A method of analyzing a sampled signal that is supplied for decimation, wherein the decimation process produces a decimated version of the signal and wherein the method comprises determining an adjustment, if any is required, to the sampling instant of the signal prior to decimation that will cause the frequency responses of the decimated signal and of a main alias to combine constructively at a given frequency.
1. A method of analyzing a sampled signal that is supplied to a decimation process that produces a decimated signal, the method comprising:
determining an adjustment to a sampling phase employed to obtain the sampled signal prior to the decimation process that will cause the frequency responses of the sampled signal and a main alias of the sampled signal to combine constructively in at least one given place in the frequency domain after decimation,
wherein determining the adjustment comprises:
calculating a product of the frequency responses after complex conjugating at least one of the frequency responses, and
filtering the product; calculating a phase of the filtered product; unwrapping the calculated phase; and deducing the adjustment from the unwrapped phase of the product.
2. A method according to claim 1 , wherein the adjustment is accumulated.
3. A method according to claim 1 , wherein the sampled signal is a High-Speed Downlink Packet Access (HSDPA) data signal that is decimated by said decimation process to its symbol rate.
4. A method according to claim 3 , wherein the HSDPA data signal has a frequency that is substantially half the symbol rate of the signal.
5. A method according claim 1 , wherein the frequency responses of the decimated signal and its main alias are calculated by a Discrete Fourier transform (DFT) process and an accumulation length in the DFT process is adjustable.