Basic characteristics

DECT is a micro-cellular radio communications system that provides cordless access between 'portable parts' (DECT handsets) and 'fixed parts' (base systems) at ranges from 30 meters indoors to three hundred meters outdoors.

DECT is an access technology. This means that it has no switching functions, but only a way to access a network. This may be a telephone network, but can also be a computer network. In the later case the DECT handsets are dataterminals exchanging information with a host computer. Also the so called portable part can be a cordless terminal adapter (CTA) providing a 'wireless local loop' as the final link between the local telephone exchange and the fixed telephone at home.

The typical characteristics are as follows

Frequency band	1880 MHz - 1900 MHz
Number of carriers	10
Transmit power	250 mW peak
Multiplex schema	Time Division Multiple Access
Multiplex frames	10 ms, devided into 24 slots
Duplexing	Time Division Duplex on same carrier
Bit rate	1152 kbps
Channel throughput	32 kbps user data (speech), 6.4 kbps control data

A duplex connection is made by transmitting bursts of data evenly spaced in the defined time slots on the same carrier. The first twelve time slots are used by the fixed part, while the portable part transmits in the last twelve time slots. Based on ten carriers this provides for 120 possible circuits. Since a radio tranciever can work on one frequency at a time, this means that in a cell the fixed part tranceiver can handle up to twelve simultaneous calls.

The protocols are designed such that system installations in the same area proves no problem. Continuous Dynamic Channel Selection (CDCS), that is checking the quality of a physical channel before and during use, and secure exchange of identities provide for a peaceful co-existance of the systems.

Furthermore the DECT protocols provide for seamless hand-over of calls, both intracell (within the coverage area of one radio tranciever from one channel to another) and intercell (from a channel to one radio tranciever to a channel on another radio). In this way the portable part can, by using CDCS, ensure the quality of the connection and maintaining it while moving around.

Traffic capacity

Traffic capacity in telephony is expressed in Erlangs (E). It is the amount of active calls per time period. Measured for a single telephone one six minute call per hour would mean a traffic load of 0.1 Erlang. To keep cost down telephone exchanges usually have a switching network that can handle only so many simultanious calls. This is called a blocking switch. If more calls have to be connected than possible the extra calls are blocked. Therefor a prediction has to be made on what traffic load can be expected. In a business environment usually a lot of telephone traffic is generated. The DECT system has to be able to support this. Based on its micro-celluar achitecture and dynamic channel selection it is capable of handling over 10000 Erlang per square kilometer. This means that it can handle up to 100000 users per square kilometer per floor generating an average load of 0.1 Erlang. Other cordless telephone systems, like CT2, are capable of handling up to 500 Erlang per square km.

Written by my own two hands and an ASCII editor. Problems? write me Last updated June 28, 1999

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