Code division multiple access system and method of operation with improved signal acquisition and processing

• US 6,549,565 B1
• Filed: 12/07/1999
• Issued: 04/15/2003
• Est. Priority Date: 12/07/1999
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Buehrer, R. Michael, Liu, Shang-Chieh
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/455,947
• Time in Patent Office: 1,225 Days
• Field of Search: 375/140, 375/142, 375/144, 375/147, 375/148, 375/150, 370/342, 370/479
• US Class Current: 375/142
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/71052 using decorrelation matrix
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2201/70707 Efficiency-related aspects

Abstract

A Code Division Multiple Access system and method of operation provides reduced interference for received signals and improved signal acquisition and processing with reduced computational complexity. The system includes a base station coupled to an antenna array of at least two or more antennas and serving a plurality of users. A receiver in the base station includes a universal inverse cross-correlation matrix coupled to the antenna array, a signal acquisition and a signal processing circuit serving each user. Each signal acquisition circuit comprises a series of delay stages in which the incoming antenna signals in each stage are correlated with a spreading code and combined in a multiplier coupled to the universal inverse cross-correlation matrix which facilitates improved time delay estimation for signal acquisition. Each multiplier combines the correlated signals of the stage with the output of the universal inverse cross-correlation matrix to provide a signal amplitude representative of the signal energy in an antenna path for a given time period, with individual delays separated by a half of chip period. The amplitudes for each of the delay stages are captured in buffers which contain threshold information for selection of the strongest received signal. The signal processing circuit combines the strongest received signal with a channel estimate and the universal inverse matrix output in a multiplier to provide an output signal for demodulation and decoding with improved signal quality due to (a) reduced interference, (b) improved synchronization for signal acquisition and processing, and (c) the universal inverse cross-correlation matrix reducing computational complexity in signal acquisition and signal processing.

Claims

1. A receiver comprising:

antenna means for receiving multiple signals

a universal inverse cross-correlation matrix coupled to the received signals;

means coupled to the universal inverse cross-correlation matrix and to the received signals for determining signal time delay of the received signals and providing a first output; and

means coupled to the universal inverse cross-correlation matrix and to the first output providing an output signal having improved signal quality.

2. The receiver of claim 1 further comprising:

means coupled to the antenna for correlating the received signals in delay periods; and

means coupling delayed correlated received signals and the universal inverse cross-correlation means to provide the first output.

3. The receiver of claim 2 further comprising:

means coupled to the first output for storing delayed correlated received signals by delay period; and

means for selecting a delayed correlated received signal of maximum amplitude as the output signal.

4. The receiver of claim 3 further comprising:

means for demodulating and decoding the selected received signal of maximum amplitude as the output signal.

5. The receiver of claim 2 further comprising:

means coupled to the antennas for delaying the received signals in delay periods related to a chip rate.

6. A code division multiple access system, comprising:

a base station receiver coupled to at least two antennas and receiving signal samples having

a spreading code and a chip rate;

a signal acquisition circuit in the receiver responsive to the received signal samples;

a signal processing circuit coupled to the signal acquisition circuit; and

a universal inverse cross-correlation matrix coupled to both the signal acquisition circuit for improved time delay estimation and to the signal processing circuit in providing an output signal of improved signal quality.

7. The system of claim 6 further comprising:

means coupled to the antennas for delaying the received signal samples in delay periods to determine the received signal sample with maximum signal amplitude.

8. The system of claim 7 wherein the delayed received signal samples are stored in a buffer for selection of the received signal sample with maximum signal amplitude.

9. The system of claim 8 further comprising:

means for combining a delayed received signal sample with an output signal from the inverse cross-correlation matrix as an input to the signal processing circuit.

10. The system of claim 7 further comprising:

means coupled to the combining means for storing the delayed received signal samples.

11. The system of claim 10 further comprising:

means for determining the stored delayed received signal sample with maximum signal amplitude.

12. In a CDMA system including an antenna array;

a signal acquisition circuit and a signal processing circuit coupled to a universal inverse cross-correlation matrix, a method of receiving signals having a spreading code and a chip rate and processing the received signals with improved synchronization for signal acquistion and processing purposes, comprising the steps of;

correlating received signal samples in delay periods and providing a first output for each delay period;

processing received signal samples in the universal inverse cross-correlation matrix and providing a second output;

combining the first and second output signals and providing a third output for each delay period to a storage means,

providing from the storage means the third output which exceeds a threshold and has reduced noise interference due to improved synchronization; and

processing the third output and the second output to obtain and an output signal of improved signal quality.

13. The method of claim 12 wherein the universal inverse cross-correlation matrix is constructed comprising the steps of:

a) setting an index Q to zero where Q is the number of vector outer products which are averaged to create a cross correlation matrix;

b) accumulating incoming received signals over N chips of the spreading code where N is a system design parameter;

c) calculating vector outer products of the received signals;

d) averaging the outer products signals over a sampling window;

e) setting Q to Q+1 and determining if Q is greater than Q+1;

f) forming a matrix inverse of the received signals if Q greater than Q+1 or returning to step b if Q less than Q+1; and

g) constructing a universal inverse cross-correlation matrix for the received signals.

14. The method of claim 12 wherein combining the first and second outputs comprises the steps of

a) shifting a delay period a selected amount for processing the third output;

b) creating a first vector and a second vector for the received signals;

c) multiplying the first and second vectors to obtain an inverse matrix which is the sum of the first and second vectors;

d) repeating steps a, b and c and accumulating results;

e) determining if the result of step d) is greater than the threshold; and

g) returning to step a) if the threshold is not exceeded; and

h) providing the third output as the combined output if the threshold is exceeded.

15. The method of claim 12 wherein processing the output signal comprises the steps of:

a) determining from the received signals a baseband as a vector after time acquisition and correlation;

b) estimating channel distortion of the received signals as a vector;

c) combining the baseband signal vector;

channel estimate vector and the universal inverse cross correlation matrix as the output signal; and

d) providing the output signal to a signal sink.