Presentation on theme: "OFDM Transmission over Gaussian Channel"— Presentation transcript:
1 OFDM Transmission over Gaussian Channel Gwo-Ruey Lee
2 Outlines OFDM Transmission over Gaussian Channel Gaussian Distribution The AWGN Channel ModelOFDM System Performance over AWGN ChannelThe Signal Constellations of Different Modulation over AWGN Channel
3 Gaussian Distribution 1/2The PDF of a Gaussian or normally distributed random variable isThe PDF of a Gaussian-distributed random variable
4 Gaussian Distribution 2/2The CDF of a Gaussian or normally distributed random variable iswhereThe CDF of a Gaussian-distributed random variable
5 The AWGN Channel Model 2/2 The received signal in the interval may be expressed aswhere denotes the sample function of the additive white Gaussian noise (AWGN) process.
6 The AWGN Channel Model 2/2 The channel is assumed to corrupt the signal by the addition of white Gaussian noise as shown below+AWGNReceived SignalTransmitted SignalChannelTransmission model for received signal passed through an AWGN channel
7 OFDM System Performance over AWGN Channel 1/6Random Data GeneratorSerial-to-Parallel ConverterSignal MapperParallel-to-Serial ConverterGuard Interval InsertionS(t)IFFTOFDM TransmitterAWGNChannel ModelSerial Data OutputGuard Interval RemovalSerial-to-Parallel ConverterSignal Dema-pperParallel-to-Serial ConverterFFTOFDM Receiver
8 OFDM System Performance over AWGN Channel 2/6Modulation of OFDM subcarrier is analogous to the modulation in conventional serial systems.The modulation schemes of the subcarriers are generally QAM or PSK in conjunction with both coherent and non-coherent detection.As the additive white Gaussian noise (AWGN) in the time domain channel corresponds to AWGN of the same average power in the frequency domain, an OFDM system performance in an AWGN channel is identical to that of a serial system.Analogously to a serial system, the bit error rate (BER) verses signal-to-noise rate (SNR) characteristics are determined by the modulation scheme used.It can be seen from the figures that the experimental BER performance of the OFDM system is in very good accordance with the theoretical BER curves of conventional serial systems in AWGN channels.
9 OFDM System Performance over AWGN Channel 3/6BER versus SNR curves for the OFDM system in AWGN channel using BPSK, QPSK, 8PSK,16-PSK .Simulation parameterValueChannelAWGNFFT size1024Subcarrier #ModulationBPSK, QPSK,8PSK, 16PSKGuard TypeCyclic PrefixSNRdB
10 OFDM System Performance over AWGN Channel 4/6PSKBPSKQPSK with Gray codeM-ary PSKwhere
11 OFDM System Performance over AWGN Channel 5/6BER versus SNR curves for the OFDM system in AWGN channel using BPSK/QPSK, 16QAM, 64QAM, 256QAM.Simulation parameterValueChannelAWGNFFT size1024Subcarrier #ModulationBPSK, QPSK, 16QAM, 64QAM, 256QAMGuard TypeCyclic PrefixSNRdB
12 OFDM System Performance over AWGN Channel 6/6QAM
13 The Signal Constellation of Different Modulation over AWGN Channel 1/6Signal-space diagram for 8-PSKSignal-space diagram for 16-QAM
14 The Signal Constellation of Different Modulation over AWGN Channel 2/6(a) BPSK, SNR=10, (b) BPSK, SNR=20(a)(b)
15 The Signal Constellation of Different Modulation over AWGN Channel 3/6(c) QPSK, SNR=10, (d) QPSK, SNR=20;(c)(d)
16 The Signal Constellation of Different Modulation over AWGN Channel 4/6(e) 8PSK, SNR=10, (f) 8PSK, SNR=20;(e)(f)
17 The Signal Constellation of Different Modulation over AWGN Channel 5/6(g) 16PSK, SNR=10, (h) 16PSK, SNR=20;(g)(h)
18 The Signal Constellation of Different Modulation over AWGN Channel 6/6(i) 16QAM, SNR=10, (j) 16QAM, SNR=20(i)(j)
19 References Richard van Nee, Ramjee Prasad, OFDM wireless multimedia communication, Artech House Boston London, 2000. Ahmad R. S. Bahai and Burton R. Saltzberg, Multi-carrier digital communications - Theory and applications of OFDM, Kluwer Academic / Plenum Publishers New York, Boston, Dordrecht, London, Moscow 1999. L. Hanzo, W. Webb and T. Keller, Single- and multi-carrier quadrature amplitude modulation – Principles and applications for personal communications, WLANs and broadcasting, John Wiley & Sons, Ltd, 2000. Zou, W.Y.; Yiyan Wu, “ COFDM: An overview ” Broadcasting, IEEE Transactions on, Vol. 41, Issue 1, pp. 1 –8, Mar Simon Haykin, Communication Systems, John Wiley & Sons, Inc., 3rd edition, 1994. Roger L. Peterson, Rodger E. Ziemer, David E. Borth, Introduction to spread spectrum communications, Prentice Hall International Editions, 1995.