Applications | Emergency Communications

In the UK today businesses and other organizations are more dependent than ever on the ability to communicate effectively . This applies locally, regionally and nationally. UK industry has become complacent as it has become used to reliable wired and wireless communications networks. These networks rarely fail but few understand how little resilience is built in to the landline and the GSM networks.

Emergency Communications

In Manchester, a single tunnel fire took out two main BT cables and plunged a large area of the city into a communications crisis for both public and private users. It would appear that no resilience had been designed in to the system. Unfortunately, experience has shown time and time again that reliance upon a single system exposes vulnerability to the unexpected. This was starkly demonstrated when the county of Hampshire lost all 999 emergency services when the main public telephone exchange at Southampton failed. Although each service (including Hampshire Fire Brigade) thought they had resilience built in to their systems, this proved not to be the case. Because all the emergency services relied primarily on the same type of connectivity they all suffered the same result. The police provided the only emergency communications available during this period via their independent VHF system for motorway traffic cars. These were deployed to key points and provided a limited level of communication and coordination during the crisis. In short, the only Plan B was of limited use.

Since the Madrid bombings and subsequent terrorist attacks in London, communications networks which are not affected can still be commandeered by the security services or even shut down in the case of the mobile phone networks due to the risk of further detonations via these systems. In either case commercial orgaizations are left without a means to inform their own staff of the local situation and are therefore vulnerable to further attack

In Louisiana following the hurricanes even the satellite networks became unusable due to congestion as this was the only method the public safety authorities could employ

The Solution – Private Mobile Radio [PMR]

Private Mobile Radio can offer a very effective solution to the problems outlined above. This is becauese PMR systems are directly under the control of the owner of the network. Networks can be as small or as large as required and provide a wireless communications capability either within a building, around a site or across an entire city.

There are variious types of PMR system available and they each provide benefits which can be tailored to the users requirements.

In all cases radio is generally used to allow user or work groups to communicate whilst mobile. This 'all informed' method of communicating can be ideal in an emergency as all users are kept aware oif the situation as it develops.

To make the radio network even more effective various signalling techniques can be included which allow different users groups to communicate amongst themsleves, or indeed to allow just 2 users to communicate with each other. A typical system might have Managers and Supervisors sharing one group with another group where everyone is a member. In addition radios can be configured with specific features to improve safety for personnel. This might include Lone Worker, Man Down, Emergency buttons, Priority calls, encryption and scanning, amongst others.

Below is a basic decription of the current systems available and the future technologies which are under development.

Conventional System

A conventional system is the lowest cost method of communicating with a wireless device over an extended area. Generally speaking a repeater or repeaters are employed to extend the coverage area. In these systems the users simply activate their radio by depressing the Press To Talk switch [PTT] and transmit to either another user or to a group of users if selective calling is configured.

The coverage area will be determined by the power of the repeater transmitter and the antenna height and type.

Quasi-synchronous System

This system uses several repeaters located at different sites where the coverage areas overlap thus creating a number of cells. Radios move from cell to cell and the system recognzes the signal strength measured at the mobile radio and allocates the best repeater accordingly. This type of system allows re use of the same frequencies and is ideal where a large geographical area needs to be covered and where there are few available frequencies.

Trunking

Trunked radio received its name from the 'trunk line' which is used in commercial telephone communications. Put simply, a 'trunk' is a communication path between two or more points, typically between the telephone company central office and one or more users. The trunk line is time-shared by several different users, but users of the telephone service do not need to be aware of this sharing. One party places a call to another party and the call is completed; the internal working of the telephone system is transparent to the users.

Radio communication over a trunked system is quite similar to such telephone systems. The transmitting and receiving radio units can be thought of as the calling and receiving parties, and a trunked radio system can be thought of as the telephone company equipment. Instead of telephone lines, the radio system uses radio channels to place calls. As with the telephone system, the radio users are not aware of which particular radio channel they are communicating over. All that is apparent is that a communication path has been established between the users.

Trunking a multi-channel radio system increases the efficiency of the radio system by dynamically managing the use of a radio channel. This is accomplished by the computer control of radio channels and the virtual elimination of the delay experienced by field units in obtaining a clear radio channel.

Every trunked radio system uses two types of radio channel designations: control (or data) and traffic (or voice) channels. One control channel must be designated at each site and the remaining channels are used as traffic channels. The control channel is used to send digital information between the radio units and the computer equipment controlling the operation of the system.

Traffic channels are used to send the actual communications (voice or data) between radios. A simplified exchange between the radio unit and the site equipment may be described as follows:

  • The radio unit continually listens to the control channel waiting for instructions.
  • When a call is to be placed, the user presses his "push-to-talk" (PTT) switch; the radio then sends a short digital message over the control channel and tells the site equipment that it needs a channel to communicate.
  • The site equipment hears the request for a channel and assigns an available working channel by sending a return digital message over the control channel.
  • The radio unit receives the working channel assignment and sets its transmit and receive frequencies to the new channel.
  • The radio unit and the working channel perform a high speed "handshake".
  • The radio audibly signals to the operator that a channel has been assigned and that communications can start.

This procedure may be repeated several times during a communications sequence, and subsequent transmissions during a communications sequence may be made over any one of the available working channels. All that is apparent is that a clear channel is available for communications. The user does not have to be aware of which particular radio frequencies the communication takes places.

A unique address code is allocated to each radio. This code identifies a calling radio to the site equipment, and allows the site equipment to call specific radio units. The radio units can be also partitioned into 'talk groups' so that radio users with similar communication requirements can communicate with each other.

The MPT1327 standard for trunked private land mobile radio systems is used mainly in Europe, Australia, Canada and other countries. It accommodates up to 1024 channels, 12.5 kHz or 25 kHz apart.

TETRA

TETRA (Terrestrial Trunked Radio) is a set of standards developed by the European Telecommunications Standardisation Institute (ETSI) that describes a common mobile radio communications infrastructure throughout Europe. This infrastructure is targeted primarily at the mobile radio needs of public safety groups such as police and fire departments, utility companies, and other organisations that require voice and data communications services.

Based on digital, trunked radio technology, TETRA is the next-generation architecture and standard for current, analogue PMR users. TETRA incorporates features from several different technological areas including mobile radio, digital cellular telephones, paging, and mobile wireless data.

TETRA-based products come with built-in encryption features to ensure the privacy and confidentiality of sensitive data and voice communications. These products are also designed with the ability to transfer data at faster rates than seen before in mobile communications.

Designed primarily as an emergency communications system TETRA is slowly becoming available to commercial users and should certainly be considered when deciding to implement an emergency communications network. The advantages of TETRA over analogue conventional or trunked systems are:-

  • Combined voice and data communications in one handset
  • Encryption – very secure voice and data communications
  • Direct mode – the radios can operate together without the need for a network.
  • Resilience – as the system was designed for public safety use there are a significant number of fall back modes available which makes the network very resistant to failure.
  • Gateway mode – a single mobile with a connection to the network can act as a gateway for other mobiles thereby extending coverage or range.

These are just some of the many solutions available from Brabourne Ltd. We have experienced consultants who can design the most cost effective solution for organizations of all sizes. If you think your organization is vulnerable and you could benefit from some advice then please contact us by email at sales@brabournecommunications.com or by telephone on 01332 363135.

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