JPH0761035B2 - Diversity receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver with antenna switching diversity.

(Prior art and its problems) In wireless communication, there is a phenomenon called so-called fading in which the reception electric field strength changes due to the influence of radio waves reflected by buildings or mountains, and radio waves cannot be received in some cases. As a measure against this fading, there is a technique called diversity which has multiple antennas and allows one antenna to receive even if the other antenna does not. As for diversity, there is a method called antenna switching diversity in which antennas are switched and used to combine received signals from the antennas. In this method, only the antenna is switched so that the receiving circuit can be one system and the circuit is simple. However, since only the electric field strength received by the antenna in use can be observed, the receiving state at the other antenna is unknown and it is always good. It is difficult to use the antenna in the state. A method of observing the status of the other antenna by increasing the switching frequency is also conceivable, but at least temporarily the bad antenna must be used, and due to the discontinuity in the received signal phase that occurs during antenna switching. It is not a good idea to switch the antennas too often because there are problems such as noise.
Therefore, conventionally, a method of setting a certain threshold value and switching the antenna when the received electric field becomes lower than the threshold value has been adopted. This method is based on the book “Microwave Mobile Communications (Micr) published by John Wiley & Sons in 1974.
owave Mobile Communications), page 401.

The problem with this method is how to set the threshold value. If the threshold value is too high, the received electric field may drop below the threshold value for both antennas when the received electric field decreases as a whole.In such a case, the receiver simply repeats antenna switching and the received electric field decreases. There is no need to fix and use the higher antenna, and noise will be generated unnecessarily.
As a measure against this, there is a method of not performing re-switching even if the received electric field is lower than the threshold value after switching the antenna, and performing the re-switching once when the received electric field becomes higher than the threshold value and then falls below the threshold value again. However, in such a method, both antennas happen to be fixedly used by chance when the received electric field is lower than the threshold value, and a sufficient diversity effect cannot be obtained.

On the other hand, if the threshold value is too low, there is a drawback that antenna switching does not occur even when a sufficiently large signal is received by the other antenna, and the effect of diversity is difficult to obtain.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the conventional diversity receiver and to provide a diversity receiver that always uses an antenna in a good state according to the fluctuation of the overall received electric field level.

(Means for Solving Problems) Means provided by the present invention for solving the above problems is a diversity receiver for switching and receiving a plurality of antennas, and antenna switching for switching the antennas. A circuit, a power detection circuit for detecting high-frequency power of the output of the antenna switching circuit, a memory for storing a threshold serving as a criterion for the antenna switching, and an output of the power detection circuit and an output of the memory for comparison. A first comparator that outputs a switching signal when the output of the power detection circuit is smaller and the output of the power detection circuit and the output of the memory are compared, and the output of the power detection circuit is a constant value. A second comparator that outputs a memory update signal when larger than the above, and an update amount control that obtains an update threshold that is a function of the output of the power detection circuit and is smaller than the output of the power detection circuit Circuit, the antenna switching circuit switches the antenna when the switching signal is output, the memory writes the output of the power detection circuit as the threshold value in the memory, and the memory update signal is output. At this time, the memory writes the output of the update amount control circuit as the threshold value.

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

FIG. 1 is a block diagram showing an embodiment of the present invention. The signal 101 of the antenna selected by the antenna switching circuit 1 is input to the power detection circuit 2 and also output from the terminal 10 to the receiving section. When the power of the received signal is obtained by the power detection circuit 2, it is compared with the switching threshold value stored in the memory 5 by the comparator 3 which is the first comparator, and when the received signal power is smaller than the switching threshold value, the comparator. 3 outputs the switching signal 103 to the antenna switching circuit 1. At the same time, the power detection circuit output 102 is written in the memory 5 as a switching threshold value. By doing so, the switching threshold becomes gradually smaller when the received signal power gradually decreases. Conversely, when the received signal power increases, the output 10 of the power detection circuit 2
Since 2 is always larger than the switching threshold of the memory 5, the switching signal 103
Does not occur. However, the comparator 4, which is the second comparator, outputs the memory update signal 104 when the difference between the received signal level and the switching threshold exceeds a certain value (hereinafter, this certain value is referred to as the maximum level difference). The update amount control circuit 6 outputs a value 106 lower than the output 102 of the power detection circuit 2 by the maximum level difference to the memory 5, and when the memory update signal 104 is output, the output 106 of the update amount control circuit 6 is output in the memory 5. Write as a switching threshold. In this way, the switching threshold is increased.

FIGS. 2 (a) to 2 (c) show how the received signal level of the conventional diversity receiver shown in FIG. 1 changes. 2 (a) and 2 (b) are based on the conventional diversity receiver, and FIG. 2 (c) is based on the receiver of the embodiment of FIG. For simplicity, it is assumed that both electric fields received by the antenna change in a triangular waveform. In FIGS. 2 (a), (b) and (c), the triangular waves of are the magnitudes of the electric fields received from the antenna 7 and the antenna 8, respectively, and the thick line portions are the received electric field strengths actually obtained after diversity. is there. In addition, the broken line indicates the reception electric field of the antenna not selected. The thin line indicates the switching threshold. First, the operation of the conventional diversity circuit will be described.

Assume that the antenna 7 having a high level is selected as the initial state. The received signal from the antenna 7 crosses the switching threshold downward at time Ta ₁ . At this time, antenna switching occurs and the antenna 8 is selected. Next, at time Ta ₂ , the reception electric field of the antenna 8 also becomes equal to or lower than the switching threshold value and the antenna 7 is switched again. At this time, the electric field received at the antenna 7 is already below the switching threshold, so that antenna switching does not occur until it rises and the switching threshold is crossed downward again. The antenna switching effect is only in the area between Ta ₁ and Ta ₂ . FIG. 2B shows a case where the switching threshold is set low in the same receiver. It is the same as (a) except that the diversity effect is seen in the state where the received electric field is lower.

FIG. 2C shows the operation of the diversity circuit of this embodiment. Since the antenna 7 is initially selected and the reception electric field of the antenna 7 is rising, the determination threshold is the antenna 7
Rise from the level of, keeping only the maximum level difference. This is because the comparator 4 always keeps outputting the memory update signal 104 when the received electric field rises and there is a maximum level difference between the received electric field and the switching threshold value. At time Tc ₁ , the rise of the received electric field stops and the comparator 4 causes the memory update signal 10
Since 4 is not output, the switching threshold becomes a constant value. Time Te ₂
Since the received electric field is below the switching threshold at
Outputs the switching signal 103 to switch the antenna, and at the same time rewrites the switching threshold of the memory 5. At this time, the switching threshold is slightly lowered, but this is ignored if the detection of the received electric field is fast, so it is ignored in this figure. Next, at time Tc ₃ , the reception electric field of the antenna 8 falls below the switching threshold and
Switch to. The switching threshold is also updated, but the change at this time is slight. In this case, the electric field received by the antenna 7 is smaller than that of the antenna 8, so that the comparator 3 switches to the antenna 8 again when the power is measured by the power detection circuit 2. At the same time, the electric field received at Tc ₃ of the antenna 7 is stored in the memory 5. Further, at Tc ₄ , the same phenomenon occurs when the reception electric field of the antenna 8 becomes equal to or lower than the switching threshold value of the memory 5.

It is a feature of the present invention that when the antenna is switched in this way, if the received electric field at the switching destination is smaller, the switching operation immediately returns to the original antenna. Therefore, a diversity receiver having a greater effect than the conventional diversity can be realized. FIG. 3 shows a specific example of the power detection circuit 2. The output 101 from the antenna switching circuit 1 is input from the input terminal 11. This value is logarithmically converted by the log amp 21, detected by the wave detector 22, converted into a digital signal by the analog / digital converter 23, and output from the terminal 12. By doing so, the following processes can all be processed by the digital circuit. Also, since it is converted into logarithm, the level adjustment can be realized by addition. Since the switching circuit 1 can be realized by a switch, the comparator 3 can be realized by a normal comparator, and the update amount control circuit 6 can be realized by a subtractor, detailed description thereof will be omitted.

FIG. 4 is a diagram showing a specific example of the second comparator 4. The reception power output from the power detector 2 is input from the input terminal 13, and the switching threshold value stored in the memory 5 is input from the input terminal 14. First, the subtracter 41 subtracts the switching threshold from the received power, and the comparator 42 compares whether the subtraction result is larger than the maximum level difference. When the subtraction result is larger than the maximum level difference, the memory update signal 104 is output from the terminal 15.

FIG. 5 shows a specific example of the memory 5. Switching signal 103 from the input terminal 16, memory update signal 104 from the input terminal 17,
The output 106 of the update amount control circuit 6 is input from the input terminal 18, and the output 102 of the power detector 2 is input from the input terminal 19. The switching signal 103 and the memory update signal 104 are considered to have signal inputs when they are in the state of "1". When the memory update signal 104 is input, the gate circuit 51 causes the output 106 of the update amount control circuit 6 to overtake. In all other cases, the outputs of the gate circuit 51 are all "0". Similarly, the gate circuit 52 outputs the output of the power detector 2 when the switching signal 103 is "1". Output of gate circuit 51 and gate circuit 52
The output of is calculated as a logical sum in the logical sum circuit 54 and is output to the 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 102 of the power detection circuit 2 is input to the register 55. It The memory update signal 104 and the switching signal 103 cannot be "1" at the same time. Further, the contents of the register 55 are rewritten by the rewriting signal 153 obtained by the logical sum circuit 53 as the logical sum of the memory update signal 104 and the switching signal 103. Therefore, the memory update signal 104
If either one of
The contents of 5 are rewritten. Register 55 contents are terminal 20
Is output as a switching threshold value 105.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to provide a diversity receiver in which the switching threshold is changed according to the fluctuation of the reception electric field to improve the diversity effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are diagrams showing the operation of a conventional diversity receiver, and FIG. 2 (c) is an operation of the FIG. 1 embodiment. FIG. 3, FIG. 3 is a diagram showing a concrete example of the power detection circuit 2 of the embodiment shown in FIG. 1, FIG. 4 is a diagram showing a concrete example of the comparator 4 of the embodiment, and FIG. It is a figure which shows one specific example of the memory 5 of an Example. 1 ... Antenna switching circuit, 2 ... Power detection circuit, 3 ...
... first comparator, 4 ... second comparator, 5 ... memory,
6 ... Update amount control circuit, 7,8 ... Antenna.

Claims (1)

[Claims] 1. A diversity receiver for receiving by switching a plurality of antennas, an antenna switching circuit for switching the antennas, a power detection circuit for detecting a high frequency power output from the antenna switching circuit, and an antenna switching circuit. A memory that stores a threshold value that serves as a determination reference; a first comparator that compares the output of the power detection circuit and 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 of the power detection circuit with the output of the memory and outputs a memory update signal when the output of the power detection circuit is larger than a certain value; And an update amount control circuit for obtaining an update threshold value smaller than the output of this power detection circuit, and when the switching signal is output, the antenna switching circuit is The antenna is switched, 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 update amount control circuit as the threshold value. And diversity receiver.