LAUSR

This letter proposes an orthogonal frequency division multiplexing (OFDM) scheme that incorporates the index modulation, spread spectrum, and C-transform techniques. The developed OFDM selects a code from a known set to spread data in frequency, uses the code’s index and $M$ -ary symbols to send information, and applies the C-transform to modulate subcarriers. Computer simulations reveal that our OFDM outperforms two competitive benchmarks and achieves gains of about 15.6 dB and 15.5 dB when spectral efficiency is SE = 1 bps/Hz and 14.5 dB and 13 dB when SE = 1.5 bps/Hz at a bit error rate of 10⁻⁴.