A number of WebWayOne Support calls are related to radio service delivery at the protected premises and there are common issues and solutions that I am sure will be interesting to the forum that are not just related to our services.

Happily radio service throughout the UK is very good from all of the providers, but we know there are locations where this is not so. My home is one. Stand in the drive and I can get voice and data to the handset, walk in the house and service is almost non-existent.

There a number of factors that affect service delivery. The most obvious is the local serving cells, where they are located in relation to the handset, how many are available, and indeed what services they support. But then there are the contours of the land, the construction of the building and where the SPT (Supervised Premises Transceiver) has been installed within said building. With regard to the last point, the location of the SPT within the premises is the most common cause of radio signalling issues. Many support calls establish that the SPT is installed next to the Intruder panel, in the basement of the building. I often ask during my training sessions, “would you go into the basement of a building to make an emergency call”. The answer is always “no”, so why should an Intruder detection system be treated any differently?

There is a solution to this issue. Alternative antennas are available and despite the inevitable loss of effectiveness in relation to the length of cable run some can be installed up to 20M from the SPT. These antennas are often referred to as “High Gain” and a common miss-conception is that aerial “boosts” the signal. This is not normally the case. The Antenna does provide some improvement, but its “special” qualities are that it can cope with the longer cable runs that allow it to be placed some distance from the GSM module. It is not unusual for a support call to determine that whilst a site with poor radio reception has been fitted with a “high gain” antenna, the aerial remains bolted to the wall next to the SPT with the cable coiled neatly underneath and there has been no noticeable improvement since fitted.

Another common miss-conception is that the antenna has to be located inside the protected area. This is simply not the case. The NSI advise a common sense approach. If the client has purchased a dual path system all means of providing two communication paths should be investigated. It is obviously preferable to install the aerial in the protected area but if service remains inadequate then an external mounting is allowed with alternate means of protection deployed by making the aerial inaccessible.

What if someone attacks the aerial when externally mounted? Monitored systems should be checking the radio interface every 10 seconds with a reporting time of the interface failure relevant to the Grading of the Alarm Transmission System (ATS). This will include signal strength checks and whether the on board radio module is operating and can register to the base station. Therefore an attack on the aerial or an attempt to locally jam the radio path will be detected rapidly.

Where the SPT has a serial interface to the control panel the SPT can be located away from the panel. For example, an RS485 serial connection to a panel will allow an active cable run of many meters. Therefore alarm systems located in a basement can remain in place whilst the SPT can be moved to a position closer to an external wall. Obviously this will require a cable to be installed, but there is a legitimate case for additional charges to install a working system.

Signal strength Indications and Site Surveys are commonly relied upon as a good representation of Service Availability. However this is not entirely correct. We are often asked what the minimum signal strength we would recommend before installing alternate antennas etc (WebWayOne devices indicate signal from 0 – A, (where A = 10, the maximum strength)). There is no clear answer; one has to combine the signal strength indication with circuit availability before you can come to an informed decision.

The Signal Strength and network registration indication is picked up from the base stations located by the SPTs gsm module. However this does not mean that data can be transmitted any further than the base station or that the module has successfully registered onto the GSM network. It is only the transmission of live data to the receiving end and a successful acknowledgement that the data has been received that can provide a true indication of circuit availability. A good example of this is cell overloading, which is indicated to your handset by three sharp tones. You will have good signal and your mobile is registered to the cell, however the cell is congested and unable to complete the call. This demonstrates that simply checking local signal and registration is not a guarantee that communication can be established.

The more frequently you monitor the radio interface and send data end to end (poll) the more accurate your statistical analysis of circuit availability becomes. At WebWayOne we monitor the availability of all of our circuits constantly, and poll both the interface and the circuit (end to end) very frequently. Our statistics show that both the fixed IP paths and GPRS paths do indeed provide very stable communication platforms with average availability figures of 99.8%. Where GPRS is concerned, these statistics can be obtained on systems that average a signal strength of 2 (on a scale of 1 – 10 with 10 the being the “best”), whilst we have some locations that have excellent signal (higher than 5) that have a circuit availability of below 95% (which equates to just over 18 days of circuit downtime in a year!).

Site Surveys have a place, but they simply provide the surveyor with a “snapshot” of the signal at the moment he carries out the test. Engineers often mention that a survey was carried out and the location of the SPT provided, but come the actual day of commissioning the system there is no mobile service available! It is within the last sentence that one word stands out as the source of the confusion; “mobile”. As users we are used to walking and driving about with our mobiles. We occasionally use them and for the majority of the time we can hold a full conversation without interruption of service. Driving about we notice service disruptions more, and we tend to get to know where the “black spots” are. However our SPT is screwed to the wall, it is not mobile and it wants to communicate all day long with the local base stations and consistently send data (polls) to the receivers. Refer back to my scenario at home. Occasionally my phone will suddenly gain service whilst indoors and I receive a call or a text message. Indeed I have been able to hold a full conversation via my mobile whilst in my kitchen, but more than often the call will fail. Now if I were a Surveyor taking a reading at that moment, I may decide that I have good signal and the location for the SPT should be the kitchen? Some locations are not as bad as my home, but the problem is the same although not as acute. The mobile reception is (as we discussed back at the beginning) influenced by many factors, even the weather and the seasons and not to mention the times when the network providers take down their service (usually in the early hours of the morning when we are tucked up in bed and not using our personal mobiles). But remember, the SPT should be trying to communicate, whatever the time of day.

The differences between voice and data services invariably have engineers confused. GSM (Global Systems for Mobile Communications) is the global term for radio services. Running over the GSM network are voice and data services. WebWayOne SPTs utilise the GPRS (General Packet Radio Service) data service for all communications, this is effectively an IP based service, the voice network is not utilised at all. Therefore, the fact that an engineer is making a voice call from a premises and he has adequate signal does not mean that the GPRS data service is present or can be transmitted reliably.

Human beings have the ability to listen and make some sense of broken voice transmissions. However data services have limited powers of deduction. A device sending data over a network requires a response to every data transmission it sends. If it does not receive a response it will continue to send the same data for a number of re-tries. There will be a defined number of these before the device ceases to resend the information, known as its “time out”. Therefore electronic communications equipment requires a much more stable network connection than we humans need in order to exchange information.

Roaming, or World SIMs will clear up the vast majority of issues by providing access to multiple provider networks. However the considerations I have provided here remain the same and indeed there may be some sites where there no coverage at all can be gained.

WebWayOne Command Centre software is utilised by our 1st Line Support. This provides accurate statistics with regards to network service availability, signal strength and registration. Where IP / GPRS is being utilised the radio status indicators from the site are updated every 30 seconds. Therefore the historical data and statistics that are available to Support are very accurate. Command Centre is available to Installers and End Users to.

In conclusion, radio, and GPRS in particular is a solid medium for the transmission of alarm information when associated with a secondary path via a fixed line. GPRS with PSTN back-up has a place but utilising the PSTN network brings in a number of limitations where polling and shorter reporting times are required. IP/GPRS provides enormous capabilities. Frequent polling, identifying failures within the tightest reporting times, providing accurate circuit availability figures and fault diagnostic capabilities that our industry has never had before.