MX2010014031A - Method for detecting gaps in the uhf spectrum for analogue television based on the correlation of a semi-complete barker code. - Google Patents

Abstract

The method for detecting gaps in the UHF spectrum for analogue television is useful for detecting spaces with absence of broadcasted television signal, which may comply with the structure of an analogue standard. The detection may be performed in noisy environments, in which a signal-noise ratio falls down to -20dB. With the detection of gaps in the UHF spectrum, it is ensured that the transmission of signals by predetermined frequency is not invading the previous frequency, also optimising the transmission and promoting the efficient reuse of the spectrum in certain frequency bands and geographical zones. In order to take advantage of the properties of the self-correlation functions of the Barker Codes, a method is proposed where, once it is applied, a coupled filter is generated for analysing the output signal and concluding if a valid pattern has been found in case a pick in the amplitude is generated, this being an indicator that an input signal is available for frequency spaces.

Description

METHOD FOR THE DETECTION OF HOLES IN THE UHF FREQUENCY SPECTRUM FOR ANALOG TELEVISION BASED ON THE CORRELATION OF A BARKER SEMICOMPLETE CODE.

FIELD OF THE INVENTION The present invention relates to methods for the synchronization and detection of signals of analog television, by means of signal couplings, time manipulation, the signal in baseband, to be able to optimize the frequency spectrum.

OBJECT OF THE INVENTION The object of the present invention is a method for the detection of gaps in the UHF frequency spectrum for analog television, that is, for the detection of spaces where there is no broadcast television signals, which must be comply with the structure of some analogous standard such as NTSC, PAL, SECAM or any of its derivatives. This method for detection can be done in environments noisy, in which a signal-to-noise ratio drops to -20dB. With hole detection in the UHF frequency spectrum, it is ensured that the transmission of signals by certain frequency, is not invading a previous transmission, and therefore optimize the transmission and spaces of analog television signals; also promotes the efficient reuse of the spectrum in certain frequency bands and geographical areas. ,.; : i BACKGROUND As a result of the relocation in the frequency spectrum of analogue television in UHF channels and the migration of technology to digital broadcasting (DTV), the opportunity arises for wireless broadband service providers to operate in vacant spectrum spaces, In order to efficiently reuse this expensive and limited resource. This is why a method is proposed for the detection of vacant (or blank) spaces in the frequency spectrum, based on a "listen-before-talk" scheme in which a "secondary" user who does not have priority over the use of the spectrum, does an analysis of the environment and ensures that there are no "primary" stations of services tendered in a certain frequency band, before starting to transmit and thus offer their services in a certain geographical region. It is known that analogous standards for the broadcasting of television signals require the insertion of specific sequences of pulses in the composite video signal, which allow the receiver to synchronize the information contained to be displayed on the screen. refers to the graphic content that 'makes' the human eye perceive continuous sequences of movement based on the 'superposition of discretized images in a certain number of horizontal lines, at rates around 30 frames per second,' depending on the standard. Each 'image is considered as a square; Each frame is split into two fields (odd and even) "depending on the type of lines that form it." Vertical synchrony "pulses or sequences are those that are added to the composite video signal at the end of each field and indicate to the receiver that should || _ ||.; || ·, 3; · · Restart the vertical sweep from the top of the screen. In the case of the NTSC standard, said sequence has a periodicity (or repetition rate) of one sixtyth of a second. The analogous television standards propose the inclusion of pulses of different work cycle with some redundancy to help the receiver 5 synchronize the content of a video signal.

The composition of the baseband synchrony sequence, as shown in Figure 1, is 30 pulses, for the American standard NTSC: 18 alternating pulses (6 equalizing pulses, followed by 6 vertical pulses, followed by 6 equalizing pulses) followed from • a sequence of 12 horizontal pulses to complete the 30 pulses. 10 The method for detecting gaps in the UHF frequency spectrum for analog television signals proposed here is based on the general knowledge of signal handling. However, in the literature no evidence was found that this problem is being solved in a manner similar to the one proposed "in this document ^ so a first approach to the proposed method is to generate a coupled filter (MFj) to 15 the complete synchronization sequence of 30 pulses contained in the composite video signal of the NTSC standard; This first approach, "can also be carried out for the European analogue tele- vision standards such as PAL ^ SECAM and its derivatives," as long as it is coupled to the corresponding amount of pulses contained in the vertical synchronization sequence of the treated standard. Once the MFi coupled filter is generated, its signal is analyzed 20 output, to determine the existence of gaps in the frequency spectrum. If the autocorrelation function of the 30-pulse sequence is detected within the signal of the output, it can be assured that there is a vertical synchronization pattern contained in the input signal. which indicates that there is no gap in the frequency spectrum; that is, a tendered station is transmitting and a secondary user can not make opportunistic use of the spectrum on that frequency. This method can be understood as the first approach to solving the problem of detecting a synchrony pattern embedded in the composite video signal, or detecting gaps in the frequency spectrum for analog television; where the method proposed in this document presents an efficiency approaching asymptotically at 18dB, unlike this first approach that has an efficiency around 3dB.

A closer approach to the proposed methodology, occurs when only the 6 vertical pulses of the baseband synchrony sequence are coupled, in order to generate a coupled filter (MF2), which takes advantage of the energy of said pulses , while eliminating additional periodic information that generates peaks in the side lobes of the filtered output signal; then said output is analyzed to detect a peak or spike when the presence of a synchronization pattern in the input signal is detected, which indicates the presence of an analog television signal in the frequency band analyzed. As in the MFl9 coupled filter, this methodology can also be applied to European standards, as long as "the pulses of longer duration are included, and" the rest is masked. ' * The aforementioned method approaches the expected efficiency of the initial idea of generating filters based on the pulses included in the vertical synchronization sequence, from which the method proposed in this document is developed. 1 If you . . i - l | -! . · || '- · - · | · · K' | '- - BRIEF DESCRIPTION OF THE FIGURES FIGURE 1. Synchronization signal for the NTSC standard.

FIGURE 2. Block diagram of the Barkerization system.

FIGURE 3. Output of the coupled filter MF3 (a) and output of the coupled filter MF4 (b), respectively.

FIGURE 4. Filter outputs coupled to a signal-to-noise ratio of -15dB.

FIGURE 5. Performance of the filters coupled to different signal-to-noise levels.

DETAILED DESCRIPTION OF THE INVENTION The method for the detection of gaps in the UHF frequency spectrum for analog television uses signals preferably in NTSC format. In order to detect whether or not there is a presence of analog television signals in the environment, it is proposed to analyze the RF activity in the desired frequency band in search of the repetitive patterns of must have a detection method capable of withstanding very low signal-to-noise (SNR) conditions when discriminating the presence or absence of periodic patterns in the input signal. The method for the detection of gaps in the spectrum of UHF frequencies for analog television takes advantage of the autocorrelation properties of the Barker Codes, which are well known in the literature, and extrapolates its application to valid patterns of vertical synchrony ( periodic sequences of pulses that per standard are included in the structure of the composite video signal) by means of a pre-processing scheme using masking of the input signal to generate an indicator signal each time the pattern is detected. Thus, the method proposed here, part of the composition of the signal in baseband, as already mentioned (see figure 1) and that is formed by thirty pulses, which constitute the vertical synchronization pattern for the American standard NTSC , although it can also be used for European standards, as long as the necessary conditions are met.

Starting from the composition of the baseband signal, the method for the detection of gaps in the spectrum of UHF frequencies for analogue television based on the correlation of a Barker pseudocode, consists of the following steps: '1' a) Pre-process the signal in baseband. The pre-processing type Baker ^ e ja segai is performed in Dancia base with "vertical synchrony" preferably of the 'standard' 'L NTSC. Barker pre-processing is done by modifying the vertical synchronization signal according to the coefficients "of the Barker code 13, using masks as indicated by the Barkerization system (figure 2); it is t ': thus , that the work cycle is not modified, simply the polarization of certain pulses is changed to correspond to the polarity of the coefficients of said Code; "1 1 L" b) Coupling the variant of the Barker Code of length 13 resulting from step a) to generate a coupled filter MF3; c) Conduct the signal in baseband with vertical synchronization through the coupled filter MF3; d) Analyze the output signal of step c) to find a peak or pin on the output signal. The output signal of the coupled filter MF3 can be analyzed visually, that is, by means of graphs, and thereby determine the presence of the vertical synchronization pattern of the analog television signal in the frequency band analyzed.

"In turn, there is another methodology, which is different from the one previously proposed. Thus, the Method for the detection of gaps in the spectrum of "UHF frequencies for analog television signals based on the correlation of a semi-complete code of Barker has the following stages: ; '^ ~! ! \ ·:?. ' .. '..'. ' · · '. ·; |: .. | 'Ü Ú! , > '! . ':,' - 1. Pre-process the signal in baseband. The Barker type preprocessing of the baseband signal is performed with vertical synchronization, preferably of the NTSC standard; 2. Widen the duty cycle of the equalizing pulses of the signal resulting from step 1); 3. Couple a semi-complete version of Barker's Code of length 13 of the signal resulting from step 2); 4. Widen the duty cycle of the equalizing pulses of the baseband signal. The widening is done from 8% in the NTSC standard to 96%, by the continuous addition of 12 delayed versions of each of these pulses. Since the duration of these pulses is 4% of an H line, adding 12 delayed pulses has a pulse that has a duration of 48% of an H line (96% of duty cycle); 5. Generate a MF4 coupled filter. The coupled filter MF4 is generated with the resulting signal 'from' step 4), it is '' to say a signal1 '' coincident with the '' complete '' version of the Barker Code of length 13; 6. Analyze the output signal from step 5) to find a peak or pin on the output signal. The output signal of the coupled filter MF4 can be analyzed visually, that is, by means of graphs, and thereby determine the presence of the vertical synchronization pattern of the analog television signal in the frequency band analyzed.

When applying the above method, for the detection of gaps in the UHF frequency spectrum for analog television based on the correlation of a code Barker semicomplete, has an efficiency that approaches asymptotically at 18dB in a noise-free environment, compared to the methods mentioned as first approaches to solve this problem, which have an efficiency of 3dB.

As a result of each of these two methodologies, each time there is a valid pattern of vertical synchrony to which each of the filters was coupled, the filter responds with a peak or a spike in the amplitude. As the vertical synchronization patterns are periodic by standard, in the analog television signal, the peaks in the signal at the output of each of the filters are also; The peak or spike that appears at the exit of each of the filters is an indicator that a valid pattern has been identified in the input signal.

As a support for the aforementioned information, FIG. 3 shows graphically the analysis made to the coupled filters MF3 and MF4 under conditions of zero ambient noise; the outputs of said filters show the peaks that indicate the presence of valid synchrony patterns in the pre-processed input signal according to what each filter requires respectively. On the other hand, Figure 4 shows the performance of the proposed coupled filters, as well as the coupled filters mentioned as the first approaches to these methodologies, in scenarios where the Signal-to-Noise Ratio (SNR) falls to -25dB. Finally, Figure 5 comparatively shows the performance of each of the coupled filters mentioned in this document, in relation to the compression level of the peak or main spike that indicates the presence of synchrony patterns belonging to valid Analog Television signals. in the environment. "-.

Claims (6)

CLAIMS Having sufficiently described the invention, I consider as a novelty and therefore claim as my exclusive property, what is contained in the following clauses:

1. A method for the detection of gaps in the spectrum of UHF frequencies for analog television based on the correlation of a Barker light code characterized in that it comprises the following stages: 1) Pre-process the signal in baseband; - 2) Widen the duty cycle of the equalizing pulses of the signal resulting from step 1); 3) Attach a semi-complete version of the Barker code of length 13": of the signal resulting from step 2); '.' '' K . ^ Enlarge the work cycle of the 'equal' of the signal in baseband; 5) Generate an MF coupled filter.

2. The method for detecting gaps in the spectrum of UHF frequencies for analog television based on the correlation of a Barker semi-complete code according to claim 1 characterized in that in stage 1) to the baseband signal with vertical synchronization, a Barker type pre-processing is performed.

3. The method for the detection of gaps in the UHF frequency spectrum for analog television based on the correlation of a Barker code in accordance with claim 1 characterized in that in step 1) the Barker pre-processing is preferably performed at the baseband signal of the NTSC standard.

4. The method for detecting gaps in the UHF frequency spectrum for analog television based on the correlation of a Barker light code according to claim 1, characterized in that in step 4) the broadening of the working cycle of the equalizing pulses of the signal in baseband, at 96% for the NTSC standard. ,

5. The method for detecting gaps in the spectrum of UHF frequencies for analog television based on the correlation of a Barker semi-complete code according to claim 4, characterized in that the broadening of the working cycle is carried out by the continuous addition of 12 versions delayed of each one of the pulses. . ..

6. The method for detecting gaps in the 'spectrb of' 'UHF frequencies for analogue television based on the correlation' of a Barker light code according to claim 1 characterized in that in step 5), the coupled filter MF4 'is generates with the serial number resulting from step 4), that is, a signal coinciding with the semi-complete version of the Barker Code of length 13.