Method and apparatus for signal detection
A method for detecting signals using an adaptive transducer arrangement, the arrangement including a transducer array having a plurality of transducers, a beamformer, and an energy detector, the method comprising: determining weights to be applied by the beamformer to signals emitted from each transducer in order to maximize a performance metric; applying the determined weights to the signals emitted from each transducer; measuring the energy received at the energy detector; comparing the measured energy with a predetermined value and based on said comparison determining whether or not one or more signals are present.
1. A method comprising:
receiving, with a beamformer, signals emitted from each of a plurality of transducers in an adaptive transducer arrangement;
determining weights to be applied by the beamformer to signals emitted from each transducer in order to maximise a performance metric based on a total signals plus noise power;
applying, with the beamformer, the determined weights to the signals emitted from each transducer and summing the weighted signals with a summing circuit;
measuring energy received at an energy detector from the summing circuit; and
comparing the measured energy with a predetermined value, which is an energy detection threshold, and based on said comparison determining whether or not one or more signals are present.
2. A method according to claim 1 , wherein said step of determining weights includes a step of determining an optimum weight vector.
3. A method according to claim 2 , wherein the step of determining the optimum weight vector, includes a step of defining the performance metric.
4. A method according to claim 3 , wherein the performance metric is defined at an input to the energy detector.
5. A method according to claim 2 , wherein the performance metric is a ratio of total signals plus noise power to noise power.
6. A method according to claim 5 , wherein the performance metric may be expressed as
λ
=
w
H
R
x
w
w
H
R
n
w
,
wherein λ is the performance metric, w is a weight vector comprising the weights, R x is a received signal matrix, and R n is a noise covariance matrix.
7. A method according to claim 6 , wherein the performance metric is maximised with respect to w.
8. A method according to claim 7 , wherein the optimum weight vector is equal to a generalized eigenvector associated with a maximum generalized eigenvalue of a matrix pencil (R x , R n ).
9. A method according to claim 2 , wherein the performance metric is a ratio of the total signals plus noise power to a norm of the optimum weight vector.
10. A method according to claim 9 , wherein the performance metric may be expressed as
λ
=
w
H
R
x
w
w
H
w
,
wherein λ is the performance metric, w is a weight vector comprising the weights, and R x is a received signal covariance matrix.
11. A method according to claim 10 , where in the performance metric is maximised with respect to w.
12. A method according to claim 11 , wherein the optimum weight vector is equal to an eigenvector associated with a maximum eigenvalue of R x .
13. A method according to claim 1 , wherein said predetermined value is proportional to noise power at an output of the beamformer.
14. A method according to claim 13 , wherein the predetermined value is given by kw H R n w, wherein w is a weight vector comprising the weights, k is a scalar value used to adjust a false alarm rate, and R n is a noise covariance matrix.
15. A method according to claim 13 , wherein if the energy measured at the energy detector is less than or equal to the predetermined value, it is determined that only noise is present.
16. A method according to claim 13 , wherein if the energy measured at the energy detector is greater than the predetermined value, it is determined that at least one signal is present.
17. A method according to claim 1 , wherein one of said transducers is designated as a reference transducer.
18. A method according to claim 17 , wherein the performance metric is a total power of a linear combination of the signals received by said reference transducer.
19. A method according to claim 1 , wherein the adaptive transducer arrangement is an adaptive antenna arrangement and the plurality of transducers is a plurality of antennas.
20. A signal detection apparatus, comprising:
a transducer array having plurality of transducers;
a beamformer adapted to apply weights to signals emitted from each transducer;
an energy detector adapted to measure a combined energy of the weighted signals received from the beamformer; and
a processor;
wherein the beamformer is further adapted to determine the weights to apply to the signals emitted from the transducers in order to maximise a performance metric based on a total signals power and noise power; and
wherein the processor is adapted to compare the measured combined energy with a predetermined energy detection threshold and determine, based on said comparison, whether or not one or more signals are present.