JP2910286B2 - Transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitting apparatus at a transmitting terminal or a relay station in a microwave digital radio communication system employing a frequency division multiplexing method, and more particularly to an interference suppressing method.

[0002]

2. Description of the Related Art A relay station in a microwave digital radio communication system is conventionally composed of a receiving apparatus A and a transmitting apparatus B 'as shown in FIG. In FIG. 2, in a receiving apparatus A, an RF signal (for example, a 16 QAM signal) received by a receiving antenna 1 is subjected to frequency conversion into an IF signal and amplification processing to a predetermined level by a receiver 3 and input to a demodulator 4. Then, the signal is demodulated into a digital signal and input to the transmitting device B '. In the transmitting device B ', the demodulated digital signal from the receiving device A is again modulated into an IF signal (16 QAM) by the modulator 5', and the modulated signal is converted into a radio frequency by the transmitting frequency converter 6, and then transmitted to the transmitting amplifier 7. And amplifies the signal to a predetermined level, and transmits the signal from the transmission antenna 2 to the wireless transmission path.

In the transmitting apparatus B ', when the modulator 5' fails, the transmitting amplifier 7 is operated as usual.
It affects the cross-modulation distortion on the adjacent radio channel. Therefore, the transmission frequency converter 6 is provided with an IF signal disconnection detection circuit (first detection means) for detecting the presence or absence of an IF signal input from the modulator 5 ′, and the output of the IF signal disconnection detection circuit is supplied to the transmission amplifier 7. It is used as a gain control signal of an ALC (automatic gain control circuit), and when the IF signal is interrupted, the gain of the transmission amplifier 7 is minimized to suppress the influence of cross-modulation distortion on an adjacent radio channel. The above is about the relay station, but the same applies to the transmitting terminal station.

[0004]

The conventional transmitting device in the transmitting terminal or the relay station in the above-mentioned microwave digital radio communication system has the following problems. That is, in this type of system, the power of the receiving device (the signal input device in the transmitting terminal) is turned off at the relay station during maintenance such as periodic inspection, and the power is turned on after the inspection or the like is completed. Behaves normally. In other words, the modulator outputs a non-modulated signal when the power of the receiving device or the like is cut off and the signal input is interrupted, and outputs a modulated signal when the power is turned on.
Since the change between the two output levels is abrupt, the ALC loop of the transmission amplifier cannot follow, causing a problem that the intermodulation distortion of the output of the transmission amplifier is deteriorated and interference may occur in an adjacent radio channel.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transmitting apparatus having means for suppressing deterioration of cross-modulation distortion of an output of a transmitting amplifier when an input signal becomes a non-signal and then recovers.

[0006]

In order to achieve the above object, a transmitting apparatus according to the present invention has the following configuration. That is,
A transmitter for modulating a digital signal; a modulator for converting the output of the modulator into a signal of a transmission frequency and outputting the signal; and a first detector for detecting the presence or absence of a signal input from the modulator A transmission frequency converter comprising: a transmission frequency converter that amplifies the converted output of the transmission frequency converter, wherein the gain of the amplifier is minimized when the output of the first detection means indicates a signal input “absent”. A transmission amplifier having control means for controlling the modulator; a second detection means for detecting the presence or absence of a digital signal input to the modulator; a logic of each output of the first and second detection means. OR means for taking a sum and providing the sum as a gain control signal to the control means.

[0007]

Next, the operation of the transmission apparatus of the present invention configured as described above will be described. When the digital signal input becomes non-signal, the modulator outputs a non-modulated signal. At this time, the absence of the signal is detected by the second detection means, and the transmission amplifier is controlled so that the gain is minimized. Then, when the digital signal input recovers, the modulator outputs the modulated signal, and the transmission amplifier is controlled so that the gain returns to the standard level. Even if it is abrupt, the change time is sufficiently short compared to the time when the transmission amplifier returns from the minimum gain to the standard gain, so that it is possible to suppress the deterioration of the cross modulation distortion of the output of the transmission amplifier,
It is possible to prevent the influence of the cross modulation distortion on the adjacent wireless channel.

[0008]

FIG. 1 shows a relay station provided with a transmitting apparatus according to an embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. Hereinafter, a description will be given mainly of a portion according to the present invention.

In the transmitting apparatus B, an input disconnection detecting circuit (second detecting means) 8 is provided in the modulator 5, an output of an IF signal disconnection detecting circuit (not shown) provided in the transmission frequency converter 6, and an input disconnection detecting circuit. And an OR circuit 9 for performing an OR operation with the output of the transmission amplifier 7.
Is controlled. That is, when the input of the modulator 5 is cut off, the gain of the transmission amplifier is minimized as in the case of the failure of the modulator 5 itself.

As a result, when the digital signal input becomes a non-signal, the modulator 5 outputs a non-modulated signal.
Is controlled to minimize the gain. Then, when the digital signal input recovers, the modulator 5 outputs a modulated signal, and the transmission amplifier 7 is controlled so that the gain returns to the standard level. Even if the level change is abrupt, the change time is sufficiently shorter than the time required for the transmission amplifier 7 to return from the minimum gain to the standard gain. The effect of modulation distortion can be prevented.

[0011]

As described above, according to the transmission apparatus of the present invention, the gain of the transmission amplifier is minimized when the input signal of the modulator is no signal. This has the effect of suppressing the deterioration and preventing the influence of the cross-modulation distortion on the adjacent wireless channel.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a relay station including a transmission device according to one embodiment of the present invention.

FIG. 2 is a configuration block diagram of a relay station including a conventional transmission device.

[Explanation of symbols]

 Reference Signs List 5 modulator 6 transmission frequency converter 7 transmission amplifier 8 input disconnection detection circuit 9 OR circuit A receiving device B transmitting device

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI H04L 27/36 H04L 27/00 F (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 1/04 H04B 7 / 208 H04J 1/12 H04L 27/18 H04L 27/36

Claims (1)

(57) [Claims] A modulator for modulating a digital signal;
The output of the modulator is converted into a signal of a transmission frequency and output, and a first signal for detecting the presence or absence of a signal input from the modulator is provided.
And a amplifier for amplifying the converted output of the transmission frequency converter, wherein the gain of the amplifier is minimized when the output of the first detection means indicates a signal input “absent”. A transmission amplifier comprising control means for controlling so as to be;
A second detector for detecting the presence or absence of a digital signal input to the modulator;
A transmission means, which takes a logical sum of the outputs of the first and second detection means and supplies the result as a gain control signal to the control means.