KR19990053522A - Cable modem down-stream system TCM decoder < RTI ID = 0.0 > - Google Patents

Abstract

The present invention relates to a demultiplexing apparatus for a cable modem downstream system TCM decoder, which receives a QAM-demapped 5-bit signal (X1, Y1, Y2, Y3, Y4) , Y1 to Y4) of the cable modem downstream system TCM decoder, wherein the switching unit (51), the first and second storage units (52, 53), and the first and second selection units 54 and 55. The switching unit 51 transfers the X1 signal to the first storage unit 52 and the Y1 to Y4 signals to the second storage unit 53, The first and second storage sections 54 and 55 sequentially select and output X1 and three neutral values N output from the first storage section 52 and Y1 through Y4 signals output from the second storage section 53,

Therefore, in the present invention, when 8 bits are transmitted to the binary convolutional decoder by demultiplexing 5 bits of QAM demapping, the signals are divided and processed according to the control signal for each of the X signal and the Y signal, , There is an effect that the input signals can be efficiently demapped.

Description

A cable modem downstream system A depuncturing device of a TCM decoder (TCM decoder in a cable modem downstream system)

The present invention relates to a cable modem downstream system TCM decoder, and more particularly, to a demultiplexing apparatus for a cable modem downstream system TCM decoder adapted to decode a QAM demapped five bits to provide 8 bits to a convolutional decoder.

The cable modem network is a remote access network system such as ISDN and xDSL. It is connected to the Internet and intranet and provides high-speed data transfer rate of Mbps to subscribers for telecommuting, video conferencing, web Search, and so on.

The concept of a cable modem network is similar to that of coaxial cable, which brings cable TV networks to the field of data communications, but cable TV connects external coaxial cable to a set-top box and then connects the TV to the set- The cable modem network, on the other hand, is a cable modem that connects the coaxial cable to the PC. At this time, the number of PCs connected to the cable modem may be one or several.

FIG. 1 is a diagram illustrating a network constructed using a general cable modem. In FIG. 1, a plurality of cable modems (CM) 11 to 14 are connected to a cable network 20, The subscriber is provided with services such as the Internet from the backbone network 40 and the cable modem terminal system 30 is located at the head end and serves to provide the uplink channel and the downlink channel . The CMTS 30 broadcasts broadband data at a transmission rate of 500 kbps to 30 Mbps on the downlink channel and each CM transmits narrowband query data on the uplink channel at a rate of 96 kbps to 10 Mbps in a point-to-point manner .

FIG. 2 is a block diagram showing a cable transmission processing step in the cable modem system. The MPEG frame unit 21, the FEC encoder 22, the QAM modulation unit 23, the MPEG frame unit 27 of the reception unit, the FEC A decoder 26, a QAM demodulator 25, and a channel 24. [

The MPEG frame unit 21 of the transmission unit receives the MPEG-2 data stream composed of 188-byte fixed-length packets and transmits the synchronization of the MPEG packet to the receiver. The FEC (Forward Error Correction) Interleaving, randomizing, and trellis coding in order to reliably transmit data through the cable channel 24. The QAM modulator 23 uses a modulation scheme of 64 QAM or 256 QAM do. The MPEG frame unit 27, the FEC decoder 26, and the QAM demodulation unit 25 of the receiving unit perform opposite functions of the transmitting unit.

2, the FEC encoder 22 includes a Reed Solomon encoder 22-1, an interleaver 22-2, a randomizer 22-3, and a Trellis encoder 22-4 And the FEC decoder 26 includes a trellis decoder 26-1, a reverse randomizer 26-2, a deinterleaver 26-3, and a Reed Solomon decoder 26-4.

The Reed-Solomon encoder 22-1 performs Reed Solomon encoding using a (128,122) code, error correction is possible up to three symbols, and the RS code is used for both 64QAM and 256QAM. The interleaver 22-2 prevents cluster noise that causes an error, and has a programmable structure in the case of 64QAM and 256QAM. The randomizer 22-3 randomizes the data for synchronization of the QAM demodulator 25 and the trellis encoder 22-4 encodes the internal code of the concatenated coding technique and encodes the transmitted signal by performing binary convolutional encoding using inner code. The TCM decoder 26-1, the randomizer 26-2, the deinterleaver 26-3 and the Reed Solomon decoder 26-4 of the FEC decoder 26 are connected to the FEC encoder 22 Function.

The TCM encoder 22-4 receives the bit stream from the randomizer 22-3 and performs QAM mapping on the bit stream and outputs the QAM to the QAM modulator 23. The TCM encoder for 64 QAM is a An input symbol distribution unit 31, an uncoded block 32, a coded block 33, and a QAM mapper 34 as shown in FIG.

A5, A4, A2, and A1), A2 symbols (A9, A6, A3, A0, A13 , A12, and A11), B1 symbols (B10, B8, B7, B5, B4, B2, B1), and B2 symbols (B9, B6, B3, B0, B13, B12, and B11) And the non-coding processing unit 32 transfers the input symbol to the QAM mapper 34 as it is. The sign processor 33 comprises a Differential Precoder 33-1 and two Binary Convolutional Coders 33-2 and 33-3. The input symbol distributor 33-1, 31, A2, A3, A9, and B2 of the A2 symbol, and 4 bits B0, B3, B6, and B9 of the B2 symbol are differentially encoded and convolutionally encoded by using the 5 bits of the encoded bits U1, U2, U3, U4 And the QAM mapper 34 outputs 4 bits which are not encoded from the non-coding processing unit 32 and encoded from the code processing unit 33 for each clock, 2 bits, total of 6 bits (C5 to C0), and converts the input symbols into 64 (= ²⁶ ) level symbols, and outputs the symbols to the QAM modulation unit (23 in FIG.

The TCM encoder for 256 QAM receives the 38 bit stream from the randomizer 22-3 and QAM-maps it to the QAM modulator 23. The configuration and operation of the QAM encoder are the same as that of the 64 QAM TCM encoder same. That is, the QAM mapper receives 8 bits (C7 to C0) of each clock outputted from the input symbol distribution unit through the unsigned processing unit and the sign processing unit, converts them into 256 (= 2 ⁸ ) level symbols, and outputs them.

In the 64 QAM and 256 QAM TCM encoders, each binary convolutional coder (BCC) of the sign processing unit has a puncturing function of 4/5 code rate. The puncturing is used to obtain a higher transmission rate, and it is employed in various digital transmission systems because a transmission rate higher than the conventional transmission rate can be obtained by 20% or more. That is, the binary convolutional encoder having a bit rate of 1/2 has to transmit 8 bits by encoding four input bits. The 8 bits to be transmitted are transmitted with only a 5 bits by a puncturing function of a 4/5 code rate , So that more data can be transmitted on the same channel.

On the contrary, in the decoder on the reception side, the demultipuning function for making the original eight bits with only the transmitted five bits is required. Therefore, it is necessary to design the demultiplexing apparatus according to the standard of the cable modem system.

Accordingly, the present invention has been made in view of the above-mentioned needs, and it is an object of the present invention to provide a TCM decoder of 64 and 256 QAM, which can transmit a QAM demapping signal to a binary convolutional decoder, The object of the present invention is to provide a handling device.

According to an aspect of the present invention, there is provided an apparatus for decoding a QAM-demultiplexed 5-bit signal (X1, Y1, Y2, Y3, Y4) ) Receives a 5-bit signal and transfers an X signal to a first storage unit according to a switch control signal (S_CONTROL), and outputs a Y signal to a second storage unit The first storage unit for storing the X1 signal and the three neutral values N and outputting the signal in accordance with the buffer control signal B_CONTROL, the buffer control signal B_CONTROL, And first and second selection units (54, 54) for sequentially selecting and outputting 4 bits from the first and second storage units according to a selection control signal (M_CONTROL) 55).

1 is a diagram illustrating a network constructed using a general cable modem,

2 is a block diagram showing a cable transmission processing step in a cable modem system;

3 is a block diagram illustrating the configuration of a TCM encoder for 64 QAM;

4 is a block diagram showing the input / output signal relationship between the convolutional encoder and the punching block,

5 is a block diagram illustrating a depuncting apparatus for a cable modem downstream system TCM decoder in accordance with the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

51: switching unit 52, 53:

54, 55:

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

First, the input / output relationship between the binary convolutional encoder and the puncturing block will be described in order to facilitate understanding of the present invention.

4 shows input and output signals of a convolutional encoder and a puncturing block. The binary convolutional encoder 41 receives four bits (S1 to S4) of 1 bit over 4 clocks, 2 > X2Y2, S3? X3Y3, and S4? X4Y4 at every time according to the coding rate of 2? When the output signal is represented by a matrix .

The puncturing block 42 receives the 8 bits encoded through the encoder 41 as a puncturing matrix (Here, 1 means to transmit and 0 means not to transmit) . The puncturing block of the cable modem system sequentially receives 'X1, Y1', 'X2, Y2', 'X3, Y3', and 'X4 and Y4' from the convolutional encoder and receives 3 bits by puncturing matrix And the remaining X1, Y1, Y2, Y3, and Y4 are sequentially transmitted to the QAM mapper.

Accordingly, the de-puncturing block receives 5 bits in the order of X1, Y1, Y2, Y3, and Y4 from the QAM demapper in the contrary to the puncturing block and outputs 'X1, Y1', 'X2, Y2' ',' X4, Y4 'to the binary convolutional decoder. At this time, in order to generate the X2, X3, and X4 signals among the signals output to the decoder, a value corresponding to the signals is set as a neutral value to be transmitted to the decoder. Accordingly, in the binary convolutional decoder, 2-bit signals such as X1, Y1 ',' N, Y2 ',' N, Y3 ',' N and Y4 'are transmitted.

FIG. 5 is a block diagram illustrating a demultipuning apparatus for a cable modem downstream system TCM decoder according to the present invention. The demultipuning apparatus of the present invention includes a switching unit 51, first and second storage units 52 and 53, And first and second selection units 54 and 55. [

The switching unit 51 sequentially receives the signals X1, Y1, Y2, Y3 and Y4 from a QAM demapping unit (not shown) and sequentially outputs the signals to the first storage unit 52 or the second storage unit 52 according to the switch control signal S_CONTROL. And transmits the first four bits Y1 to Y4 to the second storage unit 53. The first storage unit 52 stores the first X1 and the second storage unit 53 stores the X1 and Y4 signals.

The first and second storage units 52 and 53 are 4-bit storage units. The first storage unit 52 stores X1 bits received from the switching unit 51, and the remaining three- And the second storage unit 53 stores the Y1 to Y4 bits received from the switching unit 51 and outputs the Y1 to Y4 bits to the first selector 54 according to the buffer control signal B_CONTROL, And outputs it to the second selector 55 according to the buffer control signal B_CONTROL.

The first and second selectors 54 and 55 select the 4-bit signals transmitted from the first and second storage units 52 and 53, that is, X1, N, N, and N, according to the selection control signal M_CONTROL, N, and Y1, Y2, Y3, and Y4 in this order.

That is, the QAM demapping signal is divided into X and Y signals and stored in the first and second storing units 52 and 53. The first and second selecting units 54 and 55 respectively output the X1 signal and X2 The binary convolutional decoder receives the 8 bits and decodes the 8 bits by a 1/2 code rate to output 4 bits, will be.

As described above, the apparatus of the present invention divides QAM demapping 5 bits and delivers 8 bits to a binary convolutional decoder. The apparatus divides and processes the 8 bits according to a control signal according to an X signal and a Y signal, The signal is selected and output, thereby effectively demapping the input signals.

Claims (1)

The demultiplexing of the cable modem downstream system TCM decoder that receives and demultiplexes the QAM demapped 5-bit signals (X1, Y1, Y2, Y3 and Y4) and outputs 8 bits (X1 to X4, Y1 to Y4) In the apparatus, A switching unit 51 receiving the 5-bit signal and transferring the X signal to the first storage unit 52 according to the switch control signal S_CONTROL and transmitting the Y signal to the second storage unit 53; The first storage unit 52 storing the X1 signal and the three neutral values N and outputting the signal in accordance with the buffer control signal B_CONTROL; The second storage unit 53 for storing signals Y1 to Y4 and outputting the signals according to the buffer control signal B_CONTROL; And And first and second selection units 54 and 55 for receiving 4 bits from the first and second storage units 52 and 53 and sequentially selecting and outputting the 4 bits according to the selection control signal M_CONTROL, Gt; TCM < / RTI > decoder.