Receiver and method for compensating for frequency offset of receiving signal in multi-band OFDM scheme

• US 20080095250A1
• Filed: 02/12/2007
• Published: 04/24/2008
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Yun Young, Roh, Jae Ho
• Granted Patent: US 7,933,347 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

A multiband Orthogonal Frequency Division Multiplexing (OFDM) receiver, and more particularly, a receiver and method for effectively compensating for a frequency offset of a received signal in a multiband OFDM scheme. The receiver for compensating for a frequency offset of a received signal in an OFDM scheme includes: a numerically controlled oscillator (NCO) which generates a first compensation signal by processing an input signal in a time domain based on a first carrier frequency offset estimated in the time domain, and a second carrier frequency offset estimated in a frequency domain; a sampling frequency offset tracking (SFOT) unit which generates a second compensation signal by estimating a sampling frequency offset from frequency domain pilot symbols contained in the first compensation signal; and a carrier frequency offset tracking (CFOT) unit which estimates the second carrier frequency offset by using pilot symbols contained in the second compensation signal.

Claims

1. A receiver for compensating for a frequency offset of a received signal in a multiband Orthogonal Frequency Division Multiplexing (OFDM) scheme, the receiver comprising:

a numerically controlled oscillator (NCO) which generates a first compensation signal by processing an input signal in a time domain based on a first carrier frequency offset estimated in the time domain, and a second carrier frequency offset estimated in a frequency domain;

a sampling frequency offset tracking (SFOT) unit which generates a second compensation signal by estimating a sampling frequency offset from frequency domain pilot symbols which are contained in the first compensation signal; and

a carrier frequency offset tracking (CFOT) unit which estimates the second carrier frequency offset by using pilot symbols which are contained in the second compensation signal.

2. The receiver of claim 1, wherein the second carrier frequency offset corresponds to a remaining carrier frequency offset estimated in the frequency domain after the first carrier frequency offset estimated in the time domain is compensated for.

3. The receiver of claim 1, further comprising:

an analog-to-digital converter (ADC) which samples a received radio frequency (RF) signal, and converts the sampled RF signal into a digital signal;

a switch which converts the digital signal from serial form into parallel form according to a position value;

a packet detection unit which provides the position value; and

a cover sequence unit which generates the input signal by unmasking a preamble from the digital signal converted into the parallel form according to a Time Frequency Code (TFC).

4. The receiver of claim 3, wherein the position value corresponds to a value which indicates a starting position of an OFDM symbol in the sampled RF signal, and corresponds to one of 0, 1, 2, and 3.

5. The receiver of claim 3, wherein the switch processes four OFDM symbols, which consist of three OFDM symbols, each of the three OFDM symbol comprising 164 samples, and a single OFDM symbol comprising 168 samplest, within a single period with respect to an OFDM symbol comprising 165 samples.

6. The receiver of claim 5, wherein the switch inserts one sample extracted from each of the three OFDM symbols, into a tail of the single OFDM symbol according to the position value.

7. The receiver of claim 3, wherein the switch adjusts an OFDM symbol timing based on a phase error corresponding to the sampling frequency offset estimated by the SFOT unit.

8. The receiver of claim 1, further comprising:

an overlap and add (OLA) unit which overlaps and adds a predetermined sample to a header of each OFDM symbol of the received signal, the predetermined sample being acquired when the first compensation signal output from the NCO is delayed and spread;

a fast Fourier transform (FFT) unit which fast Fourier transforms signals output from the OLA unit into the frequency domain;

a channel estimation unit which estimates a signal distortion from signals output from the FFT unit; and

an equalization unit which compensates for each signal output from the FFT unit based on the estimated signal distortion, and outputs the compensated signal to the SFOT unit.

9. The receiver of claim 8, wherein the predetermined sample is within a range of 32 samples of a zero-prefix where the delaying and spreading occurs, and is added to 128 valid samples of each OFDM symbol of the received signal.

10. The receiver of claim 1, further comprising a frequency synchronization unit which estimates the first carrier frequency offset from the input signal.

11. The receiver of claim 1, further comprising a demodulation and decision unit which demodulates the second compensation signal, and provides data rate information of a Physical Layer Convergence Protocol (PLCP) header to determine the pilot symbols to be used by the CFOT unit.

12. A method of compensating for a frequency offset of a received signal in a multiband Orthogonal Frequency Division Multiplexing (OFDM) scheme, the method comprising:

generating a first compensation signal by processing an input signal in a time domain;

generating a second compensation signal by estimating a sampling frequency offset from frequency domain pilot symbols which are contained in the first compensation signal; and

estimating a second carrier frequency offset by using pilot signals which are contained in the second compensation signal,

wherein the generating of the first compensation signal comprises;

processing the input signal based on a first carrier frequency offset estimated in the time domain and the second carrier frequency offset estimated in a frequency domain.

13. The method of claim 12, wherein the second carrier frequency offset corresponds to a remaining carrier frequency offset estimated in the frequency domain after the first carrier frequency offset estimated in the time domain is compensated for.

14. The method of claim 12, further comprising:

sampling a received radio frequency (RF) signal to convert the sampled RF signal into a digital signal;

converting the digital signal from serial form into parallel form according to a position value;

providing the position value; and

generating the input signal by unmasking a preamble from the digital signal converted into the parallel form according to a Time Frequency Code (TFC).

15. The method of claim 14, wherein the position value corresponds to a value which indicates a starting position of an OFDM symbol in the sampled RF signal, and corresponds to one of 0, 1, 2, and 3.

16. The method of claim 14, wherein the switching comprises processing four OFDM symbols, which consist of three OFDM symbols, each of the three OFDM symbol comprising 164 samples, and a single OFDM symbol comprising 168 samples, within a single period with respect to an OFDM symbol comprising 165 samples.

17. The method of claim 16, wherein the switching comprises inserting one sample extracted from each of the three OFDM symbols, into a tail of the single OFDM symbol according to the position value.

18. The method of claim 14, wherein the switching comprises adjusting an OFDM symbol timing based on a phase error corresponding to the estimated sampling frequency offset.

19. The method of claim 12, wherein prior to the generating of the second compensation signal, the method further comprises:

overlapping and adding a predetermined sample to a header of each OFDM symbol of the received signal, the predetermined sample being acquired when the first compensation signal is delayed and spread;

fast Fourier transforming a signal output from the overlapping and adding into the frequency domain;

estimating a signal distortion from the fast Fourier transformed signal; and

compensating for the fast Fourier transformed signal based on the estimated signal distortion.

20. The method of claim 19, wherein the predetermined sample is within a range of 32 samples of a zero-prefix where the delaying and spreading occurs, and is added to 128 valid samples of each OFDM symbol of the received signal.

21. The method of claim 12, further comprising estimating the first carrier frequency offset from the input signal.

22. The method of claim 12, further comprising demodulating the second compensation signal, and providing data rate information of a Physical Layer Convergence Protocol (PLCP) header to determine the pilot symbols to be used.

23. A computer-readable recording medium storing a program for implementing a method of compensating for a frequency offset of a received signal in a multiband Orthogonal Frequency Division Multiplexing (OFDM) scheme, the method comprising:

generating a first compensation signal by processing an input signal in a time domain;

generating a second compensation signal by estimating a sampling frequency offset from frequency domain pilot symbols which are contained in the first compensation signal; and

estimating a second carrier frequency offset by using pilot signals which are contained in the second compensation signal,

wherein the generating of the first compensation signal comprises;

processing the input signal based on a first carrier frequency offset estimated in the time domain and the second carrier frequency offset estimated in a frequency domain.