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Fixed wireless systems are becoming increasingly attractive in a deregulated telecoms world. As these systems evolve to support the broadband services that the market is now demanding, their popularity with operators in both developed and developing economies can only increase.



Wireless access: The landscape today, the horizon tomorrow
by Scott Berman;

Wireless access to telecoms networks has undergone revolutionary changes over the past few years because of the rapid advances of radio technology since the commercial introduction of mobile cellular technology in the 1980s.

Despite their historical development from common threads of technology, for the purposes of this article a distinction is made between mobile communications 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. We exclude from this definition the vast realm of mobile communications that allow end users to move over considerable distances at considerable speed. These systems typically have switching functionality included. Access-only systems do not. Also excluded from discussion in this paper 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 billion in 2007, according to Pioneer Consulting [New York Times, June 14, 1999].

Fixed wireless access systems can co-exist with mobile systems in a given area without problem 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 centre (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 and simultaneously support V5.2 connections to WLL systems. With increasing deregulation, regulatory agencies may allow, and operators may find attractive, the offering 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 of today bring users access to a circuit switch, but we are now seeing of the emergence of products that brings users direct access to packet switches at various data rates.

Under this definition of wireless access, we note the emergence of a number of different applications and classes of product, based in part on the data speed they require or support. To categorise applications and products in such a rapidly evolving field is at best an instantaneous snapshot of dynamic movement. There exist and there are emerging products that arguably can fulfil 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 are the following:

Wireless access as a means to provide Wireless Local Loop (WLL). This is 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 kilometres 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 GHz 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, the traffic and the subscriber density needs of highly urbanised 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 kilometres from the local exchange. 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. 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 licensed bands such as 1.9 GHz and 3.4 GHz.

Wireless broadband access for short range but very high-speed data (tens of Mbps) for businesses or public institutions. These systems generally operate in recently opened bands in the 10 GHz to 42 GHz range and can provide access at distances up to approximately 25 kilometres.

Wireless local area network access using radio to replace the cables of standard private local area networks. These systems can use unlicensed frequency bands, such as 2.4 GHz. They are typically intended for indoor use. Some systems offer outdoor radio adjuncts in order to link nearby buildings.

The remainder of this article discusses these applications in greater detail. Emphasis is given to the first two, the most widely deployed applications of wireless access, now providing telephone service to several million subscribers worldwide.

Wireless local loop

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 process commonly associated with the mobile cellular industry, wireless local loop has recently become an economically attractive alternative to traditional wired outside plant. For operators of telephony networks, outside plant often constitutes the major capital expense, and the choice of WLL can impact over 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 WILL technology shares some aspects of the common architecture of mobile systems - cellular technology, sectorisation, frequency reuse, low power, etc. - the best of WILL 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 of 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 lower cost, yet provide equivalent or better service.

To be a true commercial substitute for wireline, WLL systems seek to provide transparency. WILL is most attractive when it behaves in a similar manner to high quality wireline telephony, but at considerably lower cost. This means that the dialling procedures, the voice quality, the access to and behaviour of subscriber supplementary services and the call set up time closely match those provided by high quality wired lines.

The best of WLL technologies and products available today achieve excellent transparency, both for analogue as well as digital (ISDN) telephone service. Indeed, the highest complement that can be paid to a WLL product is for a typical end user not to be able 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, to reduce interference it must operate only in licensed radio bands. 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 GHz and 3.4 GHz bands.

Some WLL radio technologies such as DECT (digital enhanced cordless telecommunications) offer advanced radio techniques such as dynamic channel selection (DCS) to provide a high level of coexistence and excellent spectrum efficiency.

There exist perhaps 8 to 10 million WLL lines contracted in the world today. Most use their WLL connection for voice and voiceband 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$ 500-600. Prices have declined rapidly in the three years since the introduction of modern WLL systems, and they can be 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.

Early predictions by industry analysts foresaw 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 WILL is indeed expanding, but at a more moderate pace than many observers initially predicted. The reasons for this are many. The economic setback in Southeast Asia, the region that initially adopted WILL most vigorously, is one. The price differential between WLL and wireline is attractive, but not always sufficient enough 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, there is a hesitancy by some operators to adopt WLL. But as the industry undergoes its inevitable shakeout, it is likely that WLL systems will become more standardised 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 pressured now to standardise and align their operations and management systems with the rest of the network. Most significantly, the demand of operators that WILL systems support ever higher data rates requires vendors to continually evolve their systems. All these factors assure that we are likely to see both price declines and expansion of functionality in WLL systems 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. This 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 previous had little or none. It is therefore no surprise that the greatest numbers of WLL lines installed to date are in developing nations of Asia, Africa and Latin America. With the International Telecommunication Union reporting 962 million households worldwide lacking a telephone, this market for WLL looks promising almost indefinitely. As the price of providing telephony service declines, more and more of the planet's lower income population will find telephone service affordable. The portion of humanity with access to modern telecommunications may increase dramatically, due in no small measure to WLL.

Yet there are clear signs of a growing interest in WLL in developed nations as well. New and competitive telephone service providers seeking to offer access may find WLL an attractive means to enroll customers quickly and economically, and to gain quick profitability.

For new operators and existing operators with tight constraints on available investment capital, it is the incremental, modular nature of WILL and its speed of deployment that are key attractions. WILL can generally bring a return on investment much faster than wireline deployment because it can be deployed faster. WILL also allows the investment to be made in smaller increments, tracking demand and return on investment.

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, xDSL, and cable modems are deployed, WILL systems are pressured to match their capabilities. 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. For 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, we are likely to see WLL systems 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 ATM 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 ISP) direction. This might consist of a few mouse clicks or the typed entry of a web address such as http://www.telecoms-mag.com. 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 (TDD), it is significantly easier to adjust to asymmetry in real time than with frequency division duplex (FDD).

On the horizon, WLL systems are likely to continually incorporate various new technological advances such as smart antenna technology, the dynamic alternation 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 access over long distance

There is another category of fixed wireless access which can bring subscribers service from a telephone exchange when the subscribers are located at distances considerably greater that 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 point to multipoint (PMP) microwave radio. Under 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 GHz 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 kilometres distant 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 over a very wide range. 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 terminals (VSAT) 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 (DAMA) technology may be deployed to optimise satellite usage. Thus satellite resources are only allocated as needed. This makes it economically viable to provide access to a very small number of subscribers in extremely remote areas.

High speed packet data Internet 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 WILL 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 PPP protocols. For these products, internet/intranet access and virtual private networks between business locations are primary applications. Voice calls may or may not be supported.

These access systems may be used by operating companies that seek to compete with the high speed Internet access offered by cable TV providers and DSL connections. Customers for these products include Internet service providers, wireless telephony service providers, PTTs and competitive access providers. End users may be residential or business.

In addition to providing high-speed data access into public networks these systems may also be used to support virtual private networks between geographically distributed business locations.

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 Mbps, for voice and data applications for business customers. Mono-cellular, lineof-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 in order 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 GHz to 42 GHz, with somewhat different licensed bands allocated in Europe and North America. Included in this application is local multipoint distribution service (LMDS), a particular frequency band (28 GHz) within the overall category of wireless broadband access.

While this technology has not yet been widely deployed, a recent estimate by the Stategis Group for the infrastructure market for LMDS alone in the United States, is US$ 8 billion in the next ten years. In the USA, 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 (LECs), interexchange carriers (IXCs), Internet service providers (ISPs) 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 chose to make the investment in fibre. The wireless access equipment may then be re-deployed 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.

Wireless local area networks

We could not conclude a survey of the landscape of wireless access without mention of another class of products that has recently emerged commercially as the wireless alternative to in-building local area networks (LANs) for data communication. Because LANs are typically operated in an indoor environment, an unlicensed frequency band (e.g. 2.4 GHz) can be used. These systems allow terminals to be easily moved from one space to another yet remain connected to the LAN. Businesses, schools and government offices are typical customers for these systems. There are available today wireless LANs that match the data speed capabilities and reliability achieved by wired LANs. They offer the key advantage of allowing office equipment (terminals, PCs, printers, etc.) to be relocated within a building much more easily.

Conclusions

Wireless access has emerged in recent years as a viable alternative to wired access in a wide variety of applications. If there is a common thread to the progress made in this field, it is that the advances made by wired access technology can now quickly be matched by wireless equivalents, which generally can be deployed more rapidly and at lower cost.

Because wireless access equipment is above ground, it is easily accessible to technicians and thus easier to maintain. Because it is installed in discrete locations, its security concerns are often less than those of wireline access. In those cases where subscriber demand declines, such as businesses moving out of a building, wireless access equipment can be recovered and re-deployed, something which typically cannot be done with underground cable.

What we are seeing in wireless access today is due in part to the tremendous commercial success of mobile cellular telephony, which fostered great advances in radio technology and amassed the capital and interest in expanding the applications of wireless technology.

The first applications of wireless access have been to provide basic voice telephony. This application has proven quite successful in lowering the cost of providing telephone service and thus allowing the rapid expansion of teledensity in the less developed nations of the world. With the replacement of voice by data as the driving engine of modern telecommunications, wireless access is rapidly evolving to support ever-higher data rates using packet technology.

Thus wireless access brings the hope of access to modern telecommunications to that half of humanity that has never made a telephone call. But it also furthers the advancement and deployment of very high-speed data services in the most developed areas of our planet. In both domains, wireless access is one of the most exciting arenas in the telecommunications world today.

Gavone
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