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Spread-Spectrum Technique and its Application to DS/CDMA Bernard H. Fleury Navigation & Communications Section (NavCom) Department of Communication Technology, Aalborg University DK - 9220 Aalborg, Fredrik Bajers Vej 7 C1 e-mail: bfl@es.aau.dk Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 #1 P R
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  Spread-Spectrum Technique andits Application to DS/CDMA Bernard H. Fleury Navigation & Communications Section (NavCom)Department of Communication Technology, Aalborg UniversityDK - 9220 Aalborg, Fredrik Bajers Vej 7 C1 e-mail:  bfl@es.aau.dk Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 1 P RINCIPLES OF  SS  TECHNIQUE Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 2   B LOCK  D IAGRAM OF A  D IGITAL  C OMMUNICATION  S YSTEM ã  Transmitter: Amplification / Filtering Bit stream10011 d ( t ) t WaveformModulatorCarrier Modulation & T  S ã  Receiver: Baseband Demodulation Bit stream10001 ˆ d ( t ) Waveform Filtering / Amplification & t Demodulator T  S Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 3  B LOCK  D IAGRAM OF A  S PREAD  S PECTRUM  S YSTEM ã  SS Transmitter: ã  SS Receiver: Widebandnoise-likesignal t GeneratorPseudo-NoiseBit stream10011 d ( t ) Pseudo-NoiseGeneratorAmplification / FilteringCarrier Modulation &Filtering/Amplification &Baseband Demodulation ˆ d ( t ) 10001Bit streamSynchronizationWaveformDemodulatorWaveformModulator T  S t T  S c ( t )ˆ c ∗ ( t ) Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 4   M AIN  F EATURES OF THE  N OISE -L IKE  W IDEBAND  S IGNAL  c ( t ) ã  Usually, the bandwidth  W   of  c ( t )  is much higher than the bandwidth B  of  d ( t ) : –  In military applications:  G   W B  ≈ 100 ... 1000 –  In UMTS/W-CDMA,  G  = 4 − 256 . ã  The signal  c ( t )  appears noise-like and random to any unintendeduser. ã  The signal  c ( t )  is easily generated by a device (pseudo-randomgenerator) the initialization setting of which (key) is known only tothe intended transmitter and receiver. ã  Synchronizationshouldbeeasilyperformedattheintendedreceiver. Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 5  M ULTIPLICATIVE  B ANDWIDTH  E XPANSION 0000000011111111 0000011111 01 01 00001111 00000000000000001111111111111111 000000111111 00000000000000001111111111111111 000000111111 0011 P  0 frequency B  ≈  1 T s c ( t ) d ( t )  d ( t ) c ( t ) 1Power spectrum of  c ( t ) Power spectrum of  d ( t ) Power spectrum of  d ( t ) c ( t ) frequency η  =  P  02 B P  0 frequency W   +  1 T s  ≈  W  P  02 W   =  ηG W  Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 6   M ULTIPLICATIVE  B ANDWIDTH  E XPANSION −3 −2 −1 0 1 2 300.20.40.60.81 Pulse Spectra. Processing Gain = 16 Frequency normalised to the symbol rate    N  o  r  m  a   l   i  s  e   d   |   S   |    2 −3 −2 −1 0 1 2 300.20.40.60.81 Tranmitted Spectrum. Processing Gain = 16 BPSK Pulse SpectrumChip SpectrumTransmitted Spectrum Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 7  M ULTIPLICATIVE  B ANDWIDTH  E XPANSION −3 −2 −1 0 1 2 300.20.40.60.81 Pulse Spectra. Processing Gain = 64 Frequency normalised to the symbol rate    N  o  r  m  a   l   i  s  e   d   |   S   |    2 −3 −2 −1 0 1 2 300.20.40.60.81 Tranmitted Spectrum. Processing Gain = 64 BPSK Pulse SpectrumChip SpectrumTransmitted Spectrum Spread-Spectrum Technique and its Application to DS/CDMA, Fall 2008 # 8 
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