OPERA: An Optimal Progressive Error Recovery Algorithm for Wireless Sensor Networks
Saad Bin Qaisar and Hayder Radha
Department of Electrical and Computer Engineering
Michigan State University
East Lansing, MI-48824, United States
Abstract—Wireless Sensor Networks (WSNs) require
robustness against channel induced errors while retransmission
based schemes prove too costly for energy constrained
sensor nodes. Channel coding with low rates can
ensure increased reliability, and it can eliminate the need
for costly retransmissions. However, low channel coding
rates on an end-to-end basis (between a source sensor
and a destination base-station) requires a large number
of transmissions of redundant data. In this paper, we
propose an Optimal Progressive Error Recovery Algorithm
(OPERA) over WSNs. Under OPERA, individual
intermediate sensors, which are relaying data toward the
base station, partially and optimally channel-decode the
incoming packets while employing a progressive decrease
in parity bits as data reaches the final destination. OPERA
requires significantly lesser processing than would be
required for complete decoding or full decoding/encoding
at the sensor nodes; and OPERA significantly reduces the
total number of transmissions when compared to optimal
end-to-end channel coding schemes. We use iteratively
decodeable LDPC codes for this purpose. OPERA not
only provides a partial processing framework, but also
an algorithm to optimally map the decoding iterations
over the multi hop network. We provide a comparison
between our iteration assignment scheme and random
iteration assignment, and show that our scheme performs
considerably better. Finally, while being naturally motivated
by the sensor reachback problem, we further develop
a fairness-based OPERA scheme for the allocation of
channel-decoding LDPC iterations to sensor nodes taking
into consideration the life-expectancy of each sensor.
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