A method to reuse base station antennas for the base station to radio network controller connection
Original Publication Date: 2002-Sep-01
Included in the Prior Art Database: 2003-Jul-23
The connection between base stations and the radio network controller is usually made by landlines or microwave connections. However, landlines have the disadvantage of high leased line cost and restricted availability and microwave connections need sepa- rate antenna systems. The acquisition of new Base Transceiver System (BTS) sites or the set up of new antenna elements are quite impossible mainly due to environmental restrictions. Universal Mobile Tele- communications Systems (UMTS) will suffer on this situation. That is why the following concept is proposed. To interconnect the base station of an UMTS system to the radio network controller, a Time Division Duplex (TDD) system is used which operates in the UMTS TDD spectrum, which is contiguously attached to the UMTS Terrestrial Radio Access (UTRA) FDD cover band. This close allocation allows the reuse of a single antenna element covering the TDD and FDD (Frequency Division Duplex) frequency band. Inter- ference effects between TDD and FDD are reduced by lowering the TDD TX power. This reduces the side band spill over the FDD band. The link connec- tion allows an engineering of the transmission path, which is optimised for this use. This can be, for example the clearance of the first Freznelzone and antenna heights significantly above roof top. Fur- thermore, extra high gain antennas may be used by the RNC site. On that site high gain antennas can be used, due to the reciprocal character of the channel, the antenna suits for uplink and downlink. The high gain reduces the interference to other point to point connections in the downlink. In the uplink, the an- tenna gain on the receive side can be directly sub- tracted from the TDD TX power on the Base Trans- ceiver System (BTS) side, which results in additional reduction of TDD to FDD co-siting interference. Additionally the polarisation of the emitted signals can be set orthogonal to the FDD system. This causes a polarisation gain up to 30dB even when the aerial elements of the different polarisation are within one housing. Sites which act as a hub for TDD connec- tions (e.g. the RNC site) need several high gain an- tennas, but the difficult to erect these antennas is concentrated to one site, which may be situated in an industrial estate, bearing less complexity to get the permissions. The high gain antennas may be made by Yagi structures or parabolic antennas. Dipole fields which are electrically tuned may be used, too.