Energy Efficiency for Cooperative MIMO Wireless Sensor Networks with Optimal Constellation Size under MPSK Modulation Scheme

We consider the energy efficiency for wireless sensor networks (WSNs) where all the nodes operate on batteries so that the total energy consumption should be minimized. One feasible and effective approach is to treat several individual single-antenna nodes which cooperative at the transmitter and receiver as multiple-antenna, i.e., cooperative MIMO. In this context, for the given bit error rate, we first analyze the total energy consumption under the MPSK modulation scheme by using space time block coding in the cooperative MIMO WSNs. Meanwhile, the upper bound of total energy consumption will be deduced. For both short and long transmission distance, we show the trend of the total energy consumption over the constellation size and obtain the optimal constellation size especially achieving the lowest system energy consumption. Additionally, the total energy consumption can be significantly saved by utilizing cooperative MIMO especially at long transmission distance.

I. Introduction

As well known, the Multiple-Input Multiple-Output (MI-MO) technique was introduced to provide reliable high-speed wireless communication links particularly in harsh environments [1] [2]. Then at the base station and access point sides, MIMO therewith was utilized in cellular networks and wireless local area networks to deal with the challenges of low reliability and low transmission rates. In Wireless Sensor Networks (WSNs), it is the fact that each sensor node operates on batteries so that the energy cost must be minimized while providing reliable communication links. However, recent WSN design requirements cannot achieve high transmission rates. Subsequently, the concept of cooperative MIMO was proposed in WSNs to offer reliable communication links in order to minimize the total consumption for networks by exploiting the collaborative features of sensor nodes [3] [4]. Cooperative MIMO expresses the concept that multiple sensor nodes cooperate to transmit and/or receive information, unlike the traditional MIMO technology where the signals are exchanged between two devices with multiple antennas for each device. Multiple sensor nodes are grouped physically in advance and then cooperate to transmit and/or receive. Therefore, compared with inter-group communication, sensor nodes communicate with relatively lower power within a group. Furthermore, by adopting the cooperative MIMO concept, we can achieve more advantages, particularly in terms of energy efficiency [5].