Paging is a wireless service that provides one- or two-way messaging to give mobile users continuous accessibility to family, friends, and business colleagues while they are away from their telephones. Typically, the mobile user carries a palmsized device (the pager or some other portable device with a paging capability) that has a unique identification number.
The calling party inputs this number, usually through the Public Switched Telephone Network (PSTN), to the paging system, which then signals the pager to alert the called party. Alternatively, callback numbers and short-text messages can be sent to pagers via messaging software installed on a PC or input into forms accessed on the Web for delivery via an Internet gateway.
Regardless of delivery method, the called party receives an audio or visual notification of the call, which includes a display of the phone number to call back. If the pager has an alphanumeric capability, messages may be displayed on the pager’s screen.
The pioneer of wireless telecommunications is Al Gross. In 1938, the Canadian inventor developed the walkie-talkie. In 1948, he pioneered Citizens’ Band (CB) radio. In 1949, he invented the pager from radio technology he used for blowing up bridges via remote control during World War II. His first attempt to sell pagers to doctors and nurses in 1960 failed because nurses did not want to disturb patients and doctors did not want to disturb their golf games.
Gross’s ideas were so far advanced that most of his patents expired before the technology could catch up to make his inventions a reality. As a result, he did not make much money. Had he been born 35 years later, he could have capitalized on his ideas to become far wealthier than Bill Gates at Microsoft.
There are many applications for paging. Among the most popular are:
- Mobile messaging Allows messages to be sent to mobile workers. They can respond with confirmation or a request for additional instructions.
- Data dispatch Allows managers to schedule work appointments for mobile workers. When they activate their pagers each morning, their itinerary will be waiting for them.
- Single-key callback Allows the user to read a message and respond instantly with a predefined stored message that is selected with a single key.
Some message paging services work with text messaging software programs, allowing users to send messages from their desktop or notebook computers to individuals or groups. This kind of software also keeps a log of all messaging activity. This method also offers privacy, since messages do not have to go through an operator before delivery to the recipient.
Several types of paging services are available.
Selective Operator-Assisted Voice Paging Early paging systems were nonselective and operator-assisted. Operators at a central control facility received voice input messages, which were taped as they came in. After an interval of time—15 minutes or so—these messages were then broadcast and received by all the paging system subscribers. This meant that subscribers had to tune in at appointed times and listen to all messages broadcast to see if there were any messages for them. Not only did this method waste airtime, it also was inconvenient and labor-intensive and offered no privacy.
These disadvantages were overcome with the introduction of address encoders at the central control facility and associated decoders in the pagers. Each pager was given a unique address code. Messages intended for a particular called party were input to the system preceded by this address. In this way, only the party addressed was alerted to switch on his or her pager to retrieve messages.
With selective paging, tone-only alert paging became possible. The called party was alerted by a beep tone to call the operator or a prearranged home or office number to have the message read back.
Automatic Paging Traditionally, an operator was always needed either to send the paging signal or to play back or relay messages for the called party. With automatic paging, a telephone number is assigned to each pager, and the paging terminal can automatically signal for voice input, if any, from the calling party, after which it will automatically page the called party with the address code and relay the input voice message.
Tone and Numeric Paging Voice messages take up a lot of airtime, and as the paging market expands, frequency overcrowding becomes a potentially serious problem. Tone-only alert paging saves on airtime usage but has the disadvantage that the alerted subscriber knows only that he or she has to call certain prearranged numbers, depending on the kind of alert tone received.
With the introduction of numeric display pagers in the mid-1980s, the alert tone is followed by a display of a telephone number to call back or a coded message. This method resulted in great savings in airtime usage because it was no longer necessary to add a voice message after the alert tone. This is still the most popular form of paging.
Alphanumeric Paging Alphanumeric pagers display text or numeric messages entered by the calling party or operator using a modem-equipped computer or a custom page-entry device designed to enter short-text messages. Although alphanumeric pagers have captured a relatively small market in recent years, the introduction of value-added services that include news, stock quotes, sports scores, traffic bulletins, and other specialized information services has heated up the market for such devices.
Ideographic Paging Pagers capable of displaying different ideographic languages—Chinese, Japanese, and others— are also available. The particular language supported is determined by the firmware (computer program) installed in the pager and in the page-entry device. The pager is similar to that used in alphanumeric display paging.
Paging System Components
The key components of a paging system include an input source, the existing wireline telephone network, the paging encoding and transmitter control equipment, and the pager itself.
Input Source A page can be entered from a phone, a computer with modem, or other type of desktop page-entry device; a personal digital assistant (PDA); or an operator who takes a phone-in message and enters it on behalf of the caller. Various forms posted on the Web also can be used to input messages to pagers.
The Web form of WorldCom, for example, allows users to send a text message consisting of a maximum of 240 characters to subscribers of its One-Way Alphanumeric service and 500 characters to subscribers of its Enhanced One-Way, Interactive (two-way), and QuickReply Interactive services. In addition, users can send a text message consisting of a maximum of 200 characters to subscribers of MobileComm. The form even provides a means to check the character count before the message is sent.
Telephone Network Regardless of exactly how the message is entered, it eventually passes through the PSTN to the paging terminal for encoding and transmission through the wireless paging system. Typically, the encoder accepts the incoming page, checks the validity of the pager number, looks up the directory or database for the subscriber’s pager address, and converts the address and message into the appropriate paging signaling protocol. The encoded paging signal is then sent to the transmitters (base stations), through the paging transmission control systems, and broadcast across the coverage area on the specified frequency.
Encoder Encoding devices convert pager numbers into pager codes that can be transmitted. There are two ways in which encoding devices accept pager numbers: manually and automatically. In manual encoding, a paging system operator enters pager numbers and messages via a keypad connected to the encoder. In automatic encoding, a caller dials up an automatic paging terminal and uses the phone keypads to enter pager numbers. Regardless of the method used, the encoding device then generates the paging code for the numbers entered and sends the code to the paging base station for wireless transmission.
Base Station Transmitters The base station transmitters send page codes on an assigned radio frequency. Most base stations are specifically designed for paging, but those designed for two-way voice can be used as well.
Pagers Pagers are essentially FM receivers tuned to the same radio frequency as the paging base station. Adecoder unit built into each pager recognizes the unique code assigned to the pager and rejects all other codes for selective alerting. However, pagers can be assigned the same code for group paging. There are also pagers that can be assigned multiple page codes, typically up to a maximum of four, allowing the same pager to be used for a mix of individual and group paging functions.
Despite all the enhancements built into pagers and paging services in recent years, the market is slowing down. Alphanumeric services—which provide word messages instead of just phone numbers—have failed to attract a wide audience largely because paging subscribers still need a phone to respond to messages. Some providers have tried to offer services that would allow callers to leave voice messages on pagers, but this too has failed to catch on.
Consequently, about four out of five of today’s paging customers still rely on cheap numeric services. Two-way paging networks may be the industry’s last hope for survival. They allow a pager—which comes equipped with a minikeyboard—to “talk” to another pager or with a telephone, e-mail address, or fax machine. Some two way services allow consumers to reply to messages with predetermined responses.
Signaling Protocols
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 signaling protocol. The signaling protocol allows individual pagers to be uniquely identified/alerted and to be provided with the additional voice message or display message, if any.
Various signaling protocols are used for the different paging service types, such as tone-only or tone and voice. 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 the Post Office Code Standardization Advisory Group (POCSAG), that allow different manufacturers to produce compatible pagers.
POCSAG is a public-domain digital format adopted by many pager manufacturers around the world. It can accommodate 2 million codes (pagers), each capable of supporting up to four addresses for such paging functions as tone-only, tone and voice, and numeric display. POCSAG operates at data rates of up to 2400 bps. At this rate, to send a single tone-only page requires only 13 milliseconds. This is about 100 times faster than two-tone paging.
With the explosion of wireless technology and dramatic growth in the paging industry in many 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 a one-way messaging protocol called Flex (feature-rich long-life environment for executing) messaging applications that is intended to transform and broaden paging from traditional low-end numeric services into a range of PCS/PCN and other wireless applications.
Relative to POCSAG, Flex can transmit messages at up to 6400 bps and permit up to 600,000 numeric pagers on a single frequency compared to POCSAG’s 2400-bps transmission rate and 300,000 users per frequency. In addition, Flex provides enhanced bit error correction and much higher protection against the signal fades common in FM simulcast paging systems.
The combination of increased bit error correction and improved fade protection increases the probability of receiving a message intact, especially longer alphanumeric messages and data files that will be sent over PCS/PCN. Motorola also has developed ReFlex, a two-way protocol that will allow users to reply to messages, and InFlexion, a protocol that will enable high-speed voice messaging and data services at up to 112 kbps.
The hardware and software used in radio paging systems have evolved from simple operator-assisted systems to terminals that are fully computerized, with such features as message handling, scheduled delivery, user-friendly prompts to guide callers to a variety of functions, and automatic reception of messages. After tremendous growth in the last decade, from 10 million subscribers in 1990 to 60 million today, the paging industry has slowed down markedly—in large part because of cutthroat competition and increasing use of digital mobile phones.
