MX2008005749A - Apparatus and method for sensing an atsc signal in low signal-to-noise ratio - Google Patents

Abstract

A Wireless Regional Area Network (WRAN) receiver includes a tuner for tuning to one of a number of channels, and a broadcast ATSC (Advanced Television Systems Committee) signal detector. The tuner is calibrated as a function of a received ATSC signal. The broadcast ATSC signal detector can be a coherent or a non-coherent ATSC signal detector.

Description

APPARATUS AND METHOD FOR DETECTING AN ATSC SIGNAL (ADVANCED TELEVISION SYSTEMS COMMITTEE) IN A LOW NOISE SIGNAL RELATION Field of the Invention The present invention relates in general to communication systems and more particularly to wireless systems, for example, terrestrial, cellular broadcast, wireless fidelity (WI-FI), satellite, etc.

BACKGROUND OF THE INVENTION A wireless regional area network (WRAN) system is being studied in the IEEE 80222 standard group. The WRAN system is intended to make use of unused broadcast television (TV) channels in the spectrum. TV, on a non-interference basis, to address, as a primary objective to rural and remote areas and low-population markets with similar levels of operation to transmission access technologies that work in urban and suburban areas. The WRAN system may also have the ability to scale to serve in denser population areas where the spectrum is available. Since a goal of the WRAN system is not to interfere with TV transmissions, an important procedure is to detect in a robust manner and Exactly the legal TV signals that exist in the area, offered by the WRAN (the WRAN area) In the United States, the TV spectrum currently c It includes ATSC transmission signals (Advanced Television Systems Committee) that co-exist with NTSC (National Television Systems Committee) transmission signals. ATSC transmission signals are also called digital TV (DTV) signals. Currently, NTSC transmission is will abandon in 2009, and at that time, the TV spectrum will only include ATSC transmission signals. As noted above, one objective of the WRAN system is not to interfere with the TV signals that exist in a particular WRAN area, it is important in a WRAN system have the ability to detect ATSC transmissions A known method to detect the ATSC signal is to look for a small pilot signal that is part of the ATSC signal Such a detector is simple and includes a phase-locked circuit with a very broadband filter narrow to extract the ATSC pilot signal In a WRAN system, this method provides an easy way to verify the transmission channel and is currently in use simply by reviewing whether the ATSC detector provides an extracted ATSC pilot signal. Unfortunately, this method is not accurate, especially in an environment of a very low signal-to-noise (SNR) ratio. In fact, false detection of a signal ATSC can occur when there is a miscellaneous signal present in the band that has a spectral component in the position of the pilot carrier Brief Description of the Invention It has been observed that increasing the accuracy of the time or frequency references of the carrier in the receiver improves the operation of the transmission signal detection techniques (whether these techniques are coherent or non-coherent). In particular and in accordance with the principles of the invention, a receiver comprises a tuner for tuning to a number of channels, a transmit signal detector coupled to the tuner for detecting whether a transmission signal exists in at least one of the channels, wherein the tuner is calibrated as a function of the received transmission signal. In an illustrative embodiment of the invention, the transmission signal is an ATSC signal (Advanced Television Systems Committee) and the receiver is a Regional Area Network receiver. Wireless (WRAN), where the tuner is calibrated as a function of the received ATSC signal and where the transmission signal detector includes a coherent ATSC signal detector In another illustrative embodiment of the invention, a transmission signal is an ATSC signal and the receiver is a WRAN receiver, wherein the tuner is calibrated as a function of the ATSC signal received and wherein the transmission signal detector includes a non-coherent ATSC signal detector. In another illustrative embodiment of the invention, the receiver is a receiver of the Wireless Regional Area Network (WRAN) and the receiver performs a method to determine a frequency band available for communications in the WRAN system. Illustratively, the receiver calibrates itself as a function of the received transmission signal, and after calibration, detects whether there are other transmission signals in at least a portion of the frequency spectrum to determine an available portion of the frequency spectrum to be used by the receiver. above and as will be evident from the reading of the detailed description, other modalities and characteristics are possible and may fall within the principles of the invention Brief Description of the Drawings Figure 1 shows Table One, which lists the television channels (TV) Figures 2 and 3 show Tables Two and Three, which list the frequency offsets under different conditions for a received ATSC signal Figure 4 shows an illustrative WRAN system in accordance with the principles of the invention. Figure 5 shows an illustrative receiver for use in the WRAN system of Figure 4, in accordance with the principles of the invention. Figure 6 shows an illustrative flow diagram for to be used in the WRAN system of Figure 4, in accordance with the principles of the invention. Figures 7 and 8 illustrate the tuner 305 and the tracking circuit 315 of the carrier of Figure 5. Figures 9 and 10 show a format for a signal ATSC DTV, and Figures 11 through 21 show various modalities of ATSC signal detectors Detailed Description of the Invention 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 transmission, receivers, networks and video coding is assumed and not they are described in detail here For example, different from the inventive concept, familiarity is assumed with the current recommendations and proposals for TV standards, such as NTSC (National Television Systems Committee), PAL (Phase Alteration Lines), SECAM (Sequential Couleur Avec) Memoire) and ATSC (Advanced Television Systems Committee) Other information on ATSC transmission signals can be found in the following ATSC standards Digital Television Standard (A / 53), Revision C, including Amendment No. 1 and Errata No. 1, Doc A / 53C, and Recommended Practice Guide to the Use of the ATSC Digital Television Standard (A / 54) In the same way, different from the inventive concept, suppose the concepts of transmission such as eight-level vestigial sideband (8-VSB), Quadrature Amplitude Modulation (QAM), orthogonal frequency division multiplexing (OFDM) or coded (COFDM), and receiver components such as the main radio-frequency (RF) end, or the receiving section, such as the low-noise block, the tuners, and demodulators, correlators, leakagers or leakagers Similarly, different from the inventive concept, the methods formatting and coding (such as the Moving Pictures Experts Group (MPEG-2) systems standard (ISO / IEC 13818-1) for generating transport bitstreams are well known and will not be described here in detail. that the inventive concept can be implemented with the use of conventional programming techniques, which as such, will not be described here. Finally, the same numbers in the Figures represent sim illa A TV spectrum for the United States, as is known in the art, is shown in Table One of Figure 1, which provides a list of TV channels in very high frequency (VHF) and ultra high frequency bands ( UHF) For each TV channel, the corresponding lower edge of the assigned frequency band is shown. For example, TV channel 2 starts at 54 MHz (million hertz), TV channel 37 starts at 608 MHz and the channel 68 of TV starts at 794 MHz, etc. As is known in the art, each TV channel or band, occupies 6 MHz of the bandwidth. As such, TV channel 2 covers the frequency spectrum (or interval) of 54 MHz. at 60 MHz, TV channel 37 spans the band from 608 MHz to 614 MHz and TV channel 68 spans the band from 794 MHz to 800 MHz As mentioned above, a WRAN system makes use of television transmission channels (TV) not used in the TV spectrum With respect to this, the WRAN system carries out a "channel detection" for Determine which of these TV channels is really active (or "operational") in the WRAN area in order to determine that portion of the TV spectrum that is actually available for use by the WRAN system. In addition to the TV spectrum shown in Figure 1, a particular ATSC DTV signal in a particular channel may also be affected by the NTSC signals, or even by other ATSC signals, which are co-located (i.e., on the same channel) or adjacent to the ATSC signal (e.g. , in the next higher or lower channel) This is illustrated in Table Two, of Figure 2, in the context of an ATSC pilot signal as it is affected by different interference conditions. For example, the first row 71 of Table Two provides the displacement of the lower edge in Hz of an ATSC pilot signal, when there is no co-located or adjacent interference of another NTSC or ATSC signal This corresponds to the ATSC pilot signal as defined in the ATSC standards described above, ie the signal pilot is presented at 30944059 KHz (thousands of Hertz) on the lower edge of the particular channel (Again, Table One, of Figure 1 provides the value of the lower edge in MHz for each channel) However, reference is now made to the hi This is labeled as 72 of Table Two, which provides the offset of the lower edge of an ATSC pilot signal, where an NTSC signal is co-located. In such a situation, an ATSC receiver will receive an ATSC pilot signal that is 338065 KHz over the lower edge In the context of NTSC and ATSC transmissions, from Table Two, it can be seen that the total number of possible displacements is 14 However, once the NTSC transmission is discontinued, the total number of possible displacements decreases to two, with a tolerance of 10 Hz, which is illustrated in Table Three of Figure 3 Because it is important that the detection of any channel is accurate, it has been observed that by increasing the accuracy in any reference time or carrier frequency in a receiver, improves the performance of signal detection, or channel detection, techniques (whether these techniques are coherent or non-coherent) In particular and with In accordance with the present invention, a receiver comprises a tuner for tuning to one of a number of channels, a transmit signal detector coupled to the tuner for detecting whether a transmission signal exists in at least one of the channels, where the tuner is calibrated as a function of the received transmission signal An illustrative mode of the invention is described in the context of using an existing ATSC channel as a reference However, the inventive concept is not limited A regional area network system 200 illustrative wireless (WRAN) incorporating the principles of the invention is shown in Figure 4 The WRAN system 200 serves as a geographical area (the WRAN area) (not shown in Figure 4) In general terms, the WRAN system comprises at least less a base station (BS) 205, which communicates with one or more user stations (CPE) 250 The latter may be stationary or mobile CPE 250 is a processor-based system and includes one or more processors and an associated memory, as represented by the processor 290 and the memory 295, shown in the form of dotted boxes in Figure 4. In this context, the computer, or software, are stored in the memory 295 to be executed by the processor 290 The latter is representative of one or more stored program control processors and these do not have to be dedicated to the function of the transmitter, for example, the processor 290 can also control other functions of the CPE 250 The memory 295 is representative of any storage device, for example, a random access memory (RAM), a read-only memory (ROM), etc., can be internal and / or external to CPE 250, and is volatile and / or non-volatile, as needed The physical layer of communication between BS 205 and CPE 250, through antennas 210 and 255, illustratively, is based on OFDM, for example, OFDMA through transceiver 285 and is represented by arrows 211 To enter a WRAN network, the CPE 250 can first "associate" with the BS 210 During this association, the CPE 250 transmits information, through the transceiver 285, with the capacity of the CPE 250 to the BS 205 through a control channel (not shown ) The reported capacity includes, for example, the maximum and minimum transmission power, and a channel list supported for transmission and reception. Regarding this, the CPE 250 carries out a "channel detection" in accordance with the principles of the invention, for the purpose of determining the TV channels that are not active in the WRAN area The resulting list of available channels that is used in the WRAN communications, then sent to the BS 205 An illustrative portion of a receiver 300 for use in the CPE 250 is shown in Figure 5. Only that portion of the receiver 300 relevant to the inventive concept is shown. The receiver 300 comprises a tuner 305, a carrier tracking circuit (CTL) 315, a ATSC signal detector 320 and a controller 325 The latter is representative of one or more stored program control processors, eg, a microprocessor (such as processor 290), and these do not have to be dedicated to the inventive concept, for example , the controller 325 can also control other functions of the receiver 300. In addition, the receiver 300 includes a memory (such as the memory 295), for example, a random access memory (RAM), a read-only memory (ROM), etc. , and may be part of or may be separate from the controller 325 For simplicity, some elements are not shown in Figure 5, such as an automatic gain control element (AGC), an analog to digital converter (ADC) when processing is in the digital domain, and the additional filtering Different to the inventive concept, these elements will be evident to those experienced in the art With regard to this, the described modalities here they may be implemented in the analog or digital domain. Furthermore, those skilled in the art will recognize that certain processing may involve complex signal paths, as necessary. Before describing the inventive concept, the overall operation of the receiver 300 is as follows. 304 input (eg, received through antenna 255 of Figure 4) is applied with tuner 305 Input signal 304 represents a digital VSB modulated signal in accordance with the aforementioned "ATSC Digital Television Standard" and is transmitted on one of the channels shown in Table One of Figure 1 Tuner 305 is tuned to different channels by controller 325 through a bidirectional signal path 326 to select particular TV channels and provides signal 306 converted to descending centered on a specific IF (intermediate frequency) Signal 306 is applied on the CTL 315, which pr ocesa the signal 306 to remove any frequency shift (such as between the local oscillator (LO) of the transmitter and the LO of the receiver) and to demodulate the signal VSB ATSC received in descending to the baseband from an intermediate frequency (IF) or near the baseband frequency, (for example, see United States Advanced Television Systems Committee, "Guide to the use of the ATSC Digital Television Standard," Document A / 54, October 4, 1995), and the Patent United States No. 6,233,295, issued May 15, 2001 to Wang, entitled "Segment Sync Recovery Network for an HDTV Receiver") CTL 315 provides signal 316 to detector 320 of signal ATSC, which processes signal 316 (described below) to determine whether the signal 316 is an ATSC signal. The ATSC signal detector 320 provides the resulting information for the controller 325 through the path 321. Referring now to FIG. 6, a flowchart is shown. Illustrative flow for use in a receiver 300 in accordance with the principles of the invention In particular, detecting the presence of ATSC DTV signals in the VHF and UHF TV bands at signal levels below those required to demodulate a signal that can be improved by having a precise carrier and time-shift information. Illustratively , the stability and the known frequency assignment of the DTV channels themselves are used to provide this information. As specified in the aforementioned ATSC A / 54A ATSC Recommended Practice, the carrier frequencies are specified to be at least 1 KHz (thousands of hertz), and closer tolerances are recommended for good practice With respect to this, in step 260, the controller 325 first scans the known TV channels, such as those illustrated in Table One of Figure 1, for an easily identifiable, existing ATSC signal In particular, the controller 325 controls the tuner 305 to select each of the TV channels The signals result tances (if any) are processed by the ATSC signal detector 320 (described below) and the results are provided to the controller 325 via the path 321 Preferably, the controller 325 searches for the strongest ATSC signal transmitted at that time in the WRAN area However, the controller 325 may stop at the first detected ATSC signal With brief reference to Figure 7, a block diagram of a tuner 305 is shown. The tuner 305 comprises the amplifier 355, the multiplier 600, the filter 365 , a division element between n 370, the voltage controlled oscillator 385 (VCO), the phase detector 375, the circuit filter 390, a division element 380 between m and the local oscillator 395 (LO) Different to the inventive concept, the elements of the tuner 305 are well known and will not be described in more detail. In general, the following relationship is maintained between the signals provided by the LO 395 and the VCO 385 F. F, m (1 ) where Fref is the reference frequency provided by LO 395, Fvco is the frequency provided by VCO 385, n is the value of the divisor represented by division element 370 between n and m is the value of the divisor represented by element 380 of division between m Equation (1) is re-escpbe as F F ni 1 K? nF "m (2) From equation (2) it can be seen that FVco can be adjusted in different ATSC DTV bands with the appropriate values of n, as adjusted by controller 325 (step 260 of Figure 6) through path 326 however , as mentioned before, the receiver 300 includes the CTL 315, which removes any uency shift, Flection There are two uency shifts The first is the error caused by the uency differences between LO 395 and the uency reference of the transmitter. second is the error caused by the value used for Fpaso, since the actual uency, , provided by LO 395 is only approximately known within a given tolerance of the local oscillator. As such, FdeSpiazam? ent includes both the error from the value of nFlow of the selected channel and the error caused by the uency differences in the local uency reference and the uency reference of the transmitter Referring now to Figure 8, an illustrative block diagram of the CTL 315 is shown. The CTL 315 comprises the multiplier 405, a phase detector 410, a cycle filter 415, a numerically controlled oscillator 420 (NCO), and a table. 425 of Sen / Cos. Different from the inventive concept, the elements of the CTL 315 are well known and will not be described here. The NCO 420 determines the FxSpray as is known in the art and these uency shifts are removed from the received signal through the Table 425 of Sen / Cos and multiplier 405 Continuing with step 270 of Figure 6, once an existing ATSC signal is found, controller 325 calibrates receiver 300 by determining at least one related uency (time) characteristic from the detected ATSC signal In particular, the general operation of the receiver 300 of Figure 5 can be represented by the following equation (3) where Fc represents the uency of the pilot signal of the detected ATSC signal With respect to the value for Fdesp? Azamiento in Ia equation (3), the controller 325 determines this value simply by having access to the associated data in NCO 420 , through a bidirectional path 327 However, although this value for n was already determined by controller 325 for the selected ATSC channel, the actual value of F despread is unknown. However, equation (3) is rewritten as "= (4) Although this solution seems straightforward, it can be renamed that the value for Fc is not determined uniquely as suggested by Table One of Figure 1. Rather, the detected ATSC DTV signal may be affected by other NTSC or ATSC signals as shown in Table Two of Figure 2 and Table Three of Figure 3. When there are NTSC and ATSC transmissions in the WRAN region, then they should take into account the 14 possible offsets, as shown in Table Two of Figure 2. However, when there are no NTSC transmissions in the WRAN region, then only two offsets should be taken into account, as shown in the Table. Three of Figure 3. For simplicity, it is assumed that there are no NTSC transmissions and only Table Three is used in this example. As such, with the use of the values in Table One and Table Three (for example, stored in the aforementioned memory), controller 325 performs two calculations to determine different values for Fpaso: F) - F r., "= (4b). wherein Fc (1) represents the lower band edge of Table One for the selected ATSC channel plus the displacement of the lower band edge of the first row of Table Three, and Fc (2) represents the lower band edge of Table One for the selected ATSC channel plus the lower band edge offset of the second row of Table Three As a result, the controller 325 determines two possible values for Fpaso to be used in the receiver 300 Thus, in step 270, the controller 325 determines the tuning parameters to be used in calibrating the receiver 300 Finally, in step 275, the controller 325 scans the TV spectrum to determine the available channel list, which comprises one or more TV channels that are not used and as such, are available to support WRAN communications For each channel that is selected by controller 325 (for example, from the list in Table One), the observations regarding the equations (3), (4), (4a) and (4b) still apply In other words, for each selected channel, the displacements shown in Table Three must be taken into account since there are two displacements shown in Table Three and there are two possible values for Fpaso are determined in step 270 (equations (4a) and (4b)), four scans are carried out (When the displacements listed in Table Two were used, there will be 142 scans or 196 scans) For example, in the first scan, the controller 325 adjusts in tuner 305 through the path 326 in different values for n for each of the ATSC channels. The controller 325 determines the values for n and FdeSpiazam? Ento from and F <; f "e? . - F - nF! Fp 'F. (5) where the value for Fpass is equal to the value determined for F (1) step and the value for Fc is equal to the lower band edge of Table One for the selected ATSC channel the lower band edge offset of the first row of Table Three (It should be noted that instead of a "floor" function in equation (5), a "roof" function can be used) However, for the second scan, while the value for Fpaso remains the same, for the value determined for F (1) step, the value for Fc is now changed to be equal for the lower band edge of Table One for the selected ATSC channel the lower band edge offset from the second row of Table Three The third and fourth scans are similar except that the value for Fpaso is now set equal to the value determined for F (2) step During each of these scans, according to the tuner 305 is tuned to provide a can to the selected, the ATSC signal detector 320 processes the received signals to determine when an ATSC signal is present in the currently selected channel The data or information, for the presence of an ATSC signal is provided to the controller 325 through the 321 A path From this information, the controller 325 builds the available channel list. In this way and in accordance with the principles of the invention, the stability and the known frequency assignment of the DTV channels themselves are used to calibrate the receiver 300 with in order to improve the detection of low ATSC DTV SNR signals As such, in step 275, the receiver 300 has the ability to scan ATSC signals that may be present even in a very low SNR environment, due to the frequency information Exact (FdeSpray and the different values for Fpaso), determined in step 270. The objective sensitivity is to detect the ATSC signals with a signal strength of -116dBm (decibels relative to the energy level of one milliwatt) This is more than 30 dB (decibels) below the visibility threshold (ToV) It should be noted, that according to the displacement characteristics of the local oscillator, it can It may be necessary to re-calibrate periodically It should also be noted that other variations can be implemented to the method described above For example, the ATSC signal detected in step 260 can be excluded from the scans carried out in step 275. In addition, any re-ca can be carried out immediately by tuning in to the ATSC signal identified from step 260 without having to perform step 260 again. Also, once an ATSC signal is detected in step 275, the associated band can be excluded from any subsequent scanning As noted above, the receiver 300 includes an ATSC signal detector 320 An example of an ATSC signal detector 320 takes advantage of the ATSC D signal format TV DTV data are modulated with the use of 8-VSB (vestigial sideband). In particular, for a receiver operating in low SNR environments, segment synchronization symbols and field synchronization symbols embedded within a signal ATSC DTV are used by the receiver to improve the probability of accurately detecting the presence of an ATSC DTV signal, which reduces the probability of false alarm In an ATSC DTV signal, in addition to the eight-level digital data stream, a synchronization of Data segment of four symbols (binary) of two levels is inserted at the beginning of each data segment An ATSC data segment is shown in Figure 9 The ATSC DTV data segment consists of 832 symbols, four symbols for segment synchronization data and 828 data symbols The data segment synchronization pattern is a binary 1001 pattern, as can be seen from Figure 9 The multiple segments Data (313 segments) comprise the ATSC data field, which comprises a total of 260,416 symbols (832x313) The first data segment in a data field is called a field synchronization segment The structure of the field synchronization segment is shown in Figure 10, where each symbol represents a bit data (two levels) In the field synchronization segment, a 511-bit pseudo-aleatopa sequence (PN511) immediately follows the data segment synchronization After the PN511 sequence, there are three identical 63-bit pseudo-random sequences. (PN63) concatenated together, with the second PN63 sequence inverted each other data field In view of the foregoing, one embodiment of the ATSC signal detector 320 is shown in Figure 11 In this embodiment, an ATSC signal detector 320 comprises a filter 505 matching that matches the PN511 sequence mentioned above to identify the presence of the PN511 sequence. Another variation is shown in Figure 12. In this Figure, the output of the matched filter accumulates multiple times to decide if there is an important peak This improves the probability of detection and reduces the probability of false alarm A disadvantage of this modality of Figure 12 is that it requires a large memory Another measure is shown in Figure 13 In this measure, the peak value is detected (520), together with its position within a field (510, 515) of data. It should be noted that the rebooted signal also increases the address counter (ie, "skip address") to store the results in different locations of the RAM 525 As such, the results are stored in multiple data fields in the RAM 525 When the peak positions are the same for a certain percentage of the data fields, then it is decided that a DTV signal is present in the DTV channel Another method to detect the presence of an ATSC DTV signal is to use data segment synchronization Since the data segment synchronization repeats Data segment is usually used for time recovery This method of time recovery is indicated in "Recommended Practice Guide to the Use of the ATSC Digital Television Standard (A / 54) However, data segment synchronization is also can be used to detect the presence of a DTV signal with the use of the time recovery circuit When the time recovery circuit provides a time-closure indication, it ensures the presence of the DTV signal with high accounting This method will work well even when the initial local symbol clock is not close to the transmitter symbol clock, as long as the clock offset is within the activation interval of the time recovery circuit. However, it should be noted that since the useful range was below 0 dB SNR, it is necessary to have an improvement of an additional 15 dB to reach the target detection of -116 dBm. can be used to detect an ATSC signal is to process the segment synchronizations independent of the time recovery mechanism employed This is illustrated in Figure 14, which shows a coherent segment synchronization detector using filter 550 infinite impulse response (MR) that includes a leak integrator (where the symbol a is a predefined constant) The use of a filter MR constructs the peak of time for detection, by reinforcing the information presented with a repetition period of a segment This assumes that carrier shift and time offset are small Different to the coherent methods described above for detecting the ATSC signal, non-coherent measurements can be used, ie, the down-conversion to the baseband is not necessary through the use of the carrier pilot This is advantageous, since the robust extraction of the pilot can be problematic in low SNR environments A non-coherent segment synchronization detector, illustrative is shown in Figure 15, which shows the delay line structure The input signal is multiplied by the conjugate, delayed version of itself (570, 575) The result is applied to a filter to match the data segment synchronization (the 580 filter) equalization of data segment synchronization) The conjugation ensures that any displacement of the carrier does not affect the amplitude after the matched filter Alternatively, an integrating and pulling measure can be taken After the matched filter 580, the magnitude (585) of the signal is taken (or more easily, the square magnitude is taken as I2 + Q2), where I and Q are in phase and the quadrature components, respectively, of the signal outside the matched filter) This value (586) of magnitude it can be examined directly to see if there is an important peak indicating the presence of a DTV signal. Alternatively, as indicated in Figure 15, the 586 signal can be re-refined further when processed with the 550 MR filter, in order to improve the robustness of the calculation over multiple segments An alternative modality is shown in Figure 16 In this modality, the integration (580) is carried out in a coherent manner (that is, maintaining the information of phase), after which the magnitude (585) of the signal is taken. Similar to the above-described modes operating in the baseband, other non-coherent modes can also use the longer PN511 sequences found within the synchronization. However, it should be noted that certain modifications will have to be made to adapt the frequency offset. For example, when the PN511 sequence is to be used as an indicator of the ATSC signal, there may be several correlators used simultaneously to detect its presence The case where the frequency shift is such that the carrier undergoes a complete cycle or rotation should be considered. In this case, the correlator output equalized between the input signal and the PN511 reference sequence will add to zero However, when the PN511 sequence is broken into N parts, each part will have an appreciable power, since the carrier will only rotate by 1 / N cycles during each part Therefore, the measure of the non-coherent correlator can be used by breaking the long correlator into smaller sequences, and approaching each sub-sequence with a non-coherent correlator, such as that shown in Figure 17 In this Figure, the sequence to be correlated is broken into N sub-sequences, numbered from 0 to N-1. The input data is delayed in such a way that the outputs of the correlator are combined (590) to produce a useful coherent non-coherent combination Another illustrative mode of an ATSC signal detector is shown in Figure 18 In order to reduce the complexity of the ATSC signal detector, a signal detector The ATSC of Figure 18 uses an equalized filter (710) that matches the PN63 sequence. The output signal of the matched filter 710 is applied to the delay line 715. In the modality of Figure 18, a consistent combination measure is used. Since the average PN63 is inverted in each other data field synchronization, two outputs y1 and y2 are generated through the adders 720 and 725, corresponding to these two cases of data field synchronization As can be seen from the Figure 18, the processing path for the output y1 includes multipliers to invert the average PN63 before the combination through the adder 720 It should be noted that the modality of Figure 18 carries out the peak detection When an important peak appears in y1 or in y2, then it is assumed that an ATSC DTV signal is present An alternative mode of an ATSC signal detector that matches the PN63 sequence is shown in Figure 19 This mode is similar to that shown in Figure 18, except that the output signal of the matched filter 710 is first applied to the element 730, which computes the square magnitude of the signal This is an example of a non-coherent combination measure As shown in Figure 18, the modality of Figure 19 performs peak detection The 735 adder combines the different elements of the delay line 715 to provide the output signal y3 When an important peak appears in y3, then it is assumed that an ATSC DTV signal is present It should be noted that when the displacement of the carrier is relatively large, the measure of the combination is not coherent of Figure 19 may be more appropriate than the coherent combination Also, it should be noted that element 730 can simply determine the magnitude of the signal Also, additional variations are shown in Figures 20 and 21 In these illustrative embodiments, the sequences PN511 and PN63 are used together for the detection of ATSC signal With reference first to the modality shown in Figure 20, the signals y1 and y2 are ge They are as described above with respect to the embodiment of Figure 18, to detect a PN63 sequence. In addition, the output of the matched filter 505 (which matches the PN511 sequence) is applied to the delay line 770, which stores data on the time interval for the three PN63 sequences The modality of Figure 20 performs the peak detection When an important peak appears in z1 or in z2, (provided through the adders 760 and 765, respectively), then it is assumed that an ATSC DTV signal is present With reference now to Figure 21, the embodiment of Figure 21 also combines the detection of the PN511 sequence with the detection of the PN63 sequence, as shown in Figure 19. In this embodiment, the signal of Equalized 505 filter output is first applied to element 780, which computes the square magnitude of the signal This is an example of another non-coherent combination measure As in Figure 20, the modality of Figure 21, to peak detection The summer 785 combines the different elements of the delay line 770 with the output signal y3 to provide the output signal z3 When an important peak appears in z3, it is assumed that an ATSC DTV signal is present. , it should be noted that the element 780 can simply determine the magnitude of the signal. Other variations are possible for the foregoing. For example, the matched filters PN63 and PN511 can be cascaded, in order to make use of their delay line structure inherent to reduce the amount of additional delay line required In another mode, three PN63 equalized filters can be used better than a single PN63 equalized filter plus delay lines This can be done with or without the use of an equal PN511 filter described above, the performance of the transmit signal detector is improved by first calibrating the tuner with a received transmission signal before explore the spectrum for other transmission signals In this way, in the context of a WRAN system, it is possible to detect the presence of ATSC DTV signals in environments with a low signal-to-noise ratio, with high accounting. It should be noted that although the receiver Figure 5 is described in the context of the CPE 250 of Figure 4, the invention is not limited and also applies for example to the receiver of a BS 205 Plus, although the receiver of Figure 5 is described in the context of a WRAN system, the invention is not limited and applies to any receiver carrying out channel detection. In view of the foregoing, only the principles of the invention are illustrated and therefore, those skilled in the art will be able to contemplate There are several alternative arrangements that although not explicitly described here, incorporate the principles of the invention and are within the scope and spirit of the invention. In the context of separate functional elements, these functional elements can be incorporated into one or more integrated circuits (IC)., although shown as a separate processor, any or all of the elements can be implemented in a processor controlled by stored program for example, a digital signal processor, which executes the associated software, for example, corresponding to one or more of the Steps shown for example, in Figure 6 In addition, the principles of the invention can be applied in other types of communication systems, for example, satellite, Wireless-Fidelity (WI-FI), cellular, etc. Certainly, the inventive concept it can also be applied to stationary or mobile receivers. Therefore, it should be understood that vain modifications may be made in the illustrative embodiments and that other arrangements may be contemplated without departing from the spirit and scope of the present invention, as defined in the claims. annexes

Claims (1)

1. CLAIMS 1 An apparatus characterized in that it comprises a tuner for tuning to one of a number of channels, a transmission signal detector coupled with the tuner to detect if there is a transmission signal in at least one of the channels, wherein the tuner is calibrated as a function of the received transmission signal 2 The apparatus according to the claim 1, characterized in that it further comprises a processor coupled with the transmission signal detector to form a list of available channel comprising those of a number of channels over which the transmission signal 3 was not detected. The apparatus according to claim 2 , characterized in that the apparatus is a receiver for receiving signals from a wireless regional area network (WRAN) 4 The apparatus according to claim 1, characterized in that it further comprises a processor coupled with the transmission signal detector to determine the parameters of tuning to be used when calibrating the tuner from a number Furthermore, it comprises a memory for storing the number of possible displacements. The apparatus according to claim 1, characterized in that the signal detector of The transmission is coherent. The apparatus according to claim 1, characterized in that the transmission signal detector is non-coherent. The apparatus according to claim 1, characterized in that the transmission signal is an ATSC signal. (Advanced Television Systems Committee) 9 A method to be used in a receiver, the method is characterized in that it comprises calibrating the receiver as a function of the received transmission signal, and after carrying out the calibration step, detecting whether there are other signals transmission in at least a portion of the frequency spectrum to determine an available portion of the frequency spectrum for use by the receiver The method according to claim 9, characterized in that the step of calibrating includes determining the tuning parameters to be used by calibrating the receiver from a number of possible offsets for the received transmission signal. The method according to claim 10, characterized in that the step of detecting includes carrying out multiple scans of the at least a portion of the frequency spectrum in each of the number of possible trips 12 The method according to claim 9, characterized in that the step of detecting is coherent. The method according to claim 9, characterized in that the step of detecting is non-coherent. The method according to claim 9, characterized in that the step of The method according to claim 9, further comprising the step of receiving a wireless regional area network (WRAN) signal in the determined available portion of the frequency spectrum