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CCU Wireless Access Tech. Lab. OFDM Transmission over Gaussian Channel Gwo-Ruey Lee.

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Presentation on theme: "CCU Wireless Access Tech. Lab. OFDM Transmission over Gaussian Channel Gwo-Ruey Lee."— Presentation transcript:

1 CCU Wireless Access Tech. Lab. OFDM Transmission over Gaussian Channel Gwo-Ruey Lee

2 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines OFDM Transmission over Gaussian Channel Gaussian Distribution The AWGN Channel Model OFDM System Performance over AWGN Channel The Signal Constellations of Different Modulation over AWGN Channel

3 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Gaussian Distribution The PDF of a Gaussian or normally distributed random variable is The PDF of a Gaussian-distributed random variable 1/2

4 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Gaussian Distribution The CDF of a Gaussian or normally distributed random variable is where The CDF of a Gaussian-distributed random variable 2/2

5 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The AWGN Channel Model The received signal in the interval may be expressed as where denotes the sample function of the additive white Gaussian noise (AWGN) process. 2/2

6 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The AWGN Channel Model The channel is assumed to corrupt the signal by the addition of white Gaussian noise as shown below Transmission model for received signal passed through an AWGN channel 2/2 + AWGN Received Signal Transmitted Signal Channel

7 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel Serial Data Output OFDM Receiver Channel Model OFDM Transmitter AWGN S(t) Guard Interval Insertion Parallel-to- Serial Converter IFFT Signal Mapper Serial-to- Parallel Converter Random Data Generator Serial-to- Parallel Converter FFT Signal Dema- pper Parallel-to- Serial Converter Guard Interval Removal 1/6

8 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel Modulation 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. 2/6

9 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel Simulation parameterValue ChannelAWGN FFT size1024 Subcarrier #1024 ModulationBPSK, QPSK, 8PSK, 16PSK Guard TypeCyclic Prefix SNR0 - 30 dB BER versus SNR curves for the OFDM system in AWGN channel using BPSK, QPSK, 8PSK,16-PSK. 3/6

10 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel PSK BPSK QPSK with Gray code M-ary PSK where 4/6

11 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel BER versus SNR curves for the OFDM system in AWGN channel using BPSK/QPSK, 16QAM, 64QAM, 256QAM. Simulation parameterValue ChannelAWGN FFT size1024 Subcarrier #1024 ModulationBPSK, QPSK, 16QAM, 64QAM, 256QAM Guard TypeCyclic Prefix SNR0 - 30 dB 5/6

12 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. OFDM System Performance over AWGN Channel QAM 6/6

13 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel Signal-space diagram for 16-QAMSignal-space diagram for 8-PSK 1/6

14 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel (a) BPSK, SNR=10, (b) BPSK, SNR=20 (a)(b) 2/6

15 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel (c) QPSK, SNR=10, (d) QPSK, SNR=20; (c)(d) 3/6

16 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel (e) 8PSK, SNR=10, (f) 8PSK, SNR=20; (e)(f) 4/6

17 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel (g) 16PSK, SNR=10, (h) 16PSK, SNR=20; (g)(h) 5/6

18 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. The Signal Constellation of Different Modulation over AWGN Channel (i) 16QAM, SNR=10, (j) 16QAM, SNR=20 (i)(j) 6/6

19 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. References [1] Richard van Nee, Ramjee Prasad, OFDM wireless multimedia communication, Artech House Boston London, 2000. [2] 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. [3] 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. [4] Zou, W.Y.; Yiyan Wu, COFDM: An overview Broadcasting, IEEE Transactions on, Vol. 41, Issue 1, pp. 1 –8, Mar. 1995. [5] Simon Haykin, Communication Systems, John Wiley & Sons, Inc., 3rd edition, 1994. [6] Roger L. Peterson, Rodger E. Ziemer, David E. Borth, Introduction to spread spectrum communications, Prentice Hall International Editions, 1995.


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