Wireless Private Branch Exchange (WPBX)

Wireless Private Branch Exchange (WPBX)
WPBX systems integrate wireless telephones with a PBX switching system. Wireless PBX telephones (handsets) communicate through wired base stations (fixed radio transmitters) to the WPBX switching system. Most WPBX systems have automatic switching call transfer that allows wireless handsets to transfer their calls to other base stations as the move through the WPBX radio coverage areas. Base stations are strategically located around the served area (both inside and/or outside) to provide contiguous radio coverage. WPBX systems can be completely, or partially, wireless between the system and the telephone instruments.

WPBX systems fill a need where all, or part, of the work force is highly mobile in a relatively small area such as a building/plant or a small commercial campus. Hospitals and manufacturing plants tend to have several types of personnel that tend to be constantly on the move: medical emergency personnel, maintenance personnel, and production-line supervisors to name a few. Such people are frequently away from their desk or other fixed telephone station set location; however, it is often quite important that they be contacted quickly.

There are several different types of WPBX systems industry standard systems and proprietary systems. Some of the standard WPBX systems include digital enhanced cordless telephone (DECT) and cordless telephony second generation (CT2). A WPBX radio system allows for voice or data communications on either an analog (typically FM) or digital radio channel. The radio channel typically allows multiple mobile telephones to communicate on the same frequency at the same time by special coding of their radio signals.

The wireless office base station is the link between the radio transmissions sent to and received from the wireless telephone and the WPBX switching system. Wireless office base stations are similar to cell sites used in mobile telephone systems as they regularly communicate directly with the WPBX switching system. Because these base stations are fairly close to the switching system, they are directly connected by cable. This allows power to be supplied by the WPBX switching system and no battery backup power supply system is required.

The cable that connects the base station to the switching system typically carries multiple voice and/or data channels. The power and data signals may be supplied over a single twisted pair or dedicated lines may be used for data and power. As the signals arrive at the base station, a communications controller divides the multiple channels, processes their signals, and routes them to the base station radio signal amplifier.

The design objectives of a WPBX base station are similar to those of a general mobile telephone system, but there are several additional requirements. WPBX base stations must be much simpler to install, relocate and service (diagnose or debug). Operations without skilled or highly trained staff are very desirable. Many WPBX base stations are almost “self configuring,” implying that the system sets the frequencies of each base station automatically, to both optimize the overall frequency plan and to avoid interference with non-radio RF sources which may be present.

The WPBX switching system coordinates the operation of all the base stations and wireless handsets in the system. The switching hardware and software for the WPBX may be incorporated into the main office telephone system (integrated), may reside in a separate switching and/or control module (external), or be completely separate from any wired system (independent). Integrated systems allow one switch to serve all the base stations and wired telephones connected to the system. An external system is used when a radio system is added to an existing system or the older system cannot be directly upgraded to support handoff switching inside the main switch. Independent systems may be used when there is no wired system installed. An independent system may only consist of WPBX handsets that can access a public cellular system for office use at a reduced billing rate.

In a WPBX installation that has handoff (call transfer between base stations) capability, there is a continual process of signaling which occurs between all the handsets which are powered up but idle and the nearest base station(s). This allows the wireless handsets to handover (call transfer) between base stations as the move to other radio coverage areas.

Figure 1 shows a sample WPBX radio system. A WPBX system typically has a switching system that is located at the company. The WPBX switch interfaces a PSTN communication line and multiple radio base stations. Radio base stations communicate with wireless office telephones that can move throughout the system. A control terminal is used to configure and update the WPBX with information about the wireless office telephones and how they can be connected to the PSTN.


Figure 1: Wireless Private Branch Exchange (WPBX)