Clear-Com manufacture professional intercom systems for ‘command and control’ (cc) applications which include television studio and outside broadcast, large theatres as well as air traffic control and the more conventional CC areas.
Wireless ‘beltpack’ add-on subsystems have long been available, but no wireless outstations existed which could provide the full set of facilities of a wired panel: all users individually addressable or contactable in multiple flexible groups, one user belonging to several groups, some with one-way and others with full duplex voice.
Our brief was to design the radio system to enable such an outstation.
We used our pre-existing DECT software intellectual property, extending it to deliver a reliable 64 kilobit per second digital stream over the air. This was partitioned to give a control data link to support a fully-featured intercom user interface in the beltpack, and a wide-band speech link to allow day-long usage without fatigue.
We implemented a radio subsystem within the beltpack, a base station which is typically deployed in quantities of 5-30 depending on the coverage needed, and a control interface to Clear-Com’s switching matrix, to manage handover between base stations.
The DECT radio standard has a number of advantages for this type of application:
- Licence-free spectrum allocated across the EU/EEA and over 100 other countries
- Large capacity as the spectrum is further divided into time-slots
- DECT was conceived from the first as a cellular radio system, suitable for enterprise telephone systems
- The DECT chips are low-cost, as more than a billion have been sold worldwide
Clear-Com achieved a world first intercom system where full intercom features were delivered at the beltpack, radio channel planning was done fully automatically by the DECT subsystem, and seamless handover occurs as a user moves from stage or studio to corridor and onwards through the area of coverage.