Downlink beamforming concepts in UTRA FDD

Abstract

Abstract. This article gives a comparison of beamforming concepts. Adaptive beamforming and fixed beam switching in WCDMA-FDD-mode are compared from a system level perspective, ordinary sectorization (three 120 • sectors) serves as a basis for comparison. Pilot channels P-CPICH (Primary Common Pilot Channel) and S-CPICH (Secondary CPICH) are considered as additional interference. For adaptive beamforming channel estimation has to be based on the pilot bit sequence on DPCCH (Dedicated Physical Control Channel) which leads to degradation especially for high mobile velocities and large angular dispersions of the multipath channel.

System capacity from UMTS smart antenna concepts

“…with and without using S-CPICHs. For high data rates (384 kbit/s and 128 kbit/s) the fixed beams outperform the degraded adaptive concept although S-CPICHs are considered, compare [10]. For lower data rates (64 kbit/s) the degraded adaptive concept is superior to the fixed beam with S-CPICH concept.…”

“…A spatial multipath channel is modelled between every user and every site in the network. The channel model used was introduced in [8], [9], and [10]. The main characteristics are summarized in Table I, where the σ represent standard deviations and the µ the average value of the according distributions.…”

“…four) antenna elements with half-wavelength spacing [1]. Thus the array response vector is given by [1], [8], [10],…”

“…Within this paper we assume perfectly known uplink covariance matrices for simplicity. The adaptive beamforming strategy investigated is to maximize the received uplink signal power while maintaining the total interference consisting of intra-, inter-cell interference, and thermal noise [1], [10]. The optimization yields a generalized eigenvalue problem where the optimum beamforming solution w opt k per user k is the generalized eigenvector corresponding to the largest eigenvalue.…”

“…A problem for ABF is to cope with is the degradation of the channel estimation which can no longer be based on the P-CPICH due to user specific antenna patterns, but has to use the pilot bit sequence on the dedicated physical control channel (DPCCH). Since this sequence is not continuously and sent out with less power than the P-CPICH, [14], a degradation of about 3 dB has to be accepted for the worst case, see [10].…”