Journal Paper

Constant Envelope OFDM(CE-OFDM)offersexcellentrobustness to nonlinear distortion and
noise, but at the cost of poor spectral efficiency (SE). This paper proposes and experimentally validates a
filtered variant, Filtered CE-OFDM (F-CE-OFDM), designed to improve SE while preserving the intrinsic
robustness of CE-OFDM. A flexible optimization framework is introduced, enabling dynamic adjustment
of the filtering parameter α according to different system requirements. Experimental results in a visible
light communication (VLC) setup demonstrate that F-CE-OFDM can consistently outperform conventional
CE-OFDM in terms of SE, achieving gains up to 3 bits/s/Hz when using α=1 and 2πh=1.6 at the
highest average received power level with only a small EVM penalty. Moreover, compared to conventional
OFDM, F-CE-OFDM achieves an EVM improvement of up to approximately 10 dB under low-SNR
conditions. These results highlight F-CE-OFDM as a compelling compromise between SE and EVM,
delivering substantial spectral efficiency enhancement while maintaining strong robustness against noise
and nonlinearities. The proposed scheme introduces only a low-complexity digital filtering stage, implying
negligible impact on implementation cost while largely preserving the power-efficiency benefits inherent
to constant-envelope modulation. Its tunable filtering parameter α enables adaptive operation, allowing the
system to prioritize either low EVM or enhanced SE depending on channel conditions and design objectives.
This versatility makes F-CE-OFDM particularly attractive for communication scenarios constrained by noise
or bandwidth, where maintaining signal integrity and efficient spectrum use are equally critical.