583 research outputs found
Local Multicoloring Algorithms: Computing a Nearly-Optimal TDMA Schedule in Constant Time
The described multicoloring problem has direct applications in the context of
wireless ad hoc and sensor networks. In order to coordinate the access to the
shared wireless medium, the nodes of such a network need to employ some medium
access control (MAC) protocol. Typical MAC protocols control the access to the
shared channel by time (TDMA), frequency (FDMA), or code division multiple
access (CDMA) schemes. Many channel access schemes assign a fixed set of time
slots, frequencies, or (orthogonal) codes to the nodes of a network such that
nodes that interfere with each other receive disjoint sets of time slots,
frequencies, or code sets. Finding a valid assignment of time slots,
frequencies, or codes hence directly corresponds to computing a multicoloring
of a graph . The scarcity of bandwidth, energy, and computing resources in
ad hoc and sensor networks, as well as the often highly dynamic nature of these
networks require that the multicoloring can be computed based on as little and
as local information as possible
Local heuristic for the refinement of multi-path routing in wireless mesh networks
We consider wireless mesh networks and the problem of routing end-to-end
traffic over multiple paths for the same origin-destination pair with minimal
interference. We introduce a heuristic for path determination with two
distinguishing characteristics. First, it works by refining an extant set of
paths, determined previously by a single- or multi-path routing algorithm.
Second, it is totally local, in the sense that it can be run by each of the
origins on information that is available no farther than the node's immediate
neighborhood. We have conducted extensive computational experiments with the
new heuristic, using AODV and OLSR, as well as their multi-path variants, as
underlying routing methods. For two different CSMA settings (as implemented by
802.11) and one TDMA setting running a path-oriented link scheduling algorithm,
we have demonstrated that the new heuristic is capable of improving the average
throughput network-wide. When working from the paths generated by the
multi-path routing algorithms, the heuristic is also capable to provide a more
evenly distributed traffic pattern
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
Energy-rate based MAC protocol for wireless sensor networks and key pre-distribution schemes
Sensor networks are typically unattended because of their deployment in hazardous, hostile or remote environments. This makes the problem of conserving energy at individual sensor nodes challenging. S-MAC and PAMAS are two MAC protocols which periodically put nodes (selected at random) to sleep in order to achieve energy savings. Unlike these protocols, we propose an approach in which node duty cycles (i.e sleep and wake schedules) are based on their criticality. A distributed algorithm is used to find sets of winners and losers, who are then assigned appropriate slots in our TDMA based MAC protocol. We introduce the concept of energy-criticality of a sensor node as a function of energies and traffic rates. Our protocol makes more critical nodes sleep longer, thereby balancing the energy consumption. Security in sensor networks is more important than traditional networks as they are deployed in hostile environments and are more prone to capture. Trusted third party authentication schemes, public-key systems are not suitable owing to their high resource requirements. Key pre-distribution was introduced in to solve this problem. Our scheme achieves identical connectivity compared to the random key pre distribution using a less number of preloaded keys in each sensor node. Our proposed key pre-distribution scheme is based on assigning keys to sensors by placing them on a grid. This approach has been further modified to use multiple mappings of keys to nodes. In each mapping every node gets distinct set of keys which it shares with different nodes. The key assignment is done such that, there will be keys in common between nodes in different sub-grids. After randomly being deployed, the nodes discover common keys, authenticate and communicate securely. The analysis and simulation results show that this scheme is able to achieve better security compared to the random schemes
Machine learning-based decentralized TDMA for VLC IoT networks
In this paper, a machine learning-based decentralized time division multiple
access (TDMA) algorithm for visible light communication (VLC) Internet of
Things (IoT) networks is proposed. The proposed algorithm is based on
Q-learning, a reinforcement learning algorithm. This paper considers a
decentralized condition in which there is no coordinator node for sending
synchronization frames and assigning transmission time slots to other nodes.
The proposed algorithm uses a decentralized manner for synchronization, and
each node uses the Q-learning algorithm to find the optimal transmission time
slot for sending data without collisions. The proposed algorithm is implemented
on a VLC hardware system, which had been designed and implemented in our
laboratory. Average reward, convergence time, goodput, average delay, and data
packet size are evaluated parameters. The results show that the proposed
algorithm converges quickly and provides collision-free decentralized TDMA for
the network. The proposed algorithm is compared with carrier-sense multiple
access with collision avoidance (CSMA/CA) algorithm as a potential selection
for decentralized VLC IoT networks. The results show that the proposed
algorithm provides up to 61% more goodput and up to 49% less average delay than
CSMA/CA.Comment: This work has been submitted to a journal for possible publication.
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