JPH07297748A - Transmission-reception system - Google Patents

Abstract

PURPOSE:To improve frequency efficiency by making additional service by a digital signal available without interference to an analog FM signal. CONSTITUTION:An analog modulation signal v(t) is given to an FM modulator 1, from which an IF band FM signal f(t) is obtained. A tracking filter circuit 2 traces an instantaneous frequency of the FM signal and an inverse filter circuit 3 forms an output of an inverse filter characteristic, it is analyzed by a frequency analyzer 4 and the result is given to a digital carrier selection circuit 5 to select a digital carrier not interfering the analog FM signal and the selected carrier is given to an OFDM modulator 7. Digital modulation data d(t) are subject to arrangement conversion by an input data arrangement converter 6, the OFDM modulator 7 modulates the data, from which a digital modulation signal s(t) is obtained. The signal s(t) is filtered by the inverse filter 3', from which a digital modulation signal s1(t) with a spurious spectrum component eliminated therefrom is obtained and it is superimposed on an FM signal by an adder 8, and the resulting signal is transmitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission / reception system, and more particularly to a transmission / reception system suitable for a superposed transmission system of an analog FM signal and a digital data signal.

[0002]

2. Description of the Related Art As one of conventional FM transmission / reception systems, particularly FM demodulation systems, for example, periodical publications "Radio Technology, 1
There is a method using a PTL (Phase Tracking Loop) demodulation circuit disclosed in the January 1978 issue, pages 284 to 289.

[0003]

Thus, FM broadcasting uses a bandwidth of 200 kHz to transmit an FM signal, but when the spectrum of the FM signal at a certain time t ₁ is instantaneously seen, Only the spectrum component of the instantaneous frequency f ₁ exists within the bandwidth of 200 kHz, and thus the frequency utilization efficiency of the conventional FM broadcasting was poor. Also conventional FM
In the multiplex system, multiplex data is transmitted using a band as shown in FIG. As is clear from the figure, the conventional F
According to the M multiplex system, since only one digital carrier is used, if interference such as fading or multipath occurs at the carrier frequency, it becomes difficult to demodulate the data in perfect form.

SUMMARY OF THE INVENTION An object of the present invention is to propose a configuration of a novel superposition system of an analog FM signal and a digital signal so as to effectively use the frequency and solve the conventional problems.

[0005]

In order to achieve the above object, the transmission system of the first invention comprises an FM modulation means for FM-modulating a first input signal and outputting an FM-modulated signal, and a variable tuning filter. Digital carrier selecting means for tracking the instantaneous frequency of the FM modulated signal and selecting a predetermined digital carrier by the inverse filter of the variable tuning filter, and digitally modulating the second input signal in accordance with the digital carrier. It is characterized by comprising digital modulating means for outputting a signal and adding means for superimposing the digital modulated signal on the FM modulated signal and transmitting it.

The transmission system of the second invention is the transmission system of the first invention, wherein the digital carrier selecting means includes the variable tuning filter, an inverse filter thereof, a frequency analyzer for frequency-analyzing an output of the inverse filter, and an analyzer thereof. A digital carrier selecting circuit for selecting a predetermined digital carrier from the output, and the digital modulating means, and an array converter for converting an array of the second input signal based on the predetermined digital carrier; It is characterized by including an OFDM modulator for digitally modulating the second input signal and an inverse filter for removing unnecessary spectral components from the digitally modulated signal.

According to a third aspect of the present invention, in the first or second aspect of the invention, the first input signal is an analog modulation signal,
The second input signal is digitally modulated data.

According to a fourth aspect of the present invention, an FM demodulation means for extracting an FM modulation signal from the received transmission signal by a variable tuning filter and performing FM demodulation, and digital modulation of the transmission signal by an inverse filter of the variable tuning filter. Digital demodulation means for extracting a signal and digitally demodulating it.

The receiving system of the fifth invention is the receiving system of the fourth invention, wherein the FM demodulation means includes a PTL demodulation circuit having the variable tuning filter, and the digital demodulation means includes the inverse filter and the OFDM demodulation circuit. It is characterized by

In the transmission / reception system of the sixth invention, the transmission system is
An FM modulation means for FM-modulating the first input signal to output an FM-modulated signal, and a variable tuning filter for tracking the instantaneous frequency of the FM-modulated signal and selecting a predetermined digital carrier by an inverse filter of the variable-tuning filter. Digital carrier selecting means, and digital modulating means for digitally modulating the second input signal according to the digital carrier to output a digital modulated signal,
And an FM demodulation unit for extracting the FM modulation signal from the received transmission signal by a variable tuning filter and performing FM demodulation, and an addition unit for superimposing the digital modulation signal on the FM modulation signal and transmitting the superposed signal. Digital demodulation means for digitally demodulating and extracting a digital modulation signal from the transmission signal by the inverse filter of the variable tuning filter,
It is characterized by consisting of.

[0011]

In the transmission system of the present invention, the variable frequency tuning filter (tracking filter) FM-modulates the first input signal to track the instantaneous frequency of the FM modulated signal, and the variable frequency tuning filter selects an inverse filter. The digital modulated signal obtained by digitally modulating the second input signal by using the digital carrier is superimposed on the FM modulated signal and transmitted. Further, in the receiving system of the present invention, the FM modulation signal is extracted from the transmission signal by the variable tuning filter and FM demodulated, and the digital modulation signal is extracted and digitally demodulated by the inverse filter of the variable tuning filter.

[0012]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows an embodiment of a transmission system of the present invention. 1 is an FM modulator, 2 is a tunable filter circuit (tracking filter), 3 and 3'is an inverse filter circuit, 4 is a frequency analyzer, and 5 is A digital carrier selection circuit, 6 is an input data array converter, 7 is an OFDM modulator (IFFT), 8 is an adder, 9 is a frequency conversion circuit, 10 is a bandpass filter (BPF), and 11 is a transmission antenna.

In FIG. 1, the analog modulation signal v (t)
Are input to the FM modulator 1 and the IF band (carrier frequency 10.
An FM signal f (t) of 7 MHz) is obtained. The tracking filter circuit 2 tracks the instantaneous frequency of the FM signal f (t), and as a result, the inverse filter circuit 3 produces a solid line tracking filter characteristic output and a dotted line inverse filter characteristic output as shown in FIG. To be This inverse filter characteristic output is analyzed by the frequency analyzer 4, and as a result, the analyzed output is input to the digital carrier selection circuit 5 to select 2 ⁿ digital carriers that do not interfere with the analog FM signal and perform OFDM modulation. Given to vessel 7. However, inside the digital carrier selection circuit 5, (2 ⁿ + m) carrier frequencies are predetermined at equal intervals for a bandwidth of 200 kHz. 2 ⁿ + m is 2 from the symbol length Ts in digital modulation as shown in FIG.
It is the number of carriers that can be set up at equal intervals in the 00 kHz bandwidth. Therefore, m is OF with respect to the characteristic of the inverse filter.
It is set to secure 2 ⁿ digital carriers used for DM modulation. It should be noted that the carrier indicated by the dotted line in FIG. 5 is not used because it interferes with the FM signal.

When a set of carrier frequencies (2 ⁿ ) used for digital modulation is determined, the digital modulation data d (t) input to the OFDM modulator 7 corresponds to the carrier used by the input data array converter 6. Then, array conversion is performed. Here, zero is inserted in the input data corresponding to the unused carriers. OFDM (Orthogonal Fre
data input to a quency division multiplec) modulator 7 (see, for example, the periodical, "Radio Technology, June 1993, p. 493 and p. 494") is inverse fast Fourier transform modulated (IFFT) (Inverse Fast). Fourier Tra
nsform) as an output and the digital modulation signal s (t)
Is obtained. By filtering this digital modulation signal s (t) with an inverse filter 3 ′ equivalent to the above-mentioned inverse filter 3, the digital modulation signal s from which unnecessary spectrum components which disturb the FM signal spectrum are removed.
₁ (t) is obtained. Furthermore, the digital modulation signal s
₁ the amplitude of the (t), as PTL circuit 14 of the receiver side does not wrong tracking the instantaneous frequency of the digital modulated signal s ₁ (t), it must be kept lower than the amplitude of the analog FM signal f (t) is there. This digital signal s ₁ (t) and the above-mentioned IF band FM signal f (t) are added (superposed) by the adder 8, and the frequency conversion circuit 9 performs band conversion to the RF band. Finally, the BPF 10 removes unnecessary frequency components, and the antenna 11 transmits the transmission signal x (t).

FIG. 2 shows an embodiment of the receiving system of the present invention.
2 is a receiving antenna, 13 is a frequency conversion circuit, 14 is PT
L demodulation circuit, 15 is an inverse filter, and 16 is an OFDM demodulation circuit (FFT). In FIG. 2, the antenna 12 receives the transmission signal x ′ (t), and the frequency conversion circuit 13 obtains the IF band reception signal f ′ (t) + s ₁ (t). Since the amplitude of s ₁ '(t) is smaller than the amplitude of f' (t), the PTL
The tracking filter 17 in the demodulation circuit 14 is a reception FM.
The instantaneous frequency of the signal f '(t) is tracked. And PT
As the output of the L demodulation circuit 14, a demodulation signal v ′ (t) of an FM signal that is not affected by the digital signal is obtained.

FIG. 3 shows an example of the configuration of the PTL demodulation circuit.
Is a tracking filter, 18 is a limiter, 19 is a Hilbert filter, 20 is a phase comparator, 21 is a loop filter, and 22 is an amplifier. Since this configuration itself is known, its specific instantaneous frequency tracking operation and FM Although the process of demodulating the signal is omitted, for details, refer to the above-mentioned "Radio Technology, January 1978", for example.

The input of the inverse filter circuit 15 is f '.
(T) + s ₁ '(t) is input. On the other hand, an inverse filter characteristic output is generated by the inverse filter circuit 15 from the tracking filter characteristic obtained in the PTL demodulation circuit 14, and the FM signal f ′ (t) is cut as a digital signal s ₁ ′ (t). Is obtained. When this s ₁ '(t) is input to the OFDM demodulation circuit 16, a digital demodulation signal d' (t) that is not affected by the FM signal is obtained. Note that the description of OFDM modulation can be found, for example, in "Radio Technology,
June 1993 issue ". OFDM demodulation
This is the reverse of the modulation process, and demodulated data can be obtained by performing a Fast Fourier Transform (FFT) on the OFDM signal.

According to the above-mentioned method, since a plurality of digital carriers can be used as shown in FIG. 5,
Even if interference occurs in a predetermined frequency band, a large amount of data that has not been interfered can be used, and therefore correction is easy.

[0019]

As described above, according to the transmission system of the present invention, since the digital signal is transmitted using the entire FM stereo broadcast bandwidth (200 kHz), it is possible to perform transmission at a high transmission rate. Therefore, a higher quality service (simulcast, image transmission, etc.) than the conventional FM multiplex system becomes possible. Further, since the digital carrier arranged other than the instantaneous frequency of the FM signal is used, the multiplexed digital signal can be transmitted without disturbing the analog FM signal. Therefore, the frequency utilization efficiency is improved. Further, according to the receiving system of the present invention, it is possible to receive high quality information data as compared with the conventional FM multiplex system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a transmission system of the present invention.

FIG. 2 is a block diagram showing an embodiment of a receiving system of the present invention.

FIG. 3 is a block diagram showing a configuration example of a PTL demodulation circuit.

FIG. 4 is a diagram showing a tracking filter characteristic (solid line) for tracking the instantaneous frequency of an FM signal and an inverse filter characteristic thereof (dotted line).

FIG. 5: As a result of frequency analysis of the inverse filter characteristic, digital data is output using the selected carrier (solid line).
It is a figure which shows the spectrum at the time of FDM modulating.

FIG. 6 is a frequency spectrum diagram of a conventional FM multiplex system.

FIG. 7 is a spectrum diagram of an FM signal and a multiplexed signal in a baseband of a conventional FM multiplexing system.

[Explanation of symbols]

 1 FM modulator 2 Tracking filter 3, 3'inverse filter 4 Frequency analyzer 5 Digital carrier selection circuit 6 Input data array converter 7 OFDM modulator 8 Adder 14 PTL demodulation circuit 15 Inverse filter 16 OFDM demodulation circuit

Claims (6)

[Claims] 1. An FM modulating means for FM-modulating a first input signal to output an FM-modulated signal, and a variable tuning filter for tracking the instantaneous frequency of the FM-modulated signal and a predetermined value for the inverse filter of the variable-tuning filter. Digital carrier selecting means for selecting the digital carrier of
It is characterized by comprising digital modulating means for digitally modulating the second input signal according to the digital carrier and outputting a digital modulated signal, and adding means for superimposing the digital modulated signal on the FM modulated signal and transmitting it. Transmission method. 2. The digital carrier selecting means, the variable tuning filter, an inverse filter thereof, a frequency analyzer for frequency-analyzing an output of the inverse filter, and a digital carrier selection circuit for selecting a predetermined digital carrier from the analysis output. And the digital modulation means includes an array converter for array-converting the second input signal based on the predetermined digital carrier, and an OFDM modulator for digitally modulating the array-converted second input signal. ,
And an inverse filter for removing unnecessary spectral components from the digitally modulated signal.
Transmission method described in. 3. The first input signal is an analog modulated signal,
The transmission system according to claim 1 or 2, wherein the second input signal is digitally modulated data. 4. An FM demodulation means for extracting an FM modulation signal from the received transmission signal with a variable tuning filter and performing FM demodulation, and a digital modulation signal from the transmission signal with an inverse filter of the variable tuning filter for digital demodulation. A reception system comprising a digital demodulation means. 5. The reception system according to claim 4, wherein the FM demodulation means includes a PTL demodulation circuit having the variable tuning filter, and the digital demodulation means includes the inverse filter and an OFDM demodulation circuit. . 6. A transmission system, wherein an FM modulation means for FM-modulating a first input signal to output an FM-modulated signal, and a variable tuning filter for tracking the instantaneous frequency of the FM-modulated signal and for the variable tuning filter. Digital carrier selecting means for selecting a predetermined digital carrier by an inverse filter, digital modulating means for digitally modulating the second input signal according to the digital carrier and outputting a digital modulated signal, and digitally modulating the FM modulated signal. An addition means for superimposing signals and transmitting the signals, and a reception method is an FM demodulation means for extracting and FM demodulating an FM modulated signal from a received transmission signal by a variable tuning filter, and the variable tuning filter from the transmission signal. Demodulation to extract the digitally modulated signal by the inverse filter of A receiving method comprising means and.