Discussion in 'Royal Signals' started by TA_sig, Jul 14, 2006.

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  1. Hey folks,

    I've been looking at some 2NC things and potentially leaping across to a related trade - has anyone got any resources on the Airwave systems that you can direct me to?

    I get the basic gist of it, TETRA system, mobile access etc (reminds me of scra and bird) - got any more info, looking to learn as much about it as possible - I have too much spare time on my hands.
  2. THIS of any use to you?
  3. The Airwave site is good and covers most points much more info available if you input airwave and tetra into google
  4. I will dig around and see if I have still got any electronic copies of course notes on it.
    Is there anything specific you want on airwave or just generics.
  5. respectfully TA-sig, that was why masturbation was invented.
  6. Airwave is the O2 implementation of TETRA, it is a nationwide fixed infrastructure system used by a number of the emergency services (lancashire police for one).

    As a starting point, think of TETRA as a mobile phone system, it has all the features you would expect of a 2G mobile phone system (it's ability to handle data is somewhat limited compared with 3G or EDGE).

    Each TETRA channel is divided into timeslots (4) one reseved for signalling and the rest for traffic (two channels = 7 slots for traffic).

    So why bother with TETRA?

    Unlike GSM TETRA support a few features that may be of interest to militaty (or emergency service) users, it supports priorty (and I think pre-emption) allowing high priority stuff to take precedence. Also TETRA is not available to joe public to is less likely to get jammed in the event of an event (see ACOLC for some details about GSM overload control).

    TETRA also supports a mode called 'direct mode' where handsets can establish comms without the need for the basestation (but no timeslots so it take an entire channel).

    A number of companies have looked into a secure version of TETRA (providing end to end encryption (GSM is only over the air)). At least one company has produced a deployable version of a TETRA basestation.

    TETRA always seems to play catch up with GSM and there was a time when it may have lost out to GSM-R but with the letting of Firelink most of the fireservices will migrate to TETRA so it looks like it is here to stay.

    At least it means that most of the emergency services will actually be able to talk to one another (and I assume anyone that 2NC supports)

    The police raised some concerns about TETRA, because it is TDM there is an approx 16Hz pulsing of the carrier which some have said may give the user a headache (I really don't know).

    Loads on the web about TETRA, enjoy!!
  7. That option has already been overused - besides, doris is on her way back from the gym and I need to gather my strength.
  8. Oh where to start.

    All Blue Light Services are being pushed toward AIRWAVE as it subsidised by the Home Office. All Police Forces now use it, including the Met who were reluctant to move due to a number of reasons. However 7/7 sems to changed that.

    TETRA is available to the public. There are 2 bands Public Safety and Public Access available across the whole of Europe as definded by ETSI. Public Safety is for Blue Light and Public Access is, well it does exactly what it says on the tin.

    Balls. Direct Mode Operation still uses timeslots.

    Its all to do with Calcium forming on the brain if a modulating signal of 16Hz is close enought to it. TETRA works at 17 and a bit and all the safety cases have been done and are out there.
  9. ?? I thought DMO made no use of the network at all, as it works where the network isn't present like Pen-y-ghent
  10. Quite correct. It doesn't use the network.

    However it still does use timeslots. With the timing and synch coming from the 'master' radio.
  11. How does that work? What I thinking about say set 1 is the master talking to set 2, but set 2 is also talking to set 3 (which is out of range of set 1).

    Whats the classification of how TETRA works? Is it an open standard (I've not seen anything official but I seen people complaining about some technical threads on this forum and I know one of the Sigs Bdes is censoring(/moderating) posts on this forum)
  12. The master radio is the one transmitting so when radio 1 transmits it is the master and radio 2 would synch with it. When radio 2 transmits radios 1 & 3 would synch with it. And so and so forth.

    As to the classification of how TETRA works, its a communications standard just like GSM, GPRS, X25, etc. which are open source.
  13. So I'd imagine that if set 2 was talking to 1 or 3, sets 4 & 5 could still communicate on a different DMO channel (still using the same frequency) as they'd utilize timing from Set 2.

    From one of the earlier posts, it seems quite easy to overload the network, especially if too many organisations are using different channel on the national network. (i.e. if 7 operators transmitted at the same time they'd take up all time slots across the UK). I'd guess national has its own system, as would regional and county (to prevent one type of user from taking others down).

    Edit to add: Obviously you'd need users on a number of separate channels, spread all over the country affliated to many seperate base stations
  14. If they're on a different channel in DMO its a different frequency.

    As with GSM there are calculations made to ensure a good quality of service (QoS) which leads to the number of channels required or the maximum number of subscribers supported. And in conjunction with this a ever changing beast called Fleetmapping is employed to ensure the network is managed correctly. Also if there is going to be surge in use in certain areas just like GSM mobile cells can be deployed.

    If you really really need to now this stuff then contact these guys
  15. Point to note with all this. When the term channel is used it is only in the sense of on the base station. You can have a transmit/recieve on one channel with 4 time slots. You can have another (used to have a capacity of 8 TRX's at the now defunct commercial tetra provider in the uk that was called Dolphin then Inquam) on a differnt channel in that same base station that are all then combined into another master channel to go out to the air interface but this depends on the equipment manufacturer.

    In tetra the phrasiology (is that a word?) is Talkgroup instead of channel. You can have as many TG's on a channel, as long and the slots are not maxed out on it, as you like as it is all controlled at the switch. The bts is only there for transmit recieve purposes. You can have national TG's that could transmit on every bts in the country that if someone is 'tuned' into that talkgroup. So you can have 1 talkgroup that covers many bts and all users can hear the transmissions of anyone else on that tg who is transmitting. You also have the advantage of point to point call( mobile to mobile or mobile to despatch), telephoney (to mobile or infrastructure) as well as the group calls.

    If a mobile is transmitting then no other mobile can over ride that transmit unless then invoke an emergency. this then kicks off all mobile users except a dispatcher. this is in case the mobile is incapacitated and the dispatcher has to guide other resources to the location.

    Also, dependant on handset manufacturer GPS info can be sent for that individual handset.