GB2260665A - Communications using fibre optics and radio - Google Patents

Abstract

A personal communications terminal is usable with signals in the radio and in the optical regions of the electromagnetic spectrum. The terminal has a 3-part modular structure comprising a front end module 1 provided with radio 7 and optical 6 communications interfaces; a processor/controller module 2 connected to the front end module and a user interface module 3 connected to the processor/controller module. Fibre optic communication is used where possible with radio available as an alternative (Figs 2a-2e). Typical, possibly hybrid deployment configurations are shown (Figs 3, 4). <IMAGE>

Description

COMMUNICATIONS This invention relates to communications and in particular to battlefield tactical communications.

Battlefield tactical communication is currently carried out by combat net radio. In the UK the family of radios employed for this is known as CLANSMAN. The aim of future battlefield systems is to replace such radios with a more advanced and capable system which matches Army requirements. The UK programme for a next generation combat radio net system is called BOWMAN.

According to the present invention there is provided a personal communications terminal usable with signals in the radio and in the optical regions of the electromagnetic spectrum.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a systems block diagram of a communications terminal; Figs. 2. to 2e illustrate various configurations of next generation system section net; Fig. 3 illustrates a number of next generation system nets in a first deployment state, and Fig. 4 illustrates a shift in the deployment of the arrangement of Fig. 3.

The current CLANSMAN system comprises a family of radios of various sizes, including large vehicle and small man portable ones, together with many possible accessories and control equipments, vehicle connections etc. We propose the adoption of a common radio architecture consisting of a small family of standard equipments. These equipments would be physically smaller than the CLANSMAN units they replace and have enhanced performance. Whilst CLANSMAN is essentially limited to voice communications, our proposed system would be able to support simultaneous voice and data transmissions and would operate over a wider frequency range than CLANSMAN. Furthermore, we propose that the same equipment be capable of communicating over a fibre-optic cable in order to achieve radio silence.

A basic feature of the proposed communications system is the concept of a personal communication terminal. The terminal is an integrated arrangement which is not just a radio but also allows access to a fibre-optic system, particularly a LAN (local area network). The terminal has a user-friendly, easy to use interface which is common to all "radios" and thus would be a familiar item. Irrespective of whether the communications will actually be carried out by radio or over a fibre-optic cable, the user is always presented with the same interface. There may be a small family of closely related user interface units, from a "bare-bones" hand held unit with minimal controls for use by unsophisticated users, for example in a small man portable terminal, to a more elaborate unit with data entry facilities for use by experienced signallers, which may be man portable or for vehicle use.

A system block diagram of a proposed common radio architecture is shown in Fig. 1. The architecture divides into three sections: a front end 1, a processing and control block 2 and a user interface 3. These basic system blocks or sections are separated by well defined interfaces 4, 5 so that common radio processing and control elements in the processing and control block 2 can support a range of different bearer mediums and frequency bands at front end 1 and be served by a number of different user interfaces 3, including remote operation. In the Fig. 1 example the front end 1 includes an optical interface 6 in parallel with the radio bearer, including RF module 7, thereby giving access to a field LAN or an intercom facility in a vehicle equipped with a LAN.The interface 4 may be other than as illustrated and, for example, to such that ADC/DAC filter 8 be incorporated in the processing/control block 2 rather than the front end 1.

The standard interface 4 from the "radio" front end 1 to the processor/controller 2 involves a digital signal stream. Digital signal processing being a key feature of the proposed system. The radio performs as much processing as possible in the digital domain, restricting analogue functions to the front end transmitter/receiver and audio input/output at the user interface. The separation of the radio front-end from the radio signal processing allows for easy interconnection for extended range networking. The processing and control block 2 and the user interface 3 are common but the "standard" front end 1 is replaced by a range extension mechanism which might involve a microwave link or a fibre optic system.

Digital signal processing provides improved radio performance over the existing radios. The use of digital filters leads to improved filtering with better demodulation characteristics. There is improved dynamic response and in-band dynamic range due to controlled filter characteristics. Furthermore, digital modulation and demodulation at baseband allows complex modulations to be exploited for spectrum efficiency and encryption.

At the same time such a system would be compatible with the previous CLANSMAN system during introduction into service of the proposed system.

The user interface illustrated in Fig. 1 includes external input/output connections, for analogue signals and speech/data as illustrated, to an audio/crypto block 9, a management system interface 10 with for example input key means (Key) for cryptographic purposes, and a control/data entry device DED 11, the latter for example comprising a respective key pad. The standard interface 3 to the processor from the user interface may involve optical connections.

One of the features of the common terminal architecture is its inherent flexibility and ability to be enhanced as technological improvements occur. Voice and data transmissions are treated as identical information streams and can be presented with identical signatures on the bearer medium. By using digital modulation, filtering and encryption techniques, the balance and proportion of voice/data can be varied as the demands on the system change.

The common terminal architecture supports a Management System interface 10 and the "radio" can therefore support some form of management function.

There are two ways in which management information and control can be passed throughout the radio net, either by a superimposed management network or alternatively by distributing the management function throughout the network. The management network could either be a "flat" structure across all combat nets, or have a hierarchical structure. It is anticipated that the radio will have at least a portion of the management function incorporated therein. It is also anticipated that the management information will use or share a logical channel on standard net radios, rather than having a separate radio bearer, at least at forward levels.

HQ communications architectures demand very high bandwidth within HQ vehicles. This can be achieved by using fibre-optic LANS to implement a network within an HQ vehicle i.e. fitted therein. The use of fibre-optic networks can be extended beyond simply fitting them in HQ vehicles and is appropriate for the "wiring" of all vehicles. By extending this idea still further and equipping every radio with a fibre-optic connection (optical interface 6), additional operating benefits can be seen.

At present communications in forward areas is "over-air" on radio nets and is susceptible to Signal Intelligence (SIGINT) and Electronic Warfare (EW) measures as well as having to attempt to find available free channels in a very crowded spectrum. If, however, fibre-optic bearer are used for "radio" traffic between some users in the forward areas, the spectral congestion will be reduced and the transmissions can be established between units which are in static deployment. This parallels the current use of field telephone or intercom facilities.

If every radio is provided with a standard fibre-optic interconnection (interface 6) and every vehicle has an external connection to its internal LAN in addition to its internal radio interfaces, a wide variety of configurations becomes possible, the radio then being a communications terminal capable of radio or optical communications instead of just radio communications. Fig. 2 shows several different deployment configurations of communications terminals in a section net.

In Fig. 2 the section net is the area 20 contained within chain line 21. Three vehicles 22 are within area 20 whilst one vehicle 23, a command vehicle, communicates with the vehicles within the area 20 and the outside world.

In Fig. 2a is illustrated the fully mounted mobile configuration. Each communications terminal user 24 is connected to the section net within area 20 using standard radio links. The command vehicle communicates with a second net (not shown) using a separate net radio 25. In this configuration the vehicles are fully mobile and communications are similar to CLANSMAN.

In the fully mounted static case of Fig. 2b, the communications within area 20 have been taken "off air" by using fibre-optic links 26 between the vehicles 22, 23. A standard external optical interface to the 1 1 LANS within the individual vehicles 22 , 23 , allows the communications terminals to be connected using vehicle internal communications distribution or interconnect systems. The laying of fibre-optic links between the vehicles can be performed rapidly in a straightforward manner. The section net is now completely radio silent and is not susceptible to EW activity. The communications into the second net are maintained over a radio link usually at VHF.

Fig. 2c illustrates the case where some troops have dismounted from their vehicles together with their communications terminals but radio silent communications is maintained by using the fibre-optic interface built into each terminal and fibre optical cables deployed between them and the LAN fitted vehicles 221 and 231. The common terminal architecture proposed above ensures that the user interface to the net is the same whether the communication was directly between terminals or via a fibre-optic equipped vehicle. Fig. 2d illustrates the case where all troops have dismounted from their vehicles 22 together with their terminals and are interconnected via a fibre-optic LAN to the command vehicle 231. Radio communication to the second net is, however, via one of the communication terminals 241 which is coupled in the LAN.

If one of the fibre-optic links breaks for any reason this would be detected automatically by the terminal concerned and it would revert to normal radio operation, assuming the latter is allowed by the net controller. The transition between LAN and broadcast operation would be transparent to the user. This provides a vehicle drive-away capability. Thus if conditions demand it a vehicle in the fully mounted static arrangement of Fig. 2b and communicating over the LAN can move off without interrupting its communications. The snapping of the fibre-optic links results in immediate restoration of communications via a radio channel. This is illustrated in Fig. 2e. If the net were operating in a "radio silent" mode using the off air feature of the fibre-optic LAN, the terminals would all be disabled from radio transmission so that a fibre break would not reveal the net.This feature allows the proposed communications system to combine the flexibility of traditional combat net radio with the ECCM advantages of line borne systems.

The connections of the fibre to the terminal should break easily to enable rapid movement and change to the radio mode. Every time a fibre link is required, "new fibre" can be taken from a reel carried by a soldier or his vehicle. To avoid the need to attach a new connector to the fibre on every occasion a simple method of connection to the communications terminal is required. The technology developed for non-intrusive tapping of fibres could be used for this application.

The fibre tip could be inserted into a medium to absorb light and minimise reflections. The non-intrusive tap could be of a form which clamps onto the fibre.

A fictional deployment is depicted in Fig. 3 which illustrates a number of nets. In the static positions illustrated the fibre optic LANS are used to keep as much communication as possible "off air".

Command nets between commanders and platoon nets are all using a standard optical field cable.

On the platoon net, communications is mainly via simple standard section terminals which allow voice data communications over the net. The terminals all interface directly to the fibre optic LAN which has been laid from spools of fibre cable carried by each individual solder and cable carried within their vehicles. Each section could easily carry approximately 10 km of cable and combined with that carried in the vehicles each platoon would have approximately 100 km of cable.

Connections to the vehicles would be via standard connections on the exterior of the vehicles and the vehicles would provide repeaters for the LAN.

Whilst in this static dispersed position the net is effectively silent from the Signals Intelligence (SIGINT) perspective and is immune to enemy Electronic Counter Measures (ECM) or other forms of Electronic Warfare (EW).

The company and battlegroup nets use 16 kbs radio links. Speech data traffic is handled over the common carrier. The cables may be laid by vehicle or hand means as convenient. Data is routed to other nets using internet gateways.

A significant change in the position is shown in Fig. 4, where a platoon has been forced to move rapidly. The majority of the command and battlegroup nets remain unaffected and fibre links continue to be used. The moving platoon has moved from its static deployment position and can no longer use fibre optic LANS for "all informed" voice communication and has thus reverted to radio links. Depending on the circumstances causing the shift of deployment, the cable may be respooled or simply snapped as the positions of the sections changed. It is considered that cheap lightweight optical fibre which would snap easily is particularly advantageous although some form of quick release connectors could alternatively be employed.

As will be appreciated from the above, the invention provides an integrated personal communications terminal which is not just a radio since it also provides access to an optical LAN. There are three main modules in such a terminal. One module is concerned with front end processing and provides an interface to either a radio or optical bearer. A second module is the processor/controller. This processor module can be common to many terminals if the software is reprogrammed as appropriate to the job performed. The third module is the user interface which is common to all terminals.

To construct a terminal various arrangements are possible. The user interface may be "clipped on" to different processor/controller modules or it may be "clipped on" to one type of processor/controller module and different software employed. The processor/controller module may be clipped on to different front end modules i.e. RF modules with different frequency bands, or different optical interfaces. The overall arrangement may be man portable or designed for vehicle installation but in either event the three basic modules are employed. In the case of a low power man portable arrangement the optical interface may be correspondingly low power, whereas the one on a vehicle "clipped on" to the vehicle internal communications may be correspondingly higher powered and larger.The terminals provided by the invention and in particular due to their modular structure enable a true communications system rather than a family of different radios to be achieved. The basic modules can be adapted and clipped together in accordance with the intended function and provide communications which is not just radio but permits the "all informed" state to readily be achieved, in articular when radio silence is required, due to the optical LAN but which can readily and automatically revert to radio communications when necessary. The user interface may present minimal controls for unsophisticated users or be more elaborate for experienced signallers and data entry purposes. In any event, the operator will not have to do anything to change from optical/radio communications. In other words there is provided a personal communications terminal particularly for use as a radio in combat radio applications but which also has interfaces enabling the user to communicate over optical fibre links wherever this is required. The terminal is of a modular structure, with interfaces designed to permit use with radio or fibre optic links, there being a relatively small number of basic modules which can be chosen as necessary and connected together to perform as required functions. In this way a communications system which is smaller, better performance, light, cheaper and capable of more functions (voice and data) than hitherto can readily be achieved.

Claims (11)

CLAIMS.

1. A personal communications terminal usable with signals in the radio and in the optical regions of the electromagnetic spectrum.

2. A terminal as claimed in claim 1 and wherein the optical signals are conveyed over a fibre optic link to the terminal.

3. A terminal as claimed in claim 2 and including means such that when operating over the fibre optic link breakage of the fibre optic link causes the terminal to switch to radio operation, whereby to maintain communications, if circumstances permit radio communication.

4. A terminal as claimed in any one of the preceding claims, and comprising three basic modules; a front end module provided with radio and optical communications interfaces; a processor/controller module connected to the front end module; and a user interface module connected to the processor/controller module.

5. A terminal as claimed in claim 4 wherein the user interface module presents the same interface to a user irrespective of whether the communications is to take place over a radio link or a fibre optic link.

6. A terminal as claimed in claim 5 wherein the interface presented to the user provides the minimum number of control functions necessary to operate the terminal for speech communications purposes.

7. A terminal as claimed in claim 5 wherein the interface presented to the user provides control functions necessary to operate the terminal for speech communications purposes and a data entry device for data communications purposes.

8. A personal communications terminal substantially as herein described with reference to Fig. 1 of the accompanying drawings.

9. A communications system comprising a plurality of personal communications terminals as described in any one of the preceding claims and capable of communicating with one another in a net either by radio or over fibre optic cables, and including at least one vehicle having an internal fibre optic LAN for communications purposes within the vehicle, and wherein the LAN has an external connection on the vehicle whereby at least one said personal communications terminal external to the vehicle can be connected for optical signal communications with the interior of the vehicle.

10. A system as claimed in claim 9 wherein a said vehicle is a command vehicle and it includes a further personal communications terminal for communications with another net.

11. A battlefield system substantially as herein described with reference to the accompanying drawings.