Ajal sree buddha

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PERFORMANCE EVALUATION OF RAKE RECEIVER USING DIRECT SEQUENCE SPREAD SPECTRUM

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Ajal sree buddha

  1. 1. 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
  2. 2. PRESENTATION OVERVIEW
  3. 3. 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 ..
  4. 4. 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..
  5. 5. BLOCK DIAGRAM—RAKE RECEIVER
  6. 6. 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
  7. 7. 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
  8. 8. INFORMATION SOURCE CONVOLUTIONAL CODER BLOCK INTERLEAVER ORTHOGONAL SPREADING PN SEQUENCE MULTIPLICATION BPSK MODULATION RF MODULE
  9. 9. CONVOLUTIONAL DE-CODER (VITERBI ) DE-BLOCK INTERLEAVER BPSK DE-MODULATION RAKE RECEIVER
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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..
  14. 14. 11. VITERBI DECODER11. VITERBI DECODER VITREBI ALGORITHMVITREBI ALGORITHM DEMYSTIFIEDDEMYSTIFIED
  15. 15. 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
  16. 16. 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
  17. 17. REFERENCE
  18. 18. QUERRIES ? ? ?

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