Previous Table of Contents Next


Cordless Telephony And Wireless Office Telecommunications Systems (WOTS)

Wireless Office Telecommunications Systems (WOTS) are adjuncts which provide cordless telephony communications capabilities behind PBXs, Electronic Key Systems, Hybrids, or Centrex. They generally are limited to voice applications, although some support low-speed data as well, typically using CDPD technology. WOTS systems involve a wireless master controller that is hard-wired to special ports on the PBX, KTS, Hybrid, or Centrex. As illustrated in Figure 12.7, the master controller, in turn, is hard-wired to subcontrollers and antennae that are distributed throughout the office complex or campus in a picocell configuration. The terminal equipment is in the form of wireless handsets, that are generally low in cost and limited in range. Some multifunction handsets exist, that can be used as traditional cellular phones when the user so desires [12-8].


Figure 12.7  Wireless Office Telecommunication System (WOTS) configuration.

Actually an extension and application of common cordless telephony, WOTS provides the advantage of mobility for select employees who must have the freedom to wander around the complex, but who must have communications capability at all times. The cost of WOTS currently is in the range of $1,000 per user, but with likely drop in the near future.

Cordless Telephony Standards

There exist multiple cordless telephony standards used to provide WOTS service including CT1, CT1+, CT2, CT2+, CT3, DECT, Part 15 and AMPS [12-14] and [12-15].

CT1 (Cordless Telephony Generation 1)
was developed in Europe, where it was known as CEPT-1. CT1 operates in the 900 MHz range over 40 channels; two separate channels are used, one for transmission and one for reception. CT1 is analog and low-cost, but limited in range. Manufacturers are numerous, including AT&T and Telenorma.
CT1+
a variation on CT1, was developed in concert by Belgium, Germany and Switzerland. CT1+ was intended as the basis for a public wireless service, along the lines of Telepoint. Although CT1+ was not successful, it did originate the concept of a Common Air Interface (CAI), which allows multiple manufacturers to develop products in support of a public cordless telephony service offering.
CT2 (Cordless Telephony Generation 2)
was developed in the U.K., where it formed the technology basis for the ill-fated Telepoint service. CT2 is a digital technology deployed in Europe, Canada, and the Asia-Pacific. While it originally supported only outgoing calling, contemporary implementations support two-way calling. CT2 uses FDMA and does not support hand-off; therefore, the user must remain within range of the antenna used to set up the call. CT2 uses 4 MHz of bandwidth divided into 40 channels—20 for transmission and 20 for reception. Dynamic channel allocation requires a frequency-agile handset. CT2 was the first international standard providing a Common Air Interface (CAI) for systems operating in the 800 MHz and 900 MHz bands. It is used in Canada and enjoys wide acceptance in Asia. Manufacturers include GPT, Multitone Electronics, Nortel (nee Northern Telecom), and SAT.
CT2+
is an improvement on CT2, supporting two-way calling and call hand-off. CT2+ uses 8 MHz of bandwidth in the 900 MHz range. CT2+ is based on dynamic channel allocation, requiring frequency-agile handsets. Encryption is supported for improved security. A common signaling and control channel offers improved call setup times, increased traffic capacity and longer battery life, as the handset must monitor only the signaling channel. CT2+ has been used in applications such as the Walkabout trial in Canberra, Australia.
CT3
developed by Ericsson in 1990, is designed for high-density office environments using TDMA. CT3 uses the same frequency bands as CT2+, supporting roaming and seamless hand-off. CT3 has application in a telepoint application (PCS), as well as in office applications (WOTS).
DECT (Digital European Cordless Telecommunications)
is the pan-European standard for digital cordless telephony, using TDMA. Ratified by ETSI in 1992, DECT operates in the 1880 to 1900 MHz frequency band that recently was set aside for that purpose in all EC member nations. Designed for high-density environments, DECT supports hand-off; the user can roam from cell-to-cell within the range of the WOTS system. Functionally, DECT is much like CT3. In addition to public cordless telephony, DECT supports wireless PBX, wireless LAN, and WLL. According to Northern Business Information and Datapro, the market for DECT-based WOTS will grow at 1 to 2 million extensions per year, solidifying DECT’s position [12-15]. Manufacturers include Alcatel, Ascom, Ericsson, Philips, and Siemens. DECT also is endorsed by ETSI for use in Wireless LANs in Europe.
Part 15
FCC frequencies are used in the United States by AT&T and others for the provisioning of WOTS. These unlicensed frequencies are in the 902 to 928 MHz range, also known as the SIM (Scientific, Industrial, and Medical) band. They, therefore, are subject to interference from industrial microwave ovens, barcode scanners, security systems, and other devices. The FCC set aside the 1.910 to 1.930 MHz spectrum for communications within buildings. At this writing, the spectrum remains to be cleared of existing microwave users. Manufacturers include AT&T, Ericsson, (Rolmphone 900) and SpectraLink.
AMPS (Advanced Mobile Phone System)
analog cellular frequencies are used in some U.S. systems, including Bell Atlantic Mobile (Office Direct) and Southwestern Bell Mobile Systems (FreedomLink). Manufacturers include Panasonic.
PCS
frequencies in the 1910-MHz to 1930-MHz band are used by some manufacturers, including Nortel. These frequencies were recently set aside by the FCC for use in private PCS applications, and do not require licensing [12-16].


Previous Table of Contents Next