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Introduction
TETRA
digital trunking communications system is a kind of wireless trunking
mobile communications system based on TDMA technology and a single
standard-based open system designed by ETSI in conjunction with
user organizations, manufacturers, testing and government authorities
to satisfy the mobile communications needs of the specialized institutions
in all the European countries. The TETRA digital trunking communications
system is able to provide command, dispatch, data transmission and
telephone services, capable not only of multi-group dispatch, but
also of providing short data message service, packet data service
and digitized full duplex mobile telephone service. The TETRA system
also supports powerful DMO mode and enables authentication, air
interface encryption and end-to-end encryption. Meanwhile, the system
also acts as a VPN, enabling a physical network to serve multiple
independent organizations. Thanks to the TETRA system’s rich service
functions, higher efficiency in frequency use, high communications
quality and flexible network modes, many new applications (such
as vehicle positioning, image transmission, mobile Internet, database
inquiry, etc.) have been made possible in the TETRA system. As a
result, the TETRA digital trunking communications system has been
growing rapidly in the world in general and in Europe in particular
in the past couple of years.
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The Dedicated TETRA Digital Trunking Communications Network Is a
Complement to the Public Communications Network
Mobile
communications can be classified by targets into the following main
categories: public mobile communications and specialized mobile
communications. A public network, built with investment from public
telecom enterprises, is open to the whole society and serves public
users, therefore a system fully open to all the users, both individual
and collective. Since there is not necessarily a positive connection
among the users, an equal call class is applied to all of them.
While the relationship between the operators and users is one between
service providers and service recipients, it is moreover a relationship
based on the exchange of equal values.
A
dedicated network is one built by the specialized institutions with
their own investment. As a semi-open system serving part of the
users, it targets certain institutions and specialized users. Although
a collective user is made up of individual users, there exists a
positive connection among them and their call classes are usually
not equal in nature. It is entirely for the purpose of providing
telecom services necessary to address internal needs that the network
operators build and operate dedicated networks. Therefore the focus
is on ensuring that the special operational needs of their own institutions
are met, rather than offering telecom services to users at large.
Mainly aimed at providing communications within or among collective
users, a dedicated network, depending on its needs, may or may not
be connected with public networks. Its communications with public
networks is made possible via a trunk interface (or simply interface)
which is not only a link between the internal users and the outside
world but also a mechanism imposing necessary restrictions on such
communications.
Compared
with public networks, a dedicated network is more focused on group
calls, broadcast calls, emergency calls, forced connect and disconnect,
calls of differing call priorities and other dispatch and command
functions and on reducing the call setup time. It normally takes
a public network user several seconds, over 10 seconds or even longer
(from dialing to getting through) to make a telephone connection.
While this is something the ordinary users are quite used to, it
is far too long for the dedicated network users. Under emergency
situation, a connection is expected to be made instantly at a touch
of a button (less than 0.5 second), otherwise it may cause very
serious consequences. Command instructions must be kept short and
concise and normally last just tens of seconds, leaving no room
for lengthy conversations. As the differences in the nature of services
of various institutions, the environment of usage and the means
of transportation have given rise to disparate use requirements,
dedicated communications systems of all descriptions have come into
being. With the development of mobile communications technologies,
people have tried as far as possible to seek common ground while
shelving differences, making it possible for dedicated mobile systems
developed to meet the needs of as many specialized institutions
as possible. It is against this backdrop that there emerged the
TETRA digital trunking communications system..
From
the perspective of the existing digital trunking technology and
the 2G public mobile communications network technology and based
on the analysis of the next generation digital trunking and the
3G public mobile communications technologies, the dedicated digital
trunking mobile communications network, a complement to the public
networks, will not be replaced by the 2G and 3G public mobile communications
networks. There is still no way of knowing if the 4G mobile network
will take the place of the dedicated network.
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The Operational Mode of TETRA Digital Trunking System
In
the opinion of the major foreign company operators, the selection
of open networking standard, lowering of the fixed asset investment
and the manufacturing of the same product by different vendors can
give rise to competition among the vendors and cut equipment and
investment costs; lead to the selection of flexible network structures
and the reduction in investment cost for network deployment; based
on user requirements, properly design system coverage, capacity
and QoS, reduce the cost of system operation and lower the risk
in investment.
VPN
offers the best solution for operation on shared dedicated networks.
The functions of VPN enables the sharing of the same platform by
multiple organizations with very diverse functional needs and system
concepts. Without having to buy basestations, switches and transmission
equipment, all the organizations have to do to build their own VPNs
is to deploy necessary dispatch and mobile stations and work independently
in the VPNs in the same way as they do in traditional dedicated
networks. In the meantime, the system also allows the user institutions
to manage the communications groups within themselves and connect
with other users in the system when necessary.
The
operation and management of the shared networks abroad mainly take
three forms: government operates and manages the networks it invests
and owns; operators operate and manage the networks invested and
owned by the government; operators invest in, own, operate and manage
the networks all by themselves. In the light of the reality in China,
we should adopt the mode in which operators operate and manage the
networks invested and owned by the government.
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The Maturing of TETRA Digital Trunking System Products
Up
to now, major foreign manufacturers have developed their own 800MHz–ready
TETRA digital trunking systems, capable not only of group calls,
broadcast calls, emergency calls, forced connect and disconnect,
priority calls, dynamic reorganization and other dispatch and command
functions provided by traditional dedicated mobile networks, but
also data transmission function (status information and SMS). So
far, circuit-based data transmission function has been developed
in the TETRA digital trunking system, with protective transmission
rate being 7.2kbit/s, low protective transmission rate 4.8kbit/s
and high protective transmission rate 2.4kbit/s. At the same time,
the newly developed data service delivered via 4 time slots simultaneously
enables real-time transmission of dynamic images. Major foreign
manufacturers have also developed TCP/IP-based data transmission
systems, making it possible for TETRA IP to achieve continuous communications
among IP users by sharing radio resources and voice services. TETRA
IP is able to provide a host of data applications such as WAP application,
enterprise intranet application, vehicle management, email, database
inquiry, scheduling, telemetry, monitoring, automatic vehicle positioning,
navigation, file delivery, etc. The TETRA WAP application provides
the on-site staff with fast and accurate database access regarding
such information as ID confirmation, addresses, vehicle information,
lost or stolen properties, various resources in operating status
and information directory services. Some companies have reported
progress in developing IP-based voice services on TETRA digital
trunking systems.
So
far as equipment manufacturing is concerned, the switches and basestations
for the 800MHz TETRA digital trunking system have already emerged
with the basestations providing fault degradation function. As the
handsets produced are equipped with Chinese interfaces, interoperability
and end-to-end encryption have been achieved among the handsets
from multiple vendors.。
In
the area of re-engineering, all the major foreign vendors have adopted
open API for the development of equipment adapted to the system’s
actual needs. Regarding component production, foreign companies
have introduced low noise RF modules in the hope of jointly developing
digital trunking systems with China.
China
is a huge market for the digital trunking systems. The development
of digital trunking systems and networks involves large amount of
hi-tech knowledge and leaves huge room for technological and knowledge
invention and innovation covering system structure, protocol composition,
code modulation, multi-address connection, adaptive countermeasures
for fading environment, test processing, network optimization, terminal
composition and many more. The Communications Research Institute
of Harbin Poly-technical University has completed the general plan
design and functional block classification according to TETRA air
interface standard and put forward requirements concerning performance
parameters, inter-module interfaces and the functions to be put
in place. At the beginning of 2001, the Communications Research
Institute of Harbin Poly-technical University has purchased with
its own money integrated TETRA testing instruments, signal generators
and signal analysis instruments from the British IFR Company to
create conditions for the R&D of digital trunking technology.
At present, the testing of the trial digital trunking system is
full steam ahead and the joint test with the European TETRA mobile
stations is expected to take place in 2002. Therefore, the Chinese
manufacturers, operators and R&D institutions should establish
close overall strategic partnerships with investors and foreign
vendors, engage in innovation with keen determination, make strong
efforts in increasing independent IPR and speed up the development
of our national digital trunking industry, so as to meet the huge
demand in the Chinese market or even the overseas market and contribute
to our overall national strength.
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The Development and Application of TETRA Digital Trunking Systems
Since
its debut in 1995, TETRA has been in a constant process of modifications
and improvements with some new standards added, including RTS/TETRA-04046（TETRA
DAWS logic link control service）, RTS/TETRA-04047（TETRA DAWS media
access control service） etc.
In
between 1999 and 2000, TETRA standard was instrumental in modifying
ETS 300 392（V+D）network design, ISI, gateway, encryption, ETS 300
396（DMO）type I router air interface, type II router air interface,
etc. and drafting mobile station to mobile station interface, the
direct mode type I router, the SDL models of direct mode gateway
, etc. 。
According
to ETSI, TETRA Version 1 standard that suits PMR/PAMR field has
won commercial success, multi-vendor support and world-wide recognition
as a mature standard. To keep up with market development and complement
“3G”, it is important to enhance TETRA standard in seeking of increased
ETSI influence globally. Therefore based on a 3-year work plan,
an estimated 130/man months are needed for studying and drafting
TETRA Version II to address the following issues:
Increase
data rate；introduce higher rate packet data; enable users to efficiently
access Internet information, real-time images, digital maps, etc;
Use
new voice encoders and decoders to improve voice quality;
It
is necessary to achieve interworking and roaming between TETRA and
UMTS/3G, to be compatible with vocoders, numbering, addressing and
ID and to enhance voice quality in order to migrate from TETRA SIM
card to USIM card;
Increase
basestation coverage radius ( ie. 120～200 km) to facilitate the
use of vehicle-mounted equipment and air to ground communications
and extend operational range;
Adopt
SIM card and make it universal;
It
is necessary to be backward compatible with TETRA Version I and
able to work on the existing TETRA frequency band;
Further
improve network efficiency, optimize air interface for increased
frequency efficiency, raise capacity and performance, improve quality
and QoS and further reduce terminal size, weight and power consumption
with network technology.
For
this purpose, it is necessary to study the initial feasibility of
the new air interface, high speed packet data, new encoder and decoder,
U-SIM card requirements, interworking and roaming with 3G systems
and enhanced air interface and coordinate V+D and DMO standard.
The
TETRA Version II is expected to be completed in 2003 and products
to be turned out after 2004. This will allow digital trunking networks
to be upgraded from TETRA Version I to TETRA Version II, which will
ensure that technology will not become antiquated in the first decade
of the 21st century and develop in a coordinated manner alongside
3G mobile communications systems.
With
the fault degradation capability in TETRA digital trunking basestations,
in the event of failures in switches and in links between switches
and basestations, individual basestations can still provide network
services to limited areas. The DMO of the TETRA digital trunking
system enables the users to communicate directly with mobile stations
by bypassing network infrastructure and using radio frequencies
not controlled by basestations and switches. Thus, the fault degradation
mode of the basestations can serve as a guarantee for communications
in the case of disasters and the DMO can act as the ultimate means
of emergency communications.
The
TETRA digital trunking system provides communications with adequate
security measures, namely authentication, air interface encryption,
end-to-end encryption, etc. to satisfy needs at ordinary, commercial,
private and confidential levels. Network access authentication constitutes
the basis of the entire network security, able to effectively prevent
unauthorized network access and mobile terminal “clones”. After
addressing the issue of access security, it is imperative to use
encryption on air interfaces to guard against professional eavesdroppers
from stealing information via air interfaces. Air interface encryption
requires different encryption keys and the change of keys on an
irregular basis. The air interface encryption technology not only
protects information delivery, shields user identities, but also
prevents the “invaders” from detecting the on-going communications.
To give special protection to sensitive information, it is also
viable to use end-to-end encryption technology.
It
is for this reason that government bodies, police, security, military
police, transportation, railway, water conservation, power, petrol,
news media, tourism, city construction (gas, running water), large
scale mines and enterprises, public health, first-aid, fire fighting,
disaster relief and many other sectors of the national economy are
in urgent need of building trunking dispatch communications networks.
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Development of TETRA Digital Trunking Systems in China
TETRA
was listed as one of the technological schemes in the industry standard
related to the digital trunking mobile communications system schemes
issued by the Ministry of Information Industry (MII) in December
of 2000. In its document No. 518 entitled “Circular on Issues Related
to the Use and Management of 800MHz Trunking Frequencies” issued
in July, 2001, MII made clear that the frequencies already assigned
to the analog trunking networks should have been sorted out by the
end of 2001, the centralized management of the digital trunking
frequencies should be stepped up, public trunking networks providing
social services be built in all the regions and due consideration
of building digital trunking networks only be given to the sectors
with special needs. Such standard and document have laid the policy
foundation for developing digital trunking systems in China.
In
the past year, Marconi Company has developed a full set of 800MHz
systems and handsets, put in place a technology trial system comprising
a switch and 3 basestations in Chengdu of Sichuan province and reported
good results from the tests conducted in March, 2001. Nokia built
a trial system with a switch and 4 basestations in Wuhan of Hubei
province and in the meantime provided dispatch stations and miniature
handsets with Chinese displays, receiving favorable comments at
the acceptance in Jinzhou, Hubei province. The trial network built
by Motorola in Hubei province in February, 2002 included a switch
and 3 switches and passed the acceptance test conducted by MII.
All these efforts have provided material basis for China to launch
digital trunking networks.
In
the area of PMR, Nokia took the lead in providing a dedicated TETRA
mobile communications system to the Hong Kong police. The project
with a total investment of 18 million Euros included a transmission
network, sea-borne voice communications system, automatic vessel
positioning system, etc. The project which started in February,
2000 is already operational. Following on the heels of this HK police
network, the Guangzhou-Kowloon Railway, Shanghai Public Security,
Tianjin Water Conservation and Guangzhou Subway have also signed
TETRA agreements. The Ministry of Railways has bidden to build TETRA
systems for three railways, namely Qinhuangdao-Shenyang railway,
Xian-Hefei railway and Xinyi-Changxin railway. In addition, the
subways in Shenzhen and Shanghai and light-rails in Beijing, Tianjin
and Wuhan have also planned to adopt TETRA as the means of wireless
transmission. Moreover, the Ministry of State Security is also intended
to bid for the construction of a TETRA network.
In
respect of PAMR, Beijing Huaxun Group, Hubei Quantong, Sichuan United
Electronics, Zhejiang Success Industry Company, Shandong Hehua as
well as Xinjiang and other provinces are also getting prepared for
constructing public TETRA digital trunking networks in their own
provinces. In addition, Qingdao Hisense, Hebei Wanguo and Inner
Mongolia Aisen are also making preparations for digital trunking
network building. Many more companies have investigated the technology,
ready to get on board. Large numbers of investors have shown keen
interest in digital trunking and been following its development
closely. Especially in the wake of the “Sep. 11” incident, the Chinese
authorities have come to understand better the role of the TETRA
digital trunking technology in command and dispatch systems and
the departments concerned are studying the feasibility of using
the technology in both military and civilian communications networks.
Obviously, the conditions for building networks with the TETRA digital
trunking technology is maturing by the day and the time of high
growth is around the corner.
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Author’s bio：
Sun Xin Associate Professor in Electronic Information Engineering
College of the Northern Jiao Tong University. Graduated from the
Communications Engineering Department of Harbin Poly-technical University
with Doctorate degree. Participated in the design, installation,
debugging and acceptance of the TETRA digital trunking trial networks.
Presently engaged in teaching and R&D in information theory,
mobile communications, digital signal processing, etc
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