KR19990053506A - Input Symbol Coupling Device of TCM Decoder in Cable Modem Downstream System - Google Patents

Abstract

The present invention relates to an input symbol combining apparatus of a TCM decoder in a cable modem downstream system, and includes a switching unit (41), first to second storage units (42 and 43), and first to second selection units (44). 45). The switching unit 41 receives group data over 5 clocks from the non-decoding processing unit (31 in FIG. 3) and the decoding processing unit (32 in FIG. 3) of the TCM decoder according to the switch control signal (S_CONTROL) and the I signal and the Q signal. Output to the first storage unit 42 and the second storage unit 43, respectively, and the first and second storage units 42 and 43 store the I and Q signals and then store the I and Q signals in the buffer control signal B_CONTROL. Accordingly, the first and second selectors 44 and 45 are output at a time, and the first and second selectors 44 and 45 are respectively output from the I signals according to the selection control signal M_CONTROL. (2) Select the B (1) and B (2) symbols in order from the symbol and the Q signal and output them. Therefore, the group data inputted by 6 bits or 4 bits every clock is stored in the buffer for each of the I and Q signals, and then the four symbols of 7 bits are sequentially selected and output according to the control signal. There is an effect that can combine symbols more efficiently.

Description

A deparser for input symbol of TCM decoder in a cablemodem downstream system

The present invention relates to a TCM decoder of a cable modem downstream system. In particular, an input symbol combining apparatus of a TCM decoder in a cable modem downstream system capable of rearranging bits obtained by QAM demapping in a TCM decoder and outputting the symbol unit. It is about.

Cable modem network is a network system of remote access area such as Integrated Information Communication Network (ISDN) and Multi-Digital Subscriber Line (xDSL) .It is connected to the Internet and intranet to provide subscribers at home with high speed data transmission speed of Mbps. Provide various services such as search.

The concept of a cable modem network is similar to a cable TV network in data communication. In terms of using coaxial cable, cable TV connects an external coaxial cable to a set-top box and connects the TV to the set-top box. Cable modem networks, on the other hand, use a cable modem to connect a coaxial cable to a PC. At this time, there may be one PC or multiple PCs connected to the cable modem.

Cable modems are divided into workgroup, multiuser, and personal. Workgroup cable modems are designed for small groups with 4 or 8 ports for connecting PCs, and small LANs can be established through them. Multi-user cable modems are relatively large in libraries, schools, and factories. Is used in large places.

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

The CMTS 30 and the CMs 11 to 14 exchange data by using a medium access control (MAC) frame which is a basic transmission unit in upstream and downstream, and the MAC frame structure is MAC. It consists of a MAC header defining the content of the frame and a data PDU (Protocol Data Unit) whose length and presence are determined according to the MAC header. The MAC frame is transmitted with a physical medium dependent (PMD) sublayer overhead in front of the MAC header in the upstream and an MPEG transport header in the downstream.

On the other hand, in the hierarchical structure of a communication method using a cable modem, a transport layer transmits a bitstream consisting of a series of 188 byte MPEG-2 packets downstream. The 188 bytes are divided into one byte for synchronization, three bytes for service definition, scrambling, and control information, and 184 bytes for MPEG-2 data or auxiliary data.

Fig. 2 is a block diagram showing the cable transmission process in the cable modem system, in which the MPEG frame unit 21, the FEC encoder 22, the QAM modulation unit 23, the MPEG frame unit 27, and the FEC unit of the transmission unit are shown. It consists of a decoder 26, a QAM demodulator 25, and a channel 24.

The MPEG frame unit 21 of the transmitter receives an MPEG-2 data stream consisting of a series of 188-byte fixed length packets, transmits the synchronization of the MPEG packets to the receiver, and the Forward Error Correction (FEC) encoder 22 Reed-Solomon coding, interleaving, randomization, and trellis coding are performed to reliably transfer data through the cable channel 24, and the QAM modulator 23 uses 64 QAM or 256 QAM modulation. do. The MPEG frame unit 27, the FEC decoder 26, and the QAM demodulator 25 of the receiver perform the opposite functions of the transmitter.

As shown in FIG. 2, the FEC encoder 22 is a Reed Solomon encoder 22-1, an interleaver 22-2, a randomizer 22-3, and a trellis encoder 22-4. The FEC decoder 26 is composed of a trellis decoder 26-1, a derandom equalizer 26-2, a deinterleaver 26-3, and a Reed Solomon decoder 26-4.

The ReedSolomon encoder 22-1 performs ReedSolomon encoding using (128,122) codes. Error correction is possible up to three symbols. 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 data for synchronization of the QAM demodulator 25, and the trellis encoder 22-4 internal code of a concatenated coding scheme. The inner code is used to perform binary convolutional encoding to encode a transmitted signal. In addition, the TCM decoder 26-1, the reverse randomizer 26-2, the deinterleaver 26-3, and the Reed Solomon decoder 26-4 of the FEC decoder 26 are opposite to the FEC encoder 22. Perform the function.

In the case of 64 QAM, the TCM encoder 22-4 receives four 7-bit symbols, that is, 28 bits, from the randomization unit 22-3, converts the data into a 64-level symbol by forming five groups of 6-bit symbols. The output device is output to the QAM modulator 23. In this case, a distribution device is essential for input symbols for rearranging the 28 bits and distributing them to meet the QAM standard.

In addition, in the case of 64 QAM, the TCM decoder 26-1 receives 64-level symbols from the QAM demodulator 25 as opposed to the TCM encoder 22-4, and demaps the QAM into five groups of 6-bit symbols. After decoding, the five 6-bit symbols, that is, the 30-bit symbols, are decoded and dedecoded to produce 28 bits, and are then converted into four 7-bit symbols and outputted to the inverse randomizer 26-2.

In this case, the TCM decoder needs to rearrange the 28-bit symbols output through QAM demapping, decoding, and undecoding to appropriately generate four symbols. Deparser is essential. However, since the decoder field has not yet been proposed for its configuration, an input symbol combiner (Deparser) for efficiently combining 28-bit input symbols and outputting them as four symbols should be designed.

Accordingly, the present invention has been made in accordance with the necessity as described above, and the present invention is provided in the TCM decoder of the cable modem downstream system so that 28-bit input symbols can be combined into four 7-bit symbols and output in symbol units. It is an object of the present invention to provide an input symbol combining apparatus of a TCM decoder.

The apparatus of the present invention for achieving the above object, in the TCM decoder of the cable modem downstream system, receives the group data for a plurality of clocks, and according to the switch control signal (S_CONTROL) for each of the I signal and Q signal respectively; Switching unit for outputting to the first and second storage unit, the first and second storage unit for receiving the I signal and the Q signal from the switching unit, respectively, and outputs the buffer according to the buffer control signal (B_CONTROL), the first storage unit A first selector for receiving an I signal from the first selector for outputting the A (1) and A (2) symbols according to a selection control signal M_CONTROL, and a Q signal from the second storage; M_CONTROL) is characterized in that it comprises a second selection unit for outputting in units of B (1), B (2) symbols.

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 showing an input / output relationship between a general input symbol combining apparatus and its periphery;

4 is a block diagram illustrating an input symbol combining apparatus according to the present invention.

＊ Explanation of symbols for main parts of drawing

41: switching unit 42,43: storage unit

44,45: selection

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

3 is a block diagram illustrating an input / output relationship between a general input symbol combiner and its periphery.

The non-decoding processing unit 31 and the decoding processing unit 32 of FIG. 3 are three bits of the I signal of the in-phase component and the Q signal of the quadrature component for 5 clocks from a QAM demapper (not shown). Three bits C0, C1, and C2 are received and transmitted to the input symbol combiner 33. The I and Q signals are as follows.

I signal Q signal C5, C4, C3 C2, C1, C0 1 clock A2, A1, U1 B2, B1, V1 2 clock A5, A4, U2 B5, B4, V2 3 clock A8, A7, U3 B8, B7, V3 4 clock A11, A10, U4 B11, B10, V4 5 clock A13, A12, U5 B13, B12, V5

The non-decoding processor 31 transfers the 30-bit I signals and the 20 signals which are not encoded among the Q signals as shown in Table 1 to the input symbol combiner 33 as it is. The 10 bits to be encoded among the Q signals are decoded to be 8 bits and transmitted to the input symbol combiner 33. Accordingly, the input symbol combiner 33 receives a total of 28 bits.

As described above, the input symbol combiner 33 receives 28 bits for 5 clocks from the non-decoding processor 31 and the decoding processor 32, rearranges them, and outputs four 7-bit symbols, each clock. Each of the 28 bits output from the decode processing unit 31 and the decoding processing unit 32 and input to the input symbol combiner 33 is shown in Table 2 below.

Input Bits from Decoding Process Input bit from decoding processor 1 bit of input bit A2, A1, B2, B1 A0, B0 2 clock input bits A5, A4, B5, B4 A3, B3 3 clock input bits A8, A7, B8, B7 A6, B6 4 clock input bits A11, A10, B11, B10 A9, B9 5 clock input bits A13, A12, B13, B12

When the bits inputted to the clocks 1 to 5 are referred to as the first to fifth groups, respectively, the input symbol combiner 33 is divided into six bits and the fifth group of the first to fourth groups as shown in Table 2 above. 4 bits, i.e., 28 bits in total, are output in order of A (1), A (2), B (1), and B (2) symbols. The symbols A (1), A (2), B (1), and B (2) are 7 bits each, and 7 bits for each symbol are shown in Table 2 below.

A group B group A (1) symbol A (2) symbol B (1) symbol B (2) symbol A10, A8, A7, A5, A4, A2, A1 A9, A6, A3, A0, A13, A12, A11 B10, B8, B7, B5, B4, B2, B1 B9, B6, B3, B0, B13, B12, B11

That is, the input symbol combiner 33 receives the 28 bits shown in Table 2 and outputs the symbols A (1), A (2), B (1), and B (2) in sequence as shown in Table 3 above. .

Next, the operation and effects of the input symbol combining apparatus of the TCM decoder according to the present invention will be described.

4 is a block diagram showing another input symbol combining device according to the present invention, wherein the switching unit 41, the first to second storage units 42 and 43, and the first to second selection units 44 and 45 are shown. Consists of

As shown in Table 2, the switching unit 41 inputs a symbol input by 6 bits or 4 bits for every clock according to the switch control signal S_CONTROL, and the first and second storage units 42 according to the I and Q signals. , 43).

That is, the switching unit 41 transmits three bits of the A symbol from the first group A2, A1, B2, B1, A0, and B0 that are input for the first storage unit 42 to the B symbol. 3 bits related to the second storage unit 43 are output to the second storage unit 43, and the second group A5, A4, B5, B4, A3, B3 is input second and the third group is input third. From the A8, A7, B8, B7, A6, and B6 and the fourth input group A11, A10, B11, B10, A9, and B9, three bits of the A symbol are respectively selected and the first storage unit ( 42) and selects 3 bits related to the B symbol and outputs it to the second storage unit 43. Finally, 2 bits of the A symbol and the B symbol in the fifth group A13, A12, B13, and B12 that are inputted are output. Two bits of are output to the first and second storage units 42 and 43, respectively.

Accordingly, the first storage unit 42 stores the I signal for the A symbol, the second storage unit 43 stores the Q signal for the B symbol, and stores the stored symbols in a buffer control signal ( B_CONTROL) to the first and second selectors 44 and 45, respectively.

The first and second selectors 44 and 45 may be implemented as a 14: 7 multiplexer, and the first selector 44 inputs 14 bits of the A symbol from the first storage unit 42. And outputs the A (1) and A (2) symbols according to the selection control signal M_CONTROL, and the second selector 45 receives 14 bits of the B symbol from the second storage unit 43. The B (1) and B (2) symbols are output according to the selection control signal M_CONTROL.

That is, in response to the selection control signal M_CONTROL, the first selector 44 first selects and outputs 7 bits corresponding to the symbol A (1) from the output of the first storage 42 and outputs the second bit. 7 bits of the A (2) symbol are selected and output from the output of the first storage section 42, and the second selection section 45 selects B (1) from the output of the second storage section 43. The 7 bits of the symbol are selected and output, and finally, the 7 bits of the B (2) symbol are selected and output from the second storage unit 43.

As described above, the input symbol combining apparatus of the present invention suitably stores the first to fifth groups of 28-bit input symbols in units of 7-bit A (1), A (2), B (1), and B (2) symbols. In the present specification, the present invention has been described only in connection with specific embodiments. However, the present invention may be modified and applied to other systems that combine data.

As described above, the apparatus of the present invention stores the group data input by 6 bits or 4 bits every clock in the buffer for each of the I and Q signals, and then, according to the control signal (CONTROL), 4 symbols of 7 bits. By selecting and outputting in order, there is an effect that the input symbols can be combined more efficiently.

Claims (1)

In the TCM decoder of the cable modem downstream system, A switching unit 41 receiving group data for a plurality of clocks and outputting the group data to the first and second storage units 42 and 43 according to the switch control signal S_CONTROL, respectively; First and second storage units 42 and 43 which receive and store I and Q signals from the switching unit 41 and output the received I and Q signals according to a buffer control signal B_CONTROL; A first selector 44 which receives an I signal from the first storage unit 42 and outputs the signal in units of A (1) and A (2) symbols according to a selection control signal M_CONTROL; And And a second selector 45 which receives the Q signal from the second storage unit 43 and outputs the signal in units of B (1) and B (2) symbols according to the selection control signal M_CONTROL. An input symbol combining apparatus of a TCM decoder in a cable modem downstream system.