University:
Boston University
Course:
CAS PY 211 | General Physics I
Academic year:

2023
Views:

437

Pages:

4
Author:

Patricia West

Asymmetrically Clipped Optical OFDM (ACO-OFDM)  Only odd carriers are modulated. This leads to a symmetry in time domain: s[n] = -s[n+N/2] (Armstrong et al., 2006) ● N = number of carriers/number of FFT points ● s[n] = time domain signal Bipolar (unclipped) cyclic prefix Unipolar (clipped) cyclic prefix ACO-OFDM Theory  Odd carriers only contain information <=> s[n] = -s[n+N/2]  Even carriers only contain information <=> s[n] = s[n+N/2]  CLIP( s[n] ) = ( s[n] + |s[n]| ) / 2 !!! This representation is important !!!  In ACO-OFDM, s[n] = - s[n+N/2] => |s[n]| = |s[n+N/2]|  Therefore, distortion from clipping falls only on the even subcarriers. Pulse-amplitude-modulated Discrete Multitone Modulation (PAM-DMT)  Carriers are modulate with imaginary symbols only. This leads to a symmetry in time domain: s[n] = -s[N-n] (Lee et al., 2009) ● N = number of carriers/number of FFT points ● s[n] = time domain signal Bipolar (unclipped) Unipolar (clipped) cyclic prefix cyclic prefix PAM-DMT Theory  Carriers are modulated with imaginary symbols <=> s[n] = -s[N-n]  Carriers are modulated with real symbols <=> s[n] = s[N-n]  CLIP( s[n] ) = ( s[n] + |s[n]| ) / 2 !!! This representation is important !!!  In PAM-DMT, s[n] = - s[N-n] => |s[n]| = |s[N-n]|  Therefore, distortion from clipping falls only on the real values in frequency domain.