PERFORMANCE EVALUATION OF RAKE RECEIVER USING DIRECT SEQUENCE SPREAD SPECTRUM

2. AJAL.A.J
PERFORMANCE EVALUATION OF RAKEPERFORMANCE EVALUATION OF RAKE
RECEIVER USING DIRECT SEQUENCERECEIVER USING DIRECT SEQUENCE
SPREAD SPECTRUMSPREAD SPECTRUM
(ASST. PROF. IN ECE, FISAT - KOCHI

3. PRESENTATION OVERVIEW

4. INTRODUCTION TO RAKEINTRODUCTION TO RAKE
RECEIVERRECEIVER
The RAKE receiver was originallyThe RAKE receiver was originally
developed in the 1970’s as adeveloped in the 1970’s as a
‘Diversity’ receiver‘Diversity’ receiver
The RAKE receiver derives its nameThe RAKE receiver derives its name
from the fact that the bank offrom the fact that the bank of
correlators has an appearance similarcorrelators has an appearance similar
to the fingers of a rake.to the fingers of a rake.
spread communication spectrumspread communication spectrum
modulaton is basic to the operation ofmodulaton is basic to the operation of
CDMA wirelessCDMA wireless ..

5. CONTD …CONTD …
Designated to equalize the effect ofDesignated to equalize the effect of
multipath.multipath.
the RAKE receiver seeks to combat thethe RAKE receiver seeks to combat the
effect of the multipath by using aeffect of the multipath by using a
correlation method to detect the echocorrelation method to detect the echo
signals individually and then select thesignals individually and then select the
strongest among them.strongest among them.
This diversity scheme is calledThis diversity scheme is called selectionselection
combiningcombining..

6. BLOCK DIAGRAM—RAKE RECEIVER

7. The finger whose correlation output is the highest isThe finger whose correlation output is the highest is
choosen for demodulationchoosen for demodulation
The output signal of the finger is the de-spreadedThe output signal of the finger is the de-spreaded
signal.signal.
This de-spreaded signal is then demodulated accordingThis de-spreaded signal is then demodulated according
to the coherent BPSK demodulation method.to the coherent BPSK demodulation method.
we use enough correlators in the receiver to span awe use enough correlators in the receiver to span a
region of delaysregion of delays
sufficiently wide to encompass all the significant echoessufficiently wide to encompass all the significant echoes
that are likely to occur in the multipath environmentthat are likely to occur in the multipath environment

8. BLOCK DIAGRAM OF THE SYSTEMBLOCK DIAGRAM OF THE SYSTEM
1. INFORMATION SOURCE1. INFORMATION SOURCE
2. CONVOLUTIONAL CODER2. CONVOLUTIONAL CODER
3. BLOCK INTERLEAVING3. BLOCK INTERLEAVING
4. ORTHOGONAL SPREADING4. ORTHOGONAL SPREADING
5. PN SEQUENCE MULTIPLICATION5. PN SEQUENCE MULTIPLICATION
6. BPSK MODULATION6. BPSK MODULATION
7. MULTIPATH CHANNEL7. MULTIPATH CHANNEL
8. RAKE RECIVER8. RAKE RECIVER
9. BPSK DEMODULATION9. BPSK DEMODULATION
10. DE-BLOCK INTERLEAVING10. DE-BLOCK INTERLEAVING
11. VITERBI DECODER11. VITERBI DECODER

9. INFORMATION
SOURCE
CONVOLUTIONAL
CODER
BLOCK
INTERLEAVER
ORTHOGONAL
SPREADING
PN SEQUENCE
MULTIPLICATION
BPSK
MODULATION
RF MODULE

10. CONVOLUTIONAL
DE-CODER
(VITERBI )
DE-BLOCK
INTERLEAVER
BPSK
DE-MODULATION
RAKE
RECEIVER

11. 1] INFORMATION SOURCE
The binary datais transmitted as frames, each of which
contains 64 bits. The data is generated at 9.6 kbps.
•2] CONVOLUTIONAL CODER
•The channel-coding scheme used is convolutional coding.
• Each frame from the source is subjected to convolution
coding.
•After convolution coding, the bit rate is 19.6 kbps.
•3] BLOCK INTERLEAVING
•Block interlacing is performed to improve the bit
error rate performance of the overall system.
•It prevents loss of signal due to burst errors

12. 4.4. ORTHOGONAL SPREADINGORTHOGONAL SPREADING
The output of the block interleaver is subject toThe output of the block interleaver is subject to
orthogonal spreading by Walsh codeorthogonal spreading by Walsh code

13. 5]5] PN Sequence MultiplicationPN Sequence Multiplication
Orthogonal spreading is required to distinguish betweenOrthogonal spreading is required to distinguish between
different users, but the cross correlation properties of washdifferent users, but the cross correlation properties of wash
codes are poor, hence we perform PN sequencecodes are poor, hence we perform PN sequence
multiplication which essentially acts as a mask.multiplication which essentially acts as a mask.
6]6] BPSK MODULATIONBPSK MODULATION
Now, all the user’s BPSK waves are superimposed on eachNow, all the user’s BPSK waves are superimposed on each
other and transmitted through the channel.other and transmitted through the channel.
7]7]MULTIPATH CHANNELMULTIPATH CHANNEL

14. 8]8]RAKE RECIVERRAKE RECIVER
The received multipath faded signal is passed to the RAKE receiver.The received multipath faded signal is passed to the RAKE receiver.
The diversity scheme used isThe diversity scheme used is SELECTING COMBININGSELECTING COMBINING..
The de-spreading is done with the PN sequenceThe de-spreading is done with the PN sequence
and the user specific Walsh codeand the user specific Walsh code..
9]9] BPSK DEMODULATIONBPSK DEMODULATION
Coherent BPSK demodulation of the selected rake finger output isCoherent BPSK demodulation of the selected rake finger output is
performed and integrated over a symbol duration.performed and integrated over a symbol duration.
10]10] DE-BLOCK INTERLEAVINGDE-BLOCK INTERLEAVING
This block performs the inverse operaion of the block interleaver.This block performs the inverse operaion of the block interleaver.
The bits received serially are into a matrix of 8 rows and 16 columnsThe bits received serially are into a matrix of 8 rows and 16 columns
row-wise and then read out column-wiserow-wise and then read out column-wise..

15. 11. VITERBI DECODER11. VITERBI DECODER
VITREBI ALGORITHMVITREBI ALGORITHM
DEMYSTIFIEDDEMYSTIFIED

16. STEP-1STEP-1
STARTING AT LEVEL j=m ; COMPUTESTARTING AT LEVEL j=m ; COMPUTE
THE METRIC FOR THE SINGLE PATHTHE METRIC FOR THE SINGLE PATH
ENTERING EACH STATE OF THEENTERING EACH STATE OF THE
ENCODERENCODER
STEP-2STEP-2
INCREMENT THE LEVEL j BY 1.INCREMENT THE LEVEL j BY 1.
COMPUTE METRIC FOR ALL THE PATHSCOMPUTE METRIC FOR ALL THE PATHS
STORE SURVIVOR & ITS METRICSTORE SURVIVOR & ITS METRIC
STEP-3STEP-3
IF LEVEL j < L + M ; REPEAT STEP- 2 ;IF LEVEL j < L + M ; REPEAT STEP- 2 ;
OTHERWISE STOPOTHERWISE STOP

19. FORGONE CONCLUSIONFORGONE CONCLUSION
Thus the paper helps to evaluateThus the paper helps to evaluate
performance of RAKE receiver inperformance of RAKE receiver in
multipath environmentmultipath environment
The following parameters areThe following parameters are
analyzed with RAKE receiveranalyzed with RAKE receiver
1] noise {AWGN}1] noise {AWGN}
2] no: of users2] no: of users
The variation of signal with noise &The variation of signal with noise &
signal no: of users are studiedsignal no: of users are studied
Graphical o/p’ s are shown withGraphical o/p’ s are shown with
MATLAB fig: windowMATLAB fig: window

20. REFERENCE

22. QUERRIES ? ? ?