6
Trunked Mobile Radio and Packet
Data Radio
In addition to the public radio telephone service and the paging service, there
are other radio services that are not accessible by the public. These radio
systems, called the non-public land mobile radio network , have access to fre-
quencies that cannot be used by the public but only by specific users or groups
of users.
Probably the best known non-public mobile radio service is analogue Pri-
vate Trunked Mobile Radio (PTMR), which has been used for many years by
large firms such as airlines, taxi and transport companies, the railways, and
ports, as well as by government departments and organizations responsible
for security. What is characteristic of previous PTMR systems is that they
have one radio channel that is used exclusively by all the mobile terminals
of a specific user group. An analysis of conventional commercial radio sys-
tems reveals a number of weaknesses that affect both the customer and the
operator:
• Because of too many PTMR users, the fixed allocation of radio channels
in congested areas leads to a frequency overload.
• Radio supply areas are too small.
• There is the possibility of eavesdropping by unauthorized persons.
• There is no link to the public telephone networks.
• There is limited support of voice and data transmission.
Frequency overload was the main reason for considering new radio systems
and infrastructures. This led to the introduction of trunked mobile radio
systems as the successors to analogue PTMR.
Although it is not possible for trunked mobile radio systems to expand the
frequency spectrum available, they are able to improve the quality of service
both for the end user and for the network operator through the optimization of
frequency utilization and increased channel use. Advances in trunked mobile
radio technology have resulted not only in providing user groups with one

6.1 The MPT 1327 Trunked Mobile Radio
System
The pacesetter in standardized trunked mobile radio systems was Great
Britain, where the Ministry of Post and Telecommunications developed the
trunked mobile radio standard MPT 1327/1343, which is also used in Ger-
many as the technical standard for the first generation of (analogue) trunked
mobile radio networks.
Following are some of the services offered in an MPT 1327 trunked mobile
radio network:
• A normal call can be either an individual or a group call.
• A priority call can be either an individual or a group call.
• The mobile telephones called do not respond when they receive a
recorded announcement.
6.1 The MPT 1327 Trunked Mobile Radio System 367
• A conventional central station call in which a radio unit wishing to make
a call is not immediately allocated a channel but is required to wait until
the central station sets up the call at a convenient time.
• A conference call in which additional users can participate in a setup
call.
• An emergency call, which can be either a voice or a data call placed by
an individual or by a group.
• A data call can take place between different signalling systems, and is
either an individual call or a group call that is transmitted either as a
normal or a priority call.
• Call forwarding or call diversion to another user or group is possible.
• Status messages can be interchanged between different radio units or be-
tween radio units and the system, whereby there are 30 different special-
purpose messages available.
• Radio telegrams are up to 184 bits long and can be interchanged between
the radio units or between the radio units and the system.

TRX
TRX
TRX
TRX
TRX
TRX
TRX
TRX
1
2
3
4
20
4
3
2
1
MSC
Area 3Area 2
Node
Area 1
2020
4
3
1
2
TRX
TRX
TRX
TRX

One example is the Chekker network operated by Deutsche Telekom AG
in Germany in accordance with the MPT 1327 standard in the 410–418 MHz
(uplink) and 420–428 MHz (downlink) frequency bands. Up to 20 radio chan-
nels, each with a 12.5 kHz bandwidth, are available per cell. One channel
can normally service 70–80 users. The maximum transmitter power per base
station is 15 W.
Messages are transmitted digitally on the control channel, whereas with
the MPT standard user information is transmitted on the traffic channels
in analogue. Mobile stations use the control channel in half-duplex mode,
whereas the base station transmits on this channel in duplex mode. The
necessary signalling data is exchanged on the allocated traffic channel during
a user connection.
Phase-shift keying (PSK) modulation has been selected for speech modula-
tion. Fast-Frequency Shift Keying modulation (FFSK) is used for data. The
transmission rate for signalling data is 1.2 kbit/s; the data transmission rate
possible is 2.4 kbit/s.
Systems with a small number of channels can employ a technique allowed
by the MPT protocol in which the control channel can be used as a commu-
nications channel if the need arises.
Mobile stations in a trunked radio system access the control channel in
accordance with a random access method, called the S-ALOHA protocol.
In a trunked radio network a call is set up through a series of steps. All
checked-in radio units follow the sequence of operations on the control channel
in standby mode. When a call request is made, indicated by a keystroke
on the mobile terminal to the central station, the central station checks the
availability of the subscriber terminal being called and informs the respective
subscriber, in some cases through a paging signal over the control channel. If
the subscriber called answers, a free traffic channel is automatically assigned
to the respective parties. The maximum call duration in the Chekker service
is 60 s (billing for the service is on a monthly fixed basis). When a call has

oped to provide frequent, high-quality and cost-effective data transmission
and support access to the public X.25 network. Data transfer in this sys-
tem is particularly frequency-economic, because it is transmitted digitally
and packet-switched, and, compared with other services, is very economical
for low-volume transmission. Because of the direct, bi-directional data trans-
fer between data processing systems and mobile data terminals, MODACOM
can provide considerable cost savings in operational organization.
The MODACOM network was initially developed for operation outdoors,
and, in contrast to GSM, was not planned to be used across borders. It is
directed towards customers who would benefit from services being expanded
from the wired, packet-switched data network to the mobile area. Applications
for the MODACOM service include:
• Database access by mobile terminals over the public X.25 network
• Scheduling applications
• Dispatching services, e.g., for shipping and haulage companies
• Telemetry applications such as emission tests, burglar alarms and pa-
rameter requests from vehicles
• Service and maintenance, i.e., remote diagnostics, fault searches or elim-
ination, access to inventory and stock data
6.2 MODACOM 371
6.2.1 Services in the MODACOM Network
After a terminal has been switched on, it searches for a free channel in the
designated channel grid and is checked into the system. After it has been
checked in, a continuous virtual connection exists over which control signals
are exchanged from time to time. These are not transmitted as data packets
until actual data is ready to be sent. Network management ensures that a
user terminal has continuous send and receive capabilities within the overall
MODACOM network as well as access to the following services or performance
characteristics:
• Transmission of status messages or file transfer (bi-directional)

Terminal
User
Terminal
User
Terminal
Network
Administration
Host
(NAH)
MT
MT
BS
BS
ACC G
GACC
ACC G
BS
BS
MT
Radio Data Network
(RDN)
RD-LAP
X.25
X.25
X.25
X.25
(Air Interface)
X.25 Data Network
9.6 kbit/s
Figure 6.2: The architecture of the MODACOM system

Bit rate 9.6 kbit/s net
Message length Max. 2048 bytes
Packet size Max. 512 bytes
Block size 12 bytes
Response time Approx. 1.5 s
Channels/carriers One data channel per carrier
Channel access Slotted DSMA
Forward error correction Trellis coding with interleaving
Error detection code CRC-check sum
Bit-error ratio Better than 10
−6
, typically 10
−8
• Reservation is not possible.
The RD-LAP protocol includes error detection and correction as well as
procedures for message segmentation and reassemling after receipt. Layer 2
is able to process messages of a maximum length of 2048 bytes segmented
into four data packets each 512 bytes in length and transmitted at 9.6 kbit/s.
The data packets are automatically acknowledged by the network, and in the
case of error a transmission attempt is repeated three times. CRC check sum
procedures (cyclic redundancy check) are used for error detection. Data is
transmitted with forward error correction procedures using trellis coded mod-
ulation and interleaving with a bit error ratio less than 10
−6
. The technical
parameters of the MODACOM system are summarized in Table 6.1 [15].
6.2.4 Different Connection Possibilities in the MODACOM
Radio Data Network
6.2.4.1 Connection of Two Mobile Terminals
This type of connection (messaging) allows the exchange of free message texts

6.2.4.2 Connection to Fixed Network
Connections between MT and the wireline fixed network are exclusively car-
ried out over the public X.25 network. The MODACOM system supports
three types of connection betwen host and MT [17]:
Type 1: Outgoing individual call These calls can be used to interrogate pub-
lic databases, etc. An outgoing individual call is always initiated by an
MT and used for interactive communication with the dialled host. The
connection between MODACOM system and host is set up as a switched
virtual channel (SVC) in the X.25 network. Figure 6.3 illustrates a Type
1 connection over a PAD (packet assembly disassembly).
In order to set up the connection, the MT sends a special data packet
that contains the ITU-T Rec. X.121 address of the target host. The
connection between MT and X.25 network is implemented through X.3-
PAD functions and the SVC connection in the wireline network. The
PAD links asynchronous (start/stop) terminals to an X.25 host.
The MODACOM system emulates only a subset of the X.3 and X.29
interfaces, whereas the X.28 specifications, which describe the config-
uration of a PAD by the asynchronous terminal, are not required. A
special data packet is sent by the MT in order to terminate a connec-
tion. A connection can also be terminated by the host using the normal
resources of the X.29 specification.
Type 2: Incoming individual call These connections are based on exclusive
switched virtual channels (SVC) that can only be set up by the host.
Figure 6.4 illustrates an example of an incoming individual call.
Since the public X.25 network is only able to connect data terminal
equipment (DTE) with an X.25 interface, the MODACOM network
RDN or its gateway node G is connected to the network as an X.25
subscriber. Every incoming call requires a connection and termination
6.2 MODACOM 375
(DTE)

X.25
X.25
X.25 - PDN
MT
Figure 6.4: Incoming individual call
SCR SCR
(RDN)
Radio Data Network Data Terminal
Equipment (DTE)
MT
C
B
MT
A
MT
A
B
C
DTE DTE
Process
C
B
A
User
One Channel for Multiple
MT Connections
Figure 6.5: Pooling
procedure. When a connection is established, the MT is allocated an
SVC connection, which must be managed exclusively by the MT if it
makes further connections. The number of MTs that can be served by a

6.2.5 Roaming and Handover
In the MODACOM system MTs are not restricted to a particular area and,
through constant accessibility by the host, can move about freely in the radio
coverage area. Logical connections are supported by a handover procedure
when there is a changeover from one radio cell to another.
If the terminal establishes that the field strength of the selected radio chan-
nel is too low or the bit-error ratio is too high, it initiates a roaming process
and assigns itself to a new base station. The MT thereby searches for a new
radio channel, evaluates the quality and the availability of the radio channel
on the basis of status messages that are regularly sent by the base station,
and, if the channel is considered satisfactory, transmits a registration packet
to register itself with the relevant base station. Two types of roaming are
differentiated in the MODACOM system:
Roaming within the home ACC area in which messages coming from the
host are merely rerouted to the other base station.
Roaming between two ACC areas occurs when an MT leaves its ACC area
and registers in another ACC area. The visited ACC checks the au-
thorization of the MT with the home ACC and, if the MT is accepted,
exchanges all the data required for the operation of the MT with the
home ACC. The MT is then registered in the visitor register of the new
ACC. All data relating to the MT is then forwarded from the home ACC
6.3 The TETRA Trunked Mobile Radio System 377
to the visited ACC. The visited ACC in turn reroutes all messages from
the MT to the home ACC.
6.3 Second-Generation Trunked Mobile Radio
Systems: The TETRA Standard
∗
Despite the introduction of GSM throughout Europe, it is expected that the
subscriber numbers for trunked mobile radio systems will continue to grow
steadily, possibly reaching around five million by the year 2000.

generation trunked radio networks, whereas the PDO standard defines a
second-generation packet radio system. Both standards use the same physical
transmission technology and largely the same transmit/receive equipment.
European-wide standardization is forcing the issue of interoperability, i.e.,
manufacturer-independency of terminal equipment in the TETRA network,
as well as interworking between different TETRA networks and the fixed net-
works. Local and regional voice and radio data applications are being replaced
by a European trunked radio system that covers all voice and data services
and satifies current requirements for bit rates and transmission delay. The
main application areas for TETRA are fleet management, telemetry, service
companies and for communication within government departments and orga-
nizations responsible for security.
Network operators, legislators, manufacturers and users were included in
the standardization process to ensure that the ETSI-TETRA standard would
have the chance of widespread implementation in the European market. The
first TETRA products were available in late 1996. In 1997 the system was
able to offer individual and group calls and data and other services described
in detail in Section 6.3.2.
6.3.1 Technical Data on the TETRA Trunked Radio System
The trunked radio system TETRA can be used as a local or a multicell net-
work. Since the transmitter power of the terminal equipment is 1 W, 3 W or
10 W, the maximum cell radius in rural areas is limited to 25 km. Several
frequencies in the ranges between 380 MHz and 470 MHz and 870 MHz up to
933 MHz have been allocated to the frequency bands for the uplink and the
downlink (see Table 6.3). The possibility of using the 1.8 GHz band is being
examined.
The TETRA system uses π/4-DQPSK modulation and offers a gross bit
rate of 36 kbit/s in a single 25 kHz channel. With an average quality of
service guaranteed by the channel coding, the net bit rate is at 19.2 kbit/s.
Without channel coding it is possible to achieve a maximum net bit rate of

are protected by FEC with code rate 2/3; continuous trans-
mission on downlink, discontinuous transmission on uplink
Neighbouring
channel protection
−60 dBc
Connection setup <300 ms circuit-switched; <2 s connection-oriented
Transmission delay
of a 100 byte refer-
ence packet
V+D: <500 ms in a connection-oriented service,
<3–10 s in a connectionless service, depending on trans-
mission priority
PDO: <100 ms with a 128-byte message
tinuously on the downlink, discontinuously on the uplink. An exact profile of
the channel coding for V+D is given in Section 6.3.4.3.
The time required to establish a connection should not exceed 300 ms for
a circuit-switched call or 2 s for a connection-oriented transmission of packet
data (Connection Oriented Network Service, CONS). The transmission delay
of a 100-byte reference packet in connection-oriented transmission with V+D
should be a maximum of 500 ms; with connectionless transmission, depending
on the respective transaction priority, it should be a maximum of 3 s, 5 s or
10 s. With PDO a transit delay of a maximum of 100 ms has been stipulated
as the upper limit for connection-oriented services for a 128-byte reference
packet.
6.3.2 Services of the TETRA Trunked Radio System
The TETRA system provides packet data services, which are offered by the
PDO and V+D standards, and circuit-switched data and voice services, which
are only available with the V+D standard. The packet-oriented services dif-
ferentiate between the following types of connections:
380 6 Trunked Mobile Radio and Packet Data Radio

or is on another call, the TETRA infrastructure informs the calling
subscriber. If not enough members in the group can be reached, the
caller can decide whether to discontinue or to maintain the call. An
option is to have the group members who initially were not available to
switch into the conversation later.
Broadcast call Point-to-multipoint connection in which the subscriber group
dialled through a broadcast number can only hear the calling subscriber.
The bearer services and teleservices provided in the standard for the pro-
tocol stack V+D and PDO are listed in Table 6.4.
The TETRA system supports the following data and text services:
6.3 The TETRA Trunked Mobile Radio System 381
Table 6.4: Bearer services and teleservices for V+D and PDO in the TETRA stan-
dard
TETRA V+D PDO
Bearer
services
7.2–28.8 kbit/s circuit-switched, unprotected speech
or data
Ö –
4.8–19.2 kbit/s circuit-switched, minimally protected
data
Ö –
2.4–9.6 kbit/s circuit-switched, highly protected data Ö –
Connection-oriented packet transmission (point-to-
point)
Ö Ö
Connectionless packet transmission in standard for-
mat (point-to-point)
Ö Ö
Connectionless packet transmission in special format

call.
• Short-number addressing (SNA), allowing a user to make a call using an
abbreviated calling number. The TETRA infrastructure converts the
abbreviated number to the subscriber number.
• Priority calls.
• Priority calls with interruption.
• Access priority.
• Advice of charge (AoC) is a service that indicates the cost of a call to a
subscriber either during or after a call.
• Discrete eavesdropping of a conversation by an authorized person.
• Ambience listening (AL), allowing the user of a mobile device to be
restricted to emergency calls only.
• Dynamic group number allocation.
• Transfer of control (TC), permitting the initiator of a multipoint con-
nection to transfer control of a call to another person involved in the
call.
• Area selection (AS), allowing an authorized user to select the cell for
setting up a call or a subscriber currently being served to determine the
cell.
• Late entry (LE) is an invitation to potential subscribers in a multipoint
connection to be switched into an existing call.
Series 10, 11 and 12 of the V+D standard contain a complete compilation
of the supplementary services, along with detailed definitions and descriptions
[10, 11, 12].
6.3.3 Architecture of the TETRA Standard
6.3.3.1 Functional Structure of the TETRA System
With few differences, the TETRA system is structured like the GSM one (see
Figure 6.6). It has the following three subsystems:
• Mobile station • Line station
• Switching and management infrastructure

Mobile Station
Man-
Machine
Interface
User
Interface
Station
Figure 6.6: The architecture of the TETRA system
Mobile station (MS) The mobile station (MS) comprises all the subscriber’s
physical equipment: the radio telephone and the interface that the subscriber
uses to access the services.
As in GSM, a mobile station consists of two parts: the telephone device,
which contains all the necessary hardware and software for the radio interface,
and a Subscriber Identity Module (SIM), which contains all the subscriber-
related information. The SIM can either be in the form of a smart card the
size of a cheque card or permanently mounted in the device. The first version
has the advantage that it allows a quick change in ownership of the mobile
station. The third option is to key in a login code to convey the subscriber-
specific information. In this case too the mobile unit is not restricted to one
particular user.
In addition to the subscriber’s identification, each mobile device has a
TETRA equipment identity (TEI) that is specific to the device. This num-
ber is input by the operator; only the operator is able to bar the use of the
device or release it for use. This means that a stolen device can be disabled
immediately and unauthorized access is virtually impossible.
The following numbers and identities are allocated to ensure that a mobile
station can be uniquely addressed and managed:
• TETRA Subscriber Identity
(TSI)
• TETRA Management

system. It contains base stations that establish and maintain communication
between mobile stations and line stations over ISDN. It carries out the required
control tasks, allocates channels and switches calls. It carries out authentica-
tion checks and supports the relevant databases such as the Home Data Base
(HDB), which contains the telephone numbers, the equipment numbers and
the subscribed basic and supplementary services for each individual subscriber
in the home network, as well as the Visited Database (VDB), which contains
information on visitors to the network copied from their HDB. It also handles
call charging.
6.3.3.2 Interfaces of the TETRA System
Subscriber interface of the mobile station A TETRA mobile station is
called a mobile termination (MT). Its functions cover radio channel resource
and mobility management, speech and data coding/decoding, transmission
security as well as data flow control. The following versions are used:
• MT0 (Mobil Termination Type 0 ) contains the named functions with
the support of non-standardized terminal interfaces that contain the
terminal equipment functions (see Figure 6.7).
• MT2 (Mobil Termination Type 2 ) also supports the named functions,
and has an R
T
interface for terminal equipment based on the TETRA
standard (see Figure 6.7).
The terminal equipment (TE2) is directly accessible by the subscriber, and
corresponds to comparable function groups of the GSM and ISDN concept.
6.3 The TETRA Trunked Mobile Radio System 385
R
T
U
m
MT0

is discussed
in Section 6.3.4.2.
6.3.4 The Voice+Data Protocol Stack
This section will cover the Voice+Data protocol stack in general. This will be
followed by detailed discussion of the radio interface, the physical layer and
the link layer, with emphasis on functions, service elements, data structures
and states.
386 6 Trunked Mobile Radio and Packet Data Radio
TL
TE1
TE1
TE1
TE2
TE2
TE2
NT2
NT2
NT1
NT1
NT1
NT1
NT1
NT1
NT2 + NT1
NT2 + NT1
TE + NT2
TA + NT2
S
T
S

T
R
T
S
T
T
TL : Transmission Line
TE : Terminal Equipment
TE1: TE presenting an ISDN Interface
NT1/2 : Network Termination
T
TETRA S Reference Point
TETRA R Reference Point
TETRA T Reference Point
TE2: TE presenting a TETRA Interface
TA : TETRA Terminal Adapting Functions
Figure 6.8: Line station network links
6.3.4.1 Structure of the Voice+Data Protocol Stack
The protocol stack comprises three layers (air interface, AI) (see Figure 6.9):
the physical layer, which is identical for both V+D and PDO; the data link
layer, which is divided into Medium Access Control (MAC) and Logical Link
Control (LLC); and the network layer (N), which is divided into several sub-
layers and offers management services to base and mobile stations. The MAC
layer is based on two protocol stacks: the user plane, which is responsible for
information transport, and the control plane for signalling.
6.3.4.2 The Radio Interface at Reference Point U
m
The radio interface U
m
is between the mobile station and the switching and

Packet Service
Conver-
gence
MM-Mobility
Management
CMCE -
Circuit Mode
Control Entity
CONP
S-CLNP
Mobile/Base Link Control Entity
Packet
Handling
C-plane
U-plane
AI-3AI-2AI-1
TETRA
MOBILE
SNAF
I
AI-1
AI-2
AI-3
C-plane
CLNS
CMCE
CONP
CONS
LLC
MM

minimum of 300 ms. Different versions of the call-reselect procedure are being
planned in the standard, with a basic version being obligatory for all mobile
stations. The versions based on it are optional and will facilitate a speedier
change of cell. It will not be imperative to have a change of FDM channel.
The TETRA system does not have any real handover functions, because the
users of mobile stations (e.g., taxi fleets) normally do not have a large radius
of action.
Frequency-Division Multiplexing Structure Several frequency bands that
have been allocated to the TETRA network in Europe do not completely
comply with the specifications of the TETRA standard [8] and use additional
frequencies above 870 MHz or 915 MHz (see Table 6.3). The frequency bands
for both uplink and downlink are the same width. The carrier frequency
separation is 25 kHz, and each uplink and downlink band is divided into N
carrier frequencies. A G kHz wide band has been added to each boundary of
the band in order to prevent interference from outside the band. Thus N and
388 6 Trunked Mobile Radio and Packet Data Radio
4
4
4
1
1
1
2
2
2
3
3
3
4
4

G constitute the total bandwidth. The following formulas can then be used
to calculate the carrier frequencies. For the uplink
F
up
(c) = F
up,min
+ 0.001G + 0.025(c − 0.5) MHz, c = 1, . . . , N
and for the corresponding downlink
F
dw
(c) = F
up
(c) + D MHz, c = 1, . . . , N
D stands for the constant duplex separation between the uplink and the down-
link carrier frequencies. F
up,min
is the cutoff frequency on the lower boundary
of the respective frequency band.
Time-Division Multiplexing Structure As can be seen in Figure 6.10, the
time axis is split into four time slots, each 14.17 ms in duration corresponding
to 510 bits through the use of the TDM technique on each carrier frequency.
A periodic time slot produces a physical TDM channel onto which a logi-
cal channel is mapped. The logical channel is characterized by its carrier
frequency and the time slot recurring at 56.67 ms intervals.
Figure 6.11 shows the TDMA structure for the Voice+Data system. It
consists of hyper-, multi- and TDMA frames as well as the time slots and
subslots which only occur in uplink traffic. A subslot (half a time slot) consists
of 255 bits and a duration of 7.08 ms. Four time slots are combined to form
a TDMA frame, and are numbered consecutively here from one to four (time
6.3 The TETRA Trunked Mobile Radio System 389

1 Modulation Bit = 250/9 µs = 27.78 µs
Figure 6.11: TDMA structure of the Voice+Data system
slot number, TN). A TDMA frame is 56.67 ms in length. Eighteen cyclically
numbered frames (frame number, FN) are combined into a multiframe, which
is 1.02 s in length.
The 18th frame of a multiframe is reserved for the signalling channels, and
is called a control frame. If required, other frames can also be reserved for
signalling purposes. A hyperframe consists of 60 multiframes, and represents
the largest structure possible. It has the length of 61.2 s. In contrast to the
downlink, the entire frame structure on the uplink is staggered by two time
slots to enable a mobile station to transmit and receive at the same time. The
frame synchronization of the mobile station is adaptively dependent on the
signal propagation delay.
A burst is a set of data bits modulated on a carrier frequency (see Fig-
ure 6.12). In V+D it represents the physical content of a time slot, in other
words the physical channel information. There are three different types of
channel:
• A control channel, Control Physical Channel (CP), which exclusively
transmits the control channel data.
• A traffic channel, Traffic Physical Channel (TP), onto which the logical
voice and data channels are mapped.
• An Unallocated Physical Channel (UP), which is not allocated to any
mobile station and is used for sending broadcast and dummy messages.