JPH09148975A - Carrier sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the most sensitive carrier sensing by setting an optimum value corresponding to a use state and a reception signal state as the threshold level of carrier sensing. SOLUTION: Antennas 4 and 5 are arranged at the interval of a half-wave for receiving a pictures transmission signal and the antenna whose electric intensity is stronger is selected. A received signal is demodulated in a demodulation circuit 9 through an AGC circuit 6. Control voltage is detected with VCO 7 during the reception operation and it is A/D-converted in I/F 12. Then, it is stored in ROM 14 as a detection value R1. The newly detected value R1 is compared with a threshold Rth stored in RAM 13. When the threshold Rth is smaller than the value R1 in the comparison, normal carrier sensing is executed. When it is large. the switch signal of the transmission/reception of packet communication detects an L level for informing switch timing and the threshold setting routine of carrier sensing is executed again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier sense device for carrying out carrier sensing of a transmission signal at the time of reception in space diversity or the like, and more particularly to setting an optimum threshold value in carrier sensing due to device variations or the like. The present invention relates to a carrier sense device that can perform.

[0002]

2. Description of the Related Art In a wireless image transmission system, image wireless transmission by a spread spectrum system is known as one of modulation systems. In such a transmission system, a wireless signal transmitted from the transmitting station side is received by a plurality of antennas on the receiving station side, the antenna with the stronger electric field strength of the received signal is selected, and the received signal is demodulated to obtain image information, etc. Is reproduced. By doing so, for example, even if the receiving station side is moving and the electric field strength of the received signal constantly changes, it is possible to receive the signal with the strongest electric field strength.

Since the electric field strength of the received carrier signal constantly changes in this way, on the receiving side, the signal received from the antenna is input to the AGC circuit, converted to a constant level, and then input to the demodulation circuit. ing. Therefore this AGC
The circuit increases the gain when the electric field strength of the carrier signal is small, and decreases the gain when the electric field strength is large. Therefore, the DC level of the output value of the AGC circuit is detected and a control voltage corresponding to the DC level is supplied to the AGC circuit.

FIG. 3 is a diagram showing the relationship between the gain and control voltage of such an AGC circuit. As shown in the figure,
The relationship between the control voltage value and the gain of the AGC circuit is
The gain decreases as the control voltage increases, and the gain increases as the control voltage decreases. And
When no carrier signal is received, the control voltage is at the lowest level in the operating range.

[0005]

Conventionally, the above-mentioned A
The characteristic of the GC circuit is used to monitor the value of the control voltage of the AGC signal in order to determine whether or not the carrier signal is being received.
As an alternative means, a signal obtained by converting an operating current necessary for amplifying to a predetermined signal level by a limiter amplifier into a signal such as an RSSI like the control voltage is used.
Signal (Receive Signal Strength)
h Indicator signal) is also used as a general method.

When the value of the control voltage being monitored exceeds a threshold level of a value obtained by adding α of the error range to a preset minimum level value, it is determined that the carrier signal is sensed, and the standby state is changed to the reception state. Is being controlled. Here, α is a minute voltage that is added to the minimum value of the control voltage of the AGC circuit to determine that the input signal has been received. The reason for adding this α is that the control voltage of the AGC circuit is fixed to the minimum value (see FIG. 4) when there is no input signal, but noise in the circuit is naturally superimposed, so it is appropriate for that noise. This is because a malfunction will occur unless the minute voltage α is added. FIG. 4 is a diagram showing the relationship between the control voltage and the reception input level. That is, when the reception input level is high, the control voltage value is also high, and when the reception input signal level is low, the control voltage value is low. Therefore, for example, if the control voltage is in the range of 2V to 4.5V, the threshold value is set to a value obtained by adding α to the lowest voltage of 2V, which is a voltage for determining that there is an input.

However, since this AGC circuit and the like are used as one semiconductor integrated circuit device, it is an unavoidable problem that the minimum level value of the control voltage varies. In addition, even when a plurality of semiconductor devices are combined to form one set of receiving system devices, similar variations are unavoidable. That is, it is the variation as in the case of the sets 1, 2, and 3 shown in FIG. Therefore, if a fixed threshold value such as 2V + α is set in advance, the threshold level of carrier sense may be higher than the lowest level of the carrier signal to be actually detected depending on the product, and the carrier sense with high sensitivity may be set. It will interfere. In other words, the set 2 in FIG. 4 is judged to be in the receiving state even though the carrier is not received, and the set 3 is judged to be in the receiving state if the reception input level of sufficient electric field strength cannot be obtained. Will not be done.

Therefore, the present invention has an object to solve the above problems, and provides a carrier sense apparatus capable of setting an optimum carrier sense threshold level even if there are variations among products or devices. To do.

[0009]

According to the present invention, the above object is to provide an intensity detection signal generating means for inputting a reception signal received from an antenna and generating an intensity detection signal corresponding to the electric field intensity of the received radio wave. And monitoring the intensity detection signal, detecting the minimum value of the intensity detection signal, storing a value obtained by adding a predetermined value to the minimum value as a carrier sense threshold value, and the threshold value and the intensity detection signal value. And a controller that determines that a carrier has been received when the intensity detection signal value is higher than the threshold value.

The detection of the minimum value of the intensity detection signal value is as follows.
Repeated by the microprocessor. And
If the newly detected value is lower than the previous minimum value,
The detected value or the minimum value is set. Therefore,
It is possible to set the optimum minimum value according to the usage state and the state of the received electric wave as the threshold value of the carrier sense.

Here, the strength detection signal may be a detection signal corresponding to a change in the electric field strength of the received radio wave, and for example, the control voltage value of the AGC signal to which the reception signal from the antenna is input, or RSSI Signals etc. can be used.

[0012]

1 is a general view of an embodiment of the present invention, and FIG. 2 is a flow chart thereof. In the embodiment of the present invention, when there is a variation for each set as shown in FIG. 4, the lowest intensity detection signal value among the intensity detection signals actually detected is detected, and the value is set to a predetermined value. α
The value obtained by adding is set as the threshold value of the carrier sense. Specifically, the microprocessor, which constantly monitors the control voltage value and RSSI signal value of the AGC circuit, constantly updates the minimum value.

In FIG. 1, 1 is a transmitting station side and 2 is a receiving station side. Reference numeral 3 denotes an antenna switch unit for receiving a spatial diversity type image transmission signal.
The antenna having the two antennas 4 and 5 separated by a distance of / 2 wavelength and the electric field strength of the received radio wave is stronger is selected. This selection is performed by the antenna selection signal 17 from the microprocessor 10. The received signal received from the antenna is AGC (Automatic Ga).
in Control) circuit 6. And
In order to keep the DC level of the carrier signal of the input received signal constant, the control voltage generator 7 detects the DC level of the output of the AGC circuit 6, which is the received input level, and controls according to the relationship shown in FIG. The voltage VCO is generated and fed back to the AGC circuit 6. The received signal having a constant level in this manner is converted into a digital signal by the A / D conversion circuit 8 and then demodulated by the demodulation circuit 9.

On the other hand, the microprocessor circuit 10 receives the carrier signal by inputting the control voltage VCO and comparing it with the set threshold level because the control voltage VCO changes according to the reception input level. It is determined whether or not there is. Then, according to the determination result, the standby signal 16 is supplied to the demodulation circuit 9.

The microprocessor circuit 10 has an A / D
The interface unit 12 having a conversion unit, the calculation unit 11, the RAM 13 as a storage memory, and the ROM 14 storing programs, various parameters, and the like are commonly used in the bus 1.
It is connected via 5. In the embodiment of the present invention, the microprocessor circuit 10 sets a threshold level for optimum carrier sensing.

The operation will be described with reference to the flowchart of FIG. First, in step 20, the transmission signal is in a standby state. The image signal transmitted by radio is transmitted by, for example, packet communication, and the data structure in that case is, for example, first the preamble portion,
Next, it is composed of a frame synchronization part, an ID number, a header, and an actual data part. Therefore, a preamble operation for confirming transmission / reception is performed while receiving the preamble portion (step 21). Then, first, the threshold level Rth is initialized. That is, for example, 4.5V which is the maximum value of the operating range of the control voltage VCO is input as an initial value, or a value which is all 1 because it is a digital value is input. This threshold level Rth is stored in the RAM area in the microprocessor circuit 10.

Therefore, the AGC corresponding to the received signal
The control voltage VCO to the circuit 6 is detected (step 23), A / D converted by the A / D conversion section in the interface section 12, and then stored in the RAM 13 as the detected value R1 (step 24). Then, in step 25, the threshold level Rth is compared with a value obtained by adding α to the detected value R1 as a voltage component for determining that there is an input. And
When R1 + α is lower than the stored threshold value Rth, the detected value R1 + α is newly stored in the RAM 13 as the threshold level Rth (step 2).
6).

By repeating the above-described operation during the preamble period, the minimum value of the control voltage VCO in that state is R as the threshold Rth of the carrier sense.
Stored in AM13.

After that, the diversity reception operation is started and reception is started. First, the antenna having the stronger electric field strength of the received signal is selected (step 28), and the received signal received from the antenna is demodulated by the demodulation circuit 9 through the AGC circuit 6 (step 29). Even during the receiving operation, the control voltage VCO is appropriately set.
Is detected, A / D converted, and stored as a detected value R1 (step 30). Then, the newly detected R1 +
A comparison is made with the stored threshold level Rth. As long as the current threshold level Rth is low, carrier sense can be normally performed. If the stored threshold level Rth is larger than the detected R1 + α, it is detected that the switching signal for transmission / reception of packet communication is at the L level indicating the switching timing, and the threshold level for carrier sense is again detected. The setting routine will be performed.

As is apparent from the above description of the flow chart, the carrier sense threshold level R is previously set as in the conventional case.
Instead of setting th in the microprocessor 10, the optimum lowest threshold level is detected from the state actually used in the field, the received signal level received, etc. ing. Therefore, the optimum value is adopted as the threshold level Rth in any of the set 1, the set 2, and the set 3 shown in FIG. 4, and the most sensitive carrier sense can be realized.

In the above embodiment, the control voltage (control voltage) VCO of the AGC circuit is detected to detect the reception input level. However, if the reception input level can be substantially detected even with another signal, it is obvious that the threshold level can be set and the carrier sense can be performed using the signal.

[0022]

As described above, according to the present invention, it is possible to set the optimum value corresponding to the state of use and the state of the received signal as the threshold level of carrier sense. Therefore, it is possible to set the optimum threshold level regardless of the variation for each device or the variation for each set device, and it is possible to perform the carrier sensing normally and with high sensitivity.

[Brief description of the drawings]

FIG. 1 is an overall view of an embodiment of the present invention.

FIG. 2 is a flowchart of the embodiment of the present invention.

FIG. 3 Gain of AGC circuit and control voltage VCO
6 is a graph showing the relationship of.

FIG. 4 is a graph showing a relationship between a reception input level and a control voltage VCO.

[Explanation of symbols]

 1 transmitting station 3 receiving station 4,5 antenna 6 AGC circuit 7 control voltage generating circuit 9 demodulating circuit 10 microprocessor (control unit)

Claims (6)

[Claims] 1. A strength detection signal generation means for receiving a reception signal received from an antenna and generating a strength detection signal corresponding to the electric field strength of the received radio wave, and monitoring the strength detection signal to detect the strength detection signal. When the minimum value is detected and a value obtained by adding a predetermined value to the minimum value is stored as a threshold value of carrier sense, the threshold value is compared with the strength detection signal value, and the strength detection signal value is higher than the threshold value. And a control unit that determines that a carrier has been received. 2. The control unit according to claim 1, wherein the intensity detection signal value is detected a plurality of times during a preamble operation period of a reception signal, and the minimum value of the detected intensity detection signal values is detected. A carrier sense device, wherein a value obtained by adding a predetermined value to the minimum value is stored as a carrier sense threshold value. 3. The control unit according to claim 2, wherein the control section appropriately detects the intensity detection signal value during the demodulation operation of the received signal and compares it with the stored threshold value to detect a lower intensity. A carrier sense device characterized in that a value obtained by adding a predetermined value to a signal value is newly stored as the threshold value. 4. The intensity detection signal according to claim 1, wherein the intensity detection signal is a control voltage signal supplied to an AGC circuit, and the AGC circuit receives a received signal from a selected antenna. A diversity receiving device, characterized in that the received signal converted to a constant level is supplied to a demodulation circuit. 5. The diversity receiver according to claim 1, wherein the strength detection signal is an RSSI signal. 6. The antenna according to any one of claims 1 to 5, wherein the wireless transmission is a spatial diversity system, the antenna is composed of a plurality of antennas spatially separated from each other, and an antenna having a higher electric field strength level of a received radio wave is selected. A carrier sense device characterized by the above.