International Journal of Ad hoc, Sensor & Ubiquitous Computing (IJASUC) Vol.2, No.2, June 2011 DOI : 10.5121/ijasuc.2011.2203 25                Praveen Kaushik 1 and Jyoti Singhai 2 1 Department of Computer Science & Engineering, MANIT, Bhopal, India kaushikp@manit.ac.in 2 Departments of Electronics & Communication, MANIT, Bhopal, India j.singhai@gmail.com ABSTRACT In wireless sensor network, devices or nodes are generally battery powered devices. These nodes have limited amount of initial energy that are consumed at different rates, depending on the power level. The lifetime of the network is defined as the time until the first node fails (or runs out of battery). In this paper different type of energy efficient routing algorithms are discussed and approach of these algorithms is to maximize the minimum lifetime of wireless sensor network. Special attention has been devoted for algorithms formulate the routing problem as a linear programming problem, which uses the optimal flow path for data transmission and gives the optimum results. Advantages, limitations as well as comparative study of these algorithms are also discussed in this paper. KEYWORDS Battery power, Lifetime of wireless sensor network, Minimum energy cost routing, Optimal flow, Linear programming problem. 1. INTRODUCTION In recent years, wireless communication has experienced exponential growth caused by the need for connectivity. Wireless networking has followed a similar trend due to the increasing exchange of data in services such as the Internet, e-mail and data file transfer. The capabilities needed to deliver such services are characterized by an increasing need for data throughput. Other applications in fields such as industrial, agricultural, vehicular, residential, medical sensors and actuators have more relaxed throughput requirements. This type of network consists of a group of nodes and each node has limited battery power. There may be many possible routes available between two nodes over which data can flow. Assume that each node generated some information and this information needs to be delivered to set of destination nodes. A node can easily transmit data to a distance node, if it has sufficient battery power. A node transmits its data to other node without any interference, if node lies in its vicinity. A large battery power is required to transmit the data to a node which is situated far from source node. After few transmissions a node reaches to its threshold battery level and it may exclude from network path and there will come a condition that no node is available for the data transmission and overall lifetime of network will decrease. Whereas network lifetime is define as the time until the first node in the network dies. For maximizing the lifetime of network, the data should be forwarded such that energy consumption is balanced among the nodes in proportion to their energy reserved, instead of routing to minimize consumed power. The minimum energy routing is proposed as in [1]