KR20010074385A - Method of and apparatus for processing bit swap in the ADSL system - Google Patents

Abstract

PURPOSE: A method and apparatus for processing a bit swapping in an asymmetrical digital subscriber line(ADSL) is provided to improve a communication efficiency by providing a data service in case that an external channel environment is changed and quickly processing the bit swapping according to the change of the external channel environment. CONSTITUTION: An AOC(ADSL Overhead Control) processing unit(402) stores an FEC(Forward Error Correction) result received from an FEC decoder(221) and executes an AOC protocol for starting a bit swapping when an error is generated in an FEC code word with a uniform quantity during a unit time, or the FEC code word which does not correct the error with the uniform quantity is generated during the unit time. The AOC processing unit(402) reallocates bits allocated in each DMT(Discrete Multi-Tone) to store the reallocated bit in a new bit allocating table and transmits a bit swapping request message to a DMT control unit. The AOC processing unit(402) transmits a superframe counter designated in a bit swapping acknowledge message and the new bit allocating table to a constellation decoder(222) using a bit swapping module when the bit swapping acknowledge is received from the DMT control unit. A table swapping unit(404) transmits the superframe counter and the new bit table to a constellation encoder/decoder when a bit table swapping is needed as a result of the AOC processing unit(402). A bit table storing unit(406) stores information of the new bit table applied to a constellation encoding/decoding and a conventional bit table.

Description

Method and apparatus for processing bit swap in asymmetric digital subscriber network system

The present invention relates to an asymmetric digital subscriber network system (ADSL) of the Discrete Multi-Tone (DMT) method, and more particularly, to exchange bits allocated to subcarriers of a DMT channel according to a channel state in a digital subscriber network system. The present invention relates to a method and apparatus for processing bit swapping.

In general, an asymmetrical digital subscriber line system (ADSL: Asymmetrical Digital Subscriber Line) focuses on the asymmetrical traffic between the network and the subscriber, and the downlink channel transmitted from the network to the subscriber allocates a wide bandwidth for high-speed transmission. It is a technology that efficiently uses the capacity of transmission line by allocating narrow bandwidth to uplink channel transmitted from network to network. That is, digital subscriber devices such as ADSL (G.dmt) and UADSL (G.lite) are transmission methods that can provide transmission speeds of several hundred Kbps to several Mbps using existing telephone lines. It can provide data rates of 640 Kbps, downlink 32Kbps to 6144Kbps, and UADSL can provide data rates of upstream 32Kbsp to 512 Kbps and downlink 64Kbps to 1536Kbps.

Such a digital subscriber device has a difference in data rate that can be provided depending on the external channel environment and the distance between the digital subscriber devices. The better the channel environment, the shorter the distance between the digital subscriber devices can provide a higher data rate. . The distance between the digital subscriber devices does not change after the first digital subscriber device (ATU-R: ADSL Transceiver Unit-Remote) and the network digital subscriber device (ATU-C: ADSL Transceiver Unit-Central Office) are connected. Even after the subscriber device is first connected, the data rate that can be provided by the bits assigned to each Discrete Multi-Tone (DMT) channel may vary due to temperature, humidity, and other external interference. have. Accordingly, there is a need for a bit swapping method that can efficiently and quickly adjust the data rate that each DMT channel can provide while providing data services according to the change of the external channel environment.

According to the present invention, after the subscriber side digital subscriber unit (ATU-R) and the network side digital subscriber unit (ATU-C) are connected for the first time, each DMT (Discrete Multi-) according to the change of the external channel environment is provided. Tone) It is an object of the present invention to provide a bit swapping processing method and apparatus that can efficiently and quickly adapt to changes in an external channel environment while providing a data service even when a data rate that a channel can provide is changed. .

1 is a block diagram illustrating an exemplary ADSL system to which the present invention may be applied;

2 is a block diagram of a transmission and reception function for processing a bit exchange according to the present invention;

3A and 3B are detailed configuration diagrams of the DMT engine shown in FIG. 2;

4 is a detailed configuration diagram of the DMT control unit shown in FIG. 2;

5 is a format of a general superframe in ADSL,

6A and 6B are flowcharts illustrating a procedure for processing bit exchange according to the present invention.

* Explanation of symbols for main parts of the drawings

210: DMT receiver 220: DMT receiver

211: FEC encoder 212, 222: DMT engine

213, 223: DMT control unit 221: FEC decoder

302, 312: tone array unit 304: constellation encoder

306: IFFT 308: FFT

310: constellation decoder 402: AOC processing unit

404: table exchange unit 406: bit table storage unit

In order to achieve the above object, the method of the present invention comprises a transmitting unit and a receiving unit to transmit a data signal to a data network through a telephone line, and to transmit a voice signal to a public telephone network through a telephone line. A bit exchange method of claim 1, further comprising: detecting error information of a received superframe by the receiver; Comparing the detected error information with a preset reference value and transmitting a bit exchange request message to the counterpart when the reference value is out of the reference value; And exchanging a bit table when a bit exchange response message is received, and transmitting a response message to the counterpart and exchanging the bit table when the transmitter receives the bit exchange request message.

In addition, in order to achieve the above object, the apparatus of the present invention, an asymmetric digital subscriber network including a transmitter comprising a FEC encoder, a DMT engine, and a DMT control unit, a receiver comprising a DMT engine, an FEC decoder, and a DMT control unit. 10. A system comprising: bit table storage means for storing each bit table with each DMT control unit; In the receiving process, when the error information received from the FEC decoder is out of the reference value, the bit exchange request message is transmitted to the counterpart according to a predetermined protocol, and when the bit exchange response message is received from the counterpart, the bit table exchange is instructed. An AOC processing unit for transmitting a bit exchange response message and instructing a bit table exchange according to a predetermined protocol when a bit exchange request message is received in the process; And a table exchange unit that reads the bit table from the bit table storage unit and provides the bit table exchange instruction to the DMT engine when the bit table exchange instruction is received from the AOC processing unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an overall configuration diagram of a typical asymmetric digital subscriber network system to which the present invention can be applied. The system includes a telephone station system 110 installed in a telephone company CO and an indoor system 120 installed in a subscriber home. do. The telephone station system 110 includes an ADSL multiplexer 111, a telephone station ADSL transceiver (ATU-C: 113a to 113n), and a splitter 115a to 115n, wherein the ADSL multiplexer 111 is a data communication network 104. ) And the STM-1 system, and the voice signals separated by the splitters 115a to 115n are transmitted to the public telephone network (PSTN) 106. The indoor system 120 is composed of splitters 121a to 121n, an ADSL transceiver (ATU-R: 123a to 123n), a personal computer (PC: 125a to 125n), and a general telephone (POTS) through a single telephone line. ) Can be connected to the public telephone network 106, and the computer (PC) can be simultaneously connected to the data network.

The ADSL system is a device for providing a high speed digital transmission function using a two-wire subscriber line installed between a subscriber and a telephone company. However, since the telephone subscriber line used is operated for the Plain Old Telephone Service (POTS), the ADSL transmission signal should be divided in the frequency band so as not to affect the telephony signal at all. That is, since the voice area used in the existing telephone is 4KHz or less, after allocating a high frequency band as a band for data communication, the voice signal and the data signal do not overlap each other by using a modulation technique of DMT or CAP.

In Fig. 1, ADSL Transceiver Unit-Central office end: 113a-113n (ATU-C) is an ADSL transceiver at a telephone station, and ADSL Transceiver Unit-Remote terminal end: 123a-123n (ATU-R) is an ADSL at a subscriber side. It is a transceiver. The splitters 115a to 115n and 121a to 121n are high-pass filters for blocking a voice (POTS) signal and separate the voice signal and the data signal. In addition, the data signal has a full-duplex communication function, but has an asymmetric structure in which the amount of communication in the downward direction is larger than that in the upper direction. For example, the transmission rate of the uplink channel from the subscriber to the network is 32K to 800 Kbps, while the transmission rate of the downlink channel transmitted from the network to the subscriber is 32K to 9 Mbps.

On the other hand, ADSL signal modulation methods include 'CAP (Carrierless AM / PM)' and 'DMT (Discrete Multi Tone)'. DMT is a multicarrier using multiple carriers and N / 2 carriers. The frequency is arranged at regular intervals of W Hz with a uniform bandwidth, each carrier acts as an independent subchannel, and the modulation and detection of the QAM modulation method is performed by the data allocated to each carrier. First, b-bit data input during T time is distributed to N / 2 subchannels. At this time, the amount of data allocated to each subchannel is not uniform, and the amount is determined according to the transmission quality index of the corresponding channel. Data allocated to each subchannel is mapped to one QAM symbol value having a complex value according to the QAM modulation scheme. If the QAM symbol value in the k-th subchannel is Xk, each symbol value represents the size and phase of the carrier as a pager of the corresponding QAM transmission signal, which is a frequency component of the ADSL transmission signal at the carrier frequency position. do. A symbol block composed of QAM symbols from each subchannel is transformed into a sample sequence in the time domain through an inverse transform (IFFT) in advance, and this pulse sequence is sequentially transmitted to a transmission path through a transmission filter. The power spectrum of the transmitted signal is uniformly distributed in the designated frequency band by making the average transmission power of the active subchannels all have the same value. This is accomplished by making the square mean values of all Xk equal when placing signal points in QAM modulation. The reception process is the reverse process of the transmission process. The received signals sampled (yi, i = 0 to N) during T time are obtained through the Fourier transform (FFT) to obtain {Yk, k = 0 to N / 2}. This output indicates the representation of the received signal in the frequency domain, which is a block of received QAM symbol values. By determining the corresponding symbol value for each subchannel, the original b-bit data content can be obtained. The entire signal transmitted during T time is called a DMT symbol by dividing it from the QAM symbols of each subchannel. Interference between DMT symbols occurs due to signal distortion of the transmission path during transmission. In order to solve this problem, a real system uses a method of inserting a prefix composed of P QAM symbols in front of the DMT symbol.

2 is a block diagram of a transmission and reception function for processing bit exchange according to the present invention, in which the DMT transmitter 210 includes an FEC encoder 211, a DMT engine 212, and a DMT control unit 213 for DMT modulation of data. The DMT demodulator 220 includes a DMT engine 222, an FEC decoder 221, and a DMT control unit 223 for DMT demodulation via a transmission line (telephone line). Afterwards, the data is reproduced and the error occurred during transmission is corrected.

In FIG. 2, the DMT engine 212 of the DMT transmitter includes a tone ordering unit 302, a constellation encoder 304, and an IFFT 306, as shown in FIG. 3A. 222 is composed of an FFT 308, a constellation decoder 310, the tone array unit 312. As shown in FIG. 4, the DMT controllers 213 and 223 provided in the DMT transmitter 210 and the DMT receiver 220 include an AOC processor 402, a table exchanger 404, and a bit table 406. .

Referring to FIG. 2, the DMT receiver 220 starts bit swapping using the result processed by the FEC decoder 221. To this end, the DMT control unit 223 of the DMT receiver sends a bit exchange request message, and the DMT control unit 213 of the DMT transmitter sends a bit exchange acknowledgment message. The DMT transmitter 210 and the DMT receiver 220 are capable of both a network-side digital subscriber device (ATU-C) and a subscriber-side digital subscriber device (ATU-R) providing (U) ADSL services, and the network-side digital subscriber device (ATU). Either -C) or the subscriber-side digital subscriber station (ATU-R) can start the bit exchange depending on the decoding result of the FEC decoder.

In FIG. 2, the DMT transmitter 210 is a digital subscriber device that transmits data, and both the network-side digital subscriber device (ATU-C) and the subscriber-side digital subscriber device (ATU-R) may be DMT transmitters. The DMT receiver 220 is a module that starts bit exchange of data received from the DMT transmitter according to the decoding result of the FEC decoder 221. The DMT engine 222 and the FEC decoder 221 ) Can detect the change of external channel environment. In general, the network-side digital subscriber station (ATU-C) and the subscriber-side digital subscriber station (ATU-R) simultaneously perform the functions of the DMT transmitter and the DMT receiver, and the DMT transmitter and the DMT receiver Can be.

The DMT engine 212 of the DMT transmitter includes a tone array unit 303, a constellation encoder 304, an IFFT 306, and the like, and modulates data to be transmitted. When bit swapping is performed at the request of the DMT receiving unit, a new bit allocation transmitted from the DMT control unit 213 at the start of the first superframe after the superframe counter included in the bit exchange acknowledgment message is performed. Apply constellation encoding by applying table. The transmitting side DMT control unit 213 processes a bit exchange request message transmitted from the receiving side DMT control unit 223, and analyzes the bit exchange request message and when the bit exchange is possible in the DMT transmitting unit 210, The bit exchange acknowledgment (Ack) message is transmitted to the DMT control unit 223 of the DMT receiving unit. The bit exchange acknowledgment (Ack) message includes a superframe counter that indicates when a new bit table to be used for constellation encoding is applied in the DMT engine. The bit exchange request message and the bit swapping acknowledgment message are transmitted in a synch byte of a super frame.

In FIG. 2, the DMT engine 222 of the DMT receiver includes an FFT module 308, a DMT decoder 310, and the like. The DMT engine 222 demodulates data transmitted from the DMT transmitter 210. Next, the constellation decoded data frame generated by the P-F decoder is transmitted to the FEC decoder 221. The FEC decoder 221 processes the data frame received from the DMT engine 222 to detect whether there is an error in the FEC codeword, and if an error occurs, corrects the error of the FEC codeword. ). The FEC decoder 221 sets the number of FEC codewords in which an error occurs in every super frame, the number of FEC codewords in which an error is corrected in every super frame, and the FEC in which an error cannot be corrected in every super frame. The number of codewords is transmitted to the DMT control unit 223.

In FIG. 2, the DMT control unit 223 of the DMT receiver analyzes the FEC calculation result received from the FEC decoder 221, and when an error occurs in a certain amount of FEC codewords at a unit time, or a certain amount of time at a unit time. If an FEC codeword that cannot correct an error occurs, bit exchange starts. The DMT control unit 213 of the DMT transmitter transmits a bit exchange response (ACK) message to the DMT control unit 223 of the DMT receiver through a sync byte of the super frame. Upon receiving the bit exchange acknowledgment (Ack) message from the DMT control unit 213 of the DMT transmitter, the DMT control unit 223 of the DMT receiver transmits a new bit allocation table to the DMT engine 222.

In FIG. 2, the DMT engine 222 of the DMT receiver includes an FFT module 308, a constellation decoder 310, and the like, and includes a DMT control unit at the start of the first superframe after the superframe counter included in the bit exchange confirmation (Ack) message. Constellation decoding is performed by applying the new bit allocation table transmitted in 223.

3A is a diagram illustrating a DMT engine configuration of the DMT transmitter of FIG. 2, wherein the DMT engine 212 includes a tone array unit 302, a constellation encoder 304, and an IFFT 306, and FIG. 3B illustrates the DMT receiver of FIG. 2. As a configuration diagram of the DMT engine 222, the DMT engine 222 includes an FFT 308, a constellation decoder 310, and a tone array unit 312.

3A and 3B, the DMT transmitter performs a Constellatin encoder and an IFFT (Inverse FFT), and the DMT receiver performs an FFT and a Constellation decoder. Before exchanging the bit allocation table, the existing bit allocation table is applied to encode the constellation. After bit swapping, the constellation encoding is applied by applying the new bit allocation table transmitted from the DMT control unit.

FIG. 4 is a block diagram of the DMT controller of FIG. 2. The DMT controller includes an AOC processor 402, a table exchanger 404, and a bit table storage unit 406 to process an ASL (ADSL Overhead Control) protocol and generate a new bit. Allocate a table and pass this bit table to the Constellation Encoder / Decoder.

In FIG. 4, the AOC processing unit 402 stores the FEC result received from the FEC decoder 221 and corrects a certain amount of error in a unit time or when an error occurs in a certain amount of FEC codewords in a unit time. This module performs the ASL (ADSL Overhead Control) protocol to start bit swapping when an FEC codeword that cannot be generated occurs. The AOC processing unit 402 reallocates the bits allocated to each DMT channel, stores them as a new bit allocation table, and transmits a bit swapping request message to the DMT control unit 213 of the DMT transmitter. If there is a bit swapping (Ack) message from the DMT control unit 213 of the DMT transmitting unit, a superframe counter and a new bit allocation assigned to the bit exchange acknowledgment (Ack) message are allocated using the bit swap module. Pass the table to the Constellation decoder 222.

In FIG. 4, when the bit table exchange is necessary according to the result of the AOC processing unit 402, the table exchanger 404 may convert a superframe counter and a new bit table into a constellation encoder / decoder 304 and 310. To pass). In FIG. 4, the bit table storage unit 406 stores information of a new bit table and an existing bit table to be applied to constellation encoding / decoding.

FIG. 5 is a diagram illustrating a superframe structure in an ADSL system. Referring to FIG. 5, a superframe of an ADSL is made up of 68 data frames (DFs) numbered from 0 to 67, and used as a DMT symbol together with a synchronization frame (SF) into which a modulator is inserted to form super frame boundaries. It is coded and modulated. In terms of bit-level and user data, the DMT symbol rate is 4000baud (period = 250msec), but the DMT symbol transmitted to insert sync-symbol is 69/68 × 4000 baud.

Each data frame in the superframe having the structure shown in FIG. 5 includes 1 byte of sync byte (SB), which is used for CRC, Indicator Bits, Embedded Operation Channel (EOC), and ADSL Overhead Control (AOC). send. That is, the CRC is transmitted in the sync byte of data frame 0, the sync byte of data frame 1 transmits IB0-IB7, the sync byte of data frame 34 transmits IB8-IB15, and the sync byte of data frame 35 transmits IB16-24, respectively. . The EOC is the sync byte of the data frame of 4n + 2, 4n + 3 (n = 0-16, n ≠ 8), and the AOC is the sync byte of the data frame of 4n, 4n + 1 (n = 1-16). Will be sent.

Next, the operation of the present invention configured as described above will be described in detail with reference to FIGS. 6A and 6B.

The DMT transmitter 210 performs FEC encoding on the data to be transmitted, modulates the data in the DMT engine 212 according to a predetermined bit table between transmission and reception, and then transmits the data through a transmission path. The DMT receiver 220 demodulates the data received through the transmission path in the DMT engine 222 according to a predefined bit table and outputs the result. The FEC decoder 221 detects an error in the super frame of the demodulated data. Correct.

At this time, the DMT receiver 220 receives the error information from the FEC decoder 221 according to the present invention and processes the bit exchange when the value of the generated error information is greater than or equal to a preset reference value. In other words, each DMT control unit 213 and 223 stores a plurality of bit tables and readjusts the number of bits allocated to each subcarrier according to the state of the transmission path. Typically, when the state of the transmission path becomes poor, the number of bits allocated is reduced, and when the state of the transmission path becomes good, the number of bits allocated is increased. In this way, the service can be satisfactorily provided by adjusting the number of bits allocated to each subcarrier according to the state of the transport channel.

Referring to FIG. 6A, in step S1, the number of FEC codewords in which an error occurs in every super frame by checking the error of the super frame received by the FEC decoder 221 of the DMT receiving unit and the FEC correcting the error in every super frame are shown. The number of codewords and the number of FEC codewords in which errors cannot be corrected every super frame are provided to the DMT control unit 223. In step S2, the receiving side DMT control unit 223 compares the values of the error information received from the FEC decoder 221 (this is simply referred to as an error value) with a preset reference value, and if the error value is greater than or equal to the reference value, The bit exchange is processed accordingly, and if it is smaller than the reference value, the current bit table is kept as it is in step S7. Here, the error information detected by the FEC decoder 221 indicates the state of the transmission channel.

If the error value is equal to or larger than the reference value, a bit swap request message is sent to the counterpart in step S3. The bit exchange request message consists of a 1 byte header and an n byte message field according to the AOC message encoding procedure. The AOC message is transmitted in a sync byte of the super frame described with reference to FIG. 5.

Then, the DMT control unit 223 of the receiving unit checks whether the bit exchange response message is received from the other party while waiting, and exchanges the bit table in step S5 when the bit exchange response message is received.

On the other hand, referring to FIG. 6B, when the transmitting side DMT control unit 213 receives the bit exchange request message from the receiving side, the transmitting side DMT controller 213 exchanges the bit table after transmitting the response message to the counterpart. As described above, the transmitting side and the receiving side exchange the bit exchange request message and the response message, and perform DMT encoding and decoding on the bit table exchanged in the corresponding super frame according to the super frame counter.

As described above, according to the present invention, even when the external channel environment is changed in the digital subscriber device such as ADSL or UADSL, while providing a data service, bit swapping is rapidly processed according to the change of the external channel environment. Communication efficiency can be improved. That is, by analyzing the FEC decoding result received from the Forward Error Correction (FEC) decoder, when an error occurs in a certain amount of FEC codewords in a unit time, or a certain amount of error is detected in a unit time. When an uncorrectable FEC codeword is generated, the DTC (Discrete Multi-Tone) data service quality of the digital subscriber device can be improved by quickly and efficiently adapting to an external channel environment by starting bit exchange.

Claims (2)

In the bit exchange method of the asymmetric digital subscriber network system having a transmitter and a receiver to transmit data signals to a data network through a telephone line, and to transmit voice signals to a public telephone network through a telephone line. The receiving unit Detecting error information of the received superframe; Comparing the detected error information with a preset reference value and transmitting a bit exchange request message to the counterpart when the reference value is out of the reference value; And Exchanging a bit table if a bit exchange response message is received; The transmitting unit And transmitting a response message to the counterpart and exchanging the bit table when receiving the bit exchange request message. In the asymmetric digital subscriber network system including a transmitter comprising a FEC encoder, a DMT engine, and a DMT control unit, and a receiver comprising a DMT engine, an FEC decoder, and a DMT control unit, Each DMT control unit Bit table storage means for storing predetermined bit tables; In the receiving process, when the error information received from the FEC decoder is out of the reference value, the bit exchange request message is transmitted to the counterpart according to a predetermined protocol, and when the bit exchange response message is received from the counterpart, the bit table exchange is instructed. An AOC processing unit for transmitting a bit exchange response message and instructing a bit table exchange according to a predetermined protocol when a bit exchange request message is received in the process; And And receiving a bit table exchange instruction from the AOC processing unit, and reading the bit table from the bit table storage unit and providing the bit table to the DMT engine. .