JP2004120061A - Digital wireless transmission method, and receiving device, transmitting device, and mobile wireless system using the same - Google Patents

Abstract

A digital radio transmission method using a multilevel modulation method such as an amplitude phase modulation method and a phase shift keying method has a good follow-up property to disturbances such as fading and a relatively high transmission efficiency.
A transmission side is based on a symbol sequence to which information is assigned by a modulation method A in which the number of modulation values is m during modulation and a modulation method B in which the number of modulation values is n (2 ≦ n <m). To modulate and transmit the signal. The receiving side obtains an amplitude and phase correction coefficient using the symbol by the modulation method B at the time of demodulation, and performs the demodulation by using the correction coefficient for correction of the amplitude and phase of the symbol by the modulation method A.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital radio transmission method, and more particularly to a multilevel modulation method such as an amplitude phase modulation method and a phase shift keying method, and more particularly to a digital radio transmission method suitable for use in mobile radio or the like in which fading or the like is likely to occur. .
[0002]
[Prior art]
Among the modulation schemes used for digital radio, a linear modulation scheme represented by QAM (Quadrature Amplitude Modulation) is often used particularly in satellite communication and the like because it is easy to perform multi-level modulation for improving the efficiency of frequency use. ing. In this QAM, transmission information is assigned to the amplitude and phase of a radio signal to be carried.
[0003]
Hereinafter, the principle of modulation and demodulation by QAM will be described with reference to FIGS.
FIG. 2 is a symbol diagram of 16QAM modulation.
FIG. 3 is a configuration diagram of a modulation device of 16QAM modulation.
FIG. 4 is a configuration diagram of a demodulator for 16QAM modulation.
FIG. 5 is an example of a signal arrangement before correction immediately after being taken out by a 16QAM modulation sampler.
FIG. 6 is an example of a signal arrangement after correction of 16QAM modulation.
[0004]
FIG. 2 shows a 16QAM signal arrangement space. 16QAM is a modulation method in which amplitude and phase are simultaneously changed, and 4-bit information is represented as one symbol by an in-phase component (I component) and a quadrature component (Q component). A symbol is a unit of modulation, and in digital transmission, digital information of a predetermined number of bits is transmitted on one symbol. The number of states that can be carried by one symbol is referred to as the number of modulation values. In the case of 16QAM, the number of modulation values is 16, which is the number of states represented by 4 bits.
[0005]
When modulating by the modulator using 16QAM, the following is performed.
[0006]
First, a transmission bit string is input from the input terminal 101 shown in FIG. Then, the transmission bit string is collected by the serial / parallel converter 102 every four bits and sent to the symbol converter 103. The symbol converter 103 selects one of 16 signal points (symbols) according to the input 4-bit pattern (16 patterns), and converts it into an in-phase component (I component) and a quadrature component (Q component). ) Output as a signal.
[0007]
Next, each of the I component and the Q component is subjected to waveform shaping and the like in transmission filters 104 and 105, and after being converted into analog signals in D / A converters 106 and 107, an LPF (low-pass filter) 108 and Unnecessary components are removed by 109.
[0008]
Then, the quadrature modulator 110 performs frequency conversion of the input signal using the signal obtained from the local oscillator 111, and outputs the result from the terminal 112 as a modulated signal.
[0009]
Next, when performing modulation by a modulator using 16QAM, the following is performed.
[0010]
As shown in FIG. 4, a reception signal is input from a terminal 201. The input received signal is converted into a base signal (baseband signal) composed of an I component and a Q component in an orthogonal transformer 202 using a signal generated by a local oscillator 203.
[0011]
The converted signals of the I component and the Q component are converted into digital signals by A / D converters 206 and 207 through LPFs (Low Pass Filters) 204 and 205, and unnecessary signals are removed by reception filters 208 and 209. Waveform shaping is performed.
[0012]
Then, the samplers 210 and 211 extract sample values at appropriate symbol timings.
[0013]
At the signal point when the signal is extracted by the sampler, a blur occurs as compared with the original modulation. That is, in the example of FIG. 5, it is observed that the reception signal point 221 which is the output of the sampler has a slightly smaller amplitude and a phase inclined to the left as compared with the transmission symbol point 222 which is the reference symbol. In general, in wireless transmission, the amplitude and phase are undefined due to the configuration of the transmitter or receiver, phase rotation / attenuation associated with wireless propagation, and the like. Correction for indefinite elements is required.
[0014]
The amplitude / phase corrector 212 shown in FIG. 4 performs correction so that the received signal point matches the reference symbol point as shown in FIG.
[0015]
As a result of this correction, as shown in FIG. 6, the I component determination boundary 231-i (i = 1, 2, 3) and the Q component determination boundary 232-i (i = 1, 2, 3) are more appropriate. Is corrected to a pattern that allows symbol determination.
[0016]
Then, the symbol is determined by the symbol determiner 213, converted into a corresponding bit string, and output. This bit string is serial-converted by the parallel / serial converter 214 and output via the decoded bit output terminal 215.
[0017]
The 16QAM of the prior art is widely used in the field of high-speed data communication because the amount of transmission data per symbol is large. However, the above amplitude and phase corrections are indispensable because they are vulnerable to disturbances such as fading.
[0018]
Hereinafter, a typical method of the conventional amplitude / phase correction method will be described with reference to FIG.
FIG. 7 is an example of a transmission symbol sequence including pilot symbols.
[0019]
Various methods have been devised for the amplitude / phase correction method, but the most common one is to periodically insert a fixed pattern symbol called a pilot symbol between transmission symbols, and to set the pilot In this method, correction is performed with reference to a received signal point of a symbol (for example, see Non-Patent Document 1).
[0020]
A pilot symbol having a period of T symbols is inserted between the information transmission symbol sequences. Usually, a pilot symbol is fixed to a certain symbol.
[0021]
The n-th received signal R (n) at the output of the samplers 210 and 211 shown in FIG. 4 can be described by the following (Equation 1), where X (n) is a transmission symbol.
[0022]
R (n) = CX (n) + N (n) (Equation 1)
Here, C is a variable representing the uncertainty factor of the amplitude and phase, and N (n) is a noise component.
[0023]
Therefore,
[0024]
X (n) = C ^-1 {R (n) -N (n)} (Formula 2)
Can determine the transmission symbol.
[0025]
In the pilot symbol, according to (Equation 1),
[0026]
R _p = CX _p + N (n) (Equation 3)
Assuming that N (n) is small enough, the estimate of C, C ', is
[0027]
C ′ = R _p / X _p (Equation 4)
It becomes.
[0028]
That is, C 'is obtained when the pilot symbol shown in FIG. 7 is received, and the amplitude and phase are corrected using (Equation 2) when the information transmission symbol up to the next pilot symbol is received.
[0029]
In this method, the pilot period T shown in FIG. 7 is an important parameter. C in (Equation 1) generally changes with time. In particular, in mobile radio, the amplitude and phase of C fluctuate drastically due to fading phenomena due to multiple propagation paths. In order to sufficiently follow this variation, it is necessary to reduce the pilot symbol period T.
[0030]
However, the pilot symbol is a symbol inserted as dummy data, so reducing T means reducing the transmission capacity for information symbols, which degrades transmission efficiency.
[0031]
In the 16QAM system, since 4 bits are allocated to one symbol, only 4 (T-1) information can be transmitted for a 4T transmittable capacity, and the transmission efficiency is 1-1 / T. Therefore, in the system design, it is necessary to appropriately set parameters that conflict with the tracking performance and the transmission efficiency.
[0032]
[Non-patent document 1]
S. Sampei and T.S. Sunaga, "Rayleigh fading compensation for QAM in digital land mobile radio communications", IEEE Trans. Veh. Technol. , Vol. 42, no. 2, PP. 137-147, 1993
[0033]
[Problems to be solved by the invention]
Therefore, the above-mentioned prior art has the following problems of the contradictory viewpoints.
(1) In order to sufficiently follow fading in mobile radio, it is necessary to shorten the insertion period of pilot symbols.
(2) The shorter the pilot symbol insertion period, the lower the information transmission efficiency.
[0034]
The present invention has been made in order to solve the above problems, and an object thereof is to follow a disturbance such as fading in a digital radio transmission method of a multilevel modulation system such as an amplitude phase modulation system and a phase shift modulation system. It is an object of the present invention to provide a digital radio transmission method which has good performance and can make transmission efficiency relatively high.
[0035]
[Means for Solving the Problems]
In the digital wireless transmission method of the present invention, the transmitting side is assigned information by a modulation method A in which the number of modulation values is m during modulation and a modulation method B in which the number of modulation values is n (2 ≦ n <m). The modulated signal is transmitted based on the symbol sequence.
[0036]
Then, the receiving side obtains the amplitude and phase correction coefficients using the symbol by the modulation method B at the time of demodulation, and performs the demodulation by using the correction coefficient for the correction of the amplitude and phase of the symbol by the modulation method A.
[0037]
That is, the symbol by the modulation method B having the smaller number of modulation values has the role of the pilot symbol.
[0038]
Although the pilot symbols of the prior art did not contribute to the transmission of information, the transmission method of the present invention can transmit information even with symbols by the modulation method B, so that the transmission efficiency can be increased as compared with the conventional technology. it can.
[0039]
In addition, since the correction coefficient is obtained using the symbol having the smaller number of modulation values, the probability of occurrence of an error at the time of correction is small, and stable transmission resistant to disturbance can be secured.
[0040]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1, 8 to 11.
[0041]
As described above, the digital wireless transmission method of the present invention uses a combination of two modulation methods with different numbers of modulation values in a multi-level modulation method. 16QAM is used as the modulation method A, and Quadrature Phase Shift Keying (QPSK) is used as the modulation method B with the larger number of modulation values.
[0042]
QPSK is one of the phase shift keying systems, and is a modulation method that generates one symbol with four different phases.
[0043]
FIG. 8 is a symbol diagram of QPSK.
[0044]
As shown in FIG. 8, in QPSK, the number of modulation values is four because four states of two bits are regarded as one symbol.
[0045]
First, the flow of the digital wireless transmission method of the present invention will be described with reference to FIG.
[0046]
FIG. 1 is a configuration diagram showing only a main part related to symbol conversion in the digital wireless transmission method of the present invention.
[0047]
In the transmitting apparatus, a serial / parallel converter A and a symbol converter A according to a modulation method A and a serial / parallel converter B and a symbol converter B according to a modulation method B are arranged in parallel, and these are switches 13, 18, and 19. Can be switched with.
[0048]
This switching is periodically performed by the switching signal generator 41 connected by the frame timing generator 40.
[0049]
First, assuming that the contacts of the switches 13, 18, and 19 are initially set to a, a case where symbol conversion is performed by the modulation method A, that is, 16QAM will be described.
[0050]
The transmitted information bit sequence is once written to the buffer memory 12 via the input terminal 11. The serial / parallel converter A14 sequentially reads out bit data from the buffer memory 12 via the contact point a of the switch 13, and sends the data to the symbol converter A15 in a unit of 4 bits.
[0051]
In the symbol converter A15, one of 16 symbols is selected according to the input 4-bit pattern (16 patterns) shown in FIG. 2, and is selected as an in-phase component (I component) and a quadrature component (Q component). Output as a signal.
[0052]
These signals are output from the modulation output terminals 20 and 21 as symbol outputs via the contacts a of the switches 18 and 19.
[0053]
Although not shown in the drawing, this signal is then input as demodulation input terminals 22 and 23 as reception sample values via a transmission high-frequency unit, a radio propagation path, a reception high-frequency unit, and the like.
[0054]
The following is the operation on the receiving device side, but also on the receiving device side, the two systems are in parallel, and the output is switched by the switch 33. This switching is performed by the switching signal generation unit 51 connected to the frame timing synchronization unit 50.
[0055]
Now, in the receiving device, the received sample value is sent to the amplitude / phase corrector 27 via the input terminals 22 and 23. The amplitude / phase corrector 27 includes a complex multiplier 24, a coefficient memory 25, and a coefficient calculator 26.
[0056]
The input signal is subjected to complex multiplication by a complex coefficient stored in a coefficient memory 25 at 24 to correct the amplitude and phase, and sends this to a symbol decision unit A28. The symbol decision unit A28 makes a symbol decision from among the 16 candidates by comparing with an appropriately set decision boundary, and outputs a corresponding 4-bit pattern. The parallel / serial converter A converts the input 4 bits into a serial signal, which is output from the decoded bit output terminal 34 via the switch 33.
[0057]
The operation described above in which the contacts of the switches 13, 18, 19 and 33 are set to a is the same as the normal 16QAM transmission / reception operation.
[0058]
Next, the operation when the contacts of the switches 13, 18, 19 and 33 are set to b will be described. In this case, modulation method B, that is, symbol conversion based on QPSK is performed.
The serial / parallel converter B16 sequentially reads out bit data from the buffer memory 12 via the contact b of the switch 13, and sends the data to the symbol converter B17 in a unit of 2 bits. In the symbol converter B17, as shown in FIG. 8, one of the four symbols is selected in accordance with the input 2-bit pattern (four patterns), and is selected as the in-phase component (I component) and the quadrature component (Q component). Component) signal. These signals are output from the modulation output terminals 20 and 21 as symbol outputs via the contacts b of the switches 18 and 19.
[0059]
It is assumed that the receiving device is also connected to the contact B of the switch 33.
[0060]
The received sample value received on the receiving device side is sent to the amplitude / phase corrector 27 via the input terminals 22 and 23. The input signal is subjected to a complex multiplication with a complex coefficient stored in the coefficient memory 25 to correct the amplitude and phase, and sends this to the symbol decision unit B30. The symbol decision unit A28 makes a symbol decision from among the four candidates by comparing it with an appropriately set decision boundary, and outputs a corresponding 2-bit pattern. The parallel / serial converter B31 converts the input 2 bits into a serial signal, which is output from the decoded bit output terminal 34 via the switch 33. The symbol converter B32 performs symbol conversion again using the result (2 bits) of the symbol determiner B32.
[0061]
This output is input to the amplitude and phase corrector 24 as a reference signal for obtaining a correction coefficient in the coefficient calculator 26. The coefficient calculator calculates a correction coefficient using this signal and the signals from the received sample value input terminals 22 and 23, and updates the correction coefficient stored in the coefficient memory 25.
[0062]
This updated correction coefficient is used when correcting the amplitude and phase of the symbol of the next modulation method A.
[0063]
Next, symbol correction in the digital wireless transmission method will be described in more detail with reference to FIGS.
FIG. 9 is an example of a symbol sequence of a sampler output in the receiving device in the digital wireless transmission method of the present invention.
FIG. 10 is an example of a signal arrangement before correction immediately after being taken out by a sampler of QPSK modulation.
FIG. 11 is an example of a signal arrangement after correction of QPSK modulation.
[0064]
Now, in the above configuration, a mode in which symbol conversion is performed by 16QAM of the modulation method A, that is, a case where the contacts of the switches 13, 18, 19 and 33 are set to a, is referred to as an A mode and a modulation method B. A mode in which symbol conversion is performed by QPSK, that is, a case where the contact is set to b, is defined as a B mode, and the temporal flow of these modes will be described with reference to FIG.
[0065]
During the continuous operation in mode A, mode B is periodically inserted. Mode A is 4-bit transmission per symbol, and Mode B is 2-bit transmission. In mode B, the correction coefficient is updated using the result of the symbol conversion.
[0066]
In mode B, symbol conversion is performed by QPSK, and the signal arrangement before correction is as shown in FIG. 10, for example.
[0067]
For example, when the transmitted pattern is “11”, a correction coefficient is obtained by correcting the lower left point to a reference symbol point in the third quadrant. That is, in mode B, four values may be obtained with two bits, and it is necessary for the receiving side to find and correct four appropriate reference symbol points.
[0068]
At this time, in mode B, since the number of modulation values is small and the distance between signals is long, the possibility of occurrence of an error when obtaining a reference symbol point is reduced, and it is expected that stable correction can be performed.
[0069]
Further, compared with the correction using the pilot symbol of the related art, the transmission efficiency can be improved, and if the transmission efficiency is the same, the insertion period of the mode B symbol can be shortened.
[0070]
Hereinafter, this will be described with reference to FIG.
FIG. 12 is a diagram comparing a symbol sequence according to the related art with the symbol sequence according to the present invention.
[0071]
As shown in FIG. 12A, when one pilot symbol is inserted at the beginning of 32 symbols, since the pilot symbol is dummy data, the number of valid transmission bits becomes 124 bits.
[0072]
However, in the present invention, as shown in FIG. 12B, even if one mode B symbol is inserted into every 16 symbols, the effective transmission bits are 124 bits. That is, even with the same transmission bit, the update interval of the correction coefficient can be reduced to half.
[0073]
The present invention is not limited to the case shown in this example, but can be easily extended to other modulation methods.
[0074]
For example, when 256QAM is used as the modulation method A having a large number of modulation values, a modulation method having a number of modulation values of less than 256 such as QPSK or 16QAM can be adopted as the modulation method B having a small number of modulation values. It is possible to minimize the deterioration of efficiency.
[0075]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the present invention, in a digital radio transmission method of a multi-level modulation system such as an amplitude phase modulation system and a phase shift modulation system, it has a good follow-up property to disturbances such as fading and the transmission efficiency can be made relatively high. A digital wireless transmission method can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing only a main part related to symbol conversion in a digital wireless transmission method according to the present invention.
FIG. 2 is a symbol diagram of 16QAM modulation.
FIG. 3 is a configuration diagram of a modulator for 16QAM modulation.
FIG. 4 is a configuration diagram of a demodulator for 16QAM modulation.
FIG. 5 is an example of a signal arrangement before correction immediately after being extracted by a 16QAM modulation sampler.
FIG. 6 is an example of a signal arrangement after correction of 16QAM modulation.
FIG. 7 is an example of a transmission symbol sequence including pilot symbols.
FIG. 8 is a symbol diagram of QPSK.
FIG. 9 is an example of a symbol sequence of a sampler output in a receiving device in the digital wireless transmission method of the present invention.
FIG. 10 is an example of a signal arrangement before correction immediately after being taken out by a QPSK modulation sampler.
FIG. 11 is an example of a signal arrangement after correction of QPSK modulation.
FIG. 12 is a diagram comparing a symbol sequence according to the related art with the present invention.
[Explanation of symbols]
11: transmission information bit input terminal, 12: buffer memory, 13: switch, 14: serial / parallel converter A, 15: symbol converter A, 16: serial / parallel converter B,
17 ... Symbol converter B, 18 ... Switch, 19 ... Switcher, 20 ... I component modulation output terminal, 21 ... Q component modulation output terminal, 22 ... I component reception sample value input terminal, 23 ... Q component reception sample value Input terminals, 24: complex multiplier, 25: coefficient memory, 26: coefficient calculator, 27: amplitude / phase corrector, 28: symbol determiner A, 29: parallel / serial converter A, 30: symbol determiner B, 31 ... Parallel / serial converter B, 32 ... Symbol converter B, 33 ... Switcher, 34 ... Decoding bit output terminal,
40: a frame timing generator, 41: a switching signal generator,
50: frame timing synchronization unit, 51: switching signal generation unit,
101: Transmission bit input terminal, 102: Serial / parallel converter, 103: Symbol converter, 104: Transmission filter, 105: Transmission filter, 106: A / D converter, 107: A / D converter, 108: LPF , 109 ... LPF, 110 ... quadrature demodulator, 111 ... local oscillator,
Reference numeral 201: reception signal input terminal, 202: orthogonal transformer, 203: local oscillator, 204: LPF, 205: LPF, 206: A / D converter, 207: A / D converter, 208: reception filter, 209: reception Filter, 210 sampler, 211 sampler, 212 amplitude / phase corrector, 213 symbol determiner, 214 parallel / serial converter, 215 decoded bit output terminal,
221: reception signal point, 222: reference symbol point,
231-i ... I component determination boundary, 232-i ... Q component determination boundary,
321 ... reception signal points, 322 ... reference symbol points,
331-i ... I component determination boundary, 332-i ... Q component determination boundary.

Claims (5)

In a digital wireless transmission method of modulating a digital signal by amplitude and phase,
The transmitting side performs modulation based on a symbol sequence to which information is assigned by a modulation method A in which the number of modulation values is m and a modulation method B in which the number of modulation values is n (2 ≦ n <m). Send a signal,
The receiving side obtains the amplitude and phase correction coefficients using the symbol according to the modulation method B during demodulation,
A digital radio transmission method, wherein demodulation is performed by using the correction coefficient for correcting the amplitude and phase of a symbol by a modulation method A. 2. The digital wireless transmission method according to claim 1, wherein the symbols of the modulation method B are arranged at a constant period. In a transmission device used for a digital wireless transmission method of modulating a digital signal by amplitude and phase,
The symbol sequence used for modulation is
A symbol sequence is mixed with a modulation method A having a modulation value number m and a modulation method B having a modulation value number n (2 ≦ n <m),
In addition, the transmitting apparatus is characterized in that the symbols of the modulation method B are a symbol sequence arranged at a constant period. In a receiving device used in a digital wireless transmission method of modulating a digital signal by amplitude and phase,
The transmitting side performs modulation based on a symbol sequence to which information is assigned by a modulation method A in which the number of modulation values is m at the time of modulation and a modulation method B in which the number of modulation values is n (2 ≦ n <m). The signal to be transmitted is determined by a symbol modulated by the modulation method B at the time of demodulation, to obtain amplitude and phase correction coefficients.
A demodulation apparatus using the correction coefficient for correcting the amplitude and phase of a symbol by a modulation method A to perform demodulation. In a mobile radio system of digital radio transmission that modulates a digital signal by amplitude and phase,
The transmitting side performs modulation based on a symbol sequence to which information is assigned by a modulation method A in which the number of modulation values is m and a modulation method B in which the number of modulation values is n (2 ≦ n <m). Send a signal,
The receiving side obtains amplitude and phase correction coefficients using the symbols modulated by the modulation method B during demodulation,
A mobile radio system for digital radio transmission, wherein demodulation is performed using the correction coefficient for correcting the amplitude and phase of a symbol by a modulation method A.

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