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Unformatted text preview: 12 by using the slope of the curve of carrier phases for pilots versus the subcarrier index n of the pilots [49]. [50] estimates by using two consecutive OFDM blocks for an AWGN frequency selective channel. [51] uses training symbols to jointly estimate the timing and frequency offset; this approach simplifies the receiver design. 2.4 Mitigation of TimeVarying Effects Timevarying channel impairments are caused by either a Doppler shift or a frequency offset. As was explained by Dr. Rappaport in class, the effect of a Doppler shift can be understood in terms of the Doppler frequency f d = ( f c *v )/ c , where f c is the carrier frequency, v is the velocity of the mobile node and c is the velocity of light. The impact of the frequencyoffset fo can be modeled as a multiplicative factor of e j2 fot . Timevarying effects of the channel cause the OFDM signal to spread in frequencydomain and generate ICI [47]. This ICI in the frequencydomain is analogous to ISI in timedomain; while ICI is caused by timevarying impairments, ISI is caused...
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 Spring '09
 Prof
 Frequency

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