Orthogonal Frequency Division Multiplexing and Related...
Transcript of Orthogonal Frequency Division Multiplexing and Related...
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EECE5984CE5984Orthogonal Frequency Division Multiplexing and Related Orthogonal Frequency Division Multiplexing and Related
TechnologiesTechnologiesFall 2007Fall 2007
Mohamed Essam Khedr
Performance of OFDM in Gaussian and Fading channels
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MatlabMatlab Assignment #1Assignment #1Thursday 4 October 2007Thursday 4 October 2007
• Develop an OFDM system with the following components– S/P– Mapping model (modulation techniques)– Coding model (conv, turbo)– IFFT– CP– Channel (Gaussian, SFFF channel)– Mapping decoding– Decoding model– FFT– CP removal– Channel Estimation (later)
• Input :pulse shaping, Number of subcarriers, symbol rate, BW, CP ratio
• Output: Signal in time, spectrum, BER, ICI (later), ISI (later)
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SingleSingle--tap, Flat Fading (Rayleigh) tap, Flat Fading (Rayleigh) vsvs AWGNAWGN
Why do we have this huge degradation in performance/reliability?
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Rayleigh Flat Fading ChannelRayleigh Flat Fading Channel
BPSK: Coherent detection.
Conditional on h,
Averaged over h,
at high SNR.
Looks like AWGN, but…
pe needs to be “unconditioned”
To get a much poorer scaling
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Typical error event is due to: channel (h) being in deep fade!… rather than (additive) noise being large.
Conditional on h,
When the error probability is very small.
When the error probability is large:
Typical Error EventTypical Error Event
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OFDM Performance over AWGN channelOFDM Performance over AWGN channel
• The performance of OFDM in AWGN is identical to that of single carrier modulation.
• However:– Problem of PAPR in OFDM: will discuss later in the course– Problem of Guard interval
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OFDM Performance over Flat fading channelOFDM Performance over Flat fading channel
• OFDM performance over Raleigh flat fading channel is similar to single carrier modulation
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OFDM Performance over Frequency Selective Fading OFDM Performance over Frequency Selective Fading channelchannel
• OFDM performance over frequency selective fading channel is similar to single carrier modulation with same modulation in flat fading channels
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Thank you