A Comparison of MAC Protocols for Ultrasonic Intra-body Sensor Networks

Wireless intra-body networks of implantable biomedical devices have the potential to enable revolutionary healthcare and clinical applications. In our previous work we investigated the use of ultrasonic waves as an alternative to radio frequency (RF) waves as physical carrier of information, and proposed Ultrasonic WideBand (UsWB), the first ultrasonic integrated physical and medium access control (MAC) layer protocol. In this paper, we compare the performance of the UsWB MAC protocol with two existing MAC protocols originally designed for wireless RF-based networks, ALOHA and Carrier Sense Multiple Access (CSMA). In particular, we discuss the protocol performance in terms of (i) average network throughput and packet drop rate, (ii) average short-term fairness, (iii) average packet delay and packet delay variation, and (iv) energy consumption per bit. We show that UsWB outperforms ALOHA in terms of throughput, while CSMA can achieve comparable performance under specific setups. However, both ALOHA and CSMA have very high packet drop rates as compared to UsWB. The latter is capable of keeping the packet drop rate under a pre-defined threshold. Moreover, UsWB significantly outperforms both ALOHA and CSMA in terms of short-term fairness, average packet delays and delay variation. Finally, CSMA has the highest energy consumption per bit, because of long idle sensing times, whereas UsWB has the lowest, and it can be further reduced by trading throughput for energy consumption through energy-minimizing rate adaptation.