JPH04207439A - Polyphase PSK modulation/demodulation method - Google Patents

Abstract

PURPOSE:To utilize the system even for satellite transmission with a tight limit in the band and the C/N by limiting an instantaneous dynamic range of a modulation signal in advance so as to attain polyphase PSK modulation in excess of 360 deg.. CONSTITUTION:A through-rate limit circuit 1 limits the amplitude of a difference signal between samples, an amplitude angle conversion circuit 2 limits a phase change between samples in the poly phase PSK modulation such as 256 phase PSK within 360 deg. so as to allow a phase rotation number discrimination circuit 32 at the demodulator side to discriminate on how many circulations on a circle of 360 deg. a current sample is located. Thus, the phase rotation of 360 deg. or over is attained and the S/N improvement is increased without widening the transmission required band. Thus, the system is utilized for the satellite transmission with a tight limit in the band and the C/N.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to a signal modulation/demodulation system, and is particularly applicable to signal transmission using a polyphase PSK modulation system and signal recording systems such as VTRs. The present invention relates to a polyphase PSK modulation/demodulation method that performs allocation over 360 degrees.

The present invention relates to a polyphase PSK modulation/demodulation method that can be used even in satellite transmission where it is difficult to obtain a sufficient CN ratio.

[Summary of the invention 1] The present invention limits the instantaneous dynamic range of the modulated signal in advance when polyphase PSK modulating and transmitting an analog signal, thereby increasing the 360-degree modulation range that was conventionally considered possible. The present invention is a modulation method that performs modulation over a range of 100 to 300 nm to further increase the modulation gain obtained with normal polyphase PSK modulation, and its demodulation method.

[Conventional technology] Conventionally, as this type of modulation method, DPA (Digital
There is a Pseudo-Analogue) method. As an example of the DPA method, the MSB of the 8-bit sample value of the modulated signal is separated, the 2 samples are combined into a 2-bit digital signal, which is transmitted using QPSK, and the remaining bits are transmitted using 128-phase PSK (pseudo There is a method of transmitting data using analog modulation.

In 128-phase PSK, if the phase gap ΔΦ is 90 degrees, there is a modulation gain of 16.5 dB, and the MSB
Since it is transmitted digitally, the S/N improvement degree increases by 6 dB, and the S/N improvement degree of 22.5 dB is obtained for the entire DPA method. However, in the case of the DPA method, if digital data is transmitted using QPSK, 2 bits correspond to 1 symbol, and as a result, 2 samples are converted into 3 symbols and transmitted, so when transmitting using 256-phase PSK, By comparison, it required 1.5 times the bandwidth.

[Problem to be solved by the invention] In DPA, 8-bit sample data is simply
Although the degree of S/N improvement is increased compared to the case of transmission using phase PSK, there is a drawback that the required band becomes wider at the cost.

In other words, only the band and S/N were exchanged.

Generally, in a signal such as an image signal, the amplitude distribution of a difference signal between samples is a Laplace distribution, and the probability of producing a difference signal with a large amplitude is very small. Furthermore, even if a difference signal with a large amplitude is clipped, the distortion generated in the image signal corresponds to the edge portion, so visually there will not be a large deterioration in image quality.

Therefore, an object of the present invention is to utilize this property to limit the amplitude of the difference signal between samples so that the amount of phase change between samples in multiphase PS modulation (for example, 256-phase PSK) is within 360 degrees. Then, on the demodulation side, the current sample is
By making it possible to determine which circumference on the 60-degree circumference the device is located at, it is possible to perform phase rotation over 360 degrees, thereby increasing the amount of S/N improvement without widening the band.

[Means for Solving the Problem 1] By limiting the instantaneous amplitude change amount of the polyphase PSK transformation modulation signal according to the present invention, the instantaneous phase change amount is prevented from exceeding 360 degrees, The present invention is characterized in that when assigning the amplitude of a modulated signal to a phase, the assignment is made over 360 degrees, and multiphase PSK modulation is performed.

In addition, the polyphase PSK demodulation method according to the present invention prevents the instantaneous phase change amount from exceeding 360 degrees by limiting the amount of instantaneous amplitude change of the modulation signal, so that the amplitude of the modulation signal is adjusted to the phase. When allocating over 360 degrees and demodulating a polyphase PSK modulated signal, the modulation side limits the instantaneous phase change so that it does not exceed 360 degrees. By using this method, determining whether the phase has changed positively or negatively, and demodulating while always tracing how many rotations the current sample is in, multiple amplitude values can be assigned. It is characterized by obtaining the original amplitude from the phase point of ~360 degrees.

[Function] According to the present invention, the amplitude of the difference signal between samples is limited so that the amount of phase change between samples in polyphase PSK modulation (for example, 256-phase PSK) is within 360 degrees, and on the demodulation side, By being able to determine the position of the current sample on a 360-degree circle, it is possible to rotate the phase by more than 360 degrees, improving S/N without expanding the required transmission band. The amount can be increased.

[Embodiment 1] Next, an embodiment in which the present invention is applied to transmission of a video signal will be described.

FIG. 1 shows the configuration of a modulator according to this embodiment. The input video signal a is digitized, and a slew rate limiting circuit 1 limits the difference value between samples to a certain value or less. As explained later, the slew rate limit is
Two types of slew rate limiting are possible: level adaptive slew rate limiting and simple slew rate limiting. The signal C that has passed through the slew rate limiting circuit is converted by the amplitude angle conversion circuit 2 into a signal C representing a phase angle of 0 to 360 degrees. In the present invention, an angle of 360 degrees or more is assigned to the total amplitude of the signal to perform modulation into a polyphase PS, so in this circuit 2, a plurality of amplitude values are converted into one phase.

FIG. 5 shows an example of the characteristics of the amplitude angle conversion circuit. In this example, 540 degrees is assigned to the total amplitude of the input signal.

The signal C representing the phase angle is decomposed by the sine conversion circuit 3 and the cosine conversion circuit 4 into two coordinate components of one orthogonal axis and the Q axis, and becomes signals d and e. Signals d and e are converted into signals f and g by a double oversampling circuit 5.6, and further band-limited and waveform-shaped by a roll-off filter 7.8 to become signals i. Signal and i are D
/A converter 9.10 and interpolation filter 11.1
2 and become analog signals of j and k.

On the other hand, the output of the oscillator 17 is divided into two signals, and one signal is given a phase difference of 90 degrees by the phase shifter 13.

The two carrier signals ρ, m and signal j obtained in this way,
k by multiplier 14.15, and n of the DSB-SC signal
and convert it to 0. Signals n and 0 are added in a combiner 16,
The desired polyphase PSK modulated wave p exceeding 360 degrees is obtained.

Next, the demodulator side will be explained. FIG. 2 shows the configuration of a polyphase PSK demodulator according to this embodiment. First, input signal a
Divide into two. On the other hand, by distributing the output of the carrier regeneration circuit 21 into two and giving one of them a 90 degree phase difference with the phase shifter 22, two orthogonal carrier signals S, c
get. These two carriers and the divided input signal a are multiplied by multipliers 23 and 24 to produce signals d and e. Next, the signals d and e are band-limited by LPFs 25 and 26 to become signals f and g, which are further converted into digital signals i by A/D converters 27 and 28. The signals i and i represent the components of the 1st axis and the Q axis, respectively.

Next, the signal i is converted into a signal j representing the phase by an arctangent circuit 29.
Convert to The signal j represents a phase of 0 to 360 degrees, but when converting it into an amplitude, it cannot be converted uniquely because one phase corresponds to a plurality of amplitude values. However, the phase represented by signal j is φ. Then, the true phase θ. is 2Nπ+φ. Expressed as, the phase θ of the previous sample
0. is known, i.e., N of the previous sample. -1
If is known, then the phase θ of the current sample. You can also know. True phase θ. has a one-to-one correspondence with the amplitude value, so as a result, φ7 represented by j can be converted into an amplitude value.

In this embodiment, since the signal is a video signal, the horizontal synchronization is a known value, so it is possible to start from the horizontal synchronization and convert phase data into amplitude values one after another.

In FIG. 2, the phase rotation number determination circuit 32 determines the amplitude value of the previous sample and the phase φ of the current sample. The number of rotations is N. This circuit detects the increase/decrease in the number of phase rotations of the current sample and outputs a signal n indicating the number of phase rotations of the current sample. Angle amplitude conversion circuit 30.3 by signal n
1, J2 is switched by the switch 33 to obtain a signal 0 indicating the original amplitude value. Furthermore, the signal ◯ is latched by the latch circuit 34 and becomes the signal q.

The map of the angle amplitude conversion circuit is shown for each phase rotation number N.
This is necessary in response to the situation. This embodiment assumes a case where there are two phase rotation numbers of N=0.1. In addition, one input signal m of the phase rotation number determination circuit is a signal q representing the amplitude value of the previous sample, but it can be used during the horizontal synchronization period (not necessarily only the horizontal synchronization period, but any section where there is known data). By switching to the signal p of the known H synchronized data memory 36 with the switch 35, the angle amplitude conversion sequence is completed in 1H, even if an error occurs in the phase rotation number judgment due to transmission noise. However, we are trying to prevent the effects from propagating for a long time. If the synchronization signal has a phase change within 360 degrees, the synchronization signal can be easily detected.

The amplitude data obtained by demodulating in this manner can be output as is as a video signal, but the following method can be considered as a countermeasure in the case where an error occurs in the angle-amplitude conversion sequence due to transmission noise.

Since a video signal has a property that there is a strong correlation between adjacent pixels, a line where an error occurs in the angle amplitude conversion sequence is
This is a method of interpolating using data from the previous line. As a method for detecting errors, the angle amplitude conversion sequence that starts from H synchronization returns to H synchronization correctly if there is no error. There is a method of determining that an error has occurred during the IH angle amplitude conversion sequence when the difference with the data exceeds a certain tolerance value.

The process of error line interpolation and error detection described above is performed from signal q to signal X in FIG. That is, the data q after angle amplitude conversion is divided into two parts, one of which is compared with the signal S of the H synchronization data memory 4o during the H synchronization period in the comparison/judgment circuit 39, and used for error detection in the angle amplitude conversion sequence. .

The output signal U of the comparison/judgment circuit 39 is II (bold circuit 4
2 is held for 1H and becomes a signal W that controls whether to output the current line or interpolate with the previous line data (or previous field data). The other signal q distributed into two is delayed by the DLY circuit 37 to match the timing with the signal W and becomes the signal F, and is further sent to the 1H memory 38.
The signal is delayed by 1H.

This is because errors in the angle-amplitude conversion sequence cannot be detected until the H synchronization period of the next line arrives.

If there is no error in the angle-amplitude conversion sequence, the output signal t of the first 18 memories 38 is selected as the output video signal X. If an angle-amplitude conversion error is detected, another 1H memory (or 1 field memory) connected in series selects the output signal V of 41, that is, the data of the previous line (or previous field), and outputs the image. Output as signal X. The above is the multiphase PS shown in Figure 2.
This is the operation of the K demodulator.

Here, if two errors occur in 1H, it may not be possible to detect the error, but the required C/N of the transmission path determined by the S/N required for the video output signal of the demodulator is suitable. If a large phase gap is set, 1) the probability of producing two errors in one is almost zero;

Next, the slew rate limiting circuit and its characteristics will be explained. FIG. 3 shows the characteristics of a simple slew rate limiting circuit, and FIG. 6 shows the characteristics of a symmetrical clipping circuit used in the simple slew rate limiting circuit. In FIG. 3, both the vertical and horizontal axes represent normalized amplitude. Further, the slew rate limit value shows a case where the normalized amplitude value for both positive and negative values is 0.5. 6th
In the figure, the horizontal axis is the standardized reference signal level,
The vertical axis is the input signal level, and the area within the diagonal line is the range of the input signal that does not cause clipping. Although it is not necessary to use a reference signal in a symmetrical clipping circuit, it was set up virtually in order to compare the characteristics with the asymmetrical clipping circuit.

First, the operation of the simple slew rate limiting circuit will be explained. Input signal X. is subtracted by the subtracter 51 from the sample Yn-1 of one clock before which is subjected to the slew rate restriction, and a difference signal d is obtained. get. d and Q are clipped by a symmetrical clipping circuit 52 which clips the positive and negative signals at the same level. shall be. A symmetrical clipping circuit is a clipping circuit in which the clipping level in the positive direction and the clipping level in the negative direction are always constant. Output q of the symmetric clip circuit 52. is added with the previous sample Yn-1 subjected to the slew rate restriction by the adder circuit 53 to obtain Y,
, and is further latched by the latch circuit 54 and output.

Next, FIG. 4 shows a characteristic example of the level adaptive slew rate limiting circuit, and FIG. 7 shows an example of the characteristics of the asymmetric clip circuit used in the level adaptive slew rate limiting circuit.

FIG. 4 represents the normalized amplitude on both the vertical and horizontal axes. Further, the slew rate limit value shows a case where the normalized amplitude value for both positive and negative values is 0.5. The horizontal axis in FIG. 7 is the standardized reference signal level, the vertical axis is the input signal level, and the area within the diagonal line is the range of the input signal that does not cause clipping.

First, the operation of the level adaptive slew rate limiting circuit will be explained. Sample Y of the input signal Xn one clock before subject to slew rate limitation. −1 is subtracted by a subtraction circuit 61 to obtain a difference value d. d is an asymmetric clip circuit 6
Clip with 2 and Q. shall be. Asymmetric clip circuit 62
The sum of the absolute values of the positive clip level and the negative clip level is the same as in the symmetric clip circuit, and is a constant value, but the ratio of the positive clip level and the negative clip level changes depending on the reference signal R. In a circuit where the reference signal R changes in the range of O to l, in the range of 0.5<H,
A negative clip level is thicker than a positive clip level (in the range 0, 5>R, on the contrary, a positive clip level has a characteristic that is larger than a negative clip level.

The reference signal R of the asymmetric clipping circuit 62 is a sample Y of one clock previous which is subject to slew rate limitation. -1. That is, by adapting to the amplitude level of the previous sample and changing the ratio of positive and negative clip levels, it is attempted to reduce the distortion that the slew rate limitation gives to the input signal. Output Q of the asymmetric clip circuit 62. is the previous sample Y subjected to slew rate limitation. -1 and adder circuit 63 add it to Y. It is then latched by the latch circuit 64 and output. The above is the operation of the slew rate limiting circuit.

Next, we will explain the multiphase PS over 360 degrees using the modulation method of the present invention.
The relationship between the phase change in the K modulated wave and the baseband signal will be explained in two ways: one using simple slew rate limiting and the other using level adaptive slew rate limiting.

FIG. 8 shows the relationship between the baseband signal and the phase change of the polyphase PSK modulated wave according to the modulation method of the present invention in the case of simple slew rate limitation. In this example, the total amplitude of the baseband signal is assigned to 540 degrees.

Furthermore, the phase gap is set to 90 degrees. Therefore, the maximum phase change between samples is ±135 degrees (27 degrees in total).
0 degree) and the total amplitude is 540 degrees, so converting this allowable maximum phase change into the amplitude of the baseband signal is:
The change between one sample is ±l/4 (with the total amplitude as 1.0)
The total is 172). The upper half of the figure shows the response of the simple slew rate limiting circuit when a step signal is input. The lower half (a) to (e) show states of PSK modulated wave phase changes between samples.

One of the major features of the polyphase PSK modulation method that exceeds 360 degrees
First, in a portion where the amplitude of the baseband signal changes, the position of the phase gap changes for each sample. In the case of simple slew rate limiting, the center of the phase gap for the next sample is always 180 degrees from the current sample, since the same phase angle is assigned in the positive and negative directions.

In the phase change from C to D shown in (C), the phase is 360
The change from the first rotation to the second rotation exceeds the limit. On the demodulation side, it can be recognized that the phase rotation number has changed when the phase exceeds 3150 degrees. Furthermore, it is possible to know whether the phase rotation number increases or decreases based on the polarity of the phase change at that time.

Next, the case of level adaptive slew rate limitation will be explained. FIG. 9 shows the relationship between the baseband signal in the case of level adaptive slew rate limitation and the phase change of the polyphase PSK modulated wave according to the method of the present invention. In this case, as in the previous example, the total amplitude of the baseband signal is assigned to 540 degrees, and the phase gap is set to 90 degrees. The step response of the level adaptive slew rate limiting circuit shown in the top half of the figure shows that the signal rise is improved compared to the case of simple slew rate limiting. In the case of level adaptive slew rate limiting, unlike the case of simple slew rate limiting, the phase relationship between the current sample and the center of the phase gap for the next sample is not constant, but changes adaptively depending on the amplitude value corresponding to the current sample. It is necessary to do so.

This is because in the case of level adaptive slew rate limiting, an asymmetric clipping circuit is used, so when replaced with a phase plane,
This corresponds to the fact that the ratio between the maximum phase change in the positive direction and the maximum phase change in the negative direction differs depending on the signal amplitude value.

However, the sum of the absolute values of the maximum phase change in the positive direction and the maximum phase change in the negative direction is constant, and in the case of FIG.
I take it seriously. In this way, there is a certain correspondence between the slew rate limiting method and the signal allocation method on the phase plane.

[Effect of the invention 1 Conventionally, in the polyphase PSK modulation method using linear orthogonal modulation,
The S/N improvement amount is 19 dB at maximum. There is a DPA method as a method to further increase the amount of S/N improvement,
Although the DPA method increases the degree of S/N improvement, it also has the drawback of increasing the required bandwidth.

On the other hand, if the present invention is applied, it is possible to increase the S/N improvement amount without increasing the required bandwidth, and it is possible to increase the amount of S/N improvement without increasing the required bandwidth.
It is possible to obtain a large S/N improvement effect by applying this method to recording systems such as the following.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a modulator when the present invention is applied to transmission of video signals. Figure 2 is a configuration diagram of the demodulator, Figure 3 is a diagram showing the configuration of a simple slew rate limiting circuit and the permissible amplitude change range in that case, and Figure 4 is a diagram showing the configuration of a level applied slew rate limiting circuit and its case. Figure 5 is a diagram showing an example of the characteristics of the amplitude phase conversion circuit used in the modulator. Figure 6 is the symmetric clip circuit used in the simple slew rate limiting circuit of Figure 3. Figure 7 is a diagram showing an example of the characteristics of the asymmetric clip circuit used in the level adaptive slew rate limiting circuit shown in Figure 4. Figure 9 shows the phase change of the baseband signal and modulated wave in polyphase PSK modulation that exceeds 360 degrees using level adaptive slew rate limiting. It is a figure showing the relationship of change. DESCRIPTION OF SYMBOLS 1... Slew rate limiting circuit, 2... Amplitude angle conversion circuit, 3... Sine conversion circuit, 4... Cosine conversion circuit, 5.6... 2x oversampling circuit, 7, 8...
... Roll-off filter, 9, IO... D/A converter, 11, 12... Interpolation filter, 13... Phase shifter, 14, 15... Multiplier, 16... Synthesizer , 21... Carrier regeneration circuit, 22... Phase shifter, 23, 24... Multiplier, 25, 26... Low pass filter (LPFI, 27,
28... A/D converter, 29... Arctangent circuit, 30, 31... Angle amplitude conversion circuit, 32... Phase rotation number determination circuit, 33... Switch, 34... Latch circuit, 35... Switch, 36... H synchronization data memory, 37... Delay (DLY) circuit, 38... LH memory, 39... Comparison/judgment circuit, 40... H synchronization Data memory, 41...1H memory, 42...1H hold circuit.

Claims (1)

[Claims] 1) By limiting the amount of instantaneous amplitude change of the modulation signal, the amount of instantaneous phase change is prevented from exceeding 360 degrees, and when assigning the amplitude of the modulation signal to the phase, 1. A polyphase PSK modulation method characterized by performing assignment beyond the range of 1 to 1 and performing polyphase PSK modulation. 2) The polyphase PSK modulation according to claim 1, wherein the instantaneous amplitude change amount of the modulation signal is limited by limiting the difference value between samples when sampling is performed. method. 3) Limit the amount of instantaneous phase change on the modulation side to less than 360 degrees, and simply limit it to less than ±180 degrees in the slew rate limiting process that allows the demodulation side to determine whether the phase change is positive or negative. 2. The polyphase PSK modulation method according to claim 1, wherein the waveform distortion imparted to the modulated signal is reduced by changing the positive/negative ratio according to the amplitude level of the signal. 4) By limiting the amount of instantaneous amplitude change of the modulation signal, the amount of instantaneous phase change is prevented from exceeding 360 degrees, and when assigning the amplitude of the modulation signal to the phase, it is not possible to assign more than 360 degrees. When demodulating a modulated signal that has undergone polyphase PSK modulation, we can use the fact that the instantaneous phase change amount is limited to not exceed 360 degrees on the modulation side to determine whether the phase has changed positively. By determining whether the change has changed negatively and demodulating while always tracing the rotation number of the current sample, the original value can be recovered from the phase point of 0 to 360 degrees to which multiple amplitude values are assigned. A polyphase PSK demodulation method characterized by obtaining amplitude. 5) When demodulating a modulated wave obtained by modulating a baseband signal including a periodic synchronization signal by the polyphase PSK modulation method according to claim 1, demodulation processing in the 1H period before the synchronization signal part 5. The method according to claim 4, wherein the image quality deterioration caused by an error in demodulation processing is improved by detecting an error in the line and, if an error is detected, replacing the signal of the line with a signal of a previous line or field. Phase PSK demodulation method.