JPH02183618A - Digital correlator - Google Patents

Abstract

PURPOSE:To obtain a soft discrimination digital correlation device with a circuit scale the same as that of a 1-bit hard discrimination digital correlation device by applying delta modulation to an input analog signal and processing the result by a 1-bit correlation device. CONSTITUTION:The input digital signal is subject to 1-bit coding by delta modulation and subject to correlation by a 1-bit digital correlation device 7 as a succeeding correlation device and demodulated by a delta demodulator 8. Thus, the soft discrimination correlation the same as that of multi-value coding with 1-bit correlation processing and one demodulator 8 is enough to be provided to the output of the 1-bit digital correlation device depending on the linearity of the delta demodulator 8 and the circuit is considerably simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital correlation device for detecting a code sequence included in an input signal by soft decision.

[Conventional technology]

Figure 5 shows a conventional digital matched filter for spread spectra.
Conskunto Envelope Spread-Spectrum Wave Forms J (/A Low-Cost
Digital Matched Filter f
or Arbitrary Con5tant-Env
elope Spread-Spectrum Wav
eforms”;It!EE Trans, on C
omIa, Vol, C0M-32, No, 4. April
This method uses the conventional hard-decision digital correlation device shown in Ill. 1984). In the figure, 1 is an input terminal for a spread spectrum received signal on which noise is superimposed; 2.
3 is a local signal that is orthogonal to each other, 4 is a mixer for mixing input signal 1 and local signal 2.3, 5 is an LPF (low pass filter) that extracts only the baseband signal, and 12 is a sampler for sampling an analog signal. sampler, 13
is a 1-bit digitizer that quantizes the output of the sampler 12 into a binary value of 1 or O; 7 is a 1-bit digital correlator for detecting a correlation signal from the spread spectrum received signal; and 9 is the 1-bit digital correlator. A squaring device 10 squares the correlation output of the device 7, and 10 is a squaring device 9 of a mutually orthogonal system.
An adder 11 for adding the outputs is an output terminal of this digital matched filter device.

On the other hand, FIG. 6 shows the 1-bit digital correlator 7 of FIG.
Here, as an example, a correlator manufactured by TRW (trade name: TDC-1023) is shown. In the figure, A to A64 are input signal delay shift registers, R1 to R64 are tlli related pattern memories, and Bl''
``'B64 is a correlation pattern input buffer, M, ~M
64 is a mask pattern.

Next, the operation will be explained.

Spread spectrum signal 5(t) received at input terminal 1 = D(tl ・C(tlc o s (ω
ct + ψ (t)) D (tli information data (±1) C (t); correlation code ω.; center frequency ψ (t); initial phase is orthogonal local signal 2.3 S, = cos ω C [ 3Q = sin ω ct After converting to baseband signal with
After being removed by F5 and sampled by the sampler 12, it is binary quantized by the 1-bit digitizer 13. This signal is correlated by a 1-bit digital correlator 7.

If the correlator is an analog correlator that performs linear operation, the two correlator outputs R+ and Ro are R+ = (1/2
) RsAx c o sψRa --(1/2)RM
AX s t nψ (R, AX are maximum correlation outputs), and the sum of squares thereof is R te + RA = (1/4) RAAx. Therefore, by taking the square sum of the two correlator outputs, the output signal becomes independent of the phase difference between the received spread spectrum signal 1 and the local signals 2 and 3.

Similar results were obtained when a 1-bit digital correlator 7 was used as the correlator, and the squarer 9 and adder 10
was created for this purpose.

(Problem to be Solved by the Invention) The conventional digital matched filter device is configured as described above, and in order to simplify the device, it is configured with a 1-bit correlator, so that the received SNR under Gaussian noise is The correlation pulse detection sensitivity for (signal-to-noise ratio) deteriorates by approximately 2 dB compared to an analog correlator, and it also deteriorates significantly against CW (continuous wave) interference.For details of these problems, please refer to the paper "An Introduction to Digital Filters J"
Introduction to Digital Ma
tched Filters”, PROCEEDING
OF TIIE IEEE, VOL, 64. NO, 7
, July 1976).

On the other hand, conventional analog matched filter devices are SAW,
This invention is composed of COD, but has problems such as deterioration due to attenuation when configured in multiple stages and difficulty in miniaturizing the device.This invention aims to solve the problems of the conventional device as described above. The purpose of this invention is to obtain a digital correlation device having soft decision characteristics similar to an analog matched filter device using a 1-bit correlator that can be made compact.

[Means to solve the problem]

A digital correlation device for soft decisions according to the present invention encodes an input analog signal by 1 bit by delta modulation, correlates it by a l-bit digital correlator as a subsequent correlator, and demodulates it by a delta demodulator. This is what I did.

[Effect]

In this invention, by using a delta modulator as an encoder, the digital correlation device can perform a soft-decision correlation operation equivalent to multilevel encoding with 1-bit correlation processing, and due to the linearity of the delta demodulator, Only one demodulator needs to be provided at the output of the 1-bit digital correlator, allowing for significant simplification of the circuit.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a digital matched filter for spread spectrum having a digital correlation device according to an embodiment of the present invention, and in the figure, 1 to 5 and 9 to 11 correspond to the corresponding parts in FIG. 4 explained in the related art. is the same as

Further, 6 is a delta modulator, 7 is a 1-bit digital correlator, and 8 is a delta demodulator.

Further, FIG. 2 is a principle diagram of a soft-decision correlator using delta modulation according to the present invention, and FIG. 3 shows a practical circuit thereof. In FIGS. 2 and 3, 6 is a delta modulator, 7
is a 1-bit digital correlator, 7a is a 1-bit shift register, 7b is a correlation coefficient multiplier, 7C is a full adder, and 8 is a delta demodulator. Further, FIG. 4 shows waveforms at various parts in FIG. 2.

Next, the operation will be explained. This example is [prior art]
The sampler 12, 1-bit digitizer 13, and 1-bit digital correlator 7 in FIG. LPF from terminal l
The operations up to 5 and from the squarer 9 to the output terminal 11 are the same as those of the conventional one.

The operation of the delta modulator 6, 1-bit digital correlator 7 and delta modulator 8 according to the present invention will be explained below with reference to FIGS. 2 and 4.

FIG. 2 is a principle diagram of a digital correlator using a delta modulator, and FIG. 4 is a waveform diagram of each part thereof.

Figure 4! The analog waveform shown in a) is input to the delta modulator 6 and encoded into a 1-bit string shown in FIG. 4(b). This code does not approximate the amplitude of a human waveform with only positive or negative binary values like the output of the 1-bit digitizer 13 shown in the [Prior Art] column;
Figure 1 shows multi-level amplitude values that are close to the input analog signal as shown in Figure 1.

One bit string of the output of this delta modulator is delayed by a shift register 7a, and input to a delta demodulator 8 for each tap of the shift register 7a corresponding to the chip interval of the spread spectrum signal, and the delayed waveform string shown in FIG. is obtained at the output of each delta demodulator 8. By multiplying these outputs by the spread signal of the spread spectrum as a coefficient and adding the results, a pulse as shown in Figure 4 (C) is generated at a time when the correlation between the coefficient and the input signal matches. .

This pulse is also called a matte pulse.

The operation of the soft-decision digital correlator using a delta modulator has been explained above using FIGS. 2 and 4.
If the delta modulator 6 and demodulator 8 operate linearly, that is, the integral of delta modulation and demodulation is a complete integral or a first-order integral, the delta demodulator 8 in FIG. 2 has the same processing order as the coefficient multiplier 7b and the adder 7C. They are equivalent even if they are replaced, and the delta demodulators 8 can be combined into one as shown in FIG.

In addition, at this time, if the correlation coefficient is a constant amplitude code sequence of +1 or -1, an exclusive OR circuit may be used in place of the normal multiplier as the multiplier 7b in FIG.

Further, in the above embodiment, a delta modulator is used as an encoder, but a differential encoder may also be used. At this time, the shift register and multiplier of the digital correlator become multivalued, but
The number of codes may be smaller than that of a normal binary encoder.

Further, the adder need not be a full adder as in the above embodiment, but may be a half adder.

Furthermore, in the above embodiment, the delta modulator is linearly operated, but CVSD (continuously variable slope delta modulator)
In A), the companding constant may be made sufficiently longer than the correlation time.

〔Effect of the invention〕

As described above, according to the digital correlation device according to the present invention, since the input analog signal is delta-modulated and then processed by the 1-bit correlator, the processing efficiency is comparable to that of the conventional 1-bit hard-decision digital correlator. This has the advantage that a digital correlation device for soft decisions can be provided with a circuit scale of .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a spread spectrum digital matched filter using a digital correlation device according to an embodiment of the present invention, FIG. 2 is a diagram showing the principle of the digital correlation device of the present invention, and FIG. Figure 4 is a diagram showing a practical circuit, Figure 4 is a diagram showing waveforms of various parts of the present invention, Figure 5 is a diagram showing an example of a conventional spread spectrum digital matched filter, and Figure 6 is a diagram showing a conventional 1-bit digital correlation. It is a figure showing an example of a container. In the figure, 1 is an input terminal, 2.3 is a local signal, and 4 is a local signal.
is a mixer, 5 is an LPF (low pass filter), 6 is a delta modulator, 7 is a 1-bit digital correlator, 7a is 1
Bit shift register, 7b is a correlation coefficient multiplier, 7C is an adder, 8 is a delta demodulator, 9 is a squarer, 10 is an adder, 11 is an output terminal, 12 is a sampler, 13 is an l-bit digitizer .

Claims (1)

[Claims] (1) A digital correlation device includes a delta modulator that encodes an input analog signal into 1 bit, a tapped shift register that delays its output code string, and a multiplier that multiplies the output of each tap by a correlation coefficient. A digital correlation device comprising: a 1-bit digital correlator comprising an adder that adds the outputs of the respective multipliers; and a delta demodulator that demodulates the output of the adder.