Broadband Wireless Systems

                                The market for broadband communications is growing rapidly, and the potential applications and services are numerous and diverse. Several technologies are currently being developed to offer such services. Both wired and wireless system solutions aim to win a share of the market. The wired contenders include digital subscriber lines (xDSL), cable modems and others. The wireless contenders include satellite communications systems, stratospheric communications systems, and terrestrial communications systems, specifically, Multipoint Multichannel Distribution Service (MMDS) and Local Multipoint Distribution Service (LMDS). While these systems do not all target identical market segments, the likely markets do overlap. The various broadband wireless access systems compete therefore more against high-speed wired solutions than against each other. Table III-1 from Allied Business Intelligence, Inc. presents a forecast of market share for various high-speed communication solutions [BWS1]. This forecast projects that wired technologies would command about 75 % of subscribers in the year 2003.

Broadband Subscribers by Technology, US Market, 2003

(source Allied Business Intelligence, Inc.)

ADSL            36 %

Cable Modem 26 %

ISDN             12 %

Satellite           12 %

LMDS          9 %

Others           5 % 

A. Terrestrial Broadband Wireless Systems

     A common way to classify broadband terrestrial, wireless fixed communications systems is to call systems using frequencies below 10 GHz MMDS systems and to call systems using frequencies above 10 GHz LMDS systems. The motivation for this classification is that the propagation characteristics are quite different at say 30 GHz than at 5 GHz. Equipment and components for frequencies under 10 GHz are mature, while equipment at higher frequencies is based on technology that still is relatively new and expensive. Systems at frequencies above 20 GHz are for fixed users. Systems below 10 GHz are also for fixed users, but may evolve to serve mobile users.

A.1 MMDS (Multipoint Multichannel Distribution Service)

     MMDS is often referred to as wireless cable [BWS2]. In 1996, the FCC auctioned off licenses in the 2150-2162 MHz band and the 2500-2686 MHz band in 493 markets within the US. In September 1998 the FCC cleared the way for using the spectrum for two-way digital services [BWS3]. New rules also allow more freedom for various other uses within these bands. This new authorization will effectively enable voice, video, and data over wireless cable. However, the bandwidth allocated to the return link is modest (2686-2689.6 MHz). A number of operators are offering commercially high-speed Internet access, where the telephone line is used as return link. Many trials are underway for wireless two-way data, voice and video communication.

A.1.1 Technical Overview.

     MMDS operators broadcast multiple TV channels or related services from an antenna located on a tower, tall building or mountain. The signals are received by microwave dishes typically about 40-50 cm in diameter, or perhaps larger in outlying areas. Information can be distributed within 25 or 30 km within line-of–sight from each main tower. A block down converter integrated into or mounted on an antenna mast translates the received signals into the band utilized by standard cable TV. A set-top converter identical in function to a standard cable TV channel selector is located near the TV receiver. Digital TV requires a set-top box for every television set. When Internet access is provided, the downstream data rate for individual subscribers can be up to 750 kbps.

     The total data rate offered by a base station is on the order of 1 Gbps, depending on coding, modulation and roll-off factor. Sectorization will however increase this number. For instance, with a reuse factor of 18 (10 degree sectors), the cumulative downstream data rate for one base station is almost 20 Gbps [BWS4]. For upstream, the available bandwidth is much smaller, and a less complex modulation scheme is likely to be used to allow low power transmitters at the subscriber location. The data rate will therefore be much smaller, on the order of 6 Mbps, without sectorization [BWS5].

A.1.2 Prediction for the Future of MMDS

      Some hard times have plagued the MMDS industry in recent years. For instance, in October 1998 Heartland Wireless Inc, America’s largest MMDS provider with approximately 165,000 subscribers, was delisted from the NASDAQ stock exchange. Heartland reportedly failed to meet minimum closing bid and net tangible asset requirements. Residential users constitute the main market for MMDS systems, even though MMDS is being offered to small and medium businesses. The main applications for MMDS include TV, either broadcasting or on demand, and Internet access. The competition from cable companies and telephony companies is hard, leading some people to question the market viability of MMDS technology. MMDS systems have however the advantage that they run at a relatively low frequency. The cost of microwave components at 5 GHz is relatively modest, permitting low-cost customer premise equipment (CPE) and components that are readily available today. Introducting cellularization and sectorization into MMDS will however add complexity and cost to the system. Another advantage of MMDS systems is easy deployment. An MMDS system can be deployed typically in from two to six months. Later this year some operators are planning to offer business Internet services over MMDS that compete directly with asymmetric digital subscriber line (ADSL) services [BWA20]. For example, DataChron, which offers MMDS in Boston and New York, charges corporate customers $99/month for access by one workstation and $249/month for access by ten or more workstations. DataChron also offers home service for $49/month. MMDS coverage for wireless digital TV is also expanding somewhat, especially in the territory covered by BellSouth.