JP2015188167A - Communication apparatus and mapping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a bit error rate in a QAM scheme.SOLUTION: A QAM mapping device for modulating data by QAM uses a mapping pattern in which bits of an upper-level side (MSB side) of a symbol are allocated to a synchronization signal per quadrant of an IQ plane representing the position of a symbol and performs synchronization processing only by the upper-level side bits. The QAM mapping device uses a mapping pattern in which bits of the same lower-level side (LSB side) are allocated to symbols adjacent to each other with I axis or Q axis in between, and reduces a bit error rate at a time of determination occurring when distance between symbols in different quadrants is short.

Description

  The present invention relates to a QAM mapping technique for reducing a bit error rate.

  In a system of 100 Gbps or more using optical transmission technology, there is a problem that distortion in the transmission line cannot be completely compensated even if a known dispersion compensation technology is used. In response to this problem, it has become possible to improve the compensation technique by introducing digital signal processing using a digital coherent signal processing technique. In addition, by using digital coherent signal processing technology, processing such as phase estimation and polarization separation can be realized by digital signal processing, and technologies such as higher-speed multi-level modulation and polarization multiplexing can be used. ing.

  Note that a case using a DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) signal is disclosed in a 100 Gbps optical transmission system (see Non-Patent Document 1). The digital coherent signal processing technology can be realized using a highly versatile DSP (Digital Signal Processor), and its introduction into commercial services is being studied.

  In the optical transmission technology, in order to realize further high speed and large capacity, it is desired to study a method using more symbols in multilevel modulation. QAM (Quadrature Amplitude Modulation), which is a type of multi-level modulation, is a method of modulating transmission data by changing both phase and amplitude, and can increase the transmission speed. In the 16QAM signal, any 16-value phase / amplitude information is superimposed on each orthogonal polarization. Therefore, for example, it is possible to transmit 25 G × 4 × 2 = 200 Gbit information by using 4 bits of information (symbol) and two polarizations for a 25 GBaud signal.

T. Kobayashi, et al., “8-Tb / s (80x127Gb / s) DP-QPSK L-band DWDM Transmission over 457-km Installed DSF Links with EDFA-only amplification”, 15th Opto Electronics and Communications Conference (OECC2010) Technical Digest ,, July 2010

The QAM system is a modulation system that combines phase change and amplitude change. When a large number of bits assigned per symbol is set, transmission efficiency is improved. However, in the QAM system, when the bit string is arranged so that the hamming distance between adjacent symbols (distance between codes: the number of bits different when comparing two binary numbers) is varied, the bit of the transmission data There is a problem that the error rate becomes high. In the QAM scheme, the larger the number of bits allocated per symbol, the closer the amplitude distance and the phase distance between symbols, so that the bit error rate of transmission data may increase. The amplitude distance is a difference with respect to the distance from the origin on the IQ plane represented by the in-phase axis and the quadrature axis, and the phase distance is a rotation angle around the origin. It is a difference.
Also, if a phase slip occurs depending on the transmission quality of the transmission line, the performance of the device, etc., the mapping state at the time of transmission cannot be restored correctly on the receiving side, so the bit error rate of transmission data increases. There is also a problem.

  Therefore, an object of the present invention is to provide a QAM mapping apparatus and a mapping method for reducing the bit error rate in the QAM scheme.

  The QAM mapping apparatus of the present invention is a QAM mapping apparatus that modulates data by QAM, and in the IQ plane that represents the position of the symbol of the QAM, as a bit string to be assigned to the symbol in the same quadrant, A mapping pattern storage unit storing a mapping pattern in which the same bit string is arranged on the MSB side (Most Significant Bit side), and reading the upper bit string of the symbol from the mapping pattern, And a mapping unit that modulates the higher-order bit string of the data based on the bit string.

  According to such a configuration, the QAM mapping apparatus can transmit only the same bit string on the upper side (MSB side), that is, the bit string of symbols in the same quadrant on the IQ plane. As a result, on the receiving side, it can be understood as what kind of bit string the transmitted bit string on the higher order side (MSB side) is received. As a result, the QAM mapping apparatus can accurately compensate for chromatic dispersion and phase noise, thereby reducing the bit error rate.

  Further, in the QAM mapping apparatus, the mapping pattern storage unit further converts the higher-order bit as a bit string of adjacent symbols across the I-axis or Q-axis of the IQ plane in addition to the higher-order bit string. A mapping pattern in which the same bit string is arranged on the lower side (LSB side; Least Significant Bit side) is stored, and the mapping unit reads the bit string of the symbol from the mapping pattern, and based on the read bit string The high-order bit sequence and the low-order bit sequence of the data are modulated.

  According to such a configuration, the QAM mapping apparatus can assign the same bit sequence to the lower side of the bit sequence of adjacent symbols across the I axis or the Q axis. Therefore, the QAM mapping apparatus can reduce the bit error rate at the time of determination that occurs when the distance between symbols in different quadrants is short.

  In the QAM mapping apparatus, the mapping pattern storage unit further converts the upper bit as a bit string of a symbol at a position rotated by 90 degrees with respect to the origin of the IQ plane, in addition to the upper bit string. A mapping pattern in which the same bit string is arranged on the lower side except the mapping pattern, and the mapping reads the bit string of the symbol from the mapping pattern, and based on the read bit string, the upper side and the lower side of the data The bit string is modulated.

  According to such a configuration, the QAM mapping apparatus can assign the same bit sequence to the lower side (LSB side) of the symbol bit sequence at a position rotated by 90 degrees with respect to the origin of the IQ plane. Therefore, the QAM mapping apparatus can reduce the bit error rate accompanying the phase slip.

  The invention relating to the mapping method has the same technical features as the above-described QAM mapping apparatus and has the same effect as the QAM mapping apparatus. The description in is omitted.

  According to the present invention, the bit error rate can be reduced in the QAM scheme.

It is a figure which shows the example of a function of a communication apparatus. It is a figure which shows an example of the mapping pattern in a comparative example. It is a figure which shows an example of the 1st mapping pattern. It is a figure which shows the relationship between the symbol at the time of using a 1st mapping pattern, and IQ value. It is a figure which shows the example of the threshold value used for the symbol determination at the time of using a 1st mapping pattern. It is a figure which shows an example of the simulation result about the transmission line with bad quality. It is a figure which shows an example of the 2nd mapping pattern. It is a figure which shows the relationship between the symbol at the time of using a 2nd mapping pattern, and IQ value. It is a figure which shows the example of the threshold value used for the symbol determination at the time of using a 2nd mapping pattern.

  A mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings as appropriate. In this embodiment, a case where the 16QAM system is used will be described as an example.

(Communication device)
An example of functions of a communication apparatus that transmits and receives data modulated by the QAM method will be described with reference to FIG.
As shown in FIG. 1, a communication apparatus 1 includes a transmission information generation unit 2, a mapping unit 3, a DA (digital / analog) conversion unit 4, an optical signal modulation unit 5, an optical signal demodulation unit 6, and an AD (analog / digital) conversion unit. 7, a determination unit 8, a reception information synchronization unit 9, a synchronization insertion information storage unit 10, a mapping pattern storage unit 11, and a threshold information storage unit 12. The mapping unit 3 and the mapping pattern storage unit 11 are functions of the QAM mapping device 13.

  The transmission information generation unit 2 receives data to be transmitted (hereinafter referred to as transmission data), divides the received transmission data into a plurality of lanes, and uses synchronization insertion information for use in synchronization processing on the reception side. It has a function of reading from the synchronization insertion information storage unit 10. The transmission information generation unit 2 has a function of generating transmission information including transmission data and synchronization insertion information and outputting the transmission information to the mapping unit 3. For example, the transmission information generation unit 2 may separate the received transmission data into two and generate polarization data for each of two orthogonal polarizations.

  The mapping unit 3 has a function of modulating the received transmission information by 16QAM method for each polarization. In the 16QAM system, 4-bit information is allocated to one of 16 symbols. The mapping unit 3 converts the received transmission information into an IQ value (in-phase I value and quadrature Q value) corresponding to the symbol position on the complex plane (IQ plane), and outputs the IQ value. The relationship information indicating to which symbol the 4-bit information is assigned is the mapping pattern. The mapping pattern is stored in the mapping pattern storage unit 11. A plurality of types of mapping patterns may be prepared.

  The mapping unit 3 receives the mapping pattern selection information, selects a mapping pattern corresponding to the mapping pattern selection information from the mapping pattern storage unit 11, and executes the modulation process. The mapping pattern selection information is determined according to information such as transmission path quality, bit error rate during transmission, and slip rate. As a result, the mapping unit 3 can select an optimum mapping pattern from a plurality of mapping patterns according to the state of the transmission path, and can reduce the bit error rate during transmission.

  The DA conversion unit 4 has a function of converting the IQ value received from the mapping unit 3 into an analog signal and outputting the analog signal to the optical signal modulation unit 5. The DA converter 4 may use a commercially available DA converter.

  The optical signal modulator 5 has a function of converting the analog signal received from the DA converter 4 into an optical signal and sending the optical signal to a transmission line such as an optical fiber. The optical signal modulator 5 may be a commercially available optical modulator.

  The optical signal demodulator 6 has a function of converting an optical signal received from a transmission line such as an optical fiber into an electrical signal and outputting the analog signal that is the electrical signal to the AD converter 7. The optical signal demodulator 6 may use a commercially available optical demodulator.

  The AD conversion unit 7 has a function of converting the analog signal received from the optical signal demodulation unit 6 into a digital signal and outputting the digital signal to the determination unit 8. The AD converter 7 may use a commercially available AD converter.

  The determination unit 8 has a function of acquiring an IQ value from the received digital signal, performing IQ value threshold processing, and determining one symbol from the 16 symbol positions. The determination unit 8 has a function of acquiring 4-bit information corresponding to the determined symbol position and outputting the acquired 4-bit information to the reception information synchronization unit 9. When performing the threshold process, the determination unit 8 acquires threshold information from the threshold information storage unit 12 and determines a symbol position.

  The reception information synchronization unit 9 has a function of detecting synchronization insertion information and performing synchronization processing. The reception information synchronization unit 9 outputs the data restored in synchronization as reception data.

The synchronization insertion information storage unit 10 stores synchronization insertion information referred to by the transmission information generation unit 2.
The mapping pattern storage unit 11 stores a mapping pattern referred to by the mapping unit 3. A specific example of the mapping pattern in the present invention will be described later.
The threshold information storage unit 12 stores threshold information referred to by the determination unit 8.

(Mapping pattern)
Next, one mapping example and two examples of the present invention (first mapping pattern and second mapping pattern) will be described below.

(Comparative example)
First, a mapping pattern based on a Gray code will be described as a comparative example.
FIG. 2 is an example of the mapping pattern of the comparative example. In the IQ plane, the 16 symbols are arranged in a 4 × 4 grid. When assigning 4-bit information to a symbol, a Gray code is generally used so that the Hamming distance between adjacent symbols is 1 (only 1 bit differs).

  In FIG. 2, two bits on the upper side (MSB side) of the 4-bit string are the same between four symbols having the same I value on the IQ plane. Also, the two bits on the lower side (LSB side) are the same between four symbols having the same Q value on the IQ plane. The mapping pattern shown in FIG. 2 is a gray code in which the hamming distance between adjacent symbols is all 1. The Gray code mapping pattern can reduce the hamming distance between adjacent symbols, thereby reducing the bit error rate. Further, since the gray code mapping pattern can make the distances between all adjacent symbols equal, the variation in bit error rate can be reduced. For this reason, the Gray code mapping pattern can prevent a decrease in transmission performance.

(First mapping pattern)
Next, an example of the mapping pattern of the present invention (first mapping pattern) will be described with reference to FIG. 3 (see FIG. 1 as appropriate).
As shown in FIG. 3, in the first mapping pattern, a bit string representing the position of each quadrant on the IQ plane is arranged in 2 bits on the upper side (MSB side) of the 4 bit strings, and the lower side (LSB side) Two bits are arranged in four symbols in each quadrant. In the first mapping pattern, 16 pieces of 4-bit information are arranged in accordance with the Gray code, similarly to the mapping pattern of the comparative example. In addition, the first mapping pattern is arranged so that the lower 2 bits (LSB side) are the same between adjacent symbols sandwiching the I axis and between adjacent symbols sandwiching the Q axis.

  In general, distortion is applied to data that has passed through a transmission path or device. For this reason, the bit error rate of the received data is increased on the receiving side by misjudging adjacent symbols with distortion (determining symbols different from those at the time of transmission). Therefore, there arises a problem that the probability of detecting the synchronization insertion information decreases.

  In order to solve the problem, since the upper 2 bits (MSB side) represent the quadrant in the first mapping pattern, on the transmitting side, the mapping unit 3 performs the upper 2 bits (MSB side). Generate data that is known in advance. Then, on the reception side, the determination unit 8 determines what bit string is received as the bit string on the higher-order side (MSB side) of the received data. Therefore, estimation of chromatic dispersion, estimation of phase noise, and the like can be performed almost accurately based on the variation in the bit string on the higher-order side (MSB side) of the received data. As a result, the communication device 1 can accurately perform chromatic dispersion compensation and phase noise compensation even under conditions of poor transmission quality due to effects of ASE (Amplified spontaneous emission) noise, transmission distance, and the like. The probability of detection can be improved as compared with the comparative example. Also, the first mapping pattern can reduce the bit error rate compared to the comparative example.

  In the first mapping pattern, two bits on the LSB side are arranged in the same manner between adjacent symbols sandwiching the I axis or Q axis indicating the boundary between quadrants of the IQ plane. Therefore, the first mapping pattern can reduce the bit error rate even when the symbol position fluctuates across the I axis or the Q axis between quadrants.

Here, the relationship between the symbol and the IQ value when the first mapping pattern is used will be described with reference to FIG. 4 (see FIG. 1 as appropriate).
The mapping unit 3 converts the transmission data into symbols every 4 bits based on the first mapping pattern, converts the symbols into IQ values (I value and Q value), and outputs them. As shown in FIG. 4, the I value is represented by any one of −Iout2, −Iout1, Iout1, and Iout2. As shown in FIG. 4, the Q value is represented by any one of −Qout2, −Qout1, Qout1, and Qout2. However, | Iout2 |> | Iout1 | and | Qout2 |> | Qout1 |.
For example, when transmitting the symbol “1001”, the mapping unit 3 outputs I value = −Iout2 and Q value = Qout1.

The I value and Q value can be set and changed as gradation values. For example, a description will be given of a case where the range in which symbols are present is expressed by the gradation of ± 32 (6 bits) on the I value axis. When the maximum value and the minimum value of the axis of the I value correspond to the range of the coordinate value of ± 1.0, gradation value = 24 corresponds to I value = 0.75 (= 24/32). Value = 8 corresponds to I value = 0.25 (= 8/32). Here, the Q value is also assumed to be Qout1 = Iout1 and Qout2 = Iout2, as in the case of the I value.
For example, when transmitting the symbol “1001”, the gradation value may be I value = −Iout2 = −0.75 and Q value = Qout1 = 0.25.

Next, an example of a threshold value used for symbol determination when the first mapping pattern is used will be described with reference to FIG. 5 (see FIG. 1 as appropriate).
The determination unit 8 sets a threshold for the IQ value of the symbol and executes threshold processing as shown by the dotted line in FIG. The threshold value of the I value is represented by, for example, -TH_I, 0, + TH_I. Further, the threshold value of the Q value is represented by -TH_Q, 0, + TH_Q. That is, the determination unit 8 divides the IQ plane into 16 regions, determines which region the IQ value of the symbol belongs to, and outputs a 4-bit string corresponding to the region. In addition, on the dotted line of the threshold value, it may be determined in advance which region belongs to. The threshold values of the I value and the Q value are stored in the threshold information storage unit 12.

  FIG. 6 shows a simulation result for a transmission line with poor quality. As can be seen from FIG. 6, on the receiving side, it can be seen that the IQ values of the symbols vary and straddle the I axis or the Q axis. Even in the case shown in FIG. 6, by using the first mapping pattern, the synchronization process can be performed accurately, and the bit error rate can be reduced.

  In the above, the case of 16QAM in which 4 bits are mapped to one symbol has been described, but the first mapping pattern can be extended when one symbol is 5 bits or more. Specifically, 2 bits on the upper side (MSB side) are used as information representing a quadrant, and 3 bits or more on the lower side (LSB side) excluding the upper side (MSB side) are used as information representing a symbol position in the quadrant. . Then, as in the case of 16QAM, the bit strings on the lower side (LSB side) of adjacent symbols across the I axis or Q axis may be made the same. In this way, a multi-value QAM scheme (for example, 32QAM, 64QAM, 128QAM, etc.) of 5 bits or more per symbol can be easily realized. The effect in that case is the same as in the case of 16QAM.

(Second mapping pattern)
Next, another example of the mapping pattern of the present invention (second mapping pattern) will be described with reference to FIG. 7 (see FIG. 1 as appropriate).
Whereas the first mapping pattern is the case where the bits on the lower side (LSB side) between adjacent symbols across the I axis or the Q axis of the IQ plane are the same, the second mapping pattern is the IQ plane. This is different from the case of the first mapping pattern in that the bits on the lower side (LSB side) of the position rotated 90 degrees around the origin of are the same.

  In the second mapping pattern, as shown in FIG. 7, 2 bits on the upper side (MSB side) out of 4 bits are used as information representing the quadrant of the IQ plane. Also, the second mapping pattern is arranged so that two bits on the lower side (LSB side) are the same in the symbol at a position rotated 90 degrees with respect to the origin of the IQ plane.

  There may be a phase slip in the received data due to the influence of various noises due to the transmission quality of the transmission path and the performance of the apparatus. On the receiving side, when phase slip is detected, phase compensation is generally performed in units of 90 degrees. Therefore, by arranging 2 bits on the lower side (LSB side) so as to be rotationally symmetric with respect to the origin of the IQ plane as shown in FIG. 7, 2 bits on the lower side (LSB side) are arranged. The bit error rate can be reduced. For example, in the case of a phase slip in units of 180 degrees, it is possible to reduce the bit error rate even if slipping in either plus or minus directions. As a result, even if the phase slip becomes large due to the influence of noise or the like, the bit error rate can be reduced.

Here, the relationship between the symbol and the IQ value when the second mapping pattern is used will be described with reference to FIG. 8 (see FIG. 1 as appropriate).
The mapping unit 3 converts the transmission data into symbols every 4 bits based on the second mapping pattern, converts the symbols into IQ values (I value and Q value), and outputs them. As shown in FIG. 8, the I value is represented by any one of -Iout2, -Iout1, Iout1, and Iout2. As shown in FIG. 8, the Q value is represented by any one of -Qout2, -Qout1, Qout1, and Qout2. However, | Iout2 |> | Iout1 | and | Qout2 |> | Qout1 |.
For example, when transmitting the symbol “1001”, the mapping unit 3 outputs I value = −Iout1 and Q value = Qout2.

The I value and Q value can be set and changed as gradation values. For example, a description will be given of a case where the range in which symbols are present is expressed by the gradation of ± 32 (6 bits) on the I value axis. When the maximum value and the minimum value of the axis of the I value correspond to the range of the coordinate value of ± 1.0, gradation value = 24 corresponds to I value = 0.75 (= 24/32). Value = 8 corresponds to I value = 0.25 (= 8/32). Here, the Q value is also assumed to be Qout1 = Iout1 and Qout2 = Iout2, as in the case of the I value.
For example, when transmitting the symbol “1001”, the gradation value may be a value of I value = −Iout1 = −0.75 and Q value = Qout1 = 0.25.

Next, an example of a threshold value used for symbol determination when the second mapping pattern is used will be described with reference to FIG. 9 (see FIG. 1 as appropriate).
The determination unit 8 sets a threshold value for the IQ value of the symbol and executes threshold processing as shown by the dotted line in FIG. The threshold value of the I value is represented by, for example, -TH_I, 0, + TH_I. Further, the threshold value of the Q value is represented by -TH_Q, 0, + TH_Q. That is, the determination unit 8 divides the IQ plane into 16 regions, determines to which region the IQ value of the symbol belongs, and outputs a 4-bit string corresponding to the region. In addition, on the dotted line of the threshold value, it may be determined in advance which region belongs to. The threshold values of the I value and the Q value are stored in the threshold information storage unit 12.

As a countermeasure against phase slip, there is a case where differential encoding / decoding of transmission data is used. However, differential encoding has a problem that a 1-bit error is expanded to a 2-bit error. Therefore, when differential encoding is performed, differential encoding is performed only on the upper 2 bits (MSB side), and differential encoding is not performed on the lower 2 bits (LSB side). And As a result, the bit information on the lower side (LSB side) remains unchanged.
On the other hand, when differential encoding is not performed, the lower 2 bits (LSB side) are not changed.
In this way, the second mapping pattern is maintained in the rotationally symmetric bit sequence on the lower side (LSB side) regardless of whether differential encoding is used or not. The bit error rate with respect to the phase slip can be reduced.

  In the above description, the case of 16QAM in which 4 bits are mapped to one symbol has been described. However, the second mapping pattern is applicable even when one symbol has 5 bits or more. Specifically, 2 bits on the upper side (MSB side) are used as information representing a quadrant, and 3 bits or more on the lower side (LSB side) excluding the upper side (MSB side) are used as information representing a symbol position in the quadrant. . Similarly to the case of 16QAM, the bit strings on the lower side (LSB side) of the symbol at the position rotated by 90 degrees with respect to the origin of the IQ plane may be made the same. In this way, a multi-value QAM scheme (for example, 32QAM, 64QAM, 128QAM, etc.) of 5 bits or more per symbol can be easily realized. The effect in that case is the same as in the case of 16QAM.

As described above, the QAM mapping device 13 of the communication device 1 according to the present embodiment uses the first mapping pattern and the second mapping pattern stored in the mapping pattern storage unit 11, and the following (1) to (3) It has the characteristics.
(1) On the IQ plane representing the position of a QAM symbol, the bit strings on the upper side (MSB side) of the symbols in the same quadrant are made the same. That is, estimation of chromatic dispersion, estimation of phase noise, and the like can be accurately performed using only the bits on the upper side (MSB side). Accordingly, the chromatic dispersion and the phase noise can be compensated more accurately than in the comparative example, so that the bit error rate can be reduced.
(2) Compare the bit error rate at the time of judgment that occurs when the same low-order (LSB side) bits are placed in adjacent symbols across the I-axis or Q-axis and the distance between symbols in different quadrants is short This can be reduced compared to the example.
(3) The same low-order (LSB side) bit is arranged in the symbol at a position rotated 90 degrees with respect to the origin of the IQ plane, and the bit error rate due to the phase slip is reduced as compared with the comparative example. it can.

  When a plurality of mapping patterns are stored in the mapping pattern storage unit 11, the mapping unit 3 selects one mapping pattern based on the received mapping pattern selection information. For example, when the first mapping pattern and the second mapping pattern are stored in the mapping pattern storage unit 11, the mapping unit 3 includes information such as transmission path quality information, bit error rate during transmission, and slip rate. Based on, mapping pattern selection information indicating the mapping pattern to be selected is received. As a result, a better mapping pattern can be selected according to the situation, so that the bit error rate can be reduced.

  In FIG. 4, the I value of the symbol has been described as being symmetric with respect to the Q axis, but may be set to be asymmetric. Similarly, the Q value of the symbol may be set to be asymmetric with respect to the I axis.

DESCRIPTION OF SYMBOLS 1 Communication apparatus 2 Transmission information generation part 3 Mapping part 4 DA conversion part 5 Optical signal modulation part 6 Optical signal demodulation part 7 AD conversion part 8 Judgment part 9 Reception information synchronization part 10 Synchronization insertion information storage part 11 Mapping pattern storage part 12 Threshold information storage unit 13 QAM mapping device

Communication device of the present invention is a communication device comprising a QAM mapping unit for modulating data using QAM, the QAM mapping unit, the IQ plane representing the position of the symbols of the QAM, assigned to the symbols in the same quadrant As a bit string, a mapping pattern storage unit storing a mapping pattern in which the same bit string is arranged on the upper side (MSB side; Most Significant Bit side) of the bit string, and reading the upper bit string of the symbol from the mapping pattern A mapping unit that modulates the higher-order bit string of the data based on the read higher-order bit string, and the communication device acquires an IQ value from a signal received from a transmission path, By performing IQ value threshold processing using predetermined threshold information, the symbol position can be determined. Characterized in that it comprises a determination unit, for performing.

According to such a configuration, QAM mapping device can transmit the same bit string of the upper side (MSB side), i.e., the bit string of the symbol in the same quadrant on the IQ plane only. As a result, on the receiving side, it can be understood as what kind of bit string the transmitted bit string on the higher order side (MSB side) is received. As a result, the communication apparatus can accurately compensate for chromatic dispersion and phase noise, thereby reducing the bit error rate.

In the communication apparatus, the mapping pattern storage unit may further exclude the upper bits in addition to the upper bit string as a bit string of adjacent symbols across the I axis or the Q axis of the IQ plane. A mapping pattern in which the same bit string is arranged on the lower side (LSB side; Least Significant Bit side) is stored, and the mapping unit reads the bit string of the symbol from the mapping pattern, and based on the read bit string The high-order bit sequence and the low-order bit sequence of data are modulated.

According to such a configuration, the QAM mapping apparatus can assign the same bit sequence to the lower side of the bit sequence of adjacent symbols across the I axis or the Q axis. Therefore, the communication apparatus can reduce the bit error rate at the time of determination that occurs when the distance between symbols in different quadrants is short.

In the communication apparatus, the mapping pattern storage unit may further exclude the upper bits in addition to the upper bit string as a bit string of a symbol at a position rotated 90 degrees with respect to the origin of the IQ plane. A mapping pattern in which the same bit sequence is arranged on the lower side is stored, and the mapping reads the bit sequence of the symbol from the mapping pattern, and based on the read bit sequence, the upper side and the lower side of the data The bit string is modulated.

According to such a configuration, the QAM mapping apparatus can assign the same bit sequence to the lower side (LSB side) of the symbol bit sequence at a position rotated by 90 degrees with respect to the origin of the IQ plane. Therefore, the communication apparatus can reduce the bit error rate associated with the phase slip.

Note that the invention according to the mapping method has substantially the same technical features as the above-described communication device, since it has the same effect as the communication device, of the "Problems that the Invention is to Solve" Description is omitted.

Claims (6)

A QAM mapping device for modulating data by QAM (Quadrature Amplitude Modulation),
In the IQ plane representing the position of the symbol of the QAM, as a bit string to be assigned to the symbol in the same quadrant, a mapping pattern in which the same bit string is arranged on the upper side (MSB side; Most Significant Bit side) of the bit string is stored. A mapping pattern storage unit;
A mapping unit that reads the upper bit string of the symbol from the mapping pattern, and modulates the upper bit string of the data based on the read upper bit string;
A QAM mapping apparatus comprising: The mapping pattern storage unit, as a bit string of adjacent symbols across the I-axis or Q-axis of the IQ plane, in addition to the higher-order bit string, further excludes the higher-order bits (LSB side; Least Significant Bit side) stores the mapping pattern in which the same bit string is placed,
The mapping unit
2. The QAM mapping apparatus according to claim 1, wherein a bit string of the symbol is read from the mapping pattern, and the upper and lower bit strings of the data are modulated based on the read bit string. The mapping pattern storage unit arranges the same bit string on the lower side excluding the upper bit, in addition to the upper bit string, as a bit string of the symbol rotated 90 degrees with respect to the origin of the IQ plane Remembered mapping pattern,
The mapping unit
2. The QAM mapping apparatus according to claim 1, wherein a bit string of the symbol is read from the mapping pattern, and the upper and lower bit strings of the data are modulated based on the read bit string. A mapping method of a QAM mapping device for modulating transmission data by QAM, comprising:
The QAM mapping device
A mapping pattern storage unit that stores a mapping pattern in which the same bit string is arranged on the upper side (MSB side) of the bit string as a bit string to be assigned to the symbol in the same quadrant on the IQ plane representing the position of the symbol of the QAM With
Reading the upper bit string of the symbol from the mapping pattern, and modulating the upper bit string of the data based on the read upper bit string;
The mapping method characterized by performing. The mapping pattern storage unit, as a bit string of adjacent symbols across the I-axis or Q-axis of the IQ plane, in addition to the higher-order bit string, further on the lower-order side (LSB side) excluding the higher-order bits. A mapping pattern in which the same bit string is arranged in bits is stored,
The QAM mapping device
5. The mapping according to claim 4, wherein a step of reading out a bit string of the symbol from the mapping pattern and modulating the upper and lower bit strings of the data based on the read bit string is performed. Method. The mapping pattern storage unit assigns the same bit string to the lower side excluding the upper bit, in addition to the upper bit string, as a bit string of the symbol rotated 90 degrees with respect to the origin of the IQ plane Remembered mapping patterns,
The QAM mapping device
5. The mapping according to claim 4, wherein a step of reading out a bit string of the symbol from the mapping pattern and modulating the upper and lower bit strings of the data based on the read bit string is performed. Method.