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Co
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Coding for the cognitive radio user
• Introduction
• A DPC(Dirty Paper Coding) scheme for the
cognitive user :
o Encoding : channel coding
source coding
o Decoding
• Reference
Most of the frequency spectrum has
already been licensed by government
agencies , such as Federal
Communication Commission(FCC).
Wireless devices have begun
proliferating turning the available
spectrum expensive and rare.
Not every channel in every band is
always in use .According to the FCC
: in some locations or at some times
of day ,70% of the allocated
spectrum is idle.
How to use this dynamically
available spectrum?
The solution may lie in cognitive
radios ,equipped with sensing
devices that detect “quiet
frequency bands” to transmit and
receive data.
Introduction
• A Cognitive Radio is a fully reconfigurable device which can
observe and change or adapt its communication parameters for
enabling secondary usage of the spectrum and yield an
efficient usage of the spectrum.
• The key motivation behind this technology is to increase
spectral utilization and to optimize the use of radio resources.
• The cognitive radio was first proposed by Joseph Mitola in a
seminar at KTH(the Royal Institute of Technology) in 1998.
Depending on transmission
and reception parameters ,
there are two main types of
cognitive radio:
Full
Cognitive
Radio(Mitol
a Radio)
Spectrum
–Sensing
Cognitive
Radio.
Characteristics of Cognitive Radio
Cognitive Capability:
• Identify the unused
spectrum at a specific time
or location (Spectrum
Holes/ White Spaces)
Reconfigurability:
• Transmit and Receive on a
variety of frequencies. Use
different access
technologies.
Cognitive Radio have two main characteristics:
Emerging Issues-Spectrum
Management
Determine which portions of the
spectrum are available : Spectrum
Sensing.
Select the best available channel :
Spectrum Decision.
Coordinate access to this channel with
other users : Spectrum Sharing.
Vacate the channel when a licensed user
is detected :Spectrum Mobility
Advantages of CRN
• Unused spectrum are determined and made use of them
automatically.
• Improves the spectrum utilization by neglecting the over
occupied spectrum channels and filling the unused spectrum
channels.
• Automatically improves and accomplishes its progress and
minimize interference
The simplest form of the cognitive radio channel (CRC)
consisting of one primary and one secondary/cognitive user
•Each user wishes to communicate some infor- mation to its
respective base-station.
•since the two users share the same frequency band, the signal
transmitted by a user interferes with the transmission of the other
•consider the extreme situation where the introduction of the
cognitive radio should have no effect whatsoever on the primary
user’s operation and performance, i.e. the primary system should be
oblivious to the presence of the cognitive user.
A DPC SCHEME FOR THE
COGNITIVE USER
• DPC (Dirty Paper Coding)is a source-channel coding
• A DPC scheme based on turbo codes
• Uses trellis coded quantization (TCQ) for source coding and
an irregular repeat accumulate (IRA) code for channel coding
Encoding
• Channel coding:
• The message sequence is first
encoded using a rate -Rpre
LDPC(low-density parity-check)
precode .
• The precoded information is then
encoded with a rate -RI IRA code
• The degree distribution of the
precoded information node is
denoted by:
λ(x) = Σ Did=2 λ d x
d-1
Di :maximum information node degree ,
λd is the fraction of edges connected to
degree “d” information nodes
• The two types of parity bits follow different degree distributions
ρi
(x) = Σ Di,pd=1 pd(i))
xd−1 , d=1
i = 1, 2, where Di,p
is the maximum degree for parity nodes of type-i and ρd(i)
is
the fraction of type-i edges connected to parity nodes of degree d.
Source coding
The channel coded bits b1[n] and
b2[n]
• V = αS + D, where α is Costa’s
MSE scaling factor S is the side-
information sequence, and D is the
random dither shared by the
encoder and the decoder.
• shifted TCQ symbol at time n is given
by
• U[n] = (b3 + 2b4) + Cb1,b2 + 4K[n] Δ,
• Δ is the step size of the TCQ codebook
Decoding
• The received sequence is first scaled by α followed by dither
removal to obtain Y ′ = αY + D.
• The decoding is done by iterative message passing between the BCJR algorithm and the BP algorithm
Reference
• A Dirty-paper Coding Scheme for the Cognitive Radio
Channel Momin Uppal‡, Guosen Yue†, Yan Xin†, Xiaodong
Wang∗, and Zixiang Xiong‡ ‡Department of Electrical and
Computer Engineering, Texas A&M University, College
Station, TX 77843 †NEC Laboratories America Inc, Princeton,
NJ 08540 ∗Department of Electrical Engineering, Columbia
University, New York, NY 10027 Emails: [email protected],
{yueg,yanxin @nec-labs.com, [email protected],
[email protected], 978-1-4244-6404-3/10/$26.00 ©2010 IEEE
.
