Broadband technologies can be classified as either one-way or two-way. One-way technologies send digital information to the end user at very high speeds, but rely on some other means (usually an analog modem and a phone line) to receive information from the end user. One-way broadband technologies include digital television (DTV) and satellite. Two-way broadband technologies, such as cable and digital subscriber lines (DSL) send and receive digital information at very high speeds over the same medium. Two-way broadband technologies usually require a wired infrastructure.

Broadband technologies transfer sounds and images as a series of numerical values (ones and zeros). Digital transfer is a more noise-immune and reliable method then analog, which characterizes data as continuous. When data is transferred digitally, it takes up much less space than analog data.

The effective increase in bandwidth can be used to:

• Deliver Internet content faster

• Deliver compelling next generation content like streaming IP, electronic magazines and 3D product visualizations

• Deliver video and data together (V+D) which adds an element of interactivity to television

• Improve the display resolution of traditional TV programming (HDTV)

• Add more programs. Digital transfer allows at least four standard definition channels to occupy the same space that one analog channel occupies today

• Deliver a dedicated data services channel

Technology

Introduction Wireless Broadband
Wireless cable, also called fixed wireless broadband, is emerging as a legitimate local access platform for the delivery of high-quality digital data, video and voice services. Like their cable competitors, wireless operators are increasingly using their spectrum to offer high-speed Internet services.

Just like wired cable, a 6 MHz wireless television channel can support 27 Mbps of downstream data throughput using cable modems with 64 QAM (quadrature amplitude modulation) technology. Historically, a telephone-return path has been used for upstream communication, but operators are now transitioning to full two-way wireless delivery.

Wireless cable technology has limitations, but it also has key benefits, most notably, the ability to rapidly introduce high-speed data access throughout a metropolitan area without the cost or delay of wired plant upgrades. Rather than stringing thousands of miles of fiber, coax or twisted-pair wiring, a wireless operator installs a headend and transmission tower and is open for business. The technology received a major endorsement in April 1999 when telecom giants Sprint and MCI WorldCom purchased three wireless operators for more than $1 billion to build a broadband wireless local loop.

Wireless Cable Primer
There are several wireless spectrum blocks in the 2.1 to 2.7 GHz band that can be used for cable television and Internet services, including multipoint distribution service (MDS), multichannel multipoint distribution service (MMDS) and instructional television fixed service (ITFS). Additionally, wireless communications service (WCS) spectrum allocated in 5 MHz and 10 MHz increments and can be used for digital data or video. UHF (ultra-high frequency) broadcast television spectrum can also potentially be used for high-speed data access with cable modem technology, as can local multipoint distribution service (LMDS) spectrum, located in the super-high 27.5 - 29.5 GHz frequency range.

Wireless Cable Spectrum in the 2.1 - 2.7 GHz Band

Frequency Range Service Type Number of Channels Channel Width
2.150 - 2.162 GHz MDS 2 6 MHz
2.305 - 2.320 GHz WCS 2 5 & 10 MHz
2.345 - 2.360 GHz WCS 2 5 & 10 MHz
2.500 - 2.596 GHz ITFS 16 6 MHz
2.596 - 2.644 GHz MMDS 8 6 MHz
2.644 - 2.686 GHz ITFS 4 6 MHz
2.686 - 2.689 GHz MMDS 31 125 KHz

In the U.S., traditional wireless cable system operators have aggregated available MDS, MMDS and ITFS spectrum in a given market, providing up to 200 MHz of bandwidth, the equivalent of 33 analog 6 MHz television channels.

Like broadcast television, MDS/MMDS/ITFS transmission is based on line-of-sight technology. Wireless cable signals are transmitted from a broadcast tower, usually located on a mountain or tall building, to special antennas affixed to residences or businesses throughout a local market.

Reliable wireless service delivery requires a direct line of sight between the transmitter and the receiving antenna. As is the case with broadcast TV, obstructions like dense tree cover, hills, tall buildings, or even heavy precipitation can hinder reception. Multipath distortion (which results from signal reflections off of buildings or other structures) can also cause problems. Distance is a consideration too, as wireless cable signals can typically only be received within a 30-mile radius of the transmitter. Wireless cable operators believe these impediments can be overcome by dispersing a number of transmitters throughout a market in a cellular architecture.

Wireless Cable Modem Access Networks
Similar to delivering wired cable data services, a cable modem router and related networking gear is installed in the wireless operator?s headend. Digital data signals, such as Internet content requests, are then modulated onto radio frequency (RF) channels for broadcast transmission to roof-top antennas at subscriber locations. Coaxial cable is run from the antenna to a downconverter (which shifts the microwave signal frequency into the cable television band) and then into the cable modem inside the customer premise. The cable modem demodulates the incoming high-speed data signal and passes it on to an individual PC or local area network (LAN) though a 10Base-T Ethernet link. Wireless operators offering Internet access have typically used a telephone-return path for upstream communication, but they are migrating to full two-way wireless data delivery.

Cable modem manufacturer Hybrid Networks estimates that one 6 MHz wireless cable channel (MDS, MMDS, ITFS or UHF) can support 650 to 1,500 simultaneous active high-seed data users, providing peak downstream burst rates up to 1.5 Mbps or more to individual users. Assuming that only 20 percent of users are online at a given time, a single channel can support 5,000 subscribers, whether they are home-based consumers or individuals connected to a business LAN.

Two-Way Wireless Cable Modem Services
In the past, a key issue facing wireless cable modem technology was the lack of two-way capabilities. Reliance on a telephone return path limits upstream transmission speeds for end-users. Furthermore, it adds costs to the wireless service provider for incoming telephone lines and dial-up modem pools.

In the U.S., the FCC is approving the use of MDS, MMDS and ITFS spectrum for upstream and downstream broadcasts. A number of operators are trialing two-way services and PCTV is now offering two-way wireless cable modem service commercially in Phoenix.

Upgrading wireless cable systems to support two-way transmission is technically challenging, as it requires operators to convert broadcast television systems into networks that more closely resemble a cellular telecommunications platform. Additionally, a "transverter" must be added at the customer premise to transmit data upstream.

BROADBAND