Demodulation device, base station, and demodulation method

Abstract

To provide a communication system capable of following fluctuations in a radio wave propagation path.SOLUTION: A demodulation device receives radio signals coming from a plurality of transmission devices, demodulates a differential phase modulated first reception signal among these radio signals, demodulates the demodulated demodulation signal into a modulation signal through differential phase modulation, estimates a propagation path from each of the transmission devices to a receiving circuit based on the received radio signals and the modulation signal, generates a first pseudo signal that simulates the first received signal from one transmission device based on the estimated propagation path, removes the first pseudo signal from the radio signals, and repeats these pieces of processing as long as demodulation is possible.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a demodulation device, a base station, and a demodulation method.

Background Art

[0002] In the future, an increase in the number of terminals connected to a wireless communication network is predicted. Therefore, for example, there is concern about the congestion of the uplink (up-link). Thus, for the purpose of increasing the number of terminals that can be connected in the uplink, the use of a technology in which the orthogonality of wireless signals is relaxed is expected. This technology is called Power Domain-Uplink Non-Orthogonal Multiple Access (PD-UL-NOMA), which utilizes the power difference in the uplink. tiple Access: PD-UL-NOMA).

[0003] FIG. 1 illustrates the situation of wireless signals in a wireless communication network to which PD-UL-NOMA is applied. The upper part of FIG. 1 illustrates the resources allocated to terminals. In PD-UL-NOMA, the same uplink resource is allocated to a plurality of terminals in a duplicated manner.

[0004] In a wireless communication network, reference signals are exchanged between a base station and a terminal for purposes such as propagation path estimation and synchronization between the base station and the terminal. Also in PD-UL-NOMA, a plurality of reference signals are orthogonal. For example, in time-division multiplexed communication, data signals overlap on the time axis, but reference signals are separated and orthogonal. In this way, by using reference signals, the communication procedure becomes complicated, but the resistance to interference signals or noise between terminals is improved.

[0005] However, in PD-UL-NOMA, the estimation accuracy of the radio wave propagation path affects the communication success rate (or error rate). Particularly in an environment where the terminal moves at high speed, since the fluctuation speed of the radio wave propagation path becomes high, a communication means that follows the fluctuation speed is desired.

[0006] By the way, in conventional wireless communication networks, as a modulation method, for example, Phase Shift Keying (PSK) has been used. This PSK is broadly classified into Coherent PSK (CPSK) and Differential PSK (DPSK). From the perspective of resistance to interference signals, noise, etc., CPSK is superior to DPSK. For this reason, CPSK has been widely used in conventional wireless communication.

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in CPSK, it is a prerequisite that the receiving station is synchronized with the reference signal by the reference signal, and the procedure becomes complicated. For this reason, in CPSK, when the fluctuation of the radio wave propagation path is fast, it is easily affected by the fluctuation. Therefore, an object of the present invention is to provide a communication method capable of following the fluctuation of the radio wave propagation path.

Means for Solving the Problems

[0009] ​ Embodiments of the disclosure are exemplified by a demodulation device. This demodulation device includes a receiving circuit that receives modulated radio signals arriving from a plurality of transmitting devices, a first demodulation circuit that demodulates a first received signal that has been differentially phase-modulated among the radio signals received by the receiving circuit, a modulation circuit that modulates the demodulated signal demodulated by the first demodulation circuit into a modulation signal by differential phase modulation, an estimation circuit that estimates the amount of fluctuation in the amplitude and phase of the propagation signal in the propagation path from the transmitting device to the receiving circuit based on the radio signal and the modulation signal modulated by the modulation circuit, a first generation circuit that generates a first pseudo signal that simulates the first received signal from the modulation signal based on the amount of fluctuation estimated by the estimation circuit, a removal circuit that extracts a signal obtained by removing the first pseudo signal from the radio signal received by the receiving circuit, and a first control circuit that repeats the processing by the first demodulation circuit, the modulation circuit, the estimation circuit, the first generation circuit, and the removal circuit to the extent possible by the first demodulation circuit.

Advantages of the Invention

[0010] This base station can provide communication with a mobile station using a communication method that can follow fluctuations in the radio wave propagation path.

Brief Description of the Drawings

[0011]

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DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a wireless communication system according to an embodiment and a demodulation method in this wireless communication system will be described with reference to the drawings. This wireless communication system 100 includes a base station 10. The base station 10 also includes a demodulation device. This demodulation device has a receiving circuit that receives modulated radio signals arriving from a plurality of transmitting devices. The receiving circuit receives the radio signals and converts them into electrical signals. The receiving circuit is, for example, a high-frequency circuit including an antenna. The receiving circuit receives the radio signals and converts them into electrical signals. The receiving circuit is, for example, a high-frequency circuit including an antenna.

[0013] Further, this demodulation device has a first demodulation circuit that demodulates a first received signal that has been differentially phase-modulated among the radio signals received by the above-described receiving circuit. That is, the first demodulation circuit performs differential phase demodulation. The first received signal is, for example, a radio signal that has been differentially phase-modulated by a certain transmitting device.

[0014] Also, this demodulation device has a modulation circuit that modulates the demodulated signal demodulated by the first demodulation circuit into a modulation signal by differential phase modulation. That is, as described above, the modulation circuit restores the transmission signal in the transmitting device of the transmission source from the data that has been differentially phase-demodulated.

[0015] Further, this demodulation device has an estimation circuit that estimates the amount of variation in the amplitude and phase of the propagation signal in the propagation path from the transmitting device to the receiving circuit based on the radio signal received by the receiving circuit and the modulation signal modulated by the above-described modulation circuit. The amount of variation in the amplitude and phase of the propagation signal in the propagation path can also be referred to as a transfer function indicating the influence of fading or the like of the propagation path.

[0016] Also, this demodulation device has a first generation circuit that generates a first pseudo signal that pseudo-simulates the first received signal from the above-described modulation signal based on the amount of variation estimated by the above-described estimation circuit. Since the amount of variation can be referred to as a transfer function indicating the influence of fading or the like of the propagation path, for example, by multiplying the modulation signal by the amount of variation, it becomes possible to pseudo-simulate the first received signal that has arrived at the receiving circuit.

[0017] Also, this demodulation device has a removal circuit that extracts a signal obtained by removing the first pseudo signal from the radio signal received by the above-described receiving circuit. As described above, the first pseudo signal simulates the first received signal. Therefore, in the signal obtained by removing the first pseudo signal from the radio signal received by the receiving circuit, the interference by the first received signal is removed. That is, the removal circuit removes the interference by the transmission signal transmitted from the first transmitting device. As a result, it becomes possible to demodulate the received signals from transmitting devices other than the first transmitting device.

[0018] Furthermore, this demodulation device has a first control circuit that repeats the processing by the first demodulation circuit, modulation circuit, estimation circuit, first generation circuit, and removal circuit to the extent possible for demodulation by the first demodulation circuit. By repeating such processing, the demodulation device can acquire reception signals from a plurality of transmission devices sequentially, such as the first transmission device, the second transmission device, and the like, while removing interference caused by the transmission signals from those transmission devices. Then, the demodulation device can separate the signals received from individual transmission devices from a signal in which the transmission signals from a plurality of transmission devices are mixed.

[0019] <First Embodiment> (Communication Method) The wireless communication system 100 according to the first embodiment will be described with reference to FIGS. 2 to 5. FIG. 2 is a diagram illustrating the configuration of the wireless communication system 100 according to the present embodiment. In the example of FIG. 2, the wireless communication system 100 includes a base station 10, wireless terminals 3-1 and 3-2, and wireless terminals 4-1 and 4-2. Among these, the wireless terminals 3-1 and 3-2 communicate with the base station 10 using DPSK. On the other hand, the wireless terminals 4-1 and 4-2 communicate with the base station 10 using CPSK. Thus, in the wireless communication system 100, the base station 10 can be simultaneously connected to both the wireless terminals 3-1 and 3-2 that communicate using DPSK and the wireless terminals 4-1 and 4-2 that communicate using CPSK.

[0020] Also, the wireless terminals 3-1 and 3-2 may be wireless terminals dedicated to DPSK, or DPS It may also be a wireless terminal that can use both K and CPSK. When wireless terminals 3-1 and 3-2 can use both DPSK and CPSK, when connecting to the base station 10, the wireless terminals 3-1 and 3-2 first access the base station 10 using either DPSK or CPSK. Then, either the wireless terminals 3-1 and 3-2 or the base station 10 determines the switching of the communication method according to the situation. And the wireless terminals 3-1 and 3-2 communicate with the base station 10 using the determined communication method. Also, the number of wireless terminals 3-1 and 3-2 is not limited to two. Figure 2 is just an example. Also, in this embodiment and other subsequent embodiments, when collectively referring to the wireless terminals 3-1 and 3-2, it is simply called the wireless terminal 3. As described above, in this embodiment, the wireless terminal 3 is a wireless terminal that communicates using DPSK.

[0021] Also, the wireless terminals 4-1 and 4-2 may be wireless terminals dedicated to CPSK, or may be wireless terminals that can use both CPSK and DPSK. When the wireless terminals 4-1 and 4-2 can use both CPSK and DPSK, when connecting to the base station 10, the wireless terminals 4-1 and 4-2 first access the base station 10 using either CPSK or DPSK. Then, either the wireless terminals 4-1 and 4-2 or the base station 10 determines the switching of the communication method according to the situation. And the wireless terminals 4-1 and 4-2 communicate with the base station 10 using the determined communication method. Also, the number of wireless terminals 4-1 and 4-2 is not limited to two. Also, in this embodiment and other subsequent embodiments, when collectively referring to the wireless terminals 4-1 and 4-2, it is simply called the wireless terminal 4. As described above, in this embodiment, the wireless terminal 4 is a wireless terminal that communicates using CPSK.

[0022] As shown in FIG. 2, the base station 10 includes a receiving device 10A, a transmitting device 10B, and a control device 10C. The receiving device 10A receives uplink signals from a plurality of wireless terminals 3, 4, etc. using PD-UL-NOMA. The receiving device 10A has a demodulation circuit for DPSK and a demodulation circuit for CPSK, and can receive modulation signals of both CPSK and DPSK. The transmitting device 10B transmits wireless signals to the wireless terminals 3, 4, etc. The control device 10C controls the receiving device 10A and the transmitting device 10B. For example, the control device 10C controls the operations of the DPSK demodulation circuit and the CPSK demodulation circuit of the receiving device 10A. The control device 10C has a Central Processing Unit (CPU) and a memory. The CPU executes processing according to a computer program developed to be executable on the memory.

[0023] CPSK is a modulation method widely used in, for example, Long Term Evolution (LTE), etc. When using CPSK, it is necessary to separately transmit a reference signal (RS). Also, the transmitted reference signal is orthogonal to other signals. In PD-UL-NOMA, in the CPSK method, there are the following problems.

[0024] Problems of the CPSK method: (1) In the CPSK method, as the number of NOMA superimpositions increases, the radio resource occupancy ratio by the reference signal increases, preventing an improvement in transmission efficiency. (2) When the fading speed is high, the estimated value of the propagation path measured by the reference signal may not be valid. (3) Since the wireless terminal 4 cannot transmit until a reference signal is assigned from the base station 10, there is a delay during this period. Also, if the assigned reference signal overlaps with the reference signals of other wireless terminals 4, etc., the communication quality deteriorates.

[0025] Therefore, in this embodiment, it is proposed to solve the problems of CPSK by DPSK. For example, by the base station 10 using both CPSK and DPSK, the above problems can be solved. By using both CPSK and DPSK, it becomes possible to combine the advantages of both as follows. In addition to using both CPSK and DPSK, in PD-UL-NOMA, instead of the CPSK method, it is also conceivable to use the DPSK method under specific conditions. It is conceivable.

[0026] Advantages of transmission by DPSK: (1) No radio resources are required for the reference signal. The reference signal needs to be orthogonal, and CPSK consumes a lot of radio resources for the reference signal. On the other hand, DPSK does not require a reference signal. As a result, it becomes possible to allocate the radio resources for the reference signal to data. (2) The influence of the error of the propagation path estimation value due to fast fading can be reduced. When the variation of fading is faster than a certain limit, the accuracy of the propagation path estimation value measured by the reference signal may not be sufficient. In this case, the error rate of CPSK deteriorates. In DPSK, propagation path estimation by the reference signal is not required, and the influence of fast fading is reduced. (3) In DPSK, low latency is achieved. That is, DPSK can be transmitted without negotiation between the base station and the terminal for the allocation of the reference signal. Therefore, there is no communication delay due to negotiation.

[0027] Advantages of transmission by CPSK: (1) In CPSK, the transmitting terminal can be grasped. That is, in CPSK, the base station 10 can grasp the number of connected transmitting terminals and identification information (ID), etc. before demodulation based on the presence or absence of the received reference signal. (2) In CPSK, the signal-to-interference-plus-noise ratio (SINR) for obtaining the same bit error rate can be reduced. That is, CPSK has higher resistance to interference and noise than DPSK. Therefore, in CPSK, it becomes possible to increase the number of terminals that can be superimposed. (3) In CPSK, it is easy to create replicas in a loop according to a Successive Interference Canceller (SIC). In the case of CPSK, since the propagation path estimation value can be obtained from the reference signal, it is easy to generate replicas. On the other hand, in DPSK, since the reference signal is not transmitted and received, the special processing described in this embodiment is required to obtain the propagation path estimation value for generating the replica for interference cancellation.

[0028] FIG. 3 illustrates the configuration of radio resources in the wireless communication system 100 of this embodiment. In the example of FIG. 3, reference signals (RS) are separated and orthogonal on the time axis. On the other hand, data signals (DATA1 to DATA5) overlap on the time axis. Among these, DATA1, DATA2, and DATA4 are CPSK radio signals. Also, DATA3 and DATA5 are DPSK radio signals. As shown in FIG. 3, in this embodiment, a method is adopted in which the DPSK signal does not overlap the radio resources of the reference signal. With such a configuration, the reference signal used in CPSK is not affected by the DPSK signal. In the resource allocation as shown in FIG. 3, the signal-to-interference-plus-noise ratio (SINR) required for demodulating the DPSK signal needs to be larger than that of the CPSK signal.

[0029] Therefore, in the example of FIG. 3, the base station 10 first demodulates the CPSK radio signals of DATA1 and DATA2 and removes their interference. Then, the base station 10 demodulates the DPSK radio signal of DATA3 and removes the interference. Further, the base station 10 demodulates the CPSK radio signal of DATA4 and removes the interference. Finally, the base station 10 demodulates the DPSK radio signal of DATA5.

[0030] However, in this embodiment, the base station 10 operates the DPSK demodulation unit and the CPSK demodulation unit in parallel. The DPSK demodulation unit and the CPSK demodulation unit operate independently, demodulate from a signal with a high signal-to-interference-plus-noise ratio (SINR), and remove interference. Therefore, for example, as shown in FIG. 3, when the interference of DATA1 and DATA2 is not removed, the demodulation result by the DPSK demodulation unit will be in error. After the interference of DATA1 and DATA2 is removed by the CPSK demodulation unit, the DPSK demodulation unit can demodulate the DPSK signal of DATA3. With such a resource configuration and demodulation procedure, the base station 10 can simultaneously connect to both the wireless terminals 3-1 and 3-2 communicating with DPSK and the wireless terminals 4-1 and 4-2 communicating with CPSK, and demodulate each data from the received signal in which DPSK and CPSK are mixed. The base station 10 can simultaneously connect to both the wireless terminals 3-1 and 3-2 communicating with DPSK and the wireless terminals 4-1 and 4-2 communicating with CPSK, and demodulate each data from the received signal in which DPSK and CPSK are mixed.

[0031] (Configuration) FIGS. 4 and 5 illustrate the configuration of the wireless communication system 100 of this embodiment. In FIGS. 4 and 5, the wireless terminal 3 and the wireless terminal 4 are also illustrated. As already described, the wireless terminal 3 is a wireless terminal communicating with DPSK. The wireless terminal 4 is a wireless terminal communicating with CPSK. Among these, FIG. 4 illustrates in detail the configuration of the DPSK demodulation unit 13 of the base station 10. FIG. 5 illustrates in detail the configuration of the CPSK demodulation unit 14 of the base station 10.

[0032] As shown in FIG. 4, the wireless terminal 3 includes a CRC unit 31, a scrambling unit 32, an error correction coding unit 33, and a differential phase modulation unit 34. Each of these units is provided, for example, by the CPU of the wireless terminal 3. The CPU executes the processing of each of the above units by a computer program developed executable in the memory. The CRC unit 31 adds a Cyclic Redundancy Check (CRC) error detection code to the data transmitted from the wireless terminal 3. The scrambling unit 32 pseudo-randomizes the error detection coded data to reduce the occurrence of a regular bit pattern. By randomizing the bit pattern, the bias of the symbol is eliminated. As a result, for example, the performance of averaging during channel estimation is improved.

[0033] The error correction encoding unit 33 performs error correction encoding on the scrambled data. The differential phase modulation unit 34 performs DPSK modulation on the error correction encoded data. The DPSK modulated data is transmitted from the transmission antenna to the base station 10.

[0034] Also, the wireless terminal 4 includes a CRC unit 41, a scrambling unit 42, an error correction encoding unit 43, a coherent phase modulation unit 44, and an RS (reference signal) generation unit 45. Each of these units is also provided by, for example, the CPU of the wireless terminal 4. Among these, the processing of the CRC unit 41, the scrambling unit 42, and the error correction encoding unit 43 is the same as that of the CRC unit 31, the scrambling unit 32, and the error correction encoding unit 33 of the wireless terminal 3. Also, the coherent phase modulation unit 44 performs CPSK modulation on the error correction encoded data. The RS generation unit 45 generates a reference signal. The generated reference signal is transmitted to the base station 10 together with the CPSK modulated data.

[0035] Also, as shown in FIGS. 4 and 5, the base station 10 includes a DPSK demodulation unit 13, a CPSK demodulation unit 14, an antenna 19, and a replica removal unit 18. The base station 10 operates the DPSK demodulation unit 13 and the CPSK demodulation unit 14 in parallel to demodulate the received signals from the antenna 19 respectively.

[0036] Antenna 19 receives modulated radio signals arriving from a plurality of transmission devices. The antenna 19 and the circuit coupled thereto can be referred to as a receiving circuit that executes a receiving process. As illustrated in FIG. 3, the received signals are orthogonal to the respective reference signals. On the other hand, the data signals overlap in resource blocks (e.g., time axis) without distinction between DPSK signals and CPSK signals. The DPSK demodulation unit 13 sequentially extracts DPSK signals from the received signals by the SIC method. That is, the DPSK demodulation unit 13 demodulates the received signals of DATA3 and DATA5 among the received signals carrying DATA1 to DATA5 illustrated in FIG. 3, for example. As described in FIG. 3, for example, the demodulation by the DPSK demodulation unit 13 is not successful until the DPSK signal of DATA3 in FIG. 3 reaches the signal-to-interference-plus-noise power ratio (SINR) required for demodulation. Therefore, the demodulation of the DPSK signal of DATA3 by the DPSK demodulation unit 13 is after the interference of DATA1 and DATA2 is removed.

[0037] Therefore, the replica removal unit 18 includes, for example, a buffer that holds a signal (data) before the replica is removed and a subtractor that removes the replica from the signal held in the buffer and writes the resulting signal after the replica is removed back into the buffer. With such a configuration, the replica removal unit 18 removes replicas based on decoded data from a plurality of wireless terminals 3, 4, etc. from the radio signal received by the antenna 19. In the SIC loop, the replica removal unit 18 removes replicas in descending order of signal-to-interference-plus-noise power ratio (SINR).

[0038] As shown in FIG. 4, the DPSK demodulation unit 13 includes a differential demodulation unit 131, an error correction decoding unit 132, a descrambling unit 133, a CRC unit 134, a scrambling unit 136, an error correction encoding unit 137, a differential phase modulation unit 138, a replica generation unit 139, and a propagation path estimation unit 13B. Each unit from the differential demodulation unit 131 to the replica removal unit 18 in FIG. 4 forms an SIC loop that executes the SIC method.

[0039] The DPSK demodulation unit 13 sequentially demodulates the differentially phase-modulated (DPSK) received signal in the loop of SIC from the first received signal with a high signal-to-interference-plus-noise ratio (SINR). Among these, the differential demodulation unit 131 demodulates the received signal received by the antenna 19 by DPSK. The differential demodulation unit 131 detects the amount of change in the phase of the current received signal from the phase of the previously received signal. However, as illustrated in FIG. 3, interference signals from a plurality of terminals are mixed in the current received signal. Also, noise is superimposed on the received signal. Therefore, the differential demodulation unit 131 processes a plurality of received signals indicating phases with different amounts of change from the phase of the previously received signal. The differential demodulation unit 131 detects the amount of change in the phase from the strongest received signal among the plurality of received signals indicating phases with different amounts of change. For example, in FIG. 3, after removing the interference of DATA1 and DATA2, the differential demodulation unit 131 demodulates the DPSK received signal of DATA3.

[0040] The error correction decoding unit 132 error correction decodes the demodulated data. The descrambling unit 133 descrambles the error correction decoded data and returns it to the bit sequence before scrambling. The CRC unit 134 performs error detection by CRC on the descrambled data. The data for which the error detection result by the CRC unit 134 is normal is sent to the upper layer of the base station 10 and delivered to the scrambling unit 136. Among these, the configuration from the differential demodulation unit 131 to the CRC unit 134 demodulates the first received signal that is differentially phase-modulated and delivers it to the upper layer of the base station 10, so it can be called the first demodulation circuit that performs the first demodulation process. Also, among the received signals received by the antenna 19, the received signal demodulated at this time is referred to as the first received signal.

[0041] Note that in this embodiment, the CRC unit 134 performs error detection but does not remove the error detection code by CRC. When the CRC unit 134 removes the detection code, the circuit may be connected so that the data descrambled by the descrambling unit 133 is delivered to the scrambling unit 136 after the error detection by the CRC unit 134. Further, a circuit for adding an error detection code by CRC again may be provided before the scrambling unit 136 after the CRC unit 134.

[0042] The scrambling unit 136, the error correction encoding unit 137, and the differential phase modulation unit 138 perform scrambling, error correction encoding, and DPSK modulation again based on the data determined to be error-free by the error detection by the CRC unit 134. Thereby, differential phase modulation data for executing SIC is generated. Therefore, the scrambling unit 136, the error correction encoding unit 137, and the differential phase modulation unit 138 can be said to be a modulation circuit that executes a modulation process of modulating the demodulated demodulation signal into a modulation signal by differential phase modulation.

[0043] The propagation path estimation unit 13B calculates a propagation path estimation value h from the reception signal received by the antenna 19 and the differential phase modulation signal output from the differential phase modulation unit 138. The propagation path estimation value h is It can be said to be the amount of fluctuation in the amplitude and phase of the propagation signal in the propagation path from each wireless terminal 3 to the antenna 19. Therefore, the propagation path estimation unit 13B can be said to be an estimation circuit that executes an estimation process of estimating the amount of fluctuation in the amplitude and phase of the propagation signal in the propagation path.

[0044] However, the received signal received by the receiving antenna 19 includes received signals from a plurality of wireless terminals. Also, the received signal received by the antenna 19 includes noise. Therefore, the propagation path estimation unit 13B averages the propagation path estimation value h over a plurality of periods during which the received signal is received. That is, the propagation path estimation unit 13B uses the received signals [r1, r2, r3, …, rN] for a plurality of periods obtained by the antenna 19 and the differential phase modulation data [s1, s2, s3, …, sN] output by the differential phase modulation unit 138 based on this. Then, the propagation path estimation unit 13B calculates the propagation path estimation value h n =r n / s n (n = 1, 2, 3, …, N) and averages them. By averaging, random interference signals and noise from other wireless terminals other than the demodulation target included in the received signal received by the antenna 19 are removed.

[0045] The replica generation unit 139 generates a replica of the DPSK signal based on the propagation path estimation value h generated by the propagation path estimation unit 13B. The replica is a simulation signal that simulates the DPSK modulation signal (the first received signal) with the maximum power received by the antenna 19. That is, the replica is a DPSK modulation signal coming from a certain wireless terminal 3 to the antenna 19 and simulates the signal with the highest signal-to-interference-plus-noise power ratio (SINR). Here, the replica of the DPSK signal is called the first pseudo signal. The replica generation unit 139 can be said to be a first generation circuit that executes a first generation process of generating a first pseudo signal that simulates the first received signal.

[0046] The replica removal unit 18 removes the replica of the DPSK signal as a first removal process from the data received by the antenna 19. In the example of FIG. 4, a simulation signal corresponding to the DPSK modulation signal with the maximum power is removed from the received signal by the loop of SIC.

[0047] The DPSK demodulation unit 13 repeats the SIC loop from the received signal until data without errors cannot be obtained by error detection by the CRC unit 134. In this way, the DPSK demodulation unit 13 demodulates the received signal by DPSK from a signal in which the received signals by DPSK and the received signals by CPSK from a plurality of wireless terminals are mixed. That is, the DPSK demodulation unit 13 demodulates the received signal by DPSK from each wireless terminal 3 communicating by DPSK and delivers it to the upper layer of the base station 10. For example, the control device 10C of the base station 10 has a CPU and executes the processing of each part of the DPSK demodulation unit 13 and the control of the SIC loop. The CPU of the base station 10 that executes the processing as the DPSK demodulation unit 13 may be called a first control circuit that repeats the processing. However, the DPSK demodulation unit 13 may have a CPU and control the SIC loop.

[0048] As shown in FIG. 4, by the SIC loop, the signal from which the analog signal corresponding to the DPSK modulation signal with the maximum power is removed from the received signal is returned to the SIC loop again and also delivered to the CPSK demodulation unit 14. As shown in FIG. 5, the CPSK demodulation unit 14 includes a demodulation unit 141, an error correction decoding unit 142, a descrambling unit 143, a CRC unit 144, a scrambling unit 146, an error correction encoding unit 147, a coherent phase modulation unit 148, a replica generation unit 149, and a propagation path estimation unit 14B. The CPSK demodulation unit 14 demodulates the received signal that has been coherently phase-modulated by the processing of each of the above units.

[0049] Among these, the propagation path estimation unit 14B calculates the propagation path estimation value between each wireless terminal 4 and the antenna 19 based on the reference signal transmitted from each wireless terminal 4. Further, each part from the demodulation unit 141 to the replica removal unit 18 in FIG. 5 forms an SIC loop that executes the SIC method.

[0050] The demodulation unit 141 performs equalization processing on the received signal received by the antenna 19 and extracts the received signals from the respective wireless terminals 4 communicating by CPSK. That is, the demodulation unit 141 extracts and demodulates the received signal from a specific wireless terminal 4 by equalization processing using the propagation path estimation value h between the demodulation unit 141 and each wireless terminal 3 generated by the propagation path estimation unit 14B. In the equalization processing, the received signal from the corresponding wireless terminal 4 is extracted based on the propagation path estimation value h between the demodulation unit 141 and each wireless terminal 4, and the received signals from other wireless terminals are suppressed.

[0051] The error correction decoding unit 142 performs error correction decoding on the demodulated data. The descrambling unit 143 descrambles the error correction decoded data and returns it to the bit sequence before scrambling. The CRC unit 144 performs error detection by CRC. The data with a normal error detection result by the CRC unit 144 is sent to the upper layer of the base station 10 and delivered to the scrambling unit 146. Among these, the configuration from the demodulation unit 141 to the CRC unit 144 demodulates the second received signal subjected to coherent phase modulation and delivers it to the upper layer of the base station 10, so it can be called a second demodulation circuit that performs the second demodulation process. Note that, among the received signals received by the antenna 19, the received signal demodulated at this time is referred to as the second received signal.

[0052] The scrambling unit 146, the error correction coding unit 147, and the coherent phase modulation unit 148 perform scrambling, error correction coding, and coherent phase modulation by CPSK again based on the decoded data. As a result, the transmission data in the wireless terminal 4 that transmitted the decoded data is restored at the base station 10. The replica generation unit 149 generates a replica of the CPSK signal received from the wireless terminal 4 by multiplying the transmission data in the wireless terminal 4 restored by the coherent phase modulation unit 148 by the propagation path estimation value h. That is, the replica is a signal that simulates the CPSK modulation signal with the maximum power received by the antenna 19. Here, the replica of the CPSK signal is called the second pseudo signal. The configuration from the scrambling unit 146 to the replica generation unit 149 generates a second pseudo signal that simulates the second received signal based on the demodulated signal demodulated by the second demodulation circuit, so it can be called a second generation circuit that executes the second generation process.

[0053] The replica removal unit 18 removes the replica of the CPSK signal as the second removal process from the wireless signal received by the antenna 19. As a result, in the example of FIG. 5, the analog signal corresponding to the CPSK modulation signal with the maximum power (the second received signal) is removed from the received signal by the loop of SIC. It can be said that the replica removal unit 18 executes a process of extracting a signal obtained by removing the second pseudo signal from the received signal. Also, since the loop of SIC is repeated, it can be said that the replica removal unit 18 removes the second pseudo signal from the extracted signal.

[0054] The CPSK demodulation unit 14 repeats the SIC loop from the received signal until data without errors cannot be obtained by error detection by the CRC unit 144. In this way, the CPSK demodulation unit 14 demodulates the received signal by CPSK from a signal in which the received signals by CPSK and the received signals by DPSK from a plurality of wireless terminals are mixed. That is, the CPSK demodulation unit 14 demodulates the received signal by CPSK from each of the individual wireless terminals 4 communicating by CPSK and delivers it to the upper layer of the base station 10. As described above, the control device 10C of the base station 10 has a CPU. For example, the CPU of the control device 10C executes the processing of each part of the CPSK demodulation unit 14 and the control of the SIC loop. The CPU of the base station 10 that executes the processing as the CPSK demodulation unit 14 may also be called a second control circuit that repeats the processing. However, the CPSK demodulation unit 14 may have a CPU and control the SIC loop.

[0055] As shown in FIG. 5, by the SIC loop, the signal from which the analog signal corresponding to the CPSK modulation signal with the maximum power is removed from the received signal is returned to the SIC loop again and is also delivered to the DPS K demodulation unit 13. In this way, the DPSK demodulation unit 13 and the CPSK demodulation unit 14 each independently execute the demodulation process in parallel, return the result of the SIC to their own SIC loop, and deliver it to the demodulation unit of the other party.

[0056] As described above, the replica removal unit 18 receives replicas from each of the DPSK demodulation unit 13 and the CPSK demodulation unit 14, and gradually removes the replicas from the radio signal received by the antenna 19. In the present embodiment, the DPSK demodulation unit 13 and the CPSK demodulation unit 14 each operate independently in parallel and demodulate in order from the one with the higher signal-to-interference-plus-noise power ratio (SINR). Then, when there is no error in either the CRC unit 134 of the DPSK demodulation unit 13 or the CRC unit 144 of the CPSK demodulation unit 14, a replica is generated by the one without error, and in the replica removal unit 18, the interference of the signal corresponding to the data demodulated without error is removed.

[0057] (Processing flow) FIG. 6 is a diagram illustrating the processing of the propagation path estimation unit 13B of the DPSK demodulation unit 13. Now, assume that the wireless terminal 3 targeted for propagation path estimation is the wireless terminal 3-A. In this processing, the propagation path estimation unit 13B estimates the propagation path between the wireless terminal 3-A, which is currently the target of propagation path estimation, and the antenna 19 without using a reference signal. For this purpose, the propagation path estimation unit 13B uses a received signal in which received signals from a plurality of wireless terminals 3 including the wireless terminal 3-A and noise are mixed. Then, in order to remove the interference signals and noise from other wireless terminals 3-B, etc. other than the wireless terminal 3-A for which the propagation path is to be estimated, the propagation path estimation unit 13B averages the propagation path estimation values over a plurality of periods.

[0058] Therefore, first, the propagation path estimation unit 13B acquires a set value of the period N for averaging the calculated propagation path estimation value h (S1). The set value of the period N may be an empirical value accumulated at the base station 10. Also, the set value of the period N may be, for example, a setting set by an administrator for the base station 10. Further, the set value of the period N may be, for example, a value set from the rate of change of the propagation path estimation value h with respect to time (such as the fading speed) determined by the propagation path estimation unit 13B in the processing of FIG. 6.

[0059] Next, the propagation path estimation unit 13B acquires the received signals r n (n = 1, …, N) from the memory (S2). The received signal r n is a received signal including signals transmitted from a plurality of wireless terminals 3 including the wireless terminal 3-A at each period (n = 1, …, N) at the antenna 19 of the base station 10. The CPU of the base station 10 that executes the processing as the propagation path estimation unit 13B stores the received signals at the antenna 19 of the base station 10 in the memory for a predetermined period on the memory.

[0060] Next, the propagation path estimation unit 13B acquires the DPSK pseudo-transmission signals s n (n = 1, …, N) from the memory (S3). The DPSK pseudo-transmission signal s nis the differential phase modulation signal generated corresponding to the wireless terminal 3-A that communicates in DPSK and output by the differential phase modulation unit 138 in FIG. 4. The CPU of the base station 10 that executes processing as the propagation path estimation unit 13B stores in the memory the differential phase modulation signal generated corresponding to the wireless terminal 3-A and output by the differential phase modulation unit 138 for a predetermined period in the memory.

[0061] Then, the propagation path estimation unit 13B calculates the propagation path estimation value h n =r n / s n (n = 1, …, N) and calculates the average value of these (S4). By calculating this average value, the interference signals and noise from sources other than the wireless terminal 3-A that is currently the target of propagation path estimation included in the received signal r n (n = 1, …, N) received at the antenna 19 are removed as random components. Such averaging is one type of statistical processing. It can be said that the propagation path estimation unit 13B statistically processes the propagation path estimation value, which is the amount of variation in the amplitude and phase of the propagation signal in the propagation path, as an estimation circuit. Also, it can be said that the replica generation unit 149 executes a process of generating a pseudo signal based on the statistically processed estimation value.

[0062] (Modification example) In the above first embodiment, as illustrated in FIG. 3, the DPSK signal does not overlap with the radio resources of the reference signal for CPSK. With such a configuration, the reference signal used for CPSK is not affected by the DPSK signal. In this case, when the DPSK signal is demodulated, it is sufficient if the signal-to-interference-and-noise power ratio (SINR) of the DPSK signal is larger than that of the CPSK signal. Therefore, it is not necessary to perform interference removal of the DPSK signal before the base station 10 acquires the reference signal. However, the base station 10 of this embodiment is not limited to such processing.

[0063] For example, as illustrated in FIG. 7, a configuration may be adopted in which a DPSK signal is superimposed on a radio resource of a reference signal for CPSK. In this case, in a radio communication network formed by radio terminals 3, 4, etc. and a base station 10, the base station 10 controls the transmission power for each radio terminal 3, 4, etc. so that the reception power of the DPSK signal at the base station 10 becomes the strongest. That is, the base station 10 makes it possible to first remove interference from the DPSK signal in the SIC loop described with reference to FIGS. 4 and 5. In the present embodiment, by setting the radio signal intensity in this way, the interference caused by the DPSK signal to the reference signal is removed first by SIC. As a result, even when the DPSK signal is superimposed on the radio resource of the reference signal for CPSK as shown in FIG. 7, when the CPSK signal is demodulated, the interference is removed and the degradation of the demodulated signal of CPSK is suppressed.

[0064] In this case, the DPSK signal received by the antenna 19 can be said to include a received signal in a resource that overlaps with a reference signal (RS) for a second received signal that is coherently phase-modulated (CPSK). Also, the DPSK signal received by the antenna 19 can be said to include a received signal that is differentially phase-modulated with a power exceeding that of the reference signal (RS).

[0065] (Simulation Results) Figs. 8 to 11 illustrate the results of simulating the wireless communication system 100 of this embodiment by modeling it. Figs. 8 and 9 are examples of simulations assuming the case where wireless terminals 3, 4, etc. move at high speed. Fig. 8 illustrates the parameters set in the simulation. In this simulation, the number of wireless terminals 3 and 4 is 2 each (4 in total), and the modulation methods are single carrier synchronous detection QPSK (CQPSK) and single carrier differentially encoded QPSK (DQPSK). The error correction code is a convolutional code with a constraint length of 6, a coding rate of 1 / 3, an inter-terminal power ratio (SIR) of 3 dB, and the moving speed is the maximum Doppler frequency fd·symbol period T, where fdT = 0.0005 to 0.0008. For example, when the symbol length is 1 microsecond, fd = 500 to 800 Hz. Also, the signal-to-noise power ratio (SNR) is 30 dB and the number of information bits is 128 bits.

[0066] Also, in the simulation, for DQPSK, without a reference signal, the propagation path estimate h n = r n / s n (n = 1, 2, 3,..., 20) was estimated by averaging. That is, the propagation path estimate h n was averaged over a 20-symbol interval.

[0067] Fig. 9 is an example of the simulation result. As shown in Fig. 9, as the moving speed of wireless terminals 3 and 4 increases, in CQPSK, the packet error rate increases. On the other hand, in DQPSK, the increase in the packet error rate is suppressed.

[0068] Figs. 10 and 11 are examples of simulations when the reference signals (RS) collide between two wireless terminals 4. Fig. 10 illustrates the parameters set in the simulation. In this simulation, wireless terminals 3 and 4 are stationary. Also, the inter-terminal power ratio SIR was changed in the range of 2 to 5 dB. The other parameters are the same as those in the case of Fig. 8. 。 Also, for CQPSK, the initial propagation path estimation value h is set to h = h1 + h2, where h1 and h2 are calculated from the collided RSs. The propagation path estimation in the second and subsequent SIC loops is the same as that of DQPSK in FIG. 9, and the propagation path estimation value h n =r n / s n (n = 1, 2, 3,..., 20) is estimated by averaging.

[0069] FIG. 11 illustrates the simulation results. Also in this simulation, generally, the packet error rate of DQPSK was lower than that of CQPSK. However, when the power SIR between four wireless terminals 3 and 4 was about 2 dB, the packet error rate of CQPSK was lower than that of DQPSK.

[0070] (Effect of the First Embodiment) As described above, the base station 10 of the present embodiment estimates the propagation path using a received signal in which transmission signals from a plurality of wireless terminals 3 are mixed without receiving a reference signal in the reception of DPSK. That is, the base station 10 restores a differential phase modulation signal generated based on data decoded from the received signals from the respective wireless terminals 3. Then, the base station 10 calculates a propagation path estimation value between each wireless terminal 3 based on the received signal in which transmission signals from a plurality of wireless terminals 3 are mixed and the restored differential phase modulation signal (FIG. 6). Then, the base station 10 generates a replica, which is an analog signal of the received signal received from each wireless terminal 3, based on this propagation path estimation value h. Then, the base station 10 can extract the received signals from the individual wireless terminals 3 by performing SIC on the received signals from the plurality of wireless terminals 3 communicating by DPSK from the signal in which the received signals from the plurality of wireless terminals 3 are mixed using the generated replica.

[0071] Also, in this case, as shown in FIG. 6, the base station 10 estimates the propagation path estimation value h for a period of N minutes n =r n / s nCalculate (n = 1, …, N) and compute their average values. Therefore, the base station 10 can remove the interference signals from the wireless terminals 3 other than the target wireless terminal 3-A and the random components of the noise.

[0072] Also, as described above, since the base station 10 can simultaneously connect a wireless terminal 3 communicating with DPSK and a wireless terminal 3 communicating with CPSK, the advantages of DPSK and CPSK can be combined.

[0073] That is, by communicating with DPSK, the following is achieved. (1) No radio resources are required for the reference signal. The reference signal needs to be orthogonalized, and CPSK consumes a lot of radio resources for the reference signal. On the other hand, DPSK does not require a reference signal. As a result, it becomes possible to allocate the radio resources for the reference signal to DATA. (2) The influence of the propagation path estimation error due to fast fading can be reduced. In DPSK, propagation path estimation by a reference signal is not required, and the influence of fast fading is reduced. (3) In DPSK, low latency is achieved. That is, DPSK can be transmitted without negotiation between the base station and the terminal for the allocation of the reference signal. Therefore, there is no communication delay due to negotiation.

[0074] Also, by CPSK, the following is achieved. (1) In CPSK, the transmitting terminal can be grasped. That is, in CPSK, the base station can grasp the number of connected terminals and the ID of the transmitting terminal before demodulation based on the received reference signal. (2) In CPSK, the signal-to-interference-plus-noise ratio (SINR) for obtaining the same bit error rate can be reduced. That is, CPSK has higher resistance to noise than DPSK. Therefore, it becomes possible to increase the number of terminals that can be superimposed. (3) In CPSK, the creation of replicas is easy. In the case of CPSK, since the propagation path estimation value is obtained from the reference signal, the generation of replicas is easy.

[0075] <Second Embodiment> The base station 10 of the above-described embodiment includes a DPSK demodulation unit 13 and a CPSK demodulation unit 14, and each operates independently in parallel. However, considering power efficiency, the base station 10 may switch and operate the DPSK demodulation unit 13 and the CPSK demodulation unit 14 according to the situation.

[0076] For example, the base station 10 may switch and operate the DPSK demodulation unit 13 and the CPSK demodulation unit 14 according to the requests at the time of connection of wireless terminals 3, 4, etc. The processing other than the processing of the wireless terminals 3, 4 and the base station 10 in this embodiment is the same as the processing of the wireless terminals 3, 4 and the base station 10 in the first embodiment. Therefore, the configurations in FIGS. 2 to 7 are also applied to this embodiment as they are, and the processing different from the first embodiment will be described below.

[0077] FIG. 12 is a diagram illustrating the process of a wireless terminal 3, 4, etc. determining a modulation method. The process in FIG. 12 is executed by the CPU of the wireless terminals 3, 4, etc. according to a computer program in the memory, but here it will be described as the process executed by the wireless terminals 3, 4, etc.

[0078] In this process, it is assumed that a payload to be transmitted occurs in the wireless terminals 3, 4, etc. (S11). Then, the wireless terminals 3, 4, etc. determine whether the amount of data to be transmitted as the payload is less than or equal to a specified value (S12). When the amount of data to be transmitted as the payload is greater than the specified value (NO in S12), the wireless terminals 3, 4, etc. select a method of transmitting DPSK data by superimposing it on the reference signal (RS) of CPSK and notify the base station 10 (S13). Thereby, the wireless terminals 3, 4, etc. can execute data transmission by DPSK including the resource of the reference signal (RS). Therefore, when the data amount is greater than the specified value, uplink transmission can be realized by efficiently using radio resources.

[0079] On the other hand, when the amount of data to be transmitted as the payload is equal to or less than the specified value (YES in S12), the wireless terminals 3, 4, etc. determine whether they have received the allocation of the reference signal (RS) from the base station (S14). When the wireless terminals 3, 4, etc. have not received the allocation of the reference signal (RS) from the base station (NO in S14), they apply a method of transmitting DPSK data within a range of resources that do not overlap with the reference signal of CPSK and notify the base station 10. Thereby, the wireless terminals 3, 4, etc. can execute data transmission by DPSK quickly and in a short time without requiring time to receive the resources of the reference signal (RS). Also, in this case, since the amount of data is equal to or less than the specified value, there is no need to use wireless resources that overlap with the reference signal.

[0080] Furthermore, when the wireless terminals 3, 4, etc. have received the allocation of the reference signal (RS) from the base station 10 (YES in S14), the wireless terminals 3, 4, etc. calculate their own moving speed using a Global Positioning System (GPS) or the like. Then, the wireless terminals 3, 4, etc. determine whether the moving speed is equal to or less than the specified value (S15). And when the moving speed is equal to or more than the specified value (NO in S15), the wireless terminals 3, 4, etc. apply a method of transmitting DPSK data within a range of resources that do not overlap with the reference signal of CPSK and notify the base station 10 (S16). Thereby, the wireless terminals 3, 4, etc. can execute data transmission by DPSK while suppressing the influence of fast fading quickly and in a short time.

[0081] Also, when the moving speed is equal to or less than the specified value (YES in S15), the wireless terminals 3, 4, etc. select a method of transmitting CPSK data and notify the base station 10 (S17). Thereby, the wireless terminals 3, 4, etc. can reduce the SIR of the power and efficiently transmit uplink data. As a result, a large number of wireless terminals 3, 4, etc. can be connected to the base station 10.

[0082] Note that in the present embodiment, as shown in FIG. 12, the process in which the wireless terminals 3, 4, etc. select DPSK and CPSK according to the situation and notify the base station 10 is illustrated. However, the wireless communication system 100 of the present embodiment is not limited to such a process. For example, the base station 10 Based on the moving speeds of the wireless terminals 3 and 4, the load of data transmission and reception, etc., the communication method of DPSK and the communication method of CPSK may be switched.

[0083] FIG. 13 exemplifies a process of switching between the communication method of DPSK and the communication method of CPSK in the base station 10. This process is executed by a computer program by the control device 10C (see FIG. 2) of the base station 10 as an example of a control unit, but will be described as being executed by the base station 10. In this process, the base station 10 first assumes that it is communicating with the wireless terminals 3, 4, etc. using DPSK. However, the process of the base station 10 in FIG. 13 is not limited to the case where communication is performed first using DPSK. The base station 10 may first be communicating with the wireless terminals 3, 4, etc. using CPSK.

[0084] Now, assume that the base station 10 has received the moving speed and data from the wireless terminal 3-A using DPSK (S21). The base station 10 first determines whether there is a designation of a communication method from the wireless terminal 3-A (S22). If there is a designation of a communication method from the wireless terminal 3-A (YES in S22), the base station 10 applies the designated communication method from the wireless terminal 3-A. That is, the base station 10 switches between DPSK and CPSK or maintains the current communication method according to the designation from the wireless terminal 3-A and responds to the wireless terminal 3-A (S23). Therefore, it can be said that the CPU, which is the control unit of the base station 10, operates either one of the DPSK demodulation unit 13, which is the first demodulation circuit, and the CPSK demodulation unit 14, which is the second demodulation circuit, according to the designations from each of the plurality of transmission devices, and stops the other.

[0085] On the other hand, when there is no designation from the wireless terminal 3-A, the base station 10 determines whether the number of currently connected wireless terminals is equal to or greater than a specified value. When the number of currently connected wireless terminals is equal to or greater than the specified value, the base station 10 applies CPSK. That is, the base station 10 sets the communication method to CPSK and responds to the wireless terminals 3, 4, etc. (S25). With CPSK, the possibility of connecting more wireless terminals 3, 4, etc. is increased.

[0086] Also, when the number of currently connected wireless terminals is less than or equal to a specified value, the base station 10 determines whether the moving speed of the wireless terminal 3-A received in S21 is greater than or equal to the specified value (S26). When the moving speed is greater than or equal to the specified value (YES in S26), the base station 10 determines whether the communication data volume from the wireless terminal 3-A is greater than or equal to the specified value (S27). The base station 10 estimates the communication data volume from the wireless terminal 3-A based on, for example, the actual value during a predetermined period. When the communication data volume is greater than or equal to the specified value, the base station 10 selects a method of transmitting DPSK data by superimposing it on the reference signal (RS) of CPSK and notifies the wireless terminal 3-A (S28). Thereby, the base station 10 can utilize the radio resources of the reference signal to receive DPSK data. On the other hand, when the communication data volume is less than the specified value, the base station 10 applies a method of transmitting DPSK data within the range of resources that do not overlap with the reference signal of CPSK and notifies the wireless terminal 3-A (S29). Thereby, the base station can receive DPSK data without interfering with the reference signal.

[0087] On the other hand, when the moving speed is less than the specified value (NO in S26), the base station 10 switches the communication method from DPSK to CPSK and responds to the wireless terminal 3-A (S2A).

[0088] Through the above processing, the CPU, which is the control unit of the base station 10, executes control according to the communication status of the plurality of transmission devices and the demodulation device. And it can be said that the base station 10 operates either the DPSK demodulation unit 13, which is the first demodulation circuit, or the CPSK demodulation unit 14, which is the second demodulation circuit, and stops the other.

[0089] As described above, according to this embodiment, the base station 10 can appropriately switch between DPSK and CPSK according to its own communication status, the status of wireless terminals 3, 4, etc., the moving speed, etc., and receive uplink communication from wireless terminals 3, 4, etc.

[0090] <Hardware Configuration> FIG. 14 is a diagram illustrating the hardware configuration of the base station 10 exemplified in the above-described first and second embodiments. The base station 10 includes a CPU 101, a memory 102, an internal interface 103, a network interface 104 for communicating with other base stations and the like, and a radio processing device 105.

[0091] The CPU 101 is also called a processor or a Microprocessor Unit (MPU). The CPU 101 is not limited to a single processor, and may have a multi-processor configuration. Further, the CPU 101 may have a multi-core configuration with a single physical CPU connected by a single socket. Furthermore, the CPU 101 may include arithmetic devices of various circuit configurations such as a Digital Signal Processor (DSP) and a Graphics Processing Unit (GPU). Also, the CPU 101 may cooperate with an integrated circuit (IC), other digital circuits, or analog circuits. The integrated circuit may include an LSI, an Application Specific Integrated Circuit (ASIC), or a programmable logic device (PLD). The PLD may include, for example, a Field-Programmable Gate Array (FPGA). Therefore, the CPU 11 may be, for example, a microcontroller (MCU), a System-on-a-chip (SoC), a system LSI, a chipset, or the like.

[0092] Memory 102 stores an instruction sequence (computer program) executed by CPU 101, or data processed by CPU 101, etc. CPU 101 and memory 12 may also be referred to as a baseband unit (BBU). Internal interface 13 is a circuit that connects various peripheral devices to CPU 101. The baseband unit can also be called a control unit or a control circuit. CPU 101 executes, for example, the processing illustrated in FIG. 13. Therefore, CPU 101 may switch the processing according to the designation from each of the plurality of transmitting devices such as wireless terminals 3 and 4, or according to the communication status of the plurality of wireless terminals 3 and 4 and base station 10. That is, CPU 101 may operate either one of DPSK demodulation unit 13 which is the first demodulation circuit and CPSK demodulation unit 14 which is the second demodulation circuit according to these communication statuses, and execute processing as a control unit or a control circuit that stops the other.

[0093] Further, CPU 101 may execute the processing illustrated in FIGS. 4 and 5. That is, CPU 101 may cause the first processing within the limit that can be demodulated by DPSK demodulation unit 13 which is the first demodulation circuit, or the second processing within the limit that can be demodulated by CPSK demodulation unit 14 which is the second demodulation circuit to be executed. Here, the first processing is the processing by differential demodulation unit 131 to CRC unit 134, from scramble unit 136 to replica generation unit 139, propagation path estimation unit 13B which is an estimation circuit, and replica removal unit 18 which is a removal circuit illustrated in FIG. 4. The second processing is the processing by demodulation unit 141 to CRC unit 144, from scramble unit 146 to replica generation unit 149, and replica removal unit 18 illustrated in FIG. 5.

[0094] Note that the CPU 101 may be provided, for example, in each of the DPSK demodulation unit 13 and the CPSK demodulation unit 14 shown in FIGS. 4 and 5. Further, the CPU 101 may be provided, for example, in a common part between the DPSK demodulation unit 13 and the CPSK demodulation unit 14 so as to control both the DPSK demodulation unit 13 and the CPSK demodulation unit 14 shown in FIGS. 4 and 5. Therefore, the CPU 101 can be referred to as a first control circuit that repeats processing by the DPSK demodulation unit 13 or the like, which is a first demodulation circuit, to the extent possible by the demodulation by the DPSK demodulation unit 13. Further, the CPU 101 can be referred to as a second control circuit that repeats processing by the CPSK demodulation unit 14 or the like to the extent possible by the demodulation by the CPSK demodulation unit 14, which is a second demodulation circuit.

[0095] The network interface 14 is a communication device for the base station 10 to access a network to which other base stations are connected. The network to which other base stations are connected is also called a backhaul. The backhaul is, for example, a wired network by optical communication.

[0096] The radio processing device 105 includes a transceiver that transmits a radio signal, a receiver that receives a radio signal, etc., and is connected to the antennas ANT-1, ···, ANT-M. The radio processing device 15 may have M systems of transceivers and receivers, respectively, the same number as the antennas ANT-1, ···, ANT-M. The radio processing device 15 is called a remote radio head (RRH), and can also be configured to be remotely installed by connecting to a baseband device via a wired network by optical communication. Further, a configuration may be such that a plurality of remote radio heads are connected to one baseband device. The network connecting the baseband device and the remote radio head is also called a fronthaul. In FIG. 14, a plurality of antennas ANT-1, ···, ANT-M are provided, but only one antenna ANT-1 may be provided. Note that in ANT-M, M is an integer and there is no limitation on the number of antennas. The antennas ANT-1, ···, ANT-M connected to the radio processing device 105 can be referred to as an example of a receiving circuit. Note that the wireless terminals 3, 4, etc. also have a processor, a memory, a radio processing device, an antenna, etc.

Explanation of Symbols

[0097] Wireless terminal communicating by 3 DPSK Wireless terminal communicating by 4 CPSK 10 Base station 13 DPSK demodulation unit 13B, 14B Propagation path estimation unit 14 CPSK demodulation unit 18 Replica removal unit 31, 41, 134, 144 CRC unit 32, 42, 136, 146 Scrambling unit 33, 43, 137, 147 Error correction coding unit 34, 138 Differential phase modulation unit 44, 148 Coherent phase modulation unit 100 Wireless communication system 101 CPU 102 Memory 103 Internal interface 104 Network interface 105 Wireless processing device 131, 141 Differential demodulation unit 132, 142 Error correction decoding unit 133, 143 Descrambling unit 139, 149 Replica generation unit

Claims

1. A receiving circuit that receives modulated radio signals arriving from a plurality of transmitting devices, a first demodulation circuit that demodulates a first received signal that has been differentially phase-modulated among the radio signals received by the receiving circuit, a modulation circuit that modulates the demodulated signal demodulated by the first demodulation circuit into a modulation signal by differential phase modulation, an estimation circuit that estimates the amount of fluctuation in the amplitude and phase of a propagation signal in the propagation path from the transmitting device to the receiving circuit based on the radio signal and the modulation signal modulated by the modulation circuit, a first generation circuit that generates a first pseudo signal that simulates the first received signal from the modulation signal based on the amount of fluctuation estimated by the estimation circuit, a second demodulation circuit that demodulates a second received signal that has been coherently phase-modulated among the radio signals received by the receiving circuit, a second generation circuit that generates a second pseudo signal that simulates the second received signal based on the demodulated signal demodulated by the second demodulation circuit, a removal circuit that extracts a signal obtained by removing the first pseudo signal or the second pseudo signal from the radio signal received by the receiving circuit, and a control circuit, wherein the control circuit repeats a first process by the first demodulation circuit, the modulation circuit, the estimation circuit, the first generation circuit, and the removal circuit within the limit of demodulation by the first demodulation circuit, or repeats a second process by the second demodulation circuit, the second generation circuit, and the removal circuit within the limit of demodulation by the second demodulation circuit. A demodulation device.

2. The estimation circuit statistically processes an estimated value of the amount of fluctuation estimated over a predetermined period, The first generation circuit generates the first pseudo signal based on the statistically processed estimated value. The demodulation device according to claim 1.

3. The radio signal received by the receiving circuit is differential phase modulation with power exceeding that of the reference signal in a resource overlapping with the reference signal for the second received signal that has been coherently phase-modulated. The demodulation device according to claim 1 or 2, including the first received signal.

4. A control unit that operates either the first demodulation circuit or the second demodulation circuit and stops the other according to the designation from each of the plurality of transmitting devices or the communication status of the plurality of transmitting devices and the demodulation device. The demodulation device according to any one of claims 1 to 3.

5. The demodulation device according to claim 1, wherein the control circuit operates either the first demodulation circuit or the second demodulation circuit and stops the other according to a designation from each of a plurality of transmission devices or according to a communication state of the plurality of transmission devices and the demodulation device.

6. A receiving circuit that receives modulated radio signals arriving from a plurality of transmission devices, A first demodulation circuit that demodulates a first received signal that has been differentially phase-modulated among the radio signals received by the receiving circuit, A modulation circuit that modulates the demodulated signal demodulated by the first demodulation circuit into a modulation signal by differential phase modulation, An estimation circuit that estimates a variation amount of an amplitude and a phase of a propagation signal in a propagation path from the transmission device to the receiving circuit based on the radio signal and the modulation signal modulated by the modulation circuit, A first generation circuit that generates a first pseudo signal that simulates the first received signal from the modulation signal based on the variation amount estimated by the estimation circuit, A second demodulation circuit that demodulates a second received signal that has been coherently phase-modulated among the radio signals received by the receiving circuit, A second generation circuit that generates a second pseudo signal that simulates the second received signal based on the demodulated signal demodulated by the second demodulation circuit, A removal circuit that extracts a signal obtained by removing the first pseudo signal or the second pseudo signal from the radio signal received by the receiving circuit, A control circuit that repeats a first process by the first demodulation circuit, the modulation circuit, the estimation circuit, the first generation circuit, and the removal circuit to the extent that demodulation by the first demodulation circuit is possible, or a second process by the second demodulation circuit, the second generation circuit, and the removal circuit to the extent that demodulation by the second demodulation circuit is possible, and a receiving device comprising: A base station having a transmission device that transmits radio signals to the plurality of transmission devices.

7. The estimation circuit statistically processes an estimated value of the variation amount estimated during a predetermined period, The base station according to claim 6, wherein the first generation circuit generates the first pseudo signal based on the statistically processed estimated value.

8. The base station according to claim 6 or 7, wherein the radio signal received by the receiving circuit includes the first received signal that has been differentially phase-modulated with power exceeding that of a reference signal in a resource overlapping with a reference signal for the second received signal that has been coherently phase-modulated.

9. The base station according to any one of claims 6 to 8, further comprising a control unit that operates either the first demodulation circuit or the second demodulation circuit and stops the other according to the designation from each of the plurality of transmission devices or the communication status of the plurality of transmission devices and the base station.

10. A demodulation device includes: a reception step of receiving, by a reception circuit, modulated radio signals arriving from a plurality of transmission devices; a first demodulation step of demodulating a first received signal that is differentially phase-modulated among the radio signals received by the reception circuit; a modulation step of modulating the demodulated signal demodulated in the first demodulation step into a modulation signal by differential phase modulation; an estimation step of estimating a variation amount of an amplitude and a phase of a propagation signal in a propagation path from the transmission device to the reception circuit based on the radio signal and the modulation signal modulated in the modulation step; a first generation step of generating a first pseudo signal that simulates the first received signal from the modulation signal based on the variation amount estimated in the estimation step; a first removal step of extracting a signal obtained by removing the first pseudo signal from the radio signal received in the reception step; a second demodulation step of demodulating a second received signal that is coherently phase-modulated among the radio signals received in the reception step; a second generation step of generating a second pseudo signal that simulates the second received signal based on the demodulated signal demodulated in the second demodulation step; a second removal step of extracting a signal obtained by removing the second pseudo signal from the radio signal received in the reception step; a demodulation method of repeating a first process by the first demodulation step, the modulation step, the estimation step, the first generation step, and the first removal step within a limit capable of demodulating by the first demodulation step or a second process by the second demodulation step, the second generation step, and the second removal step within a limit capable of demodulating by the second demodulation step.

11. In the estimation step, an estimated value of the variation amount estimated in a predetermined period is statistically processed, and in the first generation step, the first pseudo signal is generated based on the statistically processed estimated value. The demodulation method according to claim 10.

12. The radio signal received in the reception step includes the first received signal that is differentially phase-modulated with power exceeding the reference signal in a resource overlapping with a reference signal for the second received signal that is coherently phase-modulated. The demodulation method according to claim 10 or 11.

13. ​ The demodulation method according to any one of claims 10 to 12, comprising a step of causing only one of the first demodulation step and the second demodulation step to be executed according to the designation from each of the plurality of transmission devices or according to the communication status of the plurality of transmission devices and the demodulation device.

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