Lifetime Maximization for Sensor Networks with Hetrogeneous Nodes

We consider joint optimization problems among link, MAC, and routing layers for wireless sensor networks with hetrogeneous nodes where battery lifetime maximization for a certain portion of nodes is more important than the maximization across all nodes in the network. For such applications, we propose two battery lifetime maximization schemes: a sequential joint link, MAC, and routing optimization, and a receive antenna selection for burst data applications. Numerical results show that proposed schemes greatly increase the battery lifetime for the node group regarded as more critical while the total energy consumption degradation maintains in a reasonable amount. I. INTRODUCTION Wireless sensor network (WSN) has been paid continuous attention due to its wide range of applications such as secu- rity, health, and disaster monitoring applications, etc. Recent advances in hardware technology make it easier to deploy the WSN by allowing more signal processing functionality to be integrated in a single chip. In such sensor networks, sensors are normally powered by small batteries and replacement of those batteries are expensive or nearly impossible in a certain case. Consequently, maximizing battery lifetime of sensors by reducing energy consumption for end-to-end transmissions has become a key design issue for the WSN. For sensor networks, component nodes are mainly designed to cooperate together for the end-to-end transmission. Thus the energy minimization should be jointly performed across all layers of protocol stack since all layers contribute to the energy consumption during the transmission. In (1) and (2), joint optimization between link and MAC layers are considered and optimal time slot lengths are computed based on time- division multiple aceess (TDMA) scheme by minimizing the total energy consumption. In such a cross-layer design, a constellation size or the number of data bits to be transmitted is determined by the link layer optimizations according to chan- nel capacity of physical links. MAC and routing layer compute time slot lengths of the TDMA scheme which minimize the total energy consumption with appropriate constraints such as a flow conservation (3). It is therefore of great benefit to jointly minimize the energy consumption over both date rates among links and link powers which affects the channel capacity. Throughout this paper, a scenario where nodes in the network have different energy property is considered. For this scenario, we classify entire nodes into two groups where one group is more difficult to access than the other. As a system of interest in this paper, we assume some nodes in the network are responsible for collecting information at a remote site where an approach to those nodes for maintenance operations takes a long time and is very expensive. Also some other nodes are responsible for relaying the information to the base station (BS) which can be approached for periodic maintenance purposes even though it is expensive. In such a system, the battery lifetime maximization for the information collecting node is much more important than the lifetime maximization across all nodes in the network. However, it is still required for relay nodes to minimize the energy consumption as much as possible to reduce the maintenance cost provided that the battery lifetime for information collecting nodes is minimal. In this paper, we consider joint optimization problems among link, MAC, and routing layers for the WSN with these hetrogeneous nodes and propose two energy minimiza- tion schemes. First scheme we propose is a successive joint optimization across two groups. In this scheme, the energy consumption of information collecting nodes is minimized over constraints such as the flow conservation (3) and the transmission deadline as a first stage optimization. This stage of the optimization produces modulation orders and time slot lengths among each link involving information collecting nodes. By doing so, as will be shown by simulations, the energy consumption for information collecting nodes can be greatly reduced. However, since the energy minimization for remaining relay nodes is not taken into account, the total energy consumption is much higher than the energy consump- tion optimized over total nodes in the networks. To combat such problem, at the second stage, the energy consumption of relay nodes will be minimized by jointly optimizing across remaining relay nodes and the BS provided that parameters for information collecting nodes optimized at the previous stage are preserved. As a result, the proposed scheme greatly reduces the energy consumption of information collecting node while the increase in the total energy consumption is maintained in a reasonable amount at the same time. The second scheme we propose in this paper employs an antenna selection scheme (4) at relay nodes. In certain applications, relay nodes can be easily treated by maintenance processes such as the battery replacement or location changes,