KR19990071095A - 16 QAM mapping devices on cable modems that support gray coded symbol mapping and differential coded symbol mapping - Google Patents

Abstract

The present invention relates to a 16-mode QAM mapping apparatus for cable modems that support gray coded symbol mapping and differential coded symbol mapping. The present invention includes a differential coder, a multiplexer, an I-Q mapper, an I-Q value adjuster, and an I-Q value adjuster.

The differential encoding unit converts a 2-bit coded signal input to the 16 QAM mapping device into a differential coding signal, and the multiplexer selects and outputs one of the 2-bit coded signal input to the 16 QAM mapping device and an output signal of the differential coding unit, and outputs the IQ. The mapper receives the output signal of the multiplexer and the 2-bit unsigned signal input to the 16 QAM mapping device and performs differential coded symbol mapping accordingly.

In addition, the IQ value adjustment controller outputs an IQ value adjustment signal for instructing IQ value adjustment when the logic values of the 2-bit unsigned signals input to the 16 QAM mapping device are different and the logic values of the two output signals of the multiplexer are also different. When the mode selection signal is a signal for gray coded symbol mapping, the IQ value adjuster adjusts an output signal of the IQ mapper to a signal suitable for gray coded symbol mapping according to the IQ value adjustment signal.

Using the 16 QAM mapping apparatus of the present invention, by changing only the mode selection signal, there is an effect that the cable modem can be operated in any mapping mode among the gray coded symbol mapping mode and the differential coded symbol mapping mode.

Description

16 Quadrature Amplitude Modulation mapping unit of cablemodem supporting Gray-coded symbol mapping and Differential-coded symbol mapping

The present invention relates to a 16-mode quadrature amplitude modulation (QAM) mapping device of a cable modem that supports gray-coded symbol mapping and differential-coded sysmbol mapping. A device that can operate the cable modem's 16 QAM mapping device in both the gray coded symbol mapping mode and the differential coded symbol mapping mode as needed. It is about.

Cable modem network is a network system that is attracting attention along with ISDN, multi-digital subscriber line (xDSL), etc. in the field of remote access.It is connected to the Internet or intranet to transmit Mbps (Mega bits per second) high speed data. It provides subscribers with various services such as telecommuting, video conferencing, and web 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.

1 is a schematic diagram of a network constructed using a general cable modem, in which a plurality of cable modems (CM) are connected to a cable network, and a PC is connected to each cable modem to provide a subscriber with a service such as the Internet from a backbone network. The cable modem terminal system (CMTS) is provided at the head end and serves to provide an uplink channel and a downlink channel. The CMTS 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.

CMTS and CM send and receive data using Medium Access Control (MAC) frame, which is a basic transmission unit in upstream and downstream, and the structure of MAC frame includes MAC header which defines the contents of MAC frame and It consists of 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 media 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. 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 of a data transmission processing step in a cable modem system, and is composed of a MPEG frame part, a FEC encoder, a transmitter comprising a QAM modulator, an MPEG frame unit, a FEC decoder, a QAM demodulator, and a channel.

The MPEG frame part of the transmitter receives an MPEG-2 data stream composed of consecutive 188-byte fixed-length packets and transmits the synchronization of the MPEG packets to the receiver, and the FEC (Forward Error Correction) encoder reliably transmits data through the cable channel. In order to transmit, ReedSolomon coding, interleaving, randomization, and trellis coding are performed, and the QAM modulator transmits a signal to be transmitted through a channel using a QAM modulation scheme. The MPEG frame unit, the FEC decoder, and the QAM demodulator of the receiver perform a reverse function of the transmitter.

Meanwhile, as shown in FIG. 2, the FEC encoder is composed of a Reed Solomon encoder, an interleaver, a randomizer, and a trellis encoder, and the FEC decoder is composed of a trellis decoder, a derandomizer, a deinterleaver, and a Reed Solomon decoder. The Reed Solomon encoder performs Reed Solomon encoding to enable error correction up to three symbols, the interleaver performs a process to prevent cluster noise causing an error, and the randomization unit synchronizes the QAM demodulator. Randomize the data for

In addition, the trellis encoder encodes a transmitted signal by performing convolutional encoding using an inner code of a concatenated coding scheme. It receives 7-bit symbols, or 28 bits, into 5 groups of 6-bit symbols, converts them into 64-level symbols, and outputs them to the QAM modulator.

FIG. 3 is a block diagram showing the structure of a trellis encoder for 64 QAMs, which is composed of an input symbol distributor, an unsigned processor 310, a code processor 300, and an I-Q mapper 130. As shown in FIG. The input symbol divider receives a 28-bit stream consisting of four 7-bit symbols from the randomizer and distributes them to meet the QAM standard. The input symbols are divided into two groups, A symbol and B symbol. As shown in Table 1, it is divided into A (1) symbol, A (2) symbol, B (1) symbol, and B (2) symbol.

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

The input symbols are stored in the input symbol distribution unit and output to the unsigned processor 310 and the code processor 300 every time. At this time, A9, which is the upper bit (MSB) of the A (2) symbol, among the input symbols A6, A3, A0 and B9, B6, B3, A0, which are the upper bits (MSB) of the B (2) symbols, are input to the code processor 300 from the lower bits, respectively, and the remaining bits of the A (2) symbols and B ( 2) The remaining bits of the symbol, the A (1) symbol bit, and the B (1) symbol bit are input to the unsigned processor 310.

FIG. 4 is a schematic diagram of symbols output from an input symbol divider every cycle. A0, B1, B2 bits are output to the unsigned processor 310 at time T0, and A0, B0 bits are outputted from the code processor. 300), A5, A4, B5, and B4 bits are output to the unsigned processor 310 at T1 time, A3, B3 bits are output to the code processor 300, and A8, A7, B8 at T2 time. , B7 bits are outputted to the unsigned processor 310, A6, B6 bits are outputted to the coded processor 300, and at times T3, A11, A10, B11, and B10 bits are outputted to the unsigned processor 310 and A9. The B9 bits are output to the code processor 300, and the A13, A12, B13, and B12 bits are output to the unsigned processor 310 at time T4.

The A0, A3, A6, A9 bits and the B0, B3, B6, B9 bits inputted to the code processor 300 are (U1, U2, U3, U4, U5) by the binary convolutional encoder of the code processor 300, respectively. ) And (V1, V2, V3, V4, V5). In addition, the unsigned processor 310 transfers the input symbols to the I-Q mapper 130 as they are. In this way, four 7-bit symbols, that is, A0, A3, A6, A9 and B0, B3, B6, B9 of the 28 bits become 10 bits through the code processor 300, so that a total of 30 bits of symbols are mapped to the IQ. To be delivered to the device 130.

In this case, if the signals output from the code processor 300, that is, (U1, U2, U3, U4, U5) and (V1, V2, V3, V4, V5) are defined as encoded signals, these encoded signals are IQ mapped. There is a case where IQ is directly input to the device 130 and mapped to IQ (gray coded symbol mapping mode), and another case is converted to a differential coded signal and then IQ mapped (differential coded symbol mapping mode).

However, since the 16 QAM mapping apparatus of the conventional cable modem could operate only in one operation mode of the gray coded symbol mapping mode or the differential code symbol mapping mode, the 16 QAM mapping device which is supposed to operate only in one operation mode is used. In the case of using a cable modem, there is a problem in that the mapping mode cannot be easily changed, such as changing the 16 QAM mapping device itself when trying to change the operation mode.

Accordingly, the present invention has been made to solve the above problems, using only the mode selection signal, 16 QAM mapping of the cable modem that can operate in any mapping mode of gray coded symbol mapping mode or differential coded symbol mapping mode. The purpose is to provide a device.

In order to achieve the above object, the cable modem 16 QAM mapping apparatus supporting gray coded symbol mapping and differential coded symbol mapping according to the present invention is 16 of the cable modem receives a 2-bit coded signal and a 2-bit uncoded signal A QAM mapping apparatus, comprising: a differential encoding unit for differentially encoding an encoded signal; A multiplexer for selecting and outputting one of an output signal and an encoded signal of the differential encoding unit according to an arbitrary mode selection signal; An I-Q mapper that receives an output signal and an uncoded signal of the multiplexer and performs differential coded symbol mapping accordingly; An I-Q value adjustment control unit for outputting an I-Q value adjustment signal instructing I-Q value adjustment when the logic values of the unsigned signals are different and the logic values of the output signals of the multiplexer are also different; And an IQ value adjusting unit for adjusting an output signal of the IQ mapper to a signal suitable for gray coded symbol mapping according to the IQ value adjusting signal when the mode selection signal is a signal for gray coded symbol mapping. .

1 is a configuration diagram of a network constructed using a general cable modem;

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

3 is a block diagram showing the configuration of a trellis encoder for 64 QAM;

4 is a schematic diagram of symbols output from an input symbol distribution unit every cycle;

5 is a block diagram illustrating a 16 QAM mapping apparatus for a cable modem supporting gray coded symbol mapping and differential coded symbol mapping according to the present invention;

6 is a gray coded symbol mapping diagram;

7 is a differential encoding symbol mapping diagram.

* Explanation of symbols for main parts of the drawings

100: 16 QAM mapping device of the cable modem according to the present invention

110: differential encoding unit 111: 2-bit digital memory element

112: coded signal calculator 120: multiplexer

130: I-Q mapper 140: I-Q value adjusting unit

150: I-Q value adjustment control unit 300: code processing unit

310: unsigned processing unit

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

FIG. 5 is a block diagram of a cable modem 16 QAM mapping device (hereinafter, referred to as 16 QAM mapping device 100) supporting gray coded symbol mapping and differential coded symbol mapping according to the present invention. , A multiplexer 120, an IQ mapper 130, an IQ value adjustment controller 150, and an IQ value adjustment unit 140. In addition, coded signals output from the code processor 300 every two bits per cycle will be referred to as C1 and C0, respectively, and coded signals output from the unsigned processor 310 every two bits per cycle will be referred to as L1 and L0, respectively. It is called.

The differential encoding unit 110 is composed of a 2-bit digital memory element 111 and an encoded signal calculator 112. The encoded signal calculator 112 is input to the 16 QAM mapping apparatus 100 from the code processor 300. After performing the operation on the bit encoded signals C1 and C0, the 2-bit digital memory element 111 delays the output signal output from the encoded signal calculator 112 by one period of the encoded signals C1 and C0. The signal is returned to the input terminal of the coded signal calculator 112.

The multiplexer 120 passes the output signals D1 and D0 from the differential encoding unit 110 or passes the encoded signals C1 and C0 as they are.

The I-Q mapper 130 receives an output signal of the multiplexer 120 and L1 and L0, and performs differential encoding symbol mapping on the signal.

In the gray coded symbol mapping mode, the IQ value adjuster 140 converts the output signal of the IQ mapper 130 to match the gray coded symbol mapping, and the IQ value adjuster 150 determines whether the IQ value needs to be converted. It determines and sends the IQ value adjustment signal to the IQ value adjustment unit 140.

In addition, the 16 QAM mapping apparatus 100 is a mode selection signal, which is a signal for selecting one of a gray coded symbol mapping mode and a differential coded symbol mapping mode as an input signal, and a 2-bit coded signal C1 and C0 applied in parallel. And unsigned signals L1 and L0 of two bits, and the coded signal and the unsigned signal are input in parallel through four data lines.

Hereinafter, each component of the 16 QAM mapping apparatus 100 according to the present invention will be described in more detail.

The differential encoding unit 110 converts the encoded signals C1 and C0 input to the 16 QAM mapping apparatus 100 into a signal that is easy for signal demodulation at the receiving end, that is, a differential encoding signal. This conversion is defined as shown in Table 2 below by the correlation between the coded signals (C1, C0) input to the differential coding unit 110 and the signals (D1, D0) output from the differential coding unit 110 a period ago. In this case, the 2-bit digital memory element 111 delays the signals D1 and D0 output in parallel from the output terminal of the encoded signal calculator 112 by one period of the encoded signal, and then It performs the function of outputting to the input terminal.

Current input bit (C1, C0) Previously transmitted bits (P1, P0) Currently transmitted bits (D1, D0) 00 11 11 00 01 01 00 00 00 00 10 10 01 11 01 01 01 00 01 00 10 01 10 11 11 11 00 11 01 10 11 00 11 11 10 01 10 11 10 10 01 11 10 00 01 10 10 00

In Table 2, the current input bits C1 and C0 are encoded signals that are currently input to the 16 QAM mapping apparatus 100, and the previously transmitted bits P1 and P0 are encoded signals of immediately preceding periods of the currently input encoded signals. As the output signal of the differential encoding unit 110, the signal is output after being delayed for one period of the encoded signal by the 2-bit digital memory device 110, and the currently transmitted bits D1 and D0 are the differential encoding unit. A signal currently output at 110 is indicated. In other words, regardless of the mode selection signal, the differential encoding unit 110 performs an operation of differentially encoding the encoded signals C1 and C0 at all times.

The multiplexer 120 receives 2-bit signals D1 and D0 and coded signals C1 and C0 respectively output from the differential encoding unit 110 and selects one of the two signals by the mode selection signal. To print. That is, when the mode selection signal is a signal for the gray coded symbol mapping mode, the coded signals C1 and C0 are selected. When the mode selection signal is a signal for the differential coded symbol mapping mode, D1 and D0 are selected and output.

The IQ mapper 130 receives the two signals C1 and C0 or D1 and D0 and the 2-bit unsigned signals L1 and L0 output from the multiplexer 120 and then differentials regardless of the mode selection signal. Perform mapping for coded symbols. 6 shows a gray coded symbol mapping and FIG. 7 shows a differential coded symbol mapping.

The IQ mapper 130 always performs differential symbol mapping operation. The IQ mapper 130 searches for a look-up table that stores a 4-bit constellation symbol by using the input signal. Print an array symbol. However, when the 16 QAM mapping apparatus 100 operates in the gray coded symbol mapping mode, as shown in FIGS. 6 and 7, the results of performing the gray coded symbol mapping and the differential coded symbol mapping are different from each other. 130 does not output the desired correct signal.

Meanwhile, referring to the gray coded symbol mapping diagram of FIG. 6 and the differential coded symbol mapping diagram of FIG. 7, only portions indicated by dotted lines are different from each other. In the two mapping modes, the parts having different values (indicated by dashed lines) have a common logic value between the 4th bit and the 3rd bit, and the 2nd bit and the 1st bit. The 4th bit and the 3rd bit mean the output signal of the multiplexer 120, and the 2nd bit and the 1st bit mean the unsigned signals L1 and L0. Therefore, the output signals of the multiplexer 120 and the 2nd bit are uncoded. The logic values of the signals L1 and L2 are examined, and if this is the case, the IQ value adjustment signal is sent to the IQ value adjustment unit 140 to adjust the mapping.

The IQ value adjustment controller 150 receives the unsigned signals L1 and L0 and the output signals of the multiplexer 120 to determine whether the IQ value needs to be adjusted for the mapping signal output from the IQ mapper 130. If the IQ value needs to be adjusted, the IQ value adjustment unit 140 outputs an IQ value adjustment signal.

As an example of configuring the I-Q value adjusting controller 150, two exclusive OR gate elements 151 and 152 and one AND gate element 153 may be configured.

The first exclusive OR gate element 151 receives L1 and L0 as input signals, and the second exclusive OR gate element 152 receives two output signals of the multiplexer 120 as input signals. That is, when the upper two bits of the portion indicated by the dotted lines in FIGS. 6 and 7 have different logic values, the output signal of the second exclusive OR gate element 152 has the logic value '1' and the lower two bits. When the bits have different logic values, the output signal of the first exclusive OR gate element 151 has a logic value '1'.

The AND gate element 153 receives the output signals of the two exclusive OR gate elements 151 and 152, and the logic value only when the output signals of the two exclusive OR gate elements 151 and 152 both have a logic value of '1'. Print '1'. That is, the output signal of the AND gate element 153, that is, the IQ value adjustment controller 150 only when the logic values of the upper two bits are different from each other and the logic values of the lower two bits are different in the dotted lines of FIGS. 6 and 7. The logic value of the output signal (IQ value adjustment signal) becomes '1'.

The IQ value adjusting unit 140 receives an output signal of the IQ mapper 130 and also receives a mode selection signal and an output signal of the IQ value adjusting control unit 150 as control signals. In the case of the signal for the mode, since the IQ mapper 130 performs the mapping on the differential encoding symbol, the IQ mapper 130 passes the output signal as it is. However, when the mode selection signal is a signal for the gray coded symbol mapping mode, since the I-Q mapper 130 performs the mapping on the differential coded symbol, the mapping result may not match the desired mapping. In this case, the output signal of the IQ value adjustment controller 150, that is, the IQ adjustment signal is examined, and if the IQ adjustment signal has a logic value '1', the output signal of the IQ mapper 130 is gray coded symbol mapping. Convert it to match the signal.

As shown in the dotted lines of FIGS. 6 and 7, when the output signals of the IQ mapper 130 are 0101, 0110, 1010, and 1001, respectively, 0110, 0101, 1001, and 1010 to match the gray coded symbols. To convert That is, the lower two bits (the second bit and the first bit) change positions with each other. Thereafter, the output signal of the I-Q value adjusting unit 140 is sent to the QAM modulator, and the signal modulated by the QAM modulator is transmitted through the channel.

When using the 16-mode QAM mapping apparatus 100 of a cable modem that supports the gray coded symbol mapping and the differential coded symbol mapping of the present invention, only the mode selection signal is changed to change the gray coded symbol mapping mode or the differential coded symbol mapping mode. In any mapping mode, the 16 QAM mapping apparatus 100 can be operated.

Claims (1)

16. A QAM mapping apparatus for cable modems that receives a 2-bit coded signal and a 2-bit uncoded signal, comprising: a differential coder (110) for differentially encoding the coded signal; A multiplexer 120 which selects and outputs one of an output signal and an encoded signal of the differential encoding unit 110 according to an arbitrary mode selection signal; An I-Q mapper 130 for receiving the output signal and the uncoded signal of the multiplexer 120 and performing differential coded symbol mapping accordingly; An I-Q value adjustment control unit 150 for outputting an I-Q value adjustment signal instructing I-Q value adjustment when the logic values of the unsigned signals are different and the logic values of the output signals of the multiplexer 120 are also different; And When the mode selection signal is a signal for gray coded symbol mapping, the IQ value adjuster 140 adjusts an output signal of the IQ mapper 130 to a signal suitable for gray coded symbol mapping according to the IQ value adjustment signal. 16 QAM mapping device 100 of the cable modem supporting gray coded symbol mapping and differential coded symbol mapping, characterized in that comprises a.