JP7603532B2 - Wireless communication system - Google Patents

Description

The present invention relates to a wireless communication system.

Conventionally, in a wireless communication system having a transmitter and a receiver, carrier sense is performed so that the receiver can check whether the transmitter is performing wireless transmission (see, for example, Patent Document 1). Figure 4 shows a typical method of this carrier sense.

The transmitter shown in the figure transmits data periodically and repeatedly. The data transmission period of this transmitter is represented by Tt in the figure, and the data transmission time is represented by e. The transmission period Tt is set longer than the transmission time e.

On the other hand, the receiver shown in the figure periodically and repeatedly performs carrier sensing. The carrier sense period of this receiver is represented by Tr in the figure. This carrier sense period Tr is set to satisfy the condition Tr<e to prevent wireless transmissions from being missed. In other words, the carrier sense period Tr is set to be shorter than the transmission time e. By increasing this carrier sense period Tr within a range that satisfies this condition (i.e., by reducing the number of times carrier sense is performed), the power consumption required for carrier sensing can be reduced.

The receiver repeatedly performs carrier sensing, and when it detects a wireless transmission as shown in Figure 4, it receives the data after (Tt-e) seconds.

Patent No. 4075957

The present invention has been made against the background of such technology, and has an object to reduce the power consumption required for carrier sensing.

To solve the above problems, the wireless communication system of the present invention is a wireless communication system including a transmitter and a receiver, the transmitter periodically and repeatedly transmits data, the number of times the data is repeatedly transmitted is equal to or greater than a value obtained by dividing the length of the data transmission cycle by the length of the data transmission time, and the receiver periodically and repeatedly performs carrier sense, the length of the cycle for performing carrier sense is longer than the length of the data transmission cycle and shorter than the sum of the length of the data transmission cycle and the length of the data transmission time.

The present invention makes it possible to reduce the power consumption required for carrier sensing.

FIG. 1 shows a configuration of a wireless communication system 1. FIG. 1 shows a communication method of the wireless communication system 1. FIG. 13 is an explanatory diagram of a communication method according to a modified example. A diagram showing the general method of carrier sensing

1. Embodiment A wireless communication system 1 according to an embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1, which is referred to in this description, is a diagram showing a configuration of the wireless communication system 1, and Fig. 2 is a diagram showing a communication method of the wireless communication system 1.

As shown in FIG. 1, the wireless communication system 1 is composed of a transmitter 11 and a receiver 12. The transmitter 11 and receiver 12 that compose this wireless communication system 1 are, for example, a wireless fire detector, a wireless flashlight (an alarm device for notifying the hearing impaired of a fire), or a wireless repeater.

As shown in FIG. 2, the transmitter 11 repeatedly transmits data periodically. The transmission period of the transmitter 11 is represented by Tt in the figure, and the transmission time is represented by e. The transmission period Tt is set to be longer than the transmission time e.

The transmitter 11 repeatedly transmits data n times or more to prevent the receiver 12 from missing any wireless transmissions. The number of times n the data is transmitted is set to satisfy the condition n ≥ (Tt/e). In other words, the number of times n the data is transmitted is set to be equal to or greater than the value obtained by dividing the length of the data transmission period Tt by the data transmission time e.

Meanwhile, the receiver 12 periodically and repeatedly performs carrier sensing as shown in FIG. 2. The carrier sense cycle of the receiver 12 is represented by Tr in the figure. This carrier sense cycle Tr is set to satisfy the condition Tr<(Tt+e) to prevent wireless transmissions from being missed. In other words, the length of the carrier sense cycle Tr is set to be shorter than the sum of the length of the data transmission cycle Tt and the length of the data transmission time e. For example, this carrier sense cycle Tr is set to be longer than the length of the data transmission cycle Tt and shorter than the sum of the length of the data transmission cycle Tt and the length of the data transmission time e.

The receiver 12 repeatedly performs carrier sensing, and when it detects a wireless transmission as shown in Figure 2, it receives the data after (Tt-e) seconds.

As described above, by setting the number of data transmissions n to satisfy the condition n ≧ (Tt/e) and setting the carrier sense period Tr to satisfy the condition Tr < (Tt + e), the receiver 12 can reliably receive data within the number of transmissions n.

In this embodiment, in order to ensure reliable data reception, the carrier sense period Tr is set to satisfy the condition Tr<(Tt+e). In contrast, in the above background art, in order to ensure reliable data reception, the carrier sense period Tr is set to satisfy the condition Tr<e. Comparing these two conditions, the carrier sense period can be made longer by Tt in this embodiment than in the background art. Therefore, according to this embodiment, the power consumption required for carrier sense can be reduced compared to the background art.

2. Modifications The above embodiment is based on the premise that the data transmission period Tt is always constant. However, the data transmission period Tt may vary for each data transmission. Specifically, the data transmission period Tt may be longer than a predetermined period at a certain data transmission timing, and the data transmission period Tt may be shorter than a predetermined period at another data transmission timing. When the data transmission period Tt varies in this way, the number of transmissions n and the carrier sense period Tr required for reliable data reception may change, and the receiver 12 may not be able to receive data reliably. Therefore, in this modification, a communication method that allows the receiver 12 to receive data reliably even if the data transmission period Tt varies will be described with reference to FIG. 3. FIG. 3, which is referred to in this description, is a diagram for explaining such a communication method.

The upper part of the figure shows a case in which the transmitter 11 repeatedly transmits data at a minimum transmission period. In this upper case, the minimum transmission period is represented by Ttmin, and the minimum transmission time is represented by emin. The minimum transmission period Ttmin is set longer than the minimum transmission time emin.

The middle part of the figure shows a case where the transmitter 11 repeatedly transmits data at the maximum transmission period. In this middle case, the maximum transmission period is represented by Ttmax, and the minimum transmission time is represented by emin. The maximum transmission period Ttmax is set longer than the minimum transmission time emin.

The lower part of the figure shows the receiving operation of the receiver 12. The receiver 12 shown in the lower part periodically and repeatedly executes carrier sense. The carrier sense cycle of the receiver 12 is represented by Tr. The receiver 12 repeatedly executes carrier sense, and when it detects a wireless transmission as shown in the figure, it receives data after (Tt-emax) seconds.
Here, emax represents the maximum wireless transmission time, and defines the worst-case condition for advancing the timing for starting the data reception operation.

The carrier sense period Tr of the receiver 12 is set to satisfy the condition Tr < (Ttmin + emin) so that data can be reliably received when the transmission period of the transmitter 11 is the minimum transmission period Ttmin. That is, the length of the carrier sense period Tr is set to be shorter than the sum of the length of the minimum data transmission period Ttmin and the length of the minimum data transmission time emin. For example, the carrier sense period Tr is set to be longer than the length of the maximum data transmission period Ttmax and shorter than the sum of the length of the minimum data transmission period Ttmin and the length of the minimum data transmission time emin. In addition, the transmitter 11 repeatedly transmits data n or more times so that the receiver 12 can reliably receive data. The number of times n of data transmission is set to satisfy the condition n ≥ (Ttmin/emin). That is, the number of times n of data transmission is set to be greater than or equal to the value obtained by dividing the length of the minimum data transmission period Ttmin by the minimum data transmission time emin.

In this way, by setting the number of data transmissions n to satisfy the condition n ≧ (Ttmin/emin) and the carrier sense period Tr to satisfy the condition Tr < (Ttmin + emin), the receiver 12 can reliably receive data within the number of transmissions n when the transmission period of the transmitter 11 is the minimum transmission period Ttmin.

In order for the receiver 12 to reliably receive data within n transmissions when the transmission period of the transmitter 11 is the maximum transmission period Ttmax, the time e' shown in FIG. 3 is required. This time e' is the time during which the minimum transmission time emin overlaps when the transmission period is the maximum transmission period Ttmax and when the transmission period is the minimum transmission period Ttmin. In other words, it is the time during which data is transmitted whether the transmission period is the maximum transmission period Ttmax or the minimum transmission period Ttmin. If this time e' exists, the receiver 12 can reliably receive data within n transmissions when the transmission period is the maximum transmission period Ttmax.

The time e′ is expressed by the following Equation 1.

In this formula 1, ΔTterr represents the maximum error in the transmission period. The maximum error in the transmission period represented by ΔTterr is defined as ΔTterr = Ttmax - Ttmin. In other words, the maximum error in the transmission period is the difference between the maximum transmission period Ttmax and the minimum transmission period Ttmin.

If the time e' becomes a negative number, the system will no longer be valid, so from the above formula 1, the condition emin>(n-1)xΔTterr can be derived.

If the minimum data transmission time emin and the number of data transmissions n satisfy this condition, the receiver 12 can reliably receive the data within the number of transmissions n, even if the transmission period of the transmitter 11 is the maximum transmission period Ttmax.

In the present modified example described above, in order to ensure reliable data reception, the carrier sense period Tr is set to satisfy the condition Tr<(Ttmin+emin). In contrast, in the above background art, in order to ensure reliable data reception, the carrier sense period Tr is set to satisfy the condition Tr<e. Comparing these two conditions, emin and e both represent the transmission time, so the carrier sense period can be made longer by Ttmin in this modified example than in the background art. Therefore, according to this modified example, the power consumption required for carrier sense can be reduced compared to the background art. In addition, according to this modified example, the receiver 12 can receive data reliably even if the transmission period of the transmitter 11 varies.

1...wireless communication system, 11...transmitter, 12...receiver

Claims (2)

A wireless communication system comprising a transmitter and a receiver,
The transmitter repeatedly transmits data periodically;
the number of times the data is repeatedly transmitted is equal to or greater than a value obtained by dividing a length of a transmission cycle of the data by a length of a transmission time of the data,
The receiver periodically and repeatedly performs carrier sensing;
A wireless communication system, characterized in that the length of the period for performing the carrier sense is longer than the length of the data transmission period and shorter than the sum of the length of the data transmission period and the length of the data transmission time. the number of times the data is repeatedly transmitted is equal to or greater than a value obtained by dividing a length of a minimum transmission cycle of the data by a length of a minimum transmission time of the data,
a length of the period for performing the carrier sense is longer than a length of a maximum transmission period of the data and shorter than a sum of a length of a minimum transmission period of the data and a minimum transmission time of the data;
The number of times the data is repeatedly transmitted and the minimum transmission time of the data satisfy the condition expressed by the following formula:
emin>(n-1)×ΔTterr
2. The wireless communication system according to claim 1, wherein in the formula, emin represents the minimum transmission time of the data, n represents the number of times the data is repeatedly transmitted, and ΔTterr represents the difference between the maximum transmission period and the minimum transmission period of the data.

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