Its a research paper from ieee In this letter, analytical expressions are derived for

the power spectral density (PSD) of orthogonal frequency division

multiplex (OFDM) signals employing a cyclic prefix (CP-OFDM)

or zero padding (ZP-OFDM) time guard interval. Under the relatively

weak assumptions that i) the data are independent and identically

distributed on all OFDM subcarriers and ii) the OFDM

pulse shape is sufficiently localized in time, simple closed-form PSD

expressions can be obtained. These expressions are then compared

to existing OFDM PSD expressions and validated by inspecting the

power spectra of some standardized OFDM signals.