Abstract:
A signal detection method detects a digital signal in a channel. The signal detection method includes: performing a power operation and a frequency transformation operation on a signal of the channel to obtain at least one frequency-domain power set; and determining whether the channel carries the digital signal according to the at least one frequency-domain power set.

Description:
[0001]    This application claims the benefit of Taiwan application Serial No. 105110013, filed Mar. 30, 2016, the subject matter of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates in general to a signal detection method and a signal detection device, and more particularly to a signal detection method and a signal detection device capable of promptly detecting in a channel whether the channel includes a digital signal. 
       Description of the Related Art 
       [0003]    With the blooming of multimedia and the Internet, demands of common households for high-speed transmission have exponentially increased, and cable modems with a large bandwidth have gradually gained popularity among consumers. For digital television applications, a cable modem performs channel scanning on a plurality of television channels. More specifically, a cable modem detects in a television channel whether the television channel includes digital television signals. If the digital television channel does not include any digital television signals, the cable modem switches to another digital television channel to detect whether this another digital television channel includes digital television signals. In the prior art, signal detection that a cable modem performs is not based on characteristics of a digital television signal, results in a way that the cable modem may spend a loner period on channel scanning. 
         [0004]    Therefore, there is a need for a solution for the above issue. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is directed to a channel detection method capable of promptly eliminating non-digital signals to overcome the issue of the prior art. 
         [0006]    The present invention discloses a signal detection method for detecting a digital signal of a channel. The signal detection method includes: performing a power operation and a frequency transformation operation on a signal of the channel to obtain at least one frequency-domain power set; and determining whether the channel carries the digital signal according to the at least one frequency-domain power set. 
         [0007]    The present invention further discloses a signal detection device for detecting a digital signal in a channel. The signal detection device includes: a power operation circuit; a frequency transformation circuit, coupled to the power operation circuit, wherein the power operation circuit and the frequency transformation circuit perform a power operation and a frequency transformation operation on a signal of the channel to obtain at least one frequency-domain power set; and a determination circuit, determining whether the channel carries the digital signal according to the at least one frequency-domain power set. 
         [0008]    The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a flowchart of a signal detection process according to an embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic diagram of a signal; 
           [0011]      FIG. 3  is a flowchart of an operation process according to an embodiment of the present invention; 
           [0012]      FIG. 4  is a flowchart of a detection process according to an embodiment of the present invention; 
           [0013]      FIG. 5  is a block diagram of a signal detection device according to an embodiment of the present invention; and 
           [0014]      FIG. 6  is a block diagram of a signal detection device according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The IUT-T J38B standard is extensively applied in digital television systems. According to the IUT-T J38B standard, a digital television signal is modulated by quadrature amplitude modulation (QAM). However, a QAM signal is characterized in that, an ensemble average of this QAM signal to the power of 4 is a constant. More specifically, assuming that a signal S is a signal modulated by the QAM technology, an ensemble average of the signal S to the power of 4 (denoted as S 4 ), denoted as E[S 4 ], is a constant; that is, E[S 4 ]=C (where C is a constant). That is to say, time-domain sample values S 1  to S N  of the signal S in the time-domain are characterized by E[S 4 ]=C. In the above situation, when a frequency transformation operation, e.g., a fast Fourier transform (FFT), is performed on the values E[S 1   4 ] to E[S N   4 ], the corresponding frequency transformation results R 1  to R N  are expected to approximate an impulse function; that is, a frequency transformation result R m  among the frequency transformation results R 1  to R N  is far greater than other frequency transformation results among the frequency transformation results R 1  to R N . Using the foregoing characteristic of QAM, the present invention detects whether a digital signal modulated by QAM is carried in a channel. 
         [0016]      FIG. 1  shows a flowchart of a signal detection process  10  according to an embodiment of the present invention. The signal detection process  10  is applied to detect whether a channel includes a digital signal that is a signal modulated by the QAM technology. Using the above characteristic of QAM, the signal detection process  10  promptly detects whether the channel includes the digital signal. The signal detection process  10  may be applied to a cable modem, such that the cable modem may perform the signal detection process  10  to promptly detect whether a digital television channel includes a J.83B signal (the J.83B signal is modulated by the QAM technology). If the digital television channel does not include the J.83B signal, the signal detection process  10  switches to another digital television channel to perform channel scanning (i.e., detecting whether this another digital television channel includes a J.83B signal). The signal detection process  10  may be performed by a signal detection device, and includes following steps. 
         [0017]    In step  100 , the signal detection process  10  begins. 
         [0018]    In step  102 , a power operation, a frequency transformation operation and a magnitude operation are performed on a signal x of a channel to obtain frequency-domain magnitude sets Z 1  to Z K . 
         [0019]    In step  104 , it is determined whether the channel carries the digital television signal according to the frequency-domain magnitude sets Z 1  to Z K . 
         [0020]    In step  106 , the signal detection process  10  ends. 
         [0021]    Operation details of the signal detection process  10  are given as below. In step  102 , the signal detection device performs the power operation, the frequency transformation operation and the magnitude operation on the signal to obtain the frequency-domain order magnitude sets Z 1  to Z K . The power operation is a 4 th -power operation, and the frequency transformation operation is an FFT operation. More specifically, as shown in  FIG. 2 , the signal detection device may sample the signal x in time intervals T 1  to T K  to obtain time-domain sample sets X 1  to X K . Taking the time interval T 1  for example, the signal detection device samples the signal x in the time interval T 1  to obtain the time-domain sample set X 1 , which includes time-domain sample values X 1, 1 , to X 1, N . Using a mathematical vector, the time-domain sample set X 1  may be represented as X 1 =[X 1, 1 , to X 1, N ] T , where [ ] T  represents a transpose operator. Similarly, for any time interval T k , the time-domain sample set X k  includes time-domain sample values X k, 1  to X k, N ; that is, the time-domain sample set X k  may be represented as X k =[X k, 1 , . . . , X k, N ] T . 
         [0022]    Further, the signal detection device performs a power operation (i.e., 4 th -power operation) on the time-domain sample sets X 1  to X K  to obtain power sets X 1   4  to X K   4 , respectively. More specifically, when the signal detection device performs a power operation on the time-domain sample set X k , the signal detection device performs a power operation on each of the time-domain sample values X k, N  in the time-domain sample set X K  to obtain a power value X k, n   4 , which represents the time-domain sample value  k, n  raised to the 4 th  power. In other words, any sample set X k   4  in the sample sets X 1   4  to X K   4  includes power values X k, 1   4  to X k, N   4 , and so the power set X k   4  may be represented as X k   4 =[X k, 1 , . . . , X k, N ] T . 
         [0023]    Further, the signal detection device performs a frequency transformation operation on the power sets X 1   4  to X K   4  to obtain frequency-domain power sets Y 1  to Y K , in which any frequency-domain power set Y k  (or frequency-domain power values Y k, 1  to Y k, N ) is a result of the power set X k   4  having undergone the frequency transformation operation. In other words, the frequency-domain power value Y k  may be represented as Y k =FFT(X k   4 ), where FFT( ) represents an FFT operator. More specifically, the frequency-domain power set Y k  includes frequency-domain power values Y k, 1  to Y k, N , and the frequency-domain power set Y k  may be represented as Y k =[Y k, 1 , . . . , Y k, N ] T =FFT(X k   4 ). 
         [0024]    Further, the signal detection device performs a magnitude operation on the frequency-domain power sets Y 1  to Y K  to obtain frequency-domain magnitude sets Z 1  to Z K , in which any frequency-domain magnitude set Z k  includes frequency-domain magnitude values Z k, 1  to Z k, N . A frequency-domain magnitude value Z k , n in the frequency-domain magnitude values Z k, 1  to Z k, N  is the magnitude value of the corresponding frequency-domain power value Y k, n . In other words, the frequency-domain magnitude value Z k, N  may be represented as Z k, N =|Y k, n |=abs(Y k, n ), wherein |•| and abs( ) both represent magnitude operators. 
         [0025]    Operations of how the signal detection device performs the power operation, the frequency transformation operation and the magnitude operation on the signal x to obtain the frequency-domain magnitude sets Z 1  to Z K  may be further concluded to an operation process  30 .  FIG. 3  shows an operation process  30  according to an embodiment of the present invention. The operation process  30  may be performed by the signal detection device, and includes following steps. 
         [0026]    In step  300 , the operation process  30  begins. 
         [0027]    In step  302 , the index k is caused to be k=1. 
         [0028]    In step  304 , the signal x is sampled in the time interval T k  to obtain the time-domain sample values X k, 1  to X k, N  (i.e., obtaining the time-domain sample set X k ). 
         [0029]    In step  306 , the power operation is performed on the time-domain power values X k, 1  to X k, N  to obtain the power values X k, 1   4  to X k, N   4  (i.e., obtaining the power set X k   4 ). 
         [0030]    In step  308 , the frequency transformation operation is performed on the power values X k, 1   4  to X k, N   4  to obtain the frequency-domain power values Y k, 1  to Y k, N  (i.e., obtaining the frequency-domain power set Y k ). 
         [0031]    In step  309 , the magnitude operation is performed on the frequency-domain power values Y k, 1  to Y k, N  (i.e., the frequency-domain power set Y k ) to obtain the frequency-domain magnitude values Z k, 1  to Z k, N  (i.e., obtaining the frequency-domain magnitude set Z k ). 
         [0032]    In step  310 , it is determined whether the index k is equal to an integer K. Step  314  is performed if so, otherwise step  312  is performed. 
         [0033]    In step  312 , the index k is caused to be k=k+1, and step  304  is iterated. 
         [0034]    In step  314 , the operation process  30  ends. 
         [0035]    According to the time intervals T 1  to T k , the operation process  30  samples and performs the power operation and the frequency transformation operation on the signal x to obtain the frequency-domain magnitude sets Z 1  to Z K , where the integer K is an integer greater than 1. The remaining operation details of the operation process  30  may be referred from the foregoing description, and are omitted herein for brevity. 
         [0036]    Further, in step  104 , the signal detection device adds up the frequency-domain magnitude sets Z 1  to Z K  to obtain a frequency-domain accumulation set P. The frequency-domain sum set P may be represented as 
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         [0000]    includes frequency-domain accumulation values P 1  to P N , and may also be represented as P=[P 1 , . . . , R N ] T . In other words, any frequency-domain P n  in the frequency-domain accumulation values P 1  to P N  may be represented as 
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         [0037]    When the channel carries the digital signal modulated by QAM, the frequency-domain accumulation values P 1  to P N  are expected to approximate an impulse function, i.e., a maximum frequency-domain accumulation value P max  in the frequency-domain accumulation values P 1  to P N  is far greater than the remaining accumulation values. Thus, the signal detection device may determine whether the channel carries the digital signal according to the frequency-domain accumulation values P 1  to P N . In one embodiment, the signal detection device may obtain the maximum frequency-domain accumulation value P max  in the frequency-domain accumulation values P 1  to P N , and determine that the channel does not carry the digital signal (e.g., a J.83B signal) when it determines that the maximum frequency-domain accumulation value P max  is in a first predetermined range. For example, when the signal detection device determines that the maximum frequency-domain accumulation value P max  is smaller than a threshold P th1 , the signal detection device determines that the channel does not carry the digital signal, wherein the threshold P th1  may be adjusted based on actual conditions. 
         [0038]    Further, in one embodiment, the signal detection device may calculate a ratio of the maximum frequency-domain accumulation value P max  to a plurality of adjacent frequencies adjacent to the maximum frequency-domain accumulation value P max . When the signal detection device determines that the ratio is in a second predetermined range, the signal detection device determines that the channel does not carry the digital signal. How the signal detection device calculates the ratio of the maximum frequency-domain accumulation value P max  to the plurality of adjacent frequencies adjacent to the maximum frequency-domain accumulation value P max  is not limited. For example, the signal detection device may first calculate an average value P av  of the plurality of adjacent frequencies adjacent to the maximum frequency-domain accumulation value P max , and then calculate a ratio R of the maximum frequency-domain accumulation value P max  to the average value P av . 
         [0039]    More specifically, the signal detection device may first obtain a maximum frequency Q corresponding to the maximum frequency-domain accumulation value P max . The maximum frequency Q is the frequency where the maximum frequency-domain accumulation value P max  is located, and may be represented as 
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         [0000]    Further, the signal detection device obtains a plurality of adjacent frequencies Q−M−L to Q−M and a plurality of frequencies Q+M to Q+M+L adjacent to the maximum frequency Q according to the maximum frequency Q, and selects adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M+L  corresponding to the adjacent frequencies Q−M−L to Q−M and Q+M to Q+M+L from the frequency-domain accumulation values P 1  to P N . After obtaining the adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M+L , the signal detection device may further calculate an average value P av  of the adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M+L , that is the average value P av  may be represented as 
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         [0040]    The signal detection device may then calculate that the ratio R is R=P max /P av  after obtaining the average value P av , where M and L may be non-negative integers. As such, when the signal detection device determines that the ratio R is in the second predetermined range, the signal detection device may determine that the channel does not carry the digital signal. For example, when the signal detection device determines that the ratio R is greater than a threshold P th2  or smaller than a threshold P th3 , the signal detection device may determine that the signal does not carry the digital signal (e.g., a J.83B signal), where the thresholds P th2  and P th3  may be adjusted based on actual conditions. 
         [0041]    Operations of how the signal detection device determines whether the channel carries the digital signal according to the maximum frequency-domain accumulation value P max  may be concluded to a detection process  40 .  FIG. 4  shows a flowchart of the detection process  40  according to an embodiment of the present invention. The detection process  40  may be performed by the signal detection process, and includes following steps. 
         [0042]    In step  400 , the detection process  40  begins. 
         [0043]    In step  402 , the maximum frequency Q corresponding to the maximum frequency-domain accumulation value P max  is obtained. 
         [0044]    In step  404 , from the frequency-domain accumulation values P 1  to P N , the adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M +L are obtained. 
         [0045]    In step  406 , the average value P av  of the adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M+L  is calculated. 
         [0046]    In step  408 , the ratio R of the maximum frequency-domain accumulation value P max  to the average value P av  is obtained. 
         [0047]    In step  410 , when the ratio R is in the second predetermined range, it is determined that the channel does not carry the digital signal. 
         [0048]    In step  412 , the detection process  40  ends. 
         [0049]    The detection process  40  determines that the channel does not carry the digital signal according to the ratio R of the maximum frequency-domain accumulation value P max  to the adjacent frequency-domain accumulation values P Q−M−L  to P Q−M  and P Q+M  to P Q+M+L  (adjacent to the maximum frequency Q). Other operation details of the detection process  40  may be referred from the foregoing description, and such repeated details shall be omitted for brevity. 
         [0050]    According to the signal detection process  10 , the signal detection device is capable of promptly detecting whether the channel carries the digital signal. When the signal detection device determines that the channel does not carry the digital signal, the signal detection device may switch to detect another channel. In other words, the signal detection device of the present invention is capable of reducing the signal detection time for detecting whether the channel carries the digital signal. 
         [0051]    The signal detection device is not limited to be implemented in a particular structure. For example,  FIG. 5  shows a block diagram of a signal detection device  50  according to an embodiment of the present invention. The signal detection device  50  includes a sampling circuit  500 , a power operation circuit  502 , a frequency transformation circuit  504 , a magnitude operation circuit  505  and a determination circuit  506 . The sampling circuit  500  samples the signal x to obtain time-domain sample values X 1, 1  to X K, N  (or time-domain sample sets X 1  to X K ). The power operation circuit  502  performs the power operation on the time-domain sample values X 1, 1  to X K, N  to obtain power values X 1, 1   4  to X K, N   4  (or power sets X 1   4  to X K   4 ). The frequency transformation circuit  504  may be an FFT module, and performs the frequency transformation operation on the power values X 1 ,  1   4  to X K, N   4  to obtain frequency-domain power values Y 1, 1  to Y K, N  (or frequency-domain power sets Y 1  to Y K ). The magnitude operation circuit  505  performs the magnitude operation on the frequency-domain power values Y 1, 1  to Y K, N  to obtain frequency-domain magnitude values Z k, 1  to Z k, N . The determination circuit  506  determines whether the channel carries the digital signal according to the frequency-domain magnitude values Z k, 1  to Z k, N . In other words, the sampling circuit  500 , the power operation circuit  502 , the frequency transformation circuit  504  and the magnitude operation circuit  505  perform step  102  of the signal detection process  10  and the operation process  30 , and the determination circuit  506  performs step  104  of the signal detection process  10  and the detection process  40 . The sampling circuit  500 , the power operation circuit  502 , the frequency transformation circuit  504  and the determination circuit  506  may be implemented by application-specific integrated circuits (ASIC). 
         [0052]      FIG. 6  shows a block diagram of a signal detection device  60  according to an embodiment of the present invention. The signal detection device  60  includes a processing unit  602  and a storage unit  604 . The signal detection process  10 , the operation process  30  and the detection process  40  may be coded to a program code  608  and stored in the storage unit  604  to instruct the processing unit  602  to perform the signal detection process  10 , the operation process  30  and the detection process  40 . The processing unit  602  may be, for example but not limited to, a central processing unit (CPU), a digital signal processor (DSP) or a microprocessor. The storage unit  604  may be, for example but not limited to, a read-only memory (ROM), or a non-volatile memory (e.g., an electrically-erasable programmable read-only memory (EEPROM), or a flash memory). 
         [0053]    The foregoing embodiments are for illustrating the concept of the present invention, and one person skilled in the art can make appropriate modifications to the embodiments. For example, in the signal detection process  10 , the operation process  30  and the detection process  40 , the integer K is an integer greater than 1. In other embodiments, the integer may also be equal to 1. That is, the signal detection device may sample a signal and perform the power operation and the frequency transformation operation on signal in one time interval only to obtain one single frequency-domain power set, and determine whether the channel carries the digital signal according to this one single frequency-domain power set. Such modification is also encompassed within the scope of the present invention. 
         [0054]    In conclusion, using QAM characteristics, the present invention promptly detects whether a channel carries a digital signal modulated by QAM, and is capable of reducing the signal detection time needed for detecting non-digital signals in the channel. When the signal detection device detects that the channel does not carry the digital signal, the signal detection device switches to detect another channel, hence reducing the overall time needed for channel scanning. 
         [0055]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.