Pilot signal in an FDMA communication system
View Patent ↗Methods ( 500, 800 ) and corresponding systems ( 100, 200, 300, 400, 900 ) for generating a pilot symbol ( 330 ) include providing an M-point parallel transform sequence that is a discrete Fourier transform of a CAZAC sequence ( 312, 504 - 508 ). The M-point parallel transform sequence ( 312 ) is distributed ( 316, 510 ) to a set of M subcarriers among N subcarriers to form an N-point frequency-domain sequence ( 318 ) wherein the M subcarriers are evenly spaced apart. An N-point inverse fast Fourier transform ( 320, 512 ) is performed to convert the N-point frequency-domain sequence to an N-point time-domain sequence ( 322 ). The N-point time-domain sequence is converted ( 324, 514 ) to a serial sequence ( 326 ), and a cyclic prefix is added ( 328, 516 ) to the serial sequence to form a pilot symbol ( 330 ).
1. A method for receiving a pilot symbol in an single carrier frequency division multiple access (SC-FDMA) receiver comprising:
removing a cyclic prefix from a received pilot waveform to produce a modified pilot waveform;
converting the modified pilot waveform into an N-point parallel modified pilot symbol;
performing an N-point fast Fourier transform on the N-point parallel modified pilot symbol to produce a received transformed pilot symbol;
demapping M distributed subcarriers in the received transformed pilot symbol to produce an M-point received pilot signal;
multiplying the M-point received pilot signal by an M-point channel estimate multiplier to produce an M-point intermediate channel estimate, wherein the M-point channel estimate multiplier is derived from a constant-amplitude zero-autocorrelation (CAZAC) sequence; and
performing a two dimensional interpolation on the M-point intermediate channel estimate to produce a final channel estimate.
2. The method for receiving a pilot symbol according to claim 1 wherein the demapping M distributed subcarriers comprises:
receiving mapping information; and
demapping M distributed subcarriers using the mapping information.
3. The method for receiving a pilot symbol according to claim 2 wherein the multiplying the M-point received pilot signal by an M-point channel estimate multiplier comprises multiplying the M-point received pilot signal by a Fourier transformed time-reversed conjugate sequence derived from an expected pilot symbol that is a CAZAC sequence.
4. The method for receiving a pilot symbol according to claim 1 wherein the multiplying the M-point received pilot signal by an M-point channel estimate multiplier comprises multiplying the M-point received pilot signal by a Fourier transformed time-reversed conjugate sequence derived from an expected pilot symbol that is a CAZAC sequence.
5. A pilot symbol receiver comprising:
a cyclic prefix remover for removing a cyclic prefix from a received waveform to produce a modified pilot waveform;
a serial to parallel converter coupled to the modified pilot waveform for producing an N-point parallel modified pilot symbol;
an N-point fast Fourier transformer coupled to the serial to parallel converter for performing an N-point fast Fourier transform on the N-point parallel modified pilot symbol to produce a received transformed pilot symbol;
a distributed subcarrier demapper coupled to the N-point fast Fourier transformer for demapping M distributed subcarriers in the received transformed pilot symbol to produce an M-point received pilot signal; and
a multiplier coupled to the distributed subcarrier demapper for multiplying the M-point received pilot signal by an M-point channel estimate multiplier to produce an M-point intermediate channel estimate, wherein the M-point channel estimate multiplier is derived from a constant-amplitude zero-autocorrelation (CAZAC) sequence; and
a two dimensional interpolator coupled to the multiplier for performing a two dimensional interpolation on the M-point intermediate channel estimate to produce a final channel estimate.
6. The pilot symbol receiver according to claim 4 further comprising a mapping information receiver for receiving carrier mapping information, and wherein the distributed subcarrier demapper further comprises a distributed subcarrier demapper coupled to the mapping information receiver for demapping M distributed subcarriers using the carrier mapping information.
7. The pilot symbol receiver according to claim 6 wherein the multiplier comprises an M-point multiplier for multiplying the received pilot signal by a Fourier transformed time-reversed conjugate sequence derived from an expected pilot symbol that is a CAZAC sequence.
8. The pilot symbol receiver according to claim 5 further comprising a mapping information receiver for receiving carrier mapping information, and wherein the distributed subcarrier demapper further comprises a distributed subcarrier demapper coupled to the mapping information receiver for demapping M distributed subcarriers using the carrier mapping information.