JP2012175537A - Radio communication system, radio transmitter, radio receiver, and radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a wake-up type radio communication system having communication error resistance using a small scale circuit.SOLUTION: A radio transmitter includes: wake-up ID storage means for storing a codeword of an MDS code calculated in advance as a wake-up ID by associating the codeword with each of multiple radio receivers; and wake-up packet transmission means for generating and transmitting a wake-up packet obtaining the wake-up ID of a communication partner from the wake-up ID storage means. A radio receiver includes: ID storage means for storing the wake-up ID of its own node; and wake-up means which extracts the wake-up ID included in a received wake-up packet, detects a discord number between the extracted wake-up ID and the wake-up ID of the own node for each bit, and if the discord number is less than half of the minimum Hamming distance of the MDS code, activates a data communication module.

Description

  The present invention relates to a radio communication technology, and more particularly to a wake-up radio communication technology.

  Many sensors are mounted on automobiles in order to improve comfort and safety. As the number of sensors increases, there is a problem that the number of wire harnesses increases and the wiring becomes difficult. In order to solve such a problem, a method of wirelessly performing data communication of the in-vehicle sensor has been proposed.

  With the wireless sensor data communication, the sensor node installed in the vehicle is driven by a battery, so that it is necessary to reduce the power consumption of the sensor node. Many sensor nodes have a long standby time for reception, and it is necessary to reduce reception standby power.

  Application of wake-up type wireless communication has been studied for the purpose of reducing the power consumption of sensor node communication (Patent Document 1, Non-Patent Documents 1 and 2). The wake-up type wireless communication system is configured by combining a wake-up module with extremely low reception standby power and a conventional data communication module. By starting the data communication module only when the wakeup module receives a wakeup packet including the ID of its own node, it is possible to significantly reduce the reception standby power of the wakeup type wireless communication device.

Japanese Patent Laid-Open No. 9-261717

Junaid Ansari, Dmitry Pankin, Petri Maehoenen, "Radio-triggered Wake-ups with Addressing Capabilities for Extremely Low Power Sensor Network Application", International Journal of Wireless Information Networks, vol.16, no.3, pp.118-130, Sep . 2009 Takahiro Higuchi, Shigeaki Ishida, Shunsuke Saruwatari, Masateru Minami, Hiroyuki Morikawa, “Evaluation of Power Consumption for Wake-up Wireless Communication System Using Bloom Filter”, IEICE Technical Report, RCS2009-254, Jan. 2010 R.M.Roth and G. Seroussi, "On generator matrices of MDS codes", IEEE Trans. Information Theory, vol.31, pp.826-830, 1985 M. Blaum, J. Brady, J. Bruck, J. Menon, "EVENODD: An efficient scheme for tolerating double disk failures in RAID architectures", IEEE Trans. Comput., Vol.44, no.2, pp.192- 202, Feb. 1995 M. Blaum, R. M. Roth, "On lowest density MDS codes", IEEE Trans. Inf. Theory, vol.45, no.1, pp.46-59, 1999 L. Xu, J. Bruck, "X-Code: MDS array codes with optimal encoding", IEEE Trans. Information Theory, vol.45, pp.272-276, 1999

However, communication error countermeasures are not taken in the conventional wake-up type wireless communication system. In a vehicle, noise from actuators such as an engine and a motor is large. In such a poor communication environment, not limited to the inside of a vehicle, ID matching is not performed correctly due to a communication error (bit error), and a necessary node cannot be woken up, or an unnecessary node wakes up Can occur. In these cases, problems such as an increase in power consumption and a delay in starting communication occur.

  Note that, as a countermeasure against communication errors in general wireless communication, a method of performing retransmission or a method of correcting errors can be considered. In the method of performing retransmission, there arises a problem of an increase in communication start delay and a problem of an increase in power consumption due to an increase in the number of wake-up packet receptions. In addition, the error correction technique requires a large number of registers and a large number of arithmetic circuits for restoring the original bit string from a bit string including a bit error. The increase in cost accompanying the increase in the scale of the error correction circuit is a problem that cannot be ignored in a system using a large number of wake-up type wireless communication apparatuses.

  An object of the present invention is to realize a wake-up type wireless communication system having communication error tolerance with a small circuit.

  In order to solve the above problems, a wireless communication system according to the present invention has the following configuration. That is, the wireless communication system according to the present invention includes at least one wireless transmitter and a plurality of wireless receivers. Here, both the radio transmitter and the radio receiver may be radio transceivers.

The wireless transmitter includes a wakeup ID storage unit and a wakeup packet transmission unit. The wake-up ID storage means uses MDS (Maximum Distance) calculated in advance.
The code word of the Separable (maximum distance separation) code is stored as a wake-up ID in association with each of a plurality of wireless receivers. The wakeup packet transmission means acquires the wakeup ID of the communication partner from the wakeup ID storage means, and generates and transmits a wakeup packet including the wakeup ID.

  The wireless receiver includes ID storage means and wakeup means. The ID storage means stores the wakeup ID of the own node. The wake-up means extracts a wake-up ID included in the received wake-up packet, and detects a match / mismatch for each bit between the extracted wake-up ID and the wake-up ID of the own node. If the number of mismatches is less than ½ of the minimum hamming distance between codewords in the MDS code, the wakeup means activates the data communication module.

  According to the present invention as described above, since the MDS code is obtained in advance and stored in the wakeup ID storage means in the wireless transmitter, a circuit for calculating the MDS code can be omitted. In addition, since the wireless receiver only performs comparison with the wakeup ID of its own node, it is not necessary to provide a special circuit for error detection and error correction, and the circuit scale can be suppressed. In addition, since the MDS code having a large inter-code distance is used and bit mismatch is allowed to some extent in ID matching, the target wireless receiver can be appropriately woken up even in a poor communication environment. .

The wake-up means of the wireless receiver in the present invention is preferably composed of a radio wave detection circuit and an ID matching circuit. Here, the radio wave detection circuit is always operating, and the ID matching circuit is normally in a sleep state, and operates as required according to an instruction from the radio wave detection circuit. That is, when the radio wave detection circuit detects a wake-up packet, the ID matching circuit is operated. The ID matching circuit determines whether the wake-up packet is addressed to its own node. The ID matching circuit calculates an exclusive OR for each bit of the wakeup ID included in the wakeup packet and the wakeup ID of the own node by the XOR gate, and the number of “1” included in the calculation result is calculated by the counter. Can be counted. The count result is the number of mismatches for each bit of the received wakeup ID and the wakeup ID of the own node. When this is less than the predetermined value, the ID matching circuit wakes up the data communication module.

  The present invention can be understood as a wireless transmitter or a wireless receiver including at least a part of the above means. Also, it can be understood as a wireless communication method for performing these processes.

  A wireless transmitter according to an aspect of the present invention includes a wakeup ID storage unit that stores a codeword of an MDS code calculated in advance as a wakeup ID in association with each of a plurality of wireless receivers, and a wakeup of a communication partner Wakeup packet transmission means for obtaining an ID from the wakeup ID storage means and generating and transmitting a wakeup packet including the wakeup ID.

  The wireless receiver as one aspect of the present invention receives ID storage means for storing one codeword as a wakeup ID of its own node among MDS codes calculated in advance, and a wakeup packet including the wakeup ID. , The wakeup ID included in the wakeup packet is extracted, the number of mismatches for each bit between the extracted wakeup ID and the wakeup ID of the own node is detected, and the number of mismatches is 1 of the minimum Hamming distance of the MDS code. If it is less than / 2, wake-up means for activating the data communication module is included.

  In the wireless communication method as one aspect of the present invention, the code word of the MDS code calculated in advance is stored in the wireless transmitter as a wake-up ID in association with each of the plurality of wireless receivers. When starting wireless communication, a wake-up packet including the wake-up ID of the communication partner is transmitted, and the wireless receiver receives the wake-up packet, extracts the wake-up ID included in the wake-up packet, and The number of mismatches for each bit with the wakeup ID is detected. If the number of mismatches is less than ½ of the minimum hamming distance of the MDS code, the data communication module is activated.

  ADVANTAGE OF THE INVENTION According to this invention, the wake-up type radio | wireless communications system provided with communication error tolerance is realizable with a small circuit.

It is a figure which shows the outline | summary of the radio | wireless communications system in this embodiment. It is a functional block diagram of the radio transmitter in this embodiment. It is a functional block diagram of the radio receiver in this embodiment. It is a figure which shows the simulation result which calculated | required the average reception standby power when this embodiment which accept | permits a bit mismatch with an MDS code | symbol, when a serial number is employ | adopted as ID, and a Hamming code system is employ | adopted.

<Configuration>
Below, the case where the wake-up type radio | wireless communications system which concerns on this invention is applied to the sensor network in a vehicle is demonstrated as an example. A large number of sensor nodes are installed in the automobile, and each sensor node communicates with an ECU (Electronic Control Unit). In order to avoid problems due to an increase in wire harnesses, communication between the ECU and each sensor node is made wireless. Here, the wake-up type wireless communication according to the present invention is applied in order to reduce the power consumption of the communication of the sensor node.

  FIG. 1 is a functional block diagram of an ECU and a sensor node in the present embodiment. Note that only functions related to wake-up type wireless communication are described here, and descriptions of other functions of normal ECUs and sensor nodes are omitted. The ECU 10 includes a wakeup module 11 and a data communication module 12. The sensor node 20 includes a wakeup module 21 and a data communication module 24.

  In the sensor network in the vehicle, communication is started from the ECU 10. Therefore, the ECU 10 wakes up each sensor node 20 to perform communication. When the ECU 10 (data communication module 12) starts communication with a certain sensor node, a wakeup packet including the ID of the sensor node is transmitted from the wakeup module 11. When the wake-up module 21 of the sensor node 20 receives the wake-up packet, the ID included in the wake-up packet is compared with the ID of the own node. When the two IDs match (however, a bit mismatch of a predetermined number or less is allowed) Then, the data communication module 24 is woken up. When the data communication module 24 wakes up, an ACK is transmitted to the data communication module 12 of the ECU 10, and communication is started between the ECU and the sensor node.

  In this embodiment, a maximum distance separation (MDS) code is used, and ID matching that allows a certain degree of bit mismatch is applied, so that the number of retransmissions of a target sensor node is small even in a poor communication environment. Can wake up. The MDS code is a code designed to maximize the Hamming distance between the codes, and is an ideal code for communication error countermeasures.

[ECU (Transmitter)]
FIG. 2 is a more detailed functional block diagram of the wake-up module 11 of the ECU 10. The wakeup module 11 includes an ID converter 111 that associates a node ID of each sensor node with a wakeup ID, and a wakeup packet generator 112.

  Here, the MDS code is created in advance, and each codeword of the created MDS code is assigned to the sensor node as a wake-up ID. The wake-up ID is an ID used for designating a sensor node that the ECU 10 wakes up. In the present embodiment, it is assumed that the sensor node is identified by the node ID in the upper layer, and the ID converter 111 stores the node ID and the wakeup ID in association with each other. In the figure, the wakeup ID is represented as 6 bits, but actually has a longer code length. When ID converter 111 receives the node ID of the node to be woken up as an input, ID converter 111 passes the corresponding wakeup ID to wakeup packet generator 112 to generate a wakeup packet.

  Here, the assignment of the wakeup ID to the sensor node will be described in more detail. The assignment of a wakeup ID to a sensor node is realized by three steps: determination of a code length, creation of an MDS code, and assignment of an ID to a sensor node.

の関係が成り立つ。許容エラービット数ｔは、通信環境に応じて適宜設定する。符号数Ｎは、センサノードの数である。これらの値を式（１）に代入して、符号長ｎが決定される。例えば、センサ数が１０００個で許容エラービット数が５ビットの場合には、符号長ｎは２７ビットとなる。 In the first step, a code length n is determined in order to create an MDS code. The code length n is determined from the number N of codes to be created and the number t of allowable error bits. The allowable error bit number t is the number of bit mismatches allowed in ID matching. Even when a bit error occurs, ID matching can be performed correctly if the error bit number is equal to or less than the allowable error bit number t. When the number of allowable error bits is t, the minimum Hamming distance between MDS codes is 2t + 1. In the MDS code, between the allowable error bit number t, the code number N, and the code length n,

The relationship holds. The allowable error bit number t is appropriately set according to the communication environment. The code number N is the number of sensor nodes. By substituting these values into equation (1), the code length n is determined. For example, when the number of sensors is 1000 and the allowable error bit number is 5 bits, the code length n is 27 bits.

In the second step, an MDS code is created using a known technique (for example, Non-Patent Documents 3 to 6) using the allowable error bit number t, the number N of codes to be created, and the code length n as parameters. In the technique of Non-Patent Document 3, N MDS codes are created by repeating matrix operations using N × (n− [log ₂ N]) Cauchy sequences (note that the square brackets in the equation are ceilings). Represents a function, [A] means the smallest integer greater than or equal to A).

  In the third step, each codeword of the MDS code is assigned as a wakeup ID to each sensor node. Wake-up IDs are selected one by one from the MDS codes created above and assigned to each sensor node at the time of vehicle manufacture. The ID length of the wakeup ID is n, and can be assigned to a maximum of N sensor nodes. The assigned wakeup ID is stored in the wakeup ID storage unit 233 of each sensor node. In addition, the ECU stores the association between the node ID of each sensor node and the wakeup ID in the ID converter 111.

  When the ECU 10 starts communication with the sensor node, the ID converter 111 is used to convert the node ID of the communication partner sensor node into a wake-up ID. The wakeup packet generator 112 generates a wakeup packet by adding a preamble or a header to the converted wakeup ID, and transmits the generated wakeup packet.

[Sensor node (receiver)]
FIG. 3 is a more detailed functional block diagram of the wakeup module 21. The wakeup module 21 includes a radio wave detection circuit 22 and an ID matching circuit 23. Further, the ID matching circuit 23 includes a code extractor 231, a code comparator 232, a wakeup ID storage unit 233, and a mismatch number counter 234.

  The radio wave detection circuit 22 operates with power consumption of about 10 to several tens of μW, for example, and always performs radio wave detection. The ID matching circuit 23 is a circuit that receives a wake-up packet and determines a destination of communication, and is set in a sleep state in a reception standby state.

  In the reception standby state, the radio wave detection circuit 22 performs radio wave detection, and the ID matching circuit 23 and the data communication module 24 are set in a sleep state. When the radio wave detection circuit 22 detects the radio wave, the ID matching circuit 23 is woken up, and the ID matching circuit 23 receives the wake-up packet. Since the radio wave detection circuit detects radio waves other than the wakeup packet, the ID matching circuit may not be able to receive the wakeup packet. In this case, the ID matching circuit 23 returns to the sleep state and returns to the reception standby state in which only the radio wave detection circuit 22 operates.

When the ID matching circuit 23 receives the wake-up packet, it determines whether or not the wake-up packet is addressed to its own node. Specifically, the code extractor 231 extracts the wakeup ID by removing the preamble and header from the received wakeup packet. The sign comparator 232 is composed of an XOR gate, and calculates the bitwise exclusive OR (XOR) of the obtained wakeup ID and the wakeup ID 234 of its own node. The mismatch number counter 234 counts the number of bits of “1” in the calculated bit string, and the number is equal to or less than the allowable error bit number t (which can be said to be less than ½ of the minimum Hamming distance between codes in the MDS code). If there is, a wakeup signal is output to the data communication module 24. On the other hand, if the count of the mismatch counter 234 is larger than the allowable error bit number t, it is determined that the packet is not a wake-up packet addressed to the own node, the ID matching circuit 23 returns to the sleep state, and only the radio wave detection circuit 22 operates. Return to the reception standby state.

  The data communication module 24 wakes up by the wakeup signal and transmits ACK to the ECU 10. Thereby, communication is started between the ECU 10 and the sensor node 20.

<Operation / Effect of Embodiment>
According to the present embodiment, advantageous effects can be obtained over the conventional method in terms of circuit scale, reception standby power, and communication delay time. Each will be described below.

(1) Circuit scale In this embodiment, since the number of sensor nodes is determined in advance, the ECU obtains and stores in advance the MDS code to be assigned to each sensor node. Therefore, a circuit for dynamically obtaining the MDS code (wake-up ID) is unnecessary. In addition, the number of sensors mounted in the vehicle is currently several hundred, and it is expected that the number will be several thousand in the future. However, the code length necessary for the MDS code is not so large, and the ID The circuit scale of the converter can be relatively small.

  In the ID matching in the sensor node, since the wakeup ID of the own node is known, it is only necessary to compare with the received wakeup ID, and it is not necessary to specify an error bit. Therefore, the sensor node only needs to calculate the hamming distance between the received wakeup ID and the wakeup ID of its own node, and a counter (mismatch number) with the XOR gate (sign comparator) and the allowable error bit number t as a maximum value. (Counter). Error correction using a Hamming code or the like requires a large number of arithmetic circuits and registers, but this embodiment can be realized with a simpler circuit. Since this system can be configured with a simple circuit, an increase in manufacturing cost can be avoided.

(2) Reception standby power Since the MDS code is used as the wake-up ID, it is possible to avoid that the designated sensor node does not start or another sensor node is erroneously started. Less. In order to show this, a numerical simulation was performed.

Here, the numerical simulation was performed under the following conditions.
-Wake-up packet configuration: Preamble 9 bits + ID 32 bits
・ Wake-up module (sensor node)
Reception standby power: 12.4 μW
Power when receiving ID: 623.68 μW
Bit rate: 20 kbps
Data communication module Receive standby power: 55.5mW
Sleep → active transition time: 0.5ms
・ Communication environment ECU: 1 unit, sensor node: 1000 units ECU wake-up packet retransmission interval until communication with 1 sensor node and communication target node every 100 ms: 20 ms
A node that wakes up by mistake transitions to the sleep state again after 10 ms. No state transition overhead is considered.

  As an ID matching parameter, the number of allowable error bits “5” was adopted. For comparison, the serial numbers 0 (00 ... 00), 1 (00 ... 01), 2 (00 ... 10), 3 (00 ... 11),. .. and a case where error correction is performed with a code number 6 of the Hamming code for the serial number wakeup ID was also performed.

  FIG. 4 is a simulation result showing the average reception standby power in the above three cases. As can be seen from the figure, it can be seen that the method of the present embodiment using the MDS code is 1/3 or less compared to the power consumption when using a simple serial number. In the Hamming code method, the power consumption increases as the bit error rate increases, whereas in the method of the present embodiment, the power consumption does not change greatly even if the bit error rate increases. That is, lower power consumption can be achieved in a poor communication environment than in the case of the Hamming code method.

  In addition, in this embodiment, bit mismatch is allowed, so that the number of retransmissions of the wakeup packet is reduced and the number of activations of the ID matching circuit is reduced as compared with the case where the complete ID match is a condition. Electricity is reduced.

(3) Communication delay time The number of sensor nodes that wake-up packets are retransmitted or erroneously wake-up decreases, and the probability that the sensor node to be communicated can be woken up with one wake-up packet transmission increases. That is, the communication delay time associated with wake-up can be reduced as compared with other conventional methods.

<Others>
In the above description, a network including an ECU and a sensor node in a vehicle is taken as an example, but it will be apparent that the present invention can be applied to any other system. For example, in the case of an in-vehicle network, when not only sensor nodes but also body-type sensors / actuators are made wireless, it is conceivable to apply wake-up type wireless communication to these sensors / actuators. Since the power consumption of such a control system radio is larger than that of a narrowly-defined sensor system, the use of a wake-up radio provides a great effect in terms of reducing power consumption.

  Further, the system to which the present invention is applied is not limited to a network in an automobile, and it will be apparent that the present invention can be applied to any wireless communication system as long as the wireless communication device to be used is assumed in advance.

  In the above description, only one node (ECU) wakes up other nodes, but any node in the system may transmit a wake-up packet. Further, both a function for causing some or all nodes in the system to wake up other nodes (wake-up module 11) and a function for being woken up from other nodes (wake-up module 21). You may have.

10 ECU
11 Wake-up module 12 Data communication module 20 Sensor node 21 Wake-up module 22 Radio wave detection circuit 23 ID matching circuit 24 Data communication module

Claims (6)

Including at least one wireless transmitter and a plurality of wireless receivers;
The wireless transmitter
A wakeup ID storage means for storing a codeword of a previously calculated MDS (Maximum Distance Separable) code as a wakeup ID in association with each of a plurality of wireless receivers;
A wakeup packet transmitting means for acquiring a wakeup ID of a communication partner from the wakeup ID storage means, and generating and transmitting a wakeup packet including the wakeup ID;
Have
Wireless receiver
ID storage means for storing the wakeup ID of the own node;
The wakeup ID included in the received wakeup packet is extracted, the number of mismatches for each bit between the extracted wakeup ID and the wakeup ID of the own node is detected, and the number of mismatches is the minimum hamming distance of the MDS code. If less than ½, wake-up means for activating the data communication module;
Having
Wireless communication system. The wake-up means includes a radio wave detection circuit that operates constantly and an ID matching circuit that operates as necessary.
When the radio wave detection circuit detects the wake-up packet, the ID matching circuit is operated,
The ID matching circuit determines whether the wake-up packet is addressed to the own node;
The wireless communication system according to claim 1. A wakeup ID storage means for storing a codeword of a previously calculated MDS (Maximum Distance Separable) code as a wakeup ID in association with each of a plurality of wireless receivers;
A wakeup packet transmitting means for acquiring a wakeup ID of a communication partner from the wakeup ID storage means, and generating and transmitting a wakeup packet including the wakeup ID;
Including wireless transmitter. ID storage means for storing one codeword of MDS (Maximum Distance Separable) code calculated in advance as a wakeup ID of the own node;
A wakeup packet including a wakeup ID is received, a wakeup ID included in the wakeup packet is extracted, a mismatch number for each bit between the extracted wakeup ID and the wakeup ID of the own node is detected, and a mismatch is detected. If the number is less than half of the minimum Hamming distance of the MDS code, wake-up means for activating the data communication module;
Including wireless receiver. The wake-up means is composed of a radio wave detection circuit that operates constantly and an ID matching circuit that operates as necessary.
When the radio wave detection circuit detects the wake-up packet, the ID matching circuit is operated,
The ID matching circuit determines whether the wake-up packet is addressed to the own node;
The wireless receiver according to claim 4. In the wireless transmitter, the code word of the MDS (Maximum Distance Separable) code calculated in advance is stored as a wake-up ID in association with each of the plurality of wireless receivers,
When the wireless transmitter starts wireless communication, it transmits a wakeup packet including the wakeup ID of the communication partner,
The wireless receiver receives the wake-up packet, extracts the wake-up ID included in the wake-up packet, detects the number of mismatches for each bit with the wake-up ID of the own node, and the number of mismatches is the minimum of the MDS code If it is less than half of the Hamming distance, the data communication module is activated.
Wireless communication method.

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