CN108055220B - ASK amplitude self-adaptive anti-noise demodulation method and device - Google Patents
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Abstract
The invention provides an ASK amplitude self-adaptive anti-noise demodulation algorithm and device, belongs to all-digital incoherent demodulation, and realizes optimization of an ASK traditional demodulation algorithm by detecting an envelope maximum value, dynamically configuring a decision threshold and processing positive and negative bidirectional noise. The amplitude matching circuit has good anti-noise performance, can automatically match the amplitude of an input signal, is suitable for the actual application scene with unstable signal intensity, can correctly demodulate 0/1 asymmetric data, overcomes the defect of the traditional ASK demodulation, and has great practicability.
Description
Technical Field
The invention relates to the technical field of communication, in particular to an ASK amplitude self-adaptive anti-noise demodulation algorithm and device.
Background
In wireless transmission, signals are radiated to space through an antenna in the form of electromagnetic waves, and in order to obtain high radiation efficiency, the size of the antenna should be generally larger than a quarter of the wavelength of the transmitted signals, while the wavelength of lower frequency components contained in baseband signals is long, so that the antenna is too long to be realized. By modulating, the spectrum of the baseband signal is moved to a higher carrier frequency, which can greatly reduce the size of the radiating antenna. In addition, the modulation can respectively move a plurality of baseband signals to different carrier frequencies to realize the multiplexing of channels and improve the utilization rate of the channels, and meanwhile, the modulation can expand the bandwidth of the signals, improve the anti-interference and anti-fading capability of the system and improve the signal-to-noise ratio of transmission. Demodulation is the process of recovering a message from a modulated signal carrying the message, and is the inverse of modulation.
The traditional ASK digital demodulation relates to two aspects of decision threshold and symbol timing, the decision threshold obtained by mean value calculation is difficult to adapt to signal transmission with uneven distribution of 0 and 1, and the symbol timing depends on the accuracy of a synchronization algorithm.
Disclosure of Invention
In order to solve the above problems, the present invention provides an ASK amplitude adaptive anti-noise demodulation algorithm, which is characterized in that the algorithm comprises the following steps:
1) the method comprises the steps that signal envelope detection is carried out, a receiving end receives an ASK modulated signal, the ASK modulated signal is multiplied by a local carrier wave by means of a down-conversion technology to obtain an in-phase component and an orthogonal component, the in-phase component and the orthogonal component are subjected to low-pass filtering to obtain a corresponding low-frequency I, Q signal, the squares of I, Q two paths of signals are added and then are squared to obtain envelope data of a transmitted bit sequence;
2) dividing the envelope data into two paths, wherein one path is used for maximum value detection, dynamically acquiring the maximum holding value of the envelope data, storing the other path into an FIFO (first in first out), and reading the data after delaying so that the maximum holding value just corresponds to a sampling point output by the FIFO;
3) setting a signal threshold to be half of a maximum holding value within a fixed length;
4) obtaining a data range through a table look-up of the maximum holding value of the signal, and shifting the basic background noise according to the data range to obtain the background noise value of the current amplitude signal;
5) comparing the data output by FIFO fixed time delay with the signal threshold and the background noise value, if the signal amplitude is greater than the signal threshold and greater than the background noise value, judging the current value as 1, otherwise, judging the current value as 0;
6) and (4) processing positive and negative bidirectional noise, namely processing positive noise firstly, then processing negative noise, and outputting final data.
Further, the basic background noise in the step 4) is obtained by simulating a noisy signal.
Further, the positive noise in step 6) refers to that the signal transmits all 0 s for a period of time, and when the signal noise is large, a partial 1 may occur by only threshold determination, and the negative noise refers to that the signal transmits all 1 s for a period of time, and when the signal noise is large, there may be a small number of 0 s by only threshold determination.
An ASK amplitude adaptive anti-noise demodulation device based on the ASK amplitude adaptive anti-noise demodulation algorithm is characterized by comprising a signal envelope detection module, a threshold setting module and a noise processing module which are sequentially connected;
the signal envelope detection module is used for acquiring envelope data of a transmission bit sequence from a modulation signal, and specifically comprises a down-conversion unit, a low-pass filter and a signal synthesis unit;
the threshold setting module comprises a maximum value detection unit, an FIFO delay unit, a signal threshold unit, a noise threshold unit and a data threshold comparison unit;
the noise processing module is used for realizing positive and negative bidirectional noise processing.
Further, the down-conversion unit multiplies the received ASK modulated signal by a local carrier to obtain an in-phase component and a quadrature component.
Further, the low-pass filter performs low-pass filtering on the in-phase component and the quadrature component to obtain a corresponding low-frequency I, Q signal, the signal synthesis unit performs square addition on the I, Q two paths of signals and then performs squaring, and the squaring result is envelope data of the transmission bit sequence.
Further, the maximum value detection unit is configured to dynamically obtain a maximum holding value of the envelope data, and the FIFO delay unit is configured to implement data and threshold alignment.
Furthermore, the signal threshold unit sets the signal threshold to be half of the maximum holding value in the fixed length, the noise threshold unit obtains the data range through table look-up of the maximum holding value, and shifts the basic background noise according to the data range to obtain the background noise value of the current amplitude signal.
Further, the data threshold comparison unit is configured to compare the data output by the FIFO delay unit in a fixed delay with the signal threshold and the background noise value, and if the signal amplitude is greater than the signal threshold and greater than the background noise value, the current value is determined to be 1, otherwise, the current value is determined to be 0.
Further, the noise processing module processes positive noise firstly, processes negative noise secondly, and outputs final data, where the positive noise refers to that the signal sends all 0 s within a period of time, and when the signal noise is large, a part of the signals may be 1 s only by threshold determination, the negative noise refers to that the signal sends all 1 s within a period of time, and when the signal noise is large, a small amount of 0 s may exist only by threshold determination.
Drawings
FIG. 1 is an algorithm flow diagram;
FIG. 2 is a schematic diagram of the apparatus configuration;
FIG. 3 is a flow chart of current signal noise floor acquisition;
fig. 4 is a flow chart of positive and negative bi-directional noise processing.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present invention, embodiments of the present invention will now be described with reference to the accompanying drawings.
The ASK amplitude adaptive anti-noise demodulation algorithm comprises the following steps:
1) the method comprises the steps that signal envelope detection is carried out, a receiving end receives an ASK modulated signal, the ASK modulated signal is multiplied by a local carrier wave by means of a down-conversion technology to obtain an in-phase component and an orthogonal component, the in-phase component and the orthogonal component are subjected to low-pass filtering to obtain a corresponding low-frequency I, Q signal, the squares of I, Q two paths of signals are added and then squared to obtain envelope data of a transmitted bit sequence, wherein the envelope data are irrelevant to frequency offset and phase deviation;
2) dividing the envelope data into two paths, wherein one path is used for maximum value detection, dynamically acquiring the maximum holding value of the envelope data, storing the other path into an FIFO (first in first out), and reading the data after delaying so that the maximum holding value just corresponds to a sampling point output by the FIFO;
3) considering that if the decision threshold is set as the average value of the fixed-length signals, decision errors are easily caused under the condition that all 0, all 1 or 0/1 signals are unevenly distributed in the fixed length, therefore, the signal threshold is set as half of the maximum holding value in the fixed length, when the signals are all 1, the signals are more than half of the maximum holding value, the decision result is 1, and the points with a small number of 0 caused by large noise can be corrected through subsequent negative noise processing; when the signal is all 0, under the influence of channel noise, although the signal is judged to be 1, the signal can be corrected by subsequent forward noise processing;
4) considering that under the same signal-to-noise ratio, the input signal amplitude is different, the bottom noise threshold is also changed, the same input amplitude can be a useful signal of a small signal or a bottom noise of a large signal, in order to avoid misjudgment, a data range is obtained through table look-up of the maximum holding value of the signal, the base bottom noise is shifted according to the data range to obtain the bottom noise value of the current amplitude signal, if the signal amplitude is greater than half of the maximum holding value and greater than the bottom noise value, the current value is judged to be 1, otherwise, the current value is judged to be 0, and the base bottom noise is obtained according to the simulation of the noisy signal;
5) comparing the data output by FIFO fixed time delay with a signal threshold and a background noise value, if the signal amplitude is greater than the signal threshold and greater than the background noise value, judging the current value as 1, otherwise, judging the current value as 0;
6) and (2) processing positive and negative bidirectional noise, if the signal transmits all 1 within a period of time and the signal noise is large, judging that a small amount of 0 possibly exists only through a threshold, defining the small amount of 0 as negative noise, and if the signal transmits all 0 within a period of time and the signal noise is large, judging that part of 1 appears only through the threshold, defining the part of 1 as positive noise and considering that the probability of positive noise occurrence is greater than that of negative noise, therefore, processing the positive noise, processing the negative noise and outputting final data according to the sequence.
The ASK amplitude self-adaptive anti-noise demodulation device based on the algorithm comprises a signal envelope detection module, a threshold setting module and a noise processing module.
The basic configuration of the device is as follows: the baud rate of a serial port of a sending end is 9600bit/s, the baud rate of a serial port of a receiving end is equal to that of the sending end, the sampling rate of an ADC/DAC is 125Kbps, 13 sampling points are needed for transmitting one bit data, the bit width of an I/Q signal output by a low-pass filter is 24 bits, the device is realized by adopting an FPGA, and the bit width of a signal sqrt _ out [23:0] is unchanged after the device is opened.
The signal envelope detection module is used for acquiring envelope data of a transmission bit sequence from a modulation signal, and specifically comprises a down-conversion unit, a low-pass filter and a signal synthesis unit. The specific treatment process comprises the following steps:
the ASK modulated signal received by the module is:
wherein,
for the digital baseband binary bit period,
is the carrier frequency and is,
for the duration of the sampling period of the ADC,
indicates a duration of
Rectangular pulse of (1), corresponding to
A number of sample points are sampled at the time of sampling,
is a transmitted binary bit.
The down-conversion unit combines the ASK modulated signal and the local carrier
And multiplying to obtain an in-phase component and a quadrature component.
The in-phase component is:
the orthogonal components are:
due to the fact that
And low-pass filtering the in-phase component and the quadrature component by a low-pass filter to obtain a corresponding low-frequency I, Q signal, wherein the specific form is as follows:
the signal synthesis unit adds the squares of the I, Q two paths of signals and then performs squaring, and the specific operation formula is as follows:
the evolution result is envelope data of the transmitted bit sequence, which are all positive values and are irrelevant to frequency offset phase deviation, so that the signal envelope detection module can realize certain carrier frequency mismatch resistance.
The threshold setting module comprises a maximum value detection unit, an FIFO delay unit, a signal threshold unit, a noise threshold unit and a data threshold comparison unit.
The maximum value detection unit is used for dynamically acquiring the maximum holding value max _ keep of the signal after the opening.
The FIFO delay unit is used for realizing data and threshold alignment. Considering that the length of the calculation is about 128 sampling points of one byte data in the process of obtaining the maximum holding value max _ keep of the signal after the opening, 128 data are input into the system when the maximum value of the first 128 sampling points is obtained. For data and threshold alignment, while using data for maximum value detection, storing the data into the FIFO delay unit, and reading the data after delaying for 128 beats, wherein max _ keep just corresponds to 128 sampling points output by the FIFO delay unit.
If the decision threshold is set to the mean of the fixed length signal, it is easy to make decision errors if all 0, all 1 or 0/1 of the signal are unevenly distributed within the fixed length. Therefore, the improvement of the invention is that the signal threshold unit sets the signal threshold to be half of the maximum holding value max _ keep in the fixed length, when the signal is all 1, the signal is greater than max _ keep/2, the judgment result is 1, the point with 0 in a small amount caused by large noise can be corrected by subsequent negative noise processing; when the signal is all 0 s, under the influence of the channel noise, although the signal is judged to be 1, the signal can be corrected by the subsequent forward noise processing.
Under the same signal-to-noise ratio, the input signal amplitude is different, and the background noise threshold is also changed. The same input amplitude may be useful signal of small signal, and may also be background noise of large signal, if the device adopts uniform background noise threshold, it will result in missing detection of small signal or narrowing high level pulse width, and widening high level pulse width of large signal. In order to avoid misjudgment, the noise threshold unit obtains a data range by looking up a table through the maximum holding value max _ keep, shifts the basic background noise according to the data range to obtain a background noise value now _ nio of the current amplitude signal, and if the signal amplitude is larger than max _ keep/2 and is larger than now _ nio, the current value is judged to be 1, otherwise, the current value is judged to be 0. The basic base noise min _ nio is obtained according to 24-bit noisy signal simulation and is set to 512, and the lookup table is realized through an ISE IP core and is designed to be 8-bit wide and 2^16 deep.
And the data threshold comparison unit is used for comparing the data output by the FIFO fixed delay with the signal threshold and the bottom noise value, if the signal amplitude is greater than the signal threshold max _ keep/2 and greater than the bottom noise value now _ nio, the current value is judged to be 1, and if not, the current value is judged to be 0.
The noise processing module is used for realizing positive and negative bidirectional noise processing. If the signal transmits all 1 s within a period of time and the signal noise is large, it is determined that there may be a few 0 s only by the threshold, and for convenience, it is defined as negative noise. To correct such errors, the result is subjected to negative-going noise processing. If the signal transmits all 0 s within a period of time and the signal noise is large, a partial 1 condition occurs only through threshold determination, and the partial 1 condition is defined as forward noise. Also, the result is forward denoised for the error. The probability of positive noise occurrence is greater than that of negative noise, so the processing is in sequence, and the positive noise is processed first and then the negative noise is processed.
Now, taking forward noise processing as an example, a noise processing principle is explained by combining with a serial port transmission characteristic: if the signal is a single pulse signal, the high level normal holding time is 13 sampling points, which is influenced by noise and is about 13 +/-2 sampling points. However, if all 0 s are transmitted, the duration of a single pulse does not exceed 5-6 points due to the randomness of noise. Therefore, the hold time cnt _ pulse of each high-level pulse is calculated from the pulse rising edge, if cnt _ pulse > =11, the entire high-level pulse involved in the calculation is held, and if cnt _ pulse <11, the entire high-level pulse involved in the calculation is regarded as being caused by noise, and the entire pulse is set to 0. The negative noise processing is similar to the positive processing, the negative processing is performed by reversing the positive output, which is equal to performing the positive processing again, and the result of the negative processing is reversed, so that the demodulation output bit can be obtained. The only difference is that the output initial value of the positive processing is given as 0, and the initial value of the negative processing is given as 1.
The invention provides an ASK amplitude self-adaptive anti-noise demodulation algorithm and device, belongs to all-digital incoherent demodulation, and realizes optimization of an ASK traditional demodulation algorithm by detecting an envelope maximum value, dynamically configuring a decision threshold and processing positive and negative bidirectional noise. The amplitude matching circuit not only has good anti-noise performance (the application signal-to-noise ratio is as low as 14 dB), but also can automatically match the amplitude of an input signal, is suitable for the practical application scene of unstable signal intensity (gradual change + sudden change), and simultaneously can correctly demodulate 0/1 asymmetric data, overcomes the defect of the traditional ASK demodulation, and has great practicability.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.
Claims (9)
1. An ASK amplitude adaptive noise immunity demodulation method, characterized in that the method comprises the following steps:
1) the method comprises the steps that signal envelope detection is carried out, a receiving end receives an ASK modulated signal, the ASK modulated signal is multiplied by a local carrier wave by means of a down-conversion technology to obtain an in-phase component and an orthogonal component, the in-phase component and the orthogonal component are subjected to low-pass filtering to obtain a corresponding low-frequency I, Q signal, the squares of I, Q two paths of signals are added and then are squared to obtain envelope data of a transmitted bit sequence;
2) dividing the envelope data into two paths, wherein one path is used for maximum value detection, dynamically acquiring the maximum holding value of the envelope data, storing the other path into an FIFO (first in first out), and reading the data after delaying so that the maximum holding value just corresponds to a sampling point output by the FIFO;
3) setting a signal threshold to be half of a maximum holding value within a fixed length;
4) obtaining a data range through a table look-up of the maximum holding value of the signal, and shifting the basic background noise according to the data range to obtain the background noise value of the current amplitude signal;
5) comparing the data output by FIFO fixed time delay with the signal threshold and the background noise value, if the signal amplitude is greater than the signal threshold and greater than the background noise value, judging the current value as 1, otherwise, judging the current value as 0;
6) positive and negative two-way noise processing, wherein positive noise refers to that a signal sends all 0 within a period of time, when the signal noise is large, the situation that part of the signal is 1 can occur only through threshold judgment, negative noise refers to that the signal sends all 1 within a period of time, and when the signal noise is large, the situation that a small amount of 0 possibly exists only through threshold judgment; processing forward noise, counting from the rising edge of the pulse, calculating the holding time cnt _ pulse of each high-level pulse, if cnt _ pulse > =11, holding the whole high-level pulse participating in calculation, and if cnt _ pulse <11, setting the whole pulse to be 0; and processing the negative noise, wherein the negative noise processing is similar to the positive noise processing, inverting the positive output to perform negative processing, namely performing positive processing again, inverting the negative processing result, namely assigning an initial value of the negative processing to be 1, obtaining a demodulation output bit, and outputting final data.
2. The ASK amplitude adaptive anti-noise demodulation method according to claim 1, wherein the base noise in the step 4) is simulated from a noisy signal.
3. An ASK amplitude adaptive anti-noise demodulation device based on the ASK amplitude adaptive anti-noise demodulation method according to claim 1, wherein the ASK amplitude adaptive anti-noise demodulation device includes a signal envelope detection module, a threshold setting module, and a noise processing module, which are connected in sequence;
the signal envelope detection module is used for acquiring envelope data of a transmission bit sequence from a modulation signal, and specifically comprises a down-conversion unit, a low-pass filter and a signal synthesis unit;
the threshold setting module comprises a maximum value detection unit, an FIFO delay unit, a signal threshold unit, a noise threshold unit and a data threshold comparison unit;
the noise processing module is used for realizing positive and negative bidirectional noise processing.
4. The ASK amplitude adaptive anti-noise demodulation device according to claim 3, wherein the down-conversion unit multiplies the received ASK modulated signal by a local carrier to obtain an in-phase component and a quadrature component.
5. The ASK amplitude adaptive noise-immune demodulation device according to claim 4, wherein the low pass filter performs low pass filtering on the in-phase component and the quadrature component to obtain corresponding low frequency I, Q signals, the signal synthesis unit performs square addition on I, Q two signals and then performs square extraction, and the extraction result is envelope data of the transmitted bit sequence.
6. An ASK amplitude adaptive noise-immune demodulation apparatus according to claim 3, wherein the maximum value detection unit is configured to dynamically obtain the maximum hold value of the envelope data, and the FIFO delay unit is configured to achieve data and threshold alignment.
7. The ASK amplitude adaptive noise-immune demodulation device according to claim 6, wherein the signal threshold unit sets the signal threshold to be half of the maximum hold value within the fixed length, the noise threshold unit obtains the data range by looking up the table of the maximum hold value, and shifts the base noise according to the data range to obtain the noise floor value of the current amplitude signal.
8. The ASK amplitude adaptive noise-immune demodulation device according to claim 7, wherein the data threshold comparing unit is configured to compare the data output by the FIFO delay unit in fixed delay with the signal threshold and the noise floor value, and if the signal amplitude is greater than the signal threshold and greater than the noise floor value, the current value is determined as 1, otherwise, the current value is determined as 0.
9. An ASK amplitude adaptive noise-immune demodulator according to claim 3, wherein the noise processing module processes first positive noise, which indicates that all 0 s are transmitted during a period of time and only a partial 1 is determined by the threshold when the signal noise is large, and processes second negative noise, which indicates that all 1 s are transmitted during a period of time and only a small 0 s are determined by the threshold when the signal noise is large, and outputs the final data.
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