30.5 ADVANCES IN RADIO PAGING

< Day Day Up >

One-way radio paging provides a very low-cost messaging system. To make the paging system more efficient and useful, a number of improvements have been made for the basic paging system described previously.

Voice paging: Instead of sending an alphanumeric message, a voice message can be sent to the pager. This avoids taking a message from the user by the operator and then typing the message and sending it to the base station. The voice message will be sent to the voice pager, and the paging subscriber can listen to the message. However, voice paging requires higher bandwidth. To reduce the bandwidth, low bit rate voice coding techniques are used.

For example, voice can be coded at 2.4kbps using a low bit rate coding technique such as linear prediction coding (LPC). If the voice message is for 60 seconds, the total data rate is 2.4kbps × 60 = 144kbps. If 10 such messages have to be stored in the voice pager, the total memory requirement will be 1440kbits (1.44Mbits or 0.18MBytes).

Note

To reduce the transmission data rate as well as the memory required in the pagers, voice is coded at low bit rates in voice paging systems.

Automated paging systems: To avoid the operator at the paging controller, automated paging systems are used wherein users can log in to a computer at the paging controller and send a text message that will be broadcast over the paging network. With unified messaging, it is possible to send a message to a pager by sending an e-mail to the pager. The e-mail will be forwarded by the Internet service provider to the paging service provider.

Voice paging, two-way paging and multi-lingual paging are the major advances in paging systems. Operator-less paging systems are also on the anvil.

Two-way paging systems: One-way paging systems have the disadvantage that the subscriber cannot send back a message or reply to a received message. Two-way paging allows a paging subscriber to send a message. The pager contains a keyboard and a transmitter. Hence, the cost of the pager goes up.

Multi-lingual paging systems: In many Asian countries, the paging systems need to support local languages in addition to English. Paging systems that support multiple languages are known as multi-lingual paging systems. The pagers used in such systems need to support graphic characters. Presently, multi-lingual pagers are being developed using Unicode. Unicode facilitates representation of any character of any of the world language using 16-bits.

With the advent of cellular mobile communication systems that provide two-way voice communication as well as Internet access through the mobile phone, paging systems have lost their popularity in recent years. In the next chapter, we will study cellular mobile communication systems.

Summary

In this chapter, the details of radio paging systems are presented. Radio paging is a low-cost service that can be provided to people on the move. From a radio paging base station, a short message will be broadcast to all users in the service area. This message also contains the address of the pager. All the pagers in the service area will receive the message, but only the pager whose address matches the address received will display the message. Pagers can be divided into different categories: beep pagers, numeric pagers, alphanumeric pagers, and voice pagers. Presently, two-way pagers are available that allow transmission of short messages from the pager. With the advances in mobile communications that support two-way voice communication, the importance of paging systems has decreased considerably. However, even in mobile voice communications, paging is used to locate the mobile user, and therefore an understanding of the concepts of paging is very important.

References

R. Horak. Communication Systems and Networks. Third Edition, Wiley-Dreamtech India Pvt. Ltd., 2002.
http://www.bearnet.demon.co.uk You can get more information on the POCSAG standard from this site.
http://www.motorola.com Motorola is one of the leading manufacturers of paging equipment. You can obtain information about commercial paging systems from this site.

Questions

Explain the operation of a paging system.
What is simulcast paging? Explain its operation.
What are the different categories of pagers? Give the different frequency bands in which paging systems operate.

Exercises

1.	Is it possible to eliminate the need for an operator at the paging terminal interface (refer to Figure 30.1)? If so, work out the framework for achieving it. (Note: Any PSTN subscriber should be able to dial in to a computer located at the paging terminal and leave a message that will be broadcast to all the pagers. This calls for automatic speech recognition software that is not reliable. An alternative is to use a computer to send the message through a modem.)
2.	Calculate the storage requirement for a voice mail pager if the pager has to store 10 messages. Assume that each message is 30 seconds long and voice coding is done at 5.3kbps.
3.	For a voice paging system that uses 2.4kbps voice coding, what is the memory requirement on a voice pager that has to store 20 messages, each 30 seconds long?
4.	Search the Internet for POCSAG and obtain the decoder software that runs on the PC.

Answers

1.	In automatic paging systems, there is no need for an operator at the paging terminal interface. A user can dial into the paging terminal's computer and speak the paging message and the pager number. The automatic speech recognition software will convert the spoken message into text format and then send the message. However, with the present state-of-the-art, speech recognition accuracy is not very high. An alternative mechanism for automatic paging is to use a computer to send text directly to the paging terminal. The paging terminal can be Web-enabled. Any user can access the terminal's computer over the Internet and submit a message for paging.
2.	Each message is of 30 seconds duration. Voice coding is done at 5.3kbps. To store 10 messages, the storage requirement is 300 seconds × 5.3 kbps = 1590kbps = 198.8KBytes.
3.	For a voice paging system that uses 2.4kbps voice coding, the memory requirement on a voice pager that has to store 20 messages each of 30 seconds duration is 20 × 30 × 2.4 Kbits = 6 × 240 Kbits = 1440 Kbits = 180 KBytes.
4.	You can obtain the POCSAG decoder software from http://www.foni.net or http://www.qsl.net.

Projects

An Ethernet LAN can be considered a paging system because it also operates in broadcast mode. Simulate a paging system over the LAN. Use the POCSAG format for generating the paging message. The paging controller can be simulated on the LAN server.
Simulate a simulcast paging system on the LAN. The nodes on the LAN have to be separated into two groups. If your LAN has 20 nodes, assign 10 nodes to one group and 10 nodes to another group. Broadcast the paging message to the two groups separately.

< Day Day Up >