WO2023248379A1

WO2023248379A1 - Wireless communication system, reception device, and estimation method

Info

Publication number: WO2023248379A1
Application number: PCT/JP2022/024881
Authority: WO
Inventors: 知哉景山; 一光坂元; 洋輔藤野
Original assignee: 日本電信電話株式会社
Priority date: 2022-06-22
Filing date: 2022-06-22
Publication date: 2023-12-28

Abstract

This reception device comprises a Doppler shift estimation unit that receives waveform data transmitted by a wireless communication device and estimates a Doppler shift and a frequency offset affecting a reception signal indicated by the waveform data, the Doppler shift estimation unit being provided with: M first computation units (where M is an integer equal to or greater than 2) that divides the reception signal and multiplies each of M types of frequency offset correction coefficient candidates by the divided reception signals; M×N second computation units (where N is an integer equal to or greater than 2) that multiply N types of Doppler shift correction coefficient candidates by each output signal from the M first computation units; and a comparison unit that estimates, as a frequency offset estimation value and a Doppler shift estimation value used in compensation of the reception signal, the frequency offset correction coefficient candidate and Doppler shift correction coefficient candidate that are multiplied by any output signal from among output signals outputted from each of the M×N second computation units.　

Description

Wireless communication system, receiving device and estimation method

The present invention relates to a wireless communication system, a receiving device, and an estimation method.

With the development of IoT (Internet of Things) technology, the installation of IoT terminals equipped with various sensors in various locations is being considered. IoT terminals may be installed in places where it is difficult to install a base station, such as on a buoy at sea, on a ship, or in a mountainous area. Therefore, a system has been proposed in which data collected by IoT terminals installed in various locations is relayed to a base station installed on the ground using a relay device mounted on a low orbit satellite.

In the satellite sensing platform, different Doppler shifts occur in the signals transmitted from each IoT terminal depending on the location of the IoT terminal. Therefore, signals that have undergone different Doppler shifts within a frame arrive at the receiving antenna of the low orbit satellite at random times. Preambles are similarly subjected to different Doppler shifts for each IoT terminal, making time synchronization processing based on correlation with known signals difficult. Non-Patent Document 1 proposes DFS (Doppler frequency shift) estimation using a preamble and a postamble.

However, in communication systems with low data rates, overhead due to preamble insertion becomes a problem. Therefore, Doppler shift and frequency estimation that do not require a preamble are desirable. Conventionally, it has been impossible to estimate the Doppler shift and frequency offset without inserting a preamble etc. for multiple signals that are extremely high-speed, such as satellite communications, and that have different Doppler shifts for each terminal. There was a problem.

In view of the above circumstances, the present invention aims to provide a technique that can estimate Doppler shifts and frequency offsets for a plurality of signals that have undergone different Doppler shifts without inserting a preamble or the like.

One aspect of the present invention is a wireless communication system including a plurality of transmitting devices, a moving wireless communication device, and a receiving device, wherein the plurality of transmitting devices include a transmitting unit that transmits a wireless signal, and the plurality of transmitting devices include a transmitting unit that transmits a wireless signal, The wireless communication device includes one or more antennas that receive the wireless signals transmitted from the plurality of transmitting devices, and a waveform that transmits waveform data indicating a waveform of the received signal received by the one or more antennas to the receiving device. a transmitting section, the receiving device includes a receiving section that receives the waveform data transmitted by the wireless communication device, and a Doppler shift and frequency received by the received signal indicated by the waveform data received by the receiving section. a Doppler shift estimating section that estimates an offset, the Doppler shift estimating section branching the received signal and performing M (M is an integer of 2 or more) types of frequency offset corrections on each of the branched received signals. M first arithmetic units that respectively multiply by coefficient candidates; and M×N that multiply N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates to each of the output signals of the M first arithmetic units. A frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by one of the output signals outputted from each of the M×N second calculation units and the M×N second calculation units. This wireless communication system includes a comparison unit that estimates the frequency offset and the Doppler shift used for compensation of the received signal.

One aspect of the present invention is the receiving device in a wireless communication system including a plurality of transmitting devices, a moving wireless communication device, and a receiving device, the receiving device transmitting wireless signals transmitted from the plurality of transmitting devices to the wireless communication system. A receiving unit that receives data via a wireless communication device; and a Doppler shift estimating unit that estimates a Doppler shift and a frequency offset received by the received signal received by the receiving unit, and the Doppler shift estimating unit M first calculation units that branch each branched received signal and multiply each of the branched received signals by M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates; and the M first calculation units. M×N second calculation units that multiply each of the output signals by N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates, and output from each of the M×N second calculation units. Comparison of estimating the frequency offset correction coefficient candidate and Doppler shift correction coefficient candidate multiplied by one of the output signals with the estimated value of frequency offset and estimated value of Doppler shift used for compensation of the received signal A receiving device comprising:

One aspect of the present invention is an estimation method in a wireless communication system having a plurality of transmitting devices, a moving wireless communication device, and a receiving device, the plurality of transmitting devices transmitting wireless signals, and the wireless a communication device transmits waveform data indicating a waveform of a received signal received by one or more antennas that receive the wireless signals transmitted from the plurality of transmitting devices to the receiving device; The receiving device receives the waveform data transmitted by the device, branches the received signal indicated by the received waveform data, and receives M (M is an integer of 2 or more) types of signals for each branched received signal. N (N is an integer of 2 or more) types of Doppler shift correction coefficients are applied to each received signal multiplied by the M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates. Frequency offset correction coefficient candidate and Doppler shift multiplied by one of the output signals among the received signals multiplied by the N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates. This estimation method estimates a correction coefficient candidate as an estimated value of a frequency offset and an estimated value of a Doppler shift used for compensation of a received signal.

According to the present invention, it is possible to estimate Doppler shifts and frequency offsets for a plurality of signals that have undergone different Doppler shifts without inserting a preamble or the like.

1 is a configuration diagram of a wireless communication system according to an embodiment. It is a figure showing a concrete example of composition of a Doppler shift estimating part in an embodiment. It is a figure showing the example of composition of the compensation part in an embodiment. FIG. 3 is a diagram illustrating a configuration example of a replica generation unit in an embodiment. It is a figure showing an example of composition of a blanking processing part in an embodiment. FIG. 3 is a diagram for explaining processing performed by a blanking processing section in the embodiment. It is a flowchart which shows the flow of demodulation processing performed by a base station in an embodiment.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a wireless communication system 1 according to an embodiment. The wireless communication system 1 includes a plurality of terminal stations 20, a mobile relay station 30, and a base station 40. The number of terminal stations 20, mobile relay stations 30, and base stations 40 that the wireless communication system 1 has is arbitrary. It is assumed that the number of terminal stations 20 is large.

The terminal station 20 collects data such as environmental data detected by sensors and transmits it to the mobile relay station 30 wirelessly. For example, if a transmission timing is instructed by the mobile relay station 30, the terminal station 20 wirelessly transmits the collected data to the mobile relay station 30 at the instructed transmission timing. The terminal station 20 is, for example, an IoT (Internet of Things) terminal. The terminal station 20 is one aspect of a transmitting device.

The mobile relay station 30 is an example of a wireless communication device that is mounted on a mobile body and whose communicable area changes over time. The mobile relay station 30 of this embodiment is provided on a LEO (Low Earth Orbit) satellite. The altitude of a LEO satellite is 2000 km or less, and for example, when the altitude is about 350 km, it orbits above the earth in about 1.5 hours. The terminal station 20 and the base station 40 are installed on the earth, such as on the ground or on the sea. Hereinafter, the radio signal transmitted from the terminal station 20 to the mobile relay station 30 will be referred to as a terminal uplink signal, and the signal transmitted from the mobile relay station 30 to the base station 40 will be referred to as a base station downlink signal.

Since the mobile relay station 30 mounted on the LEO satellite communicates while moving at high speed, the time during which each terminal station 20 or base station 40 can communicate with the mobile relay station 30 is limited. Specifically, when viewed from the ground, the mobile relay station 30 passes over the sky in about a few minutes. Therefore, the terminal station 20 collects data such as environmental data detected by the sensor, and stores the collected data. The terminal station 20 transmits a terminal uplink signal in which the collected data is set at a timing when it can communicate with the mobile relay station 30. The mobile relay station 30 receives terminal uplink signals transmitted from each of the plurality of terminal stations 20 while moving above the earth. The mobile relay station 30 accumulates data received from each terminal station 20 using a terminal uplink signal, and sends the accumulated data to the base station using a base station downlink signal at a timing when communication with the base station 40 is possible. 40 by radio. The base station 40 acquires the data collected by the terminal station 20 from the received base station downlink signal.

The mobile relay station 30 has an antenna used for wireless communication with the terminal station 20 and an antenna used for wireless communication with the base station 40. Therefore, the mobile relay station 30 can perform wireless communication with the terminal station 20 and wireless communication with the base station 40 in parallel.

As a mobile relay station, it is possible to use a relay station mounted on a geostationary satellite, a drone, or an unmanned aircraft such as a HAPS (High Altitude Platform Station). However, in the case of a relay station mounted on a geostationary satellite, although its coverage area (footprint) on the ground is wide, the link budget for IoT terminals installed on the ground is extremely small due to its high altitude. On the other hand, relay stations mounted on drones and HAPS have a high link budget but have a small coverage area.

Additionally, drones require batteries, and HAPS require solar panels. In this embodiment, a mobile relay station 30 is mounted on a LEO satellite. Therefore, in addition to keeping the link budget within limits, LEO satellites have no air resistance and consume less fuel because they orbit outside the atmosphere. Additionally, the footprint is larger compared to installing a relay station on a drone or HAPS.

The base station 40 acquires from the mobile relay station 30 a plurality of received signals that have undergone different Doppler shifts due to transmission from each terminal station 20 to the mobile relay station 30, and performs correlation detection etc. on the acquired plurality of received signals. The Doppler shifts and frequency offsets of multiple received signals are estimated without having to Hereinafter, the Doppler shift and frequency offset estimated by the base station 40 will be referred to as an estimated Doppler shift value and an estimated frequency offset value. Furthermore, base station 40 detects a plurality of received frames using the Doppler shift estimate and the frequency offset estimate. Base station 40 is one aspect of a receiving device.

The terminal station 20 and base station 40 are installed at specific locations on the earth, such as on the ground or on the sea.

The configuration of each device will be explained.
The terminal station 20 includes a data storage section 21, a transmission section 22, and one or more antennas 23. FIG. 1 shows a case where the terminal station 20 includes one antenna 23. The data storage unit 21 stores environmental data detected by the sensor. The transmitter 22 communicates with the mobile relay station 30. The transmitting unit 22 reads the environmental data from the data storage unit 21 as terminal transmission data, and wirelessly transmits from the antenna 23 a terminal uplink signal in which the read terminal transmission data is set.

The transmitter 22 transmits a signal using, for example, LPWA (Low Power Wide Area). LPWA includes LoRaWAN (registered trademark), Sigfox (registered trademark), LTE-M (Long Term Evolution for Machines), NB (Narrow Band)-IoT, etc., but any wireless communication method can be used. The transmitter 22 may perform transmission with other terminal stations 20 by time division multiplexing, OFDM (Orthogonal Frequency Division Multiplexing), or the like. The transmitter 22 may beam-form the signals transmitted from the plurality of antennas 23 using a method predetermined in the wireless communication system to be used.

The mobile relay station 30 includes one or more antennas 31, a terminal communication section 32, a data storage section 33, a base station communication section 34, and one or more antennas 35. FIG. 1 shows a case where the mobile relay station 30 includes one antenna 31 and one antenna 35.

The terminal communication unit 32 wirelessly communicates with the terminal station 20. The terminal communication section 32 includes a receiving section 321 and a received waveform recording section 322. The receiving unit 321 receives the terminal uplink signal through the antenna 31. The received waveform recording unit 322 samples the received waveform of the terminal uplink signal received by the receiving unit 321, and generates waveform data indicating the value obtained by sampling. The received waveform recording unit 322 writes received waveform information in which the reception time of the terminal uplink signal at the antenna 31 and the generated waveform data are set in the data storage unit 33. The data storage unit 33 stores received waveform information written by the received waveform recording unit 322.

The base station communication unit 34 transmits the received waveform information to the base station 40 using a base station downlink signal of any wireless communication method.

The base station 40 includes an antenna 41, a receiving section 42, a base station signal reception processing section 43, a signal storage section 44, and a terminal signal reception processing section 45. The receiving unit 42 converts the base station downlink signal received by the antenna 41 into an electrical signal. The base station signal reception processing section 43 demodulates and decodes the received signal converted into an electrical signal by the receiving section 42, and obtains received waveform information. The base station signal reception processing section 43 causes the signal storage section 44 to store the received waveform information. The signal storage section 44 stores received waveform information obtained by the base station signal reception processing section 43.

The terminal signal reception processing section 45 includes a signal subtraction section 46, a Doppler shift estimation section 47, a signal detection section 48, a demodulation section 49, a check section 50, and an interference cancellation section 51.

The received signal that has been successfully demodulated in the interference removal unit 51 and the received waveform information stored in the signal storage unit 44 are input to the signal subtraction unit 46 . The signal subtraction unit 46 subtracts the received signal that has been successfully demodulated from the input received waveform information. Thereby, the signal subtraction unit 46 removes the components of the received signal that have been successfully demodulated from the received waveform information.

The Doppler shift estimating unit 47 estimates the Doppler shift and frequency offset based on the received waveform information (hereinafter referred to as "compensation target received signal") from which the components of the received signal successfully demodulated by the signal subtracting unit 46 have been removed. The Doppler shift estimator 47 compensates the compensation target received signal using the Doppler shift estimate and the frequency offset estimate. Specifically, the Doppler shift estimation unit 47 multiplies the compensation target received signal by the Doppler shift estimated value and the frequency offset estimated value to obtain the compensated received signal.

The signal detection unit 48 detects the compensated received signal on the frequency axis using a band-limiting filter.

The demodulation unit 49 performs demodulation processing on the compensated received signal detected by the signal detection unit 48.

The inspection unit 50 performs error detection processing on the compensated received signal that has undergone demodulation processing. For example, the inspection unit 50 performs error detection using CRC (Cyclic Redundancy Check). In this case, the inspection unit 50 extracts information corresponding to the CRC bits of the compensated received signal that has undergone demodulation processing. The inspection unit 50 performs error detection based on the extracted information corresponding to the CRC bits of the received signal after compensation, and determines whether the demodulation result is correct. Note that error detection methods other than CRC may be used for error detection performed by the inspection unit 50.

The interference cancellation unit 51 receives the error detection determination result by the inspection unit 50 and the compensated received signal that has undergone demodulation processing. The interference removal section 51 includes a replica generation section 511 and a blanking processing section 512. If the determination result by the inspection unit 50 indicates that the demodulation result is correct, the replica generation unit 511 generates a replica signal of the compensated received signal that has undergone demodulation processing. The replica generating section 511 outputs the generated replica signal to the signal subtracting section 46 as a received signal that has been successfully demodulated. If the determination result by the inspection unit 50 indicates that the demodulation result is incorrect, the blanking processing unit 512 applies blanking to the signal band of the compensated received signal that has been subjected to the demodulation process to correct the signal. Remove.

FIG. 2 is a diagram showing a specific configuration example of the Doppler shift estimating section 47 in the embodiment. The Doppler shift estimation section 47 includes M first calculation sections 471-1 to 471-M, M processing sections 472-1 to 472-M, a comparison section 473, and a compensation section 474. M is an integer of 2 or more.

The compensation target received signal is input to the first calculation units 471-1 to 471-M. The first calculation units 471-1 to 471-M multiply the compensation target received signal by M types of frequency offset correction coefficient candidates f _a (a=1,...,M). For example, the first calculation unit 471-m (1≦m≦M) multiplies the compensation target received signal by the frequency offset correction coefficient candidate f _m . In this way, the first calculation units 471-1 to 471-M multiply the compensation target received signal by mutually different frequency offset correction coefficient candidates f _a (a=1,...,M).

The output signals of the first calculation units 471-1 to 471-M are input to the processing units 472-1 to 472-M. The output signals of the first calculation units 471-1 to 471-M are compensation target received signals multiplied by different frequency offset correction coefficient candidates. For example, the compensation target received signal multiplied by the frequency offset correction coefficient candidate f _m is input to the processing unit 472-m as the output signal of the first calculation unit 471-m.

Here, the configurations of the processing units 472-1 to 472-M will be explained. Note that since each processing section 472 has a similar configuration, the processing section 472-M will be described as an example here. The processing unit 472-M includes N second calculation units 476-M-1 to 476-MN, N power calculation units 477-M-1 to 477-MN, and a comparison unit 478-M. Equipped with M. Since each processing unit 472 has a similar configuration, the Doppler shift estimation unit 47 includes M×N second calculation units 476, M×N power calculation units 477, and M comparison units 478. You will be prepared. N is an integer of 2 or more.

The output signal of the first calculation unit 471-M is input to the second calculation units 476-M-1 to 476-MN. The second calculation units 476-M-1 to 476-MN multiply the output signal of the first calculation unit 471-M by N types of Doppler shift correction coefficient candidates d _b (b=1,...,N). . For example, the second calculation unit 476-Mn (1≦n≦N) multiplies the output signal of the first calculation unit 471-M by the Doppler shift correction coefficient candidate d _n . In this way, in one processing unit 472 (for example, the processing unit 472-M), mutually different Doppler shift correction coefficient candidates d _b are applied to the output signal of the first calculation unit 471 (for example, the first calculation unit 471-M). Multiplied.

The output signals of the second calculation units 476-M-1 to 476-MN are input to the power calculation units 477-M-1 to 477-MN. The output signals of the second calculation units 476-M-1 to 476-MN are compensation target received signals multiplied by the Doppler shift correction coefficient candidates. For example, the power calculation unit 477-Mn receives the compensation target received signal multiplied by the Doppler shift correction coefficient candidate by the second calculation unit 476-Mn. The power calculation section 477-Mn calculates the power of the output signal of the second calculation section 476-Mn within the desired band.

The output value (power value) of each power calculation unit 477-M-1 to 477-MN is input to the comparison unit 478-M. The comparison unit 478-M compares the input output values of the respective power calculation units 477-M-1 to 477-MN. As a result of the comparison, the comparison unit 478-M outputs to the comparison unit 473 the combination of correction coefficient candidates (frequency offset correction coefficient candidate and Doppler shift correction coefficient candidate) with the highest power and the power in that combination.

By performing the above processing, each processing unit 472 outputs the combination of correction coefficient candidates with the highest power and the power in that combination to the comparison unit 473. For example, the processing unit 472-1 outputs to the comparison unit 473 the combination with the highest signal power among the combinations of the frequency offset correction coefficient candidate f ₁ and mutually different Doppler shift correction coefficient candidates. For example, the processing unit 472-M outputs to the comparison unit 473 the combination with the highest signal power among the combinations of the frequency offset correction coefficient candidate f _M and mutually different Doppler shift correction coefficient candidates. Comparison unit 473 compares the power output from each processing unit 472. As a result of the comparison, the comparison unit 473 selects a combination of correction coefficient candidates (frequency offset correction coefficient candidates and Doppler shift correction coefficient candidates) with the highest power as an estimated frequency offset value and an estimated Doppler shift value to be used for compensation of the received signal. It is calculated as follows. The comparator 473 outputs the estimated value of the frequency offset and the estimated value of the Doppler shift to the compensator 474.

The compensation unit 474 compensates the compensation target received signal by multiplying the compensation target received signal by the frequency offset estimate and Doppler shift estimate output from the comparison unit 473.

FIG. 3 is a diagram showing a configuration example of the compensation unit 474 in the embodiment. The compensation section 474 includes a multiplication section 4741 and a multiplication section 4742. The multiplier 4741 multiplies the compensation target received signal by the estimated value of the frequency offset output from the comparator 473. Thereby, the multiplier 4741 compensates for the frequency offset of the compensation target received signal. The multiplier 4741 outputs the compensated received signal after frequency offset compensation to the multiplier 4742. The multiplier 4742 multiplies the received signal to be compensated after frequency offset compensation by the Doppler shift correction coefficient candidate output from the comparator 473. Thereby, the multiplier 4742 compensates for the Doppler shift received by the compensation target received signal.

The maximum or minimum value of the frequency offset correction coefficient candidate f _a , the Doppler shift correction coefficient candidate d _b , the number of first calculation units 471 , and the number of second calculation units 476 is determined in advance depending on the altitude and moving speed of the mobile relay station 30 . It can be specified, but generally it can be set arbitrarily.

Next, a specific flow of processing by the terminal signal reception processing unit 45 included in the base station 40 will be explained. Here, the input waveform of the Doppler shift estimation unit 47 is assumed to be x(t). The input waveform x(t) is a signal that has undergone a Doppler shift and a frequency offset due to the high speed movement of the mobile relay station 30. The Doppler shift d _b and frequency offset _{f a} received by the input waveform x(t) are given as shown in equation (1) below.

Let x' _ab (f) be the Fourier transform of x _{' ab} (t). The power calculation unit 477 calculates the power P _ab of the output signal of the second calculation unit 476 in the range of f=−(f _w /2) to (f _w /2) based on the following equation (2). . Here, _fw is the bandwidth of the transmission signal, and is a value uniquely determined depending on the communication method, so it is set in advance according to the target communication method.

The

comparison units

473 and 478 compare the power P _ab for all a and b based on the following equation (3), and calculate a combination a' and b' of a and b that maximizes the power.

The comparison unit 478 calculates the calculated frequency offset correction coefficient f _sa' (a is a subscript of s) and Doppler shift correction coefficient d _sb' (b is a subscript of s) using the following equations (4) and (5). Calculate based on. The frequency offset correction coefficient f _sa' and the Doppler shift correction coefficient d _sb' calculated by the comparator 478 are the estimated value of the frequency offset and the estimated value of the Doppler shift.

Next, the compensation unit 474 uses the estimated value of the frequency offset and the estimated value of the Doppler shift calculated by the comparing unit 478 to perform compensation for the Doppler shift and frequency offset based on the following equation (6). The compensator 474 outputs the signal after Doppler shift and frequency offset compensation to the signal detector 48 .

The signal detection section 48 extracts a signal in the range of f=-(f _B /2) to (f _B /2) from the signal output from the compensating section 474 using a band-pass filter. Here, f _B represents the frequency band to be extracted. The demodulation unit 49 restores the bit string by performing demodulation processing on the signal extracted by the signal detection unit 48. The demodulation section 49 outputs the restored bit string to the inspection section 50.

After checking the CRC bits in the bit string, the checking unit 50 determines whether the demodulation result is correct. The inspection unit 50 outputs the determination result to the interference removal unit 51. The interference removal unit 51 performs one of the following processes based on the determination result input from the inspection unit 50.

(If the demodulation result is correct)
FIG. 4 is a diagram illustrating a configuration example of the replica generation unit 511 in the embodiment. As shown in FIG. 4, the replica generation unit 511 modulates the bit string output from the demodulation unit 49, and generates the reciprocals (e- ^j2πfa' , e- ^j2πdb't ) of the estimated value of the Doppler shift and the estimated value of the frequency offset. Channel estimation is performed from the part corresponding to the preamble included in the received frame by multiplying by . The replica generation unit 511 generates a received signal replica by multiplying the received signal by a channel. Replica generation section 511 outputs the generated received signal replica to signal subtraction section 46 .

(If the demodulation result is incorrect)
FIG. 5 is a diagram showing a configuration example of the blanking processing section 512 in the embodiment. As shown in FIG. 5, the blanking processing unit 512 performs blanking processing on the received signal, and then calculates the reciprocals (e- ^j2πfa' , e- ^j2πdb' ) of the estimated value of the Doppler shift and the estimated value of the frequency offset. ^t ). Here, the processing performed by the blanking processing section 512 will be described using FIG. 6.

FIG. 6 is a diagram for explaining the processing performed by the blanking processing unit 512 in the embodiment. In FIG. 6, three diagrams are shown in order from the top: an upper stage, a middle stage, and a lower stage. The diagram shown in the upper part of FIG. 6 represents the signal after Doppler shift compensation. The diagram shown in the middle part of FIG. 6 represents a signal on which blanking has been performed. The diagram shown in the lower part of FIG. 6 shows a signal after the blanked signal is multiplied by the estimated value of Doppler shift and the reciprocal of the estimated value of frequency offset. As shown in the middle part of FIG. 6, the blanking processing unit 512 performs blanking by setting the frequency component corresponding to the transmission signal bandwidth within the observation band to 0. Next, as shown in the lower part of FIG. 6, the blanking processing unit 512 multiplies the blanked signal by the reciprocal of the estimated Doppler shift value and the estimated frequency offset value for demodulation of the next received signal. It is output to the Doppler shift estimator 47.

Next, the demodulation algorithm will be explained. FIG. 7 is a flowchart showing the flow of demodulation processing performed by the base station 40 in the embodiment. It is assumed that the number of detected terminals T _det representing the number of terminal stations 20 to be detected is determined at the start of the process in FIG. 7 . The base station 40 sets the number i of correctly demodulated signals and the number j of signals removed by blanking to 0, that is, i=0, j=0 (step S101, step S102). The Doppler shift estimation unit 47 receives the compensation target received signal as input, and estimates the frequency offset and Doppler shift for the input compensation target received signal (step S103). Thereafter, the Doppler shift estimator 47 compensates the compensation target received signal using the estimated value of the frequency offset and the estimated value of the Doppler shift.

The signal detection unit 48 uses a band-limiting filter to detect the compensation target received signal compensated by the Doppler shift estimation unit 47 (step S104). The signal detection section 48 outputs the detected compensation target reception signal to the demodulation section 49 . The demodulator 49 performs demodulation processing on the compensation target received signal output from the signal detector 48 (step S105). The demodulation unit 49 restores the bit string through demodulation processing. The demodulation unit 49 outputs information on the restored bit string to the inspection unit 50.

The inspection unit 50 inspects the CRC bits based on the information on the bit string output from the demodulation unit 49, and determines whether the demodulation result is correct (step S106). If the demodulation result is correct (step S106-YES), the replica generation unit 511 performs channel estimation from a portion of the bit string that corresponds to the preamble of the demodulated signal (step S107). The replica generation unit 511 generates a received signal replica using the estimated channel (step S108). Replica generation section 511 outputs the generated received signal replica to signal subtraction section 46 .

The signal subtraction unit 46 subtracts the received signal replica output from the replica generation unit 511 from the received signal received via the antenna 41 (step S109). The signal subtraction unit 46 outputs the subtracted received signal to the Doppler shift estimation unit 47. The Doppler shift estimation unit 47 adds 1 to i and detects the next received signal (step S110).

In the process of step S106, if the demodulation result is incorrect (step S106-NO), the blanking processing unit 512 performs blanking of the detected signal band (step S109). The blanking processing unit 512 outputs the signal after the blanking process to the Doppler shift estimation unit 47. The Doppler shift estimation unit 47 adds 1 to j and detects the next received signal (step S112).

After the processing in step S110 or step S112, the Doppler shift estimation unit 47 determines whether or not i+j=T _det (step S113). Specifically, the Doppler shift estimation unit 47 determines whether the sum of the number of correctly demodulated signals and the number of signals removed by blanking has reached the number of detected terminals. If the sum of the number of correctly demodulated signals and the number of signals removed by blanking reaches the number of detected terminals (step S113-YES), the base station 40 ends the process.

On the other hand, if the sum of the number of correctly demodulated signals and the number of signals removed by blanking does not reach the number of detected terminals (step S113-NO), the base station 40 executes the processes from step S102 onwards. According to the above procedure, the base station 40 performs interference cancellation preferentially from signals that can be demodulated.

According to the wireless communication system 1 configured as described above, it becomes possible to estimate Doppler shifts and frequency offsets for a plurality of signals that have undergone different Doppler shifts without inserting a preamble or the like. Specifically, the base station 40 estimates the Doppler shift and frequency offset received by the receiving section 42 that receives the waveform data transmitted by the mobile relay station 30, and the received signal indicated by the waveform data received by the receiving section 42. A Doppler shift estimation unit 47 is provided. The Doppler shift estimating unit 47 includes M first calculation units 471 that branch the received signal and multiply each of the branched received signals by M types of frequency offset correction coefficient candidates, and M first calculation units Among the M×N second calculation units 476 that multiply each of the output signals of the unit 471 by N types of Doppler shift correction coefficient candidates, and the output signals output from each of the M×N second calculation units 476, a comparison unit 473 that calculates a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by one of the output signals with an estimated frequency offset value and an estimated Doppler shift value used for compensation of the received signal; Be prepared. This makes it possible to estimate Doppler shift and frequency offset without using a preamble or the like. As a result, the signal frame can be demodulated.

(Modification 1)
In the embodiment described above, the comparator 473 calculates the frequency offset correction coefficient f _sa' and the Doppler shift correction coefficient d _sb' based on equations (4) and (5). The comparison unit 473 calculates the frequency offset correction coefficient f _sa' and the Doppler shift correction coefficient d _sb' by either of the following methods (second calculation method) or (third calculation method). good. This will be explained in detail below.

(Second calculation method)
The comparison unit 473 performs error detection after performing demodulation processing on each output signal output from each of the M×N second calculation units 476, and as a result of the error detection, it is determined that the demodulation result is correct. The frequency offset correction coefficient candidate and the Doppler shift correction coefficient candidate multiplied by the output signal are estimated as the frequency offset estimated value and the Doppler shift estimated value. For example, the comparator 473 performs error detection using CRC bits after demodulating all x′ _ab (t). The comparison unit 473 calculates a combination a'', a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate (for example, a, b) multiplied by the output signal whose demodulation result is determined to be correct as a result of error detection. b'' is calculated as an estimated value of frequency offset and an estimated value of Doppler shift.

(Third calculation method)
The comparison unit 473 performs error detection after performing demodulation processing on the output signal having power exceeding a predetermined threshold among the powers calculated by each of the N power calculation units 477, and detects an error as a result of the error detection. The frequency offset correction coefficient candidate and the Doppler shift correction coefficient candidate multiplied by the output signal for which the demodulation result is determined to be correct are estimated as the estimated value of the frequency offset and the estimated value of the Doppler shift. For example, the comparator 473 performs demodulation processing on x′ _ab (t) having power exceeding a predetermined threshold value among the powers P _ab related to all a and b, and then performs an error detection process using the CRC bits. Perform detection. The comparison unit 473 calculates a combination a'', a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate (for example, a, b) multiplied by the output signal whose demodulation result is determined to be correct as a result of error detection. b'' is calculated as an estimated value of frequency offset and an estimated value of Doppler shift.

(Modification 2)
In the embodiment described above, the Doppler shift estimating section 47 has been described as having a configuration in which comparison sections are provided in multiple stages. Specifically, the Doppler shift estimating section 47 has been described using as an example a configuration in which M comparison sections 478 and one comparison section 473 are provided in multiple stages. The Doppler shift estimation unit 47 may be configured to include one comparison unit 473 instead of the M comparison units 478. When configured in this way, one comparison unit 473 receives the power value output from the power calculation unit 477 of each processing unit 472 as input, and calculates the value output from the power calculation unit 477 of each processing unit 472 that has been input. Compare the power values. One comparison unit 473 estimates a combination of correction coefficient candidates (frequency offset correction coefficient candidate and Doppler shift correction coefficient candidate) with the highest power as the frequency offset and Doppler shift used for compensation of the received signal.

A part or all of the processing performed by the base station 40 in the embodiment described above may be implemented by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed. Note that the "computer system" herein includes hardware such as an OS (Operating System) and peripheral devices. Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, magneto-optical disks, ROM (Read Only Memory), and CD-ROMs (Compact Disc-ROM), hard disks built into computer systems, etc. storage device.

Furthermore, a "computer-readable recording medium" refers to a storage medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include a device that retains a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. Further, the above-mentioned program may be one for realizing a part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system. It may be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and includes designs within the scope of the gist of the present invention.

The present invention can be applied to technology for communicating with a mobile body equipped with a mobile relay station.

DESCRIPTION OF SYMBOLS 1... Radio communication system, 20... Terminal station, 21... Data storage unit, 22... Transmission unit, 30... Mobile relay station, 40... Base station, 31... Antenna, 32... Terminal communication unit, 33... Data storage unit, 34 ...Base station communication section, 35...Antenna, 41...Antenna, 42...Receiving section, 43...Base station signal reception processing section, 44...Signal storage section, 45...Terminal signal reception processing section, 46...Signal subtraction section, 47... Doppler shift estimation section, 48... Signal detection section, 49... Demodulation section, 50... Inspection section, 51... Interference removal section, 471, 471-1 to 471-M... First calculation section, 472, 472-1 to 472- M...processing section, 473, 478, 478-M...comparison section, 474...compensation section, 476, 476-M-1 to 476-MN...second calculation section, 477, 477-M-1 to 477- MN...Power calculation unit, 511...Replica generation unit, 512...Blanking processing unit

Claims

A wireless communication system having a plurality of transmitting devices, a moving wireless communication device, and a receiving device,
The plurality of transmitting devices include a transmitting unit that transmits a wireless signal,
The wireless communication device includes:
one or more antennas that receive the wireless signals transmitted from the plurality of transmitting devices;
a waveform transmitter that transmits waveform data indicating a waveform of a received signal received by the one or more antennas to the receiving device;
Equipped with
The receiving device includes:
a receiving unit that receives the waveform data transmitted by the wireless communication device;
a Doppler shift estimation unit that estimates a Doppler shift and a frequency offset received by the received signal indicated by the waveform data received by the reception unit;
Equipped with
The Doppler shift estimator includes:
M first calculation units that branch the received signal and multiply each of the branched received signals by M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates;
M×N second calculation units that multiply the output signals of the M first calculation units by N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates;
A frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by one of the output signals output from each of the M×N second calculation units are used for compensation of the received signal. a comparison unit that estimates an estimated value of frequency offset and an estimated value of Doppler shift;
A wireless communication system equipped with
The Doppler shift estimation unit further includes N power calculation units that calculate the power of each output signal output from each of the M×N second calculation units,
The comparison unit compares each power calculated by each of the N power calculation units, and selects a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by the signal having the maximum power as the frequency estimate an offset estimate and a Doppler shift estimate;
The wireless communication system according to claim 1.
The comparison unit performs error detection after performing demodulation processing on each output signal output from each of the M×N second calculation units, and as a result of the error detection, it is determined that the demodulation result is correct. estimating a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by the output signal as the frequency offset estimate value and the Doppler shift estimate value;
The wireless communication system according to claim 1.
The Doppler shift estimation unit further includes N power calculation units that calculate the power of each output signal output from each of the M×N second calculation units,
The comparison section performs error detection after performing demodulation processing on the output signal having power exceeding a predetermined threshold among the powers calculated by each of the N power calculation sections, and detects an error as a result of the error detection. Estimating a frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by the output signal whose demodulation result is determined to be correct as the frequency offset estimate value and the Doppler shift estimate value;
The wireless communication system according to claim 1.
The Doppler shift estimation unit further compensates the received signal using the estimated frequency offset estimate and Doppler shift estimate.
The wireless communication system according to any one of claims 1 to 4.
The receiving device includes:
a signal detection unit that detects a signal in a predetermined band from the received signal compensated by the Doppler shift estimation unit;
a demodulation unit that restores a bit string by demodulating the signal detected by the signal detection unit;
a checking section that performs error detection based on the bit string demodulated by the demodulating section;
If the demodulation result is correct as an error detection result by the inspection unit, channel estimation is performed by multiplying the frequency offset and the reciprocal of the Doppler shift after modulating the bit string, and the received signal is multiplied by the estimated channel. a replica generation unit that generates a received signal replica;
If the demodulation result is incorrect as an error detection result by the inspection unit, a block that performs blanking processing on the received signal and then multiplies the frequency offset and the reciprocal of the Doppler shift and inputs the result to the Doppler shift estimation unit. A ranking processing section,
The wireless communication system according to claim 5, further comprising:
The receiving device in a wireless communication system having a plurality of transmitting devices, a moving wireless communication device, and a receiving device,
a receiving unit that receives wireless signals transmitted from the plurality of transmitting devices via the wireless communication device;
a Doppler shift estimation unit that estimates a Doppler shift and a frequency offset received by the reception signal received by the reception unit;
Equipped with
The Doppler shift estimator includes:
M first calculation units that branch the received signal and multiply each of the branched received signals by M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates;
M×N second calculation units that multiply the output signals of the M first calculation units by N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates;
A frequency offset correction coefficient candidate and a Doppler shift correction coefficient candidate multiplied by one of the output signals output from each of the M×N second calculation units are used for compensation of the received signal. a comparison unit that estimates an estimated value of frequency offset and an estimated value of Doppler shift;
A receiving device comprising:
An estimation method in a wireless communication system having a plurality of transmitting devices, a moving wireless communication device, and a receiving device, the method comprising:
The plurality of transmitting devices transmit wireless signals,
The wireless communication device transmits waveform data indicating a waveform of a received signal received by one or more antennas that receive the wireless signals transmitted from the plurality of transmitting devices to the receiving device,
the receiving device receives the waveform data transmitted by the wireless communication device,
The receiving device branches the received signal indicated by the received waveform data, multiplies each branched received signal by M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates, and Each received signal multiplied by M (M is an integer of 2 or more) types of frequency offset correction coefficient candidates is multiplied by N (N is an integer of 2 or more) types of Doppler shift correction coefficient candidates. The frequency offset correction coefficient candidate and Doppler shift correction coefficient candidate multiplied by one of the output signals among the received signals multiplied by the Doppler shift correction coefficient candidates of (integer or more) types are used for compensation of the received signal. An estimation method for estimating an estimated value of frequency offset and an estimated value of Doppler shift.