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 scheduling active and sleeping time of sensor nodes in a wireless sensor network. BACKGROUND

It is widely known that to improve power consumption, within a network is one of the significant and desirable attributes in providing a highly reliable sensing connections towards developing an energy efficient sensing systems for future generation sensor networks.

In the prior art 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 read by the sleeping node. In this case, the active node will then 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 re-transmissions.

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, even during the scheduled active time the sensor node may not be receiving any messages thus resulting to wastage of power. 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, therefore deploying a schedule which is not adapting to the traffic trend or in other words rigid schedule may not be as effective. 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 the sleeping and active time schedule for 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 and active schedule for sensor nodes within a wireless sensor network, said schedule is able to automatically adapt to the traffic trend at the respective nodes.

It is further object of the present invention to provide a method for use in a wireless sensor network, wherein the sleeping and active schedule is significantly 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 the wastage of power normally observed during active period can be reduced.

Further objects and advantages of the present invention will become apparent in the following description.

SUMMARY OF INVENTION

There is disclosed 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; characterized in that, the scheduling the active and sleeping time step further comprising the steps of determining the type of traffic threshold as low (LA) active or high active (HA) determining the status of nodes based on the traffic threshold, reducing the active time of at least one of the nodes from normal active to low active when traffic is low and increasing the active time of at least one of the nodes from normal active to high active when traffic is high.

In another aspect of the present invention, the nodes are maintained at Normal Active time in the event that the traffic is normal. 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 having static sleeping schedule;

FIG 3 shows the change of active time based on a preferred embodiment of the present invention;

FIG 4 shows the change of active time for a sensor to low active in accordance with a preferred embodiment of the present invention;

FIG 5 shows the Normal Active (NA) time in accordance with a preferred embodiment of the present invention; FIG 6 shows the change of a node from Normal Active (NA) time to High Active (HA) time in accordance with a preferred embodiment of the present invention;

FIG 7 shows the three states of active time for sensor nodes in accordance with a preferred embodiment of the present invention;

FIG 8 shows the flowchart for the overall method of the present invention.

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 for use in managing the sensor nodes within a wireless sensor network, whereby there is provided an active and sleeping mode schedule for the nodes which has adaptability feature based on network traffic.

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 of the network. FIG 3 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 3, there is defined two thresholds of traffic and three active times for the sensor node. L _T is the threshold for low traffic and H _T 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 active time as shown in FIG 4.

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 active time of the sensor node will be normal active as shown in FIG 5.

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 time as suitably shown in FIG 6.

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 sent to its address, or broadcasted and received by the node, or the messages that the sensor node has sent out to other nodes, and calculate the traffic for each cycle.

In another preferred embodiment, there is provided a feature that would aid to reduce the possibility of wasting power in the event that even during the scheduled sensor node active time, it does not receive any messages. This feature allows adaptability of traffic trend, thus creating an energy efficient schedule for the sensor nodes. As briefly mentioned, the number of requests or messages coming as instructions from clients varies, thus making it unpredictable. This will result to the inability to predict the traffic at each sensor node. Thus, the sleeping and active schedule of the sensor nodes must be adapted based on the traffic to permit efficient energy consumption and thus reducing the use of energy when the sensor node is not receiving any messages during active time.

As described above, the active time for the sensor nodes within a network are divided into three main states as also shown in FIG 7, referred herein as Low Active (LA), Normal Active (NA) and High Active (HA).

In specific, the Normal Active is the normal active time for the sensor node, the Low Active is when the active period of the sensor is reduced due to the low traffic and High Active is when the active period of the sensor node is configured to be increased due to high traffic. It is preferred that every sensor node during its active period would perform verification and then extend or reduce its active period in order to make it adaptable to traffic trend. Such verification includes, but not limiting to the following steps. It should be noted that the following describes an example of steps taken to change the status of the nodes based on traffic condition. It is understood that the change of status is interchangeable, to and from these three states subject to the condition of traffic.

EXAMPLE 1

During Normal Active time, in the event that the traffic at the sensor node during Low Active (LA) period is less than the low threshold LT, then the active period will be reduced from Normal Active (NA) to Low Active (LA). As a result to this change, the node can save power because of the traffic condition which is less than the LT , indicating that the possibility of receiving high number of messages is small. Secondly, if the traffic at the sensor node during Normal Active (NA) period is equal or more than the High threshold (HT), then the active period will be increased from Normal Active (NA) to High Active (HA). Accordingly, this can aid the node to not miss any messages because the traffic is more than HT, indicating the possibility of receiving more messages than normal is high.

Thirdly, if the traffic at the sensor node during Normal Active (NA) period is more than or equal to LT and less than HT, then the sensor node will remain in its Normal Active (NA) period. The steps involved for adaptable schedule based on traffic in accordance with a preferred embodiment of the present invention is as shown in FIG 8.

With the feature of adapting to traffic condition schedule, the sensor nodes would be able to reduce their power wastage in the event that no messages are received during that time, in addition to reducing the number of lost messages. This is significantly aided with the ability to change from one status to another based on the number of messages to be received or subject to the traffic at the nodes. Accordingly, a substantial amount of power can be conserved.

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.