JPS6317372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for improving communication quality by relieving a drop in a received electric field due to fading in land mobile communications.

In land mobile communications, a standing wave electromagnetic field distribution is formed due to reflection, refraction, and scattering from buildings, trees, etc. As the mobile station travels through this, high-speed and deep fading occurs, resulting in poor communication quality. deteriorates significantly. In order to overcome this deterioration in communication quality, there is a diversity receiving device that selectively switches the detection output of a receiver having a high received field strength among signals received by a plurality of antennas.

FIG. 1 shows a conventional receiving device, in which signals Sa and Sb received by receiving antennas 1a and 1b are supplied to receivers 2a and 2b, respectively.
The intermediate frequency signals IFa and IFb respectively obtained at 1 and 2 are passed through logarithmic amplifiers 3a and 3b and envelope detectors 4a and 4b to obtain envelope signals Ea and Eb. The comparator 5 determines the level of the envelope signals Ea and Eb, and if EaEb, the detection output signal Ba is supplied to the output terminal 7 via the fixed contact 6a of the switch 6, and if Ea<Eb, the detection output By supplying the signal Bb to the output terminal 7 via the fixed contact 6b of the changeover switch 6, a detected output signal S after switching is obtained at the output terminal 7.

Conventional receiving devices of this type require a logarithmic amplifier and an envelope detector in each diversity branch to obtain the envelope of each receiver, and due to variations in the characteristics of the logarithmic amplifier and envelope detector, the second As shown in the figure, when the antenna correlation coefficient is 1 (perfect correlation), a situation occurs where the envelopes of each branch do not match. Also,
The drawback was that the switching accuracy deteriorated significantly over time.

In order to solve these drawbacks, the present invention has the following objectives:
The present invention provides a diversity receiving device that eliminates variations in characteristics by using serial envelope detectors in a time-divisional manner.

The present invention will be explained in detail below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which signals Sa and Sb received by receiving antennas 1a and 1b are supplied to receivers 2a and 2b, respectively. Intermediate frequency signals IFa and IFb obtained at receivers 2a and 2b, respectively
is supplied to one fixed contact 8a and the other fixed contact 8b of the changeover switch 8. A switch control circuit 12 driven by a clock pulse supplied from a sampling clock pulse generator 13 switches the changeover switch 8 to sample intermediate frequency signals IFa and IFb supplied to fixed contacts 8a and 8b. The sampling frequency shall be several tens of times higher than the maximum Doppler frequency. The two sampled IF signals are level-compressed by a logarithmic amplifier 3, envelope-detected by an envelope detector 4, and envelope-detected for each of systems 1 and 2 by a changeover switch 9 controlled by the switch control circuit 12. The line detection output is distributed to a low-pass filter 10 connected to the fixed contact 9a of the changeover switch 9 and a low-pass filter 11 connected to the fixed contact 9b, smoothed here, and passed through gain correction amplifiers 14 and 15. Envelope Ea of system 1 and system 2
The envelope Eb is obtained. The comparator 5 determines the levels of the envelopes Ea and Eb, and if EaEb, the detected output signal Ba is supplied to the fixed contact 6a of the changeover switch 6,
If Ea<Eb, a switching output S is obtained at the output terminal 7 by supplying it to the fixed contact 6b.

FIG. 4 is a circuit diagram showing an example of the switch control circuit 12, in which 16 is a frequency divider, 17 is an EX-OR circuit, 18 is a NOT circuit, 19 and 20 are AND circuits,
21 is a NOT circuit, and 22 and 23 are buffer amplifiers. FIG. 5 shows a time chart of the signals at each point in FIGS. The intermediate frequency signals IFa and IFb are sequentially time-divisionally selected by the changeover switch 8 using a signal (FIG. 5) obtained by dividing the frequency of the clock pulse (FIG. 5) from the sample clock pulse generator 13 into four by the frequency divider 16 (FIG. 5). Then, the waveform shown in FIG. 5 is obtained. The signal after this switching is detected through the logarithmic amplifier 3 and the envelope detector 4, but the falling waveform is blunted as shown in FIG. Therefore, as shown in FIG. 5, the signal sampling performed by the pulse signal in the switch 9 is performed almost in the middle of the pulse-shaped switching output signal, thereby preventing leakage into other channels and switching. Efforts are being made to improve accuracy.
The dotted line and the dashed-dotted line in FIG. 5 represent the sequence in which the intermediate frequency signal after switching shown in FIG. 5 is sampled. The envelope detection outputs of systems 1 and 2 separated as shown in FIG.
After passing through gain correction amplifiers 14 and 15, it becomes the envelope Ea of system 1 and the envelope Eb of system 2.

FIG. 6 shows the envelope of each branch when the antenna correlation coefficient is 1 (perfect correlation). From this figure, it can be seen that the envelopes match perfectly, and by using the envelope detector in a time-divisional manner, there is no influence from variations in the characteristics of the envelope detector. FIG. 7 shows the envelope of each branch (FIG. 7A) and switching waveform (FIG. 7B) when there is no correlation. The switching output matches the waveform of the higher envelope output level of each branch.

With the above structure, switching accuracy can be improved by using the envelope detector in a time-division manner.

The present invention can be applied even when there are three or more diversity branches, and is a versatile diversity receiving device.

As explained above, this diversity receiving device uses a logarithmic amplifier and an envelope detector consisting of an envelope detector in one series in a time-division manner, so it has the advantage of high reliability with no variation in characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional diversity receiving device, FIG. 2 is an envelope waveform diagram in perfect correlation of each diversity branch by the conventional diversity receiving device, and FIG. 3 is an example of an embodiment of the device of the present invention. A block diagram, FIG. 4 is a circuit diagram showing an example of a switch control circuit used in the embodiment of FIG. 3, and FIG.
The figure is a time chart showing the process of sampling in the present invention, Figure 6 is an envelope waveform diagram in perfect correlation of each diversity branch by the apparatus of the present invention, and Figure 7
The figure is a waveform diagram showing the envelope of each diversity branch and the envelope switching output when there is no correlation by the device of the present invention. 1a, 1b...receiving antenna, 2a, 2b...
Receiver, 3, 3a, 3b... Logarithmic amplifier, 4, 4
a, 4b...Envelope detector, 5...Comparator, 6,
8, 9...Selector switch, 7...Signal output terminal,
10, 11...low-pass filter, 12...switch control circuit, 13...sample clock pulse generator,
14, 15...Gain correction amplifier, 16-23
...Switch control circuit components, Sa, Sb...Antenna input signal, IFa, IFb...Intermediate frequency signal,
Ea, Eb...diversity branch envelope signal, Ba,
Bb...Detection output signal, S...Detection output signal after switching.

Claims (1)

[Claims] 1. In a receiving device consisting of a plurality of receivers and a series of envelope detectors, the envelope detector consists of a logarithmic amplifier and an envelope detector, and the intermediate frequency output of each receiver is sequentially output at a high sampling frequency. The output of the envelope detector is time-divisionally selected and applied to the envelope detector, and the output of the envelope detector is sampled in a time-division manner for each receiver in accordance with the high-speed sampling frequency. The time-division outputs of the envelopes of each receiver taken out through the filter are compared by a comparator, and the one with the larger envelope level is determined, and the detection output of each receiver is instantly switched. A diversity receiving device characterized in that: