Throughput-Efficient Super-TDMA MAC Transmission Schedules in Ad Hoc Linear Underwater Acoustic Networks

Abstract

Underwater acoustic (UWA) sensor network deployments may be used in many applications for environmental, scientific, military and commercial purposes. Several topologies are in use, but the most widely used topology is linear. Indeed, placing nodes on a single line offers more opportunities in terms of large coverage and high-rate services.The UWA channel is a shared medium. Thus, a medium access control (MAC) protocol is necessary, primarily to regulate and coordinate nodes' access. MAC protocol design should take into consideration large propagation delays to favor better network throughput. Performance of most developed protocols in linear topologies does not exceed 1 in terms of normalized network throughput, or equivalently, channel utilization. We explore transmission schedules in three important contexts: (1) single collision domain with unicast traffic. In an N -node network, we develop transmission schedules achieving a normalized network throughput of 2 − (2/N ). This is the best that can be done in such a context, as demonstrated using a general greedy approach combined with an exhaustive search for small-size networks.(2) single collision domain with broadcast traffic. We propose a periodic per-node fair schedule with the shortest period. Achievable throughput in such conditions is close to N/2. Likewise, we prove that the throughput is upper bounded by N − 1 under the per-node fairness constraint. (3) partially-overlapping collision domains with unicast traffic. We consider a simple illustration of such a configuration. The proposed transmission schedule depicts a scenario where messages originate at one end of the network, and are sequentially relayed node-by-node (i.e., hop-by-hop) in the direction of the final destination located at the other end of the network. Furthermore, for all three discussed contexts, we build up computationally-efficient algorithms that generate transmission schedules regardless of network size. We explore the idea of exploiting non-zero propagation delays for linear topologies to improve network throughput. In recent UWA sensor networks, the linear topology is a fundamental component that may be used to build more complex network configurations. This study would then serve as a base for future research into this area.

A Collision-Free Hybrid MAC Protocol Based on Pipeline Parallel Transmission for Distributed Multi-Channel Underwater Acoustic Networks

“…In contention-free MAC protocols, the researches on parallel transmission were mostly focused on TDMA. Many TDMA protocols used the time domain parallel transmission to optimize their time slot allocations [6][7][8][9][10][11][12]. Some of them also made use of the network topology to reuse some time slots [8][9][10][11][12], which can be regarded as passive space domain parallel transmission.…”

“…In the contention-free MAC protocols, because CDMA and FDMA can provide each node an independent channel, which means that nodes can send data packets whenever needed, the researches on parallel transmission were mostly focused on time division multiple access (TDMA). Time and space domain parallel transmission opportunities were often used to optimize the TDMA time slot allocation [6][7][8][9][10][11][12]. Because no control information is needed in TDMA, the design of parallel transmission is simplified to the question of static communication resource allocation, which can be efficiently solved by many mathematical tools and methods.…”

UW-SVC: Scalable Video Coding Transmission for In-Network Underwater Imagery Analysis

“…The underwater acoustic channel presents problems for a coordinated and synchronized system such as TDMA, but due to the severe bandwidth constraint, it is important to use a Medium Access Control (MAC) that does not constrain vehicles to an even smaller slice of bandwidth, such as FDMA. Authors in [19] show that even in the underwater acoustic environment, and specially for multicast transmissions, TDMA can allow for efficient and collision-free communications. Other random-and controlled-access MAC solutions such as Carrier-sense Multiple Access (CSMA) transmit multiple packets through the same underwater channel, which might lead to packet collisions at the receiver [2].…”

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

“…The idea of exploiting the time overlapping of travelling waves to increase the throughput in TDMA networks has been already proposed [6,13,14]. It has been successfully applied to several topologies, like a grid mesh of sensors [15] or in a linear network [16], by means of dynamic linear programming. Nevertheless, these methods, based on a sequential decision problem slot by slot, are far from easy to implement in networks with a medium/large number of nodes.…”

“…Another key point in UWSNs is the physical topology. We consider a static monitoring network with fixed nodes anchored to the seabed, which is a realistic assumption for a monitoring or surveillance UWSN [16]. According to the number of nodes, and the area to cover for sensing, we can find the formation ranging from simple isolated linear networks (called string or chain networks) up to clusters of subnetworks linked through special nodes acting as master nodes.…”