Method for controlling beam formation in a mobile radio communication system and a base station therefor

DETAILED DESCRIPTION OF THE INVENTION FIG.
3 shows a mobile station MS at the boundary between two radio cells C1, C2 of a mobile radio communication system.
The radio cells C1, C2 are supplied by base stations BS1, BS2 which are interconnected via a data transmission network, also known as a core network (not shown in FIG.
3), via which they can exchange data with other base stations of the radio communication system or with a second telecommunication network connected to the data transmission network, or even jointly receive identical data intended for the same mobile station MS.
The two base stations BS1, BS2 use different scrambling codes for downlink transmission to the mobile stations in their relevant cells C1, C2 which enable the mobile station MS, in the case of a downlink signal received by it, to detect whether it originates from base station BS1 or BS2.
This enables the mobile station MS to assess the transmission channels between it and the two base stations BS1, BS2 individually and to create a covariance matrix R1, R2 for each base station individually.
The covariance matrices are averaged over a sufficiently long period so that they are essentially independent of variations in reception conditions caused by short-term interference phenomena.
Eigenvector analysis of the averaged covariance matrices performed by the mobile station MS provides a set of eigenvectors W.
sub.
i,.
sub.
BSj, i=1,2, .
.
.
, M, where M is the number of antennas of the base stations BS1, BS2, j=1,2.
For each covariance matrix the eigenvector with the largest eigenvalue is selected, and the two eigenvectors thereby obtained are transmitted to the base stations BS1, BS2 as weighting vectors.
The transmission of the weighting vectors takes place in intervals ranging from a few seconds to minutes, as the base vectors change at a relatively slow rate depending of the movement speed of the mobile station.
Between two base vector transmissions, the mobile station transmits only code words, here 1 bit long, which indicate to the base stations which of the two weighting vectors they are to use for transmitting to the mobile station