Signal receiving apparatus in communication system and signal processing method thereof

A signal receiving apparatus includes a signal processing circuit, an adjacent-channel interference (ACI) filter and an ACI detecting circuit. The signal processing circuit performs a signal processing process on an input signal to generate a processed signal. The ACI filter filters out ACI from the processed signal to generate a filtered signal. The ACI detecting circuit detects an energy difference between the processed signal and the filtered signal, and provides the energy difference to the signal processing circuit as a reference for adjusting the signal processing process.

This application claims the benefit of Taiwan application Serial No. 106143020, filed Dec. 7, 2017, the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a communication system, and more particularly to an adjacent-channel interference (ACI) detection technology in a communication system.

Description of the Related Art

With the advancement of electronics-related technologies, diversified communication devices are ever-increasingly popular.FIG. 1shows a partial circuit of a communication receiver. An auto-gain control circuit102applies a gain G to an input signal SIby using an amplifier102ato generate an amplified signal SA. An analog-to-digital converter (ADC)104digitalizes the amplified signal SAto generate a digital sample result SD. An adjacent-channel interference (ACI) filter106filters out ACI from the digital sample result SD, and a filtered signal SFoutputted from the ACI filter106is forwarded to a back-end digital signal processing circuit (e.g., a decoder) for further processing.

As shown inFIG. 1, the gain G that the amplifier102aapplies to the input signal SIis determined by means of feedback based on the digital sample result SD. More specifically, a gain determining circuit102busually determines the gain G according to an average of absolute values of the amplitude (to be referred to as an average amplitude) of the digital sample result SD, and aims at an operation target of causing the average amplitude to approach a reference amplitude R, wherein the reference amplitude R is set according to a characteristic of the input signal SI(e.g., a television system standard with which the input signal SIcomplies).

In a real communication environment, the input signal SImay be superimposed with ACI, and thus has a higher amplitude at certain time points.FIG. 2(A)shows an example of a relationship of absolute values of the amplitude of the input signal SIversus time. In this example, the average amplitude of the input signal SIfalls around 0.4 V, and amplitude values differing significantly (to be referred to as abnormal amplitude values) from the average value appear at three positions22,22and23indicated by dotted circles as a result of the above ACI.FIG. 2(B)shows an example of a relationship of absolute values of the amplitude of the amplified signal SAversus time. Assume that a predetermined reference amplitude R is 0.7 V, and an initial value of the gain G is 1. Because the average amplitude of the digital sample result SDis 0.4 V, modifying the gain G originally in a value of 1 causes the average amplitude of the amplified signal SAto fall around 0.7 V. In this example, a dynamic range of the input signal of the ADC104is ±1.2 V. Although most part of the amplified signal having an average amplitude of 0.7 V falls within this dynamic range, the abnormal amplitude values at three positions21′,22′ and23′ (respectively corresponding to the positions22,22and23inFIG. 2(A)) are amplified by the amplifier102ato be greater than ±1.2 V. In practice, signal contents exceeding ±1.2 V in the amplified signal SAare cut off and discarded by the ADC104due to the limitation on the dynamic range for the input signal of the ADC104, resulting in a distortion issue.

As the presence of the abnormal amplitude values cannot be reflected, determining the gain G solely according to the average amplitude of the digital sample result SDlikely causes the above distortion issue. Such distortion caused by amplitude saturation yields a huge drawback—even if the subsequent ACI filter106or another filter circuit is capable of eliminating the influences of ACI and surge interference, the original signal contents cannot be reconstructed.

SUMMARY OF THE INVENTION

The invention is directed to a signal receiving apparatus and a signal processing method thereof for resolving the above issue.

According to an embodiment of the present invention, a signal receiving apparatus is provided. The signal receiving apparatus includes a signal processing circuit, an adjacent-channel interference (ACI) filter and an ACI detecting circuit. The signal processing circuit performs a signal processing process on an input signal to generate a processed signal. The ACI filter filters out ACI from the processed signal to generate a filtered signal. The ACI detecting circuit detects an energy difference between the processed signal and the filtered signal, and provides the energy difference to the signal processing circuit to serve as a reference for adjusting the signal processing process.

According to another embodiment of the present invention, a signal processing method for a signal receiving apparatus is provided. The method includes: performing a signal processing process on an input signal to generate a processed signal; filtering out ACI from the processed signal to generate a filtered signal; and detecting an energy difference between the processed signal and the filtered signal, and using the energy difference as a reference for adjusting the signal processing process.

It should be noted that, the drawings of the present invention include functional block diagrams of multiple functional modules related to one another. These drawings are not detailed circuit diagrams, and connection lines therein are for indicating signal flows only. The interactions between the functional elements/or processes are not necessarily achieved through direct electrical connections. Further, functions of the individual elements are not necessarily distributed as depicted in the drawings, and separate blocks are not necessarily implemented by separate electronic elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows a function block diagram of a signal receiving apparatus operating in a communication system according to an embodiment of the present invention. A signal receiving apparatus300includes a signal processing circuit301, an adjacent-channel interference (ACI) filter302and an ACI detecting circuit303. In practice, the signal receiving apparatus300may be various types of communication receivers with an ACI filter function, e.g., an Advanced Television Systems Committee (ATSC) or a Digital Terrestrial Multimedia Broadcast (DTMB) receiver. Operation details of the circuits in the signal receiving apparatus300are given below.

The signal processing circuit301includes an amplifier301a, a gain determining circuit301band an analog-to-digital converter (ADC)301c. The amplifier301applies a gain G (provided by the gain determining circuit301b) to an input signal SIto generate an amplified signal SA. The ADC301cdigitalizes the amplified signal SAto generate a digital sample result SD. The ACI filter302filters out ACI from the digital sample result SDand preserves a signal within a target frequency band. A filtered signal SFoutputted from the ACI filter302may be forwarded to a subsequent digital signal processing circuit (e.g., a decoder) for further processing.FIG. 4(A)shows an example of a spectrum of the digital sample signal SD, andFIG. 4(B)shows an example of a spectrum of the corresponding filtered signal SF, wherein the horizontal axis represents a standardized frequency and the vertical axis represents energy. It is seen by comparingFIG. 4(A)andFIG. 4(B)that, after passing through the ACI filter302, the signal energy within the target frequency band (a frequency range of −0.4 to 0.4) is kept substantially unchanged, whereas the signal energy outside the target frequency band is significantly reduced. As previously described, the input signal SImay be superimposed with ACI, such that abnormal amplitude values may appear at certain time points. In general, the probability of getting an abnormal amplitude value of the input signal SI on the time axis gets larger as the ACI intensifies. The signal receiving apparatus300uses such characteristic to determine whether there is an abnormal amplitude signal in the time domain, and accordingly adaptively adjusts the gain G. Associated details are as follows.

The ACI detecting circuit303detects an energy difference DPbetween the digital sample result SDand the filtered signal SF, and provides the energy difference DPto the gain determining circuit102b. In practice, the ACI detecting circuit303may detect respective powers (to be represented by PDand PF, respectively) of the digital sample result SDand the filtered signal SFby using a power detecting circuit. For example, on the spectrum, respective accumulated powers or power spectral densities (PSD) of the digital sample result SDand the filtered signal SFare obtained. In another example, respective average powers or accumulated powers of the digital sample result SDand the filtered signal SFwithin a predetermined period on the time axis are obtained. The energy difference DPmay be a difference between the powers PDand PF, or may be a ratio obtained by dividing the power PDby the power PF.

Whether ACI exists in the digital sample signal SDcan be learned from the energy difference DP. More specifically, if the digital sample signal SDhardly contains any ACI, the difference between the powers PDand PFof signals inputted into and outputted from the ACI302is quite small. In contrast, if ACI exists in the digital sample signal SD, a noticeable difference exists between the powers PDand PF; further, the energy difference DPgets larger as the ACI intensifies.

As shown inFIG. 3, when the gain G is determined, in addition to the average amplitude of the digital sample result SD, the gain determining circuit301bfurther takes into account the energy difference DP. For example, the gain determining circuit301bmay compare whether the energy difference DPis higher than a predetermined threshold. In practice, the predetermined threshold is not limited to any specific value, while it is usually determined based on characteristics of signals of different communication systems and characteristics of ACI signals. In one embodiment, the predetermined threshold may be determined according to the tolerance of a signal processing circuit (e.g., a decoder) in the system with respect to the number of distorted signals in a received signal. As previously stated, the energy difference DPgets larger as the ACI intensifies, and the probability of an abnormal amplitude value appearing in the input signal SIalso increases. For many decoders, decoding process may fail when the probability of distorted signals is higher than a predetermined value. In contrast, when the probability of distorted signals is lower than the predetermined value, the decoder is nonetheless capable of correcting the errors and correctly perform decoding even in the presence of distorted signals. Experiments or simulations may be conducted in advance to calculate a value of the energy difference DPthat causes an excess number of distorted signals and degrades the performance of the decoder, and the predetermined threshold can be accordingly determined. If the energy difference DPis lower than the predetermined threshold, the gain determining circuit301bis not required to decrease the gain G, i.e., the gain G determined according to the average amplitude of the digital sample result SDmay be directly used. In contrast, if the energy difference DPis higher than the predetermined threshold, the gain determining circuit301bmay appropriately decrease the gain G, so as to prevent an abnormal amplitude, after having passing through the amplifier301a, from exceeding the input signal dynamic range of the ADC301cand hence from resulting in a decoding failure in the subsequent decoder. In another embodiment, the predetermined threshold may be set to zero. Thus, once the ACI detecting circuit303detects a non-zero energy difference DP, the gain determining circuit301bmay adjust the gain G according to this energy difference DP. In this embodiment, when the energy difference DPis equal to zero, the gain determining circuit301bdoes not adjust the gain G.

In one embodiment, the gain determining circuit301bdetermines a scale for decreasing the gain G according to the value of the energy difference DP. More specifically, as the energy difference DPgets larger, the scale by which the gain determining circuit301bdecreases the gain G also gets larger. Ideally, under the premise of without distorting the input signal SAof the ADC301c, the adjusted gain G gets better as it gets larger (which helps the ADC301canalyze the amplified signal SA). Thus, in one embodiment, the resolution of the ADC301cis taken into consideration when the gain determining circuit301bconfigures a lower limit of the gain G. When the value of the energy difference DPwould cause the gain G to be lower than the lower threshold, the gain G is only adjusted to the lower limit instead of being adjusted further downward along with the increasing energy difference DP. Setting the lower limit is to prevent an insufficiently small amplitude of the amplified signal SAfrom being unsuccessfully analyzed by the ADC301c.

FIG. 5(A)andFIG. 5(B)show two examples of a detailed circuit of the gain determining circuit301b. How the gain determining circuit301bin the two examples adjusts the gain G are given in respective paragraphs below.

The gain determining circuit301binFIG. 5(A)includes an amplitude detecting circuit391, an adjusting circuit392, a difference calculating circuit393and a gain generating circuit394. The amplitude detecting circuit391obtains an average amplitude A of the digital sample result SD. The adjusting circuit392generates an adjusted reference amplitude R′ according to the energy difference DPand the reference amplitude R. An adjustment ratio of the reference amplitude R have positive correlation with the value of the energy difference DP; that, the extent of the adjustment of the reference amplitude R increases as the energy difference DPgets larger. An initial value of the reference amplitude R is set according to a characteristic of the input signal SI(e.g., a television system standard with which the input signal SIcomplies). The difference calculating circuit393calculates an amplitude difference DAbetween the average amplitude A and the adjusted reference amplitude R′. Through a look-up table or calculation, the gain generating circuit394generates the gain G according to the amplitude difference DA; the amplitude difference DAhas positive correlation with the gain G. For example, if the energy difference DPindicates that the ACI power in the digital sample result SDis higher than a predetermined threshold, the adjusting circuit392adjusts the reference amplitude R′ to be lower than the reference amplitude R, so as to reduce the amplitude difference DAand to further allow the gain generating circuit394to generate a smaller gain G (compared to the gain generated according to the reference amplitude R). If the energy difference DPindicates that the ACI power in the digital sample signal SDis lower than the predetermined threshold, the adjusting circuit392can set the reference amplitude R′ to be equal to the reference amplitude R (i.e., without adjusting the reference amplitude R′). In brief, by considering the energy difference DP, the signal receiving apparatus300is capable of alleviating the issue of signal distortion caused by excessive amplification of abnormal amplitude values.

In practice, the gain determining circuit301continues dynamically adjusting the gain G. For example, if after using the gain G for a period, the energy difference DPshows that the ACI power in the digital sample signal SDis no longer higher than the predetermined threshold, the adjusting circuit392may then set the adjusted reference amplitude R′ to be equal to the reference amplitude R.

The gain determining circuit301binFIG. 5(B)includes an amplitude detecting circuit395, a difference calculating circuit396, an original gain generating circuit397and an adjusting circuit398. The amplitude detecting circuit395detects an average amplitude A of the digital sample result SD. The difference calculating circuit396calculates an amplitude difference DAbetween the average amplitude A and the reference amplitude R. Through a look-up table or calculation, the original gain generating circuit397generates an original gain G0. The adjusting circuit398adjusts the original gain Go according to the energy difference DPto accordingly generate the gain G. For example, if the energy difference DPshows that the ACI intensity in the digital sample signal SDis higher than a predetermined threshold, the adjusting circuit398sets the gain G to be lower than the original gain G0, e.g., setting the value of the gain G to be equal to 90% of the original gain G0.

One person skilled in the art can understand that, there are various circuit configurations and components capable of achieving the concept of the gain determining circuit301bwithout departing from the spirit of the present invention. In practice, the gain determining circuit301bmay be implemented by various control and processing platforms, e.g., fixed and programmable logic circuits such as programmable gate arrays, application-specific integrated circuits, microcontrollers, microprocessors and digital signal processors. Further, the gain determining circuit301bmay also be designed to complete associated tasks through executing a processor instruction stored in a memory (not shown).

It should be noted that, the energy difference DPmay be used as reference information for adjusting other signal processing processes, other than the above gain G. More specifically, the energy difference DPcan indicate whether ACI exists in the digital sample result SDand the approximate intensity of the ACI, and any circuit located before the ACI filter302and needing related information may refer to the energy difference DP.

FIG. 6shows a flowchart of a signal processing method for a signal receiving apparatus according to another embodiment of the present invention. In step S61, a signal processing process is performed on an input signal to generate a processed signal. In step S62, ACI is filtered out from the processed signal to generate a filtered signal. In step S63, an energy difference between the processed signal and the filtered signal is detected, and the energy difference is used as a reference for adjusting the signal processing process. One person skilled in the art can understand that, the operation variations in the foregoing description associated with the signal receiving apparatus300are applicable to the signal process method inFIG. 6, and shall be omitted herein.