Calibration architectures for use in UTRA adaptive antenna basestations

Abstract

The ACTS Smart Universal BEAMforining (SUNBEAM) The SUNBEAM ProjectThe SUNBEAM (Smart UNiversal BEAMforming) project has been set up under the EU ACTS research programme and builds on the success of the ACTS TSUNAMI I1 project [l]. The SUNBEAM project intends to develop innovative basestation array processing architectures, enabling technologies (antenna, digital signal processing, analogue R.F. etc) and algorithms for UMTS that are sufficiently flexible to support a range of different second and third generation air interface standards. Members of the consortium are also addressing the development and evaluation of spatial-temporal channel models.amplitude and phase weights applied to the transmitted signals.In the case of both SUNBEAM and TSUNAMI I1 this is implemented in digital baseband signal processing P I .The aim of an adaptive antenna basestation is to provide greater spectral efficiency in cellular networks [3]. These systems operate through adaptation of their radiation pattern in response to the environment in which they operate, allowing received and transmitted signals to be manipulated to provide optimal signal combination according to the requirements of the system. For example, adaptive antennas can be used effectively to determine; wanted signal bearing estimation (DOA [4]), interference suppression (SFIR [ 5 ] ) and, in the case of TDMA systems, the support of more than one user in a single channel (SDMA [6]). II Adaptive Antenna Array Operational RequirementsMost beamformer algorithms rely on the accuracy of the electrical paths to determine optimal signal combination or interference reduction, in particular when supporting full duplex transmission. As a result, a change in the characteristics of one signal path may drastically affect the operation of the system. Time variant distortions occur in the transceiver chain due to small environmental changes such as: temperature, electrical and mechanical variations and even changes in the channel centre frequency and channel gain. These distortions will effectively alter the transfer function of each adaptive antenna path. These errors in the individual paths can alter the position and depths of the nulls required for accurate steering of the adaptive antenna, which severely degrades the An adaptive antenna system operates by filtering within the spatial domain, through modification of the transmitted or received antenna array signals with respect to time, frequency and spatial response. This is accomplished by means of 0-7803-5435-4/99/$10.M) 0 1999 IEEE