IEEE 802.15.4 is a new standard, uniquely designed for low rate wireless personal area networks (LR-WPANs). It targets ultra-low complexity, cost, and power, for low-data-rate wireless connectivity. However, one of the main problems of this new standard is its insufficient, and inefficient, media access control (MAC) for priority data. This paper introduces an extended contention access period (XCAP) concept for priority packets, also an traffic adaptive contention differentiation utilizing the XCAP (TACDX). The TACDX determines appropriate transmission policy alternatively according to the traffic conditions and type of packet. TACDX achieves not only enhanced transmission for priority packets but it also has a high energy efficiency for the overall network. The proposed TACDX is verified with simulations to measure the performances.

As the need for underwater communication has recently grown, an acoustic modem has become more necessary for the sensor nodes to perform effective underwater communication. To develop acoustic modems for effective underwater communication, some limitations must be overcome, such as the limited power supply and high cost of commercial acoustic modems. Recently, low-power, low-cost acoustic modems have been developed. However, the data rates of these modems are very slow. The objective of this work is to develop an acoustic modem capable of supporting high data rates. We introduce a coherent acoustic modem that uses waterproof ultrasonic sensors to process acoustic waves. The proposed modem is based on a low-power, low-cost, short-range concept, and it also supports a high data rate as confirmed by underwater experiments. Experimental results show that our modem has the best performance among all recently developed low-power modems.

As autonomous underwater vehicles (AUVs) have been widely used to perform cooperative works with sensor nodes for data-gathering, the need for long-range AUVs has further grown to support the long-duration cooperation with sensor nodes. However, as existing data-gathering protocols for the cooperative works have not considered AUVs' energy consumption, AUVs can deplete their energy more quickly before fulfilling their missions. The objective of this work is to develop an AUV based data-gathering protocol that maximizes the duration for the cooperative works. Simulation results show that the proposed protocol outperforms existing protocols with respect to the long-range AUVs.

An Energy-efficient Flexible Beacon Scheduling (EFBS) mechanism is proposed to solve the beacon collision problem in cluster-tree healthcare systems. In EFBS, after clustering, BAN Coordinators perform power control. Then they are divided into groups and each group is assigned one contention-free time-slot. The duration of the beacon-only period is flexible. According to the simulation results, EFBS provides better performance than other beacon scheduling approaches.