We propose Plena, a packet length adaptation scheme exploiting recently proposed error estimating codes (EEC) for low-power wireless networks. We carefully consider two low-power MAC protocols in modeling the energy consumption of different packet lengths. Based on the modeling and analysis, we give closed form solutions for the optimal packet length in terms of energy efficiency. EEC allows for instant estimation of the bit error rate (BER) in a partially correct packet, making it possible for predicting packet reception ratios (PRRs) at different packet lengths without the need of direct measurement in an iterative process. Fast convergence of Plena makes it suitable for mobile environments in which the channel characteristics are frequently changing. We evaluate Plena's computation overhead based on the commonly used TelosB nodes. Results show that the computation overhead of Plena is acceptably small. We also perform extensive simulations and testbed experiments to study the performance of Plena under different configurations. Results show that Plena achieves better energy efficiency than existing works.

A body sensor network (BSN) is a wireless network of biosensors and a local processing unit, which is commonly referred to as the personal wireless hub (PWH). Personal health information (PHI) is collected by biosensors and delivered to the PWH before it is forwarded to the remote healthcare center for further processing. In a BSN, it is critical to only admit eligible biosensors and PWH into the network. Also, securing the transmission from each biosensor to PWH is essential not only for ensuring safety of PHI delivery, but also for preserving the privacy of PHI. In this paper, we present the design, implementation, and evaluation of a secure network admission and transmission subsystem based on a polynomial-based authentication scheme. The procedures in this subsystem to establish keys for each biosensor are communication efficient and energy efficient. Moreover, based on the observation that an adversary eavesdropping in a BSN faces inevitable channel errors, we propose to exploit the adversary's uncertainty regarding the PHI transmission to update the individual key dynamically and improve key secrecy. In addition to the theoretical analysis that demonstrates the security properties of our system, this paper also reports the experimental results of the proposed protocol on resource-limited sensor platforms, which show the efficiency of our system in practice.