Method for searching pilot signals to synchronize a CDMA receiver with an associated transmitter
View Patent ↗A method for synchronizing a CDMA receiver to a transmitter when an adaptive antenna is utilized to receive transmitted data, wherein a receiving antenna system is adapted between a 360° reception angle pattern (i.e., an omni-directional pattern) and a fixed reception angle (i.e., a directional pattern) by permitting the receiver to identify a pilot signal having the largest magnitude. The receiver minimizes interference from other pilot signals by steering antenna pattern nulls toward other transmitters. As a result, the time required for the receiver to acquire a valid pilot signal is significantly reduced.
1. A method for synchronizing a receiver having an adaptive antenna to a transmitter, comprising the steps of:
adapting the antenna to an omni-directional pattern;
checking PN offsets of a transmitted pilot signal;
storing PN offsets of the transmitted pilot signal which produce valid correlations of PN offsets;
reloading each PN offset which produced the valid correlations of the PN offsets;
steering the antenna to a directional pattern; and
monitoring a correlation value of the PN offset which produced a valid correlation of a PN offset while adapting the antenna to the directional pattern to synchronize the receiver to a strongest transmitted pilot signal.
2. The method of claim 1 , wherein said adapting step comprises the step of:
steering an azimuth angle of the antenna to provide specified phase angles with respect to each element in the antenna.
3. The method of claim 2 , wherein said steering an azimuth angle comprises the steps of:
setting a phase angle of perimeter elements of the antenna to zero phase; and
setting the phase angle of a middle element of the antenna to ninety degrees.
4. The method of claim 3 , wherein said step of setting phase angle comprises the steps of:
utilizing a digital to analog convertor to up-load the specified phase angles to a respective phase shifter attached to each antenna element such that the antenna system points toward a specific corresponding angle.
5. The method of claim 1 , wherein said steering step comprises:
adjusting an azimuth angle of the antenna across a predefined range;
monitoring a magnitude of the correlation value at the PN offset which produced the valid correlation of the PN offset; and
determining the azimuth angle which produces a maximum correlation value at the PN offset which produced the valid correlation of the PN offset.
6. The method of claim 5 , wherein the predefined range is from 0 to 360 degrees.
7. The method of claim 5 , further comprising the steps of:
generating a table of PN offsets and azimuth angles which produce maximum correlation values at each PN offset which produced valid correlations of PN offsets;
searching the table to locate a PN offset and an azimuth angle having the maximum correlation value; and
reloading the PN offset and azimuth angle having the maximum correlation value.
8. The method of claim 1 , wherein said checking step comprises the steps of:
comparing a threshold of the PN offsets to a predetermined value.
9. A method for synchronizing a receiver having an adaptive antenna to a transmitter, comprising:
adapting the antenna to an omnidirectional receive pattern;
detecting a PN offset of a pilot signal received by the antenna having an omnidirectional receive pattern;
further adapting the antenna to a directional receive pattern;
steering the directional receive pattern over a range of azimuth angles; and
monitoring a received signal strength of the pilot signal as the directional receive pattern is steered in order to determine an optimal azimuth angle of the directional pattern for receiving the pilot signal at the detected PN offset.
10. The method of claim 9 further comprising:
further adapting the antenna to a directional receive pattern at an azimuth angle that maximizes the received signal strength of the pilot signal.
11. The method of claim 9 wherein detecting a PN offset of a pilot signal comprises:
searching a set of PN offsets at an initial frequency;
if no pilot signal is detected,
stepping through one or more frequency bins; and
scanning the set of PN offsets at each of the one or more frequency bins until a pilot signal is detected.
12. A method for synchronizing a receiver having an adaptive antenna to a transmitter, comprising:
adapting the antenna to an omnidirectional receive pattern;
detecting a plurality of PN offsets of a multipath pilot signal by the antenna having an omnidirectional receive pattern;
for each of the plurality of PN offsets,
further adapting the antenna to a directional receive pattern;
steering the directional receive pattern over a range of azimuth angles; and
monitoring a received signal strength of the pilot signal as the directional receive pattern is steered in order to determine an optimal azimuth angle of the directional pattern for maximizing received signal strength of the pilot signal at that detected PN offset; and
synchronizing the receiver to a selected one of the plurality of PN offsets and further adapting the antenna to a directional receive pattern at an azimuth angle that produces an optimal signal strength of the pilot signal.
13. A system for synchronizing a receiver having an adaptive antenna to a transmitter, comprising at a receiver:
a pilot searcher;
an adaptive antenna comprising a plurality of antenna elements, each of the antenna elements controller by a phase shifter;
the phase shifter adapting the plurality of antenna elements to an omnidirectional receive pattern;
the pilot searcher detecting a PN offset of a pilot signal received by the adaptive antenna having an omnidirectional receive pattern;
the phase shifter further adapting the plurality of antenna elements to a directional receive pattern;
the phase shifter steering the directional receive pattern over a range of azimuth angles; and
the pilot searcher monitoring a received signal strength of the pilot signal as the directional receive pattern is steered in order to determine an optimal azimuth angle of the directional pattern for receiving the pilot signal at the detected PN offset.
14. The system of claim 13 further comprising:
the phase shifter further adapting the plurality of antenna elements to a directional receive pattern at an azimuth angle that maximizes the received signal strength of the pilot signal.
15. The system of claim 13 wherein:
the pilot searcher detects a PN offset of a pilot signal by searching a set of PN offsets at an initial frequency;
if no pilot signal is detected, the pilot searcher steps through one or more frequency bins; and scans the set of PN offsets at each of the one or more frequency bins until a pilot signal is detected.
16. A system for synchronizing a receiver having an adaptive antenna to a transmitter, comprising at a receiver:
a pilot searcher;
an adaptive antenna comprising a plurality of antenna elements, each of the antenna elements controller by a phase shifter;
the phase shifter adapting the plurality of antenna elements to an omnidirectional receive pattern;
the pilot searcher detecting a plurality of PN offsets of a multipath pilot signal by the adaptive antenna having an omnidirectional receive pattern;
for each of the plurality of PN offsets,
the phase shifter further adapting the plurality of antenna elements to a directional receive pattern;
the phase shifter steering the directional receive pattern over a range of azimuth angles; and
the pilot searcher monitoring a received signal strength of the pilot signal as the directional receive pattern is steered in order to determine an optimal azimuth angle of the directional pattern for maximizing received signal strength of the pilot signal at that detected PN offset; and
the receiver synchronizing to a selected one of the plurality of PN offsets and the phase shifter further adapting the antenna to a directional receive pattern at an azimuth angle that produces an optimal signal strength of the pilot signal.