Optimal Fair Scheduling in S-TDMA Sensor Networks for Monitoring River Plumes

Abstract

Underwater wireless sensor networks (UWSNs) are a promising technology to provide oceanographers with environmental data in real time. Suitable network topologies to monitor estuaries are formed by strings coming together to a sink node. This network may be understood as an oriented graph. A number of MAC techniques can be used in UWSNs, but Spatial-TDMA is preferred for fixed networks. In this paper, a scheduling procedure to obtain the optimal fair frame is presented, under ideal conditions of synchronization and transmission errors. The main objective is to find the theoretical maximum throughput by overlapping the transmissions of the nodes while keeping a balanced received data rate from each sensor, regardless of its location in the network. The procedure searches for all cliques of the compatibility matrix of the network graph and solves a Multiple-Vector Bin Packing (MVBP) problem. This work addresses the optimization problem and provides analytical and numerical results for both the minimum frame length and the maximum achievable throughput.

Channel Modeling for Underwater Acoustic Network Simulation

“…The first case study investigates the effects of custom beam tracing channel data on the Riverbed Modeler [25] simulations of the ALOHA protocol [86] in a singlehop UAN. The second case study applies statistical channel modeling described in Subsection V-C to investigate its effects on custom MATLAB simulations of Spatial TDMA (STDMA) [87] in a linear UAN scenario.…”

“…The job of a sensor node is to transmit its own packets up the chain and forward data packets from the nodes down the chain. The inherent sparsity of linear network topologies is wellsuited for STDMA, since it can be exploited by assigning TDMA slots to several spatially separated transmissions simultaneously without collision [87], [89], [90], thus reducing the number of slots in the TDMA frame. In fact, Chitre et al [91] show that it is theoretically possible to design packet schedules for networks with long propagation delays (UANs are a typical example of this) that exceed the throughput of networks with small propagation delays by scheduling simultaneous transmissions whilst aligning the delayed interference within a desired time window.…”

Linear TDA-MAC: Unsynchronized Scheduling in Linear Underwater Acoustic Sensor Networks

“…Although MAC protocols based on the classical TDMA frame structure can achieve scalable collision-free packet scheduling, many spatial reuse TDMA, also referred to as Spatial-TDMA (STDMA), protocols proposed in the literature are limited to fixed connectivity and interference patterns to produce efficient and analytically tractable solutions, e.g. [3] [4]. Furthermore, the main drawback of the protocols based on the classical TDMA frame structure is the need for extensive guard intervals to account for long propagation delays of acoustic waves, which often has a large negative impact on the network throughput.…”

Optimal Scheduling and Fair Service Policy for STDMA in Underwater Networks with Acoustic Communications

“…Image transmission from remote sites is the most envisaged capability of UWSNs [1,2,3]. One important case is monitoring the behavior of river-fed sediment plumes in estuaries and deltas [4], because of their influence on water quality and the environment.…”

“…Scheduling is of paramount importance in STDMA networks. Luque-Nieto, et al [4] present optimal STDMA scheduling for linear networks where the sink node collects a single packet from every node in one frame. The problem of finding the shortest frame is addressed as a bin packing problem.…”