Abstract:
A communication receiving system, an equalizer, and a method for mitigating a burst noise effect of a signal are provided. The equalizer is configured to compensate the signal received from a communication channel. The communication receiving system comprises a receiver, the equalizer, and a detection module. The receiver transmits the signal to the equalizer after receiving the signal. The equalizer compensates the signal and adapts its weighting factors by modifying a correction term upon detection of burst noise. Thereby, the burst noise effect of the signal is mitigated, and the probability that the equalizer survives the burst noise condition increases. Thus, the quality of communication systems under burst noise cases may be enhanced under without increasing the complexity of hardware.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is cross-referenced with U.S. patent application Ser. No. 11/752,440 entitled “System and Method of Detecting Burst Noise and Minimizing the Effect of Burst Noise” filed on May 23, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an equalizer and a method for processing a signal and a communication receiving system comprising the same. More particularly, the present invention relates to an equalizer and a method that calculate a correction term in order to mitigate the burst noise effect of a signal and a communication receiving system comprising the same. 
         [0004]    2. Descriptions of the Related Art 
         [0005]    Communication techniques have been rapidly developed in recent years. However, the current technique still face the difficulties of thoroughly eliminating interferences introduced during transmission. Interferences are usually caused by noises, and interferences become severe when it comes to burst noises. In the digital communication, such as cable system or other communication field, in addition to the semi-static multi-path propagation environment, the burst noises may occur due to lightening, electric switch, or other related factors. 
         [0006]      FIG. 1A  illustrates a constellation diagram for 256-Quadrature Amplitude Modulation (QAM) at a receiving end with the absence of burst noises. In  FIG. 1A , the dots represent received QAM symbols, the horizontal axis denotes the real part (i.e. signals from I-channel) of the received QAM symbols, and the vertical axis denotes the imaginary part (i.e. signals from Q-channel) of the received QAM symbols. The I-channel and the Q-channel are familiar to people skilled in the art, so their detailed descriptions are omitted for brevity. Since there are no burst noises, the values of the received QAM symbols are closed to the transmitted values. The phenomenon may be seen from  FIG. 1A , wherein each of the dots is formed almost orderly as a 16-by-16 array. 
         [0007]      FIG. 1B  illustrates that a constellation diagram for 256-QAM modulation at a receiving end with the presence of burst noises. Similarly, the dots represent received QAM symbols, the horizontal axis denotes the real part of the received QAM symbols, and the vertical axis denotes the imaginary part of the received QAM symbols. Compared with  FIG. 1A , the values of the received QAM symbols in  FIG. 1B  are not closed to the transmitted values. The burst noise phenomenon makes the receiver having difficulties in measuring the original transmitted values from the received QAM symbols. Meanwhile, long-period of burst noise might diverge from the receiving parameters and cause system failures. 
         [0008]    To recover the original information from the received data corrupted by burst noises, most developers focus on developing decoding algorithms that can corporate with hardware. For example, a de-interleaver and a Forward Error Correction (FEC) algorithm are utilized to integrate into a demodulator. However, the effectiveness of the aforementioned prior arts is based on the assumption that demodulation subsystems, such as synchronization modules and equalizer, maintain proper reception conditions. Merely focusing on a de-interleaver or FEC may not guarantee proper recovery of the original signal. For example, under the condition of occurrence of long burst noise, the equalizer coefficients might be corrupted due to misled adaptation and cannot be automatically recovered for its proper function even after the occurrence of burst noise. This crashes the communication session, and the only way to rebuild the communication is to reboot the receiver with sensible boot-up time. 
         [0009]    Accordingly, it is urgent in this field to find an approach for mitigating the effect of burst noise and design a robust equalizer while considering the fact of the burst noise to enhance communication quality. 
       SUMMARY OF THE INVENTION 
       [0010]    An objective of this invention is to provide an equalizer for processing a signal received from a communication channel. The equalizer comprises a first calculation module, a determination module, and a second calculation module. The first calculation module is configured to calculate a correction term related to the signal in response to a noise effect of the signal, wherein the correction term comprises a decision error. The determination module is configured to determine the correction term by comparing the decision error of the correction term with a predetermined threshold. The second calculation module is configured to calculate a plurality of weighting factors according to the determined correction term, wherein the weighting factors are used to mitigate the noise effect of the signal. By having the configurations, the equalizer may process the signal from the communication channel without the increase of the complexity in terms of hardware implementation. 
         [0011]    Another objective of this invention is to provide a method for processing a signal received from a communication channel. The method comprises the steps of calculating a calculated term related to the signal in response to a noise effect of the signal, wherein the correction term comprises a decision error; determining the correction term according to the decision error in the correction term, and calculating a plurality of weighting factors according to the determined correction term, wherein the weighting factors are used to mitigate the noise effect of the signal. By having the steps, the method is able to mitigate the effect caused by the burst noise. As a result, communication quality is enhanced without increase of the complexity in terms of hardware implementation. 
         [0012]    Yet a further objective of this invention is to provide a communication receiving system. The communication receiving system comprises a receiver, a detection module, and an equalizer. The receiver is configured to receive a signal from a communication channel. The detection module is configured to detect a noise effect of the signal. The equalizer is configured to calculate a correction term related to the signal, determine a decision error of the correction term being greater than a predetermined threshold, replacing the decision error if the decision error is greater than the predetermined threshold by a replacing threshold, to calculate a plurality of weighting factors according to the determined correction term, and to calculate a noise-mitigated output signal by convolving the signal and the weighting factors. As a result, the noise effect of the signal can be mitigated by the use of the weighting factors. 
         [0013]    According to the aforementioned description, the present invention calculates a correction term to adjust a plurality of weighting factors that are used to mitigate noise effect of a signal. Since weighting factors have been adjusted, noise effect of the signal can be mitigated more thoroughly. As a result, communication qualities can be enhanced without increase of the complexity in terms of hardware implementation. 
         [0014]    The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  illustrates a constellation diagram for 256-QAM modulation at a receiving end with the absence of burst noises; 
           [0016]      FIG. 1B  illustrates a constellation diagram for 256-QAM modulation at receiving end with the presence of burst noises; 
           [0017]      FIG. 2  illustrates an embodiment of a communication receiving system of the present invention; 
           [0018]      FIG. 3  illustrates a block diagram of the equalizer of the communication receiving system; and 
           [0019]      FIG. 4  illustrates an embodiment of this invention, which is a method for processing a signal received from a communication channel. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    The detailed description of embodiments of the present invention, which relates to an equalizer and a method for mitigating the burst noise effect in a signal and a communication receiving system comprising the same, is provided. However, these embodiments are not intended to limit that this invention can only be embodied in any specific context and applications described in these embodiments. Therefore, descriptions of these embodiments are only intended to illustrate rather than to limit this invention. It should be noted that elements not related to this invention are omitted from depiction in the following embodiments and attached drawings. In this description, two-dimensional signal format is assumed but not limited. 
         [0021]      FIG. 2  depicts an embodiment of a communication receiving system  2  of the present invention. The communication receiving system  2  comprises a receiver  21 , an equalizer  23 , a detection module  27 , and a de-interleaver  25 .  FIG. 3  illustrates a block diagram of the equalizer  23 , which comprises a first calculation module  231 , a determination module  232 , a second calculation module  234 , and a third calculation module  235 . 
         [0022]    The receiver  21  receives a signal  201  from a communication channel. In this embodiment, the signal  201  is analog, so the receiver  21  further converts the signal  201  into a digital signal  202 . In digital signal  202 , synchronization processing is assumed. The received signal  201  suffers from various kinds of distortion during transmission, such as channel effect, background noise, and burst noise. Therefore, as the digital signal  202  is generated from the signal  201 , the distortion effect is still remained. 
         [0023]    The equalizer  23 , and the detection module  27  form a loop. Thus, the equalizer  23  is able to process the digital signal  202  with the assistance of previous processed results. 
         [0024]    The equalizer  23  is aimed to compensate the digital signal  202  (i.e. a signal related to the signal  201 ) for the communication channel distortion. More specifically, the equalizer  23  adjusts its weighting factors to achieve the compensation. In this embodiment, the equalizer  23  uses the following update equation to update the weighting factors. 
         [0000]        W ( n+ 1)= W ( n )+α X ( n ) e *( n )   (1) 
         [0000]    wherein n denotes the time instant, W(n) represents the present weighting factors, W(n+1) represents the next weighting factors, X(n) represents the input signal vector of the equalizer, α is a constant and often called as the step-size, and e*(n) is a complex conjugate of a decision error e(n). It is noted that the decision error e(n) is fedback from the detection module  27 . In this embodiment, the decision error is a vector. The details will be described later. 
         [0025]    In the above update equation for weighting factors, αX(n)e*(n) is called a correction term, which leads the weighting factors to the right setting for channel equalization. From the update equation, it is known that the correction term αX(n)e*(n) comprises a decision error e(n). The key to compensate the digital signal  202  more accurately relies on the accuracy of the correction term αX(n)e*(n). This correction term is more error-prone in burst noise cases. In order to derive suitable correction term αX(n)e*(n) in the presence of burst noise, the equalizer  23  works on the decision error e(n) of the correction term αX(n)e*(n). 
         [0026]    After receiving the signal  201  and converting the signal  201  into the digital signal  202 , the first calculation module  231  calculates the present correction term ( i.e. αX(n)e*(n) ) in response to the multipath and noise effects, i.e. in response to the noise effect of the signal. 
         [0027]    Upon detecting the presence of burst noise (see U.S. Ser. No. 11/752,440), after the present correction term (i.e. αX(n)e*(n)) is calculated, the determination module  232  determines whether this correction term is needed to be modified according to the decision error. In the present invention, there are two approaches proposed. One is constraining approach, and the other is nullifying approach. For both approaches, the determination module  232  determines the correction term by comparing the decision error with a predetermined threshold. 
         [0028]    Specifically, for the constraining approach, the determination module  232  determines whether the value of the decision error is greater than the value of the predetermined threshold vector. For example, the determination module  232  determines whether an x-directional (horizontal direction) value of the decision error e(n)=(x,y) is greater than an x-directional value of the predetermined threshold. When the absolute value of x (i.e. the x-directional value of the decision error) is not greater than (i.e. less than or equal to) the x-directional value of the predetermined threshold, the determination module  232  of the equalizer  23  does not make changes to the x-directional value of the decision error; that is, remains unchanged. On the contrary, when the determination module  232  determines that the absolute value of x (i.e. x-directional value of the decision error) is greater than the x-directional value of the predetermined threshold, the determination module  232  replaces the x-directional value of the decision error with an x-replacing value of a predetermined replacing vector. In this embodiment, the x-replacing value of the predetermined replacing vector is related to the predetermined threshold. For example, the x-replacing value may be calculated by multiplying the absolute value of the x-directional value of the predetermined threshold with the sign of the original x-directional value of the decision error. The same procedure applies to a y-directional value of the decision error as well. In addition, the predetermined threshold, being a vector, defines the normal level of tolerance of burst noise. If the value of the decision error vector is greater than the value of the predetermined threshold, this means the burst noise is quite large. 
         [0029]    For the nullifying approach, if either the absolute value of the x-directional value of the decision error is greater than the x-directional value of the predetermined threshold or the absolute value of the y-directional value of the decision error is greater than the y-directional value of the predetermined threshold, the determination module  232  may replace the decision error with the vector of (0,0). Otherwise, the x-directional or y-directional of the decision error remains as the original value. This is saying that the decision error is set to be (0,0) while the burst error is quite large. After the decision error is updated, the second calculation module  234  updates the weighting factors from W(n) to W(n+1), which is to be used to process the next input vector X(n+1). More specifically, the second calculation module  234  first calculates the updated correction term αX(n)&lt;e*(n)&gt;, wherein &lt;e*(n)&gt; is now with the value of the updated decision error generated from the determination module  232 . Then, the second calculation module  234  adds the update term αX(n)&lt;e*(n)&gt; to W(n) to derive W(n+1), that is 
         [0000]        W ( n+ 1)= W ( n )+α X ( n )&lt; e *( n )&gt; 
         [0030]    In addition, for the case of there is no burst noise and for the case that determining there is no need to modify the decision error after the result of comparing to threshold as mentioned above, the determination module  232  forwards the correction term to the second calculation module  234  for generating W(n+1), that is 
         [0000]        W ( n+ 1)= W ( n )+α X ( n ) e *( n ) 
         [0031]    Then, the third calculation module  235  for calculating the noise-mitigated output signal  203  by convolving the digital signal  202  with the burst-noise-mitigated weighting factors W(n+1). Thereafter, the equalizer  23  output signal  203  is transmitted to the de-interleaver  25  for de-interleaving. The de-interleaver  25 , FEC processing is usually added for channel decoding purpose. The functions and the operations of the de-interleaver  25  are well-known to people skilled in the art, so the detailed description is omitted here for brevity. 
         [0032]    The detection module  27  receives the equalizer  23  output signal  203  from the equalizer  23  and produces results in order to calculate the decision error e(n). The equalizer  23  output signal  203  from the equalizer  23  is denoted as y(n). The detection module  27  performs a decision on the equalizer  23  output signal  203  by comparing y(n) with decision boundaries. It should be noted that the boundaries are designed according to various modulation types. There are decisions d(n) located in the different the decision boundaries. Once the detection module  27  detects which region, separated by the boundaries, is the y(n) belongs to, the detection module  27  assigns the decision result d(n) which can be used to calculate the decision error e(n). The decision error e(n) is derived by the equation: e(n)=d(n)−y(n). The decision error e(n) can be fedback to the equalizer  23  for equalizing the weighting factors and then updating processing. It should be noted that the subtracting step for generating e(n) may be done in the detection module  27 , in this case the detection module output  205  comprise the decision error e(n). In the other embodiments, e(n) can be produced in the equalizer  23  and in this case the detection module output  205  denotes the decision result d(n). 
         [0033]    It is noted that the receiver  21 , the de-interleaver  25 , and the detection module  27  are familiar to people skilled in the art, so only those related to the present invention are described. The receiver  21  may comprise analog to digital converter and synchronization module in practice. The equalizer  23  of the communication receiving system  2  is able to work with other receivers, de-interleaver, and detection module. The detection module  27  for detecting the burst noise may be referred to the patent application Ser. No. 11/752,440 or other method for detecting the burst noise known by one who has skill in the relevant art. 
         [0034]    According to the aforementioned arrangement, upon detecting the presence of burst noise, this embodiment calculates the correction term to adjust the weighting factors that are used to mitigate the burst noise impact on channel equalization of the digital signal  202 . Since burst noise effect on weighting factors have been mitigated, the possibility that the equalizer survives the burst noise impact increases. As a result, communication qualities can be enhanced without increase of the complexity in terms of hardware implementation. 
         [0035]      FIG. 4  depicts a method for processing a signal of the exemplary embodiment of the present invention, wherein the signal x(n) is received from a communication channel. The method is used to mitigate the burst noise effect in the signal. Initially, the method executes step S 41  to receive the signal from a communication channel. Then, step S 42  is executed to generate an equalizer output signal by convolving the input signal and the weighting factor. More specifically, step  42  may use the equation y(n)=W H (n)X(n), wherein W(n) is a weighting factor vector and X(n) is the input signal vector. Then, a decision error e(n) is generated either in the detection module  27  or equalizer  23 , wherein the decision error e(n) is a vector. The detection module  27  also determines whether the burst noise is occurred as the step S 43 . If there is no existence of the burst noise, the decision error is no need to be calculated and goes directly to step  45  to calculate a plurality of weighting. Otherwise (i.e. the result of step S 43  is no), the decision error is calculated and compare to the predetermined threshold to decide whether to adjust e(n). Next, the method executes step S 44  for compensation processing to compare an x-directional value of the decision error with an x-directional value of a predetermined threshold if the burst noise is detected, wherein the predetermined threshold is also a vector. There are two proposed approaches, the constraining and nullifying approaches, for deciding how to replace the decision error e(n)=(x,y) in the present invention. For the constraining approach, x (i.e. the x-directional value) remains unchanged if the absolute value of x is less than the horizontal directional value of the predetermined threshold (herein refers as x-threshold value), and y (i.e. the y-directional value) remains unchanged if the absolute value of the y is less than the vertical directional value of the predetermined threshold (herein refers as y-threshold value). While x is greater than the x-threshold value, x is to be replaced with a replacing value. Similarly, while y is greater than the y-threshold value, y is to be replaced with another replacing value. Those two replacing values form a vector. The replacing vector may be related to the pre determined threshold. For example, x may be replaced with the absolute value of x-threshold value with the original sign of x and y may be replaced with the absolute value of y-threshold value with the original sign of y. In addition, the threshold vector defines the normal level of tolerance of burst noise. While the decision error is greater than the predetermined threshold, this implies the burst noise is quite large. For nullifying approach, if the absolute value of x is greater than the x-threshold value or the absolute value of y is greater than y-threshold value, the decision error is set to be (0,0). If the absolute value of x is less than the x-threshold value and the absolute value of y is less than the y-threshold value, the decision error is not changed. The step S 44  generates the updated decision error. A correction term related to the signal in response to the noise effect of the signal is calculated. More specifically, the signal is received continuously, so the noise effect is detected from a previous time instant. 
         [0036]    After that, step S 45  is executed to calculate a plurality of weighting factors according to the updated correction term from step S 44  or calculate a plurality of weighting factor directly from step S 43 . If the decision error is less than the predetermined threshold, the method executes step S 45  directly. 
         [0037]    In addition to the above steps, this embodiment is able to execute all the operations and functions as those described in the embodiment of the communication receiving system. Those skilled in the art can directly understand how this embodiment can execute the operations and functions based on the aforementioned embodiment of the communication receiving system. Consequently, redundant descriptions for the operations and functions are not repeated herein. 
         [0038]    In summary, this invention provides a communication receiving system, an equalizer, and a method for eliminating a noise effect of a signal received from a communication channel. By adjusting the correction term used in the equalizer, the noise effect can be better mitigated. Thus, the quality of communication systems can be enhanced without increase of the complexity in terms of hardware implementation. 
         [0039]    The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.