ROBUST SENSING FOR DETECTING SIGNALS USING CORRELATION

• US 20100035568A1
• Filed: 03/06/2008
• Published: 02/11/2010
• Est. Priority Date: 03/06/2007
• Status: Active Grant

• Current Assignee: Entropic Communications Incorporated (Maxlinear Incorporated)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Ghosh, Monisha
• Granted Patent: US 8,483,329 B2
• Time in Patent Office: Days
• US Class Current: 455/192.100
• CPC Class Codes: H04B 1/719 Interference-related aspects
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0087 Out-of-band signals, (e.g. pilots)
• CPC Class Codes: H04L 2027/0097 Adaptive synchronisation signals
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04L 27/063 Superheterodyne receivers
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0032 Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation

Abstract

To quickly and robustly detect the presence of an incumbent user and rapidly relinquish the spectrum to the incumbent user when necessary, carrier recovery is performed in a receiver of the secondary user'"'"'s cognitive or software radio prior to performing correlation detection with an upsampled reference signal to correct for large frequency offsets and improve the performance of the correlation detector. To detect a received signal, a pilot value is added to a reference signal. The reference signal is upsampled to a sampling frequency of the received signal. The upsampled reference signal is correlated with a demodulated baseband signal to produce a correlation value. It is then determined whether the received signal is present if the correlation value is greater than a predetermined detection threshold value.

Claims

1. A method for detecting a received signal, comprising:

adding a pilot value to a reference signal;

upsampling the reference signal to a sampling frequency of the received signal;

correlating the upsampled reference signal with a demodulated baseband signal to produce a correlation value; and

determining that the received signal is present if the correlation value is greater than a predetermined detection threshold value.

2. A method for detecting the presence of a received signal in a sensor, comprising:

estimating a carrier frequency of the received signal;

using the estimated carrier frequency to demodulate the received signal to generate a complex demodulated baseband signal;

low-pass filtering the complex demodulated baseband signal;

generating an over-sampled local reference signal having the same sampling rate as the received signal;

correlating the over-sampled local reference signal with the low-pass filtered complex demodulated baseband signal yielding a complex correlation value;

taking the absolute value of the complex correlation value;

comparing the absolute value of the complex correlation value to a detection threshold; and

determining that the received signal is present if the absolute value of the complex correlation value is greater than the detection threshold.

3. The method according to claim 2, wherein the estimating further comprises:

performing a frequency domain transformation on N sections of the received signal yielding a plurality of N independent vectors;

taking the absolute value of each of the plurality of N independent vectors;

averaging the absolute value of each of the N independent vectors yielding a single averaged independent vector;

identifying a peak of the single averaged independent vector;

comparing the identified peak of the single averaged independent vector with a threshold; and

using the identified peak position of the single averaged independent vector as an estimate of the carrier frequency if the identified peak is greater than the threshold, and otherwise using a nominal pilot location of the received signal as an estimate of the carrier frequency.

4. The method according to claim 2, wherein the frequency domain transformation is an FFT transformation.

5. The method according to claim 2, wherein the FFT transformation is performed in a single dwell.

6. The method according to claim 2, wherein the FFT transformation is performed in a plurality of dwells.

7. The method according to claim 2, wherein the frequency transformation is a power spectral density transformation.

8. The method according to claim 2, wherein the received signal includes at least one pilot in a known location.

9. The method according to claim 8, wherein the low-pass filtering comprises filtering the complex demodulated baseband signal in a region around said pilot in said known location of the received signal.

10. The method according to claim 2, wherein the received signal is one of a radio frequency signal and an intermediate frequency signal.

12. The sensor according to claim 10, wherein the local reference signal generating unit (460) further comprises:

a PN511 and pilot generating unit (461) for generating local reference sequence (57);

an oversampling unit (465) for receiving local reference sequence (57) and generating local reference sequence (58); and

a second matched filter (467) for receiving the intermediate local reference sequence (58) and generating local reference signal (59).

13. The sensor according to claim 10, wherein the sensor is one of a software radio and a cognitive radio.

11. A sensor (400) for detecting the presence of a received signal (43) in a wireless system, comprising:

a tuner (410) for receiving one of a radio frequency signal (43) to produce a low IF (LIF) signal (45);

a demodulating unit (420) for demodulating the low IF (LIF) signal (45) to produce a complex demodulated baseband signal (49);

a first matched filter (430) for performing a matched filtering operation on the first complex signal (49) to produce a second complex signal (51);

a local reference signal generating unit (460) for generating an oversampled local reference signal (59);

a complex correlation unit (440) for performing a complex correlation between the oversampled local reference signal (59) and the second complex signal (51) to produce a third complex signal (53);

an absolute value unit (470) for taking the absolute value of the third complex signal (53) to produce a fourth complex signal (61); and

a threshold detector (480) for comparing the fourth complex signal (61) with a threshold value (63) to determine if the received signal (43) is present.