Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
1999-03-31
2001-06-12
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S378000, C342S383000
Reexamination Certificate
active
06246366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cellular mobile communications systems.
2. Description of the Prior Art
In order to improve carrier to interference ratios on the down link in mobile communications networks, it is proposed to transmit on the down link in a beam steered at the base station towards the mobile terminal. In order to do that it is necessary to know in which direction the mobile terminal is located.
SUMMARY OF THE INVENTION
Against this background, in accordance with the invention, there is provided a method of ascribing a direction to the location of a mobile terminal from an antenna array, comprising:
storing a sequence of symbols from each antenna in the array, the stored sequence containing a known training sequence;
space processing the sequence of stored symbols iteratively so as to produce the effect of the array having a major lobe in its polar diagram at a plurality of different successive directions;
calculating a set of crosscorrelation metrics by calculating a crosscorrelation metric for each direction between the combined signals and the known training sequence;
calculating the ratio of the crosscorrelation metric for each direction to the power of the combined signals for that direction to produce a set of direction metrics;
and ascribing a direction to the mobile terminal using the direction metrics to determine which direction is most likely.
Taking the ratio of the correlation metric to the power of the received signals rejects interferers using a different training sequence but which produce a strong signal.
The power of the combined signals may conveniently be determined by calculating the mean of the distance of the combined signals from a set level.
In order to find the training sequence in the received signals, the cross correlation metric is preferably calculated by calculating intermediate cross correlation metrics starting from different positions in the combined signals; and selecting the best intermediate crosscorrelation metric for each direction.
In order a to take into account possibly different results from a plurality of successive frames, a set of direction metrics is preferably calculated for a group of successive frames in the received signals and the metrics for each direction are summed.
Preferably an intermediate decision is made ascribing a direction in accordance with the best of the summed direction metrics for each group and periodic decision is made ascribing a direction which is the average of a the directions ascribed in a predetermined number of successive intermediate decisions.
In order to avoid distortion by wild results, the average is preferably limited to directions ascribed in intermediate decisions, which lie within a predetermined range.
Further in order to avoid wild results, the change between successive directions ascribed in periodic decisions is preferably limited to a predetermined value.
REFERENCES:
patent: 5937014 (1999-08-01), Pelin et al.
patent: 95305756 (1995-08-01), None
patent: 96305227 (1996-07-01), None
patent: 2 640 758 (1988-12-01), None
patent: PCT/FI97/00318 (1997-05-01), None
European Search Report, dated Sep. 11, 1998.
Blum Theodore M.
Goo Jimmy
Lucent Technologies - Inc.
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