User equipment for detecting short codes
A receiver employing CDMA techniques estimates background noise based on a periodically updated code. The transmitted signal includes a periodically updated code of a predetermined type and wherein the received signal has CW interference in addition to the transmitted signal. The decision circuit determines if a value representing the likelihood of detection of the code exceeds a predetermined threshold. In the case of a pilot signal not being detected within a predetermined time period which corresponds to code update period, the background noise estimator obtains a new background estimation.
1. A method for detecting the presence of a short code in a received signal including a plurality of periodically updated short codes, the method comprising:
detecting the presence of a short code in the received signal using a sequential ratio probability test wherein a background noise estimation is calculated by combining a presently updated short code with the received signal,
wherein the sequential ratio probability test comprises:
generating a likelihood ratio by comparing the background noise estimation with the received signal;
comparing the likelihood ratio with a first predetermined threshold; and,
comparing the likelihood ratio with a second predetermined threshold on a condition that the likelihood ratio is below the first threshold, wherein the short code is present on a condition that the likelihood ratio is above the second predetermined threshold.
2. The method of claim 1 further comprising:
updating the background noise estimation each time the short code is periodically updated.
3. The method of claim 1 further comprising:
comparing the likelihood ratio with a predetermined threshold, wherein if the likelihood ratio is above a predetermined threshold a short code is present.
4. The method of claim 1 , wherein the received signal is received using a rake receiver and a plurality of signal phases are generated.
5. The method of claim 4 , wherein the sequential ratio probability test comprises:
generating a likelihood ratio for each signal phase by comparing the background noise estimation with the received signal.
6. The method of claim 5 further comprising:
comparing the likelihood ratio of each signal phase with a predetermined threshold, wherein if the likelihood ratio is above a predetermined threshold a short code is present.
7. The method of claim 5 further comprising:
comparing the likelihood ratio of each signal phase with a first predetermined threshold; and
comparing the likelihood ratios of each signal phase that are greater than the first predetermined threshold with a second predetermined threshold, wherein if the likelihood ratios are above the second predetermined threshold a short code is present.