Method and arrangement for asynchronous RSRP measurement in an LTE UE receiver

1. A method for measuring reference signal receive power for use in a Long Term Evolution user equipment, comprising the steps of:

extracting time samples from a received signal that comprises reference symbols having a predefined spacing of n subcarriers;

performing a Fast Fourier Transform (FFT) operation on the extracted samples for transformation into the frequency domain;

extracting said reference symbols from the frequency domain samples to determine a reference signal receive power of the received signal;

wherein the extracting time samples step, for each OFDM symbol, comprises:

frequency shifting the received signal so that an upper or lower half band becomes centered around DC frequency;

decimating the received signal to a width of n·2 m samples per FFT duration of an OFDM symbol, wherein n corresponds to the reference symbol spacing as a number of OFDM subcarriers in the received signal and m is an integer;

extracting time samples from the decimated signal and frequency shifting said extracted time samples by a first discrete number of carriers such that one of the reference symbols falls to the DC frequency; combining the extracted time samples by dividing them into n sample vectors, wherein each of the n sample vectors which has a length equal to the subsequently applied FFT operation, and superimposing said n sample vectors to obtain a single sample vector of a length equal to the subsequently applied FFT; and

wherein said FFT operation step is performed on the superimposed signal to obtain a contiguous set of reference symbol carriers from a signal transmitted by one base station and the contiguous set of reference symbol carriers is used to determine the reference signal receive power of a signal transmitted by said base station.

2. The method of claim 1 , wherein the decimating the received signal comprises decimation by ⅜.

3. The method of claim 2 , wherein said decimation by ⅜ is split into decimation by ¾ and subsequent decimation by ½.

4. The method of claim 2 , wherein said decimation by ⅜ is split into decimation by ½ and subsequent decimation by ¾.

5. The method of claim 1 , wherein the decimating the received signal comprises decimation by ¾.

6. The method of claim 1 , wherein the method, following the decimating the received signal step, further comprises storing the decimated signal; and extracting time samples from the decimated signal and frequency shifting said extracted time samples by a second discrete number of carriers such that another one of the reference symbols falls to the DC frequency, for computing an RSRP value on the same decimated signal data for a different point in time to extract reference symbols from a signal transmitted by a second base station.

7. The method of claim 1 , wherein the FFT step comprises performing an FFT with a length of a power of two.

8. The method of claim 7 , wherein the FFT has a length of 128.

9. The method of claim 1 , wherein, in the frequency shifting step of a half band to DC frequency, the shifting direction is alternated in uniform periods.

10. The method of claim 9 , wherein the alternated period is one OFDM symbol.

11. The method of claim 9 , wherein the alternated period is one sub-frame.

12. The method of claim 9 , wherein the alternated period is one slot.

13. An arrangement for reference signal receive power measurement in a Long Term Evolution user equipment receiver, comprising:

means for extracting time samples from a received signal which comprises reference symbols having a predefined spacing of n subcarriers;

means for performing an FFT operation on the extracted time samples for transformation into the frequency domain;

means for extracting said reference symbols from the frequency domain samples to determine a reference signal receive power of the received signal; wherein the extraction means comprise:

frequency shifter means for frequency shifting the received signal so that the upper or lower half band becomes centered around DC frequency;

decimation filter means for decimating the received signal to a width of n·2 m samples per FFT duration of an OFDM symbol, wherein n corresponds to the reference symbol spacing as a number of OFDM subcarriers in the received signal and m is an integer;

means for extracting time samples from the decimated signal and for frequency shifting said extracted time samples by a first discrete number of carriers such that one of the reference symbols falls to the DC frequency; means for combining the extracted time samples by dividing them into n sample vectors of a length of 2 m each, and for superimposing said n sample vectors to obtain a single sample vector of length 2 m ; and wherein FFT the operation is adapted for an FFT duration of 2 m time samples.

14. The arrangement of claim 13 , further comprising memory means downstream the decimation filter means for buffering the decimated receive signal.

15. A Long Term Evolution user equipment receiver comprising at least cell searching means, reference measurement means, data reception means, feedback information computation means, and data transmission means; wherein said reference measurement means comprise an arrangement for reference signal receive power measurement according to claim 13 , and wherein said cell searching means and said arrangement for reference signal receive power measurement share a Fast Fourier Transform unit.