JP2024065894A - Communication device and communication system - Google Patents

Abstract

To deter the degradation of communication quality in UWB radio communication.SOLUTION: A communication device according to an aspect of an embodiment includes a controller that controls wireless communication using a UWB communication method. The controller estimates the communication status of a surrounding area and changes a used preamble length, which is the preamble length of a preamble used in wireless communication, according to the estimated communication status.SELECTED DRAWING: Figure 6

Description

The present invention relates to a communication device and a communication system.

The UWB (Ultra Wide Band) method is known as a wireless communication method. Wireless communication using the UWB method (hereinafter referred to as UWB wireless communication) is characterized by low power consumption and wide bandwidth. For example, UWB wireless communication can achieve high-speed communication over short distances.

In addition, with UWB wireless communications, multiple devices use the same frequency, making radio interference likely to occur.

However, when UWB wireless communication is used for ranging and positioning, the communication interval and frequency are short, and communication is often designed so that even if it fails due to interference, it can be retried, so degradation of communication quality due to radio interference is unlikely to be a problem.

On the other hand, when UWB wireless communication is used for data communication purposes, degradation of communication quality due to radio interference can become a fatal problem.

In response to this, there is a known technique for changing the length of the preamble of a frame transmitted and received in wireless communication in order to improve communication quality (see, for example, Patent Document 1 and Patent Document 2).

JP 2009-49694 A JP 2010-252049 A

However, conventional technology has the problem that it may not be possible to prevent degradation of communication quality in UWB wireless communications.

As mentioned above, radio wave interference is likely to occur in UWB wireless communications. In response to this, the techniques described in Patent Documents 1 and 2 may not be able to deal with degradation of communication quality caused by radio wave interference.

For example, the technology described in Patent Document 1 changes the length of the preamble depending on whether or not a beam pattern is formed toward the communication partner. Also, for example, the technology described in Patent Document 2 changes the length of the preamble in order to optimize the preamble for synchronization in the wireless frame.

However, the communication environment is constantly changing, and neither of the technologies described in Patent Document 1 nor Patent Document 2 is intended to address degradation of communication quality due to changes in the communication environment (deterioration of the communication environment).

The present invention has been made in consideration of the above, and aims to provide a communication device and a communication system that can prevent degradation of communication quality in UWB wireless communication.

To solve the above problems and achieve the object, the communication device of the present application includes a controller that controls wireless communication using the UWB communication method. The controller estimates the surrounding communication conditions and changes the preamble length used, which is the preamble length of the preamble used in wireless communication, according to the estimated communication conditions.

The present invention makes it possible to prevent degradation of communication quality in UWB wireless communications.

FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment. FIG. 2 is a diagram illustrating a communication frame. FIG. 3 is a diagram illustrating radio interference in UWB wireless communication. FIG. 4 is a block diagram illustrating an example of the configuration of a communication device according to the embodiment. FIG. 5 is a diagram showing the configuration of the preamble table 121. As shown in FIG. FIG. 6 is a communication state transition diagram showing an example of state transition in UWB wireless communication. FIG. 7 is a flowchart showing a processing procedure of the first embodiment. FIG. 8 is a state transition time chart showing an example of a UWB wireless communication state. FIG. 9 is a flowchart showing a processing procedure according to the second embodiment. FIG. 10 is a state transition time chart showing an example of a UWB wireless communication state. FIG. 11 is a flowchart showing a processing procedure of the third embodiment. FIG. 12 is a state transition time chart showing an example of a UWB wireless communication state.

Embodiments of the communication device and communication system disclosed in the present application will be described in detail below with reference to the attached drawings. Note that the invention of the present application is not limited to the embodiments described below.

First, a communication system including a communication control device according to an embodiment will be described below with reference to FIG. 1. FIG. 1 is a diagram showing an example of the configuration of a communication system according to an embodiment.

Note that Figure 1 and other figures show components necessary for explaining the features of the embodiment, and descriptions of general components are omitted.

In other words, each component shown in FIG. 1 etc. is a functional concept, and does not necessarily have to be physically configured as shown. For example, the specific form of distribution and integration of each block is not limited to that shown, and all or part of it can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc.

In addition, in the explanations from Figure 1 onwards, components that have already been explained may be given the same reference numerals, etc., and explanations may be simplified or omitted.

As shown in FIG. 1, the communication system 1 includes a communication device 10 and a communication device 20 mounted on a vehicle V1.

The communication device 10 and the communication device 20 transmit and receive data to each other by wireless communication using the UWB system (UWB wireless communication). Note that in UWB wireless communication, frequency bands such as 3.4 to 4.8 GHz, 7.25 to 10.25 GHz, and 24.25 to 29 GHz are used. In UWB wireless communication, communication is performed according to a standard such as IEEE 802.15.4z.

Note that communication device 10 and communication device 20 have the functions necessary to realize the UWB wireless communication function described below, but may be configured to realize the same UWB wireless communication function, or may be configured to realize some different UWB wireless communication functions.

For example, communication device 10 and communication device 20 are realized by an ECU (Electronic Control Unit). Furthermore, communication device 10 and communication device 20 are devices for controlling in-vehicle devices such as an air conditioner, an audiovisual system, a navigation system, a display operation panel, power windows, power seats, and wipers.

Here, consider a case where the communication device 10 transmits a control signal for the power window in response to a user operation. In this case, the communication device 20 controls the operation of the power window based on the received control signal.

First, when a user of vehicle V1 operates a power window operation button or the like, communication device 10 transmits an opening/closing signal corresponding to the operation via UWB wireless communication. Communication device 20 receives the opening/closing signal transmitted by communication device 10, and drives the drive motor of the power window in accordance with the received opening/closing signal to open or close the power window.

In addition to transmitting and receiving various control signals such as open/close signals, various signals, such as response signals confirming reception of communication (data), are transmitted and received between communication device 10 and communication device 20 as appropriate via UWB wireless communication.

In addition, not only signals related to device control are transmitted between communication device 10 and communication device 20, but also various data such as image files used for control (used to generate control signals) and display, etc.

As shown in FIG. 1, it is assumed that there is another vehicle V2 in addition to vehicle V1. Vehicle V2 is equipped with a system that performs UWB wireless communication similar to communication system 1. In this case, depending on the relative positions of vehicles V1 and V2, radio waves of the UWB wireless communication performed in vehicle V2 may cause radio wave interference with the UWB wireless communication of communication system 1. Note that radio wave interference may also occur if there is a device in vehicle V1 that is communicating simultaneously.

UWB wireless communication will be explained using Figure 2. Figure 2 is a diagram explaining the unit of data transmitted and received in UWB wireless communication, the so-called communication frame.

As shown in FIG. 2, a frame used in UWB wireless communication includes a preamble, a header section, and a data section. The preamble is a symbol string (or a bit string) of a specific length. The header section and the data section are the information section for the communication connection and the data section of the communication target, and correspond to the header section and the data section in an Ethernet (registered trademark) frame, for example.

The length of the preamble (hereinafter referred to as the preamble length) is determined by the number of symbols contained in the preamble. The preamble length is selected from patterns such as 64 symbols, 128 symbols, 256 symbols, 512 symbols, and 1024 symbols.

The preamble is a bit string with a predetermined pattern, such as "10101010...", and the preamble length is the size of the bit string. The header section is a bit string with a fixed length, such as "1010101011", that corresponds to the data indicating the communication format, communication destination, etc. The end of the preamble is a bit string with a predetermined pattern, and the end of the preamble is detected by detecting the bit string with this predetermined pattern, and the signal (bit string) that follows becomes the data frame (header section and data section).

In addition, the same preamble length must be used between devices that perform UWB wireless communication. If different preamble lengths are used between devices, differences will arise in determining whether or not there is a preamble (UWB wireless communication), and this may result in the UWB wireless communication not being performed properly (communication NG).

Figure 3 shows an example of a situation where two UWB wireless communications with different preamble lengths and communication timings are interfering with each other. As shown in Figure 3, in the UWB wireless communication that started first, the first half of the preamble is free of radio interference, so there is a high possibility that the bit string of the preamble of that communication can be detected and communication synchronization can be achieved. Therefore, even if radio interference occurs thereafter, synchronization can be maintained based on the already achieved synchronization, increasing the possibility of receiving subsequent data.

In addition, in the case of UWB wireless communications with long preambles, there are preamble portions that do not overlap with the preamble portions of the communication that is subject to radio interference, so it is highly likely that the preamble bit string can be detected in the non-overlapping preamble portion and communication synchronization can be achieved. Furthermore, because the bit string pattern is different from the header and data portions, even if it is detected, it can be determined that it is not a preamble and excluded from synchronization processing. If the preambles overlap, even if the bit string pattern of the preamble is detected, it cannot be determined which communication the preamble belongs to, and synchronization processing etc. cannot be performed properly.

In this way, UWB wireless communication has the characteristic that communication that is initiated early is more likely to be established, and that communication with a long preamble length is more likely to be established. On the other hand, communication with a long preamble length has the disadvantage that the data communication capacity increases in proportion to the length of the preamble, slowing down the communication speed.

The communication device 10 of this embodiment avoids radio interference by changing the preamble length L1 used in the communication system 1 according to the communication situation, and ensures that UWB wireless communication is performed normally (communication OK).

The configuration of the communication device 10 will be described with reference to FIG. 4. FIG. 4 is a block diagram showing an example of the configuration of a communication device according to an embodiment. As shown in FIG. 4, the communication device 10 includes a communication unit 11, a storage unit 12, and a control unit 13.

The communication unit 11 is a communication module for performing UWB wireless communication, and is composed of a transmission circuit, a reception circuit, etc. for UWB wireless communication. Under the control of the control unit 13, the communication unit 11 transmits communication data (frame) consisting of a preamble of a selected length followed by a header section and a data section.

The storage unit 12 is a storage device composed of, for example, a non-volatile memory and a data flash. The storage unit 12 stores preamble information PD and various programs, etc. The storage unit 12 is provided with a preamble table 121 that stores the preamble information PD.

Figure 5 is a diagram showing the configuration of the preamble table 121. Note that Figure 5 is a diagram showing the concept of the preamble table 121, and in reality, each piece of data is stored in the storage unit 12 by the memory management system (operating system) so as to realize this concept.

The preamble table 121 has the fields "preamble type," "preamble length," "usage status," and "selection status," and data corresponding to each field is stored in each data record.

"Preamble type" is the type of preamble, and stores data such as the preamble identification code or preamble name (shown as preamble P1 in the figure). Note that the preamble type data is the identification data of the data record, the so-called primary key data.

"Preamble length" is the length of the preamble (number of bits in the preamble), and in the case of UWB wireless communication, data of "64", "128", "256", "512", or "1024" bits is stored. "Usage status" is a data item indicating whether the preamble is being used in communications taking place around the communication device 10 (communications detected by the communication device 10), and stores data of "in use" or "not in use". "Selection status" is a data item indicating whether the communication device 10 has selected the preamble (whether it is a preamble to be used in wireless communication) or not (whether it is a preamble to be used in wireless communication), and stores data of "selected" or "not selected".

For example, in the preamble table 121 of FIG. 5, "preamble P1" is a preamble with a preamble length of "64 bits", is not used in surrounding communications, and is the preamble selected (in use) by the communication device 10.

The "usage status" data is unnecessary if the communication status determination (estimation) described below is not based on the presence or absence of communication occurring around the communication device 10, and in that case it may be deleted.

The control unit 13 is a so-called controller that controls various operations of the communication device 10. The control unit 13 includes a determination unit 131, a change unit 132, and a communication control unit 133. The control unit 13 is realized by, for example, a computer having a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input/output ports, etc., and various circuits.

The computer's CPU functions as the determination unit 131, change unit 132, and communication control unit 133 of the control unit 13, for example, by reading and executing a program stored in the ROM. In addition, at least some or all of the determination unit 131, change unit 132, and communication control unit 133 of the control unit 13 may be configured with hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

The determination unit 131 determines whether radio interference is occurring. Whether radio interference is occurring is an example of determining the communication status.

For example, the determination unit 131 determines that radio interference is occurring when communication errors occur consecutively a predetermined number of times or more in UWB wireless communication with the communication device 20, or when the occurrence rate (proportion) of communication errors in a predetermined period of time is equal to or greater than a predetermined threshold. This communication error is detected when, for example, a response signal to a transmission from the destination cannot be received despite data transmission. Note that in the process described below, both communication devices (10, 20) communicating need to determine the occurrence state of radio interference, so each communication device (10, 20) will transmit (normal communication or dummy communication) at an appropriate timing (an interval that allows good communication (preamble change process described below)).

There is also a method of determining whether radio interference is occurring based on the communication conditions around the communication device 10 (communications taking place in the vicinity). In this method, the determination unit 131 determines whether radio interference is occurring based on whether there is a lot (high frequency) of communications other than communications involving the communication device 10 around the communication device 10 (if there is a lot (high frequency) of communications other than communications involving the communication device 10, it determines that radio interference is occurring).

When the determination unit 131 determines that radio interference is occurring, the change unit 132 selects a preamble to be used for communication according to predetermined selection (change) rules described below.

As a basic preamble selection method, when radio interference is not occurring, the communication device 10 selects the preamble with the shortest preamble length from among the selectable preambles. In other words, since radio interference is not occurring, a preamble with a small communication capacity, i.e., a preamble with a short preamble length, is selected without considering radio interference resistance. Furthermore, when radio interference is occurring, the communication device 10 selects the preamble with a long preamble length from among the selectable preambles. In other words, since radio interference is occurring, a preamble with a long preamble length is selected while considering radio interference resistance. Detailed methods for selecting preambles will be described later with several examples.

The communication control unit 133 controls the communication unit 11 to perform UWB wireless communication. When performing UWB wireless communication, the communication control unit 133 controls the communication unit 11 to perform UWB wireless communication using the selected type of preamble (a preamble of the selected preamble length). Specifically, the communication control unit 133 generates a data frame for transmission using data in the data section of the data to be sent, data in the header section such as destination data, and data in the selected preamble, and outputs the data to the communication unit 11 as transmission data.

In this way, the control unit 13 changes the length of the preamble used in UWB wireless communication (used preamble length) depending on the communication conditions. As a result, according to this embodiment, it is possible to prevent degradation of communication quality due to radio interference in UWB wireless communication.

Below, several specific examples of control methods using the communication device 10 will be described in order as examples of this embodiment.

[First embodiment]
In the first embodiment, when the communication conditions deteriorate (poor) in UWB wireless communication using the default (normal use) preamble, the control unit 13 controls to change the preamble length to a selectable preamble length that is one step longer. The default preamble is the preamble with the shortest preamble length that is set as selectable by the communication device 10 in consideration of communication efficiency. Note that if the communication conditions deteriorate (poor) even after the preamble is changed, the control unit 13 controls to change the preamble length to a preamble with an even longer length.

The control unit 13 also starts UWB wireless communication using the changed preamble after a predetermined waiting time has elapsed from the time when it is determined that the communication situation has deteriorated. In the first embodiment, the preamble is changed asynchronously with the communication device (20) on the communication partner side (no process is performed to synchronize the change timing using communication, etc.). Therefore, the control unit 13 performs waiting time processing to wait for the communication device (20) on the communication partner side to change the preamble by similar processing.

In addition, taking communication efficiency into consideration, the control unit 13 reverts to the initial setting preamble a predetermined time after the preamble is changed (the time when recovery of communication conditions can be expected).

These operations will also be performed by all or some of the communication devices (10, 20, etc.) in the communication system 1 that are the communication partners (communication devices that are set to handle communication interference).

Next, a specific operation example will be described with reference to FIG. 6. FIG. 6 is a communication state transition diagram showing an example of state transition in UWB wireless communication. Note that this communication transition example is an example of a communication system in which preambles P1 with a short preamble length and preamble P2 with a long preamble length are selectable preambles. This communication transition example is also an example of a transition in which the communication state deteriorates while communicating with preamble P1, and communication is changed to communication with preamble P2. Note that communication device 10 and communication partner communication device (20) perform similar operations, although there is a slight difference in timing.

6, during the period [ _t11 , _t12 ] (the period from time t11 to time t12), the communication device 10 is in a communication state in which it is communicating using the preamble P1. Also, during the period [ _t11 , _t12 ], no deterioration in the communication state (occurrence of radio wave interference) occurs (communication OK).

In the next period [ _t12 , _t13 ], the communication state of the preamble P1 that is set for use deteriorates. At this time, the communication device 10 determines that the communication state has deteriorated (communication NG) based on the data reception state and the surrounding communication state (of other communication systems), and changes the preamble to be used to the preamble P2. This enables the communication device 10 to receive communication using the preamble P2.

The communication device 10 waits for a predetermined waiting period [t13, t14] without transmitting communication using preamble P2. This waiting is performed to absorb differences in the timing of the switching operation to preamble P2 in the communication device (20) of the communication partner that performs a similar operation. Note that this waiting time is set to a time that can adequately absorb differences in the timing of the switching operation to preamble P2.

Then, after the transmission waiting period [t13, t14] has elapsed, the communication device 10 communicates (transmits) using preamble P2 in response to the transmission request. After that, the communication device 10 changes (returns) the preamble to be used to preamble P1 at t15, a predetermined recovery time after preamble switching timing t13 has elapsed. Note that if the timing for changing the preamble occurs during communication, the communication device 10 waits until the communication ends before changing the preamble. The recovery time is the time when it is expected that the deterioration of the communication situation will be resolved, and is, for example, a time set by a designer or the like through experiments, etc.

The communication device 10 may also determine from the surrounding communication conditions that the deterioration of the communication situation has been resolved, and change the preamble with an appropriate margin of time after that determination.

When transmitting communication using preamble P1, communication device 10 waits for a predetermined waiting period [t15, t16] without transmitting. This waiting is performed to absorb differences in the timing of the switching operation to preamble P2 in the communication device (20) of the other communication partner, which performs a similar operation. Note that this waiting time is set to a time that can adequately absorb differences in the timing of the switching operation to preamble P2.

Then, after the transmission waiting period [t15, t16] has elapsed, the communication device 10 performs communication (transmission) using the preamble P1 in response to the transmission request. Thereafter, UWB wireless communication is performed with the preamble appropriately changed according to the communication state in the same manner as the above operation.

Next, the process executed by the control unit 13 to realize the above-mentioned operation will be described. Figure 7 shows the preamble change process executed by the control unit 13, which is executed when the communication device 10 is started up (based on the user turning on the power, etc.). The control unit 13 also executes a separate data transmission process as appropriate, and transmits the data to be transmitted using the preamble set in the preamble change process. Also, each preamble (selectable preamble) is a preamble of the preamble type shown in Figure 5 (the larger the value n of preamble Pn, the longer the preamble length).

In step S101, the control unit 13 sets the parameter n that specifies the preamble to be used to 1 (the parameter corresponding to the shortest selectable preamble), and proceeds to step S102. In step S102, the control unit 13 enables transmission and reception using the preamble Pn (P1) (permits execution of transmission and reception), and proceeds to step S103. As a result, the communication device 10 communicates using the preamble Pn (P1) in response to transmissions from other communication devices 20 and transmission requests from its own device. Note that the other communication devices 20 also communicate using the preamble P1 immediately after power is turned on through similar processing.

In step S103, the control unit 13 determines whether the communication situation has deteriorated. If the communication situation has deteriorated, the process proceeds to step S104. If the communication situation has not deteriorated, the process proceeds to step S109. Note that in step S103, if the preamble being used is preamble P1, the process does not proceed to step S109 but returns to step S103 to continue determining whether the communication situation has deteriorated.

In step S104, the control unit 13 sets transmission to be prohibited, and the process proceeds to step S105. Until transmission is permitted by this process, the communication device 10 cannot transmit. In step S105, the control unit 13 adds 1 to the parameter n of the preamble to be used, and the process proceeds to step S106. In step S106, the control unit 13 enables reception with preamble Pn (the first preamble change after startup will result in preamble P2) (maintaining transmission prohibited), and the process proceeds to step S107.

In step S107, the control unit 13 determines whether a predetermined waiting time has elapsed since the preamble Pn was changed, or whether a communication addressed to the control unit 13 has been detected using the changed preamble Pn. If the waiting time has elapsed or a communication addressed to the control unit 13 has been detected using the changed preamble Pn, the control unit 13 proceeds to step S108; otherwise (before the waiting time has elapsed and a communication addressed to the control unit 13 has not been detected using the changed preamble Pn), the control unit 13 returns to step S107 and continues the determination process of step S107. In step S108, the control unit 13 enables (permits) transmission using the changed preamble Pn, and proceeds to step S103.

In step S109, the control unit 13 determines whether a predetermined recovery time has elapsed since the change of the preamble Pn, and if so, proceeds to step S110, otherwise proceeds to step S111. In step S110, the control unit 13 changes the parameter n of the preamble to be used to 1 and returns to step S106.

In step S111, the control unit 13 determines whether the parameter n of the preamble Pn has reached its upper limit, that is, the parameter n for the upper limit (longest) preamble Pn that can be set (5 in the table in FIG. 5), and if it has reached the upper limit, the process returns to step S109; if it has not reached the upper limit, the process returns to step S103.

In addition, in step S109, the control unit 13 may determine whether the communication state has improved based on the surrounding communication conditions, and if it has improved, proceed to step S110, and if it has not improved, proceed to step S111. In this case, when an improvement in the communication state is detected, the preamble is changed to the shortest one (returning to the initial state).

Next, we will explain a typical example of the communication state in the above process. Figure 8 is a state transition time chart showing an example of the UWB wireless communication state.

In this example, the communication state of preamble P1 is poor during period [tb1, tb3], the communication state of preamble P2 is poor during period [tb2, tb3], and the communication state of preamble P3 is good for the entire period shown.

The communication device 10 starts up at time t0 (starts up in response to the user's power operation, etc.), and at time t3, the initial setting process ends and transmission and reception begins using preamble P1. The communication device 20 starts up at time t2 (starts up in response to the user's power operation, etc.), and at time t4, the initial setting process ends and transmission and reception begins using preamble P1. As a result, from time t4 onwards, communication device 10 and communication device 20 transmit and receive using preamble P1.

When the state of communication using preamble P1 deteriorates at time tb1, communication device 10 determines that the state of communication has deteriorated because it cannot receive a response signal from communication device 20, and changes to communication using preamble P2 at time t5 (after the time required for processing has elapsed). Note that communication device 10 performs a receiving operation using preamble P2 at time t5, but a transmitting operation using preamble P2 is prohibited. Then, at time t8, when a waiting period has elapsed from time t5, communication device 10 becomes capable of transmitting using preamble P2 (permitted state).

On the other hand, communication device 20 determines that the communication state has deteriorated because it cannot receive a response signal from communication device 10 (time t6), and changes to communication using preamble P2 at time t7 (after the time required for processing has elapsed). Note that communication device 20 performs reception operations using preamble P2 at time t7, but transmission operations using preamble P2 are prohibited. Then, at time t9, when a standby period has elapsed from time t7, communication device 20 becomes capable of transmission operations using preamble P2 (permitted state).

Then, communication device 10 and communication device 20, which are now both capable of communication (transmission and reception) using preamble P2, transmit and receive using preamble P2 as appropriate (from time t9).

When the state of communication using preamble P2 deteriorates at time tb2, communication device 20 determines that the communication state has deteriorated because it cannot receive a response signal from communication device 10, and changes to communication using preamble P3 at time t10. Note that communication device 20 performs reception operation using preamble P3 at time t10, but transmission operation using preamble P3 is prohibited. Then, at time t13, when a standby period has elapsed from time t10, communication device 20 becomes capable of transmission operation using preamble P3 (permitted state).

On the other hand, communication device 10 determines that the communication conditions have deteriorated because it cannot receive a response signal from communication device 20 (time t11), and changes to communication using preamble P3 at time t12. Note that communication device 10 performs reception operations using preamble P3 at time t12, but transmission operations using preamble P3 are prohibited. Then, typically, at time t17, when a standby period has elapsed from time t12, communication device 10 becomes capable of transmission operations using preamble P3 (permitted state).

However, in this example, at time t13, communication device 20, which is permitted to transmit and receive using preamble P3, transmits preamble P3 to communication device 10. Communication device 10, which is permitted to receive preamble P3 at time t13, detects the reception of a transmission using preamble P3 from communication device 20 at time t14, and based on this detection, communication device 20 becomes permitted to transmit using preamble P3 at time t15.

Then, communication device 10 and communication device 20, which are now both capable of communication (transmission and reception) using preamble P3, transmit and receive using preamble P3 as appropriate (from time t15).

After changing to communication using preamble P3, when the communication using preamble P3 continues to be good for a recovery period, in this example, communication device 20 changes to communication using preamble P1 at time t18, and communication device 10 changes to communication using preamble P1 at time t19. Note that communication device 20 performs reception operation using preamble P1 at time t18, but transmission operation using preamble P1 is prohibited. Then, at time t20, when a standby period has elapsed since time t18, communication device 20 becomes capable of transmission operation using preamble P1 (permitted state). Also, communication device 10 performs reception operation using preamble P1 at time t19, but transmission operation using preamble P1 is prohibited. Then, at time t21, when a standby period has elapsed since time t19, communication device 10 becomes capable of transmission operation using preamble P1 (permitted state).

Then, communication device 10 and communication device 20, which are now both capable of communication (transmission and reception) using preamble P1, transmit and receive using preamble P1 as appropriate (from time t21). After that, communication will be performed as appropriate using preambles according to the communication state.

In this way, in the first embodiment, the communication devices (10, 20) can independently change the preamble used in communication, that is, regardless of the operating state of the communication device of the communication partner, which has the advantage that the preamble change process is relatively simple. In addition, since there is no need to check the operating state of the communication device of the communication partner, the amount of communication can be reduced.

[Second embodiment]
In the first embodiment described above, the communication device 10 and the communication device 20 each independently switch preambles, so there is a period in which the preambles do not match, causing a preamble mismatch. Since communication during this period would cause communication problems, the communication device 10 and the communication device 20 are provided with a waiting period to match the preambles. Therefore, in the first embodiment, there is a problem that communication efficiency decreases due to this waiting period.

In the second embodiment, the communication device 10 and the communication device 20 aim to shorten the preamble mismatch period and suppress the decrease in communication efficiency.

Therefore, in the second embodiment, when a communication device 10 changes the preamble used for communication, it transmits to the communication device (20) of the communication partner information indicating that the preamble used for communication will be changed and information specifying the type of preamble to be changed. Then, when the communication device (20) of the communication partner receives this preamble change information, it changes the preamble it uses for communication to the preamble specified by the preamble change information. Note that when the communication device 20 changes the preamble it uses for communication, the communication device 20 transmits preamble change information to the communication device 10. Then, upon receiving the preamble change information, the communication device 10 changes the preamble it uses for communication to the preamble specified by the preamble change information.

This operation makes it possible to eliminate or reduce the waiting period for matching preambles, preventing a decrease in communication efficiency. Furthermore, since the preamble change information is a small amount of data, repeated communication is easy even in poor communication conditions, and communication is relatively easy to establish.

Next, the process executed by the control unit 13 to realize the above-mentioned operation will be described. Figure 9 shows the preamble change process executed by the control unit 13, which is executed when the communication device 10 is started up (based on the user turning on the power, etc.). The control unit 13 separately executes a data transmission process as appropriate, and transmits the data to be transmitted using the preamble set in the preamble change process. Also, each preamble (selectable preamble) is a preamble of the preamble type shown in Figure 5 (the larger the value n of the preamble Pn, the longer the preamble length).

In step S201, the control unit 13 sets the parameter n that specifies the preamble to be used to 1 (the parameter corresponding to the shortest selectable preamble), and proceeds to step S202. In step S202, the control unit 13 enables transmission and reception using the preamble Pn (P1) (permits execution of transmission and reception), and proceeds to step S203. As a result, the communication device 10 communicates using the preamble Pn (P1) in response to transmissions from other communication devices 20 and transmission requests from its own device. Note that the other communication devices 20 also communicate using the preamble P1 immediately after power is turned on through similar processing.

In step S203, the control unit 13 determines whether the communication conditions have deteriorated. If the communication conditions have deteriorated, the process proceeds to step S204. If the communication conditions have not deteriorated, the process proceeds to step S221.

In step S204, the control unit 13 adds 1 to the parameter n of the preamble to be used and proceeds to step S205. Note that at this point, the preamble to be used for communication has not yet been changed; only the parameter n that specifies the changed preamble has been changed.

In step S205, the control unit 13 transmits preamble change information (e.g., the value of parameter n) that specifies the changed preamble Pn to the communication device (20) of the communication partner, and proceeds to step S206. In step S206, the control unit 13 determines whether a response signal has been received from the communication device (20) of the communication partner, and if so, proceeds to step S207, and if not, returns to step S205 and continues the processing of steps S205 and S206 (continues transmitting the preamble change information).

In step S207, the control unit 13 enables (permits) communication (transmission and reception) with the changed preamble Pn, and proceeds to step S208. The control unit 13 may wait for transmission with the changed preamble Pn, taking into account the time required for the process of changing the preamble used in communication by the communication device (20) of the communication partner. Also, preamble change timing information may be included in the preamble change information, and each communication device (10, 20) may change the preamble based on the change timing information.

In step S208, the control unit 13 determines whether a predetermined recovery time has elapsed since the change of the preamble Pn, and if so, proceeds to step S209, otherwise proceeds to step S210. In step S209, the control unit 13 changes the parameter n of the preamble to be used to 1, and proceeds to step S211.

In step S211, the control unit 13 transmits preamble change information (e.g., the value of parameter n (1)) that identifies the changed preamble Pn (P1) to the communication device (20) of the communication partner, and proceeds to step S212. In step S212, the control unit 13 determines whether a response signal has been received from the communication device (20) of the communication partner, and if so, proceeds to step S202, and if not, returns to step S211 and continues the processing of steps S211 and S212 (continues transmitting the preamble change information).

In step S210, the control unit 13 determines whether the parameter n of the preamble Pn has reached its upper limit, i.e., the parameter n for the upper limit (longest) preamble Pn that can be set (5 in the table in FIG. 5), and if it has reached the upper limit, the process returns to step S208; if it has not reached the upper limit, the process returns to step S203.

In addition, in step S208, the control unit 13 may determine whether the communication state has improved based on the surrounding communication conditions, and if it has improved, proceed to step S209, or if it has not improved, proceed to step S210. In this case, when an improvement in the communication state is detected, the preamble is changed to the shortest one (preamble P1) (returning to the initial state).

In addition, in step S221, the control unit 13 determines whether or not a notification of preamble change information has been received from the other communication device (20), and if so, proceeds to step S222, otherwise proceeds to step S208. Note that if the preamble in use is preamble P1, the control unit 13 returns to step S203 (not shown) if a notification of preamble change information has not been received from the other communication device (20) in step S221. In step S222, the control unit 13 transmits a response signal to the other communication device (20) and proceeds to step S223. In step S223, the control unit 13 changes the parameter n of the preamble to a value based on the received preamble change information, and proceeds to step S224. In step S224, the control unit 13 enables (permits) communication (transmission and reception) with the changed preamble Pn, and proceeds to step S203.

Next, a representative example of the communication state in the above-mentioned process will be described. FIG. 10 is a state transition time chart showing an example of the UWB wireless communication state. Note that both communication device 10 and communication device 20 perform the process shown in FIG. 9 above.

In this example, the communication state of preamble P1 is poor during period [tb1, tb3], the communication state of preamble P2 is poor during period [tb2, tb3], and the communication state of preamble P3 is good for the entire period shown.

The communication device 10 starts up at time t0 (starts up in response to the user's power operation, etc.), and at time t3, the initial setting process ends and transmission and reception begins using the preamble P1. The communication device 20 starts up at time t2 (starts up in response to the user's power operation, etc.), and at time t4, the initial setting process ends and transmission and reception begins using the preamble P1. As a result, from time t4 onwards, the communication device 10 and the communication device 20 transmit and receive using the preamble P1.

When the state of communication using preamble P1 deteriorates at time tb1, communication device 10 determines that the communication state has deteriorated because it cannot receive a response signal from communication device 20, and notifies communication device 20 that it will change to communication using preamble P2. Then, communication device 20, which has received this notification of the change to preamble P2, transmits the response signal to communication device 10 (time t6). Note that it is desirable to repeat the transmission of the notification of the change to preamble P2 and the transmission of the response signal, including the response signal to the response signal, until it is confirmed that the notification of the change to preamble P2 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P2 at time t7 when the transmission of the change notification to preamble P2 is confirmed. After that, communication device 10 and communication device 20, which are both capable of communication (transmission and reception) using preamble P2, appropriately perform transmission and reception using preamble P2 (from time t7).

When the state of communication using preamble P2 deteriorates at time tb2, communication device 20 determines that the communication state has deteriorated because it cannot receive a response signal from communication device 10, and notifies communication device 10 at time t8 that it will change to communication using preamble P3. Then, communication device 10, which has received this notification of the change to preamble P3, transmits a response signal to communication device 20 (time t9). Note that it is desirable to repeat the transmission of this notification of the change to preamble P3 and the transmission of this response signal, including the response signal to the response signal, until it is confirmed that the notification of the change to preamble P3 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P3 at time t10 when the transmission of the change notification to preamble P3 is confirmed. After that, communication device 10 and communication device 20, which are both capable of communication (transmission and reception) using preamble P3, appropriately perform transmission and reception using preamble P3 (from time t10).

After changing to communication using preamble P3, when the period during which communication using preamble P3 is good continues for the recovery period (time t11), in this example, communication device 10 notifies communication device 20 that it will change to communication using preamble P1. Then, communication device 20, having received this notification of the change to preamble P1, transmits a response signal to communication device 10 (time t12). Note that it is desirable to repeat the transmission of the notification of the change to preamble P1 and the transmission of the response signal, including the response signal to the response signal, until it can be confirmed that the notification of the change to preamble P1 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P1 at time t13 when the transmission of the change notification to preamble P1 is confirmed. After that, communication device 10 and communication device 20, which are both able to communicate (transmission and reception) using preamble P1, appropriately perform transmission and reception using preamble P1 (from time t13).

In this way, in the second embodiment, the preamble used in communication is changed based on information communication regarding the preamble change between the communication devices (10, 20), so it is possible to shorten the waiting time required to absorb the time difference in the preamble change, thereby improving communication efficiency.

[Third Example]
In the first and second embodiments, there is a possibility that communication using the changed preamble is subject to radio interference, and therefore the preamble may need to be changed multiple times until good communication is achieved, which may result in a decrease in communication efficiency.

Therefore, in the third embodiment, the communication status of communications using each preamble in the own communication environment is monitored, and the preamble used in the communication with the good communication status is used. Note that in the third embodiment, the shortest preamble is used preferentially among the preambles used in the communication with the good communication status.

Next, the process executed by the control unit 13 to realize the above-mentioned operation will be described. FIG. 11 shows the preamble change process executed by the control unit 13 when the communication device 10 is started up (based on the user turning on the power, etc.). The control unit 13 also executes a separate data transmission process as appropriate, and transmits the data to be transmitted using the preamble set in the preamble change process. Also, each preamble (selectable preamble) is a preamble of the preamble type shown in FIG. 5 (the larger the value n of the preamble Pn, the longer the preamble length).

In step S301, the control unit 13 sets the parameter n that specifies the preamble to be used to 1 (the parameter corresponding to the shortest selectable preamble), and proceeds to step S302. In step S302, the control unit 13 enables transmission and reception using preamble Pn (P1) (permits transmission and reception to be performed), and proceeds to step S303. Note that other communication devices 20 also perform communication using preamble P1 immediately after power is turned on through a similar process. As a result, the communication device 10 communicates using preamble Pn (P1) in response to transmissions from other communication devices 20 and transmission requests from its own device. In addition, the control unit 13 stores the data "selected" (here, "selected" is stored in the data record of the preamble type "preamble P1") as "usage status" data in the data record of the preamble to be used for communication in the preamble table 121. Although the following description is omitted, when the preamble used in communication is changed, the control unit 13 changes the "usage status" data for the preamble used in communication to "selected" and changes the "usage status" data for the other preambles to "not selected."

In step S303, the control unit 13 measures the communication state in the surrounding area, determines the communication state in the communication using each preamble, stores each determination result in the preamble table 121, and proceeds to step S304. Specifically, the control unit 13 performs a reception process using each preamble to determine whether communication using each preamble is taking place. Then, for the preamble used in the detected communication, the control unit 13 stores data of "in use" (poor communication state: interference) as "usage status" data in the data record of the corresponding preamble in the preamble table 121.

In order not to interfere with the communication operation, the control unit 13 does not perform the process of determining the communication state in communication using each of the above-mentioned preambles during data communication, and waits until the communication ends.

In step S304, the control unit 13 uses the "usage status" data in the preamble table 121 to select the preamble Pn with the best communication status ("usage status" is not in use) and the shortest preamble length as the preamble to be used for communication, and proceeds to step S305.

In step S305, the control unit 13 transmits preamble change information (e.g., the value of parameter n) that identifies the selected preamble Pn to the communication device (20) of the communication partner, and proceeds to step S306. In step S306, the control unit 13 determines whether a response signal has been received from the communication device (20) of the communication partner, and if so, proceeds to step S307, and if not, returns to step S305 and continues the processing of steps S305 and S306 (continues transmitting the preamble change information).

In step S307, the control unit 13 enables (permits) communication (transmission and reception) using the changed preamble Pn, and proceeds to step S308. The control unit 13 may wait for transmission using the changed preamble Pn, taking into account the time required for the process of changing the preamble used in communication by the communication device (20) of the communication partner. Also, preamble change timing information may be included in the preamble change information, and each communication device (10, 20) may change the preamble based on the change timing information.

In step S308, the control unit 13 determines whether a predetermined reselection time has elapsed since the selection process of the preamble Pn (step S304 or step S313), and if so, returns to step S303, and if not, proceeds to step S309. In other words, the process of step S308 suppresses preamble changes at short intervals when communication is possible, and stabilizes communication. In step S309, the control unit 13 checks the communication status of the currently used preamble Pn based on the communication establishment status and communication data decoding status, and if the communication status has deteriorated, returns to step S303, and if not, proceeds to step S310. In other words, the process of step S308 makes it possible to quickly respond to a deterioration in the communication status.

In addition, in step S310, the control unit 13 determines whether it has received notification of preamble change information from the other communication device (20), and if it has received it, proceeds to step S311, and if it has not received it, proceeds to step S308. In step S311, the control unit 13 transmits a response signal to the other communication device (20) and proceeds to step S312. In step S312, the control unit 13 changes the preamble parameter n to a value based on the received preamble change information, and proceeds to step S313. In step S313, the control unit 13 enables (permits) communication (transmission and reception) using the changed preamble Pn, and proceeds to step S308.

Next, a representative example of the communication state in the above-mentioned process will be described. FIG. 12 is a state transition time chart showing an example of the UWB wireless communication state. Note that both communication device 10 and communication device 20 perform the process shown in FIG. 11 above.

In this example, the communication state of preamble P1 is poor during periods other than period [t0, tb1], the communication state of preamble P2 is poor during period [tb2, tb3], and the communication state of preamble P3 is good during the entire period shown.

The communication device 10 starts up at time t0 (starts up in response to the user's power operation, etc.), and at time t3, the initial setting process ends and transmission and reception begins using preamble P1. The communication device 20 starts up at time t2 (starts up in response to the user's power operation, etc.), and at time t4, the initial setting process ends and transmission and reception begins using preamble P1. As a result, from time t4 onwards, the communication devices 10 and 20 transmit and receive using preamble P1. The communication devices 10 and 20 also detect the communication status (presence or absence, etc.) using each preamble in the vicinity at appropriate time intervals (communication status detection intervals appropriate for control to ensure good communication, determined by experiments, etc.) during periods other than when communication is in progress, and store the detected status in the preamble table 121.

When the communication conditions (radio wave conditions) change at time tb1 (determined from the data in preamble table 121), communication device 10 selects preamble P2, which has the shortest preamble length among the preambles not used in surrounding communications. Communication device 10 then notifies communication device 20 that it will change to communications using the selected preamble P2 (time t5). Communication device 20 then receives this notification of the change to preamble P2 and transmits a response signal to communication device 10 (time t6). Note that it is desirable to repeat the transmission of the notification of the change to preamble P2 and the transmission of the response signal, including the response signal to the response signal, until it is confirmed that the notification of the change to preamble P2 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P2 at time t7 when the transmission of the change notification to preamble P2 is confirmed. After that, communication device 10 and communication device 20, which are both able to communicate (transmission and reception) using preamble P2, appropriately perform transmission and reception using preamble P2 (from time t7).

When the communication conditions (radio wave conditions) change at time tb2 (determined from the data in preamble table 121), communication device 20 selects preamble P3, which has the shortest preamble length among the preambles not used in surrounding communications. Communication device 20 then notifies communication device 10 that it will change to communications using the selected preamble P3 (time t8). Communication device 10 then receives this notification of the change to preamble P3 and transmits a response signal to communication device 20 (time t9). Note that it is desirable to repeatedly transmit the notification of the change to preamble P3 and the response signal, including the response signal to the response signal, until it is confirmed that the notification of the change to preamble P3 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P3 at time t10 when the transmission of the change notification to preamble P3 is confirmed. After that, communication device 10 and communication device 20, which are both capable of communication (transmission and reception) using preamble P3, appropriately perform transmission and reception using preamble P3 (from time t10).

When the communication conditions (radio wave conditions) change at time tb3 (determined from the data in preamble table 121), communication device 10 selects preamble P2, which has the shortest preamble length among the preambles not used in surrounding communications (communication using preamble P1 has not improved and is not selected). Then, communication device 10 notifies communication device 20 that it will change to communication using the selected preamble P2 (time t11). Then, communication device 20, which has received this notification of the change to preamble P2, transmits a response signal to communication device 10 (time t12). Note that it is desirable to repeatedly transmit the notification of the change to preamble P2 and the response signal, including the response signal to the response signal, until it is confirmed that the notification of the change to preamble P2 has been reliably transmitted.

Then, communication device 10 and communication device 20 switch to communication (transmission and reception) using preamble P2 at time t13 when the transmission of the change notification to preamble P2 is confirmed. After that, communication device 10 and communication device 20, which are both able to communicate (transmission and reception) using preamble P2, appropriately perform transmission and reception using preamble P2 (from time t13).

In this way, in the third embodiment, the communication conditions around the communication devices (10, 20) are monitored, and the preamble used for communication is changed to an appropriate preamble according to the communication conditions, so that communication after the preamble change can be reliably good, communication can be quickly established, and communication efficiency can be improved.

In the third embodiment, the communication device 10 selects the shortest preamble among preambles not used in surrounding communications to communicate, but it is also effective to select the preamble (the shortest preamble among them) that is least frequently used in surrounding communications (measured in the most recent period of a predetermined time length) to communicate.

For example, consider a case where the measurement results of the surrounding communication conditions show that in the last minute, preamble P2 has been used 100 times by other systems in communication, preamble P3 has been used 10 times by other systems, and preamble P4 has been used 50 times by other systems. In this case, the communication device 10 switches to preamble P3, which is the least frequently used by other systems among preamble P2, preamble P3, and preamble P4.

Another effective method is to calculate an evaluation value based on a predetermined evaluation formula (created based on experiments, etc.) using the frequency of use in surrounding communications and the preamble length, and then select the preamble with the best evaluation value (e.g., the maximum value) to carry out communication.

In addition, if there is no preamble that is not being used in surrounding communications, the communication device 10 can effectively communicate without changing the preamble, or, as described above, can select a preamble based on the frequency of use in surrounding communications, or on the frequency of use in surrounding communications and the preamble length, and then communicate.

Further advantages and modifications may readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and equivalents thereof.

V1, V2 Vehicle 1 Communication system 10, 20 Communication device 11 Communication unit 12 Storage unit 13 Control unit 121 Preamble table 131 Determination unit 132 Change unit

Claims (15)

A controller for controlling wireless communication by the UWB communication method,
The controller:
Estimate the surrounding communication conditions,
The communication device changes a preamble length used in wireless communication according to the estimated communication state. The communication status is a communication status of the communication of the own communication,
The controller:
The communication device according to claim 1 , wherein the communication device changes the preamble length when a communication condition in the communication device deteriorates. The communication status is a preamble usage status in a communication being performed in the detected surroundings,
The controller:
The communication device according to claim 1 , further comprising: determining a preamble length to be used based on the detected preamble usage status; and changing the preamble length to the determined preamble length to be used. The controller:
The communication device according to claim 3 , further comprising: determining a preamble length to be used from among preamble lengths of preambles not used in the detected communication, based on the detected preamble usage status. The controller:
The communication device according to claim 3 , further comprising: a determining unit for determining a preamble length to be used based on a frequency of use of preambles of each preamble length, based on the detected preamble use status. The controller:
The communication device according to claim 3 , further comprising: a detection unit configured to detect a preamble usage status in ongoing communication in the vicinity during a period when wireless communication is not being performed. The controller:
The communication device according to claim 1 , wherein the preamble length to be used is determined to be the shortest preamble length among available preamble lengths and is longer than the preamble length of a preamble currently being used. The communication device according to claim 1 , wherein the controller changes the preamble length to an initial setting length that is an initially set preamble length after a predetermined time has elapsed after the controller changes the used preamble length. The controller:
The communication device according to claim 3 , wherein, after changing the preamble length in use, if a communication situation using a preamble with a preamble length shorter than the preamble length of the preamble in use is good, the preamble length in use is changed to a preamble length for communication in good communication situation. The controller:
Transmitting preamble change information regarding the change in the preamble length to a communication target device that is a wireless communication destination;
The communication device according to claim 1, wherein the communication device starts communication using a preamble of the changed preamble length after a predetermined period of time has elapsed after transmitting the preamble modification information, or after receiving a response signal from the communication target device to the transmission of the preamble modification information. The preamble change information includes information on a timing to start communication using a preamble having a changed preamble length,
The controller:
The communication device according to claim 10 , wherein the communication device starts communication using a preamble having a changed preamble length based on the timing information. The controller:
The communication device according to claim 10 , wherein the preamble length is changed based on preamble change information from the target device. A communication system including a first communication device and a second communication device that perform wireless communication by an UWB communication system,
The first communication device is
Estimating a communication status between the second communication device and the
changing a preamble length used in wireless communication with the second communication device according to the estimated communication state;
The second communication device is
Estimating a communication status with the first communication device;
changing a preamble length used in wireless communication with the first communication device according to the estimated communication state;
Communications system. the first communication device starts wireless communication using a preamble having the changed preamble length after a predetermined waiting time has elapsed after changing the preamble length used;
the second communication device starts wireless communication using a preamble having the changed preamble length after a predetermined waiting time has elapsed after changing the preamble length used;
14. The communication system of claim 13. The first communication device is
When changing the preamble length to be used, transmitting preamble change information regarding the change in the preamble length to the second communication device through wireless communication using a preamble having the preamble length before the change;
The second communication device is
receiving preamble modification information transmitted from the first communication device;
changing the preamble length used based on the received preamble change information;
14. The communication system of claim 13.

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