WO2008054392A1

WO2008054392A1 - A co-channel interference detector

Info

Publication number: WO2008054392A1
Application number: PCT/US2006/042842
Authority: WO
Inventors: Aaron Reel Bouillet
Original assignee: Thomson Licensing
Priority date: 2006-11-01
Filing date: 2006-11-01
Publication date: 2008-05-08
Also published as: KR20090086976A; US20100029235A1; CN101536323A; EP2087600A1; JP2010508757A

Abstract

A receiver searches for and identifies the locations of narrowband interference by sweeping across a wideband frequency channel to measure power levels of at least three narrowband frequency regions and determines if at least one interfering signal is present as a function of the measured power levels.

Description

A CO-CHANNEL INTERFERENCE DETECTOR

BACKGROUND OF THE INVENTION

[0001] The present invention generally relates to communications systems and, more particularly, to a receiver. [0002] In some communications systems it is desirable to detect the presence of an incumbent signal or a co-channel interfering signal. For example, during the transition from analog to digital terrestrial television in the United States, both analog NTSC (National Television Systems Committee) based transmissions and digital ATSC-HDTV (Advanced Television Systems Committee-High Definition Television) based transmissions are expected to co-exist for a number of years. As such, an NTSC broadcast signal and an ATSC broadcast signal may share the same 6 MHz wide (millions of hertz) channel. This is illustrated in FIG. 1, which shows the relative spectral positions of the NTSC signal carriers (video, audio and chroma) with respect to the digital VSB (Vestigial Sideband) ATSC signal spectrum. Thus, an ATSC receiver must be able to efficiently detect and reject NTSC co- channel interference.

[0003] Likewise, a Wireless Regional Area Network (WRAN) system is being studied in the IEEE 802.22 standard group. The WRAN system is intended to make use of unused television (TV) broadcast channels in the TV spectrum, on a non-interfering basis, to address, as a primary objective, rural and remote areas and low population density underserved markets with performance levels similar to those of broadband access technologies serving urban and suburban areas. In addition, the WRAN system may also be able to scale to serve denser population areas where spectrum is available. As such, since one goal of the WRAN system is not to interfere with TV broadcasts, a critical procedure is to robustly and accurately sense the licensed TV signals (incumbent signals) that exist in the area served by the WRAN (the WRAN area).

SUMMARY OF THE INVENTION

[0004] In accordance with the principles of the invention, a receiver searches for and identifies the locations of narrowband interference by sweeping across a wideband frequency channel to measure power levels of at least three narrowband frequency regions and determines if at least one interfering signal is present as a function of the measured power levels. [0005] In an illustrative embodiment of the invention, a receiver includes an equalizer having a programmable finite impulse response (FIR) filter and a power detector. The FIR is swept across a wideband frequency channel for measuring power levels of three narrowband frequency regions and the power detector determines if an interfering signal is present as a function of the measured power levels.

[0006] In another illustrative embodiment of the invention, a receiver includes a local oscillator (LO), a filter bank having a number of filters and a power detector. The local oscillator sweeps across a wideband frequency channel for down-converting a received signal. The down converted received signal is applied to the filter bank, which filters three0 narrowband frequency regions as the LO sweeps across the wideband frequency channel. The power detector measures the power levels in the three narrowband frequency regions and determines if an interfering signal is present as a function of the measured power levels. [0007] In another illustrative embodiment of the invention, the receiver is an ATSC receiver and the receiver sweeps for an interfering co-channel NTSC signal. 5 [0008] In another illustrative embodiment of the invention, the receiver is a WRAN receiver, and the receiver sweeps for an interfering incumbent signal. [0009] In view of the above, and as will be apparent from reading the detailed description, other embodiments and features are also possible and fall within the principles of the invention. 0 BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows a comparison of an NTSC signal spectrum and a ATSC signal spectrum;

[0011] FIG. 2 shows an illustrative high-level block diagram of a receiver embodying the principles of the invention; 5 [0012] FIG. 3 shows an illustrative flow chart in accordance with the principles of the invention;

[0013] FIG. 4 shows a frequency spectrum illustrating the inventive concept;

[0014] FIG. 5 shows another frequency spectrum illustrating the inventive concept;

[0015] FIG. 6 shows an illustrative embodiment in accordance with the principles of the i0 invention;

[0016] FIG. 7 shows another illustrative embodiment in accordance with the principles of the invention; [0017] FIG. 8 shows another illustrative embodiment in accordance with the principles of the invention; and

[0018] FIGs. 9 and 10 show an illustrative embodiment of a narrowband interference remover.

DETAILED DESCRIPTION

[0019] Other than the inventive concept, the elements shown in the figures are well known and will not be described in detail. Also, familiarity with television broadcasting and receivers is assumed and is not described in detail herein. For example, other than the inventive concept, familiarity with current and proposed recommendations for TV standards such as NTSC (National Television Systems Committee), PAL (Phase Alternation Lines), SECAM (SEquential Couleur Avec Memoire), ATSC (Advanced Television Systems Committee) (ATSC) and VBI encoding is assumed. Likewise, other than the inventive concept, transmission concepts such as eight-level vestigial sideband (8-VSB), Quadrature Amplitude Modulation (QAM), and receiver components such as a radio-frequency (RF) front-end, or receiver section, such as a low noise block, tuners, and demodulators is assumed. Similarly, formatting and encoding methods (such as Moving Picture Expert Group (MPEG)-2 Systems Standard (ISO/IEC 13818-1)) for generating transport bit streams are well-known and not described herein. It should also be noted that the inventive concept may be implemented using conventional programming techniques, which, as such, will not be described herein. Finally, like-numbers on the figures represent similar elements.

[0020] A high-level block diagram of an illustrative device 10 in accordance with the principles of the invention is shown in FIG. 2. Device 10 includes a receiver 15. As described below, receiver 15 functions in accordance with the principles of the invention for receiving a broadcast signal 11 and for providing an output signal 12. Illustratively, device 10 may be a set-top box (cable, satellite, etc.), TV set, personal computer, mobile phone (e.g., with video output), etc. In this regard, the output signal 12 may be further processed by device 10 (as represented by the ellipses 13) before being transmitted to another device, or provided to a display, as represented by dashed arrow 14. For example, in the context of a set-top box, dashed arrow 14 may represent a re-modulated video signal (e.g., at a frequency corresponding to channel 4); or, in the context of a flat-panel TV, dashed arrow 14 may represent a base band video signal before application to a display element (e.g., a flat-panel, cathode-ray-tube (CRT), etc.). 10021] In this example, receiver 15 is an ATSC-compatible receiver. However, the inventive concept is not so limited and receiver 15 may be part of a WRAN system, e.g., a part of customer premise equipment (CPE), which may be stationary or mobile. In this ATSC illustration, it should also be noted that receiver 15 may be NTSC-compatible, i.e., have an NTSC mode of operation and an ATSC mode of operation such that receiver 15 is capable of processing video content from an NTSC broadcast or an ATSC broadcast. In this regard, receiver 15 is an example of a multimedia receiver. However, in the context of this description, the ATSC mode of operation is described. Receiver 15 receives a broadcast signal 11 (e.g., via an antenna (not shown)) for processing to recover therefrom an output video signal 12, e.g., an HDTV signal for application to a display (not shown) for viewing video content thereon. As noted above, and shown in FIG. 1, broadcast signal 11 is a wideband signal and may include not only a broadcast ATSC signal but also interference from a co-channel broadcast NTSC signal. In this regard, receiver 15 of FIG. 2 includes a rejection filter (not shown), for removing the NTSC signal interference and, in accordance with the principles of the invention, also includes an interference detector.

[0022] Turning now to FIG. 3, an illustrative flow chart in accordance with the principles of the invention for use in receiver 15 is shown. At this point reference should also be made to FIG. 4, which illustrates operation of the inventive concept with respect to an illustrative wideband frequency channel 51. As can be observed from graph 60 of FIG. 4, a wideband frequency channel 51 is divided into N-2 narrowband frequency regions (52). These narrowband frequency regions have the same bandwidth. However, the inventive concept is not so limited. In addition, at the boundaries of wideband frequency channel 51, two additional narrowband frequency regions are designated, 53 and 54. As such, the total number of narrowband frequency regions is N. In accordance with the principles of the invention, these N narrowband frequency regions are examined in groups of K to determine if a narrowband interfering signal is present. In this example, K = 3. Returning to FIG. 3, in step 305, receiver 15 selects the first three narrowband frequency regions. The three selected narrowband frequency regions are designated as A, B and C. This is also illustrated in FIG. 4 in graph 61. In step 310, receiver 15 filters the received signal in these three narrowband frequency regions and, in step 315, receiver 15 measures the corresponding power levels, PA, PB and Pc of the resulting narrowband signals. Other than the inventive concept, these power measurements can be done as known in the art, e.g., either through dedicated multiply-and-accumulate hardware, or a microprocessor routine that reads stored filter output samples and performs the multiply accumulate through a software routine. After having measured the power levels of any signals in the three narrowband frequency regions, receiver 15 calculates a power parameter as a function of the measured powered levels, P_A and Pc, of the outer narrowband frequency regions in step 320. In this example, the following power parameter is determined:

P_sum = (P_A + Pc)/2. (1)

However, it should be noted that the inventive concept is not so limited and other equations could be used. For example, the measurement performed in equation (1) can be averaged to take into account any spectrum tilt due to multipath effects. Further, other linear or nonlinear combinations may be used. Finally, in step 325, receiver 15 compares the measured power level P_B of the middle narrowband frequency region to P_sum. If the measured power level P_B is less than, or equal to, P_sum, then receiver 15 checks in step 330 if the entire wideband frequency channel has been swept. If the entire wideband frequency channel has not been swept yet, then receiver 15 selects the next three narrowband frequency channels. This is illustrated in graph 62 of FIG. 4. As such, the next three narrowband frequency regions are again designated as narrowband frequency regions A, B and C and receiver 15 repeats steps 310, etc. Thus, it can be observed from FIG. 4, that the entire wideband frequency channel 51 is swept in the direction of arrow 66 for the presence of a narrowband interfering signal. On the last pass (pass N-2), illustrated in graph 63 of FIG. 4, the last three narrowband frequency regions are examined. It can also be observed from FIG. 4, in view of step 325 of FIG. 3, that the narrowband regions 53 and 54 at the boundary facilitate the examination of the first and last narrowband frequency regions of wideband frequency channel 51. Once receiver 15 determines in step 330 that the entire wideband frequency has been swept without the detection of a narrowband interfering signal, receiver 15 declares an interfering signal is not present in step 335.

[0023] However, in step 325 of FIG. 3, if the measured power level P_B is greater than P _sum, then receiver 15 declares a narrowband interfering signal is present in step 340. It should be noted that other variations are possible. For example, receiver 15 may declare a narrowband interfering signal is present only when P_B is substantially greater than P_sum. Once it is determined whether a narrowband interfering signal is present or not, receiver 15 continues processing (not shown). For example, in the context of a WRAN system, receiver 15 may mark the wideband frequency channel as unavailable upon detection of a narrowband interferer.

[0024] It should be noted that even though receiver 15 detects a narrowband interferer, it may be the case that the narrowband interferer is merely representative of the presence of a^' co-channel interferer, which can be wideband or narrowband. This is illustrated in FIG. 5 in the context of receiver 15 being part of an ATSC system. FIG. 5 shows an illustrative frequency spectrum for a broadcast ATSC signal 201 and an NTSC co-channel interfering signal as represented by the presence of an NTSC video carrier 202. As can be observed from FIG. 5, and in accordance with the flow chart of FIG. 3, receiver 15 will eventually examine three narrowband frequency regions, 211(A), 212(B) and 213(C). In step 325 of

FIG. 3, receiver 15 will detect the presence of NTSC video carrier 202 within narrowband frequency region 212(B). As such, receiver 15 will declare in step 340 the presence of an

NTSC co-channel interferer. Upon detection of an NTSC co-channel interferer, receiver 15 performs NTSC co-channel interference rejection. NTSC co-channel interference rejection may be performed by a comb filter (e.g., see, United States Advanced Television Systems

Committee, "ATSC Digital Television Standard", Document A/53, September 16, 1995).

The comb filter is a 12 symbol linear feed-forward filter with spectral nulls at or near the

NTSC signal carriers, and is only applied when NTSC interference is detected (e.g., see,

United States Advanced Television Systems Committee, "Guide to the Use of the ATSC Digital Television Standard", Document A/54, October 04, 1995).

[0025] In view of the above, and in accordance with the principles of the invention, a wideband frequency channel is examined, or sampled, for the presence of at least one interfering signal. Although the inventive concept was illustrated in the context of the flow chart of FIG. 3, it should be noted that other variations are possible. For example, a priori knowledge of the frequency characteristics of the possible interfering signals may allow modification of the flow chart of FIG. 3 such that only portions of the wideband frequency channel are examined. Likewise, step 340 may be modified to also record the narrowband frequency region that contains the interfering signal. Similarly, it may be the case that the sweep continues even after the detection of a first interfering signal to determine the presence and/or location of other interfering signals. Finally, although arrow 66 of FIG. 4 illustrated one particular direction for the sweep, the wideband frequency channel, or portions thereof, can be examined in any order or direction. [0026] Turning now to FIG. 6, an illustrative portion of receiver 15 including an interference detector in accordance with the principles of the invention is shown for use in the flow chart of FIG. 3. Receiver 15 is a processor-based system and includes one, or more, processors and associated memory (not shown) as represented in dashed line form by processor 190 and memory 195. In this context, the associated memory is used to store computer programs, or software, which is executed by processor 190, and to store data. Processor 190 is representative of one, or more, stored-program control processors and these do not have to be dedicated to the interference detection function, e.g., processor 190 may also control other functions of device 10. Continuing with the description of receiver 15, an RF front-end (not shown) provides a down-converted signal 109. Down-converted signal 109 is provided to A/D converter 110, which samples the down converted signal 109 to convert the signal to the digital domain and provide a sequence of samples 111 to demodulator 115. The latter comprises automatic gain control (AGC), symbol timing recovery (STR), carrier tracking loop (CTL), and other functional blocks as known in the art for demodulating signal 111 to provide demodulated signal 116 to equalizer 120. The equalizer 120 includes a programmable finite impulse response (FIR) filter (not shown) for processing demodulated signal signal 116 in accordance with the principles of the invention. It should be noted that equalizer 120 is not adapting to the input signal. In particular, equalizer 120 is "frozen" and taps of the FIR section have been programmed to be a bandpass filter at some specific spectral location. It should also be noted that it is possible to implement an infinite impulse response (IIR) filter to achieve the same effective power response as a bandpass filter. In fact, since the phase properties of the output signal are irrelevant in this application, use of an IIR filter may lead to a simplified implementation. Equalizer 120 provides signal 121 to power detector 125, which processes signal 121 in accordance with the principles of the invention and provides a signal 126, which is representative of whether or not an interfering signal is present. In particular, for every K = 3 narrowband frequency regions, processor 190 sets, via control signal 119, the programmable FIR of equalizer 120 to one of the narrowband frequency regions A, B and C, for filtering demodulated signal 116 (step 310 of FIG. 3). Processor 190 controls, via control signal 119, power detector 125 for measuring a corresponding power level PA, P_B and Pc, of signal 121 when equalizer 120 is tuned to narrowband frequency region A, B and C, respectively (step 315 of FIG. 3). After having measured the power levels of any signals in the three narrowband frequency regions, power detector 125 calculates P_sum in accordance with equation (1) (step 320 of FIG. 3). Finally, power detector 125 compares the measured power level P_B to P_sum (step 325 of FIG. 3). If power detector 125 does not declare an interfering signal is present, via signal 126, processor 190 continues to sweep the wideband frequency channel, as described above, and selects the next three narrowband frequency regions. However, if power detector 125 declares, via signal 126, that an interfering signal is present (step 340 of FIG. 3), processor 190 marks the narrowband frequency region as containing an interfering signal. [0027] Referring now to FIG. 7, another illustrative embodiment of an interference detector 400 for use receiver 15 in accordance with the principles of the invention is shown for use in the flow chart of FIG. 3. Illustratively, detector 400 is a processor-based system and includes one, or more, processors and associated memory (not shown) as represented in dashed line form by processor 490 and memory 495. Detector 400 comprises a sweep local oscillator (LO) 450, a multiplier (mixer) 405, selection filters 410 and 430, power detectors 415 and 435, divide by 2 element 440, adder 420 and threshold comparator 425. The frequency of sweep LO 450 is adjusted by processor 490 via control signal 451. Selection filters 410 and 430 represent a lowpass filter and a bandpass filter, respectively. Lowpass filter 410 has an illustrative frequency response 481 for filtering the middle narrowband frequency region B. Similarly, bandpass filter 430 has an illustrative frequency response 482 for filtering the outer narrowband frequency regions A and C. As a result, three narrowband frequency regions are filtered as illustrated by frequency response 483. As the frequency of sweep LO 450 is adjusted by processor 490 (step 305 of FIG. 3), multiplier 405 frequency shifts input signal 404 to provide a signal 406 to lowpass filter 410 and bandpass filter 430. Signal 406 is also referred to herein as the "conversion image" of signal 404_* As a result, by changing the frequency of sweep LO 450 the frequency range of signal 406 can be shifted such that selection filters 410 and 430 filter different regions of the wideband frequency channel. As such, lowpass filter 410 filters the middle narrowband frequency region B and bandpass filter 430 filters the outer narrowband frequency regions A and C for each selected frequency region of the wideband frequency channel (step 310 of FIG. 3). The sweep LO signal can move in steps, then wait for the power detectors 415 and 435 to accumulate enough samples from filtered signals 411 and 431, respectively, to provide measured power levels 416 and 436, respectively. As described above, power detector 415 provides measured power level PB, via signal 416, and power detector 435 provides the sum of P_A and Pc, via signal 436, which is then divided by two by element 440 to provide P_sum, via signal 441 (steps 315 and 320). Adder 420 subtracts P_sum from P_B and provides the resultant signal 421 to threshold comparator 425 for indicating the presence of an interfering signal via 5 signal 426 (steps 325 and 340). If no interfering signal is detected, then the frequency of sweep LO is adjusted to examine the next three narrowband frequency regions, etc. As such, detector 400 can examine a wideband frequency channel either in its entirety, or, portions thereof, for the presence of an interfering signal.

[0028] Another illustrative embodiment of the inventive concept is shown in FIG. 8. In 0 this illustrative embodiment an integrated circuit (IC) 605 for use in a receiver (not shown) includes a power detector 620 and at least one register 610, which is coupled to bus 651. Illustratively, IC 605 is an integrated analog/digital television decoder. However, only those portions of IC 605 relevant to the inventive concept are shown. For example, analog-digital converters, filters, decoders, etc., are not shown for simplicity. Bus 651 provides5 communication to, and from, other components of the receiver as represented by processor 650. Register 610 is representative of one, or more, registers, of IC 605, where each register comprises one, or more, bits as represented by bit 609. The registers, or portions thereof, of IC 605 may be read-only, write-only or read/write. In accordance with the principles of the invention, power detector 620 includes the above-described interference detector feature, or0 operating mode, and at least one bit, e.g., bit 609 of register 610, is a programmable bit that can be set by, e.g., processor 650, for enabling or disabling this operating mode. In the context of FIG. 8, IC 605 receives an IF signal 601 for processing via an input pin, or lead, of IC 605. A derivative of this signal, 602, is applied to power detector 620 for interference detection as described above. Power detector 620 provides signal 621, which is indicative of >5 whether or not an interfering signal has been detected. Although not shown in FIG. 8, signal 621 may be provided to circuitry external to IC 605 and/or be accessible via register 610. Power detector 620 is coupled to register 610 via internal bus 611, which is representative of other signal paths and/or components of IC 605 for interfacing power detector 620 to register 610 as known in the art (e.g., to read the earlier-described integrator and counter values). IC 10 605 provides one, or more, recovered signals, e.g., a composite video signal, as represented by signal 606. It should be noted that other variations of IC 605 are possible in accordance with the principles of the invention, e.g., external control of this operating mode, e.g., via bit 610, is not required and IC 605 may simply always perform the above-described processing for sweeping a wideband ^"frequency channel for an interfering signal. [0029] As noted above, it may be the case that, upon detection of an interfering signal, receiver 15 attempts to remove, or reject, the interfering signal. An example of this is provided by the above-mentioned comb filter in the context of an NTSC co-channel interfering signal for use in an ATSC system. As such, the method of removing NTSC co- channel interference is typically to leave the comb filter enabled in the data path and compensate for its presence in a convolutional decoder (not shown) of the receiver. This adds much complexity and cost to the hardware implementation. In this regard, another illustrative narrowband interference remover 800 is shown in FIGs. 9 and 10 that reduces this complexity and cost. It should be noted that narrowband interference remover 800 is not limited to removing NTSC co-channel interference and can be used to remove other types of narrowband interference. [0030] Narrowband interference remover 800 comprises multipliers (mixers) 805 and 845, frequency synthesizer 850, selection filters 810, 815 and 820, power detectors 825 and 830, and adder 835. Frequency synthesizer 850 is alerted to the detection of a narrowband interfering signal, e.g., via signal 426 of FIG. 7. In this example, it is assumed that signal 426 also includes information as to the narrowband frequency region containing the interfering signal. Upon detection of a narrowband interfering signal, frequency synthesizer 850 generates a frequency, via signal 852, to multiplier 805 for frequency shifting input signal 804, which is representative of the received wideband signal, for removing the presence of a detected narrowband interfering signal. In this regard, selection filters have frequency responses as illustrated in FIG. 10. In particular, multiplier 805 moves the narrowband interference to DC and selection filter 810 attenuates the interferer via a notch- type response as illustrated by frequency response 701. As a result, selection filter 810 removes the detected narrowband interference and provides filtered signal 811 to multiplier 845. The latter receives a complimentary frequency from frequency synthesizer 850, via signal 851, so that the signal spectrum of output signal 846 is restored to its input spectral location (i.e., the same as that of input signal 804). Selection filters 815 and 820 filter frequency regions adjacent to the detected narrowband interference as illustrated by frequency responses 702 and 703. [0031] It should be noted that selection filters 815 and 820 act to keep the selection filter 810 squarely on the interference in the event that the interferer drifts in frequency after detection or if the initial frequency estimate is slightly in error. For example, if the interference drifts down in frequency, i.e., more toward the frequency region of selection filter 815, then the power level of signal 816 as detected by power detected 825 will increase, while the power level of signal 821, from selection filter 820, as detected by power detected 830 will decrease. Adder 835 is used to generate an error signal 836 from the measured power levels 826 and 831 provided by power detector 825 and 830, respectively. Frequency synthesizer 850 is responsive to error signal 836 to suitably adjust the frequency of signal 852 to reduce its frequency output — thus tracking the narrowband interference. In like fashion, the converse holds for the case where the interferer drifts up in frequency, i.e., more toward the frequency region of selection filter 820. In this case, error signal 836 causes frequency synthesizer 850 to increases the frequency of signal 852. It should be noted that the embodiment of FIG. 9 can be modified to handle multiple interfering signals. For example, in order to handle N multiple narrowband interferers, N detector circuits described above can be implemented in parallel to drive a corresponding N set of interference rejection circuits operating in series.

[0032] The foregoing merely illustrates the principles of the invention and it will thus be appreciated that those skilled in the art will be able to devise numerous alternative arrangements which, although not explicitly described herein, embody the principles of the invention and are within its spirit and scope. For example, although illustrated in the context of separate functional elements, these functional elements may be embodied on one or more integrated circuits (ICs). Similarly, although shown as separate elements, any or all of the elements may be implemented in a stored-program-controlled processor, e.g., a digital signal processor or microprocessor, which executes associated software, e.g., corresponding to one or more of the steps shown in FIG. 3. For example, the above-described power detector 125 of FIG. 6 may be representative of hardware, and/or one or more software subroutines that processes the received signal. Further, although shown as elements bundled within receiver 15, the elements of receiver 15 may be distributed in different units or devices. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method for use in a receiver, the method comprising: sweeping across a wideband frequency channel to measure power levels of at least three narrowband frequency regions; and determining if at least one interfering signal is present as a function of the measured power levels of the at least three narrowband frequency regions.

2. The method of claim 1, wherein the sweeping step comprises: selecting at least three narrowband frequency regions; filtering the selected narrowband frequency regions for providing respective filtered signals; and measuring resulting power levels of the filtered signals.

3. The method of claim 2, wherein the measuring step includes: (a) measuring a power level of a first signal in a middle narrowband frequency region of the at least three narrowband frequency regions; and

(b) measuring power levels of signals in narrowband frequency regions adjacent to the first narrowband frequency region.

4. The method of claim 3, wherein the determining step includes the steps of: calculating a power parameter as a function of the measured power levels of step (b); comparing the power parameter to the power level of the first signal; and determining if the first signal is an interfering signal in the wideband frequency channel as a function of the comparison.

5. The method of claim 4, wherein the determining as a function of the comparison step determines an interfering signal is present when the power level of the first signal is greater than the power parameter.

6. The method of claim 4, where the power parameter is determined as a function of a linear combination of the power levels of the signals in the narrowband frequency regions adjacent to the first narrowband frequency region.

7. The method of claim 2, wherein the filtering step includes the steps of: setting a filter to a corresponding one of the narrowband frequency regions; and filtering a received wideband signal with the filter for providing a filtered signal; and measuring the power level of the filtered signal.

8. The method of claim 7, wherein the received wideband signal is an ATSC-HDTV (Advanced Television Systems Committee-High Definition Television) signal.

9. The method of claim 7, wherein the received wideband signal is a WRAN

(Wireless Regional Area Network) signal.

10. The method of claim 1, wherein bandwidths of the narrowband frequency regions are the same.

11. Apparatus comprising: a filter for sweeping across a wideband frequency channel to provide at least three filtered narrowband signals from at least three narrowband frequency regions; and a power detector for measuring a power level of each of the at least three filtered narrowband signals and for determining if an interfering signal is present as a function of the measured power levels.

12. The apparatus of claim 11, wherein bandwidths of each narrow band frequency region are the same.

13. The apparatus of claim 11, further comprising: a processor for adjusting the filter to sweep across the wideband frequency channel and for controlling the power detector to measure the power levels.

14. The apparatus of claim 11, wherein the filter is an adjustable narrowband filter for filtering a received wideband signal in at least three narrowband frequency regions for providing at least three filtered narrowband signals.

15. The apparatus of claim 14, wherein the adjustable narrowband filter is part of an equalizer.

16. The apparatus of claim 14, wherein the received wideband signal is an ATSC-

HDTV (Advanced Television Systems Committee-High Definition Television) signal.

17. The apparatus of claim 14, wherein the received wideband signal is a WRAN (Wireless Regional Area Network) signal .

18. The apparatus of claim 11, where the power detector (a) calculates a power parameter as a function of the measured power levels in the outer narrowband frequency regions, (b) compares the power parameter to the measured power level in the middle narrowband frequency region and (c) determines if an interfering signal is present in the wideband frequency channel.

19. The apparatus of claim 18, wherein the power detector determines an interfering signal is present when the measured power level in the middle narrowband frequency region is greater than the power parameter.

20. The apparatus of claim 18, where the power parameter is determined as a function of a linear combination of the power levels of the signals in the outer narrowband frequency regions.

21. The apparatus of claim 11 , wherein the filter comprises: an adjustable local oscillator and a multiplier for use in sweeping across the wideband frequency channel; and at least three selection filters for filtering a received wideband signal provided by the multiplier in the at least three narrowband frequency regions for providing at least three filtered narrowband signals;

22. The apparatus of claim 21, wherein the received wideband signal is an ATSC- HDTV (Advanced Television Systems Committee-High Definition Television) signal.

23. The apparatus of claim 21, wherein the received wideband signal is a WRAN (Wireless Regional Area Network) signal.

24. The apparatus of claim 21, wherein the power detector comprises: a first power detector for measuring a power level of a middle narrowband frequency region; and a second power detector for measuring a power level of outer narrowband frequency regions.

25. The apparatus of claim 24, wherein the power detector includes a threshold detector for determining if an interfering signal is present as a function of the measured power levels.