AJAL.A.J

PERFORMANCE EVALUATION OF RAKE PERFORMANCE EVALUATION OF RAKE RECEIVER USING DIRECT SEQUENCE RECEIVER USING DIRECT SEQUENCE

SPREAD SPECTRUMSPREAD SPECTRUM

(ASST. PROF. IN ECE, FISAT - KOCHI

PRESENTATION OVERVIEW

INTRODUCTION TO RAKE INTRODUCTION TO RAKE RECEIVERRECEIVER

The RAKE receiver was originally The RAKE receiver was originally developed in the 1970’s as a ‘Diversity’ developed in the 1970’s as a ‘Diversity’ receiver receiver

The RAKE receiver derives its name from The RAKE receiver derives its name from the fact that the bank of correlators has the fact that the bank of correlators has an appearance similar to the fingers of a an appearance similar to the fingers of a rake.rake.

spread communication spectrum spread communication spectrum modulaton is basic to the operation of modulaton is basic to the operation of CDMA wirelessCDMA wireless . .

CONTD …CONTD …Designated to equalize the effect of Designated to equalize the effect of multipath.multipath.

the RAKE receiver seeks to combat the the RAKE receiver seeks to combat the effect of the multipath by using a effect of the multipath by using a correlation method to detect the echo correlation method to detect the echo signals individually and then select the signals individually and then select the strongest among them. strongest among them.

This diversity scheme is called This diversity scheme is called selection selection combiningcombining..

BLOCK DIAGRAM—RAKE RECEIVER

The finger whose correlation output is the highest is The finger whose correlation output is the highest is choosen for demodulationchoosen for demodulation

The output signal of the finger is the de-spreaded The output signal of the finger is the de-spreaded signal.signal.

This de-spreaded signal is then demodulated according This 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 a we use enough correlators in the receiver to span a region of delaysregion of delays

sufficiently wide to encompass all the significant echoes sufficiently wide to encompass all the significant echoes that are likely to occur in the multipath environmentthat are likely to occur in the multipath environment

BLOCK DIAGRAM OF THE BLOCK DIAGRAM OF THE SYSTEMSYSTEM

1. INFORMATION SOURCE1. INFORMATION SOURCE2. CONVOLUTIONAL CODER2. CONVOLUTIONAL CODER3. BLOCK INTERLEAVING3. BLOCK INTERLEAVING4. ORTHOGONAL SPREADING4. ORTHOGONAL SPREADING5. PN SEQUENCE MULTIPLICATION5. PN SEQUENCE MULTIPLICATION6. BPSK MODULATION6. BPSK MODULATION7. MULTIPATH CHANNEL7. MULTIPATH CHANNEL8. RAKE RECIVER8. RAKE RECIVER9. BPSK DEMODULATION9. BPSK DEMODULATION10. DE-BLOCK INTERLEAVING10. DE-BLOCK INTERLEAVING11. VITERBI DECODER11. VITERBI DECODER

INFORMATION SOURCE

CONVOLUTIONAL CODER

BLOCK INTERLEAVER

ORTHOGONAL SPREADING

PN SEQUENCE MULTIPLICATION

BPSK MODULATION

RF MODULE

CONVOLUTIONAL DE-CODER(VITERBI )

DE-BLOCK INTERLEAVER

BPSK DE-MODULATION

RAKE RECEIVER

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

4. 4. ORTHOGONAL SPREADINGORTHOGONAL SPREADING

The output of the block interleaver is The output of the block interleaver is subject to orthogonal spreading by Walsh subject to orthogonal spreading by Walsh codecode

5] 5] PN Sequence MultiplicationPN Sequence Multiplication Orthogonal spreading is required to distinguish Orthogonal spreading is required to distinguish

between different users, but the cross between different users, but the cross correlation properties of wash codes are poor, correlation properties of wash codes are poor, hence we perform PN sequence multiplication hence we perform PN sequence multiplication which essentially acts as a mask.which essentially acts as a mask.

6] 6] BPSK MODULATIONBPSK MODULATION

Now, all the user’s BPSK waves are Now, all the user’s BPSK waves are superimposed on each other and transmitted superimposed on each other and transmitted through the channel.through the channel.

7]7]MULTIPATH CHANNELMULTIPATH CHANNEL

8]8]RAKE RECIVERRAKE RECIVERThe received multipath faded signal is passed to the RAKE The received multipath faded signal is passed to the RAKE receiver.receiver.The diversity scheme used is The 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 Coherent BPSK demodulation of the selected rake finger output is performed and integrated over a symbol duration.output is performed and integrated over a symbol duration.

10] 10] DE-BLOCK INTERLEAVINGDE-BLOCK INTERLEAVING

This block performs the inverse operaion of the block This block performs the inverse operaion of the block interleaver.interleaver.The bits received serially are into a matrix of 8 rows and 16 The bits received serially are into a matrix of 8 rows and 16 columns row-wise and then read out column-wisecolumns row-wise and then read out column-wise..

11. VITERBI DECODER11. VITERBI DECODER

VITREBI ALGORITHM VITREBI ALGORITHM DEMYSTIFIEDDEMYSTIFIED

STEP-1STEP-1

STARTING AT LEVEL j=m ; COMPUTE THE STARTING AT LEVEL j=m ; COMPUTE THE METRIC FOR THE SINGLE PATH ENTERING METRIC FOR THE SINGLE PATH ENTERING EACH STATE OF THE ENCODER EACH STATE OF THE ENCODER

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

FORGONE CONCLUSIONFORGONE CONCLUSIONThus the paper helps to evaluate Thus the paper helps to evaluate performance of RAKE receiver in performance of RAKE receiver in multipath environmentmultipath environment

The following parameters are The 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 with Graphical o/p’ s are shown with MATLAB fig: windowMATLAB fig: window

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