Government and military equipment

Mobile equipment

There have been several attempts at mobile facsimile, some using narrow format (100cm) machines. The most popular method was to split the radio speech channel to keep the mobile units in speech contact during facsimile operation, normally transmitting in the direction towards the mobile terminal. These units were costly for their mobile environment and suffered as a result of needing spe­cialised radio equipment.

With the use of the TACS cellular radio system normal G3 equipment can operate when a telephone type interface is available. The Cellular Line Interface connection can be sophisticated and allows automatic answering and call origination by the G3 machine. Calls made between the mobile and normal PSTN connections provide access to the large G3 installed base.

Opinions differ about operations above 4.8kbit/s. Some believe in operating as fast as possible, while the connection is good, whilst others prefer to rely on the improved signal/noise performance at lower modem rates. Most opinions however recommend the use of CCITT ECM.

The question of facsimile use on GSM is another matter because the system codes the voice and there is no synchronous transparent channel available for facsimile. The topic is well studied but no clear proposal has emerged.

Similar requirements exist for the transmission of documents, maps, drawings, photographs etc. as in other market segments. One major difference is that for the transmission of documents classified for national security, additional high performance data encryption equipment is required. Further, to avoid plain language signals from the fax equipment itself being intercepted, and to avoid compromi­sing the encryption key generator codes, significant precautions must be taken in equipment design to reduce the relevant radiated and conductive electromagnetic emissions. These security require­ments are not normally published.

60.2.5.1 Strategic requirements

These machines normally operate in regular office environments and apart from interoperational requirements for secure fax or tactical machines, communication can usually be met by standard CCITT G3 models.

60.2.5.2 Tactical requirements

Machines for this use include military battlefield equipment to operate under inhospitable environmental conditions, fast, reliably and securely. Standards are desirable to ensure interoperation be­tween allies of different national forces. Typical features of the NATO standard are:

1. Up to 16 grey shades for photographs.

2. G3 standard and fine resolution equivalents.

3. Broadcast and duplex network operations.

4. G3 MH compression, also uncompressed and BCH forward
error correction.

To be acceptable this equipment should be lightweight, easy to operate in arduous conditions and capable of various communica­tion modes, including high speed burst mode to avoid radio location when necessary.

Дата добавления: 2015-03-31