Wireless Waffle - A whole spectrum of radio related rubbish
Underground Communicationssignal strength
Tuesday 6 June, 2006, 08:22 - Radio Randomness
july7londonA London Assembly report published yesterday (5 June 2006) into the events surrounding the terrorist attack on London on 7 July 2005 identified that the major problem suffered by the emergency services at the event was the lack of adequate radio communications. It identified that, other than the British Transport Police, none of the radio systems used by police, fire or ambulance services functioned on the London Underground. Further, it goes on to note that the different radio systems used by the different emergency services means that they are unable to effectively communicate from one service to another. It also states that the reliance on mobile phones by the emergency services (in particular the Ambulance service and for communication between senior officers) was effectively an accident waiting to happen.

What's perhaps surprising is that none of these problems were unknown. There have been plans afoot for over 10 years to install radio communications across the London Underground, including in tunnels. The project, known as 'Connect' was awarded to a consortium in 2000. The original plan was to install infrastructure across the underground to support both 'TETRA' based communications for the tube trains themselves as well as to support cellular communications. However technical difficulties have meant that the project has now been restricted to just providing TETRA for cab-to-control communications. The project is still in a 'beta' phase with no actual radios in service.

Since the emergency services first used radio, each of the services had its own radio system. In times of crisis, each service established a mobile headquarters, often in the back of a van, and as long as each services' HQ was parked near the other services, communications between the different services could be achieved by shouting from van to van, or by running hand-written paper notes between them. The events in London, however, occured in several different and diverse locations and with improvements in communication and information technology, there is less of a need for a remote HQ as everything can be dealt with from the regular HQ. As such, communication between the services is now worse than it might have been 10 or 15 years ago and in a situation such as the terrorist attacks on London last July, would have been virtually non-existent. airwaveThere is light at the end of the tunnel, however, in the form of 'Airwave'. Airwave is a TETRA based radio service being rolled-out across the UK for use by all the emergency services. Initially intended just for the police, Airwave has now been adopted by the ambulance and fire services too. Once roll-out is complete, all three main emergency services will be using the same radio technology and the same radio system so inter-service communications should be much more straight forward.

It is a well understood fact that, in times of crisis, usage of mobile phones rockets. Everyone near or involved in the crisis will wish to contact their relatives to tell them they are OK, or to call the emergency services to try and garner assistance. Mobile networks are not designed to handle such high loads and the inevitable result is severe congestion and in some cases, network failure. With this in mind, the GSM specification includes a number of features to try and ensure that emergency service users can continue to communicate at such times. Access overload class (ACCOLC) is a UK designed system in which ACCOLC enabled mobiles are given priority access to a cellular network. policemobileEach ACCOLC mobile phone is assigned a priority from 1 to 15 (normal users are randomly assigned a priority in the range 1 to 10, whilst emergency users have priorities 11 to 15). The network selectively disables the lower priority mobiles to ensure that higher priority communications can continue. Thus priorities 1 to 5 may be disabled, randomly cutting off half of all civilian users and thus freeing the network for emergency communications. There is also a feature of GSM (version 2+) known as enhanced multi-level precedence and pre-emption (eMLPP) - this too allows priority access for certain users, however it is not commonly implemented on many commercial GSM networks being reserved for those networks designed to support railway communications (GSM-R).

So from the perspectives of the communication abilities of the UK emergency services, the attacks came just at the right (or is that wrong) time, during a period of transition and when sub-terranean communications were not at their best. It is to be hoped, therefore, that even if the atrocities had not taken place, the situation would be improving. With the publishing of the London Assembly report, let us pray that adequate communications are in place before anyone else decides to take a pop at the innocent people of our capital city (or any other part of the UK or the world for that matter).
1 comment ( 1173 views )   |  0 trackbacks   |  permalink   |   ( 3 / 2704 )

What are the chances?signal strength
Thursday 4 May, 2006, 09:08 - Spectrum Management
One question which many unlicensed radio users of any kind (e.g. pirate radio operators) often ask themselves is, "What are the chances of me getting caught?" Clearly there is a lot of illegal radio usage which goes on, some of it over very prolonged periods of time, or at regular intervals, so not all transmitters get closed down.

Let's start by examining the tools available to the 'powers that be' which they can use to track down naughty radio transmitters. Most of the devices used would come under the umberella term of direction finding (DF) equipment, which often forms part of an overall spectrum monitoring system which logs details of all radio usage. directionfindingThe DF equipment informs the operator the direction from which a transmission is emanating. If such equipment is located in (or moved to) several locations within the coverage of a transmitter, the resulting direction measurements can be combined using triangulation and the location of the errant transmitter identified. The accuracy of such equipment varies: Fixed units can provide measurements to within +/- 1 degree whereas portable units may only have a resolution of +/- 10 degrees. With a resolution of 1 degree, it is not uncommon that the location of a transmitter can be identified to within about 500 metres, even with fixed receivers on the outskirts of the area of interest. Portable units are of more use close-in where the utmost accuracy is less important as the distances involved are much smaller and thus even +/- 10 degrees allows a transmitter to be located within 100 metres or so.

The last 100 metres become the most difficult. At this point the signal from the transmitter becomes so strong that direction finding equipment fails and the person doing the tracking has to resort to more traditional methods. By far the most useful method to find a transmitter when you are within 100 metres of it is to look! At this distance, the antenna may be easily visible - for pirate FM broadcasters, the 'double stack' aerials roughly strewn on top of tower blocks are a dead giveaway.

So tracking down illegal radio users is relatively straightforward and, for a continuous transmission, can be done in a couple of hours. Most (modern) radio regulators or administrations have the necessary equipment. Some even know how to use it. For sporadic or occasional transmissions, the authorities have to be ready to pounce, which is one of the reasons that so many pirate radio stations are only on-air at weekends when most radio enforcement officers are watching the football, playing golf or enjoying time with their families.

But there is a further question which needs asking... "What would cause the authorities to look for a transmission in the first place?" The simple answer is usually: Interference.
notnoticedIf an unauthorised radio transmitter is not causing anyone a problem, it will largely go unnoticed. If, however, it is causing interference to another radio user, that user will notice and will usually go straight to the authorities. For pirate stations, this situation is ameliorated by the fact that legitimate broadcasters might see a pirate as a problem, not because of interference, but because the station is taking its listeners away and thus has the potential to damage its advertising revenue (or so they would claim). The main exception to this is in certain bands where the authorities tend to use their monitoring equipment regularly, knowing in advance that illegal operation takes place. This might include, for example, the 6.6 MHz 'Echo Charlie' illegal CB band, well known pirate short-wave frequencies, or indeed the FM band itself.

So what are the chances of being caught? Once you get noticed, the chances are relatively high. Keep your head down and don't tread on anyone's toes and you might just get away with it.
add comment ( 988 views )   |  0 trackbacks   |  permalink   |   ( 3 / 3104 )

We're Jammin'signal strength
Monday 24 April, 2006, 15:08 - Radio Randomness
dragondroneThe practice of jamming radio transmissions has been around since radio was first used for military purposes when one side would attempt to inhibit the communications of the other side by transmitting on the same frequency at the same time. Indeed such military jamming is usually termed 'electronic counter-measures' or ECM and a whole industry has developed around it to try and produce radio systems that are resilient to jamming known as 'electronic counter-counter-measures' or ECCM. The picture on the right shows an example of a drone in use today for jamming - in this case one known as a Dragon. The payload of the missile is a high power transmitter which can then be sent to the area of interest and remotely activated. You can see the antenna which unfolds from the front of the device when it is deployed.

However jamming is not strictly a tool of the military. Jamming of broadcast radio stations has been a regular activity for many organisations and - and here's the disappointing bit - continues to take place even today. In the height of the cold war, countries such as Russia used to jam short-wave transmissions from countries such as the UK and USA which carried news or information which the Russians viewed as anti-communist propaganda. To try and compensate, broadcasters such as the BBC World Service, Radio Free Europe and the Voice of America used to transmit their programmes on several short-wave frequencies at the same time (usually 4 or more) in the vain hope that at least one of them would be receiveable in a given area clear of the jammers. The Cuban authorities also jammed Radio Marti, a US Government funded station aimed specifically at the country.

shortwaveAlthough they haven't admitted it, China continue to jam Mandarin language short-wave transmissions from the same kinds of stations even today (take a look at this article for example). Tune to the BBC Chinese service (try 9580, 11945, 11980 or 13970 kHz or look at the most recent programme schedule N.B. this page is in Mandarin) and you're likely to hear either the familiar 'wobble' sound over the top of the transmission or 'distorted voices' - both symptoms of a jammed frequency. It's odd that such activities still take place when, with the advent of the internet, the kind of 'propaganda' that the Chinese are trying to guard against is freely available to anyone with a computer. Of course, not all the population of China have access to a computer but with internet cafe's many do (though the Chinese authorities do their best to stop people getting access to such information). There are also case of the Chinese jamming themselves!

Whilst such overt jamming of international stations by such political regimes is virtually taken for granted, there have been deliberate attempts to block transmissions from other stations by apparently respectable regimes. Read the story of Radio Caroline whereby the British Government decided to jam its transmissions to stop them being heard during election times. The British Government pulled another fast trick in 1990 when it licensed a station in London on 558 kHz, the frequency used at the time by Radio Caroline. The choice of frequency was clearly chosen to stop Radio Caroline from being heard in London (though the plan vaguely back-fired as the London station was forced to temporarily simulcast on 990 kHz as the 558 signal was so badly interfered with by Radio Caroline).

jammingMore recently there has been a story suggesting that the US Government was deliberately jamming radio communications during the recent disaster in New Orleans. Whilst the US Government clearly could have done more for the residents of this flood-stricken town, it belies belief that they would actively try to scupper rescue attempts.

What is clear is that despite significant developments in radio technologies and in international relations, radio jamming transmitters seem to be as active today as they have always been, mucking up military communications and supressing freedom of speech. Let's hope that one day soon, neither of these uses will continue to be necessary.
add comment ( 1129 views )   |  0 trackbacks   |  permalink   |   ( 3 / 2561 )

Radio (No-)Onesignal strength
Tuesday 18 April, 2006, 15:31
twolochsThe number of radio stations in the UK has been on the increase since commercial radio was first licensed since the late 1970's. The latest raft of licences (excluding the community licences recently awarded) includes stations whose potential audience is, to put it mildly, tiny. The coverage of stations such as TwoLochs FM, LochBroom FM and Isles FM - all of which are in a highly unpopulated area of Northern Scotland - probably does not stretch to more than around 10,000 people. There is an unarguable need for these isolated communities to have local services to bring them together and broadcast radio is a good way of doing this, however one has to wonder whether it is a good use of the radio spectrum or not.

In London for example, radio spectrum is at a premium and despite there already being over 21 FM stations in the city, there is still pressure for more. Could the frequencies that have been assigned to these remote stations not be more effectively employed providing new FM services in London where the audience potential is nearly 1,000 times greater? The answer, sadly, is 'NO'. The distance between these remote stations and London is well over 600 km, so even if all the frequencies on the FM band were assigned to stations broadcasting in Northern Scotland, they could still be re-used in London without causing interference to each other.

The question of whether or not it is a good use of spectrum or not remains valid though. As an example, the programme schedule of TwoLochs FM shows that on a week-day, between 09.00 and 17.00, for a total of 8 hours, the station relays programmes from Prime Time Radio - a service which is available in the same coverage area via Sky Television on channel 0132. Now clearly any small scale radio station has to fill its schedule somehow and the availability of cheap 'filler' services such as this is no doubt a real boon for them, but it's not the local community service that the station was licensed to provide. Would it not be better to provide a local 'juke-box' service played out from a computer hard-drive which could be loaded with requests each week - at least that way the service retains a local feel.

As much as local or community radio initiatives such as this are to be applauded and the hard work of the staff and volunteers who run the station should be appreciated, the question of whether or not they represent an effective use of the radio spectrum remains largely open.
2 comments ( 1140 views )   |  0 trackbacks   |  permalink   |   ( 3 / 2573 )

<<First <Back | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | Next> Last>>