JP7678770B2 - Communication Systems - Google Patents

Description

The technology disclosed in this specification relates to communication technology.

In communication systems that realize multiplexing by carrier sense, such as wireless LAN (Local Area Network), a "hidden terminal problem" is known in which multiple slave devices that cannot sense (detect) each other's signal transmissions transmit signals simultaneously, causing the signals to collide at the master station (i.e., the signals interfere), preventing the master station from receiving the signals.

The IEEE 802.11 standard, a representative standard for wireless LANs, takes measures to avoid signal interference by using control signals to set up transmission-prohibited zones. However, while this measure works as a mechanism to avoid signal interference when a common communication method is used, it does not work when different communication methods are used in the same frequency band, and signal transmissions from multiple child devices end up interfering with each other.

In response to this, for example, Patent Document 1 discloses a method for avoiding signal interference when a cellular system uses the same frequency band as a wireless LAN as a different communication method, by incorporating a control signal compatible with the wireless LAN into the later cellular system and adding the control signal to the transmission signal of the cellular system.

International Publication No. 2015/141292

However, in the method shown in Patent Document 1, if other slave units are unable to receive the control signal due to reasons such as differences in the signal strength that can be received for each communication method, multiple slave units may transmit signals simultaneously, which may result in interference between the signals.

As shown in Patent Document 1, when a communication device that transmits a signal takes measures to avoid signal interference and employs a method such as incorporating a control signal into the signal to be transmitted, the control signal will not function in the other communication device that cannot receive the transmitted signal with the control signal incorporated, and signal transmission will begin. This may result in signal interference in the parent unit.

The technology disclosed in this specification was developed in consideration of the problems described above, and is a technology for suppressing signal interference when signals are transmitted and received using multiple communication methods.

A communication system according to a first aspect of the technology disclosed in the present specification includes at least a first communication device and a second communication device as multiple communication devices, and transmits and receives signals between the first communication device and the second communication device using a first communication method that requires carrier sensing and a second communication method that requires carrier sensing and is different from the first communication method. When the first communication device starts receiving a signal using the first communication method, the first communication device transmits a dummy signal using the second communication method, and the second communication device that receives the dummy signal using the second communication method does not start transmitting a signal to the first communication device using the second communication method.

According to at least the first aspect of the technology disclosed in the present specification, when signals are transmitted and received using multiple communication methods, when signal reception starts using one communication method, a dummy signal is transmitted using the other communication method, and control is performed so that signal transmission does not start using the other communication method, thereby suppressing interference between signals.

Furthermore, the objects, features, aspects and advantages associated with the technology disclosed in the present specification will become more apparent from the detailed description and accompanying drawings set forth below.

FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. 2 is a diagram illustrating an example of the configuration of a communication device corresponding to a terminal 1. FIG. 2 is a diagram illustrating an example of the configuration of a communication device corresponding to a terminal 2. FIG. 2 is a diagram illustrating an example of the configuration of a communication device corresponding to terminal 3. FIG. 4 is a timing chart showing communication timings of each terminal of the communication system according to the embodiment; FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. 10 is a flowchart for determining whether or not a dummy signal needs to be transmitted in the communication system according to the embodiment. FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. 10 is a flowchart for determining a transmission timing of a dummy signal in a communication system according to an embodiment.

The following describes the embodiments with reference to the attached drawings. In the following embodiments, detailed features are shown to explain the technology, but these are merely examples and are not necessarily all essential features for the embodiments to be feasible.

The drawings are schematic, and for ease of explanation, configurations may be omitted or simplified as appropriate. Furthermore, the size and positional relationships of the configurations shown in different drawings are not necessarily described accurately, and may be changed as appropriate. Furthermore, hatching may be used in drawings that are not cross-sectional views, such as plan views, to make it easier to understand the contents of the embodiments.

In addition, in the following description, similar components are illustrated with the same reference symbols, and their names and functions are also similar. Therefore, detailed descriptions of them may be omitted to avoid duplication.

In addition, in the description of this specification, when a certain component is described as "comprising," "including," or "having," unless otherwise specified, this is not an exclusive expression that excludes the presence of other components.

In addition, even if ordinal numbers such as "first" or "second" are used in the description of this specification, these terms are used for convenience to facilitate understanding of the contents of the embodiments, and the contents of the embodiments are not limited to the order that may result from these ordinal numbers.

First Embodiment
A communication system according to this embodiment will be described below.

<Communication system configuration>
1 is a diagram illustrating an example of the configuration of a communication system according to the present embodiment. As illustrated in the example of FIG. 1, the communication system includes a terminal 1, a terminal 2, and a terminal 3.

Terminal 1 is a communication device that transmits and receives data using two communication methods: communication method A that supports carrier sensing (i.e., requires carrier sensing) and communication method B that also supports carrier sensing. Terminal 2 is a communication device that communicates with terminal 1 using communication method A. Terminal 3 is a communication device that communicates with terminal 1 using communication method B.

Terminal 2 may or may not support communication method B, but terminal 3 supports only communication method B, and terminal 3 cannot receive signals transmitted by terminal 2 using communication method A.

Figure 2 is a diagram that shows a schematic example of the configuration of a communication device 101 that corresponds to terminal 1. As shown in the example in Figure 2, communication device 101 includes a modulation/demodulation unit 102, which is a modulation/demodulation circuit capable of modulation and demodulation corresponding to communication method A and communication method B, and a signal processing unit 103 that can communicate with modulation/demodulation unit 102 via communication path 104 and processes signals received by communication device 101. An example of signal processing unit 103 is a microcontroller (micro controller unit, or MCU) that calculates and records signals.

Fig. 3 is a diagram showing an example of the configuration of a communication device 201 corresponding to terminal 2. As shown in the example in Fig. 3, communication device 201 includes a modulation/demodulation unit 202 capable of modulation and demodulation corresponding to only communication method A or to communication methods A and B, and a signal processing unit 203 capable of communicating with modulation/demodulation unit 202 via communication path 204 and processing signals received by communication device 201. An example of signal processing unit 203 is an MCU.

Fig. 4 is a diagram showing an example of the configuration of a communication device 301 corresponding to terminal 3. As shown in the example in Fig. 4, communication device 301 includes a modulation/demodulation unit 302 capable of modulation and demodulation corresponding only to communication method B, and a signal processing unit 303 that can communicate with modulation/demodulation unit 302 via communication path 304 and processes signals received by communication device 301. An example of signal processing unit 303 is an MCU.

<Operation of the communication system>
Next, the operation of the communication system according to this embodiment will be described. Fig. 5 is a timing chart showing the communication timing of each terminal of the communication system according to this embodiment. Note that this timing chart applies when the signal of communication method A received by terminal 1 is equal to or lower than the carrier sense level, and does not apply when the signal of communication method A received by terminal 1 is higher than the carrier sense level.

First, in step ST21, terminal 2 starts transmitting a preamble using communication method A. Specifically, signal processing unit 203 in FIG. 3 instructs modem unit 202 to modulate the signal via communication path 204.

Then, in step ST22, terminal 1 detects the preamble transmitted by communication method A. Specifically, the modem unit 102 in FIG. 2 demodulates the received signal, and further inputs the signal to the signal processing unit 103 via the communication path 104.

Then, in step ST23, terminal 1 stops receiving the preamble in communication method A. Specifically, signal processing unit 103 in FIG. 2 controls the reception of signals via communication path 104.

Furthermore, in step ST24, transmission of a preamble as a dummy signal is started in communication method B. Specifically, the signal processing unit 103 in FIG. 2 controls the transmission of the signal via the communication path 104.

In step ST25, upon receiving the preamble in communication method B, terminal 3 uses the carrier sense function to not transmit a signal. Specifically, the modem unit 302 in FIG. 4 demodulates the received signal, and the signal is input to the signal processing unit 303 via the communication path 304, thereby controlling not to transmit a signal.

Then, in step ST26, terminal 1 stops transmitting the preamble in communication method B. Specifically, the signal processing unit 103 in FIG. 2 controls the transmission of the signal via communication path 104.

Then, in step ST27, terminal 1 resumes receiving the preamble using communication method A. Specifically, the signal processing unit 103 in FIG. 2 controls the reception of the signal via communication path 104.

After that, in step ST28, terminal 2 starts transmitting the sync word in communication method A. Specifically, the signal processing unit 203 in FIG. 3 controls the transmission of the signal via communication path 204.

Then, in step ST29, terminal 1 receives the sync word using communication method A, and continues receiving signals such as the payload. Specifically, the modem unit 102 in FIG. 2 demodulates the received signal, and inputs the signal to the signal processing unit 103 via the communication path 104. The preamble transmission period in communication method A in terminal 2 is determined taking into account the preamble transmission period as a dummy signal in communication method B in terminal 1.

In this embodiment, a communication method such as Gaussian frequency-shift keying (GFSK) is assumed, and a case is described in which terminal 1 starts transmitting a preamble in communication method B upon detection of a preamble in communication method A, but similar processing can also be performed in the STF (Short Training Field) in a communication method such as orthogonal frequency division multiplexing (OFDM).

As described above, even in an environment where terminal 3 cannot detect the signal of communication method A transmitted from terminal 2, terminal 3 can detect the signal of communication method B transmitted from terminal 1 and appropriately prohibit terminal 3 from starting to transmit the signal of communication method B to terminal 1, thereby reducing the probability that the signal of communication method B transmitted from terminal 3 and the signal of communication method A transmitted from terminal 2 will interfere with each other at terminal 1.

Second Embodiment
A communication system according to the present embodiment will be described. In the following description, components similar to those described in the above embodiment are illustrated with the same reference numerals, and detailed description thereof will be omitted as appropriate.

<Communication system configuration>
In the first embodiment, it is assumed that the terminal 1 always transmits a preamble as a dummy signal. However, if a transmission time for the preamble as a dummy signal is secured, the throughput of the entire communication system may decrease.

Meanwhile, FIG. 1 shows a case where terminal 3 is provided that communicates with terminal 1 using communication method B, but as shown in an example in FIG. 6, a communication system may also be configured with only terminal 1, which is a communication device that transmits and receives using two communication methods, communication method A corresponding to carrier sense and communication method B corresponding to carrier sense, and terminal 2, which is a communication device that communicates with terminal 1 using communication method A. Note that FIG. 6 is a diagram that shows a schematic example of the configuration of a communication system related to this embodiment.

In this case, no interference will occur between terminal 1 and terminal 2 even if a preamble as a dummy signal is not transmitted, so in preparation for possible signal interference, terminal 1 is provided with a function to monitor the signal reception status in communication method B and determine whether or not it is necessary to transmit a preamble as a dummy signal.

<Operation of the communication system>
Next, the operation of the communication system according to this embodiment will be described below: Fig. 7 is a flow chart showing the process of determining whether or not the dummy signal needs to be transmitted in the communication system according to this embodiment.

When terminal 1 determines whether a dummy signal is required (step ST41), in step ST42, terminal 1 determines whether reception has occurred via communication method B within a certain period of time.

If reception occurs via communication method B within a certain period of time, i.e., if this corresponds to "YES" branching from step ST42, an example of which is shown in FIG. 7, the process proceeds to step ST43, an example of which is shown in FIG. 7. On the other hand, if reception does not occur via communication method B within a certain period of time, i.e., if this corresponds to "NO" branching from step ST42, an example of which is shown in FIG. 7, the process proceeds to step ST44, an example of which is shown in FIG. 7.

In step ST43, it is necessary to transmit a dummy signal from terminal 1. Therefore, terminal 1 notifies terminal 2 that it is necessary to determine the transmission period of the preamble in communication method A, taking into account the transmission period of the dummy signal in communication method B. Then, the process proceeds to step ST45 and ends.

In step ST44, there is no need to transmit a dummy signal from terminal 1. Therefore, terminal 1 notifies terminal 2 that it may determine the transmission period of the preamble in communication method A without taking into account the transmission period of the dummy signal in communication method B. Then, the process proceeds to step ST45 and ends.

As explained above, by configuring terminal 1 not to transmit a dummy signal when there is no terminal communicating using communication method B, it is possible to improve the throughput of the entire communication system when no interference is occurring.

Third Embodiment
A communication system according to the present embodiment will be described. In the following description, components similar to those described in the above embodiment are illustrated with the same reference numerals, and detailed description thereof will be omitted as appropriate.

<Communication system configuration>
In the first embodiment, the case where the communication device that communicates with the terminal 2 using the communication method A is the terminal 1 alone has been shown, but as shown in the example in Fig. 8, in addition to the terminal 1 that is a communication device that transmits and receives using two types of communication methods, the communication method A corresponding to carrier sense and the communication method B corresponding to carrier sense, the terminal 2 that is a communication device that communicates with the terminal 1 using the communication method A, and the terminal 3 that is a communication device that communicates with the terminal 1 using the communication method B, a case can also be considered in which a terminal 4 that transmits and receives using two types of communication methods, the communication method A corresponding to carrier sense and the communication method B corresponding to carrier sense, and communicates with the terminal 2 using the communication method A is provided. Note that Fig. 8 is a diagram that shows an example of the configuration of a communication system according to this embodiment.

In this case, if terminal 1 receives the signal (preamble) transmitted by terminal 2 to terminal 4 using communication method A before terminal 4 does, and terminal 1 starts transmitting the preamble as a dummy signal using communication method B, the transmission of the preamble as a dummy signal from terminal 1 using communication method B and the transmission of the signal (preamble) from terminal 2 using communication method A will interfere with each other at terminal 4. To avoid this, in this embodiment, terminal 1 monitors the reception status of the signal using communication method A and determines the timing of transmitting the preamble as a dummy signal.

<Operation of the communication system>
Next, the operation of the communication system according to this embodiment will be described with reference to Fig. 9, which is a flow chart showing the process of determining the transmission timing of a dummy signal in the communication system according to this embodiment.

When terminal 1 determines the timing of transmitting a dummy signal (step ST61), in step ST62 terminal 1 searches for whether there is a terminal in the vicinity that can communicate using communication method A within a certain period of time. Specifically, the modem unit 102 in FIG. 2 is maintained in a state in which it can receive a signal transmitted using communication method A for a certain period of time, and it is determined whether a signal transmitted using communication method A is received.

If there is a nearby terminal capable of communication using communication method A within the certain period of time, i.e., if the result corresponds to "YES" branching from step ST62 shown in FIG. 9, the process proceeds to step ST63 shown in FIG. 9. On the other hand, if there is no nearby terminal capable of communication using communication method A within the certain period of time, i.e., if the result corresponds to "NO" branching from step ST62 shown in FIG. 9, the process proceeds to step ST64 shown in FIG. 9.

In step ST63, terminal 1 stores information about the following operations. Specifically, after terminal 1 detects a preamble in communication method A, it stops receiving the preamble in communication method A. Furthermore, after a random time has elapsed, terminal 1 transmits a preamble as a dummy signal in communication method B. Then, it proceeds to step ST65 and ends the process.

The random time here is a time of any length that can be set by a user or the like. The random time is, for example, a time for preventing a dummy signal from terminal 1 from being received by terminal 4 at the timing when a signal transmitted from terminal 2 to terminal 4 is received by terminal 4 (i.e., a time for shifting the timing when the dummy signal is received), and can be a time that is determined in advance based on the positional relationship between the terminals, etc. The random time may be a fixed time, or a variable time that is arbitrarily set each time step ST63 is performed.

In step ST64, terminal 1 stores information about the following operations. Specifically, after terminal 1 detects a preamble in communication method A, it stops receiving the preamble in communication method A. Furthermore, without waiting for the random time to elapse, terminal 1 transmits a preamble as a dummy signal in communication method B. Then, it proceeds to step ST65 and ends the process.

The above operations may be performed on terminal 4, or on both terminal 1 and terminal 4.

In this embodiment, the case has been described where terminal 1 and terminal 4 do not cooperate and wait for a random time to elapse before transmitting a preamble as a dummy signal using communication method B. However, it is also possible for terminal 1 and terminal 4 to cooperate, with one transmitting a preamble as a dummy signal using communication method B and the other not transmitting a preamble as a dummy signal.

As described above, when there are multiple terminals capable of communicating using communication method A and communication method B, signal interference can be suppressed by changing (delaying) the transmission timing of the preamble as a dummy signal.

When the timing of transmitting the dummy signal is delayed by a random time, as shown in the example of the first embodiment, the preamble transmission period in the communication method A in the terminal 2 is determined taking into consideration that the preamble transmission period is extended by the random time.

An example of the use of the above-described embodiment is a machine-to-machine (M2M) network in which multiple communication methods with different reception sensitivity points coexist, where communication method A has a lower reception sensitivity point than communication method B for the purpose of long-distance transmission, and a communication device that transmits and receives signals only using communication method B cannot detect the presence of signal transmission and reception using communication method A. According to the above-described embodiment, it is possible to avoid the hidden terminal problem and continue communication in such a network.

<Effects of the above-described embodiment>
Next, examples of effects produced by the above-described embodiments are shown. In the following description, the effects are described based on the specific configurations shown as examples in the above-described embodiments, but they may be replaced with other specific configurations shown as examples in the present specification as long as the same effects are produced. In other words, for convenience, only one of the corresponding specific configurations may be described as a representative below, but the representatively described specific configuration may be replaced with another corresponding specific configuration.

The replacement may also be made across multiple embodiments. That is, configurations shown as examples in different embodiments may be combined to produce the same effect.

According to the embodiment described above, in the communication system, when the first communication device starts receiving a signal in the first communication method, the first communication device transmits a dummy signal in the second communication method. Here, the first communication device corresponds to, for example, terminal 1. The first communication method corresponds to, for example, communication method A. The second communication method corresponds to, for example, communication method B. The second communication device that receives the dummy signal in communication method B does not start transmitting a signal in communication method B to terminal 1. Here, the second communication device corresponds to, for example, terminal 3.

According to this configuration, when signals are transmitted and received using multiple communication methods, when signal reception begins using one communication method, a dummy signal is transmitted using the other communication method, and control is performed so that signal transmission does not begin using the other communication method, thereby suppressing interference between signals. Also, by having the communication device receiving the signal (e.g., terminal 1 in FIG. 1) transmit the dummy signal, rather than the communication device transmitting the signal (e.g., terminal 3 in FIG. 1), the communication device (e.g., terminal 3 in FIG. 1) that may transmit a signal to the communication device receiving the signal (e.g., terminal 1 in FIG. 1) at a reception level that may cause interference between signals will not start transmitting a signal due to the carrier sense function. Therefore, interference between signals in the communication system can be effectively suppressed.

Furthermore, according to the embodiment described above, if terminal 1 receives a signal in communication method B, it transmits a dummy signal when it starts receiving a signal in communication method A. Furthermore, if terminal 1 does not receive a signal in communication method B, it does not transmit a dummy signal when it starts receiving a signal in communication method A. According to this configuration, by configuring terminal 1 not to transmit a dummy signal when there is no terminal communicating in communication method B, it is possible to improve the throughput of the entire communication system when no interference is occurring.

Furthermore, according to the embodiment described above, the communication system includes a plurality of communication devices capable of communication in both communication method A and communication method B. Then, when terminal 1 starts receiving a signal in communication method A, terminal 1 transmits a dummy signal in communication method B with a predetermined delay. According to this configuration, in a case such as that illustrated in FIG. 8 where there are a plurality of terminals capable of communication in communication method A and communication method B, by changing (delaying) the transmission timing of the preamble as the dummy signal, the timing at which the dummy signal is received can be shifted from the timing at which other signals (for example, a signal transmitted from terminal 2 to terminal 2) are received, thereby suppressing interference of the dummy signal with signals of other communication methods.

<Modifications of the above-described embodiments>
In the embodiments described above, the dimensions, shapes, relative positional relationships, and implementation conditions of each component may be described, but these are merely examples in all respects and are not limiting.

Therefore, countless variations and equivalents not shown are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, and even cases where at least one component in at least one embodiment is extracted and combined with a component in another embodiment.

Furthermore, the descriptions in this specification are incorporated by reference for all purposes related to this technology, and none of them are admitted to be prior art.

101 communication device, 201 communication device, 301 communication device, A communication method, B communication method.

Claims (3)

A communication system including at least a first communication device and a second communication device as a plurality of communication devices, transmitting and receiving signals between the first communication device and the second communication device using a first communication method that is a communication method requiring carrier sense and a second communication method that is a communication method different from the first communication method and requires carrier sense,
When the first communication device starts receiving a signal in the first communication method, the first communication device transmits a dummy signal in the second communication method;
the second communication device that has received the dummy signal in the second communication method does not start transmitting a signal in the second communication method to the first communication device;
Communication systems. A communication system according to claim 1,
When the first communication device receives a signal in the second communication method, the first communication device transmits the dummy signal when starting signal reception in the first communication method;
When the first communication device is not receiving a signal in the second communication method, the first communication device does not transmit the dummy signal when starting signal reception in the first communication method.
Communication systems. A communication system according to claim 1 or 2,
a plurality of communication devices capable of communicating in both the first communication method and the second communication method;
When the first communication device starts receiving a signal in the first communication method, the first communication device transmits the dummy signal in the second communication method with a delay of a predetermined time.
Communication systems.

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