Inter-Symbol Interference (ISI)

디지털통신 다섯째주 2강

Inter-Symbol Interference (ISI)

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

Inter-Symbol Interference (ISI)

 ISI in the detection process due to the filtering effects of the system

 Overall equivalent system transfer function

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creates echoes and hence time dispersion

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causes ISI at sampling time

Inter-Symbol Interference (ISI) ^(cont’d)

 Nyquist pulses: No ISI at the sampling time

 Ideal Nyquist pulse:

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

Inter-Symbol Interference (ISI) ^(cont’d)

 Nyquist bandwidth constraint

 Ideal Nyquist filter is not realizable.

 Goals and trade-off in pulse-shaping

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Reduce ISI

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Efficient bandwidth utilization

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Robustness to timing error (small side lobes)

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1 symbol s Hz

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Inter-Symbol Interference (ISI) ^(cont’d)

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

Inter-Symbol Interference (ISI) ^(cont’d)

 Raised-Cosine Filter

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A Nyquist pulse (No ISI at the sampling time)

3.3.2 Error-Performance Degradation

Signal Processing Lab., http://signal.korea.ac.kr Dept. of Elec. and Info. Engr., Korea Univ.

Inter-Symbol Interference (ISI) ^(cont’d)

 Square-Root Raised Cosine (SRRC) filter and Equalizer