An Adaptive TDMA-based MAC Protocol for Underwater Acoustic Sensor Networks

Acoustic propagation through water suffers from attenuation that increases with both signal frequency and transmission range, with time-varying long propagation delays. The power spectral density of underwater ambient noise also changes with frequency. As a result, the usable channel bandwidth is heavily constrained and Medium Access Control (MAC) protocol design for Underwater Acoustic Sensor Networks (UASNs) is challenging. Striking a balance between channel utilisation and network end-to-end delay is particularly difficult. The Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol has been shown to effectively minimise end-to-end delay and maximise channel utilisation, but existing approaches are reliant on synchronisation which is hard to achieve underwater. This paper introduces a novel robust MAC protocol, based on CFDAMA, exclusively designed for UASNs and called CFDAMA-NoClock. It is capable of providing an adaptive MAC solution without the need for synchronisation amongst independent node clocks. The protocol demonstrates a high level of practicality and simplicity. Both analytical models and comprehensive event-driven simulation of several underwater scenarios show that CFDAMA-NoClock can offer excellent delay/utilisation performance under two distinct traffic types and with various network parameters selected based on practical UASN technologies

TDA-MAC : TDMA without clock synchronization in underwater acoustic networks

This paper investigates the application of underwater acoustic sensor networks for large scale monitoring of the ocean environment. The low propagation speed of acoustic signals presents a fundamental challenge in coordinating the access to the shared communication medium in such networks. In this paper, we propose two medium access control (MAC) protocols, namely, Transmit Delay Allocation MAC (TDA-MAC) and Accelerated TDA-MAC, that are capable of providing time division multiple access (TDMA) to sensor nodes without the need for centralized clock synchronization. A comprehensive simulation study of a network deployed on the sea bed shows that the proposed protocols are capable of closely matching the throughput and packet delay performance of ideal synchronized TDMA. The TDA-MAC protocols also significantly outperform T-Lohi, a classical contention-based MAC protocol for underwater acoustic networks, in terms of network throughput and, in many cases, end-To-end packet delay. Furthermore, the assumption of no clock synchronization among different devices in the network is a major advantage of TDA-MAC over other TDMA-based MAC protocols in the literature. Therefore, it is a feasible networking solution for real-world underwater sensor network deployments

Traffic-aware cell management for green ultra-dense small cell networks

To reduce the power consumption of fifth-generation ultradense small-cell networks, base stations can be switched to low-power sleep modes when local traffic levels are low. In this paper, a novel sleep mode control algorithm is proposed to control such sleep modes. The algorithm innovates a concept called traffic-aware cell management (TACM). It involves cell division, cell death, and cell migration to represent adaptations of networks, where the state transitions of base stations are controlled. Direction of arrival (DOA) is adopted for distributed decision making. The TACM algorithm aims at reducing the network power consumption while alleviating the impacts of applying sleep modes, such as mitigating system overheads and reducing user transmission power. The TACM algorithm is compared with a recent consolidated baseline scheme by simulation on networks with unbalanced traffic distributions and with base stations at random locations. In contrast, the TACM algorithm shows a significant improvement in mitigating system overheads due to the absence of load information exchange overhead and up to 72 times less switching frequency. Up to 81% network power consumption can be reduced compared with the baseline scheme if considering high energy consumption of switching transient states. In addition, at a low traffic level, average uplink transmission power is reduced by 79% comparatively. Furthermore, the impact of important performance-governing parameters of the TACM algorithm is analyzed. The insensitivity to the estimation accuracy of DOA is also demonstrated. The results show that the proposed TACM algorithm has a comprehensive advantage of power reduction and overhead mitigation over the baseline scheme

Using the Man9(GlcNAc)2 – DC-SIGN pairing to probe specificity in photochemical immobilization

We demonstrate the expected preference of an immobilised oligosaccharide Man(9)(GlcNAc)(2) upon a 96-well photochemical array, for its known receptor, the cell-surface lectin Dendritic Cell-Specific ICAM3 Grabbing Nonintegrin (DC-SIGN) when compared to immobilised competing monosaccharides

Scalable adaptive networking for the Internet of Underwater Things

Internet of Underwater Things (IoUT) systems comprising tens or hundreds of underwater acoustic communication nodes will become feasible in the near future. The development of scalable networking protocols is a key enabling technology for such IoUT systems, but this task is challenging due to the fundamental limitations of the underwater acoustic communication channel: extremely slow propagation and limited bandwidth. The aim of this paper is to propose the JOIN protocol to enable the integration of new nodes into an existing IoUT network without the control overhead of typical state-of-the-art solutions. The proposed solution is based on the capability of a joining node to incorporate local topology and schedule information into a probabilistic model that allows it to choose when to join the network to minimize the expected number of collisions. The proposed approach is tested in numerical simulations and validated in two sea trials. The simulations show that the JOIN protocol achieves fast convergence to a collision-free solution, fast network adaptation to new nodes, and negligible network disruption due to collisions caused by a joining node. The sea trials demonstrate the practical feasibility of this protocol in real UAN deployments and provide valuable insight for future work on the trade-off between control overhead and reliability of the JOIN protocol in a harsh acoustic communication environment

Medial Prefrontal Cortex Predicts Intertemporal Choice

People often make shortsighted decisions to receive small benefits in the present rather than large benefits in the future, that is, to favor their current selves over their future selves. In two studies using fMRI, we demonstrated that people make such decisions in part because they fail to engage in the same degree of self-referential processing when thinking about their future selves. When participants predicted how much they would enjoy an event in the future, they showed less activity in brain regions associated with introspective self-reference—such as the ventromedial pFC (vMPFC)—than when they predicted how much they would enjoy events in the present. Moreover, the magnitude of vMPFC reduction predicted the extent to which participants made shortsighted monetary decisions several weeks later. In light of recent findings that the vMPFC contributes to the ability to simulate future events from a first-person perspective, these data suggest that shortsighted decisions result in part from a failure to fully imagine the subjective experience of one's future self.Psycholog

Auction Design Enhancements for Non-Combinatorial Auctions

We evaluate a number of possible enhancements to the FCC auctions. We consider only changes to the current auction rules that stay within the basic format of the simultaneous multiple round auction for individual licenses. This report summarizes and extends our e-mail exchanges with FCC staff on this topic. A subsequent report will cover auctions with combination bids. Overall, the FCC spectrum auctions have been an enormous success. However, there are two design goals in the auction where important improvement can be achieved within the basic rules structure. These are restricting collusion among bidders and reducing the time taken to complete the auction. This report focuses on enhancements that help to achieve these two goals. Some of the suggested changes also streamline the auction process so large auctions can be conducted more quickly without sacrificing efficiency.Auctions; Spectrum Auctions; Multiple-Round Auctions; Efficiency