A method to interconnect UTRA Basestations by using TDD systems as terrestrial link replacement
Original Publication Date: 2002-Sep-01
Included in the Prior Art Database: 2003-Jul-23
The deployment of Universal Mobile Telecommuni- cations System (UMTS) node B based on UMTS Terrestrial Radio Access (UTRA) technology re- quires the connection of node B to the RNC that serves a multitude of node B (figure 1). The physical connection is made by landlines or microwave con- nections. On top of this physical layer, a protocol is used to transmit user and control data (ATM or IP).
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A method to interconnect UTRABasestations by using TDD systemsas terrestrial link replacement
Idee: Michael Färber, München
The deployment of Universal Mobile Telecommuni-cations System (UMTS) node B based on UMTSTerrestrial Radio Access (UTRA) technology re-quires the connection of node B to the RNC thatserves a multitude of node B (figure 1). The physicalconnection is made by landlines or microwave con-nections. On top of this physical layer, a protocol isused to transmit user and control data (ATM or IP).
Fig. 1: Block diagram of an UTRAN
A problem of the UTRA deployment is, that a highnode B density (referred to densities known of sys-tems today, e.g. GSM) is needed for a high qualitycoverage. Typical cell radius for UMTS range be-tween 200m and 5km, where for a GSM systemranges up to 35km are possible. Therefore the de-ployment of UTRA systems requires more node Bsites, which have to be connected to a RNC. How-ever, the physical layer properties, especially theneeded bandwidth is usually not provided by twistedpair telephone lines. The installation of new lines orthe use of microwave equipment is cost intensive andrequires a lot of administrative work. It requiresmicrowave spectrum, permissions for the set up ofantennas or for new wiring in third parties real es-tates.
The operator can use transmission capacities he isalready licensed for in order to circumvent the costand complexity of such solutions. UTRA containstwo parts of spectrum, suitable for the multiple ac-cess schemes Frequency Division Duplex (FDD) andTime division Duplex (TDD). The limited spectrumavailable for TDD (usually TDD spectrum is lessthan FDD spectrum), the TDD terminal availabilityand the fact, that in multi mode FDD/TDD terminalequipment the TX peak power capability is ruled bythe FDD needs are reasons for the intention to useTDD in later deployment phases.
The above mentioned problems can be solved byusing the licensed UTRA spectrum for connectingnode B to RNC. To establish this connection a TDD
system at the location of the FDD BTS is used as aremote station (figure 2). This allows a capacityhandling via the remote TDD Base Transceiver Sys-tem (BTS) higher than for a usual TDD MS. The twoTDD elements can be connected by using directionalantennas. The TX power is very low also for con-necting far distant TDD elements. Interference toother TDD connections is limited by the use of highgain antennas. Further the use of directional antennasand the reduced power limits the impact on adjacentFDD spectrum. In case of line of sight connections,preferably without obstructing the first Freznelzone,multipath effects are significantly re...