Of michigan fall 2011 100 frequency hz october 22

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Unformatted text preview: ) Fall 2011 100 frequency (Hz) October 22, 2012 150 27 / 31 Lecture Notes 13 OFDM Signal and Spectrum (M =16) M=16 M=16 15 40 30 OFDM Power Spectrum (dB) OFDM Signal and Envelope 10 rms value 5 0 −5 20 10 0 −10 −20 −30 −10 −40 −15 0 0.5 time (s) EECS 455 (Univ. of Michigan) 1 Fall 2011 −50 50 100 frequency (Hz) October 22, 2012 150 28 / 31 Lecture Notes 13 OFDM Signal and Spectrum (M =64) M=64 M=64 40 20 30 15 OFDM Power Spectrum (dB) OFDM Signal and Envelope 25 rms value 10 5 0 −5 −10 −15 10 0 −10 −20 −30 −40 −20 −25 0 20 0.2 0.4 time (s) EECS 455 (Univ. of Michigan) 0.6 Fall 2011 −50 50 100 frequency (Hz) October 22, 2012 150 29 / 31 Lecture Notes 13 OFDM Summary OFDM has narrow spectrum (relative to single carrier with same data rate) OFDM has larger peak-to-average power ratio Requires larger backoff of amplifier to avoid nonlinear distortion compared to single carrier Larger backoff usually implies a smaller power efficiency for the amplifier Frequency selective fading can be mitigated in OFDM by appropriate channel estimation, coding and interleaving OFDM has lower sidelobes (smaller high frequency components) and thus can not make fast transitions of the amplitude or phase compared to unfiltered BPSK/QPSK. EECS 455 (Univ. of Michigan) Fall 2011 October 22, 2012 30 / 31 Lecture Notes 13 OFDM in Wireless Systems Parameter 802.11a (WiFi) UWB (Multiband) LTE (10 MHz) WiMax (10MHz) Bandwidth Sample Time Number of Active Carriers Number of Guard Carriers Data Carriers Pilots Carriers FFT Size Subcarrier frequency spacing 20MHz 50ns 52 12 48 4 64 0.3125MHz (20MHz/64) 3.2 µs 0.8 µs (16 samples) 4.0 µs 528 MHz 1.8939ns 112 10 100 12 128 4.125MHz (528MHz/128) 242.42ns 70.08ns (37 samples) 312.5ns 10MHz 65.104 ns 601 423 1024 15kHz 10MHz 1024 up to 914 – 1024 – 1024 10.9375kHz 66.67 µ s 4.69-5.21 µ s 91.429 µ s 11.428 µ s 71.35-71.88 µs 102.857 µs IFFT period Guard Interval OFDM Symbol Duration EECS 455 (Univ. of Michigan) Fall 2011 October 22, 2012 31 / 31...
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