【正文】 ent group of nodes using an effective power level (PTx), where (Pmin=0)PTx (Pmax=3). The different phases of this distributed protocol are described as follows. . Construction phase As soon as the nodes are deployed on the work, the sink initiates the construction phase by broadcasting a construct packet with minimum transmission power (Pmin = 0) to get connected with its immediate neighbors, as shown in Fig. 4(a). The format of the construct packet is shown in Fig. 3 and the parameters of the packet are initialized as: SID = Sink’s ID, PGID = Sink’s ID, NEL = Sink’s power level, LHC = 0, GHC = 0, PGPL = 0. Since, sink node generally receives the data, its PGPL is assigned to 0, which is different for other parent gateways of the work. Upon receiving the construct packet, the neighbors of the sink within its minimum transmission power range (Pmin = 0), scan all parameters of the packet. They wait for the random time Wi, as defined in Eq. (1), and get connected with the sink. Let Ni, be the number of neighbors of ith node, out of N nodes in the work. Upon receiving a construct packet, the waiting time of the ith node can be considered as: (1) where αi is a small random number patible with CSMACA mechanism [22]. Then, each of them rebroadcasts the construct packet using the same minimum power level Pmin = 0 to their neighbors with necessary increments to the parameters of the construct packet and waits for time Ti units, as defined in Eq. (2). (2) where Ei is the current energy level of ith node and βi is a very small random number such that βi . Fig. 3. Format of the construct packet. In order to avoid the packet collision among group of nodes in a dense work, we propose that the sink also waits for Ti units after broadcasting the construct packet and then goes to the information phase, as described in Section . It is to be noted that sink must be within at least one of the sensor node’s minimum or maximum transmission power range. However, if the sink does not find any neighbor with Pmin = 0, it goes to the information phase to construct the link with its neighbors, after the waiting time Ti has elapsed (Table 2 and Table 3). Table 2. Construction phase algorithm for the sink and any node of the work ALGORITHM 1: Construction Phase For the Sink: 1. Initialize: Parameters and Local Hop Count (LHC)=0。 177。 Topology construction 1. Introduction Recent advances in hardware and software for the wireless work technologies have enabled the development of small sized, lowpower, lowcost and multifunctional sensor nodes [1], which consist of sensing, data processing and wireless municating ponents. These nodes are operated with very low powered batteries and deployed hundreds to thousands in the wireless sensor work (WSN). In wireless sensor work, signal processing, munication activities using higher transmission power and forwarding of similar data packets along the multihop paths are main consumers of sensor energy. Besides, replenishing energy by replacing and recharging batteries on hundreds of nodes in most of the sensor work applications, particularly in harsh terrains is very difficult and sometimes infeasible too. Hence, energy conservation [2], [3] and [4] of the sensor nodes is a critical issue in WSN, as the work lifetime totally depends on the durability of the battery. Sensor nodes are generally self organized to build the wireless sensor work, monitor the activities of the target and report the event or information to the sink or the base station (BS) in a multihop fashion. There are four main reporting models of the sensor work: event driven, query driven, periodical and mixed reporting. In event driven model, nodes report the sink, while sensing some events such as fire or flood alarm. In periodical reporting model, nodes collect the sensed data and may aggregate the required information into a set and then send them to the upstream periodically. The method of bining data is called data fusion [5], [6], [7] and [8], which reduces the amount of transmitted data. Some of the examples of such applications may be cited here, like the reporting of temperature or humidity readings of a locality. So, collection of sensed data, fusing similar data to a single packet, route them in a multihop environment to the sink and thereby to save energy are also important research issues in sensor work. In [9], the power consumption parison of each unit of sensor node is analyzed and it is observed that the energy consumption of the received power and idle state are almost same and the power consumption of CPU is very low. In [10], the authors propose the transmission power control in MAC protocols for wireless sensor work to assess the ideal transmission power by the nodes through node interaction and signal attenuation. The proposed algorithm calculates the ideal transmission power by repeated refinements and stores the current ideal transmission power for each neighboring nodes. In [11], authors present a twolevel strategy for topology control in wireless sensor works, which integrates the active subwork and short hop methods to achieve the energy saving. The problem of topology control in a work of heterogeneous wireless devices with different maximum transmission ranges, where asymmetric wireless links are not unmon, is analyzed in [12]. Since, nodes are heterogeneous, they have different maximum transmission power and radio ranges, which requires omnidirectional antenna with adjustable transmission power. Taking a set of active nodes and transmission ranges of the nodes, authors in [13] propose the minimum power configuration approach to minimize the total power consumption of WSN. In [14], authors have proposed an analysis of the routing protocol based on the variable transmission range scheme. From their analysis, it