JPH0269014A - Demodulation system - Google Patents

Abstract

PURPOSE:To perform demodulation with a less arithmetic amount by shifting the carrier frequency of received signals to a fraction of an integer of a sampling frequency and simultaneously performing the demodulation and filtering processes. CONSTITUTION:The demodulation system performs demodulating operations by simultaneously performing demodulation and filtering processes by means of a DEF.ROF 4 after the carrier frequency of received signals is shifted to a fraction of an integer of a sampling frequency by multiplying a signal e<jomega>'<t> produced from the reception signals by a prescribed signal e<jomegat> by using a multiplier 3. Moreover, demodulation and filtering processes are simultaneously performed on the reception signals by shifting the carrier frequency to the fraction of an integer of the sampling frequency by using a DEM.ROF 4-1. The resultant is multiplized with the prescribed signal e<jomegat> by using a multiplier 3-1, returned to the carrier frequency of the original reception signal and demodulated by performing necessary filtering processes.

Description

[Detailed Description of the Invention] [Summary] Regarding a demodulation method for demodulating a received signal, the carrier frequency of the received signal is shifted to an integer fraction of the sampling frequency, and demodulation and filtering processing are performed simultaneously to perform demodulation with a small amount of calculation. After shifting the carrier frequency of the received signal to an integer fraction of the sampling frequency,
The configuration is such that demodulation and filtering processing are performed simultaneously using demodulation.

In addition, after demodulating and filtering the received signal at the same time using a DEM-ROF as a carrier frequency that is an integer fraction of the sub-ring frequency, the frequency is shifted back to the carrier frequency of the original received signal, and the necessary Configure to perform filtering processing.

[Industrial application field]

The present invention relates to a demodulation method that moves the carrier frequency of a received signal to an integer fraction of the sampling frequency and demodulates the signal.

[Problems to be solved by the prior art and the invention] Digital signal processing is based on the maximum frequency of 2, according to the sampling theorem.
Analog signals are sampled using a sampling frequency that is twice as high or higher, and various types of processing are performed.

At this time, as shown in the demodulation process in Figure 3, if the carrier frequency of the received signal is 1800 Hz and the sampling frequency is an integral multiple of this, for example 4 times, 7200 Hz, the positions marked with small circles in the figure Of which value “1” -1
” only need to be extracted. Therefore, when demodulating, co
Without performing the multiplication of s ωt, sin ω(, R
During the filtering process by OF, these 1” and “1”
By extracting the part '', demodulation and filtering processing can be calculated simultaneously.

However, it is generally impossible to freely select the carrier frequency and sub-frequency of the received signal, and the sampling frequency is often an integer multiple of the baud rate frequency. There was a problem in that the demodulation and filtering processes could not be calculated at the same time to reduce the amount of calculation.

An object of the present invention is to shift the carrier frequency of a received signal to an integer fraction of the sampling frequency, perform demodulation and filtering processing at the same time, and demodulate the signal with a small amount of /'A calculation.

[Means to solve problems]

Means for solving the problem will be explained with reference to FIG.

In Figure 1 (a) and (b), DEM-ROF4.4
-1 means that demodulation and filtering processing are performed simultaneously.

Multiplier 3.3-1 performs multiplication to shift the frequency.

[Effect]

In the present invention, as shown in FIG.
and a predetermined signal (ejir&) to shift the carrier frequency to an integer fraction of the sub-ring frequency, and then perform demodulation and filtering processing simultaneously by the DEF/ROF 4 for demodulation. In addition, as shown in Fig. 1 (b), the received signal
After performing demodulation and filtering processing at the same time using the M-ROF 4-1 as a carrier frequency that is an integer fraction of the sampling frequency, this is multiplied by a predetermined signal (ejwt) using the multiplier 3-1. Return to the carrier frequency of the original received signal, perform the necessary filtering processing,
I'm trying to demodulate it.

Therefore, after shifting the carrier frequency of the received signal to an integer fraction of the sampling frequency, demodulation and filtering are performed simultaneously, or the received signal is demodulated and filtered as a carrier frequency that is an integer fraction of the sampling frequency. By performing demodulation at the same time and returning to the original carrier frequency, it becomes possible to demodulate the received signal with a small amount of calculation (for example, 1/2 the amount of calculation).

〔Example〕

FIG. 1A shows an example of a configuration in which the carrier frequency of the received signal is shifted to an integer fraction of the sampling frequency, and then demodulation and filtering processing are performed simultaneously.

In FIG. 1(a), A/D1 is an analog/digital converter that converts an analog reception (ε signal) into a digital reception signal at a sampling frequency.

The π/2 phase shifter 2 shifts the phase by π/2.

The multiplier 3 multiplies the complex number ej-1 generated from the received signal by a predetermined signal e1wt, and moves the carrier frequency of the received signal to an integer fraction of the sampling frequency.

The DEM-ROF 4 performs demodulation and filtering processing simultaneously (see FIG. 2).

The operation will be explained using a specific example.

Figure 1 (At the input, the carrier frequency of the received signal is 1
900 Hz, sampling frequency is 7200 Hz
Suppose that

After ill A/Data, Hilbert filter (π/
2 phase shifter 2) is used to shift the phase of the received signal by π/2 to extract the ■ component (Imaginary component), and vectorize the received signal to generate ejw' t.

(2) ej vectorized using multiplier 3
The carrier frequency is shifted to 1800 Hz by multiplying w'L by a predetermined signal ejwt. This results in
A received signal is generated whose frequency is shifted to a carrier frequency of 1800 Hz, which is 1/4 of the sampling frequency 7200)1z.

(3) Regarding this generated received signal, Fig. 2 DE
The M-ROF 4 simultaneously performs demodulation and filtering processing, and sends out the demodulated baseband signal λFj1 from the right end in FIG. 1(A).

Note that when a Hilbert filter is used, a phase shift of π/2 can be performed regardless of the frequency. This allows calculations on the vector plane. For example, e””=a + j b...
・・・・・・・・・・file”'=c+jd・・・・
...... (2), ej''"-e"' -(ac-bd)+j (ad+
bc) ・・・・・・・・・・・・・・・・・・(3
).

Next, using FIG. 1(b), a configuration example will be shown in which demodulation and filtering processing are performed simultaneously at a carrier frequency that is an integer fraction of the sampling frequency, and then the original carrier frequency is returned to demodulation.

In FIG. 1(b), the DEM-ROF 4-1 performs demodulation and filtering processing simultaneously (see FIG. 2).

The multiplier 3-1 combines the signal demodulated and filtered by the DEM-ROF 4-1 and a predetermined signal e.
J w L to return to the original carrier frequency of the received signal.

The operation will be explained using a specific example.

In Figure 1 (b), taking the 27 modem as an example,
Assume that the carrier frequency of the received signal is 1800H2 and the sampling frequency is 9600Hz.

(11 Regarding the A/D converted digital received signal,
Carrier frequency 2400Hz (sampling frequency 9
DEM/ROF at 2400Hz (1/4 of 600Hz)
4-1 to perform demodulation and filtering processing simultaneously.

(2) The signal after demodulation and filtering processing is multiplied by e J w t by the multiplier 3-1, and the frequency is shifted to the original carrier frequency 1 of the received signal.
The frequency is then returned to 800 Hz, and then filtered by the ROF 5 and the demodulated baseband signal shown in FIG. 1 (b) is sent out.

FIG. 2 shows an example DBM-ROF. This is A on the top left
/D The input from 1 (signal obtained by digitally converting the received signal) is sequentially shifted to the right in synchronization with the sampling frequency, and the value of each tap at this time and the constant -h manually input to each multiplier in the upper stage of the diagram. , h3, -hS, hfu...-h
The R component output is sent from the right end, taking into account the sign of the sum of the results multiplied by tl. Similarly, the constants −ha, ha, h&, he input to each multiplier in the lower row of the diagram
. . h2°, and the sign of the sum of the results is taken into account and the output of the I component is sent from the right end. In this way, as explained using Fig. 3, by shifting the carrier frequency to an integer fraction of the sub-ring frequency, especially to a quarter, the small circle in Fig. 3 can be obtained. Only the "1" and -1" parts (sign only)
Since multiplication for demodulation is no longer necessary if .

〔Effect of the invention〕

As explained above, according to the present invention, the carrier frequency of the received signal is shifted to an integer fraction of the sampling frequency, and then demodulation and filtering processing are performed simultaneously to perform demodulation, or to perform demodulation to an integer fraction of the sub-ring frequency. Since the configuration employs a configuration in which the received signal is demodulated and filtered simultaneously as a carrier frequency, and then returned to the original carrier frequency and demodulated, fewer calculations N (for example,
The received signal can be demodulated by the operation ff1) of 2.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of one embodiment of the present invention, Fig. 2 is a DEM-R
OF Example, FIG. 3 shows an explanatory diagram of the prior art. In the figure, 1 represents an A/D, 2 represents a π/2 phase shifter, 3.31 represents a multiplier, and 4.4-1 represents a DEM-ROF.

Claims (2)

[Claims] (1) In the demodulation method that demodulates the received signal, after shifting the carrier frequency of the received signal to an integer fraction of the sampling frequency, demodulation and filtering processing are performed simultaneously using a DEM/ROF (4). A demodulation method characterized in that the demodulation method is configured to perform demodulation using (2) In the demodulation method of demodulating the received signal, the received signal is demodulated and filtered using DEM/ROF (4-1) as a carrier frequency that is an integer fraction of the sub-ring frequency, and then the frequency A demodulation method characterized by moving the signal back to the carrier frequency of the original received signal, and then performing necessary filtering processing.