WO2007043443A1

WO2007043443A1 - Digital modulation method, digital modulation circuit, digital demodulation method, and digital transmission system

Info

Publication number: WO2007043443A1
Application number: PCT/JP2006/319984
Authority: WO
Inventors: Kazuo Tsubouchi; Tadashi Takagi; Hiroyuki Nakase; Suguru Kameda; Fumio Ishizu; Yasushi Sogabe; Akinori Fujimura
Original assignee: Mitsubishi Electric Corporation; Tohoku University
Priority date: 2005-10-14
Filing date: 2006-10-05
Publication date: 2007-04-19
Also published as: JP5207517B2; JPWO2007043443A1

Abstract

Provided is a digital modulation method capable of narrowing a base band width while increasing the number of transmission bits per symbol. The digital modulation method deviates the phase of a carrier signal continuously thereby to transmit digital data, and limits the maximum of the phase to be deviated, when digital data of 2 bits or more is transmitted by one phase deviation. A digital modulation circuit includes a base band signal generation circuit (11) for generating a base band signal, of which the maximum of the phase to be deviated is limited, in a manner to meet the digital data of 2 bits or more to be transmitted by one phase deviation, and an orthogonal modulator (12) for modulating the generated base band signal orthogonally.

Description

Specification

Digital modulation method, digital modulation circuit, digital demodulation circuit, and digital transmission system

Technical field

The present invention relates to a digital modulation method, a digital modulation circuit, a digital demodulation circuit, and a digital transmission system for performing high-speed digital transmission.

Background art

[0002] As represented by wireless LAN, wireless communication technology has advanced to high-speed transmission exceeding 100 Mbit / s. In the future, a communication method suitable for high-speed communication that will definitely advance to 1 Gbit / s is essential. The current high-speed transmission is realized by communication using OFDM (Orthogonal Frequency Division Multiplexing). OFDM is currently capable of 54Mbit / s in the 20MHz RF (Radio Frequency) band, and 3bit transmission per 1Hz in the next generation wireless LAN standard, suitable for high-speed transmission ing.

[0003] However, when building a wireless device, backoff (linear operation) to an amplifier, mixer, etc., where the PAPR (Peak to Average Power Ratio) of the OFDM signal is large Operating margin) to increase the load on the device. A frequency band of several tens of GHz is promising as a frequency band that realizes communication at 1 Gbit per second, but the communication performance is relatively low and less burdensome on devices compared to devices below 5 GHz. Is essential.

[0004] In order to realize high-speed transmission, it is also necessary to reduce the load on the device by reducing the signal processing bandwidth in the baseband as much as possible. In addition, it is important from the viewpoint of effective frequency utilization to enable high-speed transmission using the narrowest RF band possible.

[0005] There are MSK (Minimum Shift Keying) as a modulation method that continuously changes the phase while keeping the amplitude constant, and four-value MSK that increases speed by multi-leveling (for example, Non-Patent Documents 1 and 2). Conventional MSK uses 1-bit digital data. Therefore, the phase shift is selected continuously by selecting either ± 90 degrees. On the other hand, 4-level MSK selects ± 135 degrees or 45 degrees based on the 2-bit data value of the digital data to be transmitted to improve the transmission speed.

[0006] Further, as a further modification of the MSK system, in addition to the conventional MSK having a phase shift of ± 90 degrees, which selects either ± 90 degrees depending on 1-bit digital data to be transmitted, two consecutive bits There is a method that can detect that the phase deviation is 0 degree when the data pattern is a special arrangement (see, for example, Patent Document 1). In this method, the occupied bandwidth can be reduced to 2Z3 by using a phase shift pattern different from the known MSK method.

[0007] Further, there is TFM (Tamed Frequency Modulation) as a technique for narrowing the bandwidth of the conventional MSK (see, for example, Non-Patent Document 2). To transmit 1-bit data, TFM determines the phase shift according to the 1-bit data to be sent and the past 2-bit data sent so far, that is, the data pattern of 3 bits in total. Is the method.

[0008] The rule is π Ζ2 Χ (d Z4 + d Z2 + d Z4). Where d is the data 2 bits before the transmission, d is the data 1 bit before the transmission, d is to be transmitted

0 1

It is data. Depending on the data pattern, the phase shifts of π Ζ2, π Ζ4, and 0 are taken, so the 3dB bandwidth can be narrower than the conventional MSK method.

[0009] Non-Patent Document 1: S. Pasupathy, "Minimum Shift Keying: A Spectrally Efficiency Modula tion, IEEE Communication Magazine, vol.17, pp.14—22, July 1979.

Non-Patent Document 2: Hiroshi Saito “Modulation and Demodulation of Digital Wireless Communication” The Institute of Electronics, Information and Communication Engineers P7 8-88

Patent Document 1: Japanese Translation of Special Publication 2000-511009 (Page 1, Figure 1)

Disclosure of the invention

Problems to be solved by the invention

However, the conventional techniques have the following problems. The four-value MS K in Non-Patent Document 2 is a force that can improve the transmission speed due to the multi-value key shift. The maximum value of the phase to be shifted is ± 135 degrees, which significantly increases the occupied bandwidth. As a result, the baseband band and RF band become the same as the conventional MSK system, and narrowband noise cannot be achieved. There was a problem.

[0011] In addition, the MSK modification method in Patent Document 1 can reduce the occupied bandwidth to 2Z3 compared to the conventional MSK method with only one bit transmission with one phase shift. There was a problem in that it was not possible to extend and apply to a modulation system that achieves a narrower band width that is not sufficient for narrowing the band.

[0012] Although the TFM in Non-Patent Document 2 can narrow the 3dB bandwidth compared to the conventional MSK method, the transmission is only one bit with one phase shift, and the main lobe is conventional. The problem is that it is 4Z3 times larger than the MSK.

[0013] Here, the bandwidth of the MSK modulation signal is determined by the maximum value of the vector phase change amount required when the symbol point shifts. In the normal MSK modulation system, the maximum deviation in 1-bit transmission is ± 90 degrees and the phase changes continuously, so the baseband bandwidth is 3Z4 of the symbol rate.

[0014] For example, when considering high-speed data transmission of 1 Gbit / s or more, if the number of bits transmitted in 1 symbol is 2 bits, 500 Msymbol / s is required, and the RF band is 750 MHz or more and the baseband band is 375 MHz or more. Become.

On the other hand, in the case of 4-level MSK in Non-Patent Document 2, the symbol rate is reduced to 250M symbols per second, but since the maximum value of one phase shift is ± 135 degrees, the RF band is 750 MHz.

The baseband bandwidth is 375MHz, which requires the same frequency band as the conventional MSK

. Even when the modified MSK method described in Patent Document 1 is used, the RF bandwidth is 500 MHz.

Baseband bandwidth needs to be over 250MHz.

[0016] In consideration of the ease of processing of the baseband signal, a modulation scheme that can further reduce the baseband bandwidth after increasing the number of bits per symbol is required.

[0017] The present invention has been made to solve the above-described problems, and is capable of reducing the baseband bandwidth while increasing the number of transmission bits per symbol and reducing the baseband bandwidth. It is an object to obtain a method, a digital modulation circuit, a digital demodulation circuit, and a digital transmission system.

Means for solving the problem [0018] A digital modulation method according to the present invention is a digital modulation method for transmitting digital data by continuously shifting the phase of a carrier signal, and transmitting digital data of 2 bits or more by one phase shift. In this case, the maximum value of the phase to be shifted is limited.

[0019] Further, the digital modulation circuit according to the present invention generates a baseband signal in which the maximum value of the phase to be shifted is limited corresponding to digital data of 2 bits or more to be transmitted by one phase shift. A baseband signal generation circuit to be generated and a quadrature modulator that orthogonally modulates the generated baseband signal are provided.

[0020] Furthermore, the digital transmission system according to the present invention is a digital transmission system that performs bidirectional communication between a base station and a terminal using the same carrier frequency or different carrier frequencies, and at least one of the base station and the terminal. Is provided with the digital modulation circuit of the present invention.

The invention's effect

[0021] According to the present invention, the phase change amount is limited when determining the symbol point arrangement on the phase plane after performing the multi-value key to increase the number of bits per symbol. In this way, by limiting the area of the phase plane to be arranged, the digital modulation method, the digital modulation circuit, which can increase the number of transmission bits per symbol and narrow the baseband bandwidth, A digital demodulation circuit and a digital transmission system can be obtained.

Brief Description of Drawings

FIG. 1 is a diagram showing a first transition example of multi-level MSK symbol points in Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a second transition example of multi-level MSK symbol points in Embodiment 1 of the present invention.

FIG. 3 is a diagram showing a third transition example of multi-level MSK symbol points in Embodiment 1 of the present invention.

FIG. 4 is a diagram summarizing comparison of communication performance between the third transition example and the prior art in Embodiment 1 of the present invention. FIG. 5 is a block diagram of a first modulation circuit in the first embodiment of the present invention.

FIG. 6 is a block diagram of a second modulation circuit in the first embodiment of the present invention.

FIG. 7 is a block diagram of a third modulation circuit in the first embodiment of the present invention.

FIG. 8 is a block diagram of a first demodulation circuit in the first embodiment of the present invention.

FIG. 9 is a block diagram of a second demodulation circuit in the first embodiment of the present invention.

FIG. 10 is a block diagram of a third demodulation circuit according to the first embodiment of the present invention.

FIG. 11 is an overall block diagram of a modulation circuit according to the first embodiment of the present invention.

FIG. 12 is another example of the entire block diagram of the modulation circuit in the first embodiment of the present invention.

FIG. 13 is an overall configuration diagram of a digital transmission system to which the modulation method according to Embodiment 1 of the present invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a digital modulation method, a digital modulation circuit, a digital demodulation circuit, and a digital transmission system according to the present invention will be described with reference to the drawings.

[0024] The present invention focuses on the MSK modulation method, which is a constant amplitude modulation method to reduce the burden on the RF device, and multi-values are applied to reduce the load on the baseband and to narrow the RF band. The present invention provides a digital modulation method, a digital modulation circuit, a digital demodulation circuit, and a digital transmission system suitable for high-speed transmission.

[0025] That is, the present invention provides a modulation method capable of significantly reducing the necessary band in a modulation method for transmitting digital data by continuously changing the phase while keeping the amplitude of the carrier signal constant. This makes it easy to configure the equipment in a gigabit per second ultra-high speed radio transmission system.

More specifically, according to the present invention, the phase change amount is determined when determining the symbol point arrangement on the phase plane after performing the multi-value 匕 to increase the number of bits per symbol. Therefore, it is a technical feature that the necessary bandwidth is narrowed by limiting the region of the phase plane to be arranged.

Embodiment 1.

FIG. 1 is a diagram showing a first transition example of multi-level MSK symbol points in Embodiment 1 of the present invention. In Fig. 1, the horizontal axis is the real axis of the phase space, and the vertical axis is the phase space. The imaginary axis. In this first transition example, the number of bits to be transmitted is 2 bits for each phase shift. In addition, the phase shift limit range (corresponding to the lb range in Fig. 1) from the current symbol point phase (corresponding to la in Fig. 1) is set to ± 90 degrees. There are four types of phase change corresponding to 2-bit data: φ1 to φ4 within the limit range of phase shift of ± 90 degrees.

[0028] By using such a transition, high-speed transmission is possible by using four types of phases, and by setting the maximum phase deviation amount to 90 degrees, the maximum phase deviation is 180 degrees or Compared to the case of 135 degrees, high-speed transmission with a narrow band is possible.

[0029] Although FIG. 1 illustrates the case where the maximum phase shift amount is 90 degrees, the present invention is not limited to this. By setting the maximum phase deviation to less than 135 degrees, it is possible to perform high-speed transmission while suppressing the bandwidth narrower than when the maximum phase deviation is set to 180 degrees or 135 degrees.

[0030] FIG. 2 is a diagram showing a second transition example of the symbol points of the multi-level MSK according to Embodiment 1 of the present invention. In Fig. 2, the horizontal axis is the real axis of the phase space, and the vertical axis is the imaginary axis of the phase space. In this second transition example, the number of bits to be transmitted is 3 bits for each phase shift, the maximum phase shift amount is 100 degrees, and the symbol points to be placed are symmetrical. .

As a result, from the phase of the current symbol point (corresponding to 2a in FIG. 2), the amount of phase change corresponding to 3-bit data is Zhi φ1 (= 100 degrees), Zhi φ2, Zhi φ3 , There will be 8 types of Shi φ4. Furthermore, these symbol points are characterized in that the phase to be shifted is randomly arranged within the limited maximum shift amount of 100 degrees or less (corresponding to the range 2b in FIG. 2).

[0032] By using such transitions, high-speed transmission is possible by using eight types of phases, and by setting the maximum phase deviation amount to 100 degrees, the maximum phase deviation can be reduced to 180 degrees. Compared to the case of 135 degrees, high-speed transmission with a narrow band is possible.

[0033] FIG. 3 is a diagram showing a third transition example of the symbol points of the multi-level MSK according to Embodiment 1 of the present invention. In Fig. 3, the horizontal axis is the real axis of the phase space, and the vertical axis is the imaginary axis of the phase space. In this third transition example, the number of bits to be transmitted is a single phase shift. Each bit is 2 bits, the maximum phase shift is 90 degrees, and the symbol points to be placed are symmetrical.

Furthermore, the symbol points after the shift are arranged so that the phase intervals are equal. In other words, if the current symbol point position (corresponding to 3a in Fig. 3) is phase 0 degrees, the amount of phase change corresponding to 2-bit data is ± 90 degrees and ± 30 degrees, respectively. Below 90 degrees (corresponding to the range 3b in Fig. 3), the phase intervals are all equalized at 60 degrees.

[0035] With such an equidistant arrangement, it is possible to make the noise margin uniform so as not to cause a code error and to minimize the bit error rate. However, the symbol points to be placed are not necessarily 90 degrees, 30 degrees, and positive / negative symmetric. For example, high-speed transmission can be performed without significantly degrading the bit error rate even when the signals are arranged at positions that are deviated ± 10% from the arrangement at equal intervals.

According to the third transition example in FIG. 3, for example, when realizing 1 Gbps, 4-bit transmission is performed in one symbol time (= the minimum time required for the phase to rotate to ± 180 degrees). Therefore, with a symbol rate of S250 Mbps, the required bandwidth is 187.5 MHz of the 3Z4, and it is clear from power simulation that the occupied bandwidth is half that of the known MSK system.

[0037] FIG. 4 is a diagram summarizing comparison of communication performance between the third transition example in the first embodiment of the present invention and the conventional technology. As is apparent from FIG. 4, the baseband band and the RF band in the present invention are narrower than the known technique for the same bit rate.

[0038] That is, after performing multi-value 匕 to increase the number of bits per symbol, the amount of phase change is limited when determining the symbol point arrangement on the phase plane. By using the modulation method of the present invention that limits the region of the phase plane to be arranged, it is possible to narrow the RF band and the baseband band.

[0039] By limiting the region of the phase plane, the bit error rate becomes higher than when the entire region is used. However, when realizing high-speed transmission, it is possible to reduce the bandwidth of signal processing in the baseband as much as possible to reduce the burden on the device, and problems such as heat generation become important. Even in the tens of GHz frequency band, existing devices The applied high-speed transmission is possible, and as a result, effective use of the frequency can be achieved.

[0040] Next, a modulation circuit and a demodulation circuit constituting a digital transmission system for implementing a digital modulation system based on the arrangement of symbol points as described above will be described. First, the modulation circuit will be described. FIG. 5 is a block diagram of the first modulation circuit according to the first embodiment of the present invention. The first modulation circuit includes a baseband signal generation circuit 11 that generates a baseband signal that realizes a shift of a defined vector based on digital data to be transmitted, and a local oscillator 12a. It consists of a quadrature modulation circuit 12 for modulation.

[0041] The baseband signal generation circuit 11 specifies the real and imaginary axes of the phase space shown in FIGS. 1 to 3 in order to identify symbol points on the phase space corresponding to the digital data to be transmitted. Output two values corresponding to. Then, the quadrature modulation circuit 12 performs a quadrature modulation on the two output signals from the baseband signal generation circuit 11 to generate a modulation signal corresponding to digital data.

FIG. 6 is a block diagram of the second modulation circuit in the first embodiment of the present invention. This second modulation circuit is newly provided with an inverse fast Fourier transform circuit (inverse FFT) 13 between the baseband signal generation circuit 11 and the quadrature modulation circuit 12. Different from the modulation circuit.

[0043] Then, the second modulation circuit generates a baseband signal that realizes the shift of the defined vector based on the digital data to be transmitted. A circuit combining the Fourier transform circuit 13 is used. In FIG. 6, the baseband signal generation circuit 11 and the inverse fast Fourier transform circuit 13 are separately described. The force baseband signal generation circuit 11 includes the inverse fast Fourier transform circuit 13. It is also possible.

Finally, the inverse fast Fourier transform circuit 13 outputs two values similar to the baseband signal generation circuit 11 in FIG. Furthermore, the quadrature modulation circuit 12 performs a quadrature modulation on the two output signals from the inverse high-speed Fourier transform circuit 13 to generate a modulation signal corresponding to the digital data.

FIG. 7 is a block diagram of the third modulation circuit in the first embodiment of the present invention. This first The modulation circuit 3 is composed of a control signal generation circuit 14 and a voltage control transmitter 15 that realize a deviation of a defined vector based on digital data to be transmitted. In the case of MSK, it is possible to generate a modulated wave whose phase is continuously changed by adopting such a configuration.

Next, the demodulation circuit will be described. FIG. 8 is a block diagram of the first demodulation circuit according to Embodiment 1 of the present invention. The first demodulating circuit includes an orthogonal demodulating circuit 21 having a local oscillator 21a and a baseband signal determining circuit 22.

[0047] The quadrature demodulation circuit 21 converts a baseband signal transmitted by quadrature modulation. Further, the baseband signal determination circuit 22 detects the vector shift of the received wave based on the baseband signal converted by the orthogonal demodulation circuit 21, and demodulates the received digital data.

FIG. 9 is a block diagram of a second demodulation circuit in the first embodiment of the present invention. This second demodulator circuit is further provided with a fast Fourier transform circuit (FFT) 23 between the quadrature demodulator circuit 21 provided with the local oscillator 21a and the baseband signal determination circuit 22, as shown in FIG. Different from the first demodulator circuit.

[0049] The modulation method of the present invention is essentially frequency modulation, and a frequency detection circuit is used, and the detection result power can be demodulated. Therefore, this second demodulation circuit is characterized by using a fast Fourier transform circuit (FFT) 23 in order to detect the reception frequency. In FIG. 9, the fast Fourier transform circuit 23 and the baseband signal determination circuit 22 are described separately. The baseband signal determination circuit 22 may include the high-speed Fourier transform circuit 23. Is possible.

FIG. 10 is a block diagram of a third demodulation circuit in the first embodiment of the present invention. The third demodulator circuit includes a frequency determination circuit 24 and a baseband signal determination circuit 22.

[0051] The modulation method of the present invention is essentially frequency modulation and uses a frequency detection circuit, and the detection result power can be demodulated. Therefore, the third demodulating circuit is characterized in that the frequency determining circuit 24 is used to receive a signal transmitted by orthogonal modulation and detect the received frequency. FIG. 11 is an overall block diagram of the modulation circuit according to the first embodiment of the present invention, which includes a digital data generation circuit 30, a modulation circuit 10, and an RFZIF analog circuit 40. Here, any of the first to third modulation circuits described above with reference to FIGS. 5 to 7 can be applied to the modulation circuit 10.

[0053] The digital data generating circuit 30 sequentially generates digital data to be transmitted.

The modulation circuit 10 generates a modulation signal based on the digital data. Further, the RFZIF analog circuit 40 upgrades the baseband modulation signal generated by the modulation circuit 10 to the radio frequency band and performs radio transmission. With such a configuration, the first to third modulation circuits of the present application can be realized.

FIG. 12 is another example of the entire block diagram of the modulation circuit according to Embodiment 1 of the present invention. The overall block diagram of FIG. 12 is different from the overall block diagram of FIG. 11 in that a spread modulation circuit 50 that performs spread modulation of digital data is newly provided. Here, the spread modulation circuit 50 includes a spread code generation circuit 51 that generates a spread code and a spread operation implementation circuit 52 that spreads digital data based on the spread code.

By adopting such a circuit configuration, it becomes possible to add a spreading code to the modulation scheme according to the present invention. As a result, the modulation system according to the present invention can have an effect of excellent secrecy that is strong against interference of spread coding.

FIG. 13 is an overall configuration diagram of a digital transmission system to which the modulation method according to Embodiment 1 of the present invention is applied. The digital transmission system of FIG. 13 illustrates a wireless communication system including a wireless access point 60 connected to the Internet and wireless terminals 61 to 63 connected to a plurality of notebook PCs, etc. The following shows the case where the modulation method according to is applied as a wireless LAN.

[0057] Each terminal maintains a respective communication line from the wireless access point 60 to each wireless terminal 61 to 63, and from each wireless terminal 61 to 63 to the wireless access point 60. It is possible to use the modulation system of the present invention for both or one line.

That is, in a wireless communication system to which the communication system of the present invention is applied, it is not always necessary to use a unified modulation system as the entire system. With each wireless terminal 61-63 Individual modulation schemes or different carrier frequencies can be used. Furthermore, even in the same wireless terminal, individual modulation is performed in the upstream direction (from each wireless terminal 61 to 63 to the wireless access point 60) and in the downstream direction (from the wireless access point 60 to each wireless terminal 61 to 63). It is also possible to use schemes or different carrier frequencies. In addition, it is possible to have some modulation methods coexist with conventional modulation methods.

[0059] Thereby, a radio communication system can be constructed without being restricted by a specific modulation method, and the modulation scheme of the present invention can be applied to communication that requires high-speed transmission.

[0060] As described above, according to the first embodiment of the present invention, after performing multi-value 匕 in order to increase the number of bits per symbol, the symbol point arrangement is determined on the phase plane. However, by limiting the area of the phase plane to be arranged so that the amount of phase change is limited, it is possible to increase the number of transmission bits per symbol and narrow the baseband bandwidth. An enabling digital modulation method can be obtained.

[0061] Since the modulation method of the present invention is constant-amplitude modulation, an operation margin of a power amplifier or a mixer is not particularly required. Therefore, compared with other high-speed methods using phase modulation or the like, The burden is small. Furthermore, since the GMSK multi-leveling that limits the band by the Gaussian filter is an extension by the conventional MSK filtering, the modulation method of the present invention can be applied.

[0062] Furthermore, it becomes possible to easily construct a digital modulation circuit or digital transmission system using the modulation method of the present invention, enabling high-speed transmission and realizing communication with a narrow baseband bandwidth. .

Claims

The scope of the claims

[1] In a digital modulation method for transmitting digital data by continuously shifting the phase of a carrier signal,

A digital modulation method characterized by limiting the maximum phase to be shifted when transmitting digital data of 2 bits or more by one phase shift.

[2] In the digital modulation method according to claim 1,

A digital modulation method characterized by limiting the maximum value of the phase to be shifted to less than ± 135 degrees when transmitting 2-bit digital data with one phase shift.

[3] In the digital modulation method according to claim 1,

A digital modulation method, characterized in that a phase amount determined by digital data to be transmitted of 2 bits or more is defined as an arbitrary phase amount below a limited maximum value.

[4] In the digital modulation method according to claim 1,

A digital modulation method characterized in that the phase amount determined by digital data to be transmitted of 2 bits or more is defined to be equal to or less than a limited maximum value and to be equal in phase interval between shifted phase points.

[5] A baseband signal generation circuit that generates a baseband signal in which the maximum value of the phase to be shifted is limited, corresponding to digital data of 2 bits or more to be transmitted by one phase shift,

An orthogonal modulator for orthogonally modulating the generated baseband signal;

A digital modulation circuit comprising:

[6] The digital modulation circuit according to claim 5,

The digital modulation circuit, wherein the baseband signal generation circuit includes an inverse high-speed Fourier transform circuit for generating the baseband signal.

[7] The digital modulation circuit according to claim 5 or 6,

A spread modulation circuit for generating a signal obtained by spreading the digital data in a baseband;

The baseband signal generation circuit generates the baseband signal corresponding to a signal obtained by spreading the digital data in a baseband. A digital modulation circuit characterized by the above.

[8] A control signal generation circuit that generates a phase control signal that limits the maximum value of the phase to be shifted, corresponding to digital data of 2 bits or more to be transmitted by one phase shift, and the generated A voltage-controlled oscillator that generates an oscillation signal whose phase is continuously changed according to the phase control signal;

A digital modulation circuit comprising:

[9] In the digital modulation circuit according to claim 8,

The control signal generation circuit generates the phase control signal corresponding to a signal obtained by spreading the digital data in a baseband.

A digital modulation circuit.

[10] In response to digital data of 2 bits or more to be transmitted by one phase shift, a signal obtained by quadrature modulation of a baseband signal with a maximum shift phase limit is received, and the quadrature modulation described above is received. A quadrature demodulating circuit for converting the generated signal to generate the baseband signal; a baseband signal determining circuit for detecting a vector shift of the generated received baseband signal force and demodulating the digital data;

A digital demodulation circuit comprising:

[11] In the digital demodulation circuit according to claim 10,

The baseband signal determination circuit has a fast Fourier transform circuit for detecting a vector shift of a received wave by analyzing a reception frequency of the generated baseband signal. .

[12] In response to digital data of 2 bits or more to be transmitted with a single phase shift, the maximum value of the phase to be shifted is limited, and an oscillation signal whose phase continuously changes is received. A frequency determination circuit for determining a reception frequency of the signal;

A baseband signal determination circuit for detecting a vector shift of a received wave from the determined reception frequency and demodulating the digital data;

A digital demodulation circuit comprising: In a digital transmission system that performs bidirectional communication between a base station and a terminal using the same carrier frequency or different carrier frequencies,

At least one of the base station or the terminal includes the digital modulation circuit according to any one of claims 5 and 9, and a digital transmission system according to claim 5.