Information transmission system, information transmission method, and base station program

Abstract

To perform efficient information transmission using an inexpensive terminal.SOLUTION: A clock drift estimation unit (313) estimates a latest clock drift (Td,i) representing a time deviation between a terminal (2) and a base station (3) in a latest time frame including latest reception time (tr,i) at which a latest packet (Pi) is received from a terminal on the basis of past reception time (tr,j) at which another packet was received from the terminal in the past and a past clock drift (Td,j) representing a time deviation between the terminal and the base station, in a past time frame including the past reception time. A transmission index detection unit (314) detects a time slot index (qi) on the basis of the latest reception time and the latest clock drift. An information coupling unit (315) couples first data (D1) restored using the time slot index with second data (D2) obtained by demodulating a packet to restore transmission data (D0).SELECTED DRAWING: Figure 4B

Description

[Technical field]

[0001] The present invention relates to an information transmission system, an information transmission method, and a base station program, and more particularly to an information transmission system using a terminal and a base station that perform wireless communication, an information transmission method used by this information transmission system, and a base station program used by this base station. [Background technology]

[0002] There is a demand for a large number of IoT (Internet of Things) terminals to transmit relatively small amounts of data from each to a single base station. For example, by aggregating sensor data detected by sensor devices on each terminal to a base station or gateway, the aggregating base station can obtain significant statistical data even if the amount of data from each sensor is relatively small.

[0003] Such IoT terminals need to consume little power and be capable of long-distance transmission. For this reason, standards such as LoRaWAN (Long Range Wide Area Network) have been developed as LPWA (Low Power Wide Area) wireless communication standards. LoRaWAN uses a simple MAC (Medium Access Control) layer access protocol and is known to be capable of long-distance transmission with low power consumption.

[0004] On the other hand, when multiple terminals in LoRaWAN send their respective packets to a base station, the following issues can arise:

[0005] When multiple terminals transmit packets independently, packet collisions may occur, in which two or more packets are transmitted simultaneously, resulting in a decrease in the Packet Delivery Rate (PDR).

[0006] There is a restriction on the transmission time due to the duty cycle (DC), i.e., it is difficult or impossible to increase the number of transmission packets above a certain threshold in order to expand the transmission capacity.

[0007] In general, the time interval from when each terminal transmits a packet of information to when it transmits the next packet of information is relatively long.

[0008] Inexpensive terminals may not have the configuration to synchronize their time with the base station, and clock drift may accumulate between the terminal and the base station.

[0009] In relation to the above, non-patent document 1 (LoRa Alliance, Inc., "LoRaWAN(TM) 1.0.3 Specification", 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> ) discloses the LoRaWAN specification version 1.0.3. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] LoRa Alliance, Inc., “LoRaWAN(TM) 1.0.3 Specification”, 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above circumstances, an object of the present disclosure is to provide an information transmission system, an information transmission method, and a base station program that can perform efficient information transmission using inexpensive terminals. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0012] The means for solving the problems will be explained below using the numbers used in the (Mode for carrying out the invention). These numbers are added to clarify the correspondence between the description in the (Claims) and the (Mode for carrying out the invention). However, these numbers should not be used to interpret the technical scope of the invention described in the (Claims).

[0013] According to one embodiment, the information transmission system (1) includes a terminal (2) and a base station (3). The terminal (2) determines the length of the first period (T frame ). The base station (3) receives the packets (Pi). The terminal (2) includes an information division unit (211), a transmission parameter determination unit (212), and a transmission unit (215). The information division unit (211) divides transmission data (D0) to generate first data (D1) and second data (D2). The transmission parameter determination unit (212) encodes the first data (D1) to generate a time slot index (q) indicating one of a plurality of time slots into which the time frame is divided. i The transmission unit (215) generates a packet (Pi) in which information represented by the second data (D2) is modulated, and transmits the packet (Pi) to the time slot index (q i The base station (3) comprises a clock drift estimation unit (313), a transmission index detection unit (314), and an information combination unit (315). The clock drift estimation unit (313) detects the past reception time (t r,j ) and the past reception time (t r,j) is the past clock drift (T d,j ) and the latest reception time (t r,i The latest clock drift (T d,i The transmission index detection unit (314) estimates the latest reception time (t r,i ) and the latest clock drift (T d,i ) and based on the time slot index (q i The information combination unit (315) detects the time slot index (q i ) and second data (D2) obtained by demodulating the packet are combined to restore the transmission data (D0).

[0014] According to one embodiment, the information transmission method comprises: a terminal (2) determining the length of the first period (T frame The method includes transmitting a packet (Pi) for each time frame having a time frame of q (S03 to S07), and the base station (3) receiving the packet (Pi) (S08 to S12). The transmitting (S03 to S07) includes dividing the transmission data (D0) to generate first data (D1) and second data (D2) (S04), encoding the first data (D1) to generate a time slot index (q i ) (S05), and modulating information representing the second data (D2) into a packet (Pi) based on the time slot index (q i The receiving (S08 to S12) includes transmitting during a time slot represented by a past reception time (t r,j ) and the past reception time (t r,j ) is the past clock drift (T d,j ) and the latest reception time (t r,iThe latest clock drift (T d,i ) (S09) and the latest reception time (t r,i ) and the latest clock drift (T d,i ) and based on the time slot index (q i ) (S10) and the time slot index (q i ) and combining the first data (D1) restored using the demodulated packet (Pi) with second data (D2) obtained by demodulating the packet (Pi) to restore the transmission data (D0) (S12).

[0015] According to one embodiment, the base station program (321) determines the length of the first period (T frame ) is a base station program (321) for implementing the processing of the base station (3) by the arithmetic device (31) of the base station (3) to receive a packet (Pi) transmitted for each time frame having a time frame (t r,j ) and the past reception time (t r,j ) is the past clock drift (T d,j ) and the latest reception time (t r,i The latest clock drift (T d,i ) (S09) and the latest reception time (t r,i ) and the latest clock drift (T d,i ), a time slot index (q i ) (S10) and the time slot index (q i ) and combining the first data (D1) restored using the demodulated packet (Pi) with second data (D2) obtained by demodulating the packet (Pi) to restore the transmission data (D0) (S12). Effect of the Invention

[0016] According to one embodiment, the information transmission system, the information transmission method, and the base station program can perform efficient information transmission using inexpensive terminals. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing an example of a configuration of an information transmission system according to an embodiment. [Diagram 2] FIG. 2 is a block circuit diagram showing an example of a configuration of a terminal according to an embodiment. [Diagram 3] FIG. 3 is a block circuit diagram showing an example of a configuration of a base station according to an embodiment. [Figure 4A] FIG. 4A is a part of a flowchart showing an example of an information transmission method according to an embodiment. [Figure 4B] FIG. 4B is a part of a flowchart showing an example of an information transmission method according to an embodiment. [Diagram 5] FIG. 5 is a diagram for explaining packet-type index modulation. [Figure 6A] FIG. 6A is a diagram illustrating an example of an operation of a terminal according to an embodiment. [Figure 6B] FIG. 6B is a diagram illustrating an example of an operation of the base station according to an embodiment. [Figure 7] FIG. 7 is a diagram for explaining detection of a time slot index by a base station. [Figure 8] FIG. 8 is a diagram for explaining the time difference between a terminal and a base station. [Figure 9] FIG. 9 is a diagram for explaining erroneous detection of a time slot index due to clock drift. [Figure 10A] FIG. 10A is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to an embodiment. [Figure 10B]FIG. 10B is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to an embodiment. [Figure 10C] FIG. 10C is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to an embodiment. [Figure 10D] FIG. 10D is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to one embodiment. [Figure 10E] FIG. 10E is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to an embodiment. [Figure 10F] FIG. 10F is a graph illustrating an example of a distribution of observed values ​​of clock drift between a terminal and a base station according to an embodiment. [Figure 11] FIG. 11 is a graph showing an example of a change over time in an observed value of clock drift in a terminal according to an embodiment. [Figure 12] FIG. 12 is a flowchart partially illustrating one configuration example of an information transmission method according to an embodiment. [Figure 13A] FIG. 13A is a graph showing an example of a simulation result of the information transmission system according to the embodiment. [Figure 13B] FIG. 13B is a graph showing an example of a simulation result of the information transmission system according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An information transmission system, an information transmission method, and a base station program according to the present invention will be described below with reference to the accompanying drawings.

[0019] (First embodiment) 1, an information transmission system 1 according to an embodiment includes a plurality of terminals 2A, 2B, 2C, and 2D, and a base station 3. When the terminals 2A, 2B, 2C, and 2D are not distinguished from one another, they are collectively referred to as terminal 2.

[0020] Each terminal 2 transmits information independently of the other terminals 2. In other words, each terminal 2 is not synchronized with the other terminals when transmitting information. The base station 3 receives the information transmitted from the terminals 2.

[0021] 2, the terminal 2 according to one embodiment includes a bus 20, a computing device 21, a storage device 22, a communication device 23, and a sensor device 24. The computing device 21, the storage device 22, the communication device 23, and the sensor device 24 are connected via the bus 20 so as to be able to communicate with each other.

[0022] The arithmetic device 21 includes a data generating unit 210, an information dividing unit 211, a transmission parameter determining unit 212, a modulating unit 213, a packet generating unit 214, a transmitting unit 215, an initializing unit 216, and a receiving unit 217. The storage device 22 stores terminal ID information representing a terminal ID for identifying the terminal 2, and a terminal program 221 to be executed by the arithmetic device 21. The terminal IDs of the multiple terminals 2 are different from each other. The terminal program 221 may be read from an external recording medium 220 and stored in the storage device 22. The recording medium 220 may be a non-transitory and tangible medium.

[0023] The arithmetic device 21 realizes the functions of the data generation unit 210, the information division unit 211, the transmission parameter determination unit 212, the modulation unit 213, the packet generation unit 214, the transmission unit 215, the initialization unit 216, and the reception unit 217 by reading and executing the terminal program 221 from the storage device 22. In other words, the data generation unit 210, the information division unit 211, the transmission parameter determination unit 212, the modulation unit 213, the packet generation unit 214, the transmission unit 215, the initialization unit 216, and the reception unit 217 are shown as components of the arithmetic device 21 for the sake of convenience in Fig. 2, but are functional units that realize predetermined functions in cooperation with the arithmetic device 21 and the terminal program 221. Details of these functions will be described later.

[0024] The communication device 23 performs wireless communication with the base station 3. The communication device 23 transmits packet information for reception by the base station 3 under the control of a transmitter 215, and receives signals such as a request signal transmitted from the base station 3 under the control of a receiver 217. The terminal program 221 stored in the storage device 22 may be received by the communication device 23 from the base station 3 or another external device.

[0025] The sensor device 24 measures a desired parameter representative of an ambient condition and outputs measurement data representative of the results of this measurement. As an example, the sensor device 24 may be an air temperature sensor for measuring the ambient air temperature, a humidity sensor for measuring the ambient humidity, a carbon dioxide concentration sensor for measuring the ambient carbon dioxide concentration, etc.

[0026] 3, the base station 3 according to one embodiment includes a bus 30, a calculation device 31, a storage device 32, and a communication device 33. The calculation device 31, the storage device 32, and the communication device 33 are connected via the bus 30 so as to be able to communicate with each other.

[0027] The arithmetic device 31 includes a receiving unit 310, a demodulating unit 311, a clock drift estimating unit 313, a transmission index detecting unit 314, an information combining unit 315, an initializing unit 316, and a transmitting unit 317. The storage device 32 stores a base station program 321 to be executed by the arithmetic device 31. The base station program 321 may be read from an external recording medium 320 and stored in the storage device 32. The recording medium 320 may be a non-transitory and tangible medium.

[0028] The arithmetic device 31 reads out the base station program 321 from the storage device 32 and executes it to realize the functions of the receiver 310, demodulator 311, clock drift estimator 313, transmission index detector 314, information combiner 315, initialization unit 316, and transmitter 317. In other words, the receiver 310, demodulator 311, clock drift estimator 313, transmission index detector 314, information combiner 315, initialization unit 316, and transmitter 317 are each shown as components of the arithmetic device 31 in Fig. 3 for the sake of convenience, but are functional units that realize predetermined functions through cooperation between the arithmetic device 31 and the base station program 321. Details of these functions will be described later.

[0029] The communication device 33 performs wireless communication with the terminal 2. The communication device 33 receives packet information transmitted from the terminal 2 under the control of a receiving unit 310, and transmits signals such as a request signal to the terminal 2 under the control of a transmitting unit 317. The base station program 321 stored in the storage device 32 may be received by the communication device 33 from another external device.

[0030] A configuration example of an information transmission method according to an embodiment will be described with reference to the flowcharts of FIG. 4A and FIG. 4B. An operation example of an information transmission system 1 according to an embodiment will be described by describing the information transmission method according to an embodiment. In the flowcharts of FIG. 4A and FIG. 4B, the processing performed by the base station 3 is realized by the arithmetic device 31 of the base station 3 executing the base station program 321. In the flowcharts of FIG. 4A and FIG. 4B, the part shown in FIG. 4A mainly describes the operation of the terminal 2 transmitting transmission data by the PLIM (Packet-Level Index Modulation) method. Also, in the part shown in FIG. 4B, mainly describes the operation of the base station 3 receiving transmission data by the PLIM method. Here, the PLIM method is a communication method that can simultaneously transmit and receive additional information by the amount of the transmission parameters by transmitting and receiving a packet including information representing a part of the transmission data by using transmission parameters that correspond one-to-one to another part of the transmission data, compared to a communication method that simply transmits and receives packets. The PLIM method is applicable to LoRaWAN (Long Range Wide Area Network), which is a type of LPWAN (Low Power Wide Area Network), without changing the existing communication standard.

[0031] When the flowcharts of FIG. 4A and FIG. 4B start, step S01 is executed. In step S01 of FIG. 4A, the initialization unit 216 of the terminal 2 determines whether a predetermined period has passed since the previous initialization. More specifically, the function of the initialization unit 216 is realized by the arithmetic device 21 of the terminal 2 executing the terminal program 221. Here, the initialization is the initialization of the time difference between the terminal 2 and the base station 3. When the terminal 2 starts up and executes step S01 for the first time, step S02 is executed after step S01. If the initialization unit 216 of the terminal 2 has previously initialized the time difference in step S02 described later and a predetermined period has passed since then (YES), step S02 is also executed after step S01. If the terminal 2 has previously initialized the time difference and a predetermined period has not passed since then (NO), step S03 is executed after step S01. Here, the predetermined period is, for example, 24 hours. In this case, the terminal 2 executes step S02 every 24 hours to initialize the time difference.

[0032] In step S02 of FIG. 4A, the initialization unit 216 of the terminal 2 and the initialization unit 316 of the base station 3 initialize the time difference between the terminal 2 and the base station 3. More specifically, the function of the initialization unit 216 of the terminal 2 is realized by the arithmetic unit 21 of the terminal 2 executing the terminal program 221, and the function of the initialization unit 316 of the base station 3 is realized by the arithmetic unit 31 of the base station 3 executing the base station program 321. Since the time of the terminal 2 is determined by the clock circuit of the terminal 2 and the time of the base station 3 is determined by the clock circuit of the base station 3, a time difference may occur between the time of the terminal 2 and the time of the base station 3. By the base station 3 grasping the time difference with the terminal 2, the accuracy of the subsequent communication can be improved.

[0033] The initialization unit 216 of the terminal 2 transmits a first packet for initialization at a predetermined first transmission time. The initialization unit 216 of the terminal 2 further transmits a second packet for initialization at a predetermined second transmission time. The initialization unit 316 of the base station 3 detects the time difference between the terminal 2 and the base station 3 using the first reception time when the first packet is received and the second reception time when the second packet is received, and stores the time difference in the storage device 32. Here, the base station 3 knows the first transmission time and the second transmission time in advance. More specifically, as shown in FIG. 5, in this embodiment, time is divided into a plurality of time frames, and each time frame is further divided into a plurality of time slots. As an example, the period T of the time frame is frame is 30 seconds, and the length of the time slot T slot As another example, the period of the time frame T frame is 30 seconds, the length of the time slot is T slot The transmission time may be one second. Furthermore, the terminal 2 transmits a packet for each time frame. The terminal 2 and the base station 3 share in advance information indicating in which time slot of which time frame the first packet is transmitted / received, and in which time slot of which time frame the second packet is transmitted / received. In other words, the base station 3 knows in advance the first transmission time and the second transmission time.

[0034] The time difference between the terminal 2 and the base station 3 accumulates and changes over time. The time difference accumulated up to a certain time is called the clock drift at that time. The first reception time and the second reception time are used to estimate the clock drift in step S09, which will be described later.

[0035] Note that we will ignore the time it takes for a packet to travel from terminal 2 to base station 3. In other words, the time difference between the first transmission time and the first reception time, and the time difference between the second transmission time and the second reception time are sufficiently short relative to the time frame and time slot, and can therefore be ignored.

[0036] It should be noted that, according to this embodiment, terminal 2 does not adjust the time when initializing the time difference. Terminal 2 only transmits packets at a predetermined time, and terminal 2 does not need to have a time adjustment function, so that a less expensive terminal 2 can be used. It should also be noted that base station 3 does not adjust the time when initializing the time difference. By initializing the time difference with each of the multiple terminals 2, base station 3 can grasp the time difference with each of the multiple terminals 2 using one clock circuit. After step S02, step S03 is executed.

[0037] In step S03 of FIG. 4A, the data generator 210 of the terminal 2 generates transmission data D0 to be transmitted to the base station 3. As shown in FIG. 6A, the number of bits of the transmission data D0 is B plim More specifically, the function of the data generating unit 210 is realized by the calculation device 21 of the terminal 2 executing the terminal program 221. The data generating unit 210 controls the sensor device 24 to acquire measurement data, and converts the measurement data to generate transmission data D0, which is digital data. The transmission data D0 may further include terminal ID information indicating the terminal ID of the terminal 2. After step S03, step S04 is executed.

[0038] In step S04 of Fig. 4A, the information division unit 211 of the terminal 2 divides the transmission data D0. More specifically, the function of the information division unit 211 is realized by the arithmetic device 21 of the terminal 2 executing the terminal program 221. As shown in Fig. 6A, the information division unit 211 divides the transmission data D0 to generate first data D1 and second data D2. The number of bits of the first data D1 is B pi and the number of bits of the second data D2 is B pl Here, B plim =B pi +B pl In the example of FIG. 5A, the upper B pi The bit portion is the first data D1, and the lower B plAlthough the bit portion is referred to as the second data D2, the present embodiment is not limited to this example. After step S04, step S05 is executed.

[0039] In step S05 of Fig. 4A, the transmission parameter determination unit 212 of the terminal 2 determines the transmission parameters to be used for transmitting the packet. More specifically, the arithmetic device 21 of the terminal 2 executes the terminal program 221 to realize the function of the transmission parameter determination unit 212. The transmission parameters include a parameter representing the transmission time at which the transmission is performed and a parameter representing the frequency channel to be used for the transmission. The transmission parameter determination unit 212 determines a time slot index representing a time slot of a time frame for transmitting the packet as a parameter representing the transmission time. In addition, the transmission parameter determination unit 212 determines a frequency channel index representing a frequency channel to be used for transmitting the packet from among a plurality of frequency channels as a parameter representing a frequency channel.

[0040] The frequency channel index can be expressed as a binary value with a predetermined number of bits. In the example of Fig. 5, the frequency channel index of the first frequency channel from frequency f4 to frequency f5 is "00". Similarly, the frequency channel index of the second frequency channel from frequency f3 to frequency f4 is "01", the frequency channel index of the third frequency channel from frequency f2 to frequency f3 is "10", and the frequency channel index of the fourth frequency channel from frequency f1 to frequency f2 is "11".

[0041] The time slot index can be expressed as a binary value of a predetermined number of bits. In the example of Fig. 5, in the time frame from time t10 to time t20 (or from time t20 to time t30), the time slot index of the first time slot from time t10 to time t11 (or from time t20 to time t21) is "00". Similarly, the time slot index of the second time slot from time t11 to time t12 (or from time t21 to time t22) is "01", the time slot index of the third time slot from time t12 to time t13 (or from time t22 to time t23) is "10", and the time slot index of the fourth time slot from time t13 to time t20 (or from time t23 to time t30) is "11".

[0042] The transmission parameter determination unit 212 generates a time slot index and a frequency channel index by encoding the first data D1. As an example, the first data D1 is further divided, and the upper bit portion is used as a frequency channel index, and the remaining lower bit portion is used as a time slot index. In the example of FIG. 6A, the first data D1 associated with the first packet P1 is "0100". Of these, the upper two bits "01" are used as a frequency channel index representing the second frequency channel, and the remaining lower two bits "00" are used as a time slot index representing the first time slot. Similarly, the first data D1 associated with the second packet P2 is "1001", and the upper two bits "10" are used as a frequency channel index, and the lower two bits "01" are used as a time slot index. After step S05, step S06 is executed.

[0043] In step S06 of FIG. 4A, the modulation unit 213 and the packet generation unit 214 of the terminal 2 generate a packet including information represented by the second data D2. More specifically, the calculation device 21 of the terminal 2 executes the terminal program 221 to realize the function of the modulation unit 213 and the function of the packet generation unit 214. First, the modulation unit 213 modulates the second data D2 to generate a predetermined signal symbol. This modulation may be, for example, CSS (Chirp Spread Spectrum) modulation. In CSS modulation, binary data of a predetermined number of bits is converted into one chirp signal symbol. In CSS demodulation, an inverse conversion of the CSS modulation is performed. Hereinafter, the number of bits of the amount of information that can be represented by one chirp signal symbol is referred to as the spreading factor S. Next, the packet generation unit 214 of the terminal 2 generates a packet including information represented by the second data D2 from the modulated second data D2. After step S06, step S07 is executed.

[0044] In step S07 of Fig. 4A, the transmitting unit 215 of the terminal 2 transmits a packet. More specifically, the computing device 21 of the terminal 2 executes the terminal program 221 to realize the function of the transmitting unit 215. The transmitting unit 215 controls the communication device 23 to transmit the packet on the frequency channel represented by the frequency channel index during the time slot represented by the time slot index. After step S07, step S08 of Fig. 4B is executed.

[0045] In step S08 of Fig. 4B, the receiving unit 310 of the base station 3 receives a packet as shown in Fig. 6B. More specifically, the arithmetic device 31 of the base station 3 executes the base station program 321 to realize the function of the receiving unit 310. The receiving unit 310 controls the communication device 33 to receive the packet, and stores the received packet in the storage device 32. At this time, the receiving unit 310 further detects the reception time and the frequency channel at which the packet was received, and stores them in the storage device 32 in association with the packet. After step S08, step S09 is executed.

[0046] In step S09 of Fig. 4B, the clock drift estimation unit 313 of the base station 3 estimates the clock drift. More specifically, the arithmetic device 31 of the base station 3 executes the base station program 321 to realize the function of the clock drift estimation unit 313. The clock drift estimation unit 313 estimates the clock drift that represents the time difference between the terminal 2 and the base station 3 in the latest time frame including the latest reception time when the latest packet was received. Estimating the clock drift is necessary for the transmission index detection unit 314 of the base station 3, which will be described later, to correctly detect the transmission time slot index at which the packet was transmitted from the terminal 2.

[0047] As the simplest example, a case will be described in which the clock of the terminal 2 and the clock of the base station 3 are completely synchronized and there is no clock drift. As shown in FIG. 7, the reference time of the terminal 2 is set by the time when the terminal 2 transmits the first initialization packet P 0 The time T when T0 The reference time of the base station 3 is the time when the base station 3 transmits the first initialization packet P 0 The time T when R0 If we ignore the transmission delay from terminal 2 to base station 3, the reference time T T0 and the reference time T R0 Furthermore, if the clock of the terminal 2 and the clock of the base station 3 advance at the same rate, then for any integer j, the reference time T T0 The start time of the jth time frame from T Tj and the reference time T R0 The start time of the jth time frame from T Rj In this case, the time t when the base station 3 receives the j-th packet is the same as the time t j and the length of the time frame T frame and the length of the time slot, T slot The j-th packet P is estimated based on j The time slot index q^ of the time slot in which j (To be precise, the ^ symbol is above the q symbol.) This means that terminal 2 is jThe time slot index q of the transmission time slot in which j In this case, the start time of the jth time frame T Tj The time from the start of the transmission time slot is the length of the time slot T slot Time slot index q j After that, for any integer i, the reference time T T0 The start time of the i-th time frame from T Ti and the reference time T R0 The start time of the i-th time frame from T Ri The base station 3 receives the i-th packet P i It is possible to accurately estimate the time slot index of the transmission time slot in which

[0048] Next, the case of clock drift will be described. When the clock of terminal 2 runs faster than the clock of base station 3, the length of the time frame of terminal 2 is T frame This difference is called the time difference ΔT d,1 When the clock of terminal 2 runs faster than the clock of base station 3, the time difference between terminal 2 and base station 3 accumulates and increases over time. The accumulated time difference is called clock drift. Note that the change over time in the time difference between terminal 2 and base station 3 can be roughly approximated by a linear function. This will be discussed later.

[0049] In the example of FIG. 8, the reference time T T0 The first time frame that starts at T1 is the reference time T R0 The first time frame that starts at R1 Therefore, the time difference ΔT d,1 Similarly, the time T T1 The second time frame, which starts at T2is a time difference ΔT from the time TR2 at which the second time frame that starts at the time TR1 on the clock of the base station 3 ends. d,2 At this time, the time difference is ΔT d,2 The length of time difference ΔT d,1 Furthermore, the time T T2 The third time frame, which starts at T3 is the time T R2 The third time frame, which starts at R3 Therefore, the time difference ΔT d,3 At this time, the time difference is ΔT d,3 The length of time difference ΔT d,1 When the clock of the terminal 2 runs slower than the clock of the base station 3, the time difference between the terminal 2 and the base station 3 accumulates and increases over time.

[0050] When the clock drift increases, the transmission index detection unit 314 of the base station 3 may detect a transmission time slot index different from the time slot index of the time slot in which the transmitter 215 of the terminal 2 transmitted a packet. R0 (or the reference time T T0 ) the accumulated clock drift when the time frame is repeated i times is the time difference ΔT d,1 When this clock drift exceeds the length of a time slot, the time slot index detected by the transmission index detection unit 314 of the base station 3 may differ from the original time slot index. Ri The ith packet P sent or received in the time frame starting at iThis shows an example in which the value detected by transmission index detection unit 314 of base station 3 for the time slot index of is shifted by 1 from the original value. Note that the shift of the detected time slot index from the original time slot index may increase thereafter, but will never decrease. This is because the change over time in the time shift between terminal 2 and base station 3 can be roughly approximated by a linear function.

[0051] With reference to Figs. 10A to 10F and 11, it will be described how the change over time in the time difference between the terminal 2 and the base station 3 can be approximated to a linear function. Figs. 10A to 10F are graphs showing an example of the distribution of the observed values ​​of the clock drift between six terminals 2 and the same base station 3. In these graphs, the horizontal axis represents the clock drift, and the vertical axis represents the intensity of the distribution. It was confirmed that the clock drift between each terminal 2 and the base station 3 can be approximated to a normal distribution with a fairly small variance value. This indicates that the change over time in the clock drift can be approximated to a linear function. Fig. 11 is a graph showing an example of the change over time in the observed values ​​of the clock drift in each of these six terminals 2. In this graph, the horizontal axis represents time, and the vertical axis represents the accumulated value of the clock drift. The graph in Fig. 11 includes graphs G11 to G16. Graph G11 corresponds to the terminal 2 in Fig. 10B. Graph G12 corresponds to the terminal 2 in Fig. 10C. Graph G13 corresponds to terminal 2 in Figure 10F. Graph G14 corresponds to terminal 2 in Figure 10A. Graph G15 corresponds to terminal 2 in Figure 10D. Graph G16 corresponds to terminal 2 in Figure 10E. Graphs G11 to G16 are all approximately linear, which also indicates that the change in clock drift over time can be approximated by a linear function.

[0052] In this way, in the PLIM method, since the time slot index represents a part of the transmission data, if the detected value of the time slot index deviates too much from the original value, there is a possibility that the transmission of the transmission data D0 will not be performed correctly. In order to prevent such a situation, on the one hand, when the transmitting unit 215 of the terminal 2 transmits a packet, a predetermined delay time T offset On the other hand, the clock drift estimation unit 313 of the base station 3 estimates the clock drift.

[0053] Delay time T offset As shown in FIG. 5, the length of the time slot T slot is the transmission time T that the transmitter 215 of the terminal 2 takes to transmit a packet. pckt In this case, the time slot length T slot From transmission time T pckt The delay time T less than the time subtracted from offset By doing so, the delay time T offset In order to absorb the influence of clock drift regardless of whether the clock drift is positive or negative, a separate delay time may be provided between the time when the packet transmission ends and the time slot end time. As an example, a delay time T offset is the length of the time slot T slot From transmission time T pckt The base station 3 may set the delay time T offset is known in advance.

[0054] The estimation of the clock drift will now be described. When the clock drift estimation unit 313 of the terminal 2 estimates the clock drift in step S09 of Fig. 4B, the flowchart of Fig. 12 is executed. When the flowchart of Fig. 12 starts, step S091 is executed.

[0055] In step S091, the clock drift estimation unit 313 calculates the clock drift change amount T^c,i Estimate (specifically, the hat symbol "^" is above "T") the clock drift change amount T^ c,i Here, the clock drift change amount T^ r,j refers to the amount by which the clock drift has changed from the j-th time frame including the reception time t r,i when the j-th packet was received in the past to the i-th time frame including the reception time t

[0056] when the latest i-th packet was received. Here, j and i are arbitrary integers and satisfy j < i. c,i The clock drift change amount T^

Equation

[0057] After step S091, step S092 is executed. In step S092, the clock drift estimation unit 313 estimates the time slot index q^ i (specifically, the hat symbol "^" is above "q"). Here, the time slot index q^ i represents the time slot index of the time slot including the reception time t r,i when the latest i-th packet was received.

[0058] The time slot index q^ i is estimated by the following "Equation 2".

Equation

[0059] After step S092, step S093 is executed. In step S093, the clock drift estimation unit 313 estimates the start time T^ of the time frame. i (To be precise, the hat symbol "^" is above the "T"), where T^ is the start time of the time frame. i is the reception time t r,i is the start time of the ith time frame,

[0060] Start time of the time frame T^ i is estimated by the following formula 3.

number

[0061] After step S093, step S094 is executed. In step S094, the clock drift estimation unit 313 calculates the estimated value T^ of the clock drift. d,i where the estimated clock drift T^ d,i is the estimate of the clock drift in the i-th time frame, which is used as an estimate of the past clock drift in the next executed step S091 when the next packet is received.

[0062] Clock drift estimate T^ d,i is calculated using the following formula 4.

number

[0063] When step S094 is completed, step S09 in FIG. 4B is also completed, and then step S10 is executed.

[0064] In step S10 of FIG. 4B, the transmission index detection unit 314 of the base station 3 detects a transmission index. More specifically, the calculation device 31 of the base station 3 executes the base station program 321 to realize the function of the transmission index detection unit 314. The transmission index detection unit 314 performs inverse conversion of the frequency channel detected in step S08 and the time slot index estimated in step S092 of FIG. 12 to restore the first data D1. As shown in FIG. 6B, the number of bits of the restored first data D1 is B pi After step S10, step S11 is executed.

[0065] In step S11 of FIG. 4B, the demodulator 311 of the base station 3 demodulates the packet. More specifically, the arithmetic device 31 of the base station 3 executes the base station program 321 to realize the function of the demodulator 311. The demodulator 311 demodulates the packet received in step S08 to restore the second data D2. As shown in FIG. 6B, the number of bits of the restored second data D2 is B pl After step S11, step S12 is executed.

[0066] In step S12 of FIG. 4B, the information combination unit 315 of the base station 3 restores the transmission data D0. More specifically, the arithmetic device 31 of the base station 3 executes the base station program 321 to realize the function of the information combination unit 315. The information combination unit 315 restores the transmission data D0 by combining the first data D1 restored in step S10 and the second data D2 restored in step S11. As shown in FIG. 6B, the number of bits of the restored transmission data D0 is B plim Here, B plim =B pi +B pl The restored transmission data D0 is stored in the storage device 32. After step S12, step S13 is executed.

[0067] In step S13 of FIG. 4B, the clock drift estimation unit 313 of the base station 3 judges whether the clock drift estimated in step S09 exceeds a predetermined threshold. More specifically, the arithmetic device 31 of the base station 3 executes the base station program 321 to realize the function of the clock drift estimation unit 313. If the clock drift exceeds the threshold (YES), the process proceeds to step S02 to perform initialization of the time difference again before receiving the next packet. Here, the initialization unit 316 of the base station 3 generates a request signal requesting the terminal 2 to transmit an initialization packet, and the transmission unit 317 controls the communication device 33 to transmit the request signal to the terminal 2. This request signal may include information indicating a terminal ID indicating the terminal 2 requesting the transmission of the initialization packet. In addition, this request signal may include information specifying a time frame and a time slot for transmitting the initialization packet. The reception unit 217 of the terminal 2 controls the communication device 23 to receive the request signal from the base station 3. The initialization unit 216 of the terminal 2 executes the initialization of the time difference in step S02 according to the contents of the request signal. On the other hand, if the clock drift does not exceed the threshold (NO), the process proceeds to step S01 to determine whether a predetermined period has elapsed since the previous initialization before receiving the next packet.

[0068] By implementing the information transmission method as described above, the information transmission system 1 according to one embodiment can perform efficient information transmission using the PLIM method using an inexpensive terminal 2 that does not have a time synchronization function.

[0069] 13A and 13B, an example of a simulation result of the information transmission system 1 according to an embodiment will be described. FIG. 13A shows a distribution of time lag between the terminal 2 and the base station 3, with an average μ=-1.36×10 -3 , variance σ 2 =1.98×10 -10 13B shows the simulation results for the case where the average μ=-0.28×10 -3 , variance σ 2=1.12×10 -10 This is a simulation result for the case.

[0070] FIG. 13A includes graphs G21, G22, G23, and G24. In common with these graphs, the horizontal axis indicates time T 0 The graph G21 and the graph G22 overlap each other. The graph G21 shows an example of a simulation result when the information transmission method according to the embodiment is used, and the length of the time frame T frame The probability of time slot index detection error was zero when the time frame length T frame The probability of time slot index detection error was zero when the time frame length T frame The probability of time slot index detection errors increases rapidly and converges to about 0.9 when the time frame length T is 30 seconds and the total number of time slots per time frame is 16. Graph G24 shows an example of a simulation result without using the information transmission method according to one embodiment. frame When the time slot index detection error probability is 130 seconds and the total number of time slots per time frame is 128, the time slot index detection error probability increases rapidly and converges to about 1.0.

[0071] FIG. 13B includes graphs G25, G26, G27, and G28. In common with these graphs, the horizontal axis indicates time T 0The graph G25 shows an example of a simulation result when the information transmission method according to the embodiment is used, and the vertical axis shows the elapsed time from the time frame length T frame The probability of time slot index detection error was zero when the time frame length T frame The probability of time slot index detection error was zero when the time frame length T frame The probability of time slot index detection errors increases rapidly and converges to about 0.9 when the time frame length T is 30 seconds and the total number of time slots per time frame is 16. Graph G28 shows an example of a simulation result without using the information transmission method according to one embodiment. frame When the time slot index detection error probability is 130 seconds and the total number of time slots per time frame is 128, the time slot index detection error probability increases rapidly and converges to about 1.0.

[0072] From the simulation results shown in FIGS. 13A and 13B, the effects of the information transmission system 1 and the information transmission method according to the embodiment were confirmed.

[0073] In the embodiment described above, packets are generated after the transmission parameters are determined, as shown in the flowchart of Fig. 4 A. However, as shown in Fig. 6A, the determination of the transmission parameters and the generation of the packets may be executed in parallel, or the transmission parameters may be determined after the packets are generated.

[0074] In the embodiment described above, the packet is demodulated after the transmission index is detected as shown in the flowchart of Fig. 4B. However, as shown in Fig. 6B, the detection of the transmission index and the demodulation of the packet may be performed in parallel, or the transmission index may be detected after the packet is demodulated.

[0075] Although the invention made by the inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment, and it goes without saying that various modifications can be made without departing from the gist of the invention. Furthermore, the respective features described in the embodiment can be freely combined within the scope of technical compatibility. [Explanation of symbols]

[0076] 1. Information Transmission System 2, 2A~2D terminals 20 Bus 21 Arithmetic unit 210 Data Generation Division 211 Information division section 212 Transmission parameter determination unit 213 Modulation section 214 Packet Generation Unit 215 Transmitter 216 Initialization section 217 Receiving section 22 Storage device 220 Recording media 221 Terminal Program 23 Communication Equipment 24 Sensor device 3 base station 30 Bus 31 Arithmetic unit 310 Receiving unit 311 Demodulation section 313 Clock Drift Estimation Unit 314 Transmission index detection unit 315 Information connection part 316 Initialization section 317 Transmitter 32 Storage device 320 Recording media 321 Base Station Program 33 Communication Equipment B plim , B pi , B pl Bit depth D0 Transmit data D1 First data D2 Second Data ΔT d,1 ~ΔT d,3 Time Difference f1~f5 frequency G11~G16, G21~G28 Graphs P 0 Initialization packet P1, P2, P i , P j packet q i Time Slot Index q^ i Time slot index estimate t10~t13, t20~t23, t30 time T frame Time frame length (period) T pckt Send Time T slot Time slot length T R0 , T T0 Reference time T R1 ~T R3 , T Ri ~T Ri+3 , T Rj Start time of the time frame T T1 ~T T3 , T Ti ~T Ti+3 , T Tj Start time of the time frame

Claims

1. a terminal that transmits a packet for each time frame having a length of a first period; a base station receiving the packet; Equipped with The terminal includes: an information division unit that divides the transmission data to generate first data and second data; a transmission parameter determination unit that encodes the first data to generate a time slot index that indicates one of a plurality of time slots obtained by dividing the time frame; a transmitting unit that transmits the packet modulated with information represented by the second data during the time slot represented by the time slot index; Equipped with The base station, a clock drift estimation unit that estimates a latest clock drift that represents a time difference in a latest time frame including a latest reception time when the latest packet is received from the terminal, based on a past reception time when another packet was received from the terminal in the past and a past clock drift that represents a time difference between the terminal and the base station in a past time frame including the past reception time; a transmission index detection unit that detects the time slot index based on the latest reception time and the latest clock drift; an information combining unit that combines the first data restored using the time slot index and the second data obtained by demodulating the packet to restore the transmission data; Equipped Information transmission system.

2. 2. The information transmission system according to claim 1, The clock drift estimation unit is estimating a latest clock drift change amount representing a change amount of the time offset from the past time frame to the latest time frame based on the past reception time, the past clock drift, and the latest reception time; The latest clock drift is estimated by adding the latest clock drift change amount to the past clock drift. Information transmission system.

3. 3. The information transmission system according to claim 2, The clock drift estimation unit is estimating a latest time frame start time representing a start time of the latest time frame based on the time slot index and the latest reception time; updating the estimate of the current clock drift based on the past clock drift and the latest time frame start time; Information transmission system.

4. 4. The information transmission system according to claim 3, the transmitting unit starts transmitting the packet at a time when a predetermined delay time has elapsed from a start time of the time slot; the delay time is shorter than a time difference obtained by subtracting a length of a transmission time of the packet from a length of the time slot, The clock drift estimator estimates the latest time frame start time further based on the delay time. Information transmission system.

5. 5. The information transmission system according to claim 4, The transmission unit is transmitting a first initialization packet in a time slot represented by a first time slot index known to the base station in a first time frame known to the base station; transmitting a second initialization packet in a time slot represented by a second time slot index known to the base station in a second time frame known to the base station; The base station, an initialization unit that initializes the past clock drift based on a first reception time when the first initialization packet is received and a second reception time when the second initialization packet is received; Further equipped Information transmission system.

6. 6. The information transmission system according to claim 5, The initialization unit transmits a request signal to request the transmission unit to transmit the first initialization packet and the second initialization packet when the past clock drift is greater than a predetermined threshold. Information transmission system.

7. 7. The information transmission system according to claim 5, The transmission unit transmits the first initialization packet and the second initialization packet when a predetermined period has elapsed from the first reception time at which the first initialization packet was transmitted. Information transmission system.

8. In the information transmission system according to any one of claims 1 to 7, The transmission parameter determination unit encodes the first data to further generate a frequency channel index representing a frequency channel to be used for transmitting the packet among a plurality of frequency channels; The transmission index detection unit further detects the frequency channel index based on a frequency channel on which the packet is received; The information combination unit further uses the frequency channel index to recover the second data. Information transmission system.

9. In the information transmission system according to any one of claims 1 to 8, A plurality of the terminals including the terminal, the plurality of terminals transmit packets independently of each other; The base station receives the packets from each of the plurality of terminals. Information transmission system.

10. A terminal transmits a packet for each time frame having a length of the first period; a base station receiving the packet; Including, The transmitting step includes: Dividing the transmission data to generate first data and second data; encoding the first data to generate a time slot index representing one of a plurality of time slots into which the time frame is divided; transmitting the packet modulated with information representing the second data during a time slot represented by the time slot index; Including, The receiving includes: estimating a latest clock drift representing a time difference in a latest time frame including a latest reception time when the latest packet is received from the terminal, based on a past reception time when another packet was received from the terminal in the past and a past clock drift representing a time difference between the terminal and the base station in a past time frame including the past reception time; Detecting the time slot index based on the most recent received time and the most recent clock drift; Reconstructing the transmission data by combining the first data reconstructed using the time slot index and the second data obtained by demodulating the packet. Includes Method of information transmission.

11. A base station program for implementing a process of a base station for receiving a packet transmitted by a terminal for each time frame having a length of a first period, the process being executed by a computing device of the base station, the base station comprising: The process comprises: estimating a latest clock drift representing a time difference in a latest time frame including a latest reception time when the latest packet is received from the terminal, based on a past reception time when another packet was received from the terminal in the past and a past clock drift representing a time difference between the terminal and the base station in a past time frame including the past reception time; Detecting a time slot index representing a time slot in which the packet was transmitted from among a plurality of time slots obtained by dividing the time frame, based on the latest reception time and the latest clock drift; Reconstructing the transmission data by combining the first data reconstructed using the time slot index and the second data obtained by demodulating the packet. Includes Base station program.

Images