Radio paging code No. 1

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Radio paging code No. 1 (commonly known and hereafter POCSAG called) refers to a protocol for paging services , developed by the British Post Office Code Standard Advisory Group , whose acronym is the colloquial name of the protocol. Structure and mode of operation are based on the recommendation Rec. ITU-R M.584-2 of the international telecommunications union .

functionality

A radio call always consists of at least a preamble, a sync word and a batch. A batch consists of eight frames, and each frame contains two code words.

preamble

The preamble consists of a 576 bit long 1-0 sequence, which corresponds to the length of a batch + a frame (i.e. a total of 9 frames). It is used to synchronize the receiver with the radio call.

Sync word

A sync word is always 32 bits long and serves to separate the preamble and the first batch or the batches from one another. It is always composed as follows: 01111100 11010010 00010101 11011000.

code word

A code word is also 32 bits long. A distinction is made between address and message words, which are composed as follows:

Bit (s) 1 2 to 19 20 to 21 22 to 31 32
Address word Code word description (0 for an address and 1 for a message) 18 most significant bits of the address Function bits Checksum Parity bit
News word message

Addresses

The addresses are 21 bits long. These are divided into a most significant part (18 bits) and a least significant part (3 bits).
The 18 most significant bits are transmitted within the address code word.
The three least significant bits are not transmitted within the code words , but result from the position of the address code word . For this purpose the eight frames of a batch are numbered (0-7). This numbering results in exactly 3 bits (2 3 = 8).

example

  • 18 most significant bits within the address code word: 100101101001011001.
  • The address code word is part of frame no. 3. This results in the following three least significant bits: 011.

The 18 most significant and three least significant bits now only have to be merged and result in the following address: 100101101001011001011 (1 233 611).

reception

A radio signal receiver (short: pager) is a small device with an HF receiver and a decoder for POCSAG signals. Another way to display POCSAG messages is to connect a receiver (e.g. radio scanner or radio device) to a computer and let software do the decoding. Each paging service has its own frequency and each pager has its own address, whereby group formation is also possible.

  • Skyper (converted for amateur radio POCSAG)

  • Unication Alpha Elegant / Legend digital alarm receivers

Frequencies in Germany

Example of a POCSAG transmission on amateur radio

The frequencies are assigned by the Federal Network Agency and are:

Organization (s) Frequency range
BOS ( 2 meter tape ) different frequencies in the range of 163-174 MHz
Amateur radio paging service 439.9875 MHz
Radio paging network # TeLMI (1995 to 2002) 448.425 MHz
e * message / e * Bos (runs in the 70 cm band on the old Telmi frequency) 448.425 MHz
Quix (operation 1995 to 2000) 448.475 MHz
Skyper (operating 1996 to 2013) 465.970 MHz
Cityruf / Euromessage 466.075 MHz
Scall (officially operating from 1994 to 2002, actually until 2010) 466.230 MHz

In the area of BOS radio , POCSAG is used for digital alerting in the 70 cm band and in the 2 m band - that is, fire and rescue services receive their orders, more precisely: the place and occasion (partly with geographic coordinates) of the operation sent to the detector, with the alarm in the 70 cm band being carried out throughout Germany (via around 800 transmitter stations) and the alarm in the 2 m band being limited to the appropriately equipped district or the respective city. However, the 70 cm version is a commercial offer, so the responsibility lies with the network operator. The 2-meter variant is the official variant, which is borne by districts and district-free cities, where responsibility for the system lies in one hand.

However, POCSAG is not a bidirectional communication with pager function like TETRA , which is to be aimed for in the area of ​​“authorities and organizations with security tasks” in the next few years. This means that the transmission only takes place in one direction, i.e. from the alarm transmitter to the receiver (simplex).

Frequencies in Austria

In Austria, a nationwide pager network with POCSAG protocol has been set up for the entire federal state of Lower Austria since 2004 in addition to the TETRA radio, which is also used in parallel, and is used by 144 Lower Austria emergency calls under the name pagernetz.at as an alarm means for the rescue equipment including the helicopter or First Responders as well as the fire brigades. In the state of Vorarlberg , the rescue and fire brigade control center (RFL) operates a pager network with which all organizations and authorities with security tasks can be alerted and informed across the board. In the state of Salzburg, the Red Cross Salzburg has been using a pager network for alerting people since 2002.

Software for decoding POCSAG messages

program basis License
BosMon Windows free
BOS2Web Apache / MYSQL commercially
FMS32 / FMS32pro Windows commercially
FMS Crusader Java Runtime Environment commercially
monitor Linux Predecessor of monitord
monitor Windows / Linux Open Source under GPL (v3)
MultimonNG Multiplatform (Windows, Linux, Mac, etc.) Open Source under GPL (v2)
OpenPoc Windows / Linux GNU General Public License (GPL)
PDW Windows Open Source under GPL (v3)
Poc32 Windows Open Source under GPL (v3)
Radio operator Windows commercial (GPL violation)
soRFmon Windows Freeware
pocsag-mrt GNURadio Open source under GPL

Web links

Individual evidence

  1. ↑ RECOMMENDATION ITU-R M.584-2 CODES AND FORMATS FOR RADIO PAGING. Retrieved January 20, 2019.
  2. ↑ pagernetz.at accessed on November 8, 2010
  3. ↑ Alerting quo vadis ( Memento of November 10, 2013 in the Internet Archive ) (PDF; 108 kB) pagernetz.at; Retrieved April 27, 2013
  4. ↑ Radio and alarm network in LFV Vorarlberg accessed on May 6, 2019