Talk on “Spectrum Sensing for Cognitive Radios”

The IEEE Signal Processing Society, Bangalore Chapter
and Department of Electrical communication Engineering, Indian Institute of Science

invite you to a talk on

Spectrum Sensing for Cognitive Radios

Venue: Golden Jubilee Seminar Hall, Department of Electrical Communication

Time & Date: 4 PM, January 22, 2013

Speaker: Dr. Sachin Chaudhari

Inefficient use of radio spectrum is becoming a serious problem as more
and more wireless systems are being developed to operate in crowded
spectrum bands. Cognitive radio offers a novel solution to overcome the
underutilization problem by allowing secondary usage of the spectrum
resources along with high reliable communication. Spectrum sensing is a
key enabler for cognitive radios. It identifies idle spectrum and provides
awareness regarding the radio environment which are essential for the
efficient secondary use of the spectrum and coexistence of different
wireless systems.

The focus of this talk is on the local and cooperative spectrum sensing
algorithms. Local sensing algorithms are presented for detecting
orthogonal frequency division multiplexing (OFDM) based primary user (PU)
transmissions using their autocorrelation property. The proposed
autocorrelation detectors are simple and computationally efficient. Later,
the algorithms are extended to the case of cooperative sensing where
multiple secondary users (SUs) collaborate to detect a PU transmission.
For cooperation, each SU sends a local decision statistic such as
log-likelihood ratio (LLR) to the fusion center (FC) which makes a final
decision. Cooperative sensing algorithms are also proposed using
sequential and censoring methods. Sequential detection minimizes the
average detection time while censoring scheme improves the energy

The performances of the proposed algorithms are studied through rigorous
theoretical analyses and extensive simulations. The distributions of the
decision statistics at the SU and the test statistic at the FC are
established conditioned on either hypothesis. Later, the effects of
quantization and reporting channel errors are considered. Main aim in
studying the effects of quantization and channel errors on the cooperative
sensing is to provide a framework for the designers to choose the
operating values of the number of quantization bits and the target bit
error probability (BEP) for the reporting channel such that the
performance loss caused by these non-idealities is negligible.

Later a performance limitation in the form of BEP wall is established for
the cooperative sensing schemes in the presence of reporting channel
errors. The BEP wall phenomenon is important as it provides the feasible
values for the reporting channel BEP used for designing communication
schemes between the SUs and the FC.

Dr. Sachin Chaudhari received the B.E. degree in electronics from
Visvesvaraya National Institute of Technology, Nagpur, India, in 2002. He
received the M.E. degree in telecommunication from the Indian Institute of
Science, Bangalore, in 2004. From August 2004 to May 2007, he was with
Esqube Communications, Bangalore. In June 2007, he joined the PhD program
at the Department of Signal Processing and Acoustics, Aalto University
School of Electrical Engineering, Finland, which was formerly known as
Helsinki University of Technology (TKK). He recently completed his PhD in
November 2012.

His research interests are in the field of signal processing aspects of
wireless communication systems including Cognitive Radios, OFDM systems,
and CDMA systems. Dr. Chaudhari is recipient of several scholarships such
SITRA (Finnish Innovation Fund), Nokia, Dhirubhai Ambani Foundation.

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