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Energy-hole avoidance and lifetime enhancement of a WSN through load factor

Krishna Pal SHARMA, Teek Parval SHARMA
2017 Turkish Journal of Electrical Engineering and Computer Sciences  
In wireless sensor networks, non-uniform communication load across network 1 often leads to the problem of energy-hole or hot spot i.e. nodes nearer to high activity 2 regions deplete their energy much faster than nodes elsewhere. This may partition the 3 network into unreachable segments and thus adversely affect network lifetime. The 4 problem is more acute in random and sparsely deployed networks. Therefore, we propose a 5 deployment strategy which using least possible nodes prolongs network
more » ... es prolongs network lifetime by 6 avoiding energy-holes and also ensures full sensing and communication coverage. Scheme 7 handles the energy imbalance by selecting appropriate set of communication and sensing 8 ranges for each node based on effective load on that node. After adjusting these ranges, 9 nodes are strategically placed at locations where their energy drains uniformly and thus 10 network lifetime is prolonged. The approach is verified analytically and validated through 11 ns-2 based simulation experiments. Results reveal significant improvements over existing 12 schemes. 13 Keywords: Communication range, Network lifetime, Non-uniform deployment, Sensing 14 range, Wireless Sensor Networks. 15 1 Introduction 16 Modern sensor nodes are versatile and can sense various physical parameters like 17 humidity, temperature, pressure, vibrations etc. Thus, wireless sensor networks (WSNs) are 18 used in almost every field. Most of the applications expect the network to operate for weeks 19 and months. Sensor nodes are powered by batteries having finite energy. Due to 20 deployment of these nodes in unfriendly and unattended environments, 21 replenishing/recharging of these batteries is not possible. Another facet here is the slow 22 improvement in battery power capacities over the years as compared to processing power, 23 communication and memory capacity enhancements [1]. Therefore, proper utilization of 24 available energy is the only option for prolonging network's lifetime. 25 The energy of a node is mainly consumed in sensing and transmission/reception by 26 radio [2-4]. The radio not only consumes power when transmitting and receiving, but also 27 when listening. Steam and Katz [2] show that the ratio of energy consumption during idle: 28 receive: transmit operations is 1:1.05:1.4, while more recent studies show that the ratio is 29 1:2:2.5 [3] or 1:1.2:1.7 [4]. The growing use of WSNs for monitoring complex phenomena 30 has highlighted that some sensors like pressure, humidity, flow control and proximity also 31 consume substantial energy during sensing [5]. If data acquisition period is longer than the 32 transmission time, then the power consumption in sensing is significantly more than the 33 communication. Therefore, energy consumption during sensing cannot be neglected. The 34 traditional sensors assume a sensing model with fixed sensing range. But, with 35 advancements in technology, sensors with adjustable ranges are now available. 36 Photoelectric sensors, photoelectric sensors [6], thermocouple based temperature sensors 37 [7], under water sensors [8], etc. are few of commercially available such sensors. Therefore, 38 both sensing and communication ranges can be adjusted in order to balance the energy 39 consumption of nodes. 40 In a typical WSN, certain nodes transmit more data than others and hence deplete their 41 energy faster. For example, nodes closer to sink not only transmit their data but also relay 42 the data sensed by other nodes. Thus, the relay load on nodes increases towards sink. 43 Consequently, nodes nearer to the sink deplete their energy much faster and thus exhaust 44 earlier than nodes far away. This problem is called as energy-hole creation and can be 45 avoided by reducing the energy dissipation rate of nodes nearer to sink. Hence, we propose 46 a scheme which balances the energy dissipation rate of nodes by adjusting communication 47 the same time (3) a node placement strategy is proposed for placing nodes with modified 87 ranges at appropriate locations such that they provide full coverage in terms of sensing and 88 connectivity and drain their energy uniformly. 89 3.1 Procedure for finding Load factor (Lf) 90 The load factor of a sensor node is the probable estimation of communication 91 performed by the node. All sensor nodes sample data at a specific rate and transmit it 92 towards sink. Therefore, each node has specific communication load of transmitting its own 93 data. All sensor nodes (except one hop neighbors of the sink) transmit their sampled data to 94 some intermediate nodes in their radio range for relaying it towards sink which increases 95 communication load on intermediate nodes. A node however can send its data to any of 96 intermediate node amongst all neighboring nodes in the direction of sink. Thus, increment 97 in communication load of a particular intermediate sensor node depends on the number of 98 its neighboring nodes selecting it for further relaying and their load factors. Say, an 99 intermediate sensor node sin has an initial communication load Lfin and relays the data of k 146 Therefore, a sensor node can save its energy by reducing the communication distance 147 up to dmn. But, now the question is, what communication distance should be set for a sensor 148 node and how much lifetime it needs to prolong? This intuitively means that for adjusting 149 communication and sensing ranges, a reference sensor node is required so that the lifetime 150 of rest of nodes be prolonged according to the life of this node. If we try to prolong the 151 lifetime of every sensor node as per the lifetime of a node which has maximum lifetime 152 (probably the outer sensor node which has no relay load), then it is probably a bad choice as 153 this sensor node has comparatively very less load and energy consumption rate. Balancing 154 energy consumption rate of other nodes with it may lead to a sharp reduction in 155 communication and sensing ranges and may reach minimum values just after few hops and 156 thus network may become too dense too early. The better choice here is to prolong the
doi:10.3906/elk-1508-162 fatcat:zqlm3xgsl5dnpfwhn74aeokwr4