Ben Miller
What is a Distributed
Algorithm?

 A distributed algorithm is a type of parallel
algorithm
 They are designed to run on multiple interconnected
processors
 Separate parts of the algorithm are run
simultaneously on independent processors
What is a Distributed
Algorithm?

 Each of the processors has its own memory
 The processors send messages to each other
Wireless Sensor Networks

 Wireless Sensor Networks are made up of a series of
distributed sensors
 The sensors collect data and pass it through the
network
 The sensors are designed to consume very little
power
Wireless Sensor Networks

 Each sensor node typically consists of a
microcontroller, radio, and battery
Distributed Algorithms for
Sensor Networks

Self-Spreading
Transmission Power Control
Distributed Fault Tolerant Routing
Distributed Self-Spreading
Algorithm

 One of the challenges in the field of sensor networks
is the deployment of the sensors
 The sensors must be properly spaced.
 If the sensors are too far apart the coverage regions
won’t overlap and the network could become
partitioned
 If the sensors are too close to each other they won’t
cover the entire area of interest
Distributed Self-Spreading Algorithm

 A node’s movement is based on the combined forces
acting on it due to its neighboring nodes.
Distributed Self-Spreading Algorithm

The algorithm has 4 parts:
 1: Initialization
 2: Partial Force Calculation
 3: Oscillation Check
 4: Stability Check
 Parts 2,3, and 4 repeat until the node stops moving
Transmission Power Control

The Problem:
Sensor networks use wireless communication to
transmit their observations
Sensors have a limited energy supply, so they have to
work as efficiently as possible
Radio communication uses a lot of energy
Transmission Power Control

Solution:
Sensor networks can use distributed algorithms to
dynamically adjust transmission power
Each sensor node should use the lowest possible
transmission power while remaining connected to the
network
Distributed Transmission
Power Control Algorithm

Local Mean Algorithm
 All nodes start with the same Transmission Power
 Each node periodically broadcasts a message
containing its identity
 All the other nodes that receive the message send an
acknowledgment message back to the sender
 If the number of acknowledgments received is under
a minimum threshold, the node increases
transmission power before broadcasting again
Local Mean Algorithm

 The node increases its transmission power by a
certain factor for every neighbor that is missing
towards the minimum threshold
 The node decreases its transmission power by a
certain factor for every neighbor exceeding its
maximum threshold
 The node stops adjusting its transmission power
once it is within the neighbor threshold
Local Mean Algorithm

Advantages:
Increased network lifetime compared to
fixed-transmission power assignments
Easy to implement
Highly scalable due to its dynamic nature
Distributed Fault Tolerant Routing

In large-scale Wireless Sensor Networks,
sensor nodes are grouped into clusters.
Each cluster has a leader called a Cluster
Head, or Gateway, which collects data from
the cluster and sends it to a basestation

Distributed Fault Tolerant Routing

The Problem:
Gateways consume a lot of power, and they
are often deployed in harsh environments
This makes them prone to failure
The failure of a Gateway can leave entire
clusters of sensor nodes unable to send data
to the basestation
Distributed Fault Tolerant Routing

Solution
If a gateway fails, the gateways behind the
failed gateway should send their data to a
different nearby gateway instead
Distributed Fault Tolerant Routing

The Algorithm:
Each gateway broadcasts a Hello message
If a gateway receives a Hello message from a
neighbor that is closer to the basestation, the
neighbor is added to the Forward set.
If the neighbor is not closer, it is put in a
Backup set
Distributed Fault Tolerant Routing

The Algorithm:
If a gateway is within range of the
basestation, it sends its data directly to the
basestation
If the basestation is not within range, the
gateway sends data to a neighbor in the
Forward set
If the Forward set is empty, send to a
gateway in the Backup set
Distributed Fault Tolerant Routing

Case 1: Failure of a Forward Gateway
 If a gateway in the Forward set is found to be faulty, choose
another gateway in the Forward set
Distributed Fault Tolerant Routing

Case 2: Gateway with no Forward Gateways
 If a gateway’s Forward set is empty, select a gateway from the
backup set (G3 reroutes to G2 when G7 and G8 die)
Sources

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
Lenzen, Christoph. "Distributed Algorithms for Sensor Networks." Hebrew University of Jerusalem
.
Heo, and Varshney. “Energy-Efficient Deployment of Intelligent Mobile Sensor Networks”
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.307.4273&rep=rep1&type=pdf

Kubish, Karl, Wolisz, Zhong, Rabaey, “Distributed Algorithms for Transmission Power Control in
Wireless Sensor Networks”
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1200410
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Md. Azharuddin, Prasanta K. Jana “A distributed algorithm for energy efficient and fault tolerant
routing in wireless sensor networks” August 2014
http://link.springer.com/article/10.1007%2Fs11276-014-0782-2#/page-1
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