Case Study Wiltshire Air Support and the use of their radio network Peter Paul Cert Nat Sci (open) MIEE June 2004 Solutions in Radiocommunications
An Wiltshire Appraisal Air Support of Propagation and the Modelling use of their Methods radio network Page Page 2 of 52 of 8 Wiltshire Air Support Unit The Wiltshire Air Support Unit is based at Police HQ in Devizes. From this location they can reach any part of Wiltshire within 15 minutes of take-off. They work with both the Police and Ambulance Services and operate an Explorer 902 helicopter. The helicopter, from call to lift-off, typically takes 2-3 minutes; this time is for the crew to reach the aircraft and complete the pre take-off checks. 1. Police VHF 2. Police UHF 3. Police air to ground VHF 4. Ambulance VHF Like most other emergency services, prior to the Airwave network the frequency allocation of these channels has been done on a service by service basis. However, there are limitations upon which and when the available channels can be used by the aircrew. Mr Mike Evans, Unit Executive Officer, explained, When the helicopter is on the ground all available channels can be used by the crew. Once airborne and below 500ft, only the VHF channels can be used and above 500ft only the air to ground channel can be used. He further explained that whilst the crew can monitor the selected channels, the level of breakthrough (interference) from other users and Police Forces, made the service quality very poor. When airborne, breakthrough on the UHF channels from Forces in South Wales occurs and often French fishermen could be heard on the VHF channels. This level of background interference places a high workload upon the crew when attempting to pick relevant information that is connected with their current operation from the background noise. For the Police, typical radio usage for a tasking would be as follows: WAS current Helicopter, Explorer 902 The helicopter can and does operate outside of Wiltshire; some tasks have taken them as far away as Devon and London. When operating outside the county, the crew have the ability to communicate with the local Police and Ambulance Services. It has a crew of three - pilot, paramedic and police observer. Each member of the crew has independent access and operation of the aircraft radio system. Naturally the aircraft is fitted with radios operating within the aeronautical band, however these will not be considered in any detail in this paper. The focus will be upon the Police and Ambulance current command and control radio systems on board the aircraft and how the two services operate them. This will then be compared to how they expect to operate the aircraft when, in June 2004, the Force move across onto the Airwave TETRA based network. The current system The current radio system interfaces with both the Police and Ambulance networks - up to four channels (in additional to two air traffic channels) can be used/ monitored by each of the crew. A standard selection is likely to be: Tasking issued by command and control (C&C) to the Air Support Unit. Aircrew complete helicopter start-up checks. Once done, selection of the relevant radio channels is carried out. Place radio call to C&C for an update on the incident. Lift off, put UHF channel into monitor-only mode. Once above 500ft, put all non A2G VHF channels into monitor mode. Transit to scene of incident (dependent upon the nature of the incident will dictate the amount of radio traffic to/from the aircraft). Officers on the ground instructed to switch to the Force s A2G channel for direct communication with the helicopter. Helicopter then relays relevant information to officers on the ground, again the level of radio usage is dependent upon the incident itself - ranging from a running commentary for a high speed pursuit to a single call informing C&C that the aircraft is at the location. However, the aircrew prefer to keep the airtime used to a minimum. In the case of a casualty pickup, paramedics would normally stabilise the injured person prior to transportation to hospital. Radio traffic between the paramedics and their control or the hospital would be to assist in the stabilisation process or arrange where to land at the hospital.
An Wiltshire Appraisal Air Support of Propagation and the Modelling use of their Methods radio network Page Page 3 of 85 3 of 8 Upon completion of the task, radio call back to the C&C informing that the helicopter is available. Transit back to Devizes. Land and inform C&C, shut down the helicopter. Await the next call. With the current network configuration, the Air Support Unit has the ability to either maintain communications with its own C&C or with the relevant Force s C&C, dependent upon where they are operating at the time, but not both. Added to this, the allocation of frequencies that can be used by the Wiltshire Air Support Unit means that because of the breakthrough from other users the quality of service is, at best, poor. The current network also supports a microwave radio system. This is used to transmit, from the helicopter, live pictures of what the airborne camera is seeing. This gives Forces at the C&C the same view as the Police observer s terminal. The Airwave network On 9 th June 2004, Wiltshire Police move across onto the TETRA based Airwave network. In order to conform to the CAA regulations regarding airborne TETRA terminals, the Support Unit will initially have two cradles that house a hand portable terminal. February 2005 will see the fitment of special airborne TETRA terminals to the helicopter. The Air Support Unit views the advantages of the Airwave network over its current network as: Interference from other users eliminated or at least greatly reduced. Being a digital system, improved voice quality. No need for the aircrew to be switching channels during the course of a mission. The additional functionality of telephony available. The ability to move outside the county without losing radio comms with their own C&C. However all of these points rely upon: The frequency planning of the Airwave network has been completed with the potential interference problems associated with airborne terminals in mind. The air-to-ground Airwave sites have sufficient RF carriers to support telephony. The airborne terminals have been authorised on serving sites outside the county. Police Observer s station. The Police observer operates the camera, giving him and the C&C pictures of the incident. The camera can be moved through 360º in the x axis and 90º in the y. An onboard video recorder tapes all that the camera sees ; this recording is also repeated back at Air Support operations. It is planned that this system is to be upgraded to allow full duplex operation. This will involve relocating the ground station to improve coverage and a new antenna fitment on the helicopter. The predicted coverage from the new ground location shows that countywide reception will be available and the new antenna on the helicopter should reduce the fading effects currently experienced when the helicopter banks. As regards frequency planning, spectrum within the TETRA emergency services band is not limitless. The number of RF carriers allocated specifically for A2G operation is only 10. Given the range that emissions from an airborne terminal could travel, it is highly likely that RF carriers allotted for terrestrial use will be required to fulfil part of the nationwide A2G requirement; this is currently believed to be in the order of 10 additional RF carriers. As with all frequency allocation exercises there will be a need to balance between efficient use of the spectrum and permitted interference. With the helicopter having telephony and the higher traffic demand associated with this function over group calls, some A2G sites may well require additional RF carriers, in turn placing greater pressure upon the frequency planner to achieve the requirements of the network. However, as this Police Force and, it is to be expected, many others transmit live video it is unlikely a data slot would be required on the A2G channels. The requirement for data is likely to be supported via the planned duplex microwave system. If this is repeated across the country, extra voice capacity will be gained. If the Wiltshire Air Support Unit do not have their terminal authorised for use on the sites serving adjacent counties, the advantage of roaming across county borders will be lost. Worse still, they would not be able to talk to the local
Wiltshire Air Support and the use of their radio network Page 4 of 5 An Appraisal of Propagation Modelling Methods Page of 8 An Appraisal of Propagation Modelling Methods Page 4 of 8 services during such instances! There is an additional problem, this being the Wiltshire Ambulance Service has yet to decide what its next generation of radio network is to be. If they elect to use Airwave as well, fine! Should they not however, then this will mean that the Air Support Unit will have to install extra radio equipment in the aircraft. In the meantime, the aircrew will have to continue using the existing Ambulance radio network. The Air Support Unit does foresee another disadvantage with the move to the Airwave network. Currently, the crew have the ability to select and monitor whatever channels they like they are able to monitor incidents that whilst not directly related to their current task, may actually warn and prepare them for their next. Wiltshire Air Support regards this ability as a great help and enables them on many occasions to be pro-active. With the TETRA system if the other incident is happening on a different talk group to the helicopter, then they will not be aware of it - potentially costing valuable time! This problem could be overcome, but at the cost of, a higher workload upon the aircrew which is one of the main current problems. A solution is, quite simply, to enable the TETRA radios on board the helicopter to access every talk group. Summary The Air Support Unit provides a valuable service to the Police, Ambulance Services and the people of Wiltshire. The move from its current radio network to the Airwave network brings solutions to many of its existing radio problems. However, it is expected to bring some unique problems of its own, some already identified, some not. A close partnership between the unit and Airwave will be required to resolve them as they occur. ATDI Ltd would like to thank Mike Evans and the rest of the team for the valuable time they afforded us and wish them every success in their future operations. The air support unit handles on average 5 incidents per day, 24 hours a day, 365 days a year.
ATDI Ltd Kingsland Court - Three Bridges Road Crawley - West Sussex - RH10 1HL - UK Tel. +44 (0)1293 522052 / Fax. +44 (0)1293 522521 World wide web page: http://www.atdi.co.uk E-mail: enquiries@atdi.co.uk Advanced Topographic Development and Images Limited Company Registration Number 3198786 Solutions in Radiocommunications