🚀 go-pugleaf

christophe wrote:

> As is known BT Airwave have a contract to supply TETRA services to
> police in UK.As stated before the system is not secure,and handsets
> offer potentially serious RF hazards to users,as well as interfering
> with other electrical equipment nearby(eg breathalisers).We have not
> even mentioned the problem of putting up more base stations,with the
> consequent planning problems.

ISTR one attraction of TETRA is that it fits the same VHF frequency
allocations as the old analog walkie-talkies, but is a modern digital
system offering services such as data and dial-out to PSTN that the analog
walkie talkies could never provide.  And at least you can't pick it up on a
handheld scanner without using a digitizer and some decoding software.

If TETRA runs at the same frequency as the old analog sets, then it's funny
how health issues have suddenly appeared, and how its detractors assume
that GSM handsets are safe when radiating next to the head at 2 watts.

TETRA will require far fewer base stations than a private GSM network.
 
> Push to talk GSM/GPRS is a perfectly good solution,which is being used
> elsewhere.

Requires more spectrum, which isn't free at VHF (which is desirable for
enhanced range compared with GSM).  Of course you could invent a GSM-like
service at VHF - oh, wait a minute, it would look remarkably like TETRA by
the time you'd actually visited some of the engineering compromises...

> GSM is much more secure than TETRA(particularly the A5-2/3
> algorithms),which is important when handsets may well interrogate the
> PNC and other police computer systems,wirelessly.

Implementation issue.  No reason why TETRA can't have crypto, just not as
well standardised yet as with GSM.

> GPRS with push to
> talk will allow far better data upload/download than TETRA can
> provide,and the base station network already exists,in most areas.

Of couse using more spectrum would give higher data rates.  But the existing
base station network is patchy in rural areas, and can get overloaded in
major emergencies, which can be a problem even if emergency service users
have priority status.

> If you want to see how well TETRA has done in the UK,just look at
> Dolphin,the consumer TETRA service.It's losing lots of money for it's
> new owners!

Which has everything to do with marketing, and nothing to do with technical
issues.  TETRA is a specialist product which isn't really aimed at
consumers.  I sometimes use Dolphin in remote rural areas that lack GSM
coverage - enhanced range is what it's about (and for the emergency
services, of course not relying on consumer infrastrcture is important).

- Martin.