CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefit of Taiwan application serial no. 94141427, filed on Nov. 25, 2005. All disclosure of the Taiwan application is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a method for suppressing impulse noise. More particularly, the present invention relates to a method for comparing the energy sums of a plurality of samples in a sample stream with thresholds to detect and suppress impulse noise and the device thereof, and the method is applicable to various digital communication receivers. 
   2. Description of Related Art 
   Impulse noise is composed of one or multiple pulses having large oscillation amplitude (or energy) and short period. Impulse noises may occur in, for example, electrical wire spool apparatus, central heater thermostat, lightning switch, or ignition system. These impulse noises may interrupt the decision-making regarding transmission symbols of the communication system and may reduce the performance of the entire communication system. For example, in digital terrestrial TV system, Coded Orthogonal Frequency Division Multiplexing (COFDM) is adopted in the European Digital Video Broadcasting-Terrestrial (DVB-T) standard as the transmission modulation technology of digital bit stream and which is prone to interruption of impulse noises. 
   Accordingly, suppressing impulse noise at the receiver portion has become an important method for improving system performance. In European Patent No. 1,043,874, the clipping level of an analog-to-digital converter (ADC) is used as the threshold. When the data level of a signal converted by the ADC is higher than the positive clipping level or is lower than the negative clipping level, it is determined that the data has been interrupted by impulse noise and is to be replaced with a digital value to be output. Here, the digital value may be 0 or the long-term average of the signal. 
   In European Patent No. 1,180,851, the threshold is generated dynamically by a threshold generator according to a digital stream and is provided to a comparator. The comparator compares the threshold and a digital data to determine whether the digital data is interrupted by impulse noise and is to be replaced with a digital value. Here, the digital value may be 0 or the moving average of the signal. 
   Moreover, in European Patent No. 1,309,095, several consecutive digital data in the signal are compared with the threshold by a delay chain, and it is determined that whether these digital data are interrupted by impulse noises and are to be replaced with digital values according to the comparison results. For example, when the values of more than 4 digital data in eight digital data are greater than the threshold, which means the signal has started to be interrupted by impulse noise, then it is started to replace the digital data with a digital value to output until at the same time the value of at most one digital data in the eight digital data is smaller than the threshold. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed a method for suppressing impulse noise for sequentially receiving samples, detecting the occurrence points of impulse noises and suppressing interruptions to the samples. 
   According to another aspect of the present invention, a device for suppressing impulse noise is provided for sequentially receiving samples sequentially, detecting occurrence points of impulse noises and suppressing interruptions to the samples. 
   In accordance with the above objectives and other objectives of the present invention, a method for suppressing impulse noise for sequentially receiving a sample stream x[n], detecting and suppressing interruptions of impulse noises to the sample stream x[n], wherein the sample stream x[n] includes a plurality of samples and n represents a discrete-time independent variable. The method for suppressing impulse noise includes comparing the energy sum of a (k−1) th  sample and a k th  sample multiplied by a first constant with a first threshold, comparing the energy sum of the k th  sample and a (k+1) th  sample multiplied by a second constant with a second threshold while the energy sum of the (k−1) th  sample and the k th  sample multiplied by the first constant is greater than the first threshold, and replacing the k th  sample with a first replacement sample to output while the energy sum of the k th  sample and the (k+1) th  sample multiplied by the second constant is greater than the second threshold. Wherein k is a positive integer and the first threshold may be equal to the second threshold. 
   The method for suppressing impulse noise according to an exemplary embodiment of the present invention further includes respectively comparing the energies of the (k+1) th  to the (k+m) th  samples with a third threshold while the energy sum of the (k−1) th  sample and the k th  sample multiplied by the first constant is greater than the first threshold and the energy sum of the k th  sample and the (k+1) th  sample multiplied by the second constant is greater than the second threshold, and replacing the (k+1) th  sample with a second replacement sample to output while at least one of the energies of the (k+1) th  to the (k+m) th  samples is greater than the third threshold. Wherein m is a positive integer and is greater than 1. 
   The present invention further provides a device for suppressing impulse noise for sequentially receiving a sample stream. x[n] and detecting and suppressing interruptions of impulse noises to the sample stream x[n], wherein the sample stream x[n] includes a plurality of samples obtained by sampling the signals according to a sampling period, and n represents a discrete-time independent variable. The device for suppressing impulse noise includes a first delay, a second delay and a third delay; a first energy obtainer, an adder, a comparator, a first AND gate, and a first selector. In an embodiment of the present invention, the first selector may be a multiplexer. 
   Wherein, the first delay receives the samples of the sample stream x[n] in sequence and outputs each sample after delaying a sampling period. The first energy obtainer receives the samples of the sample stream x[n] in sequence and outputs the energy of each sample. The second delay receives the output of the first energy obtainer and outputs the output of the first energy obtainer after delaying a sampling period. The adder receives the outputs of the first energy obtainer and the second delay to output the energy sum of the outputs of the first energy obtainer and the second delay. The comparator compares the energy sum of the outputs of the first energy obtainer and the second delay with a first threshold or a second threshold, and outputs a first comparison result. The third delay receives the first comparison result and delays the first comparison result a sampling period to output a second comparison result. The first AND gate receives the first comparison result and the second comparison result and performs logic AND operation to output a first control signal. The first selector selects one of the output of the first delay and a first replacement sample according to the first control signal to output as a first output signal. 
   The device for suppressing impulse noise according to an exemplary embodiment of the present invention further includes a first delay set and a second delay set; a second energy obtainer, a comparator set, an OR gate, a second AND gate and a second selector. In an embodiment, the second selector may be a multiplexer. 
   Wherein, the first delay set receives a sample stream x[n−1] which is a delayed version of the sample stream x[n] shifted by one sampling period, and outputs the samples of the sample stream x[n−1] after delaying m−1 sampling periods. The second energy obtainer receives the samples of the sample stream x[n−1] and outputs the energies of the samples. The second delay set receives the output of the second energy obtainer and delays the output of the second energy obtainer to output the energies of m−1 delayed samples, wherein the energy of the 1 st  delayed sample is the output of the second energy obtainer after delaying one sampling period, the energy of the i th  delayed sample is the energy of the (i−1 ) th  delayed sample after delaying one sampling period, and i is an integer and 1&lt;i≦m. The comparator receives the output of the second energy obtainer, the energies of the delayed samples, and a third threshold, and compares the output of the second energy obtainer and the energy of each delayed sample with the third threshold to output the comparison results. The OR gate receives the comparison results and performs logic OR operation to output a third control signal. The second AND gate receives the first control signal and the third control signal and performs logic AND operation to output a second control signal. The second selector selects one of the output of the first delay set and a second replacement sample according to the second control signal to output as a second output signal. 
   In the present invention, the energies of a plurality of samples are compared with the thresholds to determine whether the samples are interrupted by impulse noises and to suppress the samples interrupted by the impulse noises, and the structure thereof is easy to implement. Moreover, besides one-phase detection and suppression, the method and device in the present invention can also employ two-phase detection and suppression to obtain lower bit error rate (BER). 
   In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a flowchart illustrating the method for suppressing impulse noise according to an exemplary embodiment of the present invention; 
       FIG. 2A  is a block diagram of a device for suppressing impulse noise according to an exemplary embodiment of the present invention; 
       FIG. 2B  is a diagram illustrating the respective operations on the sample stream of a first phase and a second phase detecting and suppressing devices in  FIG. 2A ; 
       FIG. 2C  is a diagram illustrating samples x[k+4]˜x[k−1]; 
       FIG. 2D  is a diagram illustrating sample streams x[n] and x[n−1]; 
       FIGS. 3A and 3B  are block diagrams respectively illustrating the first phase detecting and suppressing device and the second phase detecting and suppressing device in  FIG. 2A ; 
       FIG. 4  is a block diagram of a device for suppressing impulse noise according to another exemplary embodiment of the present invention; and 
       FIG. 5  is a block diagram of a device for suppressing impulse noise according to yet another exemplary embodiment of the present invention. 
   


   DESCRIPTION OF EMBODIMENTS 
     FIG. 1  is a flowchart illustrating the method for suppressing impulse noise according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , the method for suppressing impulse noise includes two phases, i.e. the first phase S 110  and the second phase S 120 .  FIG. 2A  is a block diagram of a device  200  for suppressing impulse noise according to the method illustrated in  FIG. 1 . Device  200  includes a first phase detecting and suppressing device  210  corresponding to the first phase S 110 , a second phase detecting and suppressing device  220  corresponding to the second phase S 120 , and other input/output or control signals. In addition,  FIG. 2B  is a diagram illustrating the first phase S 110  (or the first phase detecting and suppressing device  210  in  FIG. 2A ) and the second phase S 120  (or the second phase detecting and suppressing device  220  in  FIG. 2A ) in  FIG. 1  respectively operating on the sample stream. 
   In various digital system (e.g. DVB-T system with COFDM) receivers, the received analog signals are sampled according to a sampling periods to generate a sample stream x[n]. The sample stream x[n] includes a plurality of samples, wherein the 1 st  sample is denoted as x[ 1 ], the 2 nd  sample is denoted as x[ 2 ], . . . , the k th  sample is denoted as x[k], and k is a positive integer. In addition, the energy of the sample x[ 1 ] is denoted as E[ 1 ], the energy of the sample x[ 2 ] is denoted as E[ 2 ], . . . , the energy of the sample x[k] is denoted as E[k]. 
   Moreover, as shown in  FIG. 2C , sample x[k+3] is sample x[k+4] after delaying a sampling period T, sample x[k+2] is sample x[k+3] after delaying a sampling period T, . . . , sample x[k−1] is sample x[k] after delaying a sampling period T, wherein the delays  251 ˜ 255  all have the delay time with the duration of a sampling period T. Similarly, energy E[k+3] is energy E[k+4] after delaying a sampling period T, energy E[k+2] is energy E[k+3] after delaying a sampling period T, . . . , energy E[k−1] is energy E[k] after delaying a sampling period T. 
   Referring to both  FIG. 1  and  FIG. 2B , according to the method for suppressing impulse noise, three consecutive samples (i.e. x[k−1], x[k], and x[k+1]) are processed in the first phase S 110 . In step S 111 , the energy E[k−1] of the sample x[k−1] is added to the energy E[k] of the sample x[k], while since the weights of the energies of the samples x[k−1] and x[k] may not be the same, the sum of the two energies is expressed as E[k−1]+C 1 ×E[k], wherein the first constant C 1  represents the weight ratio between the energies of the samples x[k] and x[k−1]. However, for the convenience of description, below the first constant is assigned value 1, accordingly, next, the energy sum E[k−1]+E[k] of the samples x[k−1] and x[k] is compared with the first threshold TH 1 . 
   In step S 112 , it is determined that whether the energy sum E[k−1]+E[k] is greater than the threshold TH 1 . Step S 113  is proceeded when the energy sum E[k−1]+E[k] is greater than the threshold TH 1 . In step S 113 , the energy sum E[k]+C 2  ×E[k+1] of the samples x[k] and x[k+1] is compared with the second threshold TH 2 , wherein the second constant C 2  represents the weight ratio between the energies of the samples x[k+1] and x[k]. However, for the convenience of description, below the second constant is assigned value 1, thus, whether the energy sum E[k]+E[k+1] is greater than the threshold TH 2  is determined in step S 114 . In an embodiment, the threshold TH 1  may be equal to the threshold TH 2 . 
   In step S 114 , the energy sum of the sample x[k] with its previous sample x[k−1], and the energy sum of the sample x[k] with its next sample x[k+1] both exceed the threshold if the energy sum E[k]+E[k+1] is greater than the threshold TH 2 . Here, the possibility of the sample x[k] being interrupted by impulse noise is very high, thus step S 115  is executed to suppress the impulse noise and to replace the likely interrupted sample x[k] with a first replacement sample DA 1 . 
   Thus, after the samples x[k−1], x[k], and x[k+1] are processed in the first phase S 110 , sample x[k−1], replacement sample DA 1 , and sample x[k+1] are output in sequence. Here, the replacement sample DA 1  may be the long-term average or the moving average of the signal, or may also be a digital value. 
   As to the situations of the energy sum E[k−1]+E[k] being smaller than the threshold TH 1  in step S 112 , or the energy sum E[k−1]+E[k] being greater than the threshold TH 1  in step S 112  but the energy sum E[k]+E[k+1] being smaller than the threshold TH 2  in step S 114 , the sample x[k] is determined being not interrupted by impulse noise, so the sample x[k] is not replaced. In other words, the original samples x[k−1], x[k], and x[k+1] are output in sequence after they are processed in the first phase 
   If in the first phase S 110 , the sample x[k] is determined being interrupted by impulse noise, the following several samples (i.e. x[k+1], x[k+2], . . . , x[k+m], wherein m is a positive integer and is greater than 1) have high possibility of being interrupted by impulse noises. Thus, according to the method for suppressing impulse noise, the samples x[k+1]˜x[k+m] are processed during the second phase S 120 . In the present embodiment, m=4. 
   In step S 121 , the energy E[k+1] of sample x[k+1], the energy E[k+2] of sample x[k+2], the energy E[k+3] of sample x[k+3], and the energy E[k+4] of sample x[k+4] are respectively compared with the third threshold TH 3 . In step S 122 , it is determined that whether the energy of at least one sample among the samples x[k+1]˜x[k+4] is greater than the threshold TH 3 . When there is at least one sample having its energy greater than threshold TH 3 , the possibility of sample x[k+1] being interrupted by impulse noise is very high. Here, step S 123  is executed to suppress the impulse noise and to replace the likely interrupted sample x[k+1] with a second replacement sample DA 2 . Accordingly, the replacement sample DA 2  and samples x[k+2]˜x[k+4] are output sequentially after the samples x[k+1]˜x[k+4] are processed during the second phase S 120 . In an embodiment of the present invention, the replacement sample DA 2  may be equal to the replacement sample DA 1 . 
   Referring to  FIG. 2A , the device  200  for suppressing impulse noise includes a first phase detecting and suppressing device  210  and a second phase detecting and suppressing device  220 . The first phase detecting and suppressing device  210  receives a sample stream x[n], a first threshold TH 1 , and a second threshold TH 2 , and outputs a first output signal OUT 1  and a first control signal CTRL 1 . The second phase detecting and suppressing device  220  receives a sample stream x[n−1], a first control signal CTRL 1 , and a third threshold TH 3 , and outputs a second output signal OUT 2 . Wherein, the diagrams of the sample streams x[n] and x[n−1] are illustrated in  FIG. 2D , and the sample stream x[n] is an advanced version of the sample stream x[n−1] shifted by one sampling period T. The detailed circuit block diagrams of the detecting and suppressing devices  210  and  220  are respectively illustrated in  FIGS. 3A and 3B . 
   Referring to  FIG. 3A , the first phase detecting and suppressing device  210  includes a first delay  301 , a second delay  303 , a third delay  306 , a first energy obtainer  302 , an adder  304 , a comparator  305 , a first AND gate  307  and a first selector  308 . In an embodiment of the present invention, the first selector  308  may be a multiplexer. 
   For example, the detecting and suppressing device  210  receives the sample x[k] of the sample stream x[n]. The delay  301  receives the sample x[k] and delays a sampling period T to output the sample x[k−1]. The energy obtainer  302  receives the sample x[k] and outputs the energy E[k] of the sample x[k]. The delay  303  receives the energy E[k] of the sample x[k] and delays a sampling period T to output energy E[k−1], i.e. the energy of the sample x[k−1]. The adder  304  receives the energies of the samples x[k] and x[k−1], which are respectively E[k] and E[k−1], and outputs the sum E[k−1]+E[k] of the two energies. The comparator  305  compares the energy sum E[k−1]+E[k] with the threshold TH 1  and outputs a first comparison result COMP 1 . The delay  306  receives the first comparison result COMP 1  and delays a sampling period T to output a second comparison result COMP 2 , i.e. the result of comparing the energy sum E[k]+E[k+1] and the threshold TH 2 . Based on the foregoing analysis, the result of comparing the energy sum E[k]+E[k+1] and the threshold TH 2  is generated while the detecting and suppressing device  210  receives the sample x[k+1] of the sample stream x[n], here the output of the delay  301  is the sample x[k]. 
   When the energy sum E[k−1]+E[k] of the samples x[k−1] and x[k] is greater than the threshold TH 1 , i.e. the comparison result COMP 1  is “1”, and when the energy sum E[k]+E[k+1] of the samples x[k] and x[k+1] is also greater than the threshold TH 2 , i.e. the comparison result COMP 2  is also “1”, the control signal CTRL 1  output by the AND gate  307  is “1”, which means the sample x[k] is interrupted by impulse noise. Here, the control signal CTRL 1  is “1” and controls the selector  308  to select the replacement sample DA 1  to output as the output signal OUT 1 . As to the situations of the energy sum E[k−1]+E[k] being smaller than the threshold TH 1 , or the energy sum E[k−1]+E[k] being greater than the threshold TH 1  but the energy sum E[k]+E[k+1] being smaller than the threshold TH 2 , the sample x[k] is not interrupted by impulsive noise. Here, the control signal CTRL 1  is “0” and controls the selector  308  to select the sample x[k] output by the delay  301  to output as the output signal OUT 1 . 
   Referring to  FIG. 3B , the second phase detecting and suppressing device  220  includes a first delay set  310 , a second delay set  320 , a second energy obtainer  340 , a comparator set  330 , an OR gate  350 , a second AND gate  360 , and a second selector  370 . In an embodiment of the present invention, the second selector  370  may be a multiplexer. Wherein, the delay sets  310  and  320  can both delay the inputs thereof m−1 sampling period T, i.e. the delay sets  310  and  320  both can be formed by coupling m−1 delays, which can delay one sampling period T, in series. The comparator set  330  includes m comparators. In the present embodiment, m=4. Accordingly, the delay set  310  includes delays  312 ˜ 314 , the delay set  320  includes delays  322 ˜ 324 , and the comparator set  330  includes comparators  331 ˜ 324 . 
   For example, the detecting and suppressing device  220  receives the sample x[k+4] of the sample stream x[n−1]. The delay set  310  receives the sample x[k 4] and delays three sampling period T to output a sample x[k+1]. The energy obtainer  340  receives the sample x[k+4] and outputs the energy E[k+4] of the sample x[k+4]. The delay set  320  receives the energy E[k+4] of the sample x[k+4] and delays it to output the energies of three delayed samples, wherein the energy E[k+3] of the 1 st  delayed sample x[k+3] output by the delay  322  is the output E[k+4] of the energy obtainer  340  after delaying a sampling period T, the energy E[k+2] of the 2 nd  delayed sample x[k+2] output by the delay  323  is the energy E[k+3] of the first delayed sample x[k+3] after delaying a sampling period T, and the energy E[k+1] of the 3 rd  delayed sample x[k+1] output by the delay  324  is the energy E[k+2] of the 2 nd  delayed sample x[k+2] after delaying a sampling period T. 
   The output E[k+4] of the energy obtainer  340  and the energies E[k+3]˜E[k+1] of the delayed samples are respectively received by the corresponding comparators  331 ˜ 334  in the comparator set  330  to be respectively compared with the threshold TH 3  and to output the comparison results. The OR gate  350  receives these comparison results and performs logic OR operation to output the third control signal CTRL 3 . When at least one of the energies E[k+4]˜E[k+1] is greater than the threshold TH 3 , e.g. the energy E[k+3] is greater than the threshold TH 3 , the comparison result output by the comparator  331  is, e.g. “1”, so that the control signal CTRL 3  output by the OR gate  350  is “1”. Here, if the control signal CTRL 1  is also “1” (i.e. the sample x[k] is interrupted by impulse noise), then the AND gate  360  outputs a second control signal CTRL 2  according to the control signals CTRL 1  and CTRL 3  to control the selector  370  to select the replacement sample DA 2  to output as the second output signal OUT 2 . 
   When the energies E[k+4]˜E[k+1] are all smaller than the threshold TH 3 , which means the possibility of the sample x[k+1] being interrupted by impulse noise is very low, the comparison results output by the comparators  331 ˜ 334  are, e.g. all “0”, so that the control signal CTRL 3  output by the OR gate  350  is “0”. Thus, no matter what the control signal CTRL 1  is, the control signal CTRL 2  output by the AND gate  360  are all “0”, and which controls the selector  370  to select the sample x[k+1] output by the comparator set  310  to output as the output signal OUT 2 . 
   Actually, the method for suppressing impulse noise as shown in  FIG. 1  can be achieved with only the first phase S 110 , however, with the second phase S 120  integrated, better performance, e.g. bit error rate about 1 dB lower, can be achieved. Similarly, in  FIG. 2A , the device  200  for suppressing impulse noise employing the method in  FIG. 1  can also be achieved with only a first phase detecting and suppressing device  210 , however, if integrated with the second phase detecting and suppressing device  220 , better performance can be achieved. Moreover, the method and device of the present invention are applicable to an intermediate frequency system, wherein the sample stream x[n] is a plurality of signals, but are also applicable to a baseband system, wherein the sample stream x[n] is real number signals. Furthermore, the method and device of the present invention are applicable to an orthogonal frequency division multiplexing (OFDM) system or a coded orthogonal frequency division multiplexing (COFDM) system. 
   When the device for suppressing impulse noise of the present invention includes a first phase and a second phase detecting and suppressing devices, the circuit thereof can be altered appropriately to simplify the structure, e.g. the devices for suppressing impulse noise as shown in  FIGS. 4 and 5 . 
   Referring to  FIG. 4 , the precondition of implementing the device  400  for suppressing impulse noise is that the first replacement sample and the second replacement sample respectively used by the first detecting and suppressing device and the second detecting and suppressing device should be the same (both are DA 1 ). 
   When the OR gate  409  outputs “0”, the selector  470  selects the output of the delay set  410  as its output; otherwise, when the OR gate  409  outputs “1”, the selector  470  selects the replacement sample DA 1  as its output to suppress impulse noise. Wherein, when one of the control signals CT 1  and CT 2  received by the OR gate  409  is “1”, the OR gate  409  outputs “1”. 
   Here, the control signal CT 1  being “1” means that the energy sum of the samples x[k−1] and x[k] is greater than the threshold TH 1  and the energy sum of the samples x[k] and x[k+1] is greater than the threshold TH 2 , and this can be deduced by assuming that the input of the delay set  410  is the sample x[k+3] and the output thereof is the sample x[k]. When the input of the delay set  410  is the sample x[k+3] and the output thereof is the sample x[k], the adder  404   a  outputs the energy sum of the samples x[k−1] and x[k] and compares it with the threshold TH 1  through the comparator  405   a , and the adder  404   b  outputs the energy sum of the samples x[k] and x[k+1] and compares it with the threshold TH 2  through the comparator  405   b . When the energy sum of the samples x[k−1] and x[k] is greater than the threshold TH 1  and the energy sum of the samples x[k] and x[k+1] is greater than the threshold TH 2 , the control signal CT 1  output by the AND gate  407  is “1”, so that the OR gate  409  outputs “1” to control the selector  470  to select the replacement sample DA 1 . 
   In addition, the control signal CT 2  being “1” requires both control signals CT 1 ′ and CT 3  to be “1”. Wherein, the control signal CT 1 ′ being “1” means that the sample x[k] ever be replaced by the replacement sample DA 1 , and the control signal CT 3  being “1” means that the energy of at least one of the samples x[k+1]˜x[k+4] is greater than the threshold TH 3 , which can be deduced by assuming that the input of the delay set  410  is sample x[k+4] and the output thereof is sample x[k+1]. 
   When the input of the delay set  410  is the sample x[k+4] and the output thereof is the sample x[k+1], the comparator  405   a  compares the energy sum of the samples x[k] and x[k+1] with the threshold TH 1 , and the comparator  405   b  compares the energy sum of the samples x[k+1] and x[k+2] with the threshold TH 2 . When the energy sum of the samples x[k] and x[k+1] is greater than the threshold TH 1  and the energy sum of the samples x[k+1] and x[k+2] is greater than the threshold TH 2 , the output of the AND gate  407  is “1”. Here, the output of the AND gate  407  is delayed a sampling period by the delay  408  to become the control signal CT 1 ′, which means the energy sum of the samples x[k−1] and x[k] is greater than the threshold TH 1  and the energy sum of the samples x[k] and x[k+] is greater than the threshold TH 2 , i.e. the sample x[k] will be replaced by the replacement sample DA 1 . Moreover, the comparator set  430  and the OR gate  450  are used for determining whether the energy of at least one of the samples x[k+1]˜x[k+4] is greater than the threshold TH 3 , if the energy of at least one of the samples x[k+1]˜x[k+4] is greater than the threshold TH 3 , then the control signal CT 3  output by the OR gate  450  is “1”. 
   Referring to  FIG. 5 , the precondition of implementing the device  500  for suppressing impulse noise is that the first and the second replacement samples respectively used by the first phase and the second phase detecting and suppressing devices have to be the same (both are DA 1 ), and the first and the second thresholds have to be the same (both are TH 1 ). According to the analysis of the device  400  for suppressing impulse noise as shown in  FIG. 4 , the outputs of the delay set  510  are respectively assumed to be the samples x[k] and x[k+1], so that those skilled in the art should be able to analyze the device  500  for suppressing impulse noise, so will not be described again here. 
   In summary, in the present invention, the energy sums of a plurality of samples are compared with the thresholds to determine whether the samples are interrupted by impulse noise and to suppress the samples interrupted by impulse noises, and the structure thereof is easy to be implemented. In addition, besides one phase of detection and suppression, the method and device of the present invention can also employ two phases of detection and suppression to obtain lower bit error rate. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
A method for suppressing impulse noises is provided. The method is employed to receive a sample stream x[n], and to detect and suppress the interruption of impulse noise to the samples, wherein the sample stream x[n] includes a plurality of samples and n represents a discrete-time independent variable. The method includes comparing the energy sum of a (k-1) th sample and a k th sample multiplied by a first constant with a first threshold, comparing energy sum of the k th sample and a (k+1) th sample multiplied by a second constant with a second threshold while the energy sum of the (k-1) th sample and the k th sample multiplied by the first constant is greater than the first threshold, and replacing the k th sample with a first replacement sample to output while the energy sum of the k th sample and the (k+1) th sample multiplied by the second constant is greater than the second threshold.