Operating Environments | Wireless Local Loop

WLL systems are designed to provide operators with cost-effective fixed wireless solutions as an alternative to traditional wireline system deployment. Fixed wireless system implementation can provide rapid revenue generation to existing cellular operators in areas with established subscriber bases, to entrepreneurial operators licensed to provide basic telephone service in new areas, and to existing phone companies for areas not yet served.

Some of the scenarios where WLL systems can provide a competitive advantage in the market are:

§  Existing landline operators that need to extend their networks to remote locations

§  Cellular operators that want to leverage their current network to deliver residential service

§  New service providers that need to deploy nontraditional wireless solutions to rapidly meet a community's telephone needs

As demand for basic telephone service increases in many areas of the world, alternatives to costly copper wire implementation become increasingly important to operators that are trying to meet subscriber demand. WLL systems can serve not only to supplement overloaded wireline networks in urban areas, but also to provide service to low-density rural areas.

The WLL systems are installed all over the world, but mostly in the developing countries of Asia, Africa, Latin America, and Western Europe, where a wireline infrastructure is either nonexistent or not extensive enough to keep up with the demand for communication services.

In China, for example, the Ministry of Post and Telecommunications specified WLL systems as an essential element of its five-year plan to install up to 14 million lines annually through the year 2000. The move reflects the government's efforts to establish access network standards for the entire country, as well as recognition among the highest levels of government that WLL systems are the only way to offer telecommunications services in a timely manner on such a massive scale.

In the city of Shanghai, with a population of over 12 million, 1300 new requests for telephone service are submitted to the local telecommunications authority every day. In addition, as the city undergoes extensive reconstruction projects, many potential and existing telephone users are being forced to move, which creates a substantial challenge for the telecommunications authority in planning and installing new lines.

CDMA-based WLL systems from Motorola, operating at 1.9 GHz, are being installed in Shanghai (and elsewhere in China) out of the need to reduce the telephone waiting list and to cope with continual large-scale urban changes. These systems are compliant with the European Telecommunications Standards Institute's (ETSI) V5.2 open standard interface, enabling their interconnection with existing PSTN switching platforms.

The V5.2 open interface, approved by the ETSI in 1994 and later approved as an International Telecommunications Union (ITU) standard, is intended to allow operators to mix and match local exchange equipment and local access equipment, irrespective of competing suppliers. Enhancements incorporated into the V5.2 standard allow for wireless extensions into the local telephone loop.

In 1995, Motorola and Fujitsu were among the first vendors to develop and deliver complementary products utilizing the V5.2 digital open interface for fixed wireless phone systems in the international market. The interface is available on Fujitsu's FETEX-150, a full digital switching system with an installed base of almost 30 million lines worldwide. The switch is especially popular in China, where 15 million FETEX-150 lines have been installed as of mid-1997.

Technological Approaches | Wireless Local Loop

Wireless local loop technology falls into four general categories: analog cellular, digital cellular, proprietary fixed wireless, and cordless telecommunications.

First-generation wireless local loops are based on analog cellular technologies, which have a solid track record of performance, support a relatively wide coverage area, and provide economies of scale for infrastructure and handsets. The key drawback with analog cellular is that it is optimized for mobility rather than local loop service; since user bit rates are low, wireline voice quality is elusive.

Digital cellular offers greater capacity and better voice quality than analog cellular, but it too is geared toward mobile applications. Coverage areas are usually smaller than with analog and there is a profusion of industry standards. Even when there is general agreement on standards—as there is with GSM, for example—the frequencies over which it operates may differ from country to country.

Proprietary systems—such Nortel's Proximity I Series—are designed from the start as alternatives to the copper-based local loop. They operate at higher frequencies, usually 3.5 GHz or above, where the spectrum is less crowded. They provide high-quality voice at 32 Kbps via Adaptive Differential Pulse Code Modulation (ADPCM)—versus 8 Kbps or 13 Kbps used in most WLL systems—and support voice-band data modems and high-speed fax transmission at up to 28.8 Kbps. These systems are interoperable with the PSTN and are aimed at new operators in competitive markets, where the challenger must be able to match the advanced service offerings of the wired incumbent to have any chance of success. The key disadvantage with these proprietary approaches is that they do not usually support mobility.

Some WLL systems make use of the standardized cordless telecommunications systems—including CT2, DECT, PACS, and PHS. While all are well suited for deployment in dense urban areas, and offer higher quality voice at 32 Kbps and data services up to 28.8 Kbps, each has its strong points. CT2 (Cordless Telephone Two) makes a good pair-gain system for countries with an existing, but insufficient, feeder network infrastructure. DECT (Digital Enhanced Cordless Telecommunications) is a proven technology widely used in Europe in wireless PBX implementations, while PHS (Personal Handyphone System) has been successful in Japan and is headed toward becoming a pan-Asian standard.

PHS offers high-quality, low-cost mobile telephone services using a fully digital system operating in the 1.9-GHz spectrum. Originally developed by NTT, the Japanese telecommunications giant, PHS is based on GSM technology. In addition to personal communications, PHS is being used in wireless PBX and wireless local loop applications.

PACS (Personal Access Communications System) is based on Bellcore's Wireless Access Communications System (WACS) and on Japan's PHS. Operating in the 1.9-GHz licensed PCS band, PACS provides an approach to PCS that is fully compatible with the local exchange telephone network and interoperable with existing cellular systems. PACS supports mobility better than the other standards—at vehicular speeds at over 65 miles per hour—and it also can be used for pedestrian venues, commuting routes, and indoor wireless. Although some vendors are now getting behind PACS in the United States, they face an uphill battle for market acceptance, if only because they got off to a late start—the major service providers having already committed to their WLL strategies.

All of these technologies work well enough and the costs are very attractive. In fact, WLL technology is now far more economical than copper-based local loops. Wireline local loops now cost anywhere from $1000 to $2000 per subscriber to provision, depending on the distance of the subscriber to the central office switch, while wireless local loops are down to about $500 per subscriber, regardless of the distance of the subscriber to the local switch.