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

7

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

beenarballal@gmail.com

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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