JPH02231820A - Receiver - Google Patents

Abstract

PURPOSE:To obtain a virtual space diversity effect with one antenna by driving a telescopic antenna so as to be elongated or decreased in response to an envelope detection signal of a reception signal or a gain control signal. CONSTITUTION:An envelope detection signal subjected to fluctuation of multi- path fading is outputted from an envelope detection circuit 19 and it is compared with a reference voltage E at a comparator circuit 20. When an output of a comparator circuit 10 is at a high level, an antenna drive circuit 2 drives an antenna 11 to have a ground height h1 in response to the output of high level. Moreover, when the output of the comparator circuit 10 is at a low level, the antenna drive circuit 2 drives the antenna 11 to have a ground height h2 in response thereto. When the difference of ground height h3=h2-h1 is larger than lambda/3 (lambda is wavelength), the virtual diversity effect is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application in "Industry" 2] The present invention relates to a receiver, and more particularly to an improvement of a receiver that obtains a spatial diversity effect as a countermeasure against multipath fading.

[Summary of the Invention] A reception device that has one extendable antenna and obtains a spatial diversity effect by driving the antenna to extend and contract in accordance with an envelope detection signal or a gain control signal of a received signal. It is a machine.

[Background Art] Generally, radio waves transmitted in wireless communication are reflected/diffracted by buildings and the like, and are received through various routes. Also,
The reception status also varies greatly depending on the reception location. Such a phenomenon is called "multipath fading" and is a factor that deteriorates reception performance.

In analog communication, as typified by AM receivers and FM receivers, the above multipath fading causes deterioration of sound quality, and in digital communication,
Increases bit errors in data, as typified by modems.

Therefore, countermeasures against multipath fading are required. Generally, received signals in wireless communication fluctuate irregularly, so correlation functions regarding various parameters (position, time, frequency, etc.) constituting the signal can be obtained. At two points where the correlation value is close to zero, the fluctuations regarding the parameters are nearly independent of each other. A technique for improving system characteristics by using a plurality of signal outputs that are close to statistical independence is a diversity method known as a multipath fading countermeasure.

There are various diversity methods depending on which parameters are used to consider the correlation, but the most commonly used method is the spatial diversity method.

In this method, the signal output at a point where the receiving position is spatially more than λ/3 (λ is the wavelength) is almost uncorrelated due to the autocorrelation function for the received electric field. If reception antennas are installed at a plurality of distant locations for reception, each antenna output can be used as a diversity branch output. A conceptual diagram of this method is shown in FIG.

In the figure, 1 is a receiver, 2 and 3 are antennas, and 4 is a combiner or switch.The reason why a combiner or switch is used is because there are several methods for combining (selecting) received outputs. ,
As a representative method, there is the method shown below.

(B) Maximum ratio combining diversity method (Ex) Equal gain combining diversity method (C) Switching diversity method (selection diversity method) Maximum ratio combining diversity method
The random phases of the branch outputs are aligned and added in the same phase, and during synthesis, each branch output is weighted in proportion to the input signal power-to-noise power ratio (S/N).In the equal gain combining diversity method, this weighting is done equally. It is something to do.

The selection diversity method is a method that uses only the branch output signal having the maximum level among the branch outputs.

? In other words, the receiver using the spatial diversity method in FIG. It is used by switching.

[Problems to be Solved by the Invention] However, this receiver requires a plurality of antennas (at least two). Furthermore, when combining diversity branch outputs, a phase control circuit is required for each branch in order to align the random phases of each branch output to the same phase, and a phase detection circuit is required to drive the phase control circuit. shall be. The number of phase control circuits increases proportionally as the number of antennas increases, that is, the number of branches increases, and the phase detection circuit also compares and determines the output of the phase control circuit of each branch and determines the output of each phase control circuit. It is obvious that the circuit configuration of the receiver is complicated because it is a control device.

Therefore, according to the conventional diversity method, it is difficult to construct a simple receiver because a plurality of antennas are required.

[Object of the Invention] An object of the present invention is to provide a receiver with a simple circuit configuration that does not require a plurality of antennas and can obtain a pseudo spatial diversity effect with a single antenna.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a gist of driving an expandable and retractable antenna to expand or contract in response to an envelope detection signal or a gain control signal of a received signal. shall be.

[Effect] The envelope detection signal or gain control signal is subject to multipath fading fluctuations, and the height of the antenna is controlled by this signal, so a pseudo spatial diversity effect is obtained and multipath fading The impact of

[Example code] The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of a receiver according to the invention.

In the figure, 11 is an extendable antenna, 12 is an antenna drive circuit, 13 is a bandpass filter, 14 is an amplifier, 15 is a multiplier, 16 is a local oscillator, 17 is a bandpass filter, and 18 is an AGC circuit (or amplifier). ), 1
9 is an envelope detection circuit, and 20 is a comparison circuit.

The signal received by the antenna 11 is transmitted to a high frequency stage circuit section 21 consisting of a bandpass filter 13 and an amplifier 14.
(hereinafter abbreviated as RF section), the signal is converted into an IF signal in an intermediate frequency band by a local oscillator 16 and a multiplier 5. The IF signal converted to the intermediate frequency band passes through an intermediate frequency circuit section 22 (hereinafter abbreviated as IF section) consisting of a bandpass filter 17 and an amplifier or AGC circuit 8.
It is output to the demodulator.

The received signal that has passed through the IF section is split into two, one to the demodulation section, and one to the demodulation section.
The other signal is input to the envelope detection circuit 19.

The envelope detection circuit 19 detects the envelope of the received signal. Here, if the received signal has a constant envelope, such as an FM modulated signal typified by analog communication or a PSK modulated signal typified by digital communication, the fluctuation of the detected envelope is due to the propagation path between transmitting and receiving. This can be said to be the effect of multipath fading.

However, in the case of a non-constant envelope such as an AM modulated signal, it is possible to obtain a fluctuation component due to multipath fading by setting the integration time constant τ in the envelope detection circuit 19 to an appropriate value.

As described above, various modulation methods can be applied to the baseband information, but it is preferable to use the FM or phase modulation method in which the AGC circuit for stabilizing communication operates well.

Therefore, the envelope detection circuit 19 outputs an envelope detection signal that has undergone variations due to multipath fading.
Comparison circuit 20 compares it with reference voltage E.

Note that the input of the envelope detection circuit 19 is =7= The IF section output is used, but any output may be used in the RF section or the demodulation section, as long as the fluctuation of multipath fading appears, and in that case, It goes without saying that the envelope detection circuit 19 only detects the fluctuation component of multipath fading. Furthermore, it goes without saying that the above output is amplified in the envelope detection circuit 19 to a level suitable for comparison with the reference voltage E.

Next, the reference voltage E is set to a threshold value that is a boundary line between good and bad signal states in the demodulator. Therefore, comparison circuit 1
0, the fluctuation component of the received signal is compared with the threshold value, and the received signal is compared with the reference voltage E which is the threshold value.
, the output of the comparator circuit 10 has a high potential.
is at a high level. In other words, it can be said that the influence of multipath fading is small and the reception condition is good. Conversely, when the received signal does not exceed the reference voltage E, the output of the comparison circuit 10 is in a "low level" state with a low potential. In other words, is this multipath? It can be said that the reception condition is poor due to the large effect of aging.

When the output of the comparator circuit 10 is at a "high level", the antenna drive circuit 2 drives the antenna 11 so that the height above the ground is h■ in response to this output.

Further, when the output of the comparator circuit 10 is at a "low level", in response to this, the antenna drive circuit 2 drives the antenna 11 so as to change the height above the ground to h.

In this way, the antenna drive circuit 2 is driven to expand or contract the antenna height depending on the level state of the output of the comparison circuit 10, and the antenna height is increased or decreased by the above-described antenna drive.
If < h 2, the antenna 11 is driven so as to set the antenna at a higher point above the ground when the influence of multipath fading is large and the reception condition is poor.

Ground height difference h3=h. -h〉λ/3 (λ is the wavelength), a pseudo diversity effect can be obtained. Note that it is clear that the shorter λ, that is, the higher the transmission/reception frequency, the greater the effect.

In addition, as another effect, it is effective for automatic guided vehicles that are wirelessly connected to base stations in factories, ie, wireless local area networks, and the like.

This is because when machines, people, etc. placed on the ground become obstacles and block the propagation path between transmitter and receiver, it is possible to avoid them by automatically changing the antenna height.

In this way, even if communication within line-of-sight is interrupted by some kind of obstacle, the stability of establishing a communication link can be improved.

FIG. 2 shows a second embodiment of a receiver according to the invention.

In the first embodiment, the drive control of the antenna height could only be performed with binary variable control. Therefore, the higher the antenna moves, that is, the longer the distance, the more time it takes to move.

Therefore, the receiver of the second embodiment eliminates multipath fading by providing the output of the envelope detection circuit 9 adjusted to an appropriate level directly to the input of the antenna drive circuit 2 without using the comparison circuit 10. This makes it possible to control the antenna height continuously in response to the fluctuation component of the antenna.

Therefore, according to the second embodiment, the antenna height movement time can be reduced due to continuous response.

The reception condition is best where the antenna height is lowest.
The antenna drive circuit 2 is set to drive so that as the antenna height increases, the reception condition becomes worse.

FIG. 3 shows a third embodiment of a receiver according to the invention.

This is a simplified type of the second embodiment, in which the gain control signal of the AGC circuit 18 is used as the control signal of the antenna drive circuit 2. If the receiver has an AGC circuit, the gain control signal number will be increased in response to fluctuation components due to fading, etc., so by inputting it to the antenna drive circuit and using it, the receiver can be controlled. It is more effective in reducing the cost and size.

FIG. 4 shows a fourth embodiment of a receiver according to the invention.

In a receiver that continuously controls the antenna height, the antenna height is constantly moving, so why? If the fluctuations due to aging are severe, a Doppler effect may occur. Fading becomes more accentuated due to the influence of this Doppler effect, causing performance deterioration of the receiver, so this receiver is designed to reduce this.

In this receiver, the output of the envelope detection circuit 19 is sampled and held by a sample and hold circuit 23 in response to a sample and hold control signal. Therefore, the output of the sample and hold circuit 23 becomes a temporally discrete signal, which allows the antenna drive circuit 12 to perform discrete antenna height control. Therefore, it is possible to reduce the Doppler effect.

FIG. 5 shows a fifth embodiment of a receiver according to the invention. In the figure, 24 is a switch for making the antenna height variable, and is turned on and off by the output of the comparator 20. For example, when it is turned off, the antenna 11 is
2. When turned on, it is set to h■.

[Effects of the Invention] As explained above, according to the present invention, since the antenna is expanded and contracted by the envelope detection signal or gain control signal of the received signal, the influence of multipath fading is reduced by a pseudo spatial diversity effect. can do.

[Brief explanation of the drawing]

1 to 5 are block diagrams showing first to fifth embodiments of the present invention, and FIG. 6 is a block diagram showing a conventional diversity receiver. 11・・・・・・・・・Antenna, 12・・・・・・・・・
・・Antenna drive circuit, 13.17・・・・・・・・・
Bandpass filter, 14......Amplifier,
15・・・・・・・・・Multiplier, 16・・・・・・・・・
・Local oscillator, 18...Amplifier or AGC circuit, 19...Envelope detection circuit, 20...Comparison circuit, 21...・
. . . High frequency stage circuit section, 22 . . . Intermediate frequency circuit section, 23 . . . Sample hold circuit.

Claims (2)

[Claims] (1) an extendable and retractable antenna, an envelope detection means for detecting an envelope of a received signal, and an antenna drive circuit that drives the antenna to extend or contract in response to an envelope detection signal from the means; A receiver characterized by comprising: (2) An extendable antenna, a gain control means for controlling the gain of a received signal, and an antenna drive circuit for driving the antenna to extend or contract in response to a gain control signal from the means. A receiver characterized by: