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Title:
METHOD AND APPARATUS FOR TELEVISION BAND PILOT SENSING
Document Type and Number:
WIPO Patent Application WO/2012/109744
Kind Code:
A1
Abstract:
A DTV pilot sensor generates DTV pilot tone detection decisions associated with monitored television band channels without knowledge or estimation of a noise level of the monitored channel.

Inventors:
SAMARASOORIYA VAJIRA (CA)
PAYER DANIEL (CA)
YEE JUNG (CA)
Application Number:
PCT/CA2012/050068
Publication Date:
August 23, 2012
Filing Date:
February 07, 2012
Export Citation:
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Assignee:
WI LAN INC (CA)
SAMARASOORIYA VAJIRA (CA)
PAYER DANIEL (CA)
YEE JUNG (CA)
International Classes:
H04N21/266; H04B1/76; H04R3/00; H04W72/00
Foreign References:
US20090325499A12009-12-31
US20090102981A12009-04-23
US20100309317A12010-12-09
Attorney, Agent or Firm:
BRION RAFFOUL (2515 Bank StreetOttawa, Ontario K1V 0W8, CA)
Download PDF:
Claims:
We Claim:

A DTV pilot sensor, comprising:

a spectrum smoothing filter that smoothes a power spectrum of a received television band channel;

pilot tone peak search logic that computes a peak signal power of a narrow frequency window centered around a designated DTV pilot position of the output of the spectrum smoothing filter; conditioned signal power estimation logic that estimates an average received signal power in a wide frequency window located in a designated data portion of the output of the spectrum smoothing filter; and

pilot tone detection logic that compares an output of the pilot tone peak search logic with a product of an output the conditioned signal power estimation logic multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected.

The DTV pilot sensor as claimed in claim 1 wherein the pilot tone peak search logic further comprises an interpolation filter that up-samples and shapes the narrow frequency window outputs of the spectrum smoothing filter.

The DTV pilot sensor as claimed in claim 1 wherein the interpolation filter comprises a finite impulse response filter or an infinite impulse response filter.

The DTV pilot sensor as claimed in claim 1 wherein the conditioned signal power estimation logic further comprises a signal conditioner that comprises logic that uses signal power limits to condition the output of the spectrum smoothing filter to create a conditioned signal used to estimate the average received signal power within the wide frequency window. The DTV pilot sensor as claimed in claim 4 wherein the signal conditioner comprises logic that computes the signal power limits.

The DTV pilot sensor as claimed in claim 5 wherein the signal conditioner comprises logic that examines the output of the spectrum smoothing filter and computes high and low hard power limits using knowledge about an expected power level of a data portion of the received television band channel to reduce an impact of high power levels and/or low power levels on an average power level of the conditioned signal.

The DTV pilot sensor as claimed in claim 4 wherein the signal conditioner comprises logic that retrieves the signal power limits from memory.

The DTV pilot sensor as claimed in claim 7 wherein the signal conditioner comprises logic that retrieves trained signal artifacts from the memory to condition the output of the spectrum smoothing filter.

The DTV pilot sensor as claimed in claim 8 wherein the signal conditioner comprises logic that retrieves one or more of: known-device generated interfering frequencies; and, channel-dependent interfering tones that are identified and their frequencies are stored during an initial and/or long-term training process.

10. The DTV pilot sensor as claimed in claim 4 wherein the signal conditioner comprises logic that retrieves certain ones of the signal power limits from memory and logic that computes certain ones of the signal power limits. 1 1 . The DTV pilot sensor as claimed in claim 10 wherein the signal conditioner comprises logic that retrieves from the memory a programmable constant ΚΊ indicating a number of highest power levels and a programmable constant K2 indicating a number of lowest power levels to be eliminated from the output of the spectrum smoothing filter; logic that determines the ΚΊ highest power levels, the K2 lowest power levels and logic that eliminates the respective ΚΊ and K2 power levels from the output of the spectrum smoothing filter.

The DTV pilot sensor as claimed in claim 10 wherein the signal conditioner comprises logic that retrieves from memory a programmable constant L indicating a number of median power levels to be used for signal conditioning; computes a median power level of the smoothed power spectrum, and selects the L power levels closest to the median power of the output of the spectrum smoothing filter.

A method of sensing a DTV pilot tone in a television band, comprising: tuning a radio frequency front end to a frequency associated with a television channel in the television band;

smoothing a power spectrum of a received signal associated with the television channel;

searching a narrow frequency window centered around a designated DTV pilot position of the smoothed power spectrum to locate a peak power of the narrow frequency window;

estimating an average power of a wide frequency window located in a designated data portion of the smoothed power spectrum; and comparing the peak power of the narrow frequency window with a product of the average power of the wide frequency window multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected.

The method as claimed in claim 13 wherein smoothing the power spectrum of the received signal comprises using an exponential averaging filter to smooth the power spectrum. The method as claimed in clam 13 wherein prior to searching the narrow frequency window the method further comprises using an interpolation filter to filter the smoothed power spectrum associated with the narrow frequency window.

The method as claimed in claim 15 wherein prior to estimating the average power of the wide frequency window, the method further comprises conditioning the smoothed power spectrum associated with the wide frequency window using signal power limits.

The method as claimed in claim 16 wherein the signal power limits are computed.

The method as claimed in claim 17 wherein the smoothed power spectrum is examined and high and low hard signal power limits are computed using knowledge about an expected power level of a data portion of the television channel to reduce an impact of any one or more of: high power levels; low power notches; and low power fading in the smoothed power spectrum.

The method as claimed in claim 16 further comprising retrieving the signal power limits from memory.

The method as claimed in claim 19 wherein the signal power limits retrieved from the memory comprise trained signal artifacts used to condition the smoothed power spectrum.

The method as claimed in claim 20 wherein the trained signal artifacts comprise any one or more of: known-device generated interfering frequencies; and, channel-dependent interfering tones that are identified and their frequencies are stored during an initial and/or long- term training process. The method as claimed in claim 16 wherein certain ones of the signal power limits are retrieved from memory and certain ones of the signal power limits are computed.

The method as claimed in claim 22 wherein the signal power limits retrieved from memory comprise a programmable constant ΚΊ indicating a number of highest power levels and a programmable constant K2 indicating a number of lowest power levels to be eliminated from the smoothed power spectrum, and the method further comprises determining the ΚΊ highest power levels, the K2 lowest power levels and eliminating the respective ΚΊ and K2 power levels from the smoothed power spectrum.

The method as claimed in claim 22 wherein the signal power limits retrieved from memory comprise a programmable constant L indicating a number of median power levels to be used for signal conditioning; and the method further comprises computing a median power level of the smoothed power spectrum, and selecting the L power levels closest to the median.

A TV band device comprising:

pilot tone peak search logic that searches for a peak signal power in a narrow frequency window centered around a designated DTV pilot position of a smoothed power spectrum of a signal associated with a television band channel;

conditioned signal power estimation logic that estimates an average received signal power in a wide frequency window located in a designated data portion of a smoothed power spectrum; and pilot tone detection logic that compares an output of the pilot tone peak search logic with a product of an output of the conditioned signal power estimation logic multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected. The TV band device as claimed in claim 25 wherein the pilot tone peak search logic further comprises an interpolation filter that up-samples and shapes the smoothed power spectrum of the narrow frequency window before the pilot tone peak search logic searches for the peak signal strength.

The TV band device as claimed in claim 25 wherein the interpolation filter comprises a finite impulse response filter or an infinite impulse response filter.

The TV band device as claimed in claim 25 wherein the conditioned signal power estimation logic further comprises a signal conditioner that uses signal power limits to condition the smoothed power spectrum in the wide frequency window before the average power is estimated.

The TV band device as claimed in claim 28 wherein the signal conditioner comprises logic that computes the signal power limits.

The TV band device as claimed in claim 29 wherein the signal conditioner comprises logic that examines the smoothed power spectrum and computes high and low hard power limits using knowledge about an expected power level of a data portion of the television band channel to reduce an impact of high power levels and low power levels on an average power of the conditioned signal.

The TV band device as claimed in claim 28 wherein the signal conditioner comprises logic that retrieves the signal power limits from memory.

The TV band device as claimed in claim 31 wherein the signal conditioner comprises logic that retrieves trained signal artifacts from the memory to condition the smoothed power spectrum. The TV band device as claimed in claim 32 wherein the signal conditioner comprises logic that retrieves: known-device generated interfering frequencies; and, channel-dependent interfering tones that are identified and their frequencies are stored during an initial and/or long-term training process.

The TV band device as claimed in claim 28 wherein the signal conditioner comprises logic that retrieves certain ones of the signal power limits from memory and logic that computes certain ones of the signal power limits.

The TV band device as claimed in claim 34 wherein the signal conditioner comprises logic that retrieves from memory a programmable constant ΚΊ indicating a number of highest power levels and a programmable constant K2 indicating a number of lowest power levels to be eliminated from the smoothed power spectrum; logic that determines the ΚΊ highest power levels, the K2 lowest power levels and logic that eliminates the respective ΚΊ and K2 power levels from the smoothed power spectrum.

The TV band device as claimed in claim 34 wherein the signal conditioner comprises logic that retrieves from memory a programmable constant L indicating a number of median power levels to be used for signal conditioning; logic that computes a median power level of the smoothed power spectrum, and logic that selects the L power levels closest to the median to be output as the conditioned signal.

Description:
METHOD AND APPARATUS FOR TELEVISION BAND PILOT

SENSING

FIELD OF THE INVENTION

This invention relates in general to cognitive radio and, in particular, to an efficient sensor for detecting digital television (DTV) pilot tones in the VHF/UH F television band channels.

BACKGROUND OF TH E INVENTION

The opening of available TV Band spectrum for usage by secondary TV band devices has created a need for efficient spectrum sensing mechanisms that can reliably detect available TV band white spaces to ensure that primary TV band users such as DTV broadcasters and wireless microphones are protected from interfering broadcasts by secondary TV Band device users.

Sensing for available white spaces in the VHF/UHF bands is vital to the operation of secondary TV Band devices. Protection of primary incumbent operators like digital television (DTV) stations and wireless microphone operators is designated by the United States Federal Communications Commission (FCC) and other federal authorities around the world. The DTV and wireless microphone sensing requirements set forth by the FCC are very stringent, requiring a sensing receiver sensitivity of -1 14 dBm for DTV and -107 dBm for wireless microphones. Detecting primary user broadcasts on VHF/UHF channels at the required sensing sensitivities is very challenging.

It has been suggested that all primary users of the TV Band spectrum broadcast a pilot tone at the DTV pilot position. Current methods of DTV pilot tone sensing rely on an accurate knowledge of received noise power. A signal energy contained within a narrow frequency band centered at the anticipated pilot tone position is compared against a threshold that is based on knowledge of, or an estimate of, the noise present in the channel. This technique is vulnerable to inaccuracies in the estimation of the noise, which often causes substantial degradation in performance. Furthermore, the presence of unwanted interfering tones within the DTV signal bandwidth can seriously affect DTV pilot tone detection performance.

There therefore exists a need for a method and apparatus that can detect the presence of DTV pilot tones at very low received signal strengths and in the presence of interference.

SUMMARY OF TH E INVENTION

It is therefore an object of the invention to provide a method and apparatus that can reliably detect the presence of DTV pilot tones at low received signal strength and in the presence of interference. The invention therefore provides a DTV pilot sensor, comprising: a spectrum smoothing filter that smoothes a power spectrum of a received television band channel; pilot tone peak search logic that computes a peak signal power of a narrow frequency window centered around a designated DTV pilot position of the output of the spectrum smoothing filter; conditioned signal power estimation logic that estimates an average received signal power in a wide frequency window located in a designated data portion of the output of the spectrum smoothing filter; and pilot tone detection logic that compares an output of the pilot tone peak search logic with a product of an output the conditioned signal power estimation logic multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected.

The invention further provides a method of sensing a DTV pilot tone in a television band, comprising: tuning a radio frequency front end to a frequency associated with a television channel in the television band; smoothing a power spectrum of a received signal associated with the television channel; searching a narrow frequency window centered around a designated DTV pilot position of the smoothed power spectrum to locate a peak power of the narrow frequency window; estimating an average power of a wide frequency window located in a designated data portion of the smoothed power spectrum; and comparing the peak power of the narrow frequency window with a product of the average power of the wide frequency window multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected.

The invention yet further provides a TV band device comprising: pilot tone peak search logic that searches for a peak signal power in a narrow frequency window centered around a designated DTV pilot position of a smoothed power spectrum of a signal associated with a television band channel; conditioned signal power estimation logic that estimates an average received signal power in a wide frequency window located in a designated data portion of the smoothed power spectrum; and pilot tone detection logic that compares an output of the pilot tone peak search logic with a product of an output the conditioned signal power estimation logic multiplied by a programmable power ratio to determine whether a DTV pilot tone has been detected.

BRI EF DESCRI PTION OF TH E DRAWINGS

Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a television band device provisioned with a sensor in accordance with the invention for detecting pilot tones in television band channels; FIG. 2 is a schematic diagram of ATSC sensing windows in accordance with one embodiment of the invention;

FIG. 3 is a schematic diagram of an exemplary embodiment of the pilot window peak search with higher order interpolation function of the sensor shown in FIG. 1 ; FIG. 4 is a schematic diagram of an exemplary embodiment of the interference mitigation and conditioned signal power estimation function of the sensor shown in FIG. 1 ; and FIG. 5 is a flow chart of one embodiment of a DTV pilot sensing process used by the television band device shown in FIG. 1 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a method and apparatus for detecting a DTV pilot tone in VHF/UHF television channels. DTV pilot tone detection logic searches for a pilot tone in a DTV pilot position of a smoothed power spectrum derived from a monitored down-converted UHF/VHF signal. The apparatus generates a DTV pilot tone detection decision associated with each monitored television channel. FIG. 1 is a schematic diagram of a television band device 20 provisioned with a DTV pilot tone sensor in accordance with the invention. As understood by those skilled in the art, the sensor components shown in FIG. 1 and described below may also be used for other receiver and/or signal processing functions in addition to the DTV pilot tone sensing performed by the television band device 20. It should further be understood by those skilled in the art that the DTV pilot tone sensing performed by the television band device 20 described below is performed in accordance with the provisions of the Advanced Television Systems Committee (ATSC) standard A/53 (ATSC Digital Television Standard, Parts 1 - 6, 2027). However, the methods described below can be adapted to other international television standards without departing from the scope of the invention.

The television band device 20 is equipped with a television band antenna 24, the structure and function of which is well known in the art. The antenna 24 receives television band signals 25 transmitted by Digital Television (DTV) transmitters, as well as other devices transmitting in the television band. The received signals are passed from the antenna 24 to at least one radio frequency (RF) front end 28 that is designed to selectively segregate one UHF/VHF channel at a time from the received signals. Then at least one RF front end 28 outputs a gain adjusted analog signal that is down-converted to an intermediate frequency representation of the selected channel signal. The analog down-converted signal output by the RF front end(s) 28 is passed to an analog-to-digital (A/D) converter 30, which samples the analog signal at a sampling rate of, for example, 100 MHz to convert the analog intermediate frequency to a digital signal. The digital signal is passed to an automatic gain controller (AGC) 31 , which controls the amplitude of the digital signal in a manner well known in the art. The gain-controlled signal is passed to a band pass filter 32, which filters out low and high frequency components. The filtered signal is passed to a second AGC 33, which controls the amplitude of the band pass filtered signal. The output of the AGC 33 is passed to a digital down converter and decimator 34, which down converts and decimates the gain-controlled signal and outputs a down-converted signal 35. In accordance with one embodiment of the invention, the down-converted signal 35 is centered at 5.381 MHz, which corresponds to half the ATSC symbol rate. The down- converted signal 35 is received by a Fast Fourier Transform (FFT) and power spectrum computation section 36. The FFT and power spectrum computation section 36 processes the down-converted signal 35 and outputs a power spectrum of the down-converted signal as a serial data stream to a spectrum smoothing filter 38, which smoothes the power spectrum using a power spectrum smoothing algorithm. The power spectrum smoothing algorithm may be, for example, an exponential averaging algorithm that averages a current cycle output with a previous cycle average using predetermined weighting ratio(s). The serial output of the spectrum smoothing filter 38 is passed in parallel via a signal path 39a to pilot window peak search logic 40 and via signal path 39b to conditioned signal power estimation logic 42. The pilot window peak search logic 40 searches for a peak received signal power within a specified window centered on the designated DTV pilot position, as will be explained below in more detail with reference to FIG. 3. The conditioned signal power estimation logic 42 estimates an average power of the conditioned signal within a second window located in a data portion of the frequency band of the VHF/UHF channel, as will be explained below with reference to FIG. 4. Output of the pilot window peak search logic 40 is passed via signal path 44a to pilot tone detection logic 50. Output of the conditioned signal power estimation logic 42 is passed via signal path 44b to the pilot tone detection logic 50. The pilot tone detection logic 50 determines the presence or absence of a DTV pilot tone by comparing the peak received signal power computed within the narrow window with the average conditioned signal power level estimated in the second window to determine a ratio of the two signal powers, and comparing the ratio to a predetermined threshold, as will be explained below with reference to FIG. 5.

FIG. 2 is a schematic diagram of one embodiment of the DTV pilot tone sensing windows used by the TV band device 20 shown in FIG. 1 . DTV pilot tone sensing window-1 (W-1 ) 102 is a narrow window having a width in frequency of Δ/ι and FFT indices [n n 2 ]. W-1 is centered in the 6 MHz DTV signal 100 at the designated frequency location for the DTV pilot tone 106. In one embodiment f \ is about 30-40 KHz, but may be in a range of 30-60 KHz. The DTV sensing window-2 (W-2) 1 04 has a width in frequency of Δί 2 and respective FFT indices [n 3 , n 4 ]. The DTV sensing W-2 104 is located in the DTV data portion of the 6 MHz channel 1 00. In one embodiment, 2 is about 2-4.5 MHz. The width in frequency and position of DTV sensing window-2 (W-2) 104 is largely a matter of design choice though W-2 may not overlap the bandwidth occupied by window-1 (W-1 ) 102.

FIG. 3 is a schematic diagram of one embodiment of the pilot window peak search logic 40 shown in FIG. 1 . As will be understood by those skilled in the art, this embodiment is exemplary only and other ways of implementing this logic are within the grasp of the skilled artisan. As explained above, the down- converted signal 35 is processed by the FFT and power spectrum computation section 36, which outputs respective FFT bin values to the spectrum smoothing filter 38. The spectrum smoothing filter smoothes the FFT outputs using, for example, the exponential averaging algorithm. At the beginning of each FFT cycle, the spectrum smoothing filter 38 outputs a start-of-cycle signal over connection 51 to a cycle counter 52, which increments a cycle count and compares the cycle count to at least one programmable variable. In one embodiment two programmable variables, N av -l and N av , are used and N av is set to 1024. Concurrently, the spectrum smoothing filter outputs the smoothed power spectrum values via connection 53 to a W-1 interpolation filter 54, which selects the smoothed power spectrum values associated with FFT indices [n 1r n 2 ]. The W-1 interpolation filter 54 is a finite impulse response (FIR) lowpass filter, or an infinite impulse response (MR) lowpass filter, that can estimate power peaks that occur between data samples. In one embodiment of the invention, the W-1 interpolation filter is passive until it receives a flag from the cycle counter 52 via connection 55a indicating that the next cycle of outputs from the spectrum smoothing filter 38 is to be processed using a programmable interpolation factor M and programmable filter coefficients (filter tap weights), respectively retrieved from random access memory (RAM) or electrically erasable programmable read only memory (EEPROM) 56. The interpolation factor M is used by the W-1 interpolation filter 54 to increase the sample rate of the output of the spectrum smoothing filter 38, i.e. up-sample the output of the spectrum smoothing filter 38. In one embodiment of the invention, M = 2. In another embodiment of the invention, M = 4, though other interpolation factors may also be used. The W-1 interpolation filter coefficients (filter tap weights) are used to shape the up- sampled outputs of the smoothing filter 39 in a manner known in the art. As explained above, the W-1 peak search logic 59 is passive until it receives the flag via connection 57a from the cycle counter 52 indicating that current outputs from the spectrum smoothing filter 38 are to be processed. Depending on the computational speed of the TV band device 10, that flag may be the A/ ai/ -1 or the N av i\ag. The W-1 peak search logic 59 then examines the interpolated outputs 58 in the cycle for a distinct single peak power level. If a distinct single peak power level is detected, that power level is output via connection 44a to the pilot tone detection logic 50 (FIG. 1 ). If a distinct single peak power level is not detected, any one of the peak power levels is selected and output via the connection 44a to the pilot tone detection logic 50. FIG. 4 is a schematic diagram of one embodiment of the interference mitigation and conditioned signal power estimation logic 42. In the same way as explained above with reference to FIG. 3, the cycle counter 52 counts FFT cycles and outputs the target flag via connection 55b to W-2 signal conditioner 60, which includes logic to set signal conditioning limits on receipt of the target flag. The signal conditioner logic sets the signal conditioning limits in any one or more of various ways. For example: - a programmable constant K } indicating the number of highest power levels and a programmable constant K2 indicating the number of lowest power levels to be eliminated from the W-2 power levels;

- a programmable constant L indicating a number of median power levels to be used for signal conditioning (i.e., the median power level is computed, and the L power levels closest to the median power level are output as the conditioned signal, and all other power level values are eliminated or ignored).

- the target cycle output is examined and dynamic high and low hard power limits are set using knowledge about the expected power level of the ASTC data portion of a 6 MHz TV channel to reduce an impact of high power levels and/or low power levels on an average power level of the conditioned signal;

- trained signal artifacts are used to condition the W-2 signals. Trained signal artifacts are known device-generated interfering frequencies and/or channel-dependent interfering tones that are identified and their frequencies are stored during an initial and/or long-term training process.

It should be understood that the signal conditioning logic of signal conditioner 60 may be programmed to use any two or more of these signal conditioning techniques to condition signals in the target cycle after the signal conditioning limits are set. It should also be understood that the limit setting and the signal conditioning can be accomplished in the same cycle if the computing cycles required to do so permit it. In either event, in the target cycle(s), the signal conditioning limits are applied to the outputs of the spectrum smoothing filter by the signal conditioning logic and the conditioned signal 61 is passed to the W-2 conditioned signal power estimation logic 62, which estimates an average power level of the conditioned signal 61 . The average conditioned signal power level is passed via connection 44b to the pilot tone detection logic 50, which makes a pilot tone detection decision, as will be explained below with reference to FIG. 5.

FIG. 5 is a flow chart of one embodiment of a sensing process used by the DTV pilot sensor of the television band device 20 shown in FIG. 1 . The process begins by setting (200) a channel index to an initial starting channel number in a stored list of channels to be scanned. As explained above, the RF front end 28 is tuned (202) to a first UHF/VHF channel in the channel index, and the cycle counter 52 is initialized (203). The received signal is band pass filtered (204), down converted and decimated (206), and processed (208) by the FFT and power spectrum computation section 36. The power spectrum output by the FFT and power spectrum computation section 36 is smoothed (21 0) by the spectrum smoothing filter 38, which outputs the smoothed power spectrum. The smoothed power spectrum is continuously output to the DTV pilot window peak search logic 40 and the conditioned signal power estimation logic 42, but that output is not processed until a predetermined number of cycles of the power spectrum outputs have been averaged by the spectrum smoothing filter 38, as will be explained below in more detail. Consequently, at the beginning of each power spectrum output cycle it is determined ( 212) if a current number N of cycles of the power spectrum outputs averaged by the spectrum smoothing filter 38 is equal to the pre-programmed target {N av ). If not, the cycle counter continues to be incremented with each smoothed power spectrum output cycle until N= Target, at which time the parallel processes of W-1 peak power searching and W-2 signal conditioning parameter computation and conditioned signal power estimation is begun.

Subsequently, the W-1 interpolation filter 54 performs signal interpolation (220) as described above with reference to FIG. 3. W-1 peak search logic 59 then searches (222) for the maximum signal power level of W-1 1 02, as also described above with reference to FIG. 3. Concurrently, the W-2 signal conditioner 60 computes (223) the signal conditioning parameters as described above. The W-2 signal conditioner 60 applies (224) the signal limits computed at (223) to condition the W-2 signal outputs of the spectrum smoothing filter 38, and the W-2 conditioned signal power estimation logic 62 computes (226) the average power of the conditioned signal 61 , as described above with reference to FIG. 4. The pilot tone detection logic 50, which receives the W-1 peak received signal power and W-2 estimated average power of the conditioned signal 61 , then determines (228) a power ratio (PR) for pilot tone detection by comparing the W-1 peak power with a product of the W-2 average power multiplied by a predetermined power ratio (<5). If it is determined (230) that the W-1 peak power is greater than the product, a positive pilot tone detection decision is output for the current sensing period; otherwise a negative pilot tone detection decision is output for the current sensing period. The predetermined power ratio δ is a programmable value set to keep the false alarm rate below a predetermined limit, for example 10%. In one embodiment of the invention, the predetermined power ratio 5 = 2.

After the pilot tone detection decision is made (230), a channel status matrix is updated (232) by the pilot tone detection logic 50, which combines the current pilot tone detection decision with any previous pilot tone detection decisions for the current channel in a channel status matrix (not shown). It is then determined (234) if the designated total scan time (currently 30 seconds) has elapsed. If so, all channels have been scanned at least once and the process ends. If not, it is determined (236) if another channel remains to be scanned. If so, the channel index is incremented (238) to the next channel in the channel index to be scanned and the process repeats from (202). If not, the channel index is reset (200) again to the first UHF/VHF channel to be scanned and the process repeats from (202). As will be understood by those skilled in the art, the initial list of channels to be scanned may be refined based on the results of the first scan through the list. If strong DTV signals are sensed in some channels, those channels may be removed from the list of channels to be scanned. That affords more sensing time for the remaining channels to be scanned. Using the methods described above each of the channels in the channel scan index will normally be scanned several times before the total scan time has elapsed.

The embodiments of the invention described above are intended to be only exemplary, and not a complete description of every algorithm that could be used to detect a DTV pilot tone using the methods in accordance with the invention. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.