Fixed wireless telephone service: A Unisys technical backgrounder

Business Wire, July 25, 1995

BLUE BELL, Pa.--(BUSINESS WIRE)--July 25, 1995--Today, more than 100 years after the invention of the telephone, half of the world's adult population has never made a single phone call in their entire life.

In a world of over 5 billion people, there are still only 500 million telephone lines.

Some of the major obstacles to broader, worldwide telephone penetration are the high cost and delays associated with installing and maintaining wireline service.

By and large, telephone service is today delivered over "wire" -- either copper wire or optical fiber. In particular, the last portion of the phone network that connects to the customer's office or residence -- referred to in the telephone industry as the "local loop" -- has long been the nearly exclusive bastion of copper wire.

On average, telephone companies invest between $1,000 and $1,500 in wireline plant for each and every telephone customer. Wireless technology can equip service providers with an alternative provisioning option that lowers both this initial cost as well as overall lifecycle costs (e.g., maintenance) and offers the benefit of a more rapid installation.

Unisys, Loral Communication Systems and Granger Telecom have together developed a wireless local loop solution -- an application of the spread spectrum communications technology Unisys first deployed for military uses -- that brings the economics of wireless communications to traditional telephone service.

In this wireless telephony solution, a radio base unit, attached to the telephone network and centrally positioned among the numerous subscriber sites, communicates to a subscriber unit located at each subscriber site to provide a wireless radio link from the telephone network to the end user premises.

HOW SPREAD SPECTRUM WORKS

The wireless local loop solution being developed and deployed by the three companies is based on leading-edge spread spectrum communications technology.

Spread spectrum takes digital communications signals and scatters them in a seemingly random pattern across a wide electromagnetic spectrum using very low-power signals. Originally developed by Unisys to provide secure broadband communications for the U.S. Department of Defense, the high-speed digital communications technology has numerous potential commercial benefits.

It is more secure and more immune to interference than traditional transmissions, such as those used for cellular telephone service, and able to carry multiple simultaneous signals over the same communications band. Twenty years of deployment experience in the hostile environment of military communications has shown this technology to be robust and fully field-proven under the most rugged conditions.

HOW SPREAD SPECTRUM WORKS FOR WIRELESS TELEPHONY

The capabilities of spread spectrum communications -- security and immunity to interference, multiple simultaneous communication signals and transmission over long distances with a very low- power radio signal -- work well for wireless telephony applications that need to support multiple residential and business phone subscribers distributed over a wide geographical distances.

Unlike many competing wireless alternatives, the Unisys spread spectrum-based system is capable of delivering up to 64 kilobits-per-second (kb/s) or more of both voice and data telephone service to customer locations up to 30 kilometers (18.6 miles) away.

Other wireless telephony solutions lack the flexibility to provide both a full 64 kb/s service for high-speed data and facsimile applications and services at speeds lower than 64 kb/s for bandwidth-efficient voice telephone service.

Digital wireless communications has many distinct technical advantages to analog wireless implementations, including improved voice quality, flexibility of service and the ability to seamlessly upgrade the wireless infrastructure to support future service options, including Integrated Services Digital Network (ISDN).

The advanced digital communications technology also uses Code Division Multiple Access (CDMA), rather than the more commonplace Time Division Multiple Access (TDMA), reducing the need for additional frequency allocations and allowing greater capacity with the available radio frequencies.

The topology of a wireless local loop network is comparable to current cellular telephone systems, in that a single base unit acts as the access port into the landline network much like a cellular Base Station does for the mobile cellular users in a local geographical area.

In the same manner as the cellular system, a variable number of users may access the public telephone network through a given base unit in a single cell, with any number of cells deployed in a contiguous manner to provide the appropriate coverage.

The biggest difference between a cellular network and a wireless local loop, of course, is that the subscriber unit is permanently installed on the subscriber residence so that the phone service is not mobile.

The Radio Base Unit

The Unisys wireless telephony radio base unit equipment connects to the telephone network via one or more 2.048 megabits-per-second (Mb/s) communications trunks (E1 speed) provided to each base unit site via twisted pair (copper) wire, fiber optic cable or microwave radio. The wireless base units can be easily located in existing telephone network switching offices.