METHOD AND SYSTEM FOR REDUCING POWER CONSUMPTION IN WIRELESS SENSOR NETWORKS TECHNICAL FIELD OF THE INVENTION The present invention relates to ad-hoc wireless networks. More particularly "he present invention relates to systems and methods for reducing power consumption in ad-hoc Wireless Sensor Networks. BACKGROUND A wireless network can be defined as a network of nodes that exchange data or information amongst each other using wireless communication techniques. An ad-hoc wireless network is characterized by similar behavior of alf the nodes present in the wireless net'.vo-k Ad-hoc wireless networks are a!so characterized by adaptability of the networks to movement of nodes within the network and the movement of nodes in and out of the network. Nodes can move in and out of the network by entering communication range or by being switched on or off. Wireless networks find varied applications related to real-time sensing, transmission and processing of data. In one application, nodes in wireless networks include sensors to generate data by sensing physical parameters. Such networks having nodes performing tasks of sensing or data generation, along with data processing and data communication, are called Wireless Sensor Networks. A wireless sensor node is capable of sensing physical parameters, examples of wh-ch include temperature, pressure, humidity and light intensity and converting them into a access control (MAC) module 404 and a wake-up module 406 The processing module 314 includes a parent module 408. a child module 410. an application module 412 and a network modu'e 416 The beacon module 402 interfaces with the transceiver 304 through the MAC module 404 to receive beacons from various nodes in the communication range of the node 300. Beacons are used to exchange network level information within the Wireless Sensor Network 100. Beacons can be further understood in conjunction with FIG. 6 and FIG. 7. The beacon module 402 also generates beacons to be periodically broadcasted to nodes in the communication range of the node 300. The beacon module 402 works with the network module 406 to determine trie network level information of the node 300 to be transmitted in the beacons The beacon module 402 attains information received in the beacons from various nodes in the communication range of the node 300. Further, the beacon module 402 provides the information received in the beacons to the parent module 403 for storage purposes The child module 410 helps the beacon mooule 402 in determining the number of children, which needs to be broadcasted in the beacons The MAC module 404 controls the access to the transceiver 304 by various modules of the node 300. Further, (he MAC module 404 maintains buffers for all the data packets to he t.-ansmitted over the Wireless Sensor Network 100 It should be apparent those skilled in art tnai the MAC module 404 performs other functions as required by the MAC layer in a Wireless Sensor Network The MAC module 404 further interfaces with the wake-up module 406 to control the wake-up intervals of the transceiver 304 adaptively based on the network level information. This functionality of the MAC module 404 can be better understood in conjunction with rh.r: method described in FIG 5 The network module 414 maintains the network level information of the node 30C T-ie network Sevel information may include the number of children associated with the node and the level of network traffic at the node. The examples of network level information can mciuae, but are not limited to, hop-count of the node from the root node, received signal strength ind>cat:on (RSSI) of "he link to the root node, battery level of the link to the root node and duration of past wake-up interval. The network module 414 interfaces with the beacon module 402 to determine some of the network level information, for example, the hop count of the node 300 can be obtained from the hop count of its parent node. The network module 406 further interfaces with the MAC module 404 to determine link information eg the received signal strength indication (RSSI) TOR network module 414 interfaces between the MAC module 404 and the processing module 314 The network module 414 determines the parent node to which the node 300 is associated using the parent module 408, The determination of the parent node to which the node 300 is associated is described in conjunction with FIG. 3 and FIG 9 below. The network module 414 further determines one or more redundant parent nodes to which the node 300 is connected When trie-parent node to which the node 300 is associated with becomes unfavorable for sending data, the network module 414 instructs the node 300 to disassociate with the parent node an:: associate with a redundant parent node. This is further described in conjunction with FIG, 10 and FIG H The parent module 408 provides information regarding active parent nodes to the network module 414 The network module 414 obtains the network level information of active and redundant parent nodes from the parent module 408 in order to determine whether to disassociate from the active parent node and which of the redundant parent nodes to associate with The network module 414 forwards the data received from child nodes to the parent node. The parent module 408 and the child module 410 maintain lists of parent nodes and children nodes, respectively The list of parent nodes includes tne parent node to which the node 300 forwards data and is associated with. The list of parent nodes also includes one or more redundant parent nodes to which the node 300 can be connected. The list of chi'd noaes and the list of parent nodes are refreshed periodically. The parent module 408 also maintains tie network tevef information for the nodes in the list of parent rsoc'es. The application module 412 interfaces with the sensor 302 to generate data to be transmitted towards the root node 102 The functionality of these modules is described in conjunction with the method steps shown in FIG 8 and FIG 10 FIG 5 is a flowchart illustrating a method for determining interval between periodic wake-ups of a node, in accordance with one embodiment of the present invention At bloc1* 502 network level information of the node is generated. The network level information may include the number of children associated with the node and the level of network traffic at the nocc. Other examples of the network level information include, but are no; limited to, hop-count of the node from '.he rooi node, received signal strength indication (RSS1), battery level and duration of post wake-up interval, At block 504, an Interval of periodic wake-ups of a radio or a radio transceiver is determined. The interval is determined taking into consideration the network level information determined at block 502. At biock 506, the radio wake-ups are scheduled based en the interval determined at block 504. Based on this scheduling she radio of the node wakes-up from a steep mode to an active mode in order to listen for transmissions from other nodes, mciudr-g beacons broadcasted by other nodes. It should be apparent to those skilled in the art that various combinations of network level information can be used to schedule wake-up intervals of the node. Consider, for simplicity, that the wake-up interval is controlled based on the number of children and the traffic: leve! The number of children can be a measure of contention for radio wake-up siots at a node If the number of children is fow, a node can afford to wake up less frequently saving some of the battery power. Similarly, having low traffic level may lead to wastage of power in pe-iodic radio wake-ups. As a result, reducing the number of radio wake ups may result in saving some of 'he battery power. The MAC modute 404 provides an estimate of network traffic 10 Ihe wake-up module 406. The wake-up module 406 uses the estimate of network traffic for calcjlating tne periodic wake-up intervals. FIG. 6 is a block diagram illustrating varying wake-up schedules corresponding to different traffic conditions in accordance with one embodiment of the present invention. FIG. 6 shows tnree different traffic levels between four consecutive beacons 602, 604, 606 and 608 Between two beacons, a node has 18 time slols in which its radio can wake up and communicate with other nodes Heavy traffic condition is depicted between beacons 602 and 604 The node wakes up s*x times at slots 610, 612, 614, 616. 618 and 620. The node receives data at wake-up slots 612, 614, 616, 618 and 620 A wake-up slot in which the node receives data is referred to as an occupied slot and is shown with a vertical hatch On the other hand, a wake-up slot in which the node does not receive any data is referred to as an unoccupied slot and is shown with a horizontal hatch As a result, the effective bandwidth utilization may be estimated to be five-sixths or 83.3%. This may be considered as a high traffic situation. In accordance with the method as described above, the node will increase (he number of wake-ups between its next two beacons 604 and 606 The node wakes up eight times at slots 622. 624, 626, 628. 630. 632, 634 and 636 as shown in FIG. 6. The node receives data at wake-up slots 624 and 630 As a result, the effective bandwidth utilization may be estimated to be one-fourths or 25%. Th.s may be considered as a low traffic situation The node will then decrease the number of wake-ups between the beacons 606 and 608. The node wakes up only four times at slots 638 64'J. 642 and 644 as shown in FIG 6 In the subsequent wake-ups (he node may continue estimat ng effective bandwidth utilization and adaptiveiy scheduling the waKe-ups, In the hypotneuca1. situation described above, the network traffic increased and then decreased The node responded to the varying traffic by first decreasing and then increasing the wake-up interval Thus, trie adaptive wake-up scheme serves to reduce the overall power consumption in two ways. In tow congestion parts of the Wireless Sensor Network 100, the wake-up times are more separated and nodes spend more time in sleep mode. In high congestion pans of the Wireless Sensor NCI!work 100 higher bandwidth is supported thus avoiding buffer overflows and retransmission of packets FIG 6 described adaptive wake-up of a radio in order to save power consumption A radio wake-up schedule varies as described in the previous paragraph, while the beacons are transmitted at a fixed interval of time. As a special case, a node having no children or a leaf node does not have to wake-up to receive data from other nodes and only needs to send data to its parent Therefore, ieaf nodes may no! broadcast beacons as frequently as other nodes do. The interval between two consecutive beacons of leaf nodes may be considerably higher than that of non-leaf rodes This can further save battery power It should be noted that a leaf node needs to transmit periodic beacons to allow new nodes to connect to the network In this way, periodic beacons are like "Hello" messages to nodes trying to join the network. However, leaf nodes do not need to wake up periodically to receive data as they do not have any child nodes Therefore, leaf nodes do not have a wake-up interval It will be apparent to those skilled in the art that a node may use other parameters in a similar way to determine the interval between wake-ups- The network level information may be broadcast by a node to its children and potential children, which are nodes that may want to associate with or connect to the node, as a periodic beacon, signal. Typically, a tseacen signal includes a beacon packet. The beacon packet is described further in conjunction with FIG. 7. A beacon may be used for a variety of purposes, including synchronization between nodes thai are associated or connected FIG. 7 depicts a beacon packet 700 in accordance with one embodiment of the present invention As mentioned above, the beacon packet 700 includes fields that help in synchronization and provide network information for a node. These fields include, but are not limited to, a node identification {ID) 702, a route tag 704, number of children 706, a hop count 708, a received signal strength indication (RSSI) 710 a wake-up interval 712, battery life /'14 iraffic leve' 716, and a field 718. In an embodiment, the fields node MIN_RSSI JTHRESHQLD (i.e., the RSSI must be greater than a threshold') Battery Life > MIN_BAT_THRESHOl.D (i.e., the batten/ life must be greater than a threshold) No. ot Children < MAX_CHILD_THRESHOLD (i.e . the number of children connected to the noae must be less than a threshold) Traffic Level < MAX_TRAFFIC_THRESHOLD (i.e., the traffic level in (he nose must hn less tnar, a threshold) Hop Count < MAX_HOP_COUNT (i e , the node should not be too distant from the root node) However, it should be apparent to those skilled in the art that the above criteria are neither exclusive nor exhaustive. In various embodiments of the present invention some or none of the above criteria may be used. As mentioned earlier, the RSSl is an indicator of the strength of the wireless signa between two nodes. If the signal strength between the two nodes is low, then the chances o* o<.ickei loss is high. Hence, a path having low effective RSSt :s not preferred. M1N_RSSI_THRESHOLD is a minimum threshold of effective signal strength between a node and the root noae. RSSI may be expressed as a number from 0 to 255 An exemplary value of WIN RSSl_THRESHOLD is 100 which means that an RSSI below 100 indicates a ooor link whicn should not be used "'or sending data. If a node has a very low remaining battery life it may no" be preferable for the node to have additional children, MIN_BAT_THRESHQLD is the nunimum threshold value ol remaining battery life of a node to be associated with another node as a parent node, Ar, excrnp:ary value of MIN_BAT_THRESHOI, D is 30% The greater the number of children a node nas the greater is the contention for wake-up slots resulting in higher traffic level Further, tne greater the number of children, the greater is the possibility of burst data to be received. As a result, having a number of children greater than a threshold is not preferred, MAX_CHILD_THRESHOLD is the maximum threshold value of number of children a node can have so that an additional child node associates with the node. An exemplary value for MAX_CHILD_THRESHOLD is 5. If the traff'c level a! a node is high, it may not be preferable for the node to have additional children Therefore, the MAX_TRAFFIC_THRESHOLD is a limit on the maximum traffic level at a node so iha: an additional child node associates with the node An exemplary value o' rv1AX_TRAFFIC_THRESHGLD is 60%. If the node is too distant from the roos node, then data from that node will have to travel through more nodes and hence use more baitery power MAX_HOP_COUNT is the maximum value of hop count that a node can have for children to associate with the node. An exemplary value of MAX._HOP_COUNT is 4 The above thresholds can be applied to the network level parameters of table 900 received in beacons frorr the set of nodes in the communication range of a node As can be seen from FIG. 9 only the nodes with node IDs 1, 2 or 4 satisfy all the criteria, Therefore, only the nodes with node IDs 1, 2 or 4 are capabfe of being a first parent node of any given node. In one embodiment, the; Wireless Sensor Network 100 may be configured to have identical conditions in the first and second set of criteria in that case, a node will select its set of second parent nodes from node IDs 1 2 ano 4 too The node may then select parents based on the favorable values of network level information For example, a node can select the node with node ID 1 as its first parent node as this node satisfies the set of criteria in the best possible manner, i.e., lowest traffic level, low number of children, highest battery life, and maximum RSSt. The method as described above is applicable when a new node joins the wireless network 100 In another embodiment, all nodes monitor t:ie network level information of the node to whsch they are associated or connected, i.e., their -Vst parent node and set of second parent nodes. When the network level information of ihe first parent node fails to meet the first set of criteria, the node chooses to disassociate from the firs: ps'ent node. and associate with one of the set of second parent nodes to which it is connected The list of second parent nodes is also periodically updated using the beacons received by She node so that the list is up-to-date. This ensures that when the node changes its first parent node, a selects she best node from amongst the set of second parent nodes. This contributes !o the ad-hoc nature of the Wireless Sensor Network 100 while conserving battery life. However, in cena-.n cases, selecting a second parent node considering only the factors mentioned above can lead to loss of connectivity with the root node 102. For example, referring to FIG 1, consider thai the node 116 becomes unfavorable for associating with as a first parent node. The node 126 may listen to beacons from nodes within its communication range and decide that ihe node 124 is the best candidate for associating with as it happened to meet the first set of criteria However, the node 124 is itself associated with the node 116. Therefore. Instead of improving the network configuration, the node 126 has connected to a node that may not remain connected to the root node for long. The overall hop count for the node 126 has also increased. Therefore in case a node needs to change its first parent node, it is preferred that the node find a node thnt provides an atternate path to the rool node 102. A method for ensuring this is described in conjunction with FIG 2 above and FIG. 10 below FIG. 10 is a flowchart illustrating a method for cnanging the first parent node =n accordance with one embodiment of the present invention. At block 1002, a node listens for a beacon from a first parent node to which it is associated. At block 1004. the node extracts network level information from the beacon At block 1006, the node determines whether the network level information of the first parent node complies with a third set of criteria. The third set of criteria is a set of conditions to determine whether the first parent node is favorable for sending data to. In one embodiment. the third set of criteria is the inverse of the first set of criteria. In accordance so one of the invention, the third set of criteria are: RSSI <= MINRSSIJTHRESHOLD Battery Life <= MIN_BAT_THRESHOLD No. of Children >= MAX_CHILD_THRESHOLD Traffic Level >= MAX..TRAFFIC_THRESHOLD Hop Count >= MAXJHOP_COUNT However, it should be apparent to those skilled in the art that the above criteria are neither exclusive nor exhaustive, In various embodiments of the present invention, some or none of the above criteria may be used If the first parent node does not comply with any one of the third set of criteria Ihen Hie step depicted in block 1008 is performed. Block 1008 depicts the step of waiting for the next beacon This means that the node checks the status of the first parent node on receiving each beacon. To further conserve battery power, the node may check the network level information with the tnird set of criteria once in 5 or 10 beacons or when it transmits some data to the firs' parent node. If the first parent node complies with any one of the third set of criteria, the first parent node is considered unfavorable or unsuitable for data transmission. At block 1010, the node selects a second parent node from set of second parent nodes to which it is connected. This selection may be performed" by identifying the most favorable amongst ".he set of second parent nodes The node then disassociate from the first parent node as block 1012. and at block '0'