The launch of Quintel UK, resulting from an agreement signed between QinetiQ (formerly the larger part of DERA) and The Rotch Group (one of the UK’s largest landlords) will lead to a dramatic reduction in the number of radio masts and antennas currently in use throughout the UK and Europe.
At present, radio masts are often shared but have several antennas attached to them from any, or all, of the UK telecommunications licence holders. Now, however, thanks to a technology developed by QinetiQ, each antenna can be capable of receiving and transmitting all five 3G operators radio signals at once, combining services for all of the licence holders to a single roof-top or mast antenna unit.
To complete the roll-out of 3G Mobile Telecommunications, the UK’s licence holders (Hutchison, Orange, BTCellnet, One2One and Vodafone) could all require up to 20,000 sites each (100,000 total). Quintel is currently in negotiations with all these licence holders outlining the new technology that allow them all to offer 3G on the same antenna unit without any loss of performance.
The antenna-sharing concept relies on the use of a radio frequency (RF) unit inserted between the operator transceivers and the antenna. Co-locating a number of different transceivers in close proximity is fraught with technical problems that stem from interactions between the individual transmitters and receivers, and careful design of Quintel ‘s RF unit was required to ensure that performance of the 3G system would not be degraded.
A key consideration is that the insertion of the RF unit between the shared antenna system and the network transceivers must not impact on the signal power transmitted to mobile handsets. In addition, it must not impair the sensitivity of the base-station receivers.
To combat this, the Quintel RF unit contains a ‘combining network’ that allows transmitter signals to be fed to the shared antenna system, and a distribution network that allows handset signals received by the base-station antenna system to be fed to the appropriate operator ‘s receiver.
In the UK, the five licensed network owners have been allocated 12 carrier transmission frequencies for 3G between them. Such a mix can cause interference and that the level of any inter-modulation products coupled into the receiver must be kept low by careful design and selection of appropriate technology.
Another technical challenge stems from the finite amount of RF spectrum allocated to 3G frequencies. The individual frequency bands allocated to five UK network operators are very close together, so conventional transmitter combining methods cannot be used.
The QinetiQ team has developed a combining approach to overcome the problem that is the subject of a patent application.
As well as using its technology for the interface between base-station and mobile handset, the Quintel base-station architecture includes a shared backhaul link that connects the base-station to the 3G core networks, enabling mobile-to-mobile and mobile-to-land line communications as well as management functions.
A microwave point-to-point link is often used for backhaul and the site-sharing approach from Quintel allows the backhaul links from all operators to be combined through a single microwave antenna dish, thereby maintaining a lower visual impact.