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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/25943600.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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