Detecting presence/absence of an information signal
A method and apparatus for detecting the presence of an information signal in received inputs. Inputs are received and an expected variance of the received inputs is determined based on an assumed statistical distribution of power values. Using the determined expected variance of the received inputs, a first hypothesis is tested that the received inputs include an information signal to detect a presence of the information signal.
1. A method for detecting a presence of an information signal in a received signal, comprising:
receiving an electrical signal;
correlating the received signal with a spreading code;
processing the correlated signal to produce a sequence of power values;
for a most recent power value, updating a mean power value over a plurality of power values in the sequence;
determining a range of mean power values defined by the updated mean power value bounded by a selected multiple of a variance of the plurality of mean power values according to a selected statistical distribution; and
comparing the range of mean power values with a signal threshold value;
wherein the presence of an information signal in the received signal is detected responsive to the comparing step indicating that the range of mean power values exceeds the signal threshold.
2. A method as claimed in claim 1 , wherein determining the range of mean power values comprises:
algebraically determining a mean of the square of input values corresponding to the correlated signal;
algebraically determining an updated variance of the power values from the mean of the square of input values;
algebraically determining a variance of the mean power values from the updated variance of the power values; and
determining the range as the mean power value plus or minus a selected multiple of a square root of the variance of the mean power values.
3. A method as claimed in claim 1 , wherein the statistical distribution is a chi-squared distribution of the power values.
4. A method as claimed in claim 1 , wherein determining the range of mean power values comprises:
updating a variance of power values from the updated mean power value; and
algebraically determining a variance of the mean power values from the updated variance of the power values; and
determining the range as the mean power value plus or minus a selected multiple of square root of the variance of the mean power values.
5. A method as claimed in claim 1 , wherein the signal threshold is a constant.
6. A method as claimed in claim 1 , wherein the signal threshold is dependent upon the upper boundary of the range of probable values for the mean of the inputs if they do not include a signal.
7. A method as claimed in claim 1 , further comprising
responsive to the comparing step indicating that the range of mean power values does not exceed the signal threshold, comparing the range of mean power values to noise threshold;
wherein an absence of an information signal in the received signal is detected responsive to the comparing step indicating that the range of mean power values does not exceed the noise threshold.
8. A method as claimed in 7 , wherein the noise threshold is a constant.
9. A method as claimed in 7 , wherein the noise threshold is an expected mean of the inputs if there is no signal.
10. A method as claimed in claim 1 , wherein the information signal is cyclostationary.
11. A method as claimed in claim 1 , wherein the information signal has a mean of zero.
12. A non-transitory computer readable medium embodying a computer program comprising program instructions for causing a computer to perform the method of claim 1 .
13. An apparatus comprising:
a power converter configured to receive input signal values, and process the received input signal values to provide a sequence of power values; and
processing circuitry, for detecting presence of an information signal within a received signal corresponding to the input signal values, configured to
for a most recent power value, update a mean power value over a plurality of power values in the sequence;
determine a range of mean power values defined by the updated mean power value bounded by a selected multiple of a variance of the plurality of mean power values according to a selected statistical distribution; and
compare the range of mean power values with a signal threshold value;
wherein the presence of an information signal in the received signal is detected responsive to the range of mean power values exceeding the signal threshold.
14. An apparatus as claimed in claim 13 wherein the operation of the processing circuitry is controlled by computer program instructions.
15. An apparatus as claimed in claim 13 wherein the processing circuitry is dedicated hardware.
16. An apparatus as claimed in claim 13 , wherein the received input signal values correspond to correlations of Code Division Multiple Access radio signals with a spreading code.
17. An apparatus as claimed in claim 13 , wherein the received input signal values are non-coherently integrated power values for received radio signals.