ASCENT: Adaptive SelfConfiguring sEnsor Networks Topologies

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ASCENT Adaptive Self-Configuring sEnsor Networks
Topologies
AND
Alberto Cerpa and Deborah Estrin Laboratory for
Embedded Collaborative Systems --
http//lecs.cs.ucla.edu

• LECS

Goal To exploit the redundancy provided by high
density sensor networks to extend the
system lifetime while providing communication and
sensing coverage.
Why self-configuration?
What are the challenges?

• Smart and cheap sensors will be deployed to form
  densely distributed wireless networks.
• It will be far easier to deploy larger numbers
  of nodes initially than to deploy additional
  nodes or additional energy reserves at a later
  date (similar to the economics of stringing cable
  for wired networks)
• Ad-hoc deployment
• Nodes must self-configure to form a topology
  because the sensor field will not be deployed in
  a regular fashion. More importantly, uniform
  deployment does not correspond to uniform
  connectivity (unpredictable propagation effects
  when antennae are close to the ground, obstacles)
• Unattended operation under dynamics
• The large number of elements in these systems
  will preclude manual configuration, and the
  environmental dynamics will preclude design-time
  pre-configuration.

• Level of dynamics
• The large number of nodes will introduce
  increased levels of system dynamics.
• High level of environmental dynamics.
• Energy constraints imposed by unattended systems
• These systems must be long-lived and operate
  without manual intervention.
• The system must execute the measurements and
  adaptive configuration in an energy constrained
  fashion
• Scaling challenges
• Associated with the large numbers of nodes that
  will co-exist to achieve desired spatial coverage
  and robustness.

Problem Finding the right balance in the number
of nodes that build the basic topology
Basic Tradeoff

• Deploy too few nodes
• The distance between neighboring nodes will be
  too great and the packet loss rate will increase
  or
• The energy required to transmit the data over the
  longer distances will be prohibitive.

• Use all deployed nodes simultaneously
• The system will be expending unnecessary energy
  and
• The nodes may interfere with one another by
  congesting the communication channel.

Solution ASCENT, an adaptive self-configuring
scheme using localized algorithms.
 
How does it work?
Initial Results

• The nodes can be in active or passive state.
• Active nodes are part of the topology and forward
  data packets (using an orthogonal routing
  mechanism that runs on the topology).
• Nodes in passive state can be sleeping or
  collecting network measurements. They do not
  forward any packets.
• Each node measures the number of neighbors and
  message loss locally.
• Each node then makes an informed decision to join
  the network topology or to perform some form of
  adaptation (e.g. reducing its duty cycle to save
  energy).
• Active nodes with poor connectivity request help
  to other passive neighbor in the vicinity to
  improve coverage.

• Implementation on our SCADDS testbed
• Low-power Radiometrix RPC radio and PC104
  stacks.
• Run real experiments with up to 30 nodes (not
  simulations).

Future Work Tiered Architecture

• Use of heterogeneous hardware components. One
  size does not fit all.
• Some of the nodes will be able to use higher
  power, long range radios in addition to the low
  power, short range ones.
• Develop self-configuring algorithms that could
  detect and fix network partitions of the short
  range radio topology.
• Additional research issues
• Interaction between ASCENT and data dissemination
  protocols.
• Relation between simulation and real experiments.

Ref Cerpa and Estrin, ASCENT Adaptive
Self-Configuring sEnsor Networks Topologies,
Submitted for publication, February 2001.