overall category of wireless broadband access.
While this technology has not yet been widely deployed, a recent estimate by the Strategis Group for the infrastructure market in the US for LMDS alone is US$8 B in the next 10 years. In the US, a developed economy by all measures, only one-tenth of the office buildings are currently connected with optical fibre, leaving great opportunity for wireless broadband access.
Potential applications include, but are not limited to, video on demand, interactive video and Internet access. Purchasers of wireless broadband access equipment are likely to include PTTs, local exchange carriers, interexchange carriers, Internet service providers and new network operators. End users are initially likely to be small- and medium-size businesses that cannot justify the cost of leased optical fibre.
As a market entry strategy, an operator might use wireless broadband to establish an initial base of broadband business customers. The modular flexibility of wireless access, allowing incremental investment and quick revenue return, permits an easier market entry. Once a particular geographic location has sufficient end users generating enough revenue, the operator might then choose to make the investment in fibre. The wireless access equipment may be redeployed elsewhere in a locale where the operator seeks to do business.
Ultimately, wireless broadband may prove attractive to residential customers as well. Advanced interactive video services and very high speed Internet access are seen as likely applications. With fibre to the home estimated to cost several thousand dollars per customer, wireless broadband solutions might prove very attractive.
The “Migration through EDGE” segment was contributed by Ukko Lappalainen, head of marketing and business, 3G Technology at Nokia; the “TETRA” segment was contributed by Luciano Maciotta, managing director at Marconi Mobile Networks; the “Wireless Access” segment was supplied by A. Scott Berman from Bell Laboratories, TRT Lucent Technologies.
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