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7
Paging Systems
It is often important to be able to reach certain people very quickly. The
conventional telephone network is not always optimal, because a line may be
engaged or the person being called might not be available. Mobile telephone
systems offer a high degree of reachability of a mobile subscriber, but MSs are
not always switched on and are expensive to use.
Paging systems fill a particular gap (see Table 7.1). They allow unidi-
rectional transmission of information in the form of a tone or a numeric or
alphanumeric message to the person being contacted, whose location area is
not known (see Table 7.2). A terminal is required that is constantly ready
to receive but cannot transmit, and consequently is small, lightweight and
inexpensive.
A paging message is automatically initiated when a telephone user dials
the paging service and, using a telephone keyboard, an Internet terminal or a
PC, conveys the pager number of the called person or a short message for it
to the computer that responds (see Figure 7.1).
One characteristic of the paging system is that the person sending the
message can never be certain that it has been received. There can also be
a considerable gap between the time a message has been sent and when it
is received by the addressee, and during peak load times this can amount to
10 minutes.
Table 7.1: Public operation of paging systems in Europe
Since 1974 European Paging Service (Eurosignal)
Since 1989 Cityruf
Since 1990 Euromessage
Since 1996 ERMES
Table 7.2: Call types of different paging systems
Call type Eurosignal Cityruf ERMES
Tone only [No. of paging no.] Up to 4 Up to 4 Up to 8
Numeric [No. of num. char.] — Up to 15 20–16 000

Alphanumeric [No. of char.] — Up to 80 400–9000
Transparent data transm. [max. length] — — 4000 bits
Mobile Radio Networks: Networking and Protocols. Bernhard H. Walke
Copyright © 1999 John Wiley & Sons Ltd
ISBNs: 0-471-97595-8 (Hardback); 0-470-84193-1 (Electronic)
440 7 Paging Systems
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Paging Service
Switching
Centre
- Telex
- Telephone
Networks like:

- ISDN
- Internet
(DTMF Dialing)
Call Centre
Figure 7.1: Principle of paging
Strengths and Weaknesses of Paging Systems
Strengths
• Inexpensive alerting and information service.
• Small receivers.
• The user of a paging system can be reached anywhere if the receiver is
carried on his/her person.
• No additional antenna required (this applies only partially in the case
of Eurosignal).
• Discrete communication of messages (messages are signalled through
vibration, messages can be read on display).
Weaknesses
• The sender of a paging message receives no confirmation that the mes-
sage has been received.
• Falsified paging messages and pages by malicious callers can cause the
user of a pager to take inappropriate action.
Types of Calls
Individual calls The paging message is transmitted to the defined paging areas
(one or more) or in the dialled paging area.
Collective calls A collective call number consists of n individual telephone
numbers (receivers with different addresses). The receivers within a
paging area are called in consecutive order.
7.1 Paging Service “Cityruf” 441
Group calls Several receivers with the same address are called simultaneously
in one or several paging areas.
Target calls By dialling additional numbers, the caller specifies the paging

area in which the paging message should be transmitted.
It is anticipated that the number of users of pagers will increase in the
future, despite the availability of services such as the short-message service
(SMS) offered by GSM that are regarded as competition. A pager is an ideal
extension to the mobile telephone because it can often be reached in places
outside the radio coverage range of mobile telephone systems.
The miniaturization of terminals, including waterproof wristwatches that
incorporate a radio pager receiver, offer the potential for a mass market for
paging services that will extend beyond commercial applications to private
and leisure use.
7.1 Paging Service “Cityruf”
Paging systems that operate in different frequency bands (150–170 MHz or
440–470 MHz) in accordance with POCSAG-Code (the Post Office Code Stan-
dardization Advisory Group pager system was developed as long ago as 1981)
(CCIR Radio-Paging Code No.1 ) are now being used in many parts of Eu-
rope. Subscribers can be reached by practically all communications networks
over the POCSAG radio calling service (see Table 7.3). A typical example of
the POCSAG paging service is Cityruf, which was introduced in Germany in
March 1989.
A radio paging system based on POCSAG (see Figure 7.1) consists of:
• A paging service switching centre that forms the link between the vari-
ous communications services (telephone, data, etc.) and the paging net-
work, in which incoming data is prepared for processing in the paging
computer.
• Paging transmitters with transmitter power up to 100 W.
• A paging concentrator, which is used to switch on a paging transmitter
at the paging service switching centre and is allocated a paging measure-
ment receiver for the automatic propagation control of the modulation
paths.
• A paging receiver.

As the name implies, the Cityruf network is not envisaged to be a wide-
area service. It is a regional paging service for cities, and its coverage area
is divided into internetworked paging areas. About 50 paging areas with a
maximum diameter of 70 km have been implemented in the final configuration.
However, subscribers to the Cityruf service are not only booked in locally
442 7 Paging Systems
or regionally but in several paging areas and, in fact, throughout Germany.
The transmitter systems of Cityruf are designed in such a way that they can
guarantee reception within buildings without the need for additional antennas.
The maximum number of subscribers that the system is capable of addressing
is two million. Fifteen paging messages can be sent in one second.
Users of Cityruf have a choice between different calling classes based on
different monthly charges:
Calling class 0 (tone only) Input is over the telephone. Tone-only devices
issue up to four optically and acoustically different signals.
Calling class 1 (numeric) A maximum of 15 digits or special characters can
be entered directly over the telephone using a supplementary device or
with a dual-tone multiple-frequency (DTMF) signal generator, and then
appear in the display of the terminal.
Calling class 2 (alphanumeric) Text messages up to 80 characters long can
be entered, for example over the Internet or using an acoustic coupler
device over the PSTN. Several messages can be transmitted in succes-
sion.
The following types of calls are available for the three calling classes:
Individual calls A radio call is broadcast in the registered paging areas or to
the selected paging area.
Group calls A number of receivers are addressed over a group number at the
same time.
Collective calls Up to 20 individual paging numbers are assembled in a list
and then dialled up automatically in succession.

Target calls The receiver of a call is assigned a special number. To reach this
person, a caller first dials the paging number and then the suffix number
of the radio paging area in which the call is to be transmitted.
In addition to terminals and accessories for Cityruf, radio paging network
operators offer the supplementary service Inforuf, which allows the user to
receive information such as stock market updates, business news and weather
reports. To access this information, users require a special Inforuf receiver
that receives the Inforuf signals along with the Cityruf signals and is capable
of storing 80 000 characters and reading them out on its 80-character dis-
play. The current information providers include Reuters, Telerate and pooled
information services.
Cityruf is transmitted on the following frequencies:
• 465.970 MHz • 466.075 MHz • 466.230 MHz
7.1 Paging Service “Cityruf” 443
S
C
17 Code Words
= SC + 8 Frames
1 20/1
32
2-19 Address Bits
22-31 Coding Bits
Code Word
Frame of Two
Code Words
Message Flag Function Even
Bits Parity0 = Address Word
1 = Message Word
Synchronization
Preamble First Batch Second Batch

Subsequent
Batches
1.0625 s1.125 s 1.0625 s
Figure 7.2: Message coding and block format with POCSAG
The transmission rate is 512 bit/s or 1200 bit/s. The digital signals are NRZ
(Non-Return to Zero) coded and modulated through the use of differential
frequency-shift keying (DFSK). The transmitters emit bursts of data blocks
with code words (see Figure 7.2) [2].
Each burst begins with a 1.125 s long preamble, which is followed by a num-
ber of data blocks of 1.0625 s duration. The preamble enables synchronization
to take place on the signal pulse on the receiver side, and is a prerequisite for
error-free message coding. The data blocks consist of 17 code words, the first
of which is used in the synchronization. The remaining 16 code words, each
with 32 bits, contain an initial bit that indicates whether the code word is an
address or a message, 20 address or message bits, 10 bits for error detection
and correction, and a parity bit. The 16 code words form eight frames, each of
which contains two code words. Each terminal is only addressed in a specific
frame. The message for a receiver can be of any length, and is sent in the form
of message words based on the address of the person receiving the message.
Paging areas can be divided into several radio coverage areas, with all
transmitters within an area transmitting in a common frequency. The three
frequencies are not used simultaneously in a transmitting zone, but are stag-
gered and cyclical. Transmission never takes place simultaneously on the same
frequency in the adjacent transmitting zones, so that a three-site cluster oc-
curs. The time (time slot) during which transmission can take place on a
frequency can be adapted to traffic volume. The advantages of this procedure
are that adjacent zones can be decoupled through radio engineering and a
receiver only needs to be operational when its frequency is being sent. If no
messages are being sent on the frequency of the receiver or if it recognizes
that a radio call is not directed at it, the receiver remains in battery-saving

idle state.
Cityruf receivers are small in size, include storage options for characters
which are received and use minimal power only. Table 7.3 lists the service
codes required for network access.