FIELD OF INVENTION The preferred embodiments of the present invention direct to a method for use in a wireless sensor network, and more particularly to an energy saving method for managing the active and sleeping time of sensor nodes in a wireless sensor network.

BACKGROUND

The need to improve power consumption, particularly to provide energy efficient sensing systems within a network has been progressively emerging and thus placed as a significant target among researchers of the relevant art when developing advanced wireless systems paradigm. The main challenges are to provide cost and energy efficient in addition to reliable sensing connections for future generation sensor networks.

Nowadays, in many cases related to wireless sensor-based applications, the sensor nodes would be equipped with conventional AA alkaline batteries as power source. In the event that the sensor nodes are deployed unattended in the subject environment for sensing purposes typically for a substantial period of time, the battery gradually drain out and in many cases changing of batteries may not be convenient for users. In order to accommodate the limitation as described above, progressive advancements in sensor network systems has created the possibility to save power on sensor nodes, whereby one of the known solutions is allowing or putting the sensor nodes in sleep mode if they are not assigned with any task. This condition is shown in FIG 1.

By putting the sensor nodes in sleeping mode, it is observed that the power consumption can be reduced significantly. However, a trivial drawback in putting sensor nodes in sleeping mode is that in the case when another node sends a message to the particular sensor which is in sleeping mode, the message will not be received and thus not read by the sleeping node. In this case, the active node will then would have to re-transmit the message, which obviously a task that also consumes power. Therefore, in order to have an optimized power conservation technique, it should be ensured that the sensor nodes are in sleeping mode as much as possible however not missing the messages sent for them thus avoiding retransmissions.

Other drawbacks associated to current techniques in putting nodes into sleeping mode include losing messages and the latency in receiving reply messages due to delay from sensor node which has yet to be activated from sleeping mode.

When there is provided wake up and sleep time for the sensor nodes, the timing however depends on the application of the wireless sensor network, whereby in some applications it might be required that the sensor nodes are active most of the time while in other cases the sensor nodes will be required to be put to sleep most of the times. Therefore, setting active and sleeping mode time may not be advantageous considering the diversity of applications nowadays.

As described earlier, FIG 2 illustrates the situation of nodes in the event that the sensor nodes are not configured based on sleeping mode schedule. Accordingly, it is seen that if an active sensor node sends a message to a sleeping node, the sleeping node will miss the message, due to the fact the sensor nodes are not synchronized allowing some nodes to be in active mode and some in sleeping mode. As a result, re-transmitting the message has to take place. Further under another circumstance, an active node sends a message to a sleeping node, and a reply is anticipated. However, reply will be received in a much delayed time as the node is still in sleeping mode, and further actions will not be taken until the sleeping node is in active mode again.

In addition, within a wireless sensor network, traffic is not the same for all sensor nodes, as it depends on the position of the sensor nodes. For instance, the sensor nodes which are closer to the base station or gateway would have higher traffic owing to the fact that they have to route messages from the other nodes within the network to the gateway. These sensor nodes therefore should stay active most of the times. If they are put to sleep because of the sleeping schedule timing, messages may be lost or missed. As opposed to these nodes, the nodes which are located at the corners of the network or within a place with reduced traffic would preferably by in sleeping mode most of the times. Conclusively, traffic varies for all sensor nodes within a network as seen in FIG 3 As discussed above, developing a system and method that is suitable to accommodate the drawbacks in conserving energy with respect to sensor networks has been difficult.

Recognizing the aforementioned shortcomings, the present invention has been accomplished to significantly improve the conventional methods and systems.

Accordingly, it is a primary object of the method of the present invention to provide a method and system for use in managing sensor nodes within a sensor network.

It is therefore another object of the present invention to provide a method for use in providing a dynamic sleeping schedule for sensor nodes within a wireless sensor network.

It is further object of the present invention to provide a method for use in a wireless sensor network, wherein the sleeping schedule is based on the traffic of the network.

It is yet another object of the present invention to provide a method for use in a wireless sensor network, wherein the message loss in the network can be reduced by increasing the active period of the sensor node when traffic is increasing.

It is a further object of the present invention to provide a method for use in a wireless sensor network, wherein there is provided a time synchronization ability so to synchronize the sleeping schedules. Further objects and advantages of the present invention will become apparent in the following description. SUMMARY OF INVENTION

In one aspect of the invention, there is provided a method for use in managing at least two sensor nodes in a wireless sensor network comprising the step of scheduling the active and sleeping time for the sensor node based on the type of traffic at said sensor nodes.

In another aspect of the present invention, there is provided a method comprising the step of determining the traffic based on active period in a current active period. In another aspect of the present invention, there is provided a method comprising the step of adjusting the next active period based on the current active period.

In yet another aspect of the present invention, the method further comprising the step of synchronizing the active state of all sensor nodes with a base station.

BRIEF DESCRIPTION OF THE FIGURES

FIG 1 shows the difference between a node which is always active and a node which has sleeping schedule; FIG 2 shows a prior art system whereby it illustrates the nodes in the event that the sensor nodes are not configured based on sleeping mode schedule;

FIG 3 shows the traffic variety for all sensor nodes;

FIG 4 illustrates the change of active time of the sleeping schedule in the sensor nodes based on their traffic, in accordance with a preferred embodiment of the present invention. FIG 5 shows the low active time in accordance with a preferred embodiment of the present invention;

FIG 6 shows the normal active time in accordance with a preferred embodiment of the present invention;

FIG 7 shows the high active time in accordance with a preferred embodiment of the present invention;

FIG 8 shows the sleeping schedule for all sensor nodes in accordance with a preferred embodiment of the present invention;

FIG 9 shows the process involved for traffic based sleeping schedule for wireless sensor networks in accordance with a preferred embodiment of the present invention; FIG 10 shows the sleeping and active time of the sensor nodes changing according to the average traffic at the sensor node.

The invention will be more understood by reference to the description below taken in conjunction with the accompanying drawings herein:

DETAILED DESCRIPTION

In addition to the drawings, further understanding of the object, construction, characteristics and functions of the invention, a detailed description with reference to the embodiments is given in the following.

In one embodiment, the present invention provides a method and system for use in managing the sensor nodes within a wireless sensor network, whereby there is provided a dynamic active and sleeping mode schedule for the nodes which is based on network traffic. Accordingly, each node is configured to monitor the inflow and outflow of traffic, and if the traffic reduces, the sensor node will reduce its active time.

It should be noted that "traffic" in this context refers to messages that are either sent to the node or have been broadcasted and the node have received them, or the messages that the sensor node has sent out to the network.

FIG 4 illustrates the change of active time of the sleeping schedule in the sensor nodes based on their traffic, in accordance with a preferred embodiment of the present invention. As seen in FIG 4, there is defined two thresholds of traffic and three active times for the sensor node. L _T is the threshold for low traffic and Ητ is the threshold for high traffics at the sensor node. It is preferred that the traffic ranges and so the active time types of the sensor nodes are as below:

1. Low Active - (LA) : in the event that the traffic at the sensor node is less or equal to LT, the traffic is considered low and the active time of the sensor will be reduced by half of the normal time in the next active time as shown in FIG

5.

2. Normal Active - (NA): in the event that the traffic at the sensor node is more than LT and less than or equal to HT, then the traffic at the node is considered as normal traffic. Therefore the next active time of the sensor node will be normal active as shown in FIG 6. 3. High Active - (HA): in the event that the traffic at the sensor node is more than HT, the traffic at the sensor node is considered as high traffic and the sensor node will change its active time to high active for the next active time as suitably shown in FIG 7. In accordance with a preferred embodiment of the present invention, the sensor nodes are supposed to be synchronized with the gateway of base station. Therefore, when all the nodes are turned on or active, they will get time synchronized with the gateway and thus will have the same sleeping schedule as seen in FIG 8. Subsequently, the nodes start their tasks, conduct readings based on the environment and reply to the requests coming from the respective gateway. In this method, each sensor node will count the number of messages that are either sent to its address or broadcasted or the messages that the sensor node has sent out to other nodes and calculate the traffic for each cycle. Accordingly, the node will check its traffic and define the active period for the next active time. This process is as shown in FIG 9.

In conclusion, reducing and increasing the active time of the sensor node aids significantly to optimize the life time of the sensor nodes as shown in FIG 10, whereby there is shown the sleeping and active time of the sensor node which changes according to the average traffic at the sensor node.

The present invention may be modified in light of the above teachings. It is therefore understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.