Chapter 5

PAGING SIGNALLING PROTOCOLS (ENCODING FORMATS)

In a paging system, the paging terminal, after accepting an incoming page and validating it, will encode the pager address and message into the appropriate paging signalling protocol. The signalling protocol allows individual pagers to be uniquely identified/alerted and to be provided with the additional voice message or display message if any.

Various signalling protocols are used for the different paging service types, such as tone- only, tone and voice, etc. Most paging networks are able to support many different paging formats over a single frequency. Many paging formats are manufacturer-specific and often proprietary, but there are public domain protocols, such as POCSAG, which allow different manufacturers to produce compatible pagers.



ANALOG OR DIGITAL FORMAT

All formats fall into one of the two basic coding techniques: Tone Coding Format or Binary Coded Format. The first format uses an analog transmission technique while the second uses a digital transmission technique to transfer information to the pagers. In digital transmission, the signal to be transmitted is first digitized, i.e. it is converted into a form where it is represented by a series of ones and zeros. Digital transmission has many advantages over analog transmission, a very important one being its better performance in the presence of noise.

In the following, various analog and digital coding formats are described and compared.



TONE CODING FORMAT

In this format, a sequence of audio tones is used to identify each pager. As an example, we can use 3 tones f1, f2 and f3, combined two at a time to represent six pagers' identities as: f1f2, f1f3, f2f1, f2f3, f3f1 and f3f2.

Details of 2-tone and 5/6-tone paging formats can be found in Appendix A. Compared with binary coding formats, tone coding formats are slower and can support fewer subscribers. However, many paging systems still support this format because of existing old pagers.



BINARY CODED FORMAT

In binary coded formats, the address codes and information to be sent to the pagers are coded by the paging terminal into binary form, i.e. a series of ones and zeros. The binary code words are then sent to the pagers using the transmitter carrier signal. The carrier is made to vary between two discrete frequencies as the binary code words vary between ones and zeros. For example, with a carrier of 154.6 MHz, a digital "one" can be represented by 154.604 MHz and a digital "zero" by 154.596 MHz. This digital modulation (of the carrier frequency) method is called Frequency Shift Keying (FSK).

Binary coded formats provide the following improvement and features over the previous analog formats discussed:

a ) Larger number of codes with multiple address capability
b ) Expanded group call size and flexibility
c ) Multifunction capability: tone alert, tone and voice, and data paging
d ) Efficient battery saver operation
e )Fast signalling speed
f )Excellent error correction and reception probability



POCSAG
(POST OFFICE CODE STANDARDISATION ADVISORY GROUP)

This is a public domain digital paging format adopted by many manufacturers around the world.



Code Capacity

POCSAG can accommodate two million codes (pagers) each capable of supporting up to four addresses (for functions like tone-only, tone and voice, numeric display, etc).



Speed

POCSAG operates at speeds of up to 2400 data bits per second. At this rate, to send a single tone-only page requires only 13 milliseconds. This is about 100 times faster than 2- tone paging.



Error Detection/Correction

On top of the speed advantage is the error detection/correction capability built into digital coding formats. This allows errors in transmission to be detected and corrected. Details of the POCSAG format and its other features like efficient battery-saver operation, group call size and flexibility can be found in Appendix B.



FLEXTM High Speed Paging Code

With the explosion of wireless technology and dramatic growth in the paging industry in many Asian markets, existing networks are becoming more and more overcrowded. In addition, RF spectrum is not readily available because of demands by other wireless applications. In response to this problem, Motorola has developed the new FLEX high speed paging codes which will enhance a system's throughput and efficiency, allowing new and powerful features to be built into pagers as well as the networks. The new features will benefit both system operators and pager users.

One of the design goals for FLEX was to provide improved performance over POCSAG. Relative to POCSAG 1200, FLEX provides more than four times the number of pagers on an RF channel while providing much higher protection against signal fades common in FM simulcast paging systems. The combination of increased bit error correction capability of FLEX and superior fade protection improves the probability of receiving a message intact, especially longer alphanumeric messages.

More details on the new FLEX codes can be found in Appendix C or on our FLEX Product Family pages.



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Copyright 1995, 1996, Motorola, Inc. All Rights Reserved.
Last updated: June 5, 1996