A novel reliability based routing protocol for power aware communications in Wireless Sensor Networks Long Tran-Thanh and Janos Levendovszky Budapest University of Technology and Economics, Dept. of Telecommunications, H-1117 Magyar tud. krt. 2, Budapest, Hungary. Emails: ttl@cs.bme.hu, levendov@hit.bme.hu Abstract—In this paper a Rayleigh fading model based reliability-centric routing algorithm is proposed for Wireless Sensor Networks (WSNs). The proposed scheme is optimized with respect to minimal power consumption to improve longevity as well as to ensure reliable packet transmission to the Base Station (BS). Reliability is guaranteed by selecting path over which the probability of correct packet reception of the transmitted packet will exceed a predefined threshold at the BS. It will be pointed out that reliable and power efficient packet forwarding over WSN can be mapped into a constrained optimization problem. This optimization is then reduced to a shortest path problem with specific link metrics solved in polynomial time. Index Terms—wireless sensor networks, reliability, Rayleigh fading model, power awareness I. I NTRODUCTION Due to the recent advances in electronics and wireless communication, the development of low-cost, low-energy, multifunctional sensors have received increasing attention [4]. These sensors are compact in size and besides sensing they also have some limited signal processing and communication capabilities. However, these limitations in size and energy make the WSNs different from other wireless and ad-hoc networks [5]. As a result, new protocols must be developed with special focus on power effectiveness in order to increase the lifetime of the network which is crucial in case appli- cations, where recharging of the nodes is out of reach (e.g. military field observations, living habitat monitoring etc., for more details see [5]). This paper addresses reliable packet transmission in WSN when packets are to be received on the Base Station (BS) with a given reliability in terms of keeping the error probability under a given threshold. Since the success of every individual packet transmission depends on the distance and the power of transmission, the probability of correct reception will diminish exponentially with respect to the number hops, in the case of multi-hop packet transfers. In the paper new optimized algorithm is proposed which have minimal power subject to the constraint of guaranteeing reliable packet transfer to the BS. Our concern is to derive the appropriate path with the corresponding transmission energies needed to achieve a given reliability and to minimize the overall power consumption at the same time. The optimal path from source node i to BS is represented by a set of indices ℜ opt =(i 1 ,i 2 , ..., i L ) where the nodes i j ,j =1, ..., L are selected for packet forwarding from node i (where the packet is originated) to the BS. The reliability of this packet transfer is Reliab = L  j=1 P ij-1ij , where P ij-1ij denotes the probability of successful packet transfer from node i j-1 to node i j . The reliability constraint imposes that Reliab = L  j=1 P ij-1ij ≥ 1 - ε for a given ε. In this paper we will demonstrate that the selection of ℜ opt can be carried out in polynomial time by using any of the shortest path search algorithms. We compare the achieved lifespan and reliability to the corresponding parameters of the traditional protocols by performing extensive simulations. The remainder of the paper can be organized as follows. In Section 2, we give an overview of the related work. In Section 3, we introduce our model for the WSN. The optimal solution for the case of given routing paths is described in Section 4. Section 5 deals with the general case when routing paths can be arbitrary and in Section 6 we take the receiving energy consumption into account as well. Performance analysis is evaluated in Section 7. Finally, the last section concludes this paper. II. RELATED WORK Many research works have been published in the topic of reliable data transport in WSNs recently. These proposed solutions can be classified into two groups: (i) guaranteed delivery approaches; and (ii) stochastic delivery approaches [11]. In guaranteed delivery (or in other words, packet-loss re- covery [10]) approaches, one must guarantee the successful arrival of the packet at the destination. Hence, lost packets are recovered by retransmissions. Considering the technique of recovery, these retransmissions can be end-to-end recovery or per-hop recovery. Recently, per-hop recovery was advocated in many research works [12], [15], since it is easy to manage. On the other hand, end-to-end recovery is believed to be not suitable for WSNs due to the big latency and the large energy cost. In [20], the authors summarized the major research challenges of end-to-end recovery protocols. Examples for guaranteed delivery approaches can be found in [12](PSFQ) or in [13] and [14]. In stochastic delivery (or in other words, packet-loss avoid- ance [10]) approaches, one must choose routing paths such that