This application is based upon and claims the benefit of priority of the prior Japanese Application No. 2015-014715 filed on Jan. 28, 2015, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a transmission apparatus, a reception apparatus, and a communication system.
Intermittent reception is one of methods of reducing power consumption of a node on a reception side of nodes that perform wireless communication with each other. In the intermittent reception, the node on the reception side performs the following operation. That is, the node on the reception side carries out carrier sense at certain intervals (also referred to as monitoring intervals). When a carrier (a wireless frame transmitted from a node on a transmission side) is detected in the carrier sense, the node on the reception side receives data contained in the wireless frame. The node on the reception side is in a power-off state (referred to as power saving mode) during not carrying out the carrier sense, except for a predetermined function. As described above, the intermittent reception can be considered as a method of releaseling the power saving mode at predetermined intervals to try sensing a frame from a transmission apparatus and receiving data contained in a wireless frame when the wireless frame can be detected.
In the intermittent reception, when a transmission time period of a wireless frame is shorter than the time length of the monitoring interval, the node on the reception side in some cases fails to detect a transmitted wireless frame during the monitoring interval. For that reason, the transmission time period of a wireless frame is set to be longer than the monitoring interval. For example, when the monitoring interval is two seconds, a sequence of a wireless frame in which a preamble having a length of, for example, about 2.2 seconds is followed by a synchronization word (Sync Word), a payload, and a CRC part, is transmitted. The reception of the data is made by the reception of data contained in the payload.
For further information, see Japanese Laid-Open Patent Publication No. 2000-209299, and Japanese Laid-Open Patent Publication No. 2013-5419.
The node on the reception side receives a payload when a synchronization word matches a synchronization word saved (stored) in the node on the reception side. For that reason, when a carrier (a preamble) is detected, the node on the reception side stands by for the reception of a synchronization word. Until the synchronization word is detected, a state continues where the power saving mode is released.
As mentioned above, when the time length of the preamble is about 2.2 seconds, a time period of two seconds or more may be taken from the sensing of the preamble up to the reception of a synchronization word. It is not preferable that the power saving mode is released over such a time period, from a viewpoint of power consumption reduction.
According to one aspect, a transmission apparatus includes a transmission unit configured to transmit, to a reception apparatus performing intermittent reception, a frame in which a subframe is repeated at intervals each being shorter than an interval for the intermittent reception, the subframe containing at least a preamble, a synchronization word, and data for the reception apparatus.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.
Hereinafter, an embodiment will be described with reference to the accompanying drawings. The configurations of the embodiment are merely an example, and the present invention is not limited to the configurations of the embodiment.
First, a related art will be described.
In
The RF LSI of the transmission apparatus illustrated in
Meanwhile, the RF LSI of the reception apparatus releases the power saving mode at predetermined monitoring intervals (hereafter, simply referred to as intervals or CS intervals) and carries out carrier sense (CS) on a wireless signal from the transmission apparatus. During a time period for the carrier sense, power is consumed. When a carrier is detected in the carrier sense, the RF LSI stands by for a synchronization word (waits for a Sync Word). After the confirmation of the synchronization words matching, the reception (taking in) of a payload (data) is performed.
During the carrier sensing, the synchronization word standby, and the payload reception, the RF LSI is in an active state (active mode). For that reason, consumed power is more than the power consumption in the power saving mode. Not during the time period for the carrier sensing, the synchronization word standby, and the payload reception, the RF LSI transits to a non-active state without a predetermined function, namely, the power saving mode.
When the RF LSI receives the payload (data), the MCU of the reception apparatus releases the power saving mode to transit to the active state (active mode). The MCU performs a process on the received data and transits to the power saving mode again when the process is finished. Therefore, during the data processing by the MCU, consumed power is more than the power in the power saving mode.
When an interval of monitoring the carrier, illustrated in
In an embodiment to be described below, there will be described a method of transmitting frames, a wireless communication apparatus, and the like, the method being capable of reducing power consumption by shortening the above-described time period of synchronization word waiting (a time period during which the power saving mode is released).
The payload 14 contains information used to calculate the end (end time) of the frame 10, and the other data. The information for the end calculation contains, for example, information that represents the number of remaining repetitions of the subframe 11. In addition, the information for end calculation may further contain, for example, information that represents the length (size) of the subframe 11. For example, the subframe length may be calculated from the length (size) of the frame 10 and the number of repetitions, the length (size) of the frame 10 being represented by information contained in the payload 14. In the present embodiment, in one wireless frame 10, the subframe 11 is transmitted in a repetitive manner. The contents of the subframes 11 can be made the same except for the information for end calculation. However, the contents of the subframes 11 may differ, among them, in information other than the information for end calculation.
The LSI 20 includes an RF processing unit 22 that is connected to an antenna 21, a reception detecting unit 23 that is connected to the RF processing unit 22, a synchronization word identification unit 24 that is connected to the reception detecting unit 23, and a reception notification unit 25 that is connected to the synchronization word identification unit 24. Furthermore, the LSI 20 includes a reception unit 26 that is connected to the synchronization word identification unit 24, a buffer 26A that is connected to the reception unit 26, and a control unit 27 that is connected to the reception unit 26. Furthermore, the LSI 20 includes a timer 28 that is connected to the control unit 27, and a transmission unit 29 that is connected to the control unit 27, the transmission unit 29 being connected to the RF processing unit 22.
The MCU 30 is electrically connected to the LSI 20 and includes a Read Only Memory (ROM) 31 and a Random Access Memory (RAM) 32. The RF processing unit 22 performs the receiving process of a wireless signal that is received from the antenna 21 and the transmitting process of a wireless signal to be transmitted from the antenna 21.
The reception detecting unit 23 carries out carrier sense for a frame 10 to detect carrier that is received by the RF processing unit 22. The carrier sense is carried out at monitoring intervals set in advance. Specifically, the reception detecting unit 23 detects the reception when the reception strength (Received Signal Strength Indicator (RSSI)) of radio waves received by the antenna 21 exceeds a threshold value.
The synchronization word identification unit 24 stands by for a synchronization word 13 in the carrier when the carrier is detected by the reception detecting unit 23. The synchronization word identification unit 24 has a standby timer for the synchronization word 13. If a synchronization word 13 is received before the standby timer expires, the synchronization word identification unit 24 determines whether or not the synchronization word 13 matches a synchronization word that is saved in advance in the LSI 20. The reception notification unit 25 transmits a reception notification to the MCU 30 with an interrupt when the synchronization words match in the synchronization word identification unit 24, and causes the MCU 30 to release the power saving mode (causes the MCU 30 to transit to the active mode).
The reception unit 26 receives the payload 14 and stores the payload 14 in the buffer 26A when the synchronization words 13 match in the synchronization word identification unit 24. The buffer 26A has, for example, a queue (FIFO (First-In First-Out)) in which payloads 14 are stored in order of arrival.
The control unit 27 controls the operation of the units of the LSI 20. For example, the control unit 27 performs the setting of the interval (a monitoring interval) for the carrier sense with the timer 28, the setting of a time to be counted by the standby timer for the synchronization word 13 included in the synchronization word identification unit 24, the assembly of a frame 10, and the like. The transmission unit 29 performs the transmitting process of a frame 10. The timer 28 is a timer that manages the monitoring interval. The LSI 20 is an example of the transmission unit and the reception unit. Note that a calculating process of the end time of a frame 10 and a generating process of a frame 10 performed by at least the control unit 27 of the LSI 20 may be performed by a processor executing a program. The processor includes a CPU, a microcomputer, a microcontroller, or the like.
The MCU 30 loads a program stored in the ROM 31 into the RAM 32 and executes the program to perform various processes. For example, the MCU 30 performs a process of setting an interval for intermittent reception to the LSI 20. In addition, the MCU 30 performs a process on data received by the LSI 20.
In 02, the MCU 30 sets an interval (a monitoring interval) for the intermittent reception of the LSI 20. The MCU 30 transmits a setting instruction that contains the value of the interval, to the control unit 27 of the LSI 20. In the LSI 20, the control unit 27 sets the interval under the setting instruction.
In 03, the MCU 30 transits to the power saving mode. That is, the MCU 30 is brought into a state of standing by for a reception notification with an interrupt from the LSI 20 (04 and 05). In the power saving mode, the MCU 30 is brought into a state (power off) of stopping its operation and processing except for standing by for a reception notification.
When the reception notification is received in 05 (Yes in 05), the MCU 30 releases the power saving mode to transit to the active mode (06). The MCU 30 takes out data stored in the payload 14 from the queue of the buffer 26A and performs a predetermined process on the data (07). When the processing to the data is finished, the processing returns to 03 and the MCU 30 transits to the power saving mode again.
When finishing the initialization, the LSI 20 stands by for a setting instruction of the interval for the intermittent reception from the MCU 30 (102 and 103). When the setting instruction is input from the MCU 30, the interval setting for the intermittent reception is performed (104). That is, the control unit 27 receives the setting instruction from the MCU 30 and sets the interval specified by the setting instruction to the timer 28. This causes the carrier sense to be carried out by the reception detecting unit 23 whenever the timer 28 expires. The carrier sense is an example of a trial of sensing a wireless frame.
When the setting of the interval is finished, the LSI 20 transits to the power saving mode and comes into a state of standing by for a carrier sense (CS) timing. That is, the LSI 20 waits for the expiration of the timer 28. In the power saving mode of the LSI 20, the LSI 20 comes into a state (power off) of stopping its operation and processing except for the function in which that the control unit 27 stands by for the expiration of the timer 28.
When the expiration of the timer 28, namely, the CS timing comes (Yes in 106), the LSI 20 transits from the power saving mode to the active mode, and the reception detecting unit 23 carries out the carrier sense (107). That is, the reception detecting unit 23 measures the Received Signal Strength Indicator (RSSI) of radio waves received by the antenna 21 and determines whether or not the RSSI exceeds a predetermined threshold value (108). When the RSSI do not exceed the threshold value (No in 108), it is considered that no carrier is detected, the processing returns to 105, where the LSI 20 transits to the power saving mode to stand by until the next CS timing.
On the other hand, when the RSSI exceeds the threshold value (Yes in 108), the processing proceeds to 109. In 109, the synchronization word identification unit 24 sets the standby timer for a synchronization word 13 and stands by for the reception of a synchronization word 13 (110). When a synchronization word 13 is received before the expiration of the standby timer (Yes in 110), the processing proceeds to step 111. On the other hand, when the standby timer expires (Yes in 109), the LSI 20 transits to the power saving mode and waits for the next CS timing (105).
In 111, the synchronization word identification unit 24 checks the synchronization word. That is, the synchronization word identification unit 24 compares the received synchronization word 13 with a synchronization word that is saved in advance in the LSI 20 to determine whether or not the both of them match. At this point, when the synchronization words 13 do not match (No in 111), the processing returns to 105. On the other hand, when the synchronization words 13 match (Yes in 111), the reception unit 26 receives the payload 14 following the synchronization word 13 and stores the payload 14 in the buffer 26A (112). At this point, the reception unit 26 performs CRC check, and when a CRC check result is OK, the payload 14 is stored in the buffer 26A. When the CRC check is NG, the payload 14 is not stored, and the LSI 20 comes in a state of standing by for the next CS timing.
When the payload 14 is successfully stored in the buffer 26A, the reception notification unit 25 transmits a reception notification to the MCU 30 with an interrupt (113). In this manner, the MCU 30 performs the processes of steps 06 and 07 in
In 114, the control unit 27 refers to the information for end calculation contained in the payload 14 (
In the next 115, a waiting process of the remaining time of the frame 10 is performed. That is, the control unit 27 sets the timer 28 such that the timer 28 expires with a CS timing that first comes after the end time of the frame 10 based on the calculation result in 114 (the end time of the frame 10). Afterward, the processing returns to 105, where the LSI 20 transits to the power saving mode. Note that, the waiting process of the remaining time will be described later in detail.
The MCU 30 of the transmission apparatus 1A operates in the active mode during the generation of a frame 10 and the operation time of the LSI 20, consuming more power than in the power saving mode. The LSI 20 of the transmission apparatus 1A operates in the active mode during the transmission time period of the frame 10, consuming more power than in the power saving mode.
The LSI 20 of the reception apparatus 1B carries out carrier sense (CS) at, for example, intervals shorter than the time length of the frame 10. However, the interval of CS being shorter than the time length of the frame 10 is not a requisite. It is noted however that the time length of the subframe 11 (
The frame 10 has a format in which the subframe 11 with the same content containing a synchronization word 13 is repeated (
In addition, the repetition of the subframe 11 with the same content in the frame 10 allows the reception apparatus 1B to gain a plurality of reception opportunities of a synchronization word 13 from the sensing of the frame 10 up to the end of the frame 10. That is, depending on timing of the sensing the frame 10, there may be a case where the synchronization word 13 of a subframe 11 fails to be received in sensing. However, with the next subframe 11, the synchronization word 13 of the next subframe 11 can be received. Also in this case, the waiting time will not be long as compared with the related art.
In addition, the time length of the preamble 12 of the frame 10 is short as compared with the related art, and thus the expiration time (waiting time) of the standby timer for the synchronization word 13 can be shortened. The waiting time may be set in accordance with, for example, the time length of the preamble 12, or may be set in accordance with the time length of the subframe 11.
Alternatively, when the payload 14 has a fixed length, the waiting time is set at a time period obtained by adding a predetermined margin time to a time length from the head of some subframe 11 up to the payload 14 of the next subframe 11. This enables sensing the synchronization word 13 of either a subframe 11 in sensing the frame 10 (the second leftmost subframe 11 in
Since an interfering radio wave does not contain a synchronization word, the reception apparatuses stands by for the reception of a synchronization word until the standby timer expires. In the comparative example, a waiting time longer than the length of the preamble is set, and thus when the preamble is 2.2 seconds, the RF LSI operates in the active mode for 2.2 seconds or more. In contrast, since the reception apparatus 1B can shorten the waiting time for the above-described reason, it is possible to shorten a time period during which the LSI 20 operates in the active mode. As seen from the above, according to the reception apparatus 1B, it is possible to avoid a waste of power with the reception of an interfering radio wave.
Lastly, the waiting process of the remaining time will be described.
As illustrated in
However, when the transmission time period of the frame 10 is sufficiently shorter than the interval for CS, the reception apparatus 1B may receive the same payloads (data items) in a duplicate manner. The lower chart in
The method of avoiding duplicate reception of such the same data is the waiting process of the remaining time. As has already been described, as the waiting process of the remaining time, the end time of the frame 10 is calculated using the information for end calculation of the frame 10 that is contained in the received payload 14. For example, the end time of the frame 10 can be calculated from the number of remaining repetitions of the subframe 11 and the length of the subframe 11. According to the setting of the timer 28 by the control unit 27, the LSI 20 maintains the power saving mode until a CS timing occurring after the end time.
This causes, as illustrated in
According to the embodiment, it is possible to achieve shortening a time period during which power saving mode is released in a reception apparatus. The configurations according to the first through fourth embodiments discussed above may be properly combined.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
2015-014715 | Jan 2015 | JP | national |