Paging technology: Systems and services Part 1-From simple alerting to voice storage, numeric and alphanumeric services, answer-back paging and computer linking, here is a look at the technology behind the fast-growing paging industry.
RF communications is one of the fastest growing markets in the world today. An integral part of this growth and success is the service offered to paging subscribers. Pagers were first used by business professionals, and the introduction of cellular telephone service raised concern that the pager market would decline. With the increasing use of pagers by all ages for both business and personal reasons, it seems more likely that there is a market for both types of communication and that subscribers will make the choice between the two based on cost and intended use. The paging market is expected to continue its huge rate of growth, and because of this there is an increasing interest in paging technology. This article series will include an overview of paging systems and some of today’s and tomorrow’s paging formats. Functional blocks of a pager will be discussed, as will pager measurements and measurement techniques.
The pager Pagers are designed to listen to one frequency channel. Information contained on this one frequency can be tone, voice or digital data. When the pager receives the identification signal, the pager beeps, vibrates or flashes a light to notify the subscriber that a paging message has been received. Figure 1 above shows the most popular type of pager in use today, a numeric pager. It has a small liquid crystal display (LCD) that is capable of displaying 20 digits, typically the caller’s phone number. Also shown is an alphanumeric pager. With this type of pager, the subscriber does not have to make a call to receive the message.
Alphanumeric paging is becoming increasingly popular. The first pagers were analog only, and each pager was assigned a separate frequency. Later, digital technology allowed many pagers to share one frequency. A single frequency could be coded in such a way that thousands-even millions-of pagers could share the same frequency without interfering with each other. Where is pager technology going in the future? Two-way paging systems are now being released. With two-way paging, the receipt of messages can be acknowledged, and the subscriber can transmit a programmed reply to a received message.
Types of paging services Paging services come in several forms: tone only. tone and voice. numeric. alphanumeric. computer interface.
Tone-only paging alerts the subscriber that someone wants to communicate. This type of service is most useful when the subscriber only needs to call one place, such as an office. Tone-and-voice paging, the follow-up of tone-only, allows the subscriber to receive a voice message. Unfortunately, the voice message can be missed if the subscriber has the pager turned off or is out of transmitter range. Numeric paging is the most popular in the market today. A caller dials the phone number assigned to the pager and then, using a Touch-Tone phone, enters the number of a phone for a reply. The numeric pager notifies the subscriber that a call has been received, for example, by a beep or vibration, and the subscriber can retrieve the phone number of the caller from the pager display.
An alphanumeric pager requires the caller to have access to an alphanumeric terminal or a message center that can send alphanumeric messages to the pager. This type of service is the most expensive, but it can be valuable if the pager subscriber benefits by having immediate information rather than having to call someone for it. Paging network
Information is sent to a pager via a paging network. (See Figure 2 on page 28.) A paging network begins at the connection to the public switched telephone network (PSTN) or telephone lines. For example, the caller accesses one of three things: voice mail. a paging operator. a Touch-Tone telephone dial.
The resulting paging messages are assembled in the paging terminal and sent to the network controller where they are combined into batches, based on their final destination. All billing and management is also controlled at this point.
Many paging companies cover more than just one geographical area. For example, the company may serve an entire state or country. The network controller specifies the site controller(s) for which the batched messages are intended and sends them out. Each site, covering a particular geographical location, may contain one or more paging transmitters. Once the site controller receives the batch of pages, it uplinks them to the paging transmitter(s), which then transmit the batch of messages at the same time on the same frequency using a simulcast technique. Simulcasting allows two or more transmitters to transmit identical information at the same time. It allows the system to provide seamless coverage on a single frequency.
There are many different types of paging formats currently in use today. Analog formats use a multitone (two, five or six tones) pager signaling sequence. These formats can transmit numeric information, such as phone numbers, or a voice. In addition to the analog formats, several digital formats are in use today. The most common, and the only worldwide standard at this time, is POCSAG, also known as RPC1. Others are Golay (a Motorola-proprietary format), NTT and NEC. Digital formats include Motorola Flex protocol, ERMES and RCR-43.* The Flex protocol is receiving worldwide attention. Several successful field trials were performed in the United States and Flex products were introduced in 1995. The Flex protocol is being implemented in North America and soon will be in China, Indonesia, Singapore and Thailand. ERMES is being developed mainly for use in Europe. Japan is working on its own paging format, RCR-43 which is based on the Flex protocol.
Next month: A focus on the digital formats. *POCSAG stands for Post Office Code Standardisation Advisory Group. RPC1 stands for Radiopaging Code No. 1, a designation of the International Radio Consultative Committee (CCIR). Golay sequential code is named after Marcel Jules Edouard Golay (b. 1902), a physicist who constructed the code about 1955. NTT is Nippon Telephone & Telegraph. NEC is Nippon Electric Company. “Flex” is short for flexible wide-area synchronous protocol. ERMES stands for European Radio Message System. RCR Std-43 stands for Research and Development Center for Radio Systems standard No. 43.