Wireless Sensor Networks (WSNs) are used in various application areas, including industrial process monitoring and control, environment and habitat monitoring, traffic control, building automation, healthcare applications, etc. In some such applications a powered sensor may be used in a harsh environment, and it is desirable for the sensor to be untethered after deployment for as long as possible. However, most sensors are powered by batteries, and limited battery capacity is a major limitation for deployment of untethered sensor nodes. Finite sensor node lifetime implies finite lifetime of the applications or additional cost and complexity to replace batteries. In order for a sensor node to connect to the WSN, it must receive a specific data transmission, beacon, from a coordinator within the WSN providing the service set identification (SSID) and other connection information for the network. The coordinator transmits beacons periodically in any channel within the network. There are no dedicated channels for beacon transmission. Furthermore, the beacon channel may change from slot frame to slot frame in a random pattern. In other words, the coordinator may transmit the beacons in any channel while the channel for beacon transmission may change from slot frame to slot frame. Thus, it may take a substantial amount of time for a sensor node to connect to the network because the sensor node must scan each channel to receive the beacon. Because the sensor node must maintain an active radio while attempting this connection and due to the substantial amount of time awaiting connection, battery drainage may occur limiting the lifetime of the sensor node, and thus, the WSN.
Systems and methods for identifying beacon channel information in a Wireless Sensor Network are disclosed herein. In some embodiments, the system includes a controller, a scanner, and a transceiver. The controller is configured to identify a number of channels in which a beacon signal may be wirelessly transmitted. The number of channels is less than a total number of channels available for receiving transmissions. The scanner is configured to scan each of the number of channels for a first beacon signal. The transceiver is configured to receive the first beacon signal from one of the number of channels.
In another illustrative embodiment, a method includes identifying a plurality of channels in which a beacon signal may be transmitted, scanning each channel within the plurality of channels for a first beacon signal transmission, and receiving the first beacon signal from one of the plurality of channels. The plurality of channels has a number of channels less than a total number of channels available for receiving transmissions.
In yet another illustrative embodiment, a system includes a controller and a transceiver. The controller is configured to identify beacon channel transmission patterns. The transceiver is configured to transmit beacon channel information.
In a further illustrative embodiment, a method includes identifying beacon transmission patterns and transmitting beacon channel information. Both the identifying and transmitting are accomplished through the use of a first wireless device.
For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which:
Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. Further, the term “software” includes any executable code capable of running on a processor, regardless of the media used to store the software. Thus, code stored in memory (e.g., non-volatile memory), and sometimes referred to as “embedded firmware,” is included within the definition of software. The recitation “based on” is intended to mean “based at least in part on.” Therefore, if X is based on Y, X may be based on Y and any number of other factors.
The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.
In order to maintain battery life of a sensor node within a WSN, efficiently connecting the sensor node to the network is beneficial. Because maintaining an active radio consumes a large amount of power, it is desirable to design the network to reduce connection times, thereby, reducing the time the radio need be active. Thus, power consumption is reduced. Embodiments of the present disclosure provide an efficient design for connecting sensor nodes to a WSN by reducing the time the radio of the sensor nodes need be active.
The sensor(s) 208 include one or more transducers that detect conditions about the wireless sensor node 106 and provide measurements of the conditions to the controller 202. For example, embodiments of the sensor(s) 208 may measure temperature, pressure, electrical current, humidity, or any other parameter associated with the environment of the wireless sensor 106. The transceiver 206 converts signals between electrical and electromagnetic forms to allow the wireless sensor node 106 to communicate with the sensor nodes 104 and 108, the coordinator 102, and other devices. Scanner 204 scans available frequency channels for transmissions from the sensor nodes 104 and 108 and/or coordinator 102. The energy source 216 provides power to operate the controller 202, the memories, 212, 214, and other components of the wireless sensor node 106. The energy source 216 may include a battery, an energy harvesting system, and/or other power source suitable for use in the wireless sensor node 106.
To connect to network 100, sensor node 106 must first receive a beacon from the coordinator 102 providing the service set identification (SSID) and other connection information for the network 100. In some embodiments, the network 100 operates in accordance with IEEE 802.15.4e in a sub-gigahertz or 2.4 GHz ISM band. There may be 16 channels for use within the 2.4 GHz band, each with 2 MHz of bandwidth and 5 MHz of channel separation available for coordinator 102 and sensor nodes 104-108 to transmit and receive data. In some embodiments, other frequencies and/or with a different number of channels, so long as the frequencies and channels are suitable for use in the network 100, may be used by the coordinator 102 and sensor nodes 104-108 to transmit and receive data.
In some embodiments, beacon transmission from coordinator 102 is limited to a number of channels less than the total number of channels available for transmission. For example, in the 2.4 GHz band utilizing 16 channels for transmission, only 15 or less channels may be utilized for beacon transmission. In some embodiments, the number of available channels for beacon transmission is only 3. For example, channels 1, 8, and 16 may be designated as channels available for beacon transmission. The beacons then may be transmitted by coordinator 102 in one of the channels designated for beacon transmissions. In some embodiments, the channels for beacon transmission are programmed into coordinator 102 prior to entry into the network 100 and are thus, preset.
A certain amount of time after the coordinator 102 transmits the first beacon signal, the coordinator 102 may transmit a second beacon signal in a different channel of the channels designated for beacon transmissions. Again, after a certain amount of time, the coordinator 102 may transmit a third beacon signal in a different channel of the channels designated for beacon transmissions than the first beacon signal and the second beacon signal. In some embodiments, this may continue, with the coordinator 102 transmitting beacon signals in the channels designated for beacon transmissions selecting the channel to send the beacon transmission based on a preset pattern.
Controller 202 of sensor node 106 may be configured to identify channels on which the beacon may be transmitted. In other words, when the transmission of a beacon is limited to certain channels less than the total number of channels available for receiving transmissions, controller 202 is configured to identify which of the channels the beacon may be transmitted. The number of channels and the specific channels in which a beacon may be transmitted may be programmed directly into the sensor node 106 during network 100 set up. Hence, in some embodiments, scanner 204 only scans each of the channels designated for beacon transmission and does not scan all of the available channels. Transceiver 206 is configured to receive beacon transmissions from coordinator 102.
By limiting the number of channels scanner 204 needs to scan for beacon transmissions, there is a higher likelihood that scanner 204 finds a beacon signal in a reduced amount of time. Scanning time, the time it takes for scanner 204 to find a beacon signal, sometimes referred to as listening time, may be identified by the following equation:
Node Listening≧n*x
where n is the number of channels available for beacon transmission and x is the beacon time interval. In some embodiments, the beacon time interval is 10 seconds or less. Thus, with the reduction of channels selected to transmit the beacon, the time for node listening will be reduced.
In some embodiments, the number of channels selected by coordinator 102 for beacon transmission is not reduced from the total number of channels available for transmissions. For example, if 16 channels are available for transmissions, all 16 channels are available for beacon transmission as well. Controller 202 of sensor node 106 may be configured to identify beacon channel transmission patterns. This may be accomplished utilizing scanner 204 to scan all of the channels for a beacon. Once the beacon is identified, transceiver 206 receives the beacon. Controller 202 then may identify which channel the beacon was received and the time offset for beacon transmissions. Controller 202 then may identify the pattern of channels in which future beacons will be transmitted by coordinator 102.
Sensor node 106 may then transmit beacon channel information to sensor nodes 104 and 108 within packet communications which may include other information exclusive of beacon channel information. Beacon channel information may comprise from which channel the beacon was received, the time offset for beacon transmissions, and/or the pattern of channels in which future beacons will be transmitted by coordinator 102. Sensor nodes 104 and 108 then may each use its own controller to determine the beacon channel transmission patterns based on the beacon channel information transmitted by sensor node 106. This enables the sensor nodes within the network 100 to switch to the particular channel at a particular time to listen for beacons, thereby enabling sensor nodes 104 and 108 to quickly receive the beacon and join the network 100. In some embodiments, not all packets would be required to carry the beacon channel information; however, this information may be sent in every packet. If the beacon channel information is not sent in every packet, a subset of frame slots may be selected to transmit this information.
In block 404, method 400 continues with scanning each channel within the plurality of channels for a first beacon signal. Scanner 204 of sensor node 106 may conduct the scanning.
The method 400 continues in block 406 with transmitting a plurality of beacon signals, one at a time, each in separate channels within the plurality of channels based on a preset pattern. Coordinator 102 may transmit the plurality of beacon signals.
The method 400 then includes receiving the first beacon signal from one of the plurality of channels, as shown in block 408. The transceiver 206 of sensor node 106 may receive the beacon signal.
In block 504, the method 500 continues with transmitting, by the first wireless device, beacon channel information. Beacon channel information may include which channel the beacon was received, the time offset for beacon transmissions, and/or the pattern of channels in which future beacons will be transmitted. The transmission may be performed by transceiver 206.
The method 500 continues in block 506 with receiving, by a second wireless device, the beacon channel information. The second wireless device may be sensor nodes 104 or 108.
In block 508, the method 500 continues with identifying, by the second wireless device, beacon channel transmission patterns based on the beacon channel information. Thus, the first wireless device transmits beacon channel information to the second wireless device which identifies beacon channel transmission patterns based on the information received.
The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.
The present application claims priority to U.S. Provisional Patent Application No. 61/600,925, filed on Feb. 20, 2012 (Attorney Docket No. TI-72049PS); which is hereby incorporated herein by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
61600925 | Feb 2012 | US |