Estimating signal to interference ratio in a wireless communications receiver
A method and corresponding system for generating an estimate of at least one of a signal power, a noise power and a signal to interference ratio for signal samples received via first and second wireless channels, the signal samples corresponding to pilot symbols transmitted in respective different structures via the first and second wireless channels. The method comprises: calculating first and second variables, each variable being a sequence of values computed from the received signal samples and the pilot symbols for each respective first and second wireless channel; generating first and second channel estimates from the first and second variables; combining the first and second channel estimates to generate a combined channel estimate; and generating at least one of the signal power, noise power and SIR using the combined channel estimate.
1. A method of generating an estimate of a signal power, a noise power and a signal to interference ratio (SIR) for signal samples received via first and second wireless channels via a first and second antenna, said signal samples corresponding to pilot symbols transmitted in via said first and second wireless channels wherein a length of the pilot symbols is N p and N p ≧2, the method comprising:
calculating first and second variables corresponding to the first and second antennas, each variable being computed from the received signal samples and said pilot symbols for each respective first and second wireless channel;
generating a first and second channel estimate corresponding to the first and second antennas from the first and second variables;
combining the first and second channel estimates to generate a combined channel estimate; wherein,
if N p =2, generating the signal power estimate from the combined channel estimate, a noise power estimate by filtering the combined channel estimate, and the SIR using the signal power estimate and the filtered noise power estimate;
otherwise, generating the signal power from the combined channel estimate, the noise power from the first and second variables; and the SIR using signal power and the noise power.
2. The method according to claim 1 , comprising:
generating an estimate of signal power using the combined channel estimate;
generating an estimate of noise power using the combined channel estimate; and
generating an estimate of SIR from the estimate of signal power and estimate of noise power.
3. The method according to claim 2 , comprising the step of filtering the estimate of signal power and the estimate of noise power prior to generating the estimate of SIR.
4. The method according to claim 3 , wherein the step of filtering the signal power and noise power estimates uses settable filtering parameters.
5. The method according to claim 1 , wherein the step of calculating the first and second variables is performed depending on the length of the pilot symbols on the first and second channels.
6. The method according to claim 1 , wherein the step of generating the first and second channel estimates from the first and second variables comprises summing the values in the sequence for each of the first and second variables respectively and dividing it by the number N p of pilot symbols in the pilot symbol structure.
7. A wireless receiver for use in a wireless communications system, the receiver comprising:
a first and second antenna for receiving a sequence of signal samples via first and second wireless channels;
a memory for storing pilot symbol which have been transmitted over the first and second wireless channels, each pilot symbol having a length N p ; where N p ≧2; and
a processor for generating an estimate of a signal power, a noise power and a signal to interference ratio (SIR) for the sequence of signal samples received via the first and second wireless channels, said processor programmed to implement the following steps:
calculating first and second variables corresponding to the first and second antennas, each variable being computed from the received sequence of signal samples and said pilot symbols for each respective first and second wireless channel;
generating a first and second channel estimate corresponding to the first and second antennas from the first and second variables;
combining the first and second channel estimates to generate a combined channel estimate; wherein,
if N p =2, generating the signal power from the combined channel estimate, the noise power by filtering the combined channel estimate, and the SIR using the signal power and the filtered noise power;
otherwise, generating an estimate of the signal power from the combined channel estimate, the noise power from the first and second variables, and the (SIR) using the signal power and the noise.
8. The receiver according to claim 7 , wherein the processor is programmed to carry out the steps of:
generating an estimate of signal power using the combined channel estimate;
generating an estimate of noise power using the combined channel estimate; and
generating an estimate of SIR from the estimate of signal power and estimate of noise power.
9. The wireless receiver according to claim 8 , comprising a filter for filtering the combined channel estimate prior to the step of generating an estimate of noise power from the combined channel estimate.
10. A wireless communications system comprising:
a transmitter arranged to transmit via first and second antennas first and second wireless signals, the first wireless signal comprising a first pilot symbol structure and the second wireless signal comprising a second pilot symbol structure; and
the wireless receiver according to claim 7 .