This application claims the benefit of Taiwan application Serial No. 106130956, filed Sep. 11, 2017, the subject matter of which is incorporated herein by reference.
The invention relates in general to signal processing in a display apparatus, and more particularly to an impulsive interference detecting circuit applied to a display apparatus and an associated signal processing method.
In the Digital Video Broadcasting—Second Generation Terrestrial (DVB-T2) standard, impulsive interference is regarded as an issue that severely affects image display. Impulsive interference has large sudden and periodical amplitudes, and is usually generated by factors in the ambient environment, e.g., an operating washing machine or dishwasher, and a fast automobile passing by. In the prior art, whether a received signal has impulsive interference is determined by means of detecting whether the noise intensity in a signal is higher than a constant threshold. However, such detection method may result in misjudgment. For example, when the threshold is set to an overly high value and the energy of impulsive interference in a signal is weak, the impulsive interference being lower than the threshold may be regarded as a part of common noise, such that whether the signal has impulsive interference cannot be correctly determined. On the other hand, if the threshold is set too low, common noise may be misjudged as impulsive interference. Therefore, there is a need for a solution that provides an appropriate threshold for determining the presence of impulsive interference.
It is an object of the present invention to provide a circuit applied to a display apparatus and an associated signal processing method, which are capable of providing an appropriate threshold for accurately determining whether a received signal is affected by impulsive interference so as to solve issues of the prior art.
According to an embodiment of the present invention, a circuit applied to a receiver in a display apparatus includes a noise detecting circuit and a threshold determining circuit. The noise detecting circuit detects noise in a received signal to generate a plurality of noise intensity values. The threshold determining circuit, coupled to the noise detecting circuit, determines a threshold according to the plurality of noise intensity values to accordingly determine whether the received signal has impulsive interference. In one embodiment, the noise determining circuit includes a sorting circuit and a selecting circuit. The sorting circuit sorts an order of the plurality of noise intensity values. The selecting circuit selects, from the plurality of noise intensity values, the Mth noise intensity value as a predetermined noise intensity value. The threshold determining circuit determines the threshold according to the predetermined noise intensity value.
According to another embodiment of the present invention, a signal processing method applied to a receiver in a display apparatus includes: performing noise detection on a received signal to generate a plurality of noise intensity values; sorting an order the plurality of noise intensity values; selecting, from the plurality of noise intensity values, the Nth smallest noise intensity as a predetermined noise intensity value; and determining a threshold according to the predetermined noise intensity value. The threshold is used to determine whether the received signal has impulsive interference.
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.
As stated in the description of prior art, determining the presence of impulsive interference by means of a constant threshold can easily result in misjudgment. Therefore, the present invention provides a dynamic threshold determining method for solving the issues of the prior art. In one embodiment, noise of a signal includes common noise (e.g., additive white Gaussian noise (AWGN)) and impulsive interference. Thus, the embodiments of the present invention first determine an intensity of common noise, multiply the intensity of common noise by a ratio parameter (e.g., 2) to generate a threshold, and then determine whether the signal has impulsive interference according to the threshold (e.g., impulsive interference is present if the noise is higher than the threshold). However, when the signal has impulsive interference and the intensity of impulsive interference is weak, the intensity of common noise can overwhelm the impulsive interference. In the above situation, the threshold determined may be higher than the intensity of impulsive interference, causing a failure in determining such impulsive interference having a weak intensity.
To solve the above issue, the present invention further provides a method for dynamically determining a threshold to ensure that the intensity of common noise determined does not include any part associated with impulsive interference, such that whether a signal has impulsive interference can be correctly determined according to a threshold determined according to the intensity of common noise. Associated details are described in the embodiments below.
In the circuit 100, the noise detecting circuit 110 performs noise detection on a received signal to sequentially generate a plurality of noise intensity values. For example, assuming that the received signal adopts an orthogonal frequency-division multiplexing (OFDM) modulation scheme, the noise detecting circuit 110 performs noise detection sequentially on a plurality of symbols to generate a plurality of noise intensity values respectively corresponding to the plurality of symbols. The sorting circuit 120 sorts an order of the plurality of noise intensity values received, i.e., sorting the noise intensity values in an increasing or decreasing order. The selecting circuit 130 selects, from the plurality of noise intensity values, the Mth noise intensity value as a predetermined noise intensity value. In this embodiment, assuming that the number of the plurality of noise intensity values is K, M is between 1 and (K/2), where M and K are individually positive numbers. For example, assuming that the noise detecting circuit 110 generates 16 noise intensity values that are then sorted by the sorting circuit 120, the selecting circuit 130 selects from the noise detecting circuit the 3rd noise intensity value as the predetermined noise intensity value. The adjusting circuit 140 then generates the threshold TH according to the predetermined noise intensity value for the receiver to determine whether the received signal has impulsive interference. Further, the control circuit 150 shown in the diagram is for controlling settings and operations of the sorting circuit 120 and the selecting circuit 130, e.g., determining a sorting method of the sorting circuit 120 and the value M in the selecting circuit 130.
The control circuit 150 controls the selecting circuit 130 to select the Mth noise intensity value as an output. For example, the control circuit 150 can keep the switch SW3 conducted and the remaining switches turned off (not conducted), such that the selecting circuit 130 outputs the 3rd noise intensity value as the predetermined noise intensity value.
The adjusting circuit 140 performs predetermined calculation on the predetermined noise intensity value. For example, the adjusting circuit 140 may serve as a scaling circuit to multiply the predetermined noise intensity value by a ratio parameter (e.g., 2) to generate a product as the threshold TH. In another embodiment, the ratio parameter may also be set as “1”, or the adjusting circuit 140 is omitted and the output from the selecting circuit 130 is directly used as the threshold TH.
It should be noted that, in the embodiment in
In the description associated with the embodiment in
In step 500, the process begins.
In step 502, noise detection is performed on a received signal to generate a plurality of noise intensity values, each of which corresponds to one symbol.
In step 504, the plurality of noise intensity values are sorted in order.
In step 506, the Mth noise intensity value from the plurality of noise intensity values is selected as a predetermined noise intensity value.
In step 508, a threshold is generated according to the predetermined noise intensity value, wherein the threshold is used to determine whether the received signal has impulsive interference.
The circuit 100 is applicable to a receiver in a display apparatus.
In the receiver 600, the analog front-end circuit 610 processes the analog input signal from an antenna to generate a digital input signal. More specifically, the analog front-end circuit 610 can include components such as a radio-frequency (RF) to intermediate frequency (IF) mixer, a bandpass filter, an analog-to-digital converter (ADC), an IF to baseband mixer and a low-pass filter, so as to process the received analog input signal to generate the digital input signal. The CP removing circuit 620 removes a cyclic prefix from the digital input signal to generate a CP removed digital input signal. The time-domain/frequency-domain conversion circuit 630 converts the CP removed signal from a time domain to a frequency domain to generate a frequency-domain signal, and may be implemented by a fast Fourier transform (FFT) operation. Referring to
The pilot capturing circuit 640 captures a plurality of pilot cells (which may be edge pilot cells and/or scattered pilot cells, with scattered pilot cells being used as an example in the description below) of one symbol from the frequency-domain signal. Operations of the noise detecting circuit 110, the sorting circuit 120, the selecting circuit 130, the adjusting circuit 140 and the control circuit 150 are as previously described. Further, the noise detecting circuit 110 performs noise detection sequentially on a plurality of symbols according to the plurality of pilot cells captured by the pilot capturing circuit 640 to generate a plurality of noise intensity values respectively corresponding to the plurality of symbols. Further, in this embodiment, the noise detecting circuit 110 may be used as an impulsive interference detecting circuit, so as to determine whether the symbol has impulsive interference according to the noise intensity values of the plurality of pilot cells and the threshold TH generated by the threshold determining circuit 115 to generate a detection result. It should be noted that, the noise detecting circuit 110 generates the noise intensity value corresponding to a symbol without referring to the noise intensity of a plurality of data cells. Next, the microprocessor 660 controls the channel estimating circuit 670 to adopt different calculation methods to calculate, according to the detection result, a channel frequency response corresponding to the symbol in the frequency-domain signal. On the other hand, the data capturing circuit 642 captures a plurality of data cells of the symbol from the frequency-domain signal, and the equalizer 680 performs equalization on the plurality of data cells according to the channel frequency response calculated by the channel estimating circuit 670 to generate an equalized signal. The SNR estimating circuit 690 performs SNR estimation on the equalized signal according to the estimation result of the channel estimating circuit 670 to generate an estimated SNR result and provides the estimated SNR result to the microprocessor 660 to serve as reference for signal processing. The de-interleaving circuit 692 performs a de-interleaving operation on the equalized signal to generate a de-interleaved signal. The de-mapping circuit 694 performs a de-mapping operation on the de-interleaved signal to generate a plurality of code words. The decoder 696 performs low-density parity-check (LDPC) code and Bose-Chaudhuri-Hocquenghem (BCH) code decoding to obtain a plurality of decoded signals for further processing by the subsequent frame processing circuit 698.
In summary, in the circuit applied to a display apparatus of the present invention, the Mth noise intensity value, from a plurality of noise intensity values, is selected as the intensity of common noise, and the value of M is smaller than one-half of the number (i.e., quantity) of the plurality of noise intensity values. Thus, it is ensured that the noise intensity value selected does not include any part associated with impulsive interference, and whether a signal has impulsive interference can be correctly determined according to the threshold determined according to the intensity of common noise.
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.
Number | Date | Country | Kind |
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106130956 | Sep 2017 | TW | national |