Eecs 455 univ of michigan fall 2011 october 22 2012 6

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Unformatted text preview: (Univ. of Michigan) Fall 2011 October 22, 2012 6 / 31 Lecture Notes 13 Receiver for two carriers √ 2P cos(2π f1 t ) Low Pass Filter Parallel to Serial Data Sink Low Pass Filter √ 2P cos(2π f2 t ) EECS 455 (Univ. of Michigan) Fall 2011 October 22, 2012 7 / 31 Lecture Notes 13 OFDM Two data streams transmitted on two orthogonal carriers. The output (ideally) of each would only depend on the corresponding transmitted signal at that frequency. The bandwidth of each carrier is relatively narrow so there is not significant distortion due to frequency selective fading. Guard intervals (cyclic prefix) are added to mitigate the multipath interference from one data symbol to the next data symbol. EECS 455 (Univ. of Michigan) Fall 2011 October 22, 2012 8 / 31 Lecture Notes 13 OFDM with Multipath s(t ) h (t ) r (t ) L− 1 h(t ) = l =0 αl δ(t − τl ) L− 1 H (f ) = l =0 EECS 455 (Univ. of Michigan) αl exp(−j 2π f τl ) Fall 2011 October 22, 2012 9 / 31 Lecture Notes 13 OFDM with Multipath h(t ) τ0 τ1 EECS 455 (Univ. of Michigan) τ3 τ2 Fall 2011 τ4 October 22, 2012 t 10 / 31 Lecture Notes 13 Multipath 4 15 3 10 |H ( f ) | (dB) ℑ (exp( j 2 πf τl ) 2 1 0 −1 5 0 −5 −2 −10 −3 −4 −4 −2 0 2 4 ℜ (e x p j 2 π f τ l ) ( EECS 455 (Univ. of Michigan) −15 0 5 10 f (Hz ) Fall 2011 October 22, 2012 11 / 31 Lecture Notes 13 3GPP Standard: Typical Urban Multipath −5 h(t ) (dB) −10 −15 −20 0.5 1.0 1.5 2.0 t (µs) Reference: http://www.quintillion.co.jp/3GPP/Specs/25943-600.pdf EECS 455 (Univ. of Michigan) Fall 2011 October 22, 2012 12 / 31 Lecture Notes 13 Multipath 2 15 10 1 |H ( f ) | (dB) ℑ [αl exp( − j 2 πf τl )] 1.5 0.5 0 −0.5 5 0 −5 −1 −10 −1.5 −2 −2 0 2 ℜ [ α l e x p − j 2 π f τ l )] ( EECS 455 (Univ. of Michigan) Fall 2011 −15 0 5 10 f (MHz ) October 22, 2012 13 / 31 Lecture Notes 13 OFDM with Multipath 6 5 Data Symbol 1 Guard Data Symbol 2 Guard τ1 4 Data Symbol 1 Guard Data Symbol 2 Guard τ2 3 Data Symbol 1 Guard 2 Data Symbol 2 Guard τ3 1 Data Symbol 1 Guard Data Symbol 2 Guard No Intersymbol Interference 0 0 1 2 EECS 455...
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