Combining Parallel Sequence Spread Spectrum (PSSS) with OFDM - Concept and Simulation Results

In this paper, we present a novel multi-carrier spread spectrum (MCSS) system which uses Parallel Sequence Spread Spectrum (PSSS) as its spreading transform. This technique called PSSS-OFDM, allows flexible control over the amount of spreading to provide a variable rate link at minimal complexity gain over standard OFDM, requiring only a simple correlator before the IFFT block. Using a single-tap phase correction equalizer, simulations show a gain of at least 4 dB in Eb/N0 over plain PSSS at BER ≤ 0.1 over plain PSSS. PSSS-OFDM is also shown to provide diversity gain over standard BPSK-OFDM by trading robustness for lower spectral efficiency. PSSS-OFDM achieves comparable BER to standard OFDM with the trade-off of having approximately half of its spectral efficiency through the use of precoding. The scheme also performs progressively better against OFDM as RMS delay spread is increased. Thus, PSSS-OFDM could be used to provide OFDM with multipath robustness in channels with high delay spread as a substitute for coded OFDM and has potential for use in high data rate systems such as WLANs.