JPS6247222A - Diversity receiver - Google Patents

Abstract

PURPOSE:To improve the diversity effect by changing a switching threshold in accordance with the variance of a reception electric field. CONSTITUTION:A signal 101 of the antenna selected by an antenna switching circuit 1 is not only inputted to a power detecting circuit 2 but also outputted to a receiving part from a terminal 10. When the power of the reception signal is obtained by the power detecting circuit 2, it is compared with the switching threshold stored in a memory 5 by a comparator 3 as the first comparator, and the comparator 3 outputs a switching signal 103 to the antenna switching circuit 1 if the reception signal power is smaller than the switching threshold. Simultaneously, a power detection circuit output 102 is written in the memory 5 as the switching threshold. If the reception signal power is reduced gradually by this operation, the switching threshold is made smaller gradually. If the reception signal power is increased contrarily, the switching signal 103 is not generated because the output 102 of the power detecting circuit 2 is always larger than the switching threshold in the memory 5. A comparator 4 as the second comparator outputs a memory update signal 104 when the difference between the reception signal level and the switching threshold exceeds a certain value.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a diversity receiver with antenna switching diversity.

(Prior art and its problems) In wireless communications, there is a phenomenon called fading, in which the received electric field strength changes due to the influence of radio wave reflections from buildings, mountains, etc., and in some cases, it becomes impossible to receive radio waves. As a measure against this fading, there is a technique called guibandi which uses a plurality of antennas so that even if one antenna cannot receive the signal, the other antenna can receive the signal. Diversity includes a method called antenna switching diversity, in which antennas are switched and used to combine received signals from antennas. This method uses only the antenna.

By switching, the receiving circuit is simple and requires only one system, but since you can only observe the electric field strength being received by the antenna in use, you cannot know the receiving condition at the other antenna, so the one antenna that is always in good condition difficult to use. A method of increasing the frequency of switching and observing the status of the other antenna can be considered, but this method requires the use of the worse antenna at least temporarily, and the discontinuity of the received signal phase that occurs when switching antennas. It is not a good idea to switch antennas too frequently because it may cause problems such as noise generation. Therefore, conventionally, a method has been adopted in which a certain threshold value is set and the antenna is switched when the received electric field becomes lower than the threshold value. This kind of method is 197
4th grade Siri Willie and Sons (JohnWil)
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ons) J, page 401.

The problem with this method lies in how the threshold is determined. If the threshold value is too high, the received electric field of both antennas may become lower than the threshold value when the received electric field as a whole decreases.In such a case, the receiver will just repeat antenna switching and the received electric field Since the higher antenna is not used in a fixed manner, unnecessary noise can be generated.

As a countermeasure for this, there is a method in which after switching the antenna, the antenna is not switched again even if the received electric field is lower than the threshold value, and the antenna is switched again when the received electric field becomes higher than the threshold value and falls below the threshold value again. However, in such a system, when the received electric field is lower than the threshold value, an antenna selected by chance is fixedly used, and a sufficient diversity effect cannot be obtained.

On the other hand, if the threshold value is too low, antenna switching will not occur even if a sufficiently large signal is being received by the other antenna, resulting in a disadvantage that it will be difficult to achieve a diversity effect.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a diversity receiver that eliminates the above-mentioned drawbacks of the conventional diversity receiver and uses an antenna that is always in good condition in response to fluctuations in the overall received electric field level. be.

(Means for Solving the Problems) Means provided by the present invention in order to solve the above-mentioned problems is a diversity receiver that switches between a plurality of antennas for reception, and includes an antenna switching system that switches between the antennas. a power detection circuit for detecting high frequency power output from the antenna switching circuit; a memory for storing a threshold value serving as a criterion for determining the antenna switching; and a comparison between the output of the power detection circuit and the output of the memory. a first comparator that outputs a switching signal when the output of the power detection circuit is smaller; and a first comparator that compares the output of the power detection circuit and the output of the memory and determines that the output of the power detection circuit is a constant value; It consists of a second comparator that outputs a memory update signal when the switching signal is greater than or equal to the switching signal. When the output is completed, the antenna switching circuit switches the antenna, the memory writes the output of the power detection circuit into the memory as the threshold value, and when the memory update signal is output, the memory performs the update amount control. It is characterized in that the output of the circuit is written as the threshold value.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. A signal 101 of the antenna selected by the antenna switching circuit 1 is input to the power detection circuit 2 and output from the terminal 10 to the receiving section. When the power of the received signal is determined by the power detection circuit 2, it is compared with the switching threshold stored in the memory 5 by the first comparator 3, and if the received signal power is smaller than the switching threshold, the comparator 3 is switching signal 10
3 is output to the antenna switching circuit 1. At the same time, the power detection circuit output 102 is written into the memory 5 as a switching threshold. By doing this, when the received signal power gradually decreases, the switching threshold gradually becomes smaller. Conversely, when the received signal power increases, the switching threshold becomes smaller. When the output 102 of the power detection circuit 2 is always higher than the switching threshold of the memory 5, the switching signal 103 is not generated.However, in the comparator 4, which is the second comparator, the difference between the received signal level and the switching threshold is greater than a certain value. (hereinafter, this constant value will be referred to as the maximum level difference), the memory update signal 104 is output.Update amount control circuit 6
Then, a value 106 that is lower than the output 102 of the power detection circuit 2 by the maximum level difference is output to the memory 5. When the memory update amount @104 is output, the memory 5 outputs the update amount control circuit 6.
The output 106 of is written as switching TR(I?f).In this way, the switching threshold is increased.

2(a) to 2(c) show how the received signal l/bell changes in the embodiment of FIG. 1 and the conventional diversity receiver. (C) is the result of the receiver of the embodiment shown in Fig. 1.For simplicity, it is assumed that the electric field received by the antenna changes in the form of a triangular wave in both cases. Fig. 2 (
In a), (b) and (c), the triangular waves ■ and ■ are the magnitude of the electric field received from antenna 7 and antenna 8, respectively, and the thick line portion is the received electric field strength actually obtained after diversity. Furthermore, the broken line indicates the received electric field of the antenna that was not selected. The thin line ■ indicates the switching threshold. First, the operation of a conventional diversity circuit will be explained.

Assume that the antenna 7 with a high level is selected as an initial state. The received signal from antenna 7 crosses the switching threshold downward at time Ta.

At this time, antenna switching occurs and antenna 8 is selected. Next, at time Ia, the received electric field of the antenna 8 also becomes less than the switching threshold, and the antenna is switched again to the antenna 7. At this time, since the received electric field at the antenna 7 is already below the switching threshold, antenna switching will not occur until this field increases and crosses the switching threshold downward again. The effect of antenna switching is Ta2 and T8. Only the part between. Figure 2 (b
) is the case when the switching threshold is set low in the same receiver.

This is the same as (a) except that the diversity effect is seen when the received electric field is lower.

FIG. 2(c) shows the operation of the diversity circuit of this embodiment. Initially, antenna 7 is selected and the received electric field of antenna 7 is rising, so the determination threshold is antenna 7.
Increases from the level of by keeping only the maximum level difference. This is because the comparator 4 continues to output the memory update signal 104 whenever the received electric field increases and there is a maximum level difference between the received electric field and the switching threshold. At time Tc, the received electric field stops rising and the comparator 4 no longer outputs the memory update signal 104, so the switching threshold becomes a constant value. Since the received electric field becomes less than the switching threshold at time Te, the comparator 3 outputs the switching signal 103 to switch the antenna and simultaneously rewrites the switching threshold in the memory 5. At this time, the switching threshold value decreases slightly, but this is ignored in this figure because it will become smaller if the received electric field is detected faster. Next, at time Ics, the received electric field of antenna 8 becomes less than the switching threshold, and the antenna is switched to antenna 7. The switching threshold value can also be updated, but the change at this time is slight. In this case, the received electric field at antenna 7 is smaller than that at antenna 8, so when power is measured by power detection circuit 2, comparator 3 switches to antenna 8 again. At the same time, the received electric field at Tcs of the antenna 7 is stored in the 7-mori 5. Furthermore, Tc4
A similar thing occurs when the received electric field of the antenna 8 becomes below the switching threshold of the memory 5.

A feature of the present invention is that when the antenna is switched in this manner, if the received electric field at the destination is smaller, the switching operation occurs immediately to return to the original antenna. Therefore, it is possible to realize a diversity receiver that is more effective than conventional diversity receivers. FIG. 3 shows a specific example of the power detection circuit 2. In FIG. Antenna switching circuit 1 from input terminal 11
The output 101 from is input. This value is log amplifier 2
1 is converted into a logarithm, detected by a detector 22, and then converted to a digital signal by an analog-to-digital converter 23.
Output from 2. By doing this, all of the following processing can be performed by digital circuits. Furthermore, since the values are converted into logarithms, the level can be adjusted by addition. The switching circuit 1 can be implemented by a switch, the comparator 3 can be implemented by a normal comparator, and the update amount control circuit 6 can be implemented by a subtracter, so a detailed description thereof will not be given.

FIG. 4 is a diagram showing a specific example of the second comparator 4. The received power, which is the output of the power detector 2, is input from the input terminal 13, and the switching threshold stored in the memory 5 is input from the input terminal 14.

First, a subtracter 41 subtracts the switching threshold from the received power, and a comparator 42 checks whether the subtraction result is greater than the maximum level difference.
Compare with. When the subtraction result is greater than the maximum level difference, a memory update signal 104 is output from the terminal 15.

FIG. 5 shows an example of the memory 5. The switching signal 103 is sent from the input terminal 16, the memory update signal 104 is sent from the input terminal 17, the output 106 of the update amount control circuit 6 is sent from the input terminal 18, and the output 10 of the power detector 2 is sent from the input terminal 19.
2 are input respectively. When the switching signal 103 and the memory update signal 104 are each in the state of "1", it is assumed that there is a signal input. When the memory update signal 104 is input, the gate circuit 51 outputs the output 106 of the update amount control circuit 6.
to follow. In other cases, all outputs of the gate circuit 51 become "0".

Similarly, in the gate circuit 52, the output of the power detector 2 is output when the switching signal 103 is "1". Gate circuit 5
The output of 1 and the output of the gate circuit 52 are logically summed by an OR circuit 54 and output to a register 55.

Therefore, when the memory update signal 104 is "1", the output 106 of the update amount control circuit 6 is input to the register 55, and conversely, when the switching signal 103 is "1", the output 106 of the update amount control circuit 6 is input to the register 55.
The output 102 of is input to the register 55.

゛Memory update signal 104 and switching signal 103 are “1” at the same time
“It is impossible that the memory update signal 10
The contents of the register 55 are rewritten by the rewrite signal 153 obtained by the OR circuit 53 as the logical sum of 4 and the switching signal 103. Therefore, the memory update signal 104 and the switching signal 10
3, the contents of the register 55 are rewritten. The contents of register 55 are output from terminal 20 as switching threshold 105.

(Effects of the Invention) =11- As described in detail above, according to the present invention, it is possible to provide a diversity receiver in which the switching threshold value is changed in accordance with fluctuations in the received electric field and the diversity effect is improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 (
a) to (b) are diagrams showing the operation of a conventional diversity receiver, FIG.
The figure shows a specific example of the power detection circuit 2 of the embodiment shown in FIG. 1, FIG. 4 shows a specific example of the comparator 4 of the embodiment, and FIG. 5 shows the memory 5 of the embodiment. It is a figure showing an example of one body. 1... Antenna switching circuit, 2... Power detection circuit,
3...first comparator, 4...second comparator, 5...
-Memory, 6... Update amount control circuit, 7, 8... Antenna. Agent Patent Attorney Shinsuke Honjo Figure 1 Figure 2 TCI Te3 Te3 TC4 Figure 3 Figure 4 Figure 4 = own da;55 2゜

Claims (1)

[Claims] A diversity receiver that switches between a plurality of antennas for reception, includes an antenna switching circuit that switches the antennas, a power detection circuit that detects high frequency power output from the antenna switching circuit, and a threshold value that is a criterion for determining the antenna switching. a first comparator that compares the output of the power detection circuit with the output of the memory and outputs a switching signal when the output of the power detection circuit is smaller; a second comparator that compares the output with the output of the memory and outputs a memory update signal if the output of the power detection circuit is larger than a certain value; It consists of an update amount control circuit that determines an update threshold smaller than the output of the detection circuit,
When the switching signal is output, the antenna switching circuit switches the antenna, the memory writes the output of the power detection circuit as the threshold value in the memory, and when the memory update signal is output, the memory writes the output of the power detection circuit as the threshold value. A diversity receiver characterized in that an output of an update amount control circuit is written as the threshold value.