MX2008009094A - Detection of the presence of television signals embedded in noise using cyclostationary toolbox - Google Patents

Abstract

A method for detecting the presence of a television signal embedded in a received signal including the television signal and noise is disclosed. Either first-order or second order cyclostationary property of the signals may be used for their detection. When the first-order cyclostationary property is used, the following method is used, the method comprising the steps of upsampling the received signal by a factor of N, performing a synchronous averaging of a set of M segments of the upsampled received signal, performing an autocorrelation of the signal;and detecting the presence of peaks in the output of the autocorrelation function. When the second order cyclostationary property of the signal is used, the method comprising the steps of delaying the received signal by a fixed delay (symbol time), multiplying the received signal with the delayed version, looking for a tone (single frequency) in the output.

Description

DETECTION OF THE PRESENCE OF TELEVISION SIGNALS INTEGRATED IN NOISE USING A CYCLESTATIONARY TOOL BOX DESCRIPTION OF THE INVENTION The invention is related to the field of Radios Cognitive and more specifically with detecting the presence or absence of a television signal for its timely use by Cognitive Radios. Agile spectrum radios (also known as Cognitive Radios) represent an emerging approach to wireless communications where parts of the frequency spectrum are used on a basis as required. Cognitive Radios adjust their transmission characteristics based on the external environment. This means that if a part of the spectrum is assigned to an authorized user and is not being used at a given time and place, (FCC rules allow) agile radios can use this spectrum. Agile radio devices generally verify that there is no authorized device so their transmissions do not cause harmful interference to authorized devices. Cognitive radios can be used in short-range wireless situations, such as in patient monitoring in hospitals or long-range wireless situations, such as wireless local loop access. REF .: 194092 Note that television receivers that participate in a television service do not transmit. Therefore its presence is difficult to detect. However, television receivers need a minimum level of signal from a TV broadcast station to operate. Therefore techniques that can detect the presence of TV signals deeply integrated in noise are a critical part of the agile / cognitive radios. Accordingly, there is a need in the industry for the development of methods for identifying TV signals that are deeply integrated into noise. A method, device and computer product for detecting the presence of a television signal integrated in a received signal including the television signal and noise is described. The method comprises the steps of determining a peak energy of the received television signal and determining the periodicity of the television signal based on the determined peak energy. In an aspect of the invention the step of determining the peak energy comprises the steps of oversampling (increasing the sampling rate) the received signal by a factor of N, performing a synchronized average of a set of M segments of the received signal oversampled, carry out the autocorrelation of the signal and detect the presence of peaks in the output of the autocorrelation function. In other aspect of the invention, the method comprises the steps of oversampling the desired signal by a factor of N, carrying out delay-multiplication of the signal, carrying out a tone analysis and detecting a single signal at the tone analysis output . Figures 1A and IB illustrate a time representation and a frequency representation of a conventional analog TV signal, respectively. Figures 2A and 2B illustrate a frequency representation and a frame structure of an exemplary digital TV (ATSC) signal. Figures 3A and 3B illustrate a cyclic correlation density and spectral correlation of conventional NTSC (analog) TV signals. Figure 3C illustrates a method for detecting an output to noise signal ratio (SNR) to obtain a TV signal. Figure 4 illustrates results of the detection of a conventional analog NTSC signal in accordance with the principles of the present invention. Figure 5 illustrates the results of the detection of an exemplary ATSC (digital) TV signal in accordance with the principles of the present invention and Figure 6 illustrates a system for carrying out the processing shown herein.

It should be understood that these figures are only for the purpose of illustrating the concepts of the invention and are not designed as a definition of the limits of the invention. The embodiments shown in the figures herein and described in the accompanying detailed description should be used as illustrative modalities and should not be considered as the only way to carry out the invention. Likewise, the same reference numbers, possibly supplemented with reference characters when appropriate, have been used to identify similar elements. Traditionally, a cystationary toolbox is used to detect signals that are integrated into noise. A cystationary property arises in a signal if the signal has periodic average values and periodic variance (higher order cycloestacionary, so to speak of the fourth order, can also be displayed). Figures 1A and IB illustrate the periodic nature of a conventional analog TV signal in the time and frequency domains, respectively. Referring to Figure 1A, a conventional TV signal has a periodic time property (H), where a "horizontally synchronized" signal is generated after each data frame (458 lines). The horizontal synchronized signal is repeated 30 times per second. Figure IB illustrates the periodic signal in the frequency domain, in where the signal energy is grouped into frequencies separated by the line period, represented as "H". With reference to Figures 1A and IB, it can be seen that the spectrum of a conventional TV signal has a high degree of self-correlation and, therefore, possesses a cystationary property. Figures 2A and 2B illustrate a similar cytostatic property for digital signals. With respect to FIG. 2A, the spectrum of a digital TV signal (IEEE ATSC 53) shown includes a suppressed carrier in a predetermined portion of the frequency spectrum and the entire band is similarly set. Figure 2B illustrates the repeated frame structure of the IEEE ATSC 53 digital signal in which 313 segments are transmitted in a 24.2 millisecond frame. For analog signals, the cyclic auto-correlation function. { R? (t.}.), and the cyclic spectral density function (S? a (f)), (equations 1 and 2), are shown in Figures 3 A and 3 B, respectively. These functions can be determined as: Ra (t) = lim -i- T2 x. { t + -) x. { t - -) e-i2n? dt (1) Sxa. { f) = JF- or Rxa. { t) e-i2 * tdt (2) where Rxa (t) is the auto-correlation function of the received signal (x); Sxa (f) is the Fourier transformation of the cyclic auto-correlation function and t is the delay between two signals. Most of the existing methods propose the use of delay-multiplication to detect the presence of cystationary signals (of periodic variance). For digital signals the output SNR_ (Osnr) for a delay-multiplication circuit is given by where Osnr is the output SNR; Is Ns the integration time or number of FFT points and? change over different detection schemes. Nevertheless, ? it is small and is equal to typically 0.0012. Figure 3C illustrates a method for determining the value of?. In accordance with the principles of the invention, the synchronized average (which exploits a first-order cytostatic property) or delay-multiplication followed by detection signals based on tone detection (which exploits a second-order cytostatic property) is used to determine the hidden periodicity of a signal received that contains a television signal and noise and also to detect the presence of the analog and / or digital television signals received. More specifically, the method of the present invention, which exploits a first-order cytostatic property, can be summarized as comprising the steps of: a. oversampling the desired signal by a factor of N; b. carry out synchronized average of a set of M segments; c. carry out a self-correlation of the signal and d. detect the presence of peaks in the output of the auto-correlation. Based on a calculation of the periodicity of "H" (as shown in Figure lA) at the receiver (since the clock recovery is not completely determined, a search is performed on B adjacent frequency niches), the received input signal (TV signal and noise) can be segmented and M of these segments are averaged together. B is selected based on the accuracy of the clock in the receiver, that is, if the clock is very precise, B is small, whereas, if the clock is less precise, B is a larger number.

Since "H" is large, errors in the calculation of the clock value do not have a significant impact on detection (in addition, the search on B adjacent frequency niches partially mitigates this problem). After this, detection of matching filter types is used to detect the presence of the synchronization pattern in the analog TV signal. In a second aspect, the method of the present invention, which exploits a cyclestationary property of second order, can be summarized as comprising the steps of (carried out on B adjacent frequency niches): a. oversampling the desired signal by a factor of N; b. carry out delay-multiplication of the signal; c. carry out a tone analysis and d. detect a single signal in the output of the tone analysis. Figure 4 illustrates the results of synchronized average based on the cycloestationary detection of a conventional NTSC analog TV signal for segments of size M = 5, 10, 15 and 20 in accordance with the principles of the invention. The oversample factor N is typically taken as several orders of magnitude larger than the analog TV sampling rate of 13.5 Mhz and the digital TV sampling rate of 10.75 Mega symbols / second. As illustrated, increasing the number of selected segments (M) increases the output SNR for a known input SNR. That is to say that at increasing the number of segments used, the noise in the received signal is averaged over a larger number of segments allowing a higher signal-to-noise ratio and a better probability of detecting the hidden periodicity in the received signal. Consequently, M as a known multiple of an estimate of the periodicity (H) of the expected signal. Figure 5 illustrates the detection results based on delay-multiplication and synchronized average according to the principles of the invention of an exemplary digital TV signal. In this illustrated presentation, the correlation-1 represents the auto-correlation of the signal followed by the threshold detection for the detection of the field synchronized signal (i.e., the horizontal axis in Figure 2A) and the correlation-2 represents the synchronized average, as described above, applied to ATSC (digital) signals for the detection of segment synchronization (ie, the vertical axis in Figure 2A). As would be recognized, the processing shown herein may be executed by software code and / or hardware operating in a computer or processing system. The system can include a programmable memory, that is, PROM, RAM, FLASH, etc., that stores code that provides necessary instructions to the processing system. The code can be pre-stored in the memory or can be downloaded by means of one or more readable media by computer or over a network. In another aspect, the code may be hardware code loaded into an FPGA or ASIC that provides necessary instructions to the processing system. The processing system may also receive inputs from one or more sensors that provide indications of the movement of the portable device. Figure 6 illustrates a conventional processor system 600 for executing the processing shown herein. The processor system 600 includes a processor 610 in communication with a memory 615 and an input / output device 620 on a communication bus 625. The memory 615 can include instructions or computer code that when executed by the 610 processor carry out the processing described here. The input / output device 620 provides a means for the processor 610 and / or memory 615 to receive information from or transmit information to a second processing system or visual information display systems. Although not shown, it would be recognized that the information may be transmitted over one or more networks between the display device or I / O 620 or a second processor system and I / O 620 device. For example, the computer code may be transmitted to memory over a network through the I / O 620 device. Although they have been shown, described and pointed out Fundamental new features of the present invention applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the described apparatus, in the form and details of the described devices, and in their operation, can be made by those skilled in the art. the technique without departing from the spirit of the present invention. It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same manner to achieve the same results are within the scope of the invention. Substitutions of elements from one described modality to another are also attempted and fully contemplated. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (15)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A method for detecting the presence of a television signal, which exhibits cycloestationary properties, integrated in a received signal that includes the television signal and noise, characterized in that it comprises the steps of: determining a peak energy of the received television signal and determining the periodicity of the television signal based on the determined peak energy. The method according to claim 1, characterized in that the step of determining the peak energy comprises the steps of: oversampling the received signal by a factor of N; carry out a synchronized average of a set of M segments of the oversampled received signal; carry out a self-correlation of the signal and detect the presence of peaks in the output of the auto-correlation function. 3. The method according to claim 2, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and conducts a search on B adjacent frequency niches. 4. The method according to claim 1, characterized in that the step of determining the peak energy comprises the steps of: a. oversampling the desired signal by a factor of N; b. carry out delay-multiplication of the signal; c. carry out a tone analysis and d. detect a single signal in the output of the tone analysis. The method according to claim 4, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and a search on B adjacent frequency niches is carried out. 6. A device for detecting the presence of a television signal, which exhibits cycloestationary properties, integrated into a received signal that includes the television signal and noise, characterized in that it comprises: a processor in communication with a memory, the processor executes the steps of: determining a peak energy of the received television signal and determine the periodicity of the television signal based on the determined peak energy. The device according to claim 6, characterized in that the step of determining the peak energy comprises the steps of: oversampling the received signal by a factor of N; carry out a synchronized average of a set of M segments of the oversampled received signal; Carry out autocorrelation of the signal and detect the presence of peaks in the output of the auto-correlation function. The device according to claim 7, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and a search on B adjacent frequency niches is carried out. The device according to claim 6, characterized in that the step of determining the peak energy comprises the steps of: a. oversampling the desired signal by a factor of N; b. carry out delay-multiplication of the signal; c. carry out a tone analysis and d. detect a single signal in the output of the tone analysis. 10. The device according to claim 9, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and a search on B adjacent frequency niches is carried out. 11. A computer-readable medium, characterized in that it provides instructions to a processing system to detect the presence of a television signal, which exhibits cycloestationary properties, integrated in a received signal that includes the television signal and noise, the instructions make The processing system executes the steps of: determining a peak energy of the received television signal and determining the periodicity of the television signal based on the determined peak energy. 12. The computer readable medium according to claim 11, characterized in that the step of determining the peak energy comprises the steps of: oversampling the received signal by a factor of N; carry out a synchronized average of a set of M segments of the overmurred received signal; Carry out autocorrelation of the signal and detect the presence of peaks in the output of the auto-correlation function. 13. The computer readable medium according to claim 12, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and the search on B adjacent frequency niches is carried out. 14. The computer readable medium according to claim 11, characterized in that the step of determining the peak energy comprises the steps of: a. oversampling the desired signal by a factor of N; b. carry out delay-multiplication of the signal; c. carry out a tone analysis and d. detect a single signal in the output of the tone analysis. 15. The computer-readable medium according to claim 14, characterized in that the value of N is at least one magnitude greater than the sampling rate of the TV signal, and a search on B adjacent frequency niches is carried out. .