KR20000037876A - Method for mapping qam symbol of cable modem - Google Patents

Abstract

PURPOSE: A method for mapping a QAM symbol of a cable modem is provided to reduce a size of a hardware by performing a symbol mapping using one 256 QAM constellation. CONSTITUTION: A method for mapping a QAM symbol of a cable modem comprises the following steps. Four symbols of 8 bits corresponding to a 256 QAM constellation coordinate are designated as one bundle. Total number is 64. Any one 8-bit symbol of each bundle is designated as a representative symbol. A symbol mapping performed by the 256 QAM constellation if data of the 8 bits are inputted. The 64 QAM symbol mapping is performed by ignoring 2 bits of the representative symbols of the 8 bits if data of 6 bits are inputted.

Description

Quadrature Amplitude Modulation Symbol Mapping Method for Cable Modem

TECHNICAL FIELD The present invention relates to a cable modem, and in particular, to a symbol modem, a quadrature amplitude modulation symbol mapping method for mapping symbols using 64 QAM constellations in common by one 256 QAM constellation. It is about.

Currently, computer communication is actively used as a method for acquiring a lot of information using a computer at home or office.

Through such computer communication, it is possible to acquire not only text information but also image information, audio information, and the like, and to send and receive necessary information by communication with a counterpart.

Furthermore, video communication that can communicate while face-to-face with the other party has been developed, and in the future, it will be extended to areas such as video on demand.

As one of the most widely used computer communication schemes, as shown in FIG. 1, an analog modem 110 is built in or external to the computer 100 and connected to the telephone station 130 through the telephone line 120. 130 is connected to a service company in charge of a communication service to perform communication.

That is, when the user enters the telephone number of the service company through the computer 100 in order to communicate with the computer, the analog modem 110 dials it and transmits the telephone number to the telephone station 130 through the telephone line 120. do.

The telephone station 130 connects a line between the computer 100 and the service company by connecting to a communication service company corresponding to the telephone number dialed by the user.

Then, when the user inputs the data to be transmitted through the computer 100, the analog modem 110 converts it into an analog signal and transmits it to the telephone station 130 through the telephone line 120.

Therefore, the telephone station 130 transmits data input from the user to the communication service company to connect with other users.

Meanwhile, when the user receives data from the other party, the analog modem 110 receives the data through the telephone line 120 connected to the telephone station 130, and then converts the received data into a digital signal so that the user can enter the computer 100. ), You can check the received data.

By the way, when performing the communication through the telephone line 130 using the analog modem 110 as described above, the communication speed is limited, so that a large amount of data can be quickly exchanged, and there are many restrictions.

That is, the maximum speed that can transmit and receive data through the telephone line 130 is 56kbps is limited because of its characteristics, so the delay time is increased when sending and receiving video information, especially on-demand video, such as the service itself is impossible do.

Therefore, in order to solve such a problem, a communication scheme using a cable modem has recently been devised.

The cable modem is connected to a high-speed dedicated cable, for example, to be able to communicate by using a dedicated cable of a cable television currently being watched at home.

FIG. 2 is a circuit block diagram of a typical cable modem. When the data of the packet modem RS (Reed-Solomon) encoder 200 is inputted in the unit of packet data to be uploaded, error correction by RS code, that is, error of burst noise Correction is made.

This RS code is a code capable of correcting a large number of errors in a partition which is a kind of non-binary cyclic code, and has excellent ability to correct cluster errors.

Packet data corrected by the RS encoder 200 is applied to the scrambler 210 to perform scrambling, which is a receiver designed according to this rule by mixing a unique arrangement or characteristic of a digital signal into a promised rule. Only this signal can be restored to the original signal, to prevent the loss of bit boundary information of successive digital signals, and to prevent cross-modulation in the channel caused by a single frequency component caused by periodic data.

The output of the scrambler 210 is applied to the symbol mapping unit 220 and data input as symbols suitable for modulation are mapped and output. This will be described with reference to FIGS. 3, 5, and 6.

FIG. 3 is a detailed block diagram of the symbol mapping unit 220. When 6 bits of data are input from the scrambler 210, the 64 QAM symbol mapper 221 receives the 64 QAM cone as shown in FIG. 6-bit data input by the stealization is mapped and output. On the other hand, when 8-bit data is input, the 256-QAM constellation as shown in FIG. 6 is received by the 256 QAM symbol mapper 222. The 8-bit data input by MAP is mapped and output.

Accordingly, the outputs of the 64 QAM symbol mapper 221 and the 256 QAM symbol mapper 222 are selected by the switching means 223 and provided to the filter 230, and the filter 230 receives the frequency bandwidth. Filtering is performed to limit

The output of the filter 230 is applied to the modulator 240, modulated into a quadrature phase shift keying (QPSK) signal, and then transmitted to a cable modem termination system (CMTS) through a cable network.

Therefore, the CMTS receives the data transmitted from the cable modem and performs demodulation, descrambling, and RS decoding to restore the original data.

However, since a symbol mapper having different constellations is required for the number of bits of data input during symbol mapping in the cable modem, that is, the 64 QAM signal and the 256 QAM signal, each symbol mapper must be set up separately. There is a problem that the size and size of the hardware is increased.

Therefore, in view of the above problems of the related art, the present invention provides simplicity of design and hardware by mapping symbols using 64 QAM constellations in common by one 256 QAM constellation in symbol mapping. An object of the present invention is to provide a quadrature amplitude modulation symbol mapping method for a cable modem to reduce its size.

1 is a diagram for explaining a communication state of an analog modem using a general telephone line.

2 is a circuit block diagram of a typical cable modem.

3 is a detailed block diagram of a symbol mapping unit of FIG. 2;

4 illustrates a symbol mapping apparatus for realizing the present invention.

5 is a view for explaining a process of generating a 64 QAM constellation by 256 QAM constellation according to the present invention.

6 is a block diagram of a 64 QAM constellation newly constructed in accordance with the present invention.

<Description of the code | symbol about the principal part of drawing>

200: RS encoder 210: scrambled part

220: symbol mapping unit 230: filter

240: modulator 300: QAM symbol mapper

310: bit selector

In order to achieve the above object, the quadrature amplitude modulation symbol mapping method of a cable modem has a total of 64 bundles of four 8-bit symbols corresponding to 256 QAM constellation coordinates. Any one 8-bit symbol is designated as a representative symbol of each bundle, and when 8-bit data is input, symbol mapping is performed by the 256 QAM constellation. When 6-bit data is input, the 8-bit symbol is performed. 64 QAM symbol mapping is performed by ignoring the lower 2 bits of the representative symbols of.

This will be described in detail with reference to the accompanying drawings.

First, the process of generating 64 QAM constellations by 256 QAM constellations according to the present invention will be described.

As shown in FIG. 5, four 256 8-bit symbols corresponding to each coordinate of the general 256 QAM constellation are grouped into one bundle. For example, four 8-bit symbols in the A portion of the upper right part are shown. These are 11001111, 11111111, 11001100, and 11111100, and a total of 256 8-bit symbols exist in 64 bundles by using these four symbols in a bundle.

At this time, each bundle has one representative symbol, which is represented by a circle, for example, the value of the representative symbol of the A portion is 11111111.

The representative symbol represented by this circle has a different value for each 64 bundles, and the upper 6 bits of this representative symbol are the same as each symbol of the 64 QAM constellation as shown in FIG.

Of course, instead of using the representative symbol specified in the present invention, one of the remaining three symbols in a bundle may be selected, and only six bits of the eight bits may be selected as the representative symbol.

Accordingly, by this method, symbols of 64 QAM constellations can be designated using 256 QAM constellations as shown in FIG.

Therefore, when 8-bit data, that is, 256 QAM data, is input from the scrambler 210, the bit selector 310 detects the number of bits and performs symbol mapping for 64 QAM, or symbol mapping for 256 QAM. Determine whether or not.

In this case, since the symbols of the 64 QAM constellation are designated in the 256 QAM constellation in the QAM symbol mapper 300, when the 6-bit data, that is, the 64 QAM data is input from the scrambler 210, the bit selector 310 is input. Since it is determined that symbol mapping for 64 QAM is performed, ignoring data of the lower 2 bits among the representative symbols of 64 QAM specified in the 256 QAM constellation of the QAM symbol mapper 300 has only the symbols of the upper 6 bits. A command is applied to the QAM symbol mapper 300 to perform symbol mapping on the input 6-bit data.

Accordingly, the QAM symbol mapper 300 disregards the lower two bits of data among the eight ratio representative symbols and maps the symbols by the upper six bits, and provides the mapped result to the filter 230.

On the other hand, it is determined that it is a symbol mapping for 256 QAM in which 8 bits of data are input from the scrambler 210, and bit selection is performed so that a symbol for 8 bits of data directly input can be mapped by 256 QAM constellation. The unit 310 outputs a command thereof to the QAM symbol mapper 300 to perform symbol mapping, and then provides the mapped result to the filter 230.

As described above, the quadrature amplitude modulation symbol mapping method of the cable modem of the present invention reduces the simplicity of the design and the hardware size by mapping the symbols by using a common 64 QAM constellation by one 256 QAM constellation in symbol mapping. There is an effect to be.

Claims (3)

Four groups of eight 8-bit symbols corresponding to 256 QAM constellation coordinates are combined into a total of 64 bundles, and one of the eight-bit symbols is designated as the representative symbol of each bundle. When the bit data is input, symbol mapping is performed by the 256 QAM constellation. When the 6 bit data is input, 64 QAM symbol mapping is performed by ignoring 2 bits of the 8-bit representative symbols. Quadrature amplitude modulation symbol mapping method of a cable modem. 2. The method of claim 1, wherein in the case of 64 QAM symbol mapping, the lower 2 bits of the 8-bit representative symbol are ignored. The method of claim 1, wherein one of the remaining three 8-bit symbols other than the representative symbol of each bundle can be selected and designated as the representative symbol.