KR100612264B1 - Apparatus and Method for Downstream Power Monitoring in Cable Modem - Google Patents

Abstract

According to an aspect of the present invention, there is provided a method for indicating a downlink signal power of a cable modem, wherein the downlink signal monitoring stores at least one auto gain control value calculated for each frequency and power of a downlink signal input from the cable network to the cable modem. A data collecting step, creating a downstream power monitoring (DPM) table including the collected data, adjusting a downlink signal input from the cable network to the cable modem to a down power of a TOP (take over point) level, The frequency range is divided into at least one level and the DPM sample data having at least one TOP value measured for each frequency and the TOP value obtained in the downlink signal measuring step having an approximate value in the DPM table. Select Downlink to display downlink signal from cable network And a display step.

Description

Apparatus and Method for Downstream Power Monitoring in Cable Modem}             

1 is a configuration diagram of a cable broadcasting environment to which the present invention is applied.

2 is a relationship between IF_AGC, RF_AGC, and TOP.

3 is a characteristic diagram of RF_AGC.

4 is a characteristic diagram of IF_AGC.

* Description of the symbols for the main parts of the drawings *

100: cable modem 101: tuner (Tuner)

102: CPU 111: variable attenuator

112: fixed attenuator 120: UP converter

130: CMTS 140: monitoring PC

The present invention relates to down signal power display of a cable modem, and more particularly, to a data input method in a Downstream Power Monitoring (DPM) implementation for detecting and displaying a down signal of a cable communication system through a tuner in a cable modem that is an indoor device. The present invention relates to an apparatus and a method for indicating downlink power of a cable modem which shortens the DPM setting time through the improvement.

A cable modem is a device that connects a personal computer (PC) to a cable TV line and receives data at speeds up to 10 Mbps. All cable modems must be connected to the cable TV company's coaxial cable to communicate with the Cable Modem Termination System (CMTS) at the local cable station. All cable modems can only exchange data with the CMTS. The actual bandwidth of a cable TV line for Internet service is up to 40 Mbps down (downstream from the subscriber side) and up to 30 Mbps upstream (from the subscriber side towards the station).

Cable modems are designed to display power for downlink signals according to Data Over Cable Service Interface Specifications 2.0 (DOCSIS 2.0), which is called Downstream Power Monitoring (DPM).

In the cable modem, the frequency range of the downlink signal is 90 to 860 MHz, and the power range is +15 dBmV to 15 dBmV. The cable modem should detect the downlink signal through the tuner in all frequency bands and power range bands in 6MHz bandwidth units, and the function of displaying the detected frequency and power is DPM. The range to meet the DOCSIS 2.0 specification should be within +/- 3dB of the actual downlink signal power.

In order to implement DPM, the AGC (Auto Gain Control) value of each tuner measured for each frequency and power should be stored in flash memory. Have

In order to meet the DOCSIS 2.0 specification, AGC values should be calculated for each frequency and power in theory, but since it is not practical, in practice, 9 frequencies and 10 power levels of the total frequency and power range are set up to 99 times per cable modem. You are entering data.

That is, since the characteristics of AGC vary slightly depending on the tuner, AGC values are obtained for 9 frequencies and 11 power levels among the tuner input power levels in the 90 to 860 MHz frequency range and the +15 dBmV to 15 dBmV range. will be. The process is done in the following way.

1) The downlink frequency is set to 93 MHz by controlling the UP converter in the monitoring PC 140.

2) Control the variable attenuator on the monitoring PC 140 to control the downstream power by +15 dBmV, +12 dBmV, +9 dBmV, +6 dBmV, +3 dBmV, 0 dBmV, -3 dBmV, -6 dBmV, -9 dBmV, Set to -12 dBmV and -15 dBmV in turn, and then use the serial port such as RS232C through the monitoring PC 140 to allow the cable modem's CPU to record the measured RF_AGC and IF_AGC voltage values in flash memory. (Write).

3) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 189 MHz, and the operation 2) is repeated.

4) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 285 MHz, and the operation 2) is repeated.

5) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 381 MHz, and the operation 2) is repeated.

6) Control the UP converter in the monitoring PC 140 to set the downlink frequency to 477MHz, and repeat operation 2).

7) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 573 MHz, and the operation 2) is repeated.

8) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 669 MHz, and the operation 2) is repeated.

9) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 765MHz, and the operation 2) is repeated.

10) The UP PC is controlled by the monitoring PC 140 to set the downlink frequency to 857 MHz, and the operation 2) is repeated.

When the above process is performed, 99 RF_AGC and IF_AGC values are stored in the flash memory. When tuning random frequencies based on the sample data (this is called DPM TABLE), the RF_AGC and IF_AGC values are best compared to the RF_AGC and IF_AGC values. As an approximation, indicate the downward power level. Therefore, the DPM setting method per cable modem is not only time-consuming, but since the downlink power deviation management through the attenuator is very important, it is necessary to precisely set the offset at every mass production. Big.

 As such, since the DPM data has to be obtained 90 times for each cable modem by the tuner deviation, it takes a lot of time to calculate the DPM data and requires accuracy and precision in terms of equipment setting.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide an apparatus and method capable of satisfying a standard while reducing the number of power levels of frequencies that are DPM data input conditions of a cable modem.

According to an aspect of the present invention, there is provided a method for indicating a downlink signal power of a cable modem, wherein the downlink signal monitoring stores at least one auto gain control value calculated for each frequency and power of a downlink signal input from the cable network to the cable modem. A data collecting step, creating a downstream power monitoring (DPM) table including the collected data, adjusting a downlink signal input from the cable network to the cable modem to a down power of a TOP (take over point) level, The frequency range is divided into at least one level and the DPM sample data having at least one TOP value measured for each frequency and the TOP value obtained in the downlink signal measuring step having an approximate value in the DPM table. Select Downlink to display downlink signal from cable network Call display step.

The automatic gain control value is divided into IF (Intermediate Frequency) automatic gain control and RF (Radio Frequency) automatic gain control, and the IF auto gain control and RF auto gain control characteristic curves are characterized by linearity.

The TOP value may be an RF auto gain control value and an IF auto gain control value at a TOP point where the RF auto gain control and the IF auto gain control point of time intersect.

The downlink signal display step selects a TOP table having data closest to the TOP value for each frequency to be measured, and grasps an automatic gain adjustment value corresponding to a frequency on the TOP table that is close to the frequency value of the actually measured downlink signal. In this case, the power level of the downlink signal is displayed using the linear characteristics of the automatic gain control curve.

The downlink signal power display device of the cable communication system according to another aspect of the present invention is a CMTS for routing the local data of the cable communication system, and transmits a cable signal to a network connected by a coaxial cable, which is transmitted through the coaxial cable from the CMTS A UP converter for outputting a fixed power signal by converting a frequency band of the signal into one channel, a fixed attenuator for attenuating the output power of the UP converter with a fixed attenuation, and a variable value of the intensity of the output signal of the fixed attenuator A variable attenuator for attenuating and outputting a signal, a cable modem for receiving a downlink signal outputted from the attenuator, tuning to a corresponding frequency, and performing automatic power regulation control for the downlink signal, the UP converter, the attenuator, and the cable Connected to a modem to monitor the status of each device and control its operation Including a monitoring PC, and adjusts the value of the Downstream Power Monitoring (DPM) table created by collecting the downlink signal monitoring data and the downlink signal input from the cable network to the cable modem to the down power of the TOP (Take Over Point) level The frequency range is divided into at least one level to compare at least one TOP value measured for each frequency to select DPM sample data having a value closest to the TOP value to display a downlink signal of a cable network.

The cable modem includes a tuner for tuning the downlink signal of the cable signal system to one frequency and a CPU for interfacing with the tuner in the form of serial data and transmitting an automatic gain control voltage to the tuner to adjust gain. Characterized in that.

In addition, the CPU lowers the automatic gain control voltage when the input power is high, and raises the automatic gain control voltage when the input power is low, and maintains the same output level even when the downward power level input to the CPU changes.

The UP converter and the monitor PC are connected by an Ethernet line, the variable attenuator and the monitor PC are connected by a serial line, and the cable modem and the monitor PC are parallel. It is characterized in that connected to the line.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the drawings.

1 shows a cable broadcasting environment configuration to which the present invention is applied.

CMTS (130) (Cable Modem Termination System) is a kind of HFC (Hybrid Fiber Coaxial cable) that allows the connection between each other by connecting the cable modem 100 using a coaxial cable and the Internet network using Ethernet (Ethernet): Optical coaxial mixed cable) router. The CMTS 130 provides several functions, including routing to store local data in the cable system, filtering to protect cable operators from unwanted hacking, and traffic shaping to ensure the quality of service to subscribers.

The CMTS 130 typically transmits downlink signals at 44 MHz center frequency and +42 dBmV power with a bandwidth of 6 MHz.

The UP converter 120 receives a signal transmitted from the CMTS 130 and converts the signal into one channel of the 90 to 860 MHz frequency, and the output power is fixed at +60 dBmV.

The fixed attenuator 112 attenuates the output power of the UP converter 120 to a fixed intensity. The roughly attenuated signal through the attenuator 112 is subjected to the attenuation to a more sophisticated value by the variable attenuator 111 once more. The variable attenuator 111 may attenuate and output the intensity of the input signal to a variable value. The variable attenuator attenuates the output power of the UP converter 120 and outputs power of +15 to 15 dBmV.

The cable modem 100 adjusts a signal to a 44 MHz center frequency and a constant power through tuning and demodulation of a built-in tuner. The tuning frequency and gain adjustment function is performed by the CPU 102 in the cable modem 100. The CPU 102 interfaces with the tuner in the form of serial data, and the gain is AGC (Auto). Gain Control: It controls by transmitting voltage to tuner. In other words, if the input power of the CPU 102 is high, the AGC voltage is lowered. If the input power is low, the AGC voltage is increased. AGC can be viewed as a function or device that adjusts the gain to maintain the same output level at all times, even if the downstream power level changes.

The monitoring PC 140 is connected to the UP converter, the attenuator, and the cable modem to monitor the status of each device and control its operation.

AGC control is divided into RF_AGC (Radio Frequency AGC) and IF_AGC (Intermediate Frequency AGC), while adjusting the input gain of the entire input signal between 90 and 860 MHz is RF_AGC. IF_AGC. In other words, it is RF_AGC that adjusts the gain of the entire downlink signal at once and IF_AGC adjusts the gain only for the demodulated signal.

The CPU 102 of the cable modem 100 commands the tuner to tune the frequency and adjust the AGC gain. Since the CPU 102 is required to input signals of the same power level, the role of the AGC is necessary. Among AGC control, there is a point where IF_AGC and RF_AGC control intersect and are distinguished. This is called TOP (Take Over Point).

2 shows the relationship between IF_AGC, RF_AGC, and TOP.

Referring to FIG. 2, when the tuner input power level is small, both the voltages of IF_AGC and RF_AGC are increased to match the input level to the CPU.

If the input power of the tuner is higher than the input power level to the CPU 102, the IF_AGC voltage is lowered first among IF_AGC and RF_AGC, and if the input power rises, the IF_AGC voltage is lowered and IF_AGC is maintained at a specific input power level, and the RF_AGC voltage is lowered. To begin with, this point is called TOP. Therefore, it can be seen that the operations of IF_AGC and RF_AGC intersect with TOP.

3 is a graph showing the characteristics of RF_AGC.

3 represents the uncorrected gain, and the abscissa represents RF_AGC (V). Referring to FIG. 3, it can be seen that the gain is minimum when the voltage of RF_AGC is 0.5V and the gain is maximum at 2.5V. Note that there is a variation in AGC voltage per tuner, but it should be noted that any tuner is linear.

4 is a graph showing the characteristics of IF_AGC.

Like the RF_AGC characteristic graph of FIG. 3, it can be seen that the characteristic graph of IF_AGC is also linear. 4 represents the uncorrected gain, and the horizontal axis represents IF_AGC (V).

The present invention is developed using the above-described deviation and linearity on the RF_AGC and IF_AGC graphs, and TOP.

The CPU 102 of the cable modem 100 receives signals at a fixed IF frequency and power level through RF frequency tuning and AGC operations. TOP indicates the downlink power level at which the IF_AGC and RF_AGC roles of the tuner are transferred. Therefore, TOP must be set to recognize the signal through the tuner. This is separate from the DPM function, and the present invention uses the AGC value at the time of this TOP setting to perform the DPM function.

The TOP value can change due to tuner deviation, meaning that the input power level is set to TOP at a specific frequency. Here, the TOP value refers to the voltage value of the IF_AGC and the voltage of the RF_AGC at the time point of TOP, which is different for each tuner.

For example, suppose that you want to set the TOP to -13dBmV over the entire 90-860MHz band. This 13dBmV is a fixed value in product design. However, the IF_AGC voltage and RF_AGC voltage values at -13dBmV are different due to the tuner deviation of each product.

According to the UP converter 120 and the attenuator, the power level of a specific downlink frequency is input so that the CPU 102 of the cable modem 100 inputs the IF_AGC voltage value and the RF_AGC voltage value at this time, while the RF_AGC maintains the maximum voltage and the IF_AGC. Only the voltage value is lowered and the value is entered into the flash memory. Therefore, the CPU 102 of the cable modem 100 knows the IF_AGC voltage value at the TOP power level, which is determined by the RF_AGC gain deviation and the IF_AGC gain deviation.

This means that once the TOP is known, the gain by the IF_AGC and RF_AGC at its downstream power level is also determined. If a power higher than TOP is input thereafter, only the RF_AGC voltage value is lowered, that is, the gain is lowered, thereby performing AGC operation.

Knowing the TOP, the respective voltage values according to the tuner IF_AGC gain and RF_AGC gain are determined at the downstream power level that the CPU 102 can recognize, and can be predicted by the AGC curve having the linearity according to the tuner standard. .

In order to realize this theoretical prediction, it is possible to implement the actual IF and RF voltage values and the voltage value according to the tuner standard by referring to the TOP value, but a more precise method is required to satisfy the DOCSIS 2.0 specification (within +/- 3dB). As required, DPM sample data (DPM table) is required. The more DPM tables possible, the higher the precision.

A preferred embodiment of a downlink signal power display method of a cable modem according to the present invention will be described.

Since the RF_AGC and IF_AGC characteristic graphs vary linearly with each tuner, the instrument is sampled by sampling six frequencies and one power level (TOP level) among the tuner input power levels in the 90 to 860 MHz frequency range and the +15 dBmV to -15 dBmV range. To enter.

In consideration of the production equipment and time, it is difficult to set -13dBmV TOP in the entire 90 to 860MHz band, so in this embodiment, seven frequencies and one power level (-13dBmV) are sampled and input.

a) controlling the UP converter 120 from the monitoring PC 140 to set the downlink frequency to 93MHz, and controlling the variable attenuator 111 to set the downlink power to the TOP level. At this time, the monitoring PC 140 causes the CPU 102 of the cable modem 100 to read the TOP value (the RF_AGC and IF_AGC voltage values at the TOP point) at this time and store it in the flash memory using a serial port such as RS232C. do.

b) Repeat the above a) with downlink frequency of 190MHz.

c) Repeat step a) with a downlink frequency of 360 MHz.

d) Repeat step a) above with 520 MHz downlink frequency.

e) Repeat step a) with the downlink frequency at 740MHz.

f) Repeat step a) with the downlink frequency of 813MHz.

The RF_AGC and IF_AGC values at the TOP points, which are performed six times in the above manner, are stored in the flash memory, and one of the DPM tables previously input to the flash is selected based on the TOP values. In this case, when tuning an arbitrary frequency based on the DPM table, the downward power level is displayed as an approximation compared with the RF_AGC and IF_AGC voltage values.

It is also possible to set the frequency level at intervals different from the above embodiment, and the number of measurement levels can also be changed. However, the above embodiment is a preferable case because a satisfactory downlink power value can be obtained and the set time is short.

The DPM table shows the voltage values (actually digitally changed) of RF_AGC and IF_AGC according to frequency (in MHz) and power level (in dBmV). Therefore, the DPM table may be expressed in a format as shown in Table 1 below.

RF_AGC / IF_AGC -15 (dBmV) -12 (dBmV) -9 (dBmV) -6 (dBmV) -3 (dBmV) 0 (dBmV) 3 (dBmV) 6 (dBmV) 9 (dBmV) 12 (dBmV) 15 (dBmV) 93 (MHz) 3.0 / 3.0 3.0 / 2.5 2.5 / 2.5 2.3 / 2.5 2.0 / 2.5 1.8 / 2.5 1.5 / 2.5 1.2 / 2.5 1.0 / 2.5 0.8 / 2.5 0.5 / 2.5 189 (MHz) … … … … … … … … … … … 857 (MHz) 2.9 / 2.9 2.9 / 2.4 2.4 / 2.4 2.2 / 2.4 1.9 / 2.4 1.7 / 2.4 1.4 / 2.4 1.1 / 2.4 0.9 / 2.4 0.7 / 2.4 0.4 / 2.4

The DPM table expressed in the format shown in Table 1 is different for each tuner. Therefore, the more DPM tables, the better. Therefore, the DPM table is prepared through the downlink signal monitoring data collection for at least one cable modem, and it is preferable that data collection for as many cable modems as possible be made within the measurable range.

If the TOP value is measured at 2.95 / 2.45 (RF_AGC value / IF_AGC value) at 813 MHz, -13 dBmV in the production product, the CPU 102 will return 2.95 / 2.45 at -13 dBmV at the corresponding TOP power level of 857 MHz closest to the frequency of 813 MHz. We will search in the DPM table with a value close to.

If the DPM table shown in Table 1 has the closest value, the measured values are compared among the values corresponding to 857 MHz closest to 813 MHz. For example, if the input frequency measured in any cable modem 100 is 857 MHz and the tuner's RF_AGC / IF_AGC value is measured as 1.3 / 2.4, based on the linearity of RF_AGC and IF_AGC, the cable modem 100 is supplied to the cable modem 100. The power level of the downlink signal can be expressed as about 4dBmV.

As described above, the DPM setting method according to the present invention can significantly reduce the set time compared to the prior art, thereby reducing the production cost, and is much easier to manage the equipment, which is also useful in terms of quality control.

As a result of measuring the DPM setting time according to the method according to the present invention, the DPM setting time was reduced to as much as 80% compared to the conventional DPM setting time of 2 minutes and 40 seconds.

The present invention, by using the DPM sample data, the linearity of the AGC, and TOP to reduce the number of DPM setting times, and the time and production cost of the DPM setting is reduced, it is easy to manage the equipment is also useful in terms of quality control.

Claims (13)

In the downlink signal power display method of the cable modem, A downlink signal monitoring data collection step of storing at least one auto gain control value calculated for each frequency and power of the downlink signal input from the cable network to the cable modem; Creating a downstream power monitoring (DPM) table composed of the collected data; The downlink signal input from the cable network to the cable modem is adjusted to down power of a TOP (Take Over Point) level, and the frequency range is divided into at least one level, and RF automatic gain control and IF automatic gain are measured for each frequency. A downward signal measurement step of obtaining a TOP value which is an RF auto gain control value and an IF auto gain control value at a TOP point where the adjustment time points are crossed; And And a downlink signal displaying step of displaying the downlink signal of a cable network by selecting DPM sample data having the closest value among the DPM tables from the TOP value obtained in the downlink signal measuring step. The method of claim 1, The automatic gain control value is a downlink signal power display method of the cable modem, characterized in that divided into IF (Intermediate Frequency) automatic gain control and RF (Radio Frequency) automatic gain control. The method of claim 2, And the IF auto gain control and the RF auto gain control value have a linearity characteristic. delete delete The method of claim 1, The downward signal display step, Select the TOP table that has the data closest to the TOP value for each frequency to be measured, identify the auto gain adjustment value corresponding to the frequency on the TOP table that is close to the frequency value of the downlink signal actually measured, and determine the linearity of the auto gain control curve. The downlink signal power display method of a cable modem, characterized in that to display the power level of the downlink signal using a characteristic. In the down signal power display device of the cable communication system, A CMTS for routing local data of the cable communication system and transmitting cable signals to a network connected by coaxial cables; An UP converter for converting a frequency band of a signal transmitted from the CMTS through a coaxial cable into one channel and outputting a fixed power signal; A fixed attenuator for attenuating the output power of the UP converter with a fixed iron; A variable attenuator for attenuating and outputting the intensity of the output signal of the fixed attenuator to a variable value; A cable modem that receives the downlink signal output from the attenuator, tunes to a corresponding frequency, and performs automatic power adjustment control on the downlink signal; And A monitoring PC connected to the UP converter, the attenuator, and the cable modem to monitor the status of each device and control its operation, A value of the Downstream Power Monitoring (DPM) table collected by collecting downlink signal monitoring data and a downlink signal input from the cable network to the cable modem are adjusted to down power of a TOP (Take Over Point) level, and the frequency range is at least one. The RF value is adjusted at each frequency and the RF value is adjusted at the point where the IF automatic gain control point intersects, and the value of the TOP value, which is the IF automatic gain control value, is compared. A downlink signal power display device of a cable communication system for displaying a downlink signal of a cable network by selecting DPM sample data having a value. delete The method of claim 7, wherein The cable modem, A tuner tuned to one frequency of the downlink signal of the cable signal system; Wow And a CPU for interfacing with the tuner in the form of serial data and transmitting an automatic gain control voltage to the tuner to adjust the gain. The method of claim 9, The CPU lowers the automatic gain control voltage when the input power is high, and increases the automatic gain control voltage when the input power is low, so that the CPU maintains the same output level at all times even when the down power level input to the CPU changes. Down signal power display device of cable communication system. The method of claim 7, wherein Down signal power display device of the cable communication system, characterized in that connected between the UP converter and the PC for the monitor (Ethernet) line. The method of claim 7, wherein Down signal power display device of the cable communication system, characterized in that connected between the variable attenuator and the monitor PC in a serial line. The method of claim 7, wherein Down signal power display device of a cable communication system, characterized in that connected between the cable modem and the PC for the monitor in parallel (Parallel) line.

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