Method and related mobile device for cell searching with low memory requirement
View Patent ↗The present solution relates to a method for searching for a cell in a cellular mobile communication system having low memory requirement. The method comprises: receiving in a receiver a signal carrying a reference signal having a first data rate, decimating the signal to generate a down-sampled signal having a second data rate, phase-compensating a phase distortion introduced by the decimating, and correlating the down-sampled signal against a phase-compensated local reference signal or a phase-compensated down-sampled signal against a local reference signal. When buffering the down-sampled signal prior or subsequent to phase-compensating, the buffer size is minimized as 1× oversampling is employed compared to 2× oversampling of current solutions.
1. A method for searching for a cell in a cellular mobile communication system, the method comprising: receiving in a receiver a signal carrying a reference signal having a first data rate, decimating the signal to generate a down-sampled signal having a second data rate, compensating a phase distortion introduced by the decimating step to generate a phase-compensated down-sampled signal, and correlating the down-sampled signal against a phase-compensated local reference signal or the phase-compensated down-sampled signal against a local reference signal.
2. The method according to claim 1 , the method further comprising:
buffering the down-sampled signal prior or subsequent to compensating a phase distortion.
3. The method according to claim 1 , wherein compensating a phase distortion comprises pre-compensating the reference signal to generate the phase-compensated local reference signal.
4. The method according to claim 1 , wherein correlating the down-sampled signal against a phase-compensated local reference signal comprises using a poly-phase correlator.
5. The method according to claim 1 , wherein correlating the down-sampled signal against a phase-compensated local reference signal comprises using a two-phase correlator.
6. The method according to claim 1 , wherein compensating a phase distortion comprises compensating a phase distortion of the down-sampled signal either in time domain or in frequency domain to generate the phase-compensated down-sampled signal.
7. The method according to claim 1 , the method comprising:
receiving a signal carrying a reference signal, the reference signal comprising a first reference sub-signal and a second reference sub-signal;
decimating the signal to generate a down-sampled signal;
buffering the down-sampled signal;
compensating in time domain a phase distortion introduced by the decimating by pre-compensating the first reference sub-signal to generate a first local reference signal;
poly-phase correlating in time domain the down-sampled signal against the first local reference sub-signal;
compensating in frequency domain a phase distortion introduced by the decimating by compensating a phase distortion of the down-sampled signal to generate a phase-compensated down-sampled signal; and
correlating in frequency domain the phase-compensated down-sampled signal against a second local reference sub-signal being identical to the second reference sub-signal.
8. The method according to claim 1 , the method comprising:
receiving a signal carrying a reference signal, the reference signal comprising a first reference sub-signal and a second reference sub-signal;
correlating in time domain the signal against a first local reference sub-signal being identical the first reference sub-signal;
decimating the signal to generate a down-sampled signal;
buffering the down-sampled signal;
compensating in frequency domain a phase distortion introduced by the decimating by compensating a phase distortion of the down-sampled signal to generate a phase-compensated down-sampled signal; and
correlating in frequency domain the phase-compensated down-sampled signal against a second local reference sub-signal being identical to the second reference sub-signal.
9. The method according to claim 1 , the method comprising:
receiving a signal carrying a reference signal, the reference signal comprising a first reference sub-signal and a second reference sub-signal;
decimating the signal to generate a down-sampled signal;
buffering the down-sampled signal;
compensating in time domain a phase distortion introduced by the decimating by compensating a phase distortion of the down-sampled signal to generate a phase-compensated down-sampled signal;
correlating in time domain the phase compensated down-sampled signal against a first local reference sub-signal being identical to the first reference sub-signal; and
correlating in frequency domain the phase-compensated down sampled signal against a second local reference sub-signal being identical to the second reference sub-signal.
10. The method according to claim 7 , wherein the first reference sub-signal is a primary synchronization signal (PSS) of a Long Term Evolution (LTE) system and wherein the second reference sub-signal is a secondary synchronization signal (SSS) of the LTE system.
11. The method according to claim 10 , wherein compensating in frequency domain a phase distortion comprises further compensating a phase distortion due to a 0.5 sample offset between PSS and SSS.
12. The method according to claim 11 , wherein compensating a phase distortion comprises pre-computing an aggregate phase as a sum of a linear phase due to the 0.5 sample offset between PSS and SSS and a pre-compensated phase due to the decimating and compensating a phase distortion once per SSS hypothesis using the aggregate phase.
13. The method according to claim 12 , wherein phase-compensating a 0.5 sample offset between PSS and SSS comprises zero-padding in time domain and applying a 128 point FFT when transforming from time domain to frequency domain.
14. The method according to claim 1 , wherein the second data rate is lower than the first data rate and wherein the second data rate is a lowest sample rate to obtain a pre-defined accuracy of the method.
15. The method according to claim 1 , wherein the second data rate is 0.96 Ms/s.
16. The method according to claim 1 , wherein the first data rate is 1.92 Ms/s.
17. A mobile device comprising: means for receiving a signal carrying a reference signal having a first data rate, means for decimating the signal to generate a down-sampled signal having a second data rate, means for compensating a phase distortion introduced by the decimating to generate a phase-compensated down-sampled signal, and means for correlating the down-sampled signal against a phase-compensated local reference signal, and means for correlating the phase-compensated down-sampled signal against a local reference signal or the down-sampled signal against a phase-compensated local reference signal.
18. The mobile device according to claim 17 , the mobile device further comprising means for buffering the down-sampled signal prior or subsequent to phase-compensating.
19. The mobile device according to claim 18 , the mobile device comprising:
a receiver for receiving a signal carrying a reference signal comprising a PSS and a SSS; and
a synchronization and cell detection module comprising:
a decimator for decimating the signal;
a time domain processing stage connected to the decimator;
a poly-phase PSS-correlator connected to the time domain processing stage for correlating a decimated signal against a pre-compensated PSS;
a buffer connected to the time domain processing stage;
a Fast Fourier Transform (FFT) stage for transforming the decimated signal from time domain to frequency domain connected to the buffer;
a phase-compensation stage connected to the FFT stage for compensating in frequency domain a phase distortion of the decimated signal; and
a SSS correlator connected to the phase-compensation stage for correlating a phase-compensated down-sampled signal against the SSS.
20. The mobile device according to claim 18 , the mobile device comprising:
a receiver for receiving a signal carrying a reference signal comprising a PSS and a SSS; and
a synchronization and cell detection module comprising:
a time domain processing stage for processing the signal;
a PSS for correlating the signal against the PSS;
a decimator for decimating the signal;
a buffer connected to the decimator;
a Fast Fourier Transform (FFT) stage for transforming the decimated signal from time domain to frequency domain;
a phase-compensation stage connected to the FFT stage for compensating in frequency domain a phase distortion of the decimated signal; and
a SSS correlator connected to the phase-compensation stage for correlating a phase-compensated down-sampled signal against the SSS.
21. A non-transitory computer readable medium having computer-executable instructions for performing the method according to claim 1 .