Signal power estimation

1. A method of evaluating the fraction of the power that is attributable to a wanted signal, as opposed to extraneous signals, within a received signal acquired by a receiver from a plurality of transmission sources, the method comprising:

a. populating a first version of an auto-covariance matrix of the received signal with entries obtained by way of calculating products of samples of the received signal with complex-conjugated samples of the received signal; and

b. finding a value of said fraction that causes a second version of the received signal's auto-covariance matrix to be a good match to said first version;

wherein:

c. said second version is a weighted sum of:

i) an auto-covariance matrix of the wanted signal, populated on the basis of channel impulse response estimate terms for a composite channel through which the wanted signal can be said to be received from said sources, and

ii) a plurality of auto-covariance matrices, each relating to extraneous signals emitted by a respective one of said sources and each populated on the basis of channel impulse response estimate terms for the channel linking its respective source with the receiver; and

d. at least some of the weights in the sum are functions of said fraction.

2. A method according to claim 1 , wherein the wanted signal is transmitted using closed loop transmit diversity.

3. A method according to claim 1 , wherein cost function optimisation is used to determine a good match between the second and first versions of the received signal's auto-covariance matrix.

4. A method according to claim 1 , wherein the cost function used in said optimisation is the norm of the difference between two vectors, one being a row of said first version and the other being the equivalent row of said second version.

5. Apparatus for evaluating the fraction of the power that is attributable to a wanted signal, as opposed to extraneous signals, within a received signal acquired by a receiver from a plurality of transmission sources, the apparatus comprising a processor and a memory containing instructions to be carried out by the processor, wherein the processor is arranged to:

a. populate a first version of an auto-covariance matrix of the received signal with entries obtained by way of calculating products of samples of the received signal with complex-conjugated samples of the received signal; and

b. find a value of said fraction that causes a second version of the received signal's auto-covariance matrix to be a good match to said first version; wherein:

c. said second version is a weighted sum of:

i) an auto-covariance matrix of the wanted signal, populated on the basis of channel impulse response estimate terms for a composite channel through which the wanted signal can be said to be received from said sources, and

ii) a plurality of auto-covariance matrices, each relating to extraneous signals emitted by a respective one of said sources and each populated on the basis of channel impulse response estimate terms for the channel linking its respective source with the receiver; and

at least some of the weights in the sum are functions of said fraction.

6. Apparatus according to claim 5 , wherein the wanted signal is transmitted using closed loop transmit diversity.

7. Apparatus according to claim 6 , wherein the processor is arranged to use cost function optimisation to determine a good match between the second and first versions of the received signal's auto-covariance matrix.

8. Apparatus according to claim 7 , wherein the cost function used in said optimisation is the norm of the difference between two vectors, one being a row of said first version and the other being the equivalent row of said second version.

9. A receiver for a telecommunications network, the receiver comprising the apparatus of claim 6 .