JPH03123147A - Demodulating device - Google Patents

Abstract

PURPOSE:To surely and exactly correct the frequency by a single local oscillator control by correcting an input signal frequency error estimated by a digital processing, by the digital processing. CONSTITUTION:A receiving signal S(t) is subjected to orthogonal detection in multipliers 2, 3 with an output of a local oscillator 1, and they are converted to signals P(t), Q(t) of a base band zone, respectively. The signals P(t), Q(t) become digital signals Pn, Qn, respectively in A/D converters 5, 6, inputted to a frequency error estimating device 7 and a frequency error DELTAF is estimated, and a digital VCO 8 outputs prescribed digital signals Rn, In. These digital signals Rn, in are multiplied as complex numbers in a complex multiplier 9, and demodulated digital signals Pn', Qn' are outputted. In such a way, an input frequency error can be corrected completely by a single local oscillator control.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a demodulation device, and particularly to initial demodulation synchronization when there is large uncertainty in the receiving frequency of a quadrature-modulated signal such as in satellite communication. Automatic frequency control (AFC)
Regarding the method.

[Prior Art] Conventionally, the AFC method in this type of demodulator first estimates the frequency error of the received signal by some method, and then calculates the frequency error by estimating the frequency of a local oscillator in the intermediate frequency (IF) band. The frequency error was corrected by changing the frequency by the same amount.

[Problem to be solved by the invention] In the conventional AFC method described above, the frequency of the local oscillator in the IF band is controlled, but it is extremely difficult to change the frequency of the local oscillator by an arbitrary value with high precision. . Therefore, it is not possible to completely correct the input frequency error by controlling the local oscillator only once, but it is necessary to perform the control several times.

As a result, there is a drawback that the time required to establish synchronization becomes longer.

[Means for Solving the Problems] A demodulation device according to the present invention is a demodulation device that receives an orthogonally modulated signal as a received signal, demodulates the received signal, performs orthogonal quasi-synchronous detection on the received signal, orthogonal detection means for outputting first and second baseband signals that are orthogonal to each other; and converting the first and second baseband signals from analog to digital to output first and second digital signals. In the demodulation device having analog/digital conversion means, digital processing means digitally processes the first and second digital signals and outputs first and second demodulated signals from which frequency errors have been removed. has.

[Example] An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a demodulator according to an embodiment of the present invention.

The received signal S (t) is orthogonally detected by the output of the local oscillator 1 and the multiplier 2.3, and converted into baseband signals P (t) and Q (t), respectively.

If the baseband signals P (t) and Q (t) are collectively expressed as a complex number such as P+iQ.

Baseband signals P (t) and Q (t) are 1
It is expressed as follows using baseband signals Pa (t) and Qo (t) when there is no frequency error Δf [Hz].

p teni Q-(Po teni Qo) e 12″ht
+Next, the baseband signals P (O, Q (t)) are input to the A/D converters 5 and 6 at a frequency f.

[11z] and becomes a digital signal P0°Q, . Digital signal P. JQn can be expressed as.

P n + iQ n It can be expressed as

Digital signal P. , Qo are input on the one hand to a frequency error estimator 7, where the frequency error Δf is estimated.

The estimated frequency error Δf is input to the digital VCO 8. A digital VCO is expressed by a quadratic equation,
outputs two digital signals R7I In.

Rn +i I r+ m e -”':snThis digital signal R11 and ■.
The output P. +Q, and the demodulated digital signal p, which is multiplied as a complex number by the complex multiplier 9 and is expressed by a linear equation.
Qn/ is output.

P, +1Q11 − (Pa +iQn)(R,, tIn) Therefore.

Namely.

The following is a blank space, and the baseband signal when there is no frequency error in the demodulated digital signals p% and Q0 is that number P. (t), Qo (t) is equal to the signal digitally sampled at frequency f, and one frequency error Δ
A baseband signal from which f has been removed can be obtained.

[Effects of the Invention] As explained above, the present invention can perform accurate frequency correction by correcting the input signal frequency error estimated by digital processing using digital processing. This has the advantage that it can be done reliably in one go.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a demodulator according to an embodiment of the present invention. 1... Local oscillator, 2.3... Multiplier, 5, 6
... A/D converter, 7... Frequency error estimator, 8.
...Digital VC0,9...Complex multiplier.

Claims (1)

[Scope of Claims] 1. A demodulator that receives an orthogonally modulated signal as a received signal and demodulates the received signal, which performs orthogonal quasi-synchronous detection on the received signal and detects first and second signals that are orthogonal to each other. an orthogonal detection means for outputting a baseband signal; and an analog/digital conversion means for converting the first and second baseband signals from analog to digital to output first and second digital signals. In the demodulator,
A demodulation device comprising digital processing means for digitally processing the first and second digital signals and outputting first and second demodulated signals from which frequency errors have been removed. 2. The digital processing means is configured to process the first and second digital processing means.
frequency error estimating means for estimating the frequency error from the digital signal and outputting the estimated frequency error signal; and first and second sine wave signals orthogonal to each other controlled by the estimated frequency error signal. voltage controlled oscillation means for outputting a voltage controlled oscillation means for multiplying the first and second digital signals by the first and second sine wave signals in a complex manner to obtain the first and second demodulated signals. 2. The demodulation device according to claim 1, further comprising complex multiplication means.