Rake receiver for spread spectrum signal demodulation

• US 20020176488A1
• Filed: 05/08/2002
• Published: 11/28/2002
• Est. Priority Date: 08/23/1996
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: Data Fusion Corp.
• Inventors: Thomas, John K., Vis, Marvin L., Kober, Wolfgang
• Granted Patent: US 6,788,734 B2
• Time in Patent Office: Days
• US Class Current: 375/147
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H04B 1/1081 Reduction of multipath noise by equalising H04B7/005
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 7/0845 per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch rake receivers as such H04B1/7115
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity

Abstract

The architecture of the present invention is premised upon an algorithm involving integration of oblique correlators and RAKE filtering to null interference from other spread spectrum signals. The oblique correlator is, of course, based on the non-orthogonal projections that are optimum for nulling structured signals such as spread spectrum signals. RAKE filtering is used to rapidly steer the beam of the multi-antenna system and to mitigate the effects of multipath.

Claims

1. A system for receiving a structured signal, comprising:

an antenna adapted to receive a signal, the signal having a first signal segment attributable to a first source and a second signal segment attributable to a source other than the first source; and

,

oblique projecting means for determining the first signal segment of the signal, the first signal segment of the signal defining a first space, the oblique projecting means being in communication with the antenna and determining the first signal segment of the signal by obliquely projecting a signal space defined by the signal onto the first space.

2. The system of claim 1 wherein the signal space is obliquely projected onto the first space along a second space corresponding to the second signal segment of the signal.

3. The system of claim 1 wherein the system includes:

a) a plurality of antennas, each of which receives a portion of the signal, and

b) a plurality of oblique projecting means corresponding with a plurality of antennas and being in communication therewith, each of the plurality of oblique projecting means being adapted to determine by oblique projection the first signal segment of the respective signal portion received by the corresponding antenna.

4. The system of claim 3 including a plurality of RAKE processors corresponding with the plurality of oblique projecting means, wherein each of the plurality of oblique projecting means produces a respective oblique projecting means output which is received as a RAKE processor input by its corresponding RAKE processor, the respective output of each of the plurality of oblique projecting means being delayed relative to one another, each of the plurality of RAKE processors being adapted to align and scale their respective inputs to produce a compensated output.

5. The system of claim 4 wherein the compensated outputs of each of the plurality of RAKE processors is delivered to a summing correlator.

6. The system of claim 1 including a RAKE processor having a RAKE input, wherein the oblique projecting means produces an oblique projecting means output which is coupled to the RAKE processor input.

7. The system of claim 1, wherein the first signal segment comprises a plurality of multipath signal segments and the oblique projecting means outputs a correlation function having a plurality of peaks corresponding to the plurality of multipath signal segments, and further comprising:

threshold detecting means, in communication with the oblique projecting means, for generating timing information defining a temporal relationship among the plurality of peaks.

8. The system of claim 7, wherein the system comprises a plurality of antennas in communication with a corresponding threshold detecting means and further comprising:

timing reconciliation means for determining a reference time based on timing information received from each of the threshold detecting means.

9. The system of claim 8, further comprising:

a RAKE processing means, in communication with the oblique projecting means and the timing reconciliation means, for aligning the plurality of multipath signal segments in at least one of time and phase as a function of at least one of the magnitudes of the plurality of multipath signal segments, the reference time, and the phase, the phased RAKE means outputting an aligned first signal.

10. The system of claim 9, further comprising:

a plurality of RAKE processing means, each RAKE processing means being in communication with a corresponding one of the plurality of antennas and producing a corresponding aligned first signal; and

a demodulating means, in communication with the plurality of RAKE processing means, for demodulating at least a portion of each corresponding aligned first signal, the at least a portion of each corresponding aligned first signal defining a respective aligned first space, the demodulating means determining the respective corresponding aligned first signals by obliquely projecting a respective signal space defined by a corresponding aligned signal onto the respective aligned first space.

11. A system for receiving a spread spectrum signal, comprising:

an antenna adapted to receive a spread spectrum signal and adapted to generate an output signal, the output signal comprising;

(i) a first signal attributable to a first source,

(ii) a second signal portion attributable to a second source other than the first source,

(iii) a noise portion, the noise portion having a magnitude; and

,

oblique projecting means for determining the first signal of the output signal, the oblique projecting means being in communication with the antenna and determining the first signal of the output signal by the following equation;

(y^TH(H^T(I−

S(S^TS)<sup>−

1</sup>S^T)H)<sup>−

1</sup>H^T(I−

S(S^TS)<sup>−

1</sup>S^T)y)/σ

²

wherein y corresponds to the output signal, H is related to an interference code matrix of the first source, S is related to an interference code matrix of the second source, ^T denotes the transpose operation, I denotes the identity matrix, and σ

² corresponds to the variance of the magnitude of the noise portion.

12. The system of claim 11 wherein the antenna includes a receiver and at least a portion of the noise is generated by the receiver.

13. The system of claim 11 including a plurality of oblique projecting means corresponding to a plurality of antennas and being in communication therewith, each of the plurality of oblique projecting means being adapted to determine a respective first signal of a corresponding portion of the spread spectrum signal received by each of the plurality of antennas and determine the respective first signal of the spread spectrum signal by the equation:

(y^TH(H^T(I−

S(S^TS)<sup>−

1</sup>S^T)H)<sup>−

1</sup>H^T(I−

S(S^TS)<sup>−

1</sup>S^T)y)/σ

².

14. The system of claim 13 including a plurality of RAKE processors corresponding with the plurality of oblique projecting means, wherein each of the plurality of oblique projecting means produces an oblique projecting means output which is received as a RAKE processor input by its corresponding RAKE processor, the output of each of the plurality of oblique projecting means being delayed relative to one another, each of the plurality of RAKE processors being adapted to align and scale their respective inputs to produce a compensated output.

15. The system of claim 14 wherein the compensated outputs of each of the plurality of RAKE processors are delivered to a second oblique projecting means for determining a refined first signal of each of the compensated outputs by the equation (y^TH(H^T(I−

S(S^TS)<sup>−

1</sup>S^T)H)<sup>−

1</sup>H^T(I−

S(S^TS)<sup>−

1</sup>S^T)y)/σ

².

16. The system of claim 11, wherein the first signal comprises a plurality of multipath signal segments and the oblique projecting means outputs a correlation function having a plurality of peaks corresponding to the plurality of multipath signal segments, and further comprising:

threshold detecting means, in communication with the oblique projecting means, for generating timing information defining a temporal relationship among the plurality of peaks.

17. The system of claim 16, wherein the system comprises a plurality of antennas in communication with a corresponding threshold detecting means and further comprising:

timing reconciliation means for determining a reference time based on timing information received from each of the threshold detecting means.

18. The system of claim 17, further comprising:

a RAKE processing means, in communication with the oblique projecting means and the timing reconciliation means, for aligning the plurality of multipath signal segments in at least one of time of phase based on the magnitudes of the plurality of multipath signal segments and the reference time to form an aligned first signal.

20. The method of claim 19 wherein, in the obliquely projecting step, the signal space is obliquely projected onto the first space a second space corresponding to the second signal.

21. The method of claim 19 wherein the obliquely projecting step determines the magnitude of the first signal.

22. The method of claim 19, wherein the first signal comprises a plurality of multipath signal segments and further comprising:

aligning at least one of a received time and phase of the multipath signal segments to produce an aligned first signal.

23. The method of claim 22, further comprising:

scaling the multipath signal segments.

24. The method of claim 19, wherein the first signal comprises a plurality of multipath signal segments, each of the plurality of multipath signal segments being received at different times, and further comprising:

assigning to a portion of each of the plurality of multipath signal segments a respective time of receipt.

25. The method of claim 24, further comprising:

determining a reference time of receipt based on the respective times of receipt.

26. The method of claim 25, further comprising:

first summing the plurality of multipath signal segments without regard to the differing times of receipt to form a summated peak magnitude;

second aligning the plurality of multipath signal segments relative to the reference time of receipt to form a plurality of aligned signals;

scaling each of the multipath signal segments to form a plurality of scaled signals; and

third summing at least one of the aligned signals and the scaled signals.

27. The method of claim 21, further comprising:

determining an actual time of transmission of the first signal;

determining an actual received time for the first signal; and

repeating step (b) using the actual time of transmission and the actual received time.

19. A method for demodulating a structured signal, the structured signal comprising a first signal attributable to a first source and a second signal attributable to a second source other than the first source, the first signal corresponding to a first vector, the method comprising the steps of:

(a) receiving the structured signal; and

,

(b) obliquely projecting a signal space corresponding to the signal onto a first space defined by the first signal.