KR100425504B1 - Method for bit loading in digital subscriber line - Google Patents

Abstract

The present invention provides a bit allocation method for a digital subscriber line, comprising: a first step of performing channel modeling to set a bit value close to each channel as an initialization value; A second step of performing an efficiency operation by iteration after the first step; And a third step of performing energy tightness and bit tightness after the second step, thereby initializing a bit table value initialized to allocate an optimized bit to each allocated channel during an initialization process of the xDSL modem. By updating each time this operation is performed, the amount of calculation can be minimized.

Description

Method for bit loading in digital subscriber line

The present invention relates to a bit allocation method of a digital subscriber line (DSL), and more particularly, to bit allocation of a digital subscriber line suitable for allocating an optimized bit to each allocated channel during an initialization process of an xDSL modem. It is about a method.

In general, DSL is a technology for transmitting information at high speed to homes or small businesses through ordinary copper telephone lines. xDSL is a generic term for several different variants of DSL, including ADSL, HDSL, and RADSL. If your home or business is close enough to the office of the telephone company that provides DSL services, you can receive data at speeds of up to 6.1 Mbps to enable continuous transmission of video, audio, and even three-dimensional effects. More typical individuals will be served at speeds ranging from 1.544 Mbps down to 512 Kbps down and up to 128 Kbps upstream. DSL lines can carry both data and voice signals, and the data line portion remains connected.

DSL is a technique that assumes that you need to convert digital data into analog form and then never restore it. Digital data is delivered directly to the user's computer as digital data, which allows the phone company to use more bandwidth to deliver it to the user. Also, depending on the user's choice, part of the bandwidth can be used to transmit analog signals, allowing the phone and computer to be used simultaneously on a single line.

In these DSLs, bits must be allocated. Currently published algorithms include Rative Algorithm (RA) and Margin Algorithm (MA) through Chow's On / OFF Energy-Distribution calculation.

Such a chew algorithm aims at the convenience of the algorithm so that it is practically easy to apply to the device, and can be applied to the ADSL modem device that is actually used because it guarantees a fixed calculation time. However, the optimization of allocated bits is somewhat insufficient. The Campello algorithm is also reported to produce better results than the Chew's algorithm in the correct bit allocation method.

Chew's algorithm determines the real bit value from the Signal to Noise Ratio (SNR) estimate and rounds it up. Therefore, there is a drawback in not using the given energy efficiently. The remaining energy is evenly divided across the entire sub-channels through energy rescaling, which sets the margin different from the initial value. This chew algorithm is described in US Pat. No. 5479447.

1 is a flowchart of a reactive algorithm of a bit allocation method of a conventional digital subscriber line.

As shown therein, the steps of calculating the SNR value (ST11) (ST12); Sorting the calculated SNR values in descending order (ST13); Obtaining a bit value by continuously updating and increasing the channel to have a maximum bit value after the alignment (ST14 to ST19); Obtaining total energy by calculating energy according to the obtained bit value of each channel (ST20); Performing energy rescaling to match the total energy (ST22) is performed.

2 is a flowchart of a margin algorithm of a bit allocation method of a conventional digital subscriber line.

As shown therein, calculating the SNR value (ST31); Sorting the calculated SNR values in descending order (ST32); Obtaining maximum margin values using the total bits determined after the alignment (ST33 to ST38); Calculating the bits of each channel using the obtained maximum margin value, and matching all bits by comparing the target bits with the target bit value due to the round error generated in the calculation (ST39 to ST44); Obtaining a total energy by the bit value (ST45); In step ST46, energy rescaling is performed to match the total energy.

1 and 2, where SNR is the signal to noise ratio, B is the total bit, E _total is the total energy, r is the margin, and E (i) is is the energy corresponding to the i channel, Γ is the SNR gap (= 9.8 + r _m -r _c ), r _m is the margin, B _i is the bit value corresponding to the i channel, and N is The maximum value of the channel used.

Therefore, ADSL modems use Digital Multi Tone (DMT) to configure and communicate with devices. Bits allocated to each channel are assigned a fixed value of 0,2_15bit. Each channel is assigned a bit for optimal energy distribution by the SNR value. This process is called bit loading, which uses Chew's algorithm or Campello's algorithm to perform this process.

Chew's algorithm includes Rate-Adaptive loading and Margin-Adaptive loading. Each method is as follows.

(1) Rate Adaptive Allocation Algorithm (see Figure 1)

First, calculate the SNR value.

The SNR values are sorted in ascending order.

As each channel is increased, the channel is continuously updated to have the maximum bit value.

Calculate the energy according to the bit value of each channel.

Energy rescaling is performed to match the total energy.

(2) margin adaptive allocation algorithm (see Figure 2)

First, calculate the SNR value.

The SNR values are sorted in ascending order.

The maximum margin is obtained based on the determined total bits.

Calculate the bit of each channel with the maximum margin value.

The total bit is matched against the target bit value due to round error in the calculation.

An energy rescaling process is performed to fit the total energy.

However, such a conventional chew algorithm has a problem in that it is not possible to efficiently use a given energy because it is determined by rounding up after obtaining a real bit value from an SNR estimate.

In addition, the remaining energy is divided evenly over the entire sub-channels through energy rescaling, which causes a problem of margin change. The purpose of rate-adaptive allocation here is to achieve the maximum transmission rate with a given energy, but there is a problem that energy inefficiency occurs due to the change of margin.

The biggest problem with the Campello algorithm is that it has a lot of computation. In other words, Campello's EF (efficiency) algorithm continues to iterate until it is optimized to optimize the bit, which has a problem of guaranteeing computation time and delay time.

Accordingly, the present invention has been proposed to solve the conventional problems as described above, and an object of the present invention is to initialize an xDSL modem by assigning a bit table value initialized to allocate an optimized bit to each allocated channel during an initialization process of the xDSL modem. It is to provide a bit allocation method of the digital subscriber line that can minimize the amount of calculation by updating every time this operation.

Bit allocation method of a digital subscriber line according to an embodiment of the present invention to achieve the above object,

Performing a channel modeling to set a bit value close to each channel as an initialization value; A second step of performing an efficiency operation by iteration after the first step; And a third step of performing energy tightness and bit tightness after the second step.

1 is a flowchart of a reactive algorithm of a bit allocation method of a conventional digital subscriber line.

2 is a flowchart of a margin algorithm of a bit allocation method of a conventional digital subscriber line.

3 is a block diagram for bit allocation of a digital subscriber line to which the present invention is applied.

4 is a flowchart of a bit allocation method of a digital subscriber line according to the present invention.

5 is a graph showing SNR values according to general channel characteristics.

Explanation of symbols on the main parts of the drawings

10: FFT 20: FEQ

30: SNR unit 40: determination unit

50: decoder 60: tone deordering unit

70: DSP 71: Gain Table

72: bit allocation table

Hereinafter, an embodiment according to the present invention configured as described above, the technical spirit of the bit allocation method of the digital subscriber line will be described in detail with reference to the drawings.

3 is a block diagram for bit allocation of a digital subscriber line to which the present invention is applied.

Here, reference numeral 10 is FFT (Fast Fourier Transform), 20 is FEQ (Frequency Equalizer), 30 is SNR part, 40 is Decision part, 50 is Constellation Decoder ), 60 is a tone ordering unit, 70 is a digital signal processor (DSP), 71 is a gain table, and 72 is a bit loading table.

4 is a flowchart of a bit allocation method of a digital subscriber line according to the present invention.

As shown therein, a first step (ST51) of performing a channel modeling to set a bit value close to each channel as an initialization value; A second step ST53 (ST54) for performing efficiency by iteration after the first step; After the second step, a third step (ST55 to ST59) of performing energy tightness (ET) and bit tightness (BT) is performed.

In the first step, when the digital subscriber line (DSL) modem is operated, the optimized bit table value is updated again and initialized.

In FIG. 4, B is a total bit, E _total is total energy, E (i) is an energy corresponding to i channel, and Γ is an SNR gap (= 9.8 +). r _m -r _c ), B _i is the bit value corresponding to i channel, m is the index number of the minimum energy to increase 1 bit, n is the index number of the maximum energy to decrease 1 bit, and N is The maximum value of the channel used, e _i is the energy required to increase or decrease 1 bit of the i channel.

The operation of the bit allocation method of the digital subscriber line according to the present invention configured as described above will be described in detail with reference to the accompanying drawings.

First of all, during the initialization of xDSL modem, the optimized bit is allocated to each allocated channel.

Therefore, in the present invention, in order to minimize the computational speed of the EF (efficiency) algorithm, which is the preprocessing of the E-Tightness (ET) algorithm and the B-Tightness (BT) algorithm of the Campello algorithm, general channel modeling is performed to obtain the closest bit value. Set to an initialization value. After the DSL modem is installed, the environment of the channel is changed little by little due to external factors. When the modem is operated again with the bit allocation table 72 created by the initial iteration, the previously updated bits are used. The update time can be minimized based on the allocation table 72.

In addition, when the Chu's algorithm is used, the energy efficiency is lower than that of the Campello algorithm, thereby reducing the time required for bit allocation, thereby preventing the problem caused by the time delay that may occur during the initialization of the DSL modem.

In addition, the present invention allows the DSP 70 to perform within a given time while training from other blocks in the overall structure of the actual ADSL modem. The DSP 70 reads a noise power value calculated from an external input / output device to calculate an SNR value, and performs a bit allocation algorithm more efficiently since the DSP 70 does not go through a sorting process of the algorithm. Can be.

Therefore, the hardware burden can be reduced by this software process.

Referring to the operation of the present invention in more detail as follows.

Therefore, in the operation of the present invention, in applying the Campello algorithm with respect to bit allocation during the initialization of the ADSL modem, the initialization bit value of the EF algorithm is approximated to each channel in order to improve the processing speed. Assigns, maintains the value of the optimized bit allocation table 72 obtained by performing the EF algorithm, and updates the bit allocation value of the optimized bit allocation table 72 again when the ADSL modem is reinitialized to converge the EF algorithm. To improve speed.

FIG. 5 is a graph showing an SNR value according to general channel characteristics, and a general channel shape has the same shape as the SNR value of FIG. 5.

Therefore, if you train the initialization bit to approximate the channel for bit allocation, you can converge in the shortest time. Since a general bit form has a distribution form as shown in FIG. 5, an initial bit value is set to a value as shown in FIG. 5, and training is performed.

And the SNR value of the channel can be changed a lot by the influence of the distance and the outside of the channel. Therefore, after training with the initialization value, it is optimized according to the change of the channel by updating the initialization value with the newly obtained bit value. It is possible to quickly estimate the allocation of allocated bits.

Accordingly, the bit allocation performance can be improved by reducing the number of iterations of the Campello algorithm.

The method of the EF algorithm is optimized by increasing the bits of the bin with the lowest energy when each subchannel increases the current bit by one bit, and decreasing the bits of the subchannel with the highest energy when decreasing one bit. Iteration is performed while obtaining the allocated bit allocation. In this case, when the initial bit value is approximated with the optimized bit allocation to reduce the iteration, the convergence speed is reduced by that, and thus, as shown in FIG. 4, in order to match the target energy with the optimized bit allocation.

Therefore, in FIG. 4, the preprocessing process of the Campello EF algorithm is performed, and the bit and gain values of the used channel are finally obtained by performing the ET algorithm.

The EF algorithm has an SNR value and the initial bit setting value B = {b ₀ , b ₁ ,. … , b _i-1 } = {4, 4,... … , 4} or the EF algorithm is pre-defined by approximating the general channel values. The assigned bit values are then optimized B '= {b' ₀ , b ' ₁ ,... … , b ' _i-1 }. Since the initial bit value is updated while the EF algorithm is executed, the convergence speed of the EF algorithm is minimized by referring to the updated bit value when the ADSL modem is operated again. That is, the number of iterations in the ST53 is reduced among the parts of updating the EF algorithms of the reference numbers ST53 and ST54 in FIG. 4.

After the execution of the ST53 condition, the updated bit values are replaced with the new B '= {b' ₀ , b ' ₁ ,... … , b ' _i-1 }. The ET algorithm is executed from the value of B ' _i , and finally bit allocation is performed to obtain a bit value and a gain value.

In addition, in reference numerals ST55 to ST59 of FIG. 4, since only the bit is optimized in the EF algorithm but does not consider the total energy of the channel, the total energy S is obtained using the bit values obtained from the EF algorithm to match the total energy. We do this until the energy (S) value is equal to the energy (E _total ) assigned to the channel, or until the "E _total -S" value, i.e. the difference between the two energies, is less than the minimum energy to increase one bit of the channel. do.

Finally, the operation is completed by performing energy rescaling to compensate for the error of the total energy of the obtained energy.

As a result, the bit allocation table 72 and the gain table 71 are obtained, which plays an important role in determining the transmission rate of the ADSL modem.

Therefore, when the ADSL modem performs initialization, the SNR unit 30 calculates an SNR value using the data received from the FFT 10. With the calculated SNR value, the DSP 70 performs the Campello algorithm with the value of the bit allocation table 72 stored in the memory.

In addition, the bit allocation table 72 and the gain table 71 exchange the table values between the exchange and the base station in the initialization mode, thereby completing communication setup.

As such, the present invention minimizes the calculation amount by updating the bit table value initialized during the initialization of the xDSL modem every time the xDSL modem is operated.

Although the preferred embodiment of the present invention has been described above, the present invention may use various changes, modifications, and equivalents. It is clear that the present invention can be applied in the same manner by appropriately modifying the above embodiments. Accordingly, the above description does not limit the scope of the invention as defined by the limitations of the following claims.

As described above, the bit allocation method of the digital subscriber line according to the present invention updates the initialized bit table value every time the xDSL modem operates to allocate the optimized bit to each allocated channel during the initialization process of the xDSL modem. By doing so, it is possible to minimize the amount of computation.

Claims (2)

Performing a channel modeling to set a bit value close to each channel as an initialization value; A second step of performing an efficiency operation by iteration after the first step; And performing a third step of performing energy tightness and bit tightness after the second step. The method of claim 1, wherein the first step, And re-initializing the optimized bit table value when the digital subscriber line modem is operated.