Method for searching pilot signals to synchronize a CDMA receiver with an associated transmitter

• US 20080225991A1
• Filed: 06/14/2007
• Published: 09/18/2008
• Est. Priority Date: 02/23/2000
• Status: Active Grant

• Current Assignee: IPR Licensing Incorporated (InterDigital, Inc.)
• Original Assignee: IPR Licensing Incorporated (InterDigital, Inc.)
• Inventors: Rouphael, Antoine J., Hoffmann, John E., Proctor, James A., Nelson, George R.
• Granted Patent: US 7,916,772 B2
• Time in Patent Office: Days
• US Class Current: 375/340
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70775 Multi-dwell schemes, i.e. multiple accumulation times
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 2027/0087 Out-of-band signals, (e.g. pilots)
• CPC Class Codes: H04L 27/2273 associated with quadrature demodulation, e.g. Costas loop
• CPC Class Codes: H04W 56/001 Synchronization between nodes

Abstract

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.

Claims

1. A method of searching for, and optimizing reception of, a pilot signal in a CDMA wireless communication system, comprising the steps of:

setting an antenna to a receiving pattern;

loading a frequency offset stored in an offset memory;

setting a pseudorandom number (PN) sequence offset to zero;

detecting a signal from the antenna and comparing a magnitude of the signal to a threshold;

changing the PN offset by a predetermined offset increment if the magnitude is less than the threshold;

determining if a PN epoch is beginning and, if so, determining if a significant pilot signal is present for the frequency offset, PN offset, and antenna receiving pattern; and

ending the method if a pilot signal of sufficient magnitude is detected.

2. The method of claim 1, further comprising the step of initially setting the antenna receiving pattern to an omnidirectional receiving pattern.

3. The method of claim 1, further comprising the steps of:

if the signal magnitude is greater than the threshold, increasing the threshold to a new threshold;

changing the PN offset by a predetermined offset increment if the magnitude is less than the new threshold.

4. The method of claim 2, further comprising the steps of:

changing the receiving pattern of the antenna from omnidirectional to directional if the magnitude exceeds a predetermined maximum threshold;

sweeping a reception angle of the antenna in predetermined increments;

determining an optimal reception angle for the antenna and storing the optimal reception angle;

changing the PN offset by the predetermined offset increment; and

determining if a PN epoch is beginning and, if so, determining if a significant pilot signal is present for the frequency offset, PN offset, and directional antenna receiving pattern.

5. The method of claim 1, further comprising the steps of:

determining if the frequency offset is greater in magnitude than a predetermined offset maximum if a significant pilot signal is not present and

ending the method if the frequency offset is greater than the offset maximum.

6. The method of claim 5, further comprising the steps of:

increasing the frequency offset by a predetermined offset increment if the frequency offset is not greater in magnitude than the predetermined offset maximum; and

performing the step of setting the PN sequence offset to zero.

7. The method of claim 1 further comprising the steps of

if the PN epoch is not beginning, setting the threshold to an initial value;

and

performing the step of detecting and comparing to the threshold.

8. The method of claim 6, further comprising the steps of:

storing the increased frequency offset in the offset memory, to be used as an initial frequency offset.

9. An apparatus for searching for, and optimizing reception of, a pilot signal in a CDMA wireless communication system, comprising:

a steerable antenna comprising a plurality of antenna elements;

phase shifters coupled to respective antenna elements for steering the antenna and setting the antenna to an omnidirectional pattern;

a processing circuit comprising a pseudorandom noise (PN) sequence generator and configured to receive and process a signal from the antenna;

a threshold circuit configured to set and adjust a threshold and determine if the processed signal exceeds the threshold, and

a searching circuit configured to search for, and optimize detection of, the pilot signal in the processed signal.

10. The apparatus of claim 9, wherein the searching circuit further comprises:

a first memory storing a phase angle;

a digital-to-analog converter receiving the phase angle and supplying antenna direction setting information to the phase shifters;

a second memory for storing a frequency offset;

frequency incrementing electronics configured for incrementing the frequency offset by a predetermined offset increment; and

PN offset electronics configured for applying a PN offset to the PN sequence from the PN sequence generator;

wherein the apparatus detects and optimizes reception of the pilot signal by incrementing the frequency offset, incrementing the PN offset, comparing the processed signal to multiple thresholds, and steering the antenna.