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post office code standardisation advisory group (mobile communications) (POCSAG)

Post Office Code Standardisation Advisory Group (POCSAG) is a signaling code for paging systems. A paging call consists of the receiver message and the receiver address, which is sent in the header before the message. The paging receiver ( pager) recognizes its own address when it is switched on and can demodulate this message and display it on the pager's display.

POCSAG-based paging systems transmit at 512 bit/s, and newer systems also transmit at 1.2 or 2.4 kbit/s. Pocsag supports messagingon the lower three layers as one-way communication, since no return channel is provided for paging systems. POCSAG can address up to 2 million pagers per frequency, and all call classes - tone-only, numeric and alphanumeric - can be transmitted. In addition, the current- slot technique used in POCSAG enables effective, power-saving pager designs.

The POCSAG data frame consists of a preamble of at least 576bits in a 0-1 sequence and a number of code word groups. The number of codeword groups depends on the traffic offer and on the number of call repetitions. The typical duration for a time slot is 28 seconds, which corresponds to 24 codeword groups at a 512 bit/s transmission rate. At a transmission rate of 1.2 kbit/s, it is 54 codeword groups. A codeword with 18 bits is available for the receive address and 2 further bits for the sub-address, which determines the call class. Check and parity bits complete the transmission frame.

If the pager is also to be used for group calling, then it requires a complete second addressing as well as four additional bits for call class transmission.

Informations:
Englisch: post office code standardisation advisory group (mobile communications) - POCSAG
Updated at: 08.07.2011
#Words: 256
Links: code, paging, receiver, message (MSG), address (A)
Translations: DE
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