Radio Network Congestion
One of the major causes of our radio problems is congestion on the network. When a channel is heavily loaded, it takes longer for the messages to run through the queues and time-outs can occur. Timeouts are one of the causes of the dreaded red resend popup. In many ways, Dial-a-Cab’s radio network has become a victim of the unprecedented success of the Society. Turnover has increased by 34 % over the last 2 years and consequently the message load over the network has increased by at least the same amount. The challenge for Dial-a-Cab is finding a way to add extra capacity to the network at the same rate as we are adding extra work.
   To continue the analogy, the roads on a radio network are of course the channels through which the messages flow. Each channel requires two radio frequencies, one to transmit and one to receive. These are like the opposite sides of a two-way street passing traffic to and from the base station. These frequencies are grouped into bands. Dial-a-Cab’s frequencies fall into the VHF high band group.
   In the United Kingdom, frequencies are allocated and controlled by OFCOM. Dial-a-Cab has recently applied to OFCOM for more frequencies, but that application has been denied. As a result, we have to find ways of using our existing frequencies more effectively.

Building New Roads
Back in 1997/98, Dial-a-Cab applied to the Radio Communications Agency (now known as OFCOM) for two new frequencies. On this occasion, the application was granted and the new frequencies became channel 7 and channel 8. The channels were located at Shooters Hill and Tolworth Tower. Neither channel performed well.
   Last year we decided that channel 8, which held less than a dozen cabs, should be moved to the Barbican. This was a success and channel 8, now co-located with channel 5 at Lauderdale Tower, regularly holds over 100 cabs.
   This year we added channel 9, which is co-located with channel 3 on top of the Park Lane Hilton. Since the vast majority of drivers used mobile phones to communicate with dispatch rather than the voice channel, we realised that this precious frequency was not being used to its full potential. Since we were unable to procure any new frequencies, it was decided to use the voice channel frequency as an additional data channel. At the time of writing, around a quarter of the fleet have been upgraded with the capability to operate on channel 9. As more of the fleet are upgraded, the load on our busiest channels (1 and 3) will be shared by the new channel 9.
   One of the downsides of moving channel 8 from Tolworth Tower to Barbican is that cabs at Heathrow have to use channel 1, which is further away from the airport. We are currently in the process of installing a new aerial site on the top of Brunel University Runnymede, in Englefield Green. This location overlooks Heathrow Airport, which is just 5 miles to the northeast. This new site will re-use the same frequency that we currently use at Shooters Hill. Since the two aerial sites are so far  from each other, we are able

SIGNALS: JOHN AND THERESA GO ON THE ROAD!
And it’s from the horse’s mouth!

to use the same frequency on both without them interfering with one another. We are hopeful that this new site will be operational early in the New Year. This channel will be identified on the terminal as either channel 7 or channel 10.

Improving the existing roads
In 2005, we employed a consultant from the US to analyse the effectiveness of our aerial sites. He recommended and fitted a set of crystal filters to each aerial combiner unit. Last year, we replaced all of the base station radios at our aerial sites with new Tait equipment. The more modern Taits are better able to compensate for the massive amount of interference caused by London’s busy and congested airwaves. Also last year, as we prepared to move our infrastructure to our new building, it became apparent that we were going to struggle to find the additional Motorola communications controllers necessary to enable a smooth transition from Brunswick House to Dial-a-Cab House.
   These old workhorses of the network were becoming very long in the tooth and almost impossible to source. I bought the last one off eBay!
   We were also unable to source any more Gandalf modems, the devices that send the messages from our dispatch system over the phone lines to our aerial sites. Even eBay failed me with the Gandalfs. We had to decide whether to completely replace our entire radio infrastructure at a cost of millions of pounds and massive amounts of disruption to drivers and customers, or find a way of upgrading it with compatible yet modern and therefore readily available equipment.
   The answer came in the form of a product from San Diego California. The system supported the MMP31 protocol running in our cabs. After some teething trouble the system was successfully installed. The old Gandalf modems were replaced by fully digital kilostreams from BT. This new office based infrastructure now gave us the ability to expand the network and duplicate equipment in the new building to ensure a seamless move.

Reducing Traffic
Mayor Ken’s answer to reducing traffic is the Congestion Charge, but don’t worry, Brian has no such ideas! We have taken some steps to try to reduce the number of messages that go over the air. For instance, we have removed many of the unrealistic back-up zones so that more trips will go into bids. That way these trips will not be thrown to drivers who are almost certain to reject them. Receiving a job from bids requires a lot less network resource than transmitting the job numerous times only to have it rejected.

Improving the Software
No matter how much time, effort and money is spent on our radio network, the radio reception will never be perfect. We have to start from that premise. What we can improve is the way that the software that runs on the terminal copes with the reception problems. We have had mixed results with the latest software release. Some drivers say that it is much better, some that it is much worse. This places us in a very difficult position. At the time of writing, I have decided to stop the rollout of the new software until we can determine exactly what it is that makes the release worse for some drivers.
   In order to test more effectively, we have purchased an old TX1 and fitted it with 3 terminals, signal attenuators, a laptop and an in-cab network. We are driving around London in this cab trying different releases of the

Where do we go from here?
With OFCOM refusing to release any more VHF frequencies, we have very few options in terms of expanding the network and thereby improving its performance. I ‘ve made enquiries with other users of VHF High Band frequencies to see if anyone is willing to sell us their frequencies, so far without success. This really just leaves us with the option of running over the public GPRS (cellular) network. GPRS is a very expensive medium to use exclusively. We are currently testing a method whereby the terminal will switch to the GPRS network when it fails to reach our private network. This will also mean that cabs will be able to operate outside of the M25, indeed anywhere in the UK. When the terminal becomes aware that the private network is available again, it will switch back.
   We are also in the process of purchasing another batch of Tait mobile radios to replace some of the older radios currently installed on the fleet. Roman Way will make the decision whether or not your radio will be replaced.

What can drivers do to help?
Having driven around doing testing in the cab, I can identify with how utterly frustrating it is for a driver when the terminal does not perform properly. However, if the response from the terminal does slow down, pressing a button over and over again will actually make the problem worse. Also, when the terminal shows Busy, no matter how many times a button is pressed, the message will not get through. The correct action is to wait until the Busy situation clears and a good channel is settled upon. If your terminal is frequently in a Busy state for more than 2 minutes at a time, you should go to Roman Way and let the guys check out your system.
   Another thing I would ask you to do is consider this; the radio network is not an unlimited resource. Every time you request a queue position, every time you send a text message, every time you reject a job you are burning part of a finite resource. We always notice the message to job ratio drop considerably after 9pm when more jobs become non-rejectable. When this ratio falls, the performance of the radio network improves and visa versa.
   Early in the New Year, we will be starting a Drivers Technical User Group. This group will be made up of two day men, two night men, Dana Thananjeyan from Roman Way and Theresa Whitfield and myself from the IT Department. The purpose of the group will be to solicit constructive feedback as to the performance and functionality of the system from a driver’s point of view.
   We have also set up an email account through which drivers can directly feedback issues to the IT Department. I would like to invite drivers to use the email address for constructive comments and reports about the operation of the in-cab equipment. The email address is driverfeedback@dialacab.co.uk. If you are reporting a specific instance of signal problems, it will help tremendously if you include the time of the incident, your location and the channel you were on. Please always include your call sign on every email.

Conclusion
I have heard it said by drivers that no one is doing anything about signal problems. I remember being told that by a driver at the end of an all-night signal testing shift and it didn’t go down too well. I hope this article will assure you that every effort is being made to improve the situation.
   If the solution were simple, we would have done it by now. If it were just a case of throwing money at the problem, we would have done it by now. Be assured that no stone is being left unturned and no expense is being spared to resolve what we regard as one of the most critical issues facing the Society today.

John Bankes
DaC IT Director