WO2008017274A1 - Method and device for controlling line communication quality - Google Patents

Abstract

A method and device for controlling line communication quality. In the method, the subscriber line modem transmits data during the iterative water filling, and data transmission rate thereof adopts the data transmission rate determined by the subscriber line which has been degraded during every water filling cycle of the iterative water filling. An embodiment of present invention overcomes the drawbacks of prior art, the subscriber line modem transmits data during every water filling cycle of iterative water filling, bit table corresponding to data transmission rate thereof adopts the overmeasure which is the transmission powers Sk n of respective subcarrier TONE occurred during every waterfilling cycle of iterative water filling and which makes the value of objective function Wn bkn - λn Skn to be the largest minus the noise power of other lines which has been increased. Therefore, the problem of working instability caused by noise changing of other subscriber lines when certain subscriber line is transmitting data during the iterative water filling could be avoided.

Description

 Method and device for controlling communication quality of a line The present application claims priority to a Chinese patent application filed on August 4, 2006 by the Chinese Patent Office, Application No. 200610062019.4, and entitled "A Method for Controlling Communication Quality of Lines" The entire contents of which are incorporated herein by reference. Technical field

 The present invention relates to Digital Subscriber Line (DSL) technology, and in particular to a method and apparatus for controlling line communication quality.

Background technique

 DSL technology is a high-speed transmission technology for data transmission over telephone twisted pair, Unshielded Twist Pair (UTP), including Asymmetrical Digital Subscriber Line (ADSL), very high speed digital Very-high-bit-rate Digital Subscriber Line (VDSL), Integrated Services Digital Network (ISDN)-based Digital Subscriber Line (IDSL) and single-pair high-speed digital subscriber line ( Single-pair High-bit-rate Digital Subscriber Line, SHDSL), etc.

 In various digital subscriber line technologies (xDSL), in addition to DSL for baseband transmission such as IDSL and SHDSL, DSL with passband transmission utilizes frequency division multiplexing technology to enable DSL and traditional telephone services (Platform Old Telephone Service, POTS). Coexisting on the same pair of twisted pairs, where DSL occupies a high frequency band, POTS occupies a baseband portion below 4 kHz, and POTS signals and DSL signals are separated or combined by a splitter/splitter.

The xDSL for passband transmission is modulated and demodulated using Discrete Multi-Tone Modulation (DMT) technology. A system that provides multiple DSL access is called a DSL Access Multiplexer (DSLAM). The system diagram is shown in Figure 1. The D SLAM 120 includes a client transceiver unit 121 and a split/integrator 122. In the uplink direction, the client transceiver unit 121 receives the DSL signal from the computer 110 and amplifies the received signal to transmit the processed DSL signal. To the split/integrator 122; the split/integrator 122 will send and receive orders from the client The DSL signal of element 121 and the POTS signal of telephone terminal 130 are integrated; the integrated signal is transmitted through multiplexed UTP 140, received by split/conformer 151 in the opposite DSLAM 150; the split/integrator 151 will receive The signal is separated, and the POTS signal is sent to a Public Switched Telephone Network (PSTN) 160, and the DSL signal is sent to the central office transceiver unit 152 of the DSLAM 150. The received signal is amplified and sent to a Network Management System (NMS) 170. In the downstream direction of the signal, the signals are transmitted in the reverse order of the above.

 In the existing xDSL standard, BIT (bit) entries and GAIN (gain) entries are used to indicate the number of bits and transmit power that each subcarrier can carry. Bit swapping technology is mainly achieved by adjusting these two entries.

The BIT entry (bit table) is shown in Table 1:

 Table 1

 Each bit table entry b represents the number of bits that can be carried by the corresponding subcarrier TONE on the xDSL line. The standard stipulates that each item cannot exceed 15, and the size of the number of bits determines the line rate of the corresponding sub-band, and adjusts the bit table entry. The size of the sub-band can be changed. The NSC in the table is short for Number of SubCarrier, which is the number of subcarriers.

 A BIT table determines a unique line rate. Conversely, the line rate can be obtained by a number of different BIT entries. For some precondition, there is a unique optimal BIT table.

The GAIN entry (gain table) is shown in Table 2:

 Table 2

Wherein, each gain entry g represents the data transmission power of the corresponding sub-band TONE on the xDSL line. The size of the power determines the amount of data carried in the corresponding sub-band, and adjusts the size of the gain entry. The data transmission power of the sub-band can be changed.

 Because the user cable basically contains multiple pairs (25 pairs or more) of twisted pair, a variety of different services may be run on each twisted pair, and various types of xDSL may cause crosstalk between each other when working simultaneously. Some lines can experience a sharp drop in performance due to crosstalk. When the line is long, some lines cannot open any form of DSL service at all.

 With the increase in the frequency band used by xDSL technology, crosstalk, especially in the high frequency band, has become increasingly prominent. 2A and 2B are schematic diagrams of near-end crosstalk and far-end crosstalk in xDSL, respectively. As shown in FIG. 2A, port 1 and port 2 of the DSLAM 210 are respectively connected to a remote terminal unit (RTU) 211 through a cable. Since xDSL uplink and downlink channels are used for frequency division multiplexing, near-end crosstalk (NEXT) ) does not cause much harm to the performance of the system; as shown in Figure 2B, port 1 and port 2 of the DSLAM 220 are connected to the RTU 221 via a cable respectively. Since the xDSL uplink and downlink channels are frequency division multiplexed, the far end crosstalk is used. (FEXT) can seriously affect the transmission performance of the line. When multiple users in a bundle of cables are required to open xDSL services, some line rates will be low, performance is unstable, or even impossible to open due to FEXT, resulting in a lower DSLAM outline rate. Especially in the case of a mixed application of Central Office/Remote Terminal (CO/RT), the short-line has a large influence on the crosstalk of the long line, and the influence of the second line 32 on the first line 31 in FIG. It is much larger than the influence of the first line 31 on the second line 32.

 In a communication model of N users and K TONEs using Discrete Multi-Tone (DMT), the signal transmission on each TONE can be independently expressed as:

公式 (2) 其中 表示第《条线路在第 A个子载波上的传输函数； 表示第 m条线 路在第 A个子载波上对第《条线路的串扰函数； ^表示第《条线路在第 A个子载 波上的噪声功率； 表示第《条线路在第 A个子载波上的发送功率； 表示第 m 条线路在第 A个子载波上的发送功率。 y _k = _k x _k + a _k formula ( ₁₎ Under normal circumstances, the receiving end of each xDSL modem (modem) will interfere with itself by other modems as noise, then the "users can be on the Ath The data rate reached can be calculated using the Shannon channel capacity formula:

Equation (2) where represents the transfer function of the "th line" on the A-subcarrier; represents the m-th line The crosstalk function of the line on the Ath subcarrier; ^ indicates the noise power of the "the line on the A subcarrier; the transmission power of the "the line" on the A subcarrier; indicates the mth The transmit power of the line on the A-subcarrier.

 It can be seen from equation (2) that crosstalk seriously affects the transmission capacity of the line, that is, the line rate is reduced.

 Using frequency management to study the spectral characteristics of various DSL modulation technologies and crosstalk between various DSLs, respectively, specify Power Spectral Density (PSD), transmission power, etc., to achieve so-called spectrum compatibility. Dynamic Spectrum Management (DSM) is a method for dynamically managing the power spectrum. It adjusts the spectrum control parameters in real time or periodically without violating spectrum compatibility, so that the system always works in the best state. .

 Specifically, the DSM automatically adjusts the transmission power on each modem in the network to achieve the purpose of eliminating crosstalk, that is, by adjusting the transmission power to achieve a maximum between each modem to achieve its own rate and reduce the crosstalk effect on other modems. balance.

 Specifically, DSM technologies include Iterative Water Filling (IFF) and Optimal Spectrum Balance (OSB).

The IWF method only considers the influence of the change of "the transmission power of the A-th TONE on the user line" on the "user line rate", and does not consider the interference to other lines from the perspective of optimization. The objective function can Written as Λ _≡ = w _n b _k "- ^ ΐ , where ^w "and ^Λ " respectively represent the number of bits in the nth cycle and the weight coefficient of the transmit power, indicating the bit carried by the second TONE on the "user line" number. The existing iterative water injection process is shown in Figure 4: There are a total of N users, each user has K TONE. Set an initial value, such as: ^w - ^{= l} , ^λ - ⁼ \ First select a user (can be the first user) to repeat the following loop:

The first is the inner loop, step 410: using each of the user's TONE ( ^{= 1} , ² , ···, ) The value of ( ^{K = 2} ' ^K ) which maximizes the value of _W? A" - I is obtained by the method. After each transmission power of each TONE is calculated, the BIT table can be calculated based on the transmission power and the noise power of the receiving end. 420. When the transmit power spectrum on all TONEs has been found, the value is updated.

The rules for updating the value of _η , Κ _η are: First, determine whether the sum of the transmission powers of all TONEs has exceeded the total transmission power limit ( ^P « ). If not, press (∑^ ^{3⁄4! _} ) ^]+ Update the A value, which indicates the target rate of the "strip channel; otherwise, press ^[/1 " (∑^ ^{_ 3} ") ^]+ to update the A value. Step 430, determine whether the updated value is the same as the previous value. If they are not the same, continue to execute the inner loop until the same, indicating that they have converged. The main purpose of the inner loop is to find the power that the corresponding modem should transmit and the corresponding number of transmittable bits when the target function takes the maximum value.

 The second user (which may be the second user) is selected to repeat the above inner loop, and finally until the user used is completed in turn, and if the result of the first round does not converge, then the above process is continued until convergence.

 If there are N users, then N users cycle through the functions of the inner loop in a certain order. N users continuously cycle, and finally reach a balance point, which is a local optimal solution of the IWF.

 In the above iterative water injection process, each line is required to complete the search function of the power spectrum that maximizes the objective function in a certain order, that is, a water injection process. As shown in Figure 5, it can be in the ascending order of C01, C02, C03 to COn, or it can be decremented or any other specified order. If you want to complete in a certain order, it means that you need an overall timing control circuit in the implementation process to complete the real-time timing control. If the CO end to be controlled is in one line, the sequential circuit is the internal control of the DSLAM 50; but if the CO end to be controlled is not in a DSLAM 50, then the interface between the DSLAMs must be provided, thereby making the entire implementation method very complicated.

Because the process of convergence in the iterative water injection cannot be correctly predicted and the convergence time is long, The initial value is related to the actual situation. Therefore, it is impossible to determine how long the water injection process of the entire IWF takes. If the line does not perform normal communication during the whole iteration, the user waits for a long time.

 In the process of implementing the present invention, the inventor has found through research that: if the entire iteration water injection has not been completed, if a certain line uses the data transmission corresponding to the BIT entry calculated by the loop in the line and the corresponding GAIN entry. The ability to communicate, then the other lines are still performing the iterative water injection process, while the transmission power of other lines is constantly changing during the iterative water injection process, and the resulting crosstalk is constantly changing. In other words, the signal-to-noise ratio of the line is constantly changing, which will lead to unstable operation of the line.

Summary of the invention

 Embodiments of the present invention provide a method and apparatus for controlling communication quality of a line, which can prevent the user line modem from being unstable in communication while performing iterative water injection.

 The embodiment of the invention uses the following technical solutions:

 A method of controlling line communication quality includes the following steps:

 In the process of iterative water injection, the subscriber line modem determines the bit table Bi according to the transmission power of each subcarrier of each subscriber line generated by each water injection cycle;

 The data transmission rate corresponding to the bit table entry in the Bi table is subtracted from the data transmission rate due to the noise increase margin, and a new Bi table is updated, and the data corresponding to the bit table entry in the new Bi table is updated. The transmission rate transmits data on each subcarrier.

 A method for controlling communication quality of a line, characterized in that it comprises:

 In the process of iterative water injection, the subscriber line modem determines the bit table Bi according to the transmission power of each subcarrier of each subscriber line generated by each water injection cycle;

 Determine whether the iterative water injection has converged, if the iterative water injection does not converge, then

 The data transmission rate corresponding to the bit table entry in the Bi table is subtracted from the data transmission rate due to the noise increase margin, and a new Bi table is updated, and the data corresponding to the bit table entry in the new Bi table is updated. The transmission rate transmits data on each subcarrier.

 A device for controlling the communication quality of a line, comprising:

An iterative water injection unit for implementing a water injection cycle of iterative water injection of a subscriber line; An obtaining unit, configured to obtain a bit table Bi determined according to a transmission power of each subcarrier of each subscriber line generated by each water injection cycle of the iterative water injection unit;

 And an updating unit, configured to subtract a data transmission rate corresponding to the bit increase in the Bi table obtained by the obtaining unit by a data transmission rate of the noise increase margin, and obtain a new Bi table;

 a transfer unit, configured to implement the water injection cycle in the iterative water injection unit, to

The data transmission rate corresponding to the bit table entry in the Bi table transmits data on each subcarrier.

 In the embodiment of the present invention, the user line modem transmits data at the same time in each iteration cycle of the iterative water injection, and the bit table item of the transmission data rate uses the maximum value of the target function ^—^ generated according to the water injection cycle of the iterative water injection. The transmission power of each subcarrier TONE is subtracted from the margin due to the noise increase of other lines, which can avoid the instability of the operation of one user line when the data is transmitted during the iterative water injection due to other user line noise changes. problem. DRAWINGS

 1 is a schematic diagram of an xDSL system in the prior art;

 2A and 2B are schematic diagrams of xDSL crosstalk in the prior art;

 3 is a schematic diagram of crosstalk in a scenario of a CO/RT hybrid application in the prior art;

 4 is an iterative water injection flow chart in the prior art;

 5 is a schematic diagram of an iterative water injection according to a certain timing in a plurality of user lines in the prior art; FIG. 6 is a flowchart of a method according to an embodiment of the present invention;

 FIG. 7 is a structural block diagram of an apparatus according to an embodiment of the present invention.

In the embodiment of the present invention, the user circuit is in the inner loop of the iterative water injection (the solution described in the embodiment of the present invention can be applied to the process of completing the iterative water injection in a certain order for each user line, and can also be applied to each The user line independently completes the iterative water injection process. In order to distinguish from the prior art, in the following, the water injection cycle is used to refer to the inner circulation of a certain subscriber line. During the process of iterative water injection, each data injection cycle simultaneously transmits data and transmits data. The bit table is generated by each injection cycle according to the iterative water injection. By making the transmission power of each subcarrier TONE with the largest value of the objective function ^w "minus the margin due to the noise increase of other lines, it is possible to avoid the other users when transmitting data in the process of iterative water injection. Line noise changes cause problems in their operation.

 The function module for completing the iterative water injection process is located at the CO end, and the detailed process of the embodiment of the present invention is illustrated by taking a water injection cycle of a certain subscriber line as an example.

 After the CO and the Customer Premises Equipment (CPE) are started, the handshaking, initialization, and other functions are completed in accordance with the relevant standards until the normal operation (showtime). The relevant standard mentioned here means that if the CO and CPE support ADSL, the above process is completed by the ADSL standard. If the CO and CPE support the second generation VDSL (VDSL2), the VDSL2 standard is used to complete the above process. When the CO and CPE complete the above process, they obtain parameters such as a Bi (BIT) table, a Gi (GAIN) table, and noise of each subcarrier.

 The implementation process of the iterative water injection described in the embodiment of the present invention is as shown in FIG. 6, and includes the following steps:

601. At the same time of iterative water injection, the subscriber line (assumed to be the first subscriber line) simultaneously transmits data, and at this time, the modem of the subscriber line uses the entries in the Gi table obtained by the above initialization process as the transmission power of each TONE for transmitting data. At the same time, the table in the Bi table obtained by the above initialization process is subtracted from the value of the noise increase of other lines Binew as the transmission rate of each TONE transmitting the data;

 At the same time, the subscriber line begins to iterate the water injection cycle of the water, for each TONE of the user

( k = l, 2, -, K _)? Use the enumeration method to find the value of ( Α = 1, 2, · · ·, ) that maximizes the value of Α, and calculate the transmission power of each TONE, based on the transmission. The power and the noise power at the receiving end can be used to calculate a new Bi table, and a new Gi table can be obtained.

602. The modem of the subscriber line uses a new Bi table entry minus a value due to the noise increase of other lines. Binew is used as the transmission rate of each TONE for transmitting data, and uses the entry in the new Gi table. As the individual TONE transmit power for transmitting data; at the same time, the subscriber line begins to iterate the next water injection cycle of water injection, only after iterative water injection After the rule is updated, the value of each TONE is calculated for each TONE of this user ( k = l, 2 , K using the enumeration method to find the value that maximizes the value ( Α = 1, ² , · · ·, ) Then, according to the transmit power and the noise power of the receiving end, a new Bi table can be calculated, and a new Gi table can be obtained. 603. If the iterative water injection converges, the modem of the user line uses the latest water injection cycle. The new Bi table entry is subtracted from the value of the noise increase of other lines Binew as the transmission rate of each TONE transmitting the data, and the entry in the new Gi table obtained in step 601 is used as the transmission data. Each TONE transmits power, and the subscriber line enters normal operation;

 If the iterative water injection does not converge, step 602 is repeated, and each time the user line performs an iterative water injection cycle to obtain a new Bi and Gi, the modem of the subscriber line uses the updated Binew and Gi to complete the data transfer.

 How to judge that the iteration water injection has converged, and how to calculate the Binew table from the Bi table can be implemented by the following two schemes, as follows:

 The first scheme: Compare the transmit power variance or the bit number variance of two adjacent times before and after

 The convergence condition is directly judged. If the convergence modem is used, the Bi table is used directly. If the modem is not converged, the Binew table is used.

 If the variance of the power spectrum calculated twice adjacently is relatively small or the variance of Bi calculated twice adjacently is relatively small, it indicates that convergence has occurred.

即可 满足要求。 一般的情况下， 有 6dB的裕量已经比较足够， 所以取 Δ_; =2。 当然 也可以取其他的值。 Taking the variance of Bi as an example: Let Bi be β calculated in the previous time, and Bi calculated as B2 _{t in the} latter time, then the variance of the two Bi tables is ( . - 32 _; ) ² . If the variance value is less than or equal to the determined threshold, for example 1, the iteration is considered to have converged. In order to further confirm whether the convergence is convergent, the variance value may be calculated multiple times (for example, 7 times). When the variance values of the plurality of consecutive times satisfy the condition, it is judged that the iteration water injection has converged. When it is judged that the iterative water injection has converged, the final Gi and Bi tables are used for normal work. The Binew table is calculated from the Bi table, where the value of Binew can be calculated using the following scheme: _ = max(@ - Δ _; ), 0), where ζ· =1, 2, 3, · ··, . Here Δ _; = 2 , it is also possible to take any positive integer less than 15, and each may be different. It means that a margin is added on the basis of Bi. When the transmission power of other lines changes during the iterative water injection, the noise of the line also changes, and may increase or decrease. As long as the amount of increase is not more than 3

Can meet the requirements. In general, a 6dB margin is already sufficient, so take Δ _; =2. Of course, other values can also be taken.

 The second scheme: Determine whether to converge in the process of calculating the Binew table from the Bi table.

The convergence condition is not directly judged, and the judgment of the convergence condition is expressed in the process of calculating Binew from the Bi table. The calculated Binew table converges to the Bi table according to the convergence of the iterative water injection. In other words, when the iteration water converges, the calculated Binew table is basically equal to the Bi table. The Bmew table in this scheme is also calculated according to the formula ^^ ^{= max} ((A- )' ⁰ ), the difference is Δ _; the value is not a constant, but a number that changes with the convergence of the iterative water injection . When the iterative water flooding converges, all ^ values should tend to zero. Therefore, the Binew table in this scheme can be found using the following formula: ^ = ^max (( - )'0) ,

其中 和 分别为前后两次计算出的发送功率谱。 当迭代 注水收敛后， 前后两次注水量应该基本相同， 这样 Δ.也就基本趋近于零。 此外需要说明的是，本领域普通技术人员可以理解实现上述实施例方法中 的全部或部分步骤是可以通过程序指令相关的硬件来完成，所述的程序可以存 储于一计算机可读取的存储介质中， 所述的存储介质，如： ROM/RAM、磁碟、 光盘等。 Δ _;

The sum is the transmission power spectrum calculated twice before and after. When the iterative water injection converges, the water injection volume should be basically the same before and after, so that Δ. is basically close to zero. In addition, it should be understood that those skilled in the art can understand that all or part of the steps of implementing the above embodiments may be completed by hardware related to program instructions, and the program may be stored in a computer readable storage medium. The storage medium is, for example, a ROM/RAM, a magnetic disk, an optical disk, or the like.

FIG. 7 is a structural block diagram of an apparatus according to an embodiment of the present invention, including an iterative water injection unit 710, The obtaining unit 720, the updating unit 730, and the transmitting unit 740: wherein:

 An iterative water injection unit 710, which implements a water injection cycle process of iterative water injection of the user line;

 The obtaining unit 720 is configured to obtain a Bi table determined according to a transmit power of each subcarrier of each user line generated by each water injection cycle of the iterative water injection unit 710;

 The updating unit 730 is configured to update the data transmission rate corresponding to the bit table entry in the Bi table acquired by the obtaining unit 720 by the data transmission rate due to the noise increase margin, and update the new Bi table, that is,

Binew table; the data transmission rate due to noise increase margin is a value corresponding to two bits;

 The transfer unit 740, in the process of implementing the water injection cycle by the iterative water injection unit 710, to update the unit

The data transmission rate corresponding to the bit table entry in the Binew table obtained by 730 transmits data on each subcarrier.

 In addition, the foregoing embodiment may further include a determining unit 750, configured to determine whether the iterative water injection is converged; when the determining unit 750 determines that the iterative water injection does not converge, the obtaining unit 720 generates each of the current water injection cycles according to the iterative water injection. Determining the Bi table by the transmission power of the subscriber line in each subcarrier; and updating the data transmission rate corresponding to the bit table entry in the Bi table acquired by the obtaining unit 720 by the updating unit 730 by subtracting the data transmission rate due to the noise increase margin, updating Obtaining a Binew table; the transmitting unit 740 transmits data on each subcarrier in a data transmission rate corresponding to the bit table entry in the Binew table obtained by the updating unit 730 in the process of implementing the water injection cycle by the iterative water injection unit 710; When determining the iterative water injection convergence, the transmitting unit 740 directly transmits data on each subcarrier with the data transmission rate corresponding to the bit table entry in the Bi table determined by the obtaining unit 720.

The determining unit 740 may determine whether to converge by comparing the power consumption variances of two adjacent transmission powers, or whether the data transmission rate variance corresponding to the bit table entries in the Bi table is less than or equal to the determined threshold value, for example, whether the variance value is compared. Less than or equal to 1, if yes, it is determined that the iteration water injection has converged; otherwise Make sure the iteration water injection does not converge.

 It should be noted that, before the user line completes the iterative water injection first water injection cycle, the updating unit 730 may subtract the data transmission rate corresponding to the bit table entry in the Bi table generated by the initialization by the noise increase margin. The amount of data transfer rate is updated to get the Binew table.

 As described in the background art, the process of iterative water injection is that each user line is completed in a certain order, but according to the theory of the game, the water injection process is not completed in accordance with the prescribed order (each user line is completed independently at the same time). The water injection process) also achieves the final equilibrium point, and the convergence of the entire iterative process is faster, meaning that the entire process can be completed in a shorter time than the sequential method described above.

 In the embodiment of the present invention, the user line modem transmits data at the same time in each iteration cycle of the iterative water injection, and the bit table item of the transmission data rate uses the maximum value of the target function ^—^ generated according to the water injection cycle of the iterative water injection. The transmission power of each subcarrier TONE is subtracted from the margin due to the noise increase of other lines, which can avoid the instability of the operation of one user line when the data is transmitted during the iterative water injection due to other user line noise changes. problem.

 The technical solution described in the embodiments of the present invention can be applied to the process of completing the iterative water injection in turn in each user route of the iterative water injection in a certain order, or applicable to the completion of the water injection process in the order of each user line.

Claims

Rights request  A method for controlling communication quality of a line, characterized in that it comprises:  In the process of iterative water injection, the subscriber line modem determines the bit table Bi according to the transmission power of each subcarrier of each subscriber line generated by each water injection cycle;  The data transmission rate corresponding to the bit table entry in the Bi table is subtracted from the data transmission rate due to the noise increase margin, and a new Bi table is updated, and the data corresponding to the bit table entry in the new Bi table is updated. The transmission rate transmits data on each subcarrier.  2. The method according to claim 1, wherein said subscriber line modem uses bits in the Bi table generated by initialization before said subscriber line completes said iterative water injection first water injection cycle The data transmission rate corresponding to the entry minus the data transmission rate due to the noise increase margin is transmitted.  3. The method according to claim 1, further comprising:  The user line uses the iterative water injection to transmit data of the transmission power of each subcarrier of each subscriber line generated by each water injection cycle.  4. The method according to claim 1, wherein the data transmission rate due to the noise increase margin is a value corresponding to two bits.  The method according to claim 1, wherein the user line performs the iterative water injection process in turn according to a certain sequence.  6. The method of claim 1 wherein said user line independently performs said iterative water injection process.  7. A method of controlling communication quality of a line, characterized by comprising:  In the process of iterative water injection, the subscriber line modem determines the bit table Bi according to the transmission power of each subcarrier of each subscriber line generated by each water injection cycle;  Determine whether the iterative water injection has converged, if the iterative water injection does not converge, then  The data transmission rate corresponding to the bit table entry in the Bi table is subtracted from the data transmission rate due to the noise increase margin, and a new Bi table is updated, and the data corresponding to the bit table entry in the new Bi table is updated. The transmission rate transmits data on each subcarrier. 8. The method according to claim 7, further comprising: if iterating water injection Convergence, data is transmitted on each subcarrier at a data transmission rate corresponding to the bit table entry in the Bi table.  The method according to claim 7 or 8, wherein the determining whether the iterative water injection has converged specifically comprises:  Compare the transmit power variances of two adjacent times, or whether the data transmission rate variance corresponding to the bit table entry in the Bi table is less than or equal to the determined threshold, and if so, determine that the iterative water injection has converged; otherwise, it is determined that the iterative water injection does not converge.  10. The method according to claim 9, wherein the threshold value is 1.  11. A device for controlling communication quality of a line, characterized by comprising:  An iterative water injection unit for implementing a water injection cycle of iterative water injection of a subscriber line;  An obtaining unit, configured to obtain a bit table Bi determined according to a transmission power of each subcarrier of each user line generated by each water injection cycle of the iterative water injection unit;  And an updating unit, configured to subtract a data transmission rate corresponding to the bit increase in the Bi table obtained by the obtaining unit by a data transmission rate of the noise increase margin, and obtain a new Bi table;  a transfer unit, configured to implement the water injection cycle in the iterative water injection unit, to The data transmission rate corresponding to the bit table entry in the Bi table transmits data on each subcarrier.  12. The apparatus according to claim 11, wherein said updating unit is configured to initialize the generated Bi table before said user line completes said iterative water injection first water injection cycle The data transfer rate corresponding to the bit table entry is subtracted from the data transfer rate due to the noise increase margin, and a new Bi table is updated.  13. The device according to claim 11, further comprising:  a determining unit, configured to determine whether the iterative water injection is converged;  The transmitting unit is configured to: when the iterative water injection unit implements the water injection cycle, when the determining unit determines the iteration water injection convergence, the data transmission rate corresponding to the bit table item in the Bi table is in each subcarrier Transmitting data; when the determining unit determines that the iterative water injection does not converge, transmitting data on each subcarrier at a data transmission rate corresponding to the bit table entry in the new Bi table. 14. The apparatus according to claim 13, wherein the determining unit compares a variance of a transmission power of two adjacent times, or a variance of a data transmission rate corresponding to a bit entry in the Bi table. Whether it is less than or equal to the determined threshold, and if so, it is determined that the iterative water injection has converged; otherwise it is determined that the iterative water injection does not converge.  15. Apparatus according to claim 14 wherein said threshold is one.  The apparatus according to claim 11, wherein the data transmission rate due to the noise increase margin is a value corresponding to two bits.