MAC Protocol for Two-Tier Underwater Wireless Networks With Distance-Dependent Propagation Delay Variation

In this paper, we consider a two-tier communication scenario for the data transmission of underwater sensor network. The underwater sensor nodes form single-hop clusters around the gateway nodes and communicate with them via acoustic wireless links, while the gateway nodes communicate to the remotely located sink node directly via radio frequency (RF) wireless links. Thus, the field data is collected at the sink node via two-hop communication links. The first hop acoustic communication link is characterized by long propagation delay and distance-dependent delay variance, whereas the second hop is considered to be connected by satellite links which is characterized by long propagation delay but negligible propagation delay variance. We use ( $X$ , $Y$ ) to denote that medium access control (MAC) protocol $X$ is used at first hop and MAC protocol $Y$ is used at second hop. For the first hop communication, we propose and analyze the performance of dynamic reservation protocol (DRP) in presence of transmitter-receiver distance-dependent propagation delay variance. Then, considering TDMA-reservation protocol (TRP) in the second hop, we analyze (DRP, TRP) protocol performance at the sink. Further, we study the optimum cluster size that maximizes the overall network utilization and compare the performance with the (Aloha, Aloha) protocol. We show that, for Exponentially distributed large message the utilization of our protocol set (DRP, TRP) is approximately thrice the utilization of (Aloha, Aloha) protocol. Also, the delay of (DRP, TRP) is significantly less than the delay of (Aloha, Aloha) with long message size as well as with high load scenario. The analytical results are supported by discrete event based random network simulation studies.