This application claims priority to and the benefit of Korean Patent Application No. 2004-102911, filed on DEC. 8, 2004, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a cable transmission system, and more particularly, to a QAM (Quadrature Amplitude Modulation) symbol mapping method and apparatus for a 64 QAM mode and a 256 QAM mode in downstream transmission.
2. Discussion of Related Art
In a cable transmission system, downstream transmission is performed according to ITU-T Recommendations J. 83, Annex B.
The trellis encoder 240 performs a TCM, which is a channel coding method for obtaining a high coding gain from a bandwidth-limited channel, and is embodied in a combined format of a coding technology and a modulation technology. The TCM structure is comprised of a 64/256 QAM modulator and a convolutional encoder having a limited state.
Korean Patent Publication No. 2000-14483 entitled “QAM MAPPER AND DEMAPPER FOR DOWNSTREAM TRANSMISSION OF CABLE MODEM” discloses a QAM mapping apparatus in which, in order to reduce a size of a memory used in a symbol mapping lookup table, phase information of a QAM symbol is determined by mapping two convolution coded bits of a QAM-TCM modulation mode to any one of four phases according to a method for differential coding between QAM symbols continuous on a time axis, and amplitude information uses a remaining bit pair as is.
However, the QAM mapping apparatus has a drawback in that since the method for extracting the phase information of the QAM symbol differs depending on the differential coding methods, a hardware structure should be changed to match differential coding mechanisms. Further, since the QAM mapping apparatus also uses memory and therefore its operation speed is limited by memory access time, it is not suitable for a high-speed data transfer system.
Accordingly, it is required to develop a QAM symbol mapping apparatus that is capable of extracting the phase information of the QAM symbol irrespective of differential coding mechanisms and does not use a memory so that it can be suitably applied to a high-speed data transfer system.
The present invention is directed to implementation of a QAM symbol mapping method and apparatus for determining a QAM symbol irrespective of differential coding mechanisms.
The present invention is also directed to implementation of a QAM symbol mapping method and apparatus for determining phase information of a QAM symbol using certain relations between input bits, which may be obtained by analysis of a constellation diagram.
The present invention is also directed to implementation of a QAM symbol mapping method and apparatus for separating I and Q symbols from input bits representing amplitude information, using certain relations between input bits, which may be obtained by analysis of a constellation diagram, without using a memory.
One aspect of the present invention provides a QAM (Quadrature Amplitude Modulation) symbol mapping method, including the steps of: determining phase information on the basis of predetermined relations between two bits representing set partitioning information and two LSBs (Least Significant Bits) of bits representing amplitude information, among bits input for QAM symbol mapping; separating I and Q signals of a first quadrant from the bits representing the amplitude information; and mapping the I and Q signals of the first quadrant to actual positions on the basis of the determined phase information.
Another aspect of the present invention provides a QAM (Quadrature Amplitude Modulation) symbol mapping apparatus, including: a phase information extraction means for performing predetermined arithmetic operations between two bits representing set partitioning information and two LSBs (Least Significant Bits) of bits representing amplitude information, among bits input for QAM symbol mapping, to extract phase information; an I/Q signal separating means for separating I and Q signals of a first quadrant from the bits representing the amplitude information; and a mapping means for receiving the phase information from the phase information extraction unit, and mapping the separated I and Q signals of the first quadrant to actual positions on the basis of the received phase information.
The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the exemplary embodiments disclosed below, but can be implemented in various types. Therefore, the present exemplary embodiment is provided for complete disclosure of the present invention and to fully inform the scope of the present invention to those ordinarily skilled in the art.
As shown in
First, to aid in understanding a bit signal input to the QAM symbol mapping apparatus 400, referring again to
Referring to
As shown in Table 1, the phase information can be extracted through logic arithmetic operation between C3 and C0 representing the set partitioning information and C2 and C1 corresponding to the two LSBs of the amplitude information in the 64 QAM. In other words, “P1” denoting the phase value of the first quadrant is output as “1” when C3=C1 and C0=C2 are simultaneously satisfied, otherwise, it is output as “0.” “P2” denoting the phase value of the second quadrant is output as “1” when C3=
Similarly, referring to
As shown in Table 2, in the 256 QAM, only corresponding bits differ like C4=C5 and C0=C1, and the relations between two LSBs of the amplitude information and the set partitioning information are identical. In other words, the phase information “P1” representing the first quadrant is output in the case the C4=C5 and C0=C1, the phase information “P2” representing the second quadrant is output in the case the C4=
Accordingly, the inventive phase extraction unit 410 performs the logic arithmetic operations between the two bits of the set partitioning information and two LSBs of the amplitude information, based on the results of Tables 1 and 2, to extract the phase information of the symbol. A logic arithmetic circuit diagram of the phase extraction unit 410 is illustrated in
The phase extraction unit 410 includes four input units I1, I2, I3 and I4. In the 64 QAM mode, the bits C2 and C1 corresponding to the two LSBs of the amplitude information are respectively input to the input units I1 and I2, and the bits C3 and C0 representing the set partitioning information are respectively input to the input units I3 and I4. In the 256 QAM mode, the bits C1 and C5 corresponding to the two LSBs of the amplitude information are respectively input to the input units I1 and I2, and the bits C4 and C0 representing the set partitioning information are respectively input to the input units I3 and I4. Phase extraction is performed through the logic arithmetic operations between the bits input to the input units I1 and I2, and the bits input to the input units I3 and I4. It will be understood by those skilled in the art that the logic arithmetic operation of
Now, the analysis results of the constellation diagrams of the 64 QAM and the 256 QAM of
Accordingly, the inventive I/Q signal separation unit 420 separates the I and Q signals of the first quadrant from the amplitude information on the basis of the constellation diagram analysis result. Here, the output I and Q signals are expressed using the signals of the first quadrant. The amplitude information input to the QAM symbol mapping apparatus is not separated as I and Q signals. Accordingly, the conventional art uses the input amplitude information as an address of a memory, to extract the corresponding I and Q signals, but the present invention adopts a method for directly extracting the I and Q signals from the input bit information in order to avoid use of a memory.
As shown in
Referring again to
As shown in
As described above, in the inventive QAM symbol mapping method and apparatus, the phase information is extracted on the basis of the constellation diagram fixedly determined depending on the modulation mode, irrespective of a differential coding method. And, I and Q signals can be directly calculated from the amplitude information without using the memory, thereby using hardware efficiently, reducing cost, increasing process speed, and enhancing extendibility.
While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
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10-2004-0102911 | Dec 2004 | KR | national |
Number | Date | Country |
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2334862 | Sep 1999 | GB |
1020000014483 | Mar 2000 | KR |
Number | Date | Country | |
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20060140299 A1 | Jun 2006 | US |