JP2003244030A - Method for equalizing cable loss - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately execute cable loss equalization under a light load. <P>SOLUTION: A digital processing section 221 requests stop of transmission directly after application of power or the like, and a control section 218 controls a transmission/reception multicoupler 215 to disconnect a transmission system from an antenna 24. Then a modulation section 222 transmits a continuous wave and a detection section 216 detects its input power. In a state of ordinary burst transmission/reception, the control section 218 controls the gain of a variable gain amplifier 212 in the transmission system of an outdoor apparatus 21 and the digital processing section 221 controls the gain of a variable gain amplifier 224 in a reception system of an indoor apparatus 22 on the basis of the result of detection. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device in which devices are connected by a cable and a burst wave is transmitted through the cable, and more particularly to a method for equalizing signal power loss, that is, cable loss generated in the cable.

[0002]

2. Description of the Related Art As shown in FIG. 3, a base station 10 and subscriber stations 20A, 20B and 20C are wirelessly P-MP (Poin).
t to MultiPoint) The system configuration for connection is FWA (F
ixed Wireless Access) etc. In this figure, three subscriber stations (20A, 20
Although only B, 20C) are shown, the number of subscriber stations that can be accommodated by one base station 10 is generally larger.
In addition, radio communication between the base station 10 and the subscriber stations 20A, 20B, 20C uses a common radio frequency in the upstream (subscriber station → base station) direction and the downstream (base station → subscriber station) direction. This is performed by the TDD (Time Division Duplex) method used and by a burst wave whose schedule is managed as shown in FIG. In FIG. 4, A, B and C represent ON periods of burst signals for the subscriber stations 20A, 20B and 20C, respectively. The schedule management is control so that subscriber stations whose on-burst periods are different from each other do not overlap, and are executed by the IFU 12 of the base station 10, for example.

The base station 10 is a radio frequency unit (RF
U) 11 and interface unit (IFU) 12 are wiredly connected by a coaxial cable 13 or the like. Similarly, subscriber stations 20A, 20B and 20C are also RFUs.
21 and the IFU 22 are connected by a coaxial cable 23 or the like by wire. The RFUs 11 and 21 are units that perform up-conversion of transmission burst waves, down-conversion of reception burst waves, amplification of these signals, and the like. The IFUs 12 and 22 are units that execute burst modulation / demodulation of transmission / reception burst waves, data modulation / demodulation thereof, amplification / data processing, and the like, and IFU of the base station 10.
12 also executes the above-mentioned schedule management and the like.

Further, the RFU 11 of the base station 10 is installed at a high place by using a columnar structure such as a utility pole or the roof of a high-rise building together with an antenna (not shown), and the IFU 12
Will be installed in a low location, which is advantageous in terms of maintenance and connection with the telecommunications carrier's line. In addition, the subscriber stations 20A, 2
The RFU 21 of 0B and 20C is equipped with an antenna (not shown) and uses, for example, a balcony or a roof of a subscriber's house for R
Installed at a location where it can communicate with FU11, IFU22
It is installed in the room of the subscriber's house so that it can be connected to the personal computer used by the subscriber and its network-related equipment. The coaxial cables 13 and 23 are connected to the station (10,
Depending on the installation environment of 20A, 20B, 20C), the shortest length may be several meters and the longest length may be several hundred meters.

[0005]

As described above, in a communication device which is a single communication device but needs to be divided into a plurality of units for convenience of maintenance, network connection, etc. A signal power loss, that is, a cable loss, occurs due to a cable connecting the two. Since the amount of cable loss varies depending on the type, length, manufacturer, etc. of the cable, it varies from communication device to communication device. In the example shown in FIG. 3, since the structure of the subscriber's house, which is the installation site, and the arrangement of devices and equipment in the subscriber's house (the position of the room in which the personal computer is installed, etc.) are generally different, the subscriber station 20
In most cases, the cable loss in the coaxial cable 23 of A and the cable loss in the coaxial cable 23 of the subscriber station 20B have different values.

In order to make the operation of the unit receiving the signal via the cable suitable, it is generally necessary to equalize the different cable loss for each communication device (for each station). For example, the coaxial cable 23 of the RFU 22
A variable gain amplifier and a variable attenuator are provided in the circuit portion for inputting a transmission signal via the. If the cable loss in the coaxial cable 23 is known, the gain or the attenuation rate of the variable gain amplifier or the variable attenuator is set or controlled so that the deviation of the cable loss, that is, the difference between the stations is compensated based on the cable loss value. It is possible to The transmission system circuit in the RFU 22 up-converts and amplifies the transmission burst wave in which the deviation of the cable loss is compensated. RFU22
The internal control circuit detects the arrival of a transmission burst wave and responds accordingly by using a switch for antenna sharing (transceiver duplexer).
To perform operations such as controlling. Thus, by eliminating the influence of the cable loss deviation for each communication device (station) in the input circuit portion of the unit that receives the signal among the units that configure the communication device, Unit operation is the same (cable loss equalization).

In order to realize the cable loss equalization, the cable loss value which is a value that determines the target of the gain or the attenuation rate, or the deviation amount from the reference cable loss value is calculated for the unit receiving the signal. Need to give. As a method therefor, firstly, there is a method of manual setting by a cable builder. For example, RFU21 and R, which are units that receive a transmission burst wave from the IFU22
A cable builder gives information indicating the type and length of the coaxial cable 23 to the IFU 22, which is a unit that receives the received burst wave from the FU 21, by operating a switch or the like.
Alternatively, it is a method of inputting / setting a value of the cable loss or its deviation according to the type and length of the coaxial cable 23. In this method, there are some problems such as the problem that the cable builder bears the work load, and it is impossible or difficult to deal with the factors such as the difference of cable manufacturers and the difference of characteristics (attenuation amount) of each cable individual product. There was a problem.

As a method of giving the cable loss or its deviation, secondly, some measure is performed by the unit on the side which receives the burst wave from another unit via the cable, and the cable loss or the cable loss estimated from the measurement result is calculated. There is a method of automatically determining a control target of gain or attenuation rate based on the deviation. For example, the IFU 22 applies a DC voltage of a predetermined value to the coaxial cable 23, and the RFU 21
Of the DC voltage appearing at the connection with the coaxial cable 23, and by extension, the amount of the drop from the predetermined value. The DC voltage drop is a value that varies depending on the length and type of the cable and has a tentative correlation with the cable loss, so that the cable loss or its deviation can be estimated from the DC voltage drop. Alternatively, the IFU 22 sends a signal to the coaxial cable 23 at a predetermined timing, the RFU 21 detects the arrival timing of the signal, and measures the elapsed time from the predetermined timing. The measured time, that is, the signal propagation required time, is a value that changes depending on the cable length, etc., and since it has a tentative correlation with the cable loss, the cable loss or its deviation is estimated from the signal propagation required time. can do. A method in which when a signal is received from the IFU 22 via the coaxial cable 23, the RFU 21 loops the signal back to the IFU 22 and the IFU 22 measures the signal round-trip required time may be used. Since all of these methods are based on actual measurement, they are more accurate than the first method described above, that is, the manual setting at the time of construction, and can be used for different cable manufacturers and different characteristics of individual cable products. It has the advantage that it can be handled for the time being and the work burden on the cable builder can be reduced. However, even if it is actually measured, it is a measurement of the DC voltage drop or the time required for signal propagation, and since the cable loss or its deviation itself is, so to speak, derived indirectly, it is still inaccurate. Remains.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is necessary to obtain the cable loss or its deviation more accurately and without the work load, and to carry out the lighter and more accurate cable loss. Its purpose is to be able to equalize.

[0010]

In order to achieve such an object, the present invention (1) transmits a transmission burst wave from a first unit to a second unit via a cable, and further, A cable loss equalization method executed by a communication device transmitting from the unit 2 to the outside, comprising: (2)
A cable loss measurement operation in which the first unit sends a loss detection signal of a predetermined power to the cable, and the second unit inputs the loss detection signal from the cable and measures the cable loss or its deviation. , The second unit is controlled by the request from the first unit to the second unit in the transmission stop state, and is executed (3) at least during the burst-on period of the transmission burst wave, the second unit In order to compensate for the cable loss appearing in the transmission burst wave and according to the information obtained by the above measurement, the gain or attenuation rate in the circuit provided inside the transmission burst wave is automatically adjusted.

Further, according to the present invention, (1) a transmission burst wave is transmitted from a first unit to a second unit via a cable and further transmitted from the second unit to the outside, while a burst wave is transmitted. A cable loss equalization method executed by a communication device in which the second unit receives from the outside and further transmits the received burst wave from the second unit to the first unit via a cable, ) A cable loss measurement operation in which the first unit sends a loss detection signal of predetermined power to the cable, and the second unit inputs the loss detection signal from the cable to measure the cable loss or its deviation. Is executed in a state in which the second unit is controlled to be in the transmission stop state by the request from the first unit to the second unit, and (3) at the end of the cable loss measurement operation, the second unit is executed. Informs the first unit of the information obtained by the above measurement, and (4) at least during the ON period of the transmission burst wave, so that the second unit is compensated for the cable loss appearing in the transmission burst wave. Further, according to the information obtained by the above measurement, the gain or the attenuation rate in the circuit provided inside which the transmission burst wave passes is automatically adjusted, while the first unit compensates the cable loss appearing in the reception burst wave. In addition, according to the information notified from the second unit, the gain or the attenuation rate in the circuit provided inside the unit through which the received burst wave passes is automatically adjusted.

As described above, in the present invention, the loss detection signal transmitted from the first unit is input via the cable to the second unit which receives the transmission burst wave from the first unit via the cable. The cable loss or its deviation is actually measured. Therefore, since the cable loss compensation operation in the present invention is a direct measurement of the cable loss or its deviation, it is lighter and more accurate than the conventional method involving manual setting by the cable builder, and the DC voltage drop or It is more accurate than the conventional method that involves indirect measurement by measuring the time required for signal propagation. In particular, the normal transmitted wave and received wave are burst waves, but the loss detection signal can be a continuous wave that is not burst-modulated to ensure a sufficient detection time, which results in stable cable loss (deviation ) Measurement can be realized. Furthermore, since it is only necessary to set the gain or the attenuation rate based on the information obtained by the cable loss measurement operation, and it is not necessary to change the gain or the like by burst on / off, the circuit operation becomes stable in that respect as well. Further, the cable loss measurement operation in the present invention is performed by, for example, turning on the power to the first unit, operating a switch attached to the first unit, or issuing a command from a control terminal attached to the first unit. Accordingly, if the execution is started, it is possible to prevent the malfunction from occurring in the normal signal transmitting / receiving operation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Since the present invention can be applied to the subscriber stations 20A, 20B, 20C shown in FIG. 3,
Although an example of application to a subscriber station will be described below, the present invention can be applied to the base station 10. Further, more generally, the present invention can be applied to a communication device using a burst wave, particularly a communication device having a plurality of units connected via a cable.

FIG. 1 shows the configuration of a subscriber station 20 according to an embodiment of the present invention. Subscriber station 20 according to the present embodiment
Has a configuration in which an outdoor unit 21 which is an RFU and an indoor unit 22 which is an IFU are connected by a cable 23. Further, both the outdoor device 21 and the indoor device 22 have a circuit system of a transmission system and a reception system, and the antenna 24 connected to the outdoor device 21 is the base station 10 of the TDD system.
It is shared by the circuits of the transmission system and the reception system while being switched for wireless communication with.

The circuit system of the transmission system includes the digital processing unit 221 of the indoor unit 22, the modulation unit 222, the distribution unit 223,
The coaxial cable 23, the distribution unit 211 of the outdoor device 21, the variable gain amplifier 212, the frequency conversion unit 213, and the RF circuit 21.
4 and the duplexer 215 to reach the antenna 24. During normal burst transmission operation, in this system,
Based on the information signal supplied from the digital processing unit 221, and under the control of the digital processing unit 221, the modulation unit 222 generates a transmission burst wave that turns on and off at a predetermined timing, and the distribution unit 223 generates the transmission burst wave. 23 is supplied to the connection terminal side. This transmission burst wave is transmitted to the outdoor device 21 by the coaxial cable 23. The distribution unit 211 of the indoor device 21 is the coaxial cable 2
A variable gain amplifier 2 receives the transmission burst wave input via
12 is supplied to the up-conversion circuit in the frequency conversion unit 213, and the frequency conversion unit 213 up-converts the transmission burst wave from the intermediate frequency to the radio frequency.
The RF circuit 214 power-amplifies the transmission burst wave up-converted to the radio frequency, and the duplexer 215 supplies the power-amplified transmission burst wave to the antenna 24. By such an operation, the information signal input from the indoor device of the subscriber's house, for example, the personal computer to the indoor device 22 and further to the digital processing unit 221 thereof is wirelessly transmitted by the burst wave from the antenna 24.

The circuit system of the reception system is from the antenna 24 to the duplexer 215 of the outdoor unit 21, the RF circuit 214, the frequency conversion unit 213, the distribution unit 211, the coaxial cable 23, the distribution unit 223 of the indoor unit 22, and the variable gain amplifier. It goes to the digital processing section 221 through the 224 and the demodulation section 225. During normal burst reception operation, in this system,
The duplexer 215 of the outdoor device 21 supplies the burst wave received by the antenna 24 to the RF circuit 214, and the RF circuit 2
14 performs low noise amplification on the received burst wave, a down conversion circuit in the frequency conversion unit 213 down-converts the received burst wave from the radio frequency to the intermediate frequency, and the distribution unit 211 converts the received burst wave of the intermediate frequency. Supply to the connection terminal side with the shaft cable 23 to be carried. The received burst wave is transmitted to the indoor device 22 via the coaxial cable 23. The distribution unit 223 of the indoor device 22 distributes the received burst wave input via the coaxial cable 23 to the demodulation unit 225 via the variable gain amplifier 224, and the demodulation unit 225.
Demodulates the received burst wave, and the digital processing unit 22
1 reproduces information from the demodulation result. By such an operation, the burst wave radio-received by using the antenna 24 is transmitted to the indoor unit 22 and further to the digital processing unit 221 thereof.
Is output as a demodulated information signal to the indoor device of the subscriber's house.

The feature of this embodiment is that the subscriber station 20, which is a device for performing wireless communication by the burst wave in accordance with the TDD method, equalizes the cable loss in the coaxial cable 23 and installs the coaxial cable 23. The point is that it can be performed accurately without imposing an extra burden on the operator, and in particular, a cable loss correction procedure including direct measurement of the cable loss or its deviation is introduced for that purpose.

FIG. 2 shows a cable loss correction procedure. In this embodiment, when the user turns on the power of the indoor unit 22 or resets the operating state of the indoor unit 22 by operating a switch or the like attached to the indoor unit 22, digital processing of the indoor unit 22 is performed. The unit 221 determines that "request has occurred" and starts the cable loss correction procedure (301). A control terminal connected to the indoor unit 22 (a personal computer or the like in the subscriber's house may be used)
Even when the cable loss correction command is received from, it is determined that “request has occurred”.

As will be described later, in the cable loss correction procedure according to this embodiment, a signal for detecting the cable loss or its deviation is supplied from the indoor device 22 to the outdoor device 21 via the coaxial cable 23. In addition, the signal is not a burst wave used for normal communication for measurement of the cable loss or its deviation in order to ensure sufficient time to stably perform input power measurement in the outdoor device 21, and is modulated. Or unmodulated continuous wave. As described above, the digital processing unit 221 does not radiate a signal different from a normal transmission wave from the antenna 24 by radio.
When starting the procedure, first, the outdoor device 21 is requested to stop transmission (302). The control unit 218 provided in the outdoor device 21 disconnects the circuit system of the transmission system from the antenna 24 by controlling the duplexer 215 in response to this request (303). For example, antenna 2
4 is connected to the circuit system of the receiving system (transceiver duplexer 215
Has two states of transmission / reception) or is disconnected from both transmission / reception systems (when the duplexer 215 has the third state). The signal for the transmission stop request is the digital processing unit 22 in the figure.
1, the signal line bypassing the modulator 222 and connected to the distributor 223, the coaxial cable 23, and the distributor 2
11 is transmitted using a signal line connecting the control unit 218 and the control unit 218. These signal lines are communication lines by ASK modulation, for example.

Thereafter, the digital processing section 221 requests the modulation section 222 to send out a detection signal, for example, a continuous modulated wave (304), and the modulation section 222 sends out a signal corresponding to this request (305). The outdoor device 21 receives this signal via the coaxial cable 23 and measures the signal power (306). Therefore, in the transmission system circuit system of the outdoor device 21, a unit for detecting the signal power is provided in a stage before the device that performs variable gain amplification or variable attenuation of the transmission burst wave. In the illustrated example, the distribution unit 2 is connected to the connection terminal with the coaxial cable 23 before the variable gain amplifier 212.
A detection unit 216 that outputs a detection voltage according to the signal power is provided at a portion located between the detection unit 11 and the connection unit 11. This detected voltage is transmitted to the control unit 218 via the A / D converter 217.
(307). The control unit 218 stores a table that associates the detected voltage with the cable loss,
By referring to the table according to the detection voltage input via the A / D converter 217, the cable loss value or the value of the deviation thereof is detected (308). The deviation here is a difference with respect to a predetermined reference input power. Further, here, it is said that the cable loss value or the deviation amount is detected, but this does not mean that the absolute values of them must be obtained. For example, it is possible to adopt a method of detecting a difference from the previously detected value.

While the control unit 218 stores the detection result in its internal memory (309), the fact that the actual measurement has been completed and the result thereof are indicated in the route opposite to the route in which the transmission wave stop request was first received. Then, the digital processing unit 2 of the indoor unit 22
21 is notified (310). Digital processing unit 221
Starts signal power control based on the notified cable loss value or its deviation (311). For example, the variable gain amplifier 22 on the reception system circuit of the indoor unit 22
Control of gain and attenuation rate in devices such as 4 is started. This is a control for equalizing the cable loss deviation appearing in the received burst signal. On the other hand, the control unit 218 starts signal power control based on the detection value stored in the memory (312). That is, the control of the gain or the attenuation rate in the device such as the variable gain amplifier 212 on the transmission system circuit system of the outdoor unit 21 is started. This is control for equalizing the cable loss deviation appearing in the transmission burst wave. In the present embodiment, the TDD method is assumed, and since it is assumed that the intermediate frequencies of the transmission burst wave and the reception burst wave are the same, the cable loss (deviation) common to the outdoor device 21 and the indoor device 22 is detected. Values are available. Note that it is not necessary to switch the gain or the attenuation rate by burst on / off. That is, since the gain or the attenuation rate can be kept constant after shifting to the normal operation, the circuit operation is stable in that respect as well.

Then, the digital processing unit 221 of the indoor unit 22 requests the outdoor unit 21 to cancel the transmission stoppage (313), and the control unit 218 of the outdoor unit 21 accordingly responds to the duplexer. The switching operation of 215 is shifted to the normal operation, that is, the switching operation synchronized with burst on / off (31
4). After that, the transmission / reception by the burst wave is executed as usual. At least during the ON period of the transmission burst wave (more preferably, always during normal operation regardless of burst ON / OFF), the cable loss deviation appearing in the transmission burst wave is equalized by the variable gain amplifier 212, and at least the reception burst wave. During the ON period of (more preferably, always during normal operation regardless of burst ON / OFF), the cable loss deviation appearing in the received burst wave is equalized by the variable gain amplifier 224, so that the amplifier 21
Circuits subsequent to 2, 224 are not affected by the cable loss deviation and operate properly.

As described above, according to the present embodiment, the (un) modulated continuous wave is sent from the indoor unit 22 onto the coaxial cable 23 immediately after the power is turned on, and the outdoor unit 21 measures its signal power. The cable loss is equalized based on the result. Therefore, in contrast to the conventional technology in which the cable builder sets the cable loss approximate value and the conventional technology in which the cable loss or its deviation is indirectly measured through the measurement of the DC voltage drop or the signal propagation required time, The work load can be reduced, the cable loss can be accurately equalized, and the allowable range of the length, manufacturer, and type of the coaxial cable 23 can be expanded.

Further, for example, 1 μsec per burst
The subscriber station 20 and the base station 1 that perform wireless communication based on the TDD system with a short signal transmission time by the burst wave.
At 0, it is difficult to detect the signal power during normal burst communication and equalize the cable loss at any time. That is, the time required for the gain or attenuation rate of the variable gain amplifier or variable attenuator to be controlled to stabilize is apt to be too long to ignore for the burst-on period, and as a result, the burst wave There is a problem that some parts are missing and the transmission rate is substantially lowered. That is, if it is a communication device that communicates by continuous wave, information loss will not occur except immediately after power is turned on even if power measurement and cable loss due to the result are performed during communication. If simply applied to a communication device for communication, there is a result that information loss occurs at each burst-on period. On the other hand, the method according to the present embodiment is a method that is executed using a continuous wave at a timing when transmission by a burst signal is not executed, such as immediately after power-on, and does not change the gain during the burst-on period. Therefore, cable loss equalization can be realized without loss of burst signals. Variable gain amplifier 212, 22
Even if 4, the response to the gain control signal is not so fast can be used.

Further, since the procedure shown in FIG. 2 can be activated at any time by operating a switch, etc., there is a change in cable loss such as relocation of the subscriber station 20 or its constituent units, replacement of the coaxial cable 23, and attachment / detachment of its connector. The gains of the variable gain amplifiers 212 and 224 can be optimized as needed. Further, since this procedure is automatically started when the power is turned on, it is not necessary for the user to be particularly conscious of starting this procedure unless a reset operation is necessary for some reason.

The detecting unit 216 is the indoor unit 2
The duplexer 2 which detects the arrival of the transmission burst wave from
In the operation of controlling 15 and connecting the antenna 24 to the transmission system, the one used for arrival detection can be diverted / combined.

Then, the FDD (Freq
The present invention can be implemented by a communication device based on the uency Division Duplex) method.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a control procedure in the present embodiment.

FIG. 3 is a diagram showing an example of a system in which an apparatus according to the present invention can be used.

FIG. 4 is a diagram conceptually showing transmission by a burst wave.

[Explanation of symbols]

10 base stations, 11 base station radio frequency units (R
FU), 12 Base station interface unit (IF
U), 13,23 coaxial cable, 20,20A, 20
B, 20C subscriber stations, 21 outdoor units of subscriber stations (R
FU), 212 variable gain amplifier, 216 detector, 21
7 A / D converter, 218 control unit, 22 indoor unit (IFU) of subscriber station, 221 indoor unit digital processing unit, 222 modulation unit.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiro Toriyama             5-1-1 Shimorenjaku, Mitaka City, Tokyo Japan             Wireless Co., Ltd. (72) Inventor Tetsuya Shiramizu             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Fumihiro Honma             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 5J100 JA01 LA00 LA11 QA01 QA02                       SA02                 5K046 AA01 DD14

Claims (3)

[Claims] 1. A cable loss equalization method executed by a communication device that transmits a transmission burst wave from a first unit to a second unit via a cable and further transmits the second unit to the outside. A cable in which the first unit sends a loss detection signal of a predetermined power to the cable, and the second unit inputs the loss detection signal from the cable to measure the cable loss or its deviation. The loss measurement operation is executed in a state in which the second unit is controlled to be in the transmission stop state in response to a request from the first unit to the second unit, and at least during the burst-on period of the transmission burst wave, the second unit However, the transmission burst wave is provided inside the transmission burst wave so that the deviation of the cable loss appearing in the transmission burst wave is compensated and according to the information obtained by the above measurement. Cable loss equalization method characterized by automatically adjusting the gain or attenuation rate in the road. 2. The cable loss equalization method according to claim 1, wherein the second unit receives the burst wave from the outside, and further the received burst wave is received from the second unit via the cable to the first unit. In the cable loss equalization method executed by the communication device transmitting to the second unit, at the end of the cable loss measurement operation, the second unit notifies the first unit of the information obtained by the above measurement, and at least receives the information. During the burst-on period of the burst wave, the first unit is provided therein so that the cable loss appearing in the received burst wave is compensated and according to the information notified from the second unit, the received burst wave passes through. A cable loss equalization method characterized by automatically adjusting a gain or an attenuation factor in a circuit. 3. The cable loss equalization method according to claim 1 or 2, wherein power is turned on to the first unit, operation of a switch attached to the first unit, or control attached to the first unit. A cable loss equalization method characterized by starting execution of a cable loss measurement operation in response to a command from a terminal.