power efficient rake receiver for interference reduction in
TRANSCRIPT
RAKE RECEIVERS FOR INTERFERENCE
REDUCTION IN MOBILE COMMUNICATION
GUIDED BY
HELEN MASCREEN
HEAD OF THE DEPARTMENT
ECE
AKASHVIJAYAN
REG NO:13142802
ECE
CONTENTS
INTRODUCTION
MAJOR CRISIS IN MOBILE COMMUNICATION
WHAT IS RAKE RECEIVER?
RAKE RECEIVER –MULTIPATH FADING
RAKE RECEIVER OVERALL STRUCTURE
BASIC PRINCIPLE OF RAKE RECEIVER
RAKE RECEIVER IN WCDMA.
RAKE RECEIVER –FINGER
SELECTION SORTED QR DECOMPOSITION
MIMO SYSTEMS BASED ON PAIRWISE COLUMN SYMMETRISATION
OFDMA
SQRD IN OFDMA
CONCLUSION2
INTRODUCTION
RAKE receiver are the widely used receivers in wireless
communication systems.
Multipath fading and co channel interference are the major crisis
in mobile communication systems.
Mobile communications are mostly based on CDMA,WCDMA
and OFDMA.
MIMO based systems override most of the problems of SISO.
Sorted QR decomposition based system is the advanced and
efficient scheme in real mobile scenario.
SQRD can be performed in different ways for different scenarios
also discussed.
3
Major Crisis arised in mobile
communication
1.Interference Problem
In CDMA and WCDMA cellular systems , reducing the
interference results in direct increase in system capacity
Which results in increased power consumption .
Co-Channel Interference-Co-channel
interference is the cross talk between two different radio
transmitters using the same frequency
radio frequency as is the case with the co-channel cells.
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2.MULTIPATH
Figuire-1
MULTIPATH FADING
Fading : Fluctuation in the received signal power due to
Variations in the received signal amplitude
Variations in the signal phase
Variations in the received signal angle of arrival received signal(different paths travelling different distances may have different phases & angle of arrival).
Reflections and diffraction from object create many different EM waves which are received in mobile antenna.
In the receiver, the waves are added either constructively or destructively and create a Rx signal.
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WHAT IS RAKE RECEIVER ?
A rake receiver is a radio receiver designed to counter the effects
of multipath fading. It does this by using several "sub-receivers"
each delayed slightly in order to tune in to the individual multipath
components.
Each component is decoded independently, but at a later stage
combined in order to make the most use of the different
transmission characteristics of each transmission path.
This could creat a very well result in higher SNR or (Eb/No) in a
multipath environment than in a "clean" environment
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RAKE RECEIVER – MULTIPATH FADING
Rake receiver mitigates multipath fading effect
Multipath fading is a major cause of unreliable wireless channel characteristic
x(t)
y(t) = a1x(t)+a1x(t-d1)+a2x(t-d2)
figure2
8
RAKE RECEIVER – OVERALL ARCHITECTURE
Searcher
Descrambler/Despreader
Descrambler/Despreader
Descrambler/Despreader
combiner
Delay
Delay
Delay
r(t)
d1, d
2, d
3a
1, a
2, a
3Detects delay spread
Compensates propagation delay recombine signal terms without delay
figure3 9
Rake receiver
Finger 1
Finger 2
Channel estimation
Received baseband multipath signal
Finger 3
Output signal
(to decision circuit)
Rake receiver Combining (MRC)
(Generic structure, assuming 3 fingers)
Weighting
Figure-4 10
RAKE RECEIVER(CONTINUED)
The RAKE receiver was designed to equalize the effects of multipath.
It uses a combination of co-relators, code generators, and delays, or “fingers”, to spread out the individual echo signals of the multipath.
Each signal is then delayed according to peaks found in the
received signal. The same sympols obtained via different paths are then combined
together by schemes like MRC.
This combined out puts are fed on to a decision device to decide on the transmitted bits.
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BASIC PRINCIPLE OF RAKE RECEIVER...
Because WCDMA and CDMA has high time- resolution, different path delay of WCDMA AND CDMA signals can be discriminated. Therefore, energy from all paths can be summed by adjusting their phases and path delays.
This is a principle of RAKE receiver.Path Delay
Po
we
r path-1
path-2
path-3
CDMA
Receiver
CDMA
Receiver
•••
Syn
ch
ron
iza
tion
Adder
Path Delay
Po
we
r
CODE A
with timing of path-1
path-1
Po
we
r
path-1
path-2
path-3
Path Delay
Po
we
r
CODE A
with timing of path-2
path-2
interference from path-2 and path-3
•••
Figure-512
RAKE RECEIVER IN WCDMA
In WCDMA system, multi-path propagation improves
the signal quality by use of RAKE receiver.
Time
Po
we
r
Detected Power
RAKEreceiver
Less fluctuation of detected power, because of adding all energy .
Po
we
r
path-1
path-2
path-3
Figure-6 13
Delay ( )
Channel estimation circuit of Rake receiver selects
strongest samples (paths) to be processed in the Rake
fingers:
In the Rake receiver example to follow, we assume L = 3.
1 2 3
Only one path chosen, since adjacent paths may be correlated
Only these paths are constructively
utilized in Rake fingers
L= 3
RAKE RECEIVER- FINGER
SELECTION
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SORTED QR DECOMPOSITION
SQRD method is centered on the QR decomposition decoding
method.
It is based linear algebra decomposition of the channel matrix
H
Here nr ni H is decomposed into unitary matrix Q and
upper triangular matrix R.
Ie,H=QR.
The received symbol vector y is multiplied with
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CONTINUED…
Therefore from the elimination algorithm we can see that transmitted symbol from
the last antenna is
detected first.
These procedure
continues until the symbols are detected.
Since R is an upper
triangular matrix ,the k-thelement of y is mathematically
can be expressed as
yK
Hence y is free interference from layers
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Since Interference is cancelled in each step
The SQRD is based on the modified Gram-Schmidt algorithm.
This method ensures that symbols with larger channel
coefficients are detected first while smaller at later stages,thus
reduces the effect of error propagation.
SQRD can be performed in different ways according to channel
matrixes and can attain better efficiency WCDMA and CDMA .
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MIMO Systems Based on Pairwise Column Symmetrization
Sorted QRD (SQRD) is a famous algorithm to perform QRD
with the layer sort.
The symbol detection is performed sequentialy through layers
proposed algorithm performs QRD based on the modified
Gram-Schmidt (MGS) process.
The column vectors of a real-valued channel matrix are
rearranged pairwise so as to maintain the symmetry between
adjacent column vectors.
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By using this method we can obtain improved error performance
and computational efficiency than other methods.
SQRD can be performed in different ways according to channel
matrixes and can attain better efficiency.
The proposed algorithm rearranges column vectors so as to
maintain the symmetry,
The BER performance is improved with the appropriate
detection order of layers determined by SQRD,
The computational complexity of the conventional SQRD is
increased
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Orthogonal frequency-division multiplexing
FDM in which sub-channels overlap without
interfering
OFDM
Single Carrier Transmission
(WCDMA etc)
Orthogonal Frequency
Division Multiplexing
5 MHz
e.g. 5 MHz
Subcarriers
20
BLOCK DIAGRAM OF OFDMA
21
SQRD IN OFDMA
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CONTINUED…
The process till the mean-square-error of channel
estimate is converged or the expected iterations reach.
Computational complexity for QRD channel estimation
is approximately linearly proportional with number of
transmit antenna and channel length
Iterative QR decomposition can be an ultimate solution
for high performance efficiency.
Thus the interpolation between pilot carriers reduced.
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CONCLUSION
A simplified and power efficient system for reducing multipath
fading useful in a realistic scenario is considered that is based on
Sorted QR decomposition (SQRD)
a) Reduces multipath fading in WCDMA
b) Increase in quality of received signal
c) Reduce BER & Power Dissipation
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REFERENCES
2.Tae-Hwan Kim, Member, IEEE 2014”Low-Complexity Sorted QR
Decomposition for MIMO Systems based on Pairwise Column Symmetrization”
IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 13, NO. 3,
MARCH 2014
3.Andrea Goldsmit “Wireless communications”copyright © 2005 by Cambridge
University press
1.A. Alimi, J. J. Popoola, and K. F. Akingbade “ A power efficient rake
receiver for interferenc reduction in mobile communication systems”
Department of electrical and electronics engineering ,federal
university of engineering ,akure nigeria
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4.Isiaka A. Alimi1, *, Oluyomi Aboderin2 “adaptive mobile
interference reduction in mobile communication systems“ 1Department of Electrical and Electronics Engineering, School of Engineering and
Engineering Technology, Federal University of Technology, Akure,Nigeria
2Department of Engineering and Space Systems, National Space Research and Development
Agency, Abuja, Nigeria
5.Gabriel L. Nazar ,Christina Gimmle,,Norbert Wehn
“Implementation Comparisons of the QR Decomposition for MIMO
Detection”1Instituto de Informática - Universidade Federal do Rio Grande do Sul
Av. Bento Gonçalves, 9500, Bloco IV - Porto Alegre, RS, Brazil
2Fachbereich Elektrotechnik und Informationstechnik -Technische Universität Kaiserslautern
Erwin-Schrödinger-Straße - 67663 Kaiserslautern, Germany
B.Vasavi#1,Mounika Marepalli#2, Leepika
“Evolution of 4G-Research Directions Towards Fourth Generation
Wireless Communication” 3Associate Professor#1 , Computer Science and
EngineeringHyderabad Institute of Technology and Management (HITAM)
Hyderabad, A P, India26
Beena R. Ballal1, Ankit Chadha2, Neha Satam orthogonal frequency
division multiplexing and its applications 1 Assistant Professor, Electronics and Telecommunication,VIT, WadalaMumbai, India
2 Student, Electronics and Telecommunication,VIT, Wadala Mumbai
3 Student, Electronics and Telecommunication,VIT, WadalaMumbai,
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Thank You!!!
THANK YOU
…
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