2012 Volume 4 Issue 3 Pages 116-125
By combining two complex signals into one, Four Orthogonal Single Sideband Elements (4-SSB) Modulation has the potential to double the information rate of any transmission system using Quadrature Amplitude Modulation (QAM), including multi-carrier systems, such as Orthogonal Frequency Division Multiplexing (OFDM) or Single Carrier Frequency Division Multiple Access (SC-FDMA). However, effective demodulation of 4-SSB signals remained until now an open issue. This paper shows for the first time that 4-SSB modulation applied to QPSK can be demodulated with vanishing error rate in both AWGN and Rayleigh fading conditions when using a turbo structure at the receiver. We design a turbo equalization technique specifically designed to tackle the challenges of the demodulation of 4-SSB signals. Computer simulations show that Bit Error Rate (BER) performances of 4-SSB QPSK can converge toward the performances of QPSK with the proposed receiver structure. To improve the convergence toward the performance limit, we also present a feedback interference canceller (FIC) at the receiver. Incorporated into the turbo structure, this filter enables a trade-off between transmitter and receiver complexity levels, so as to adapt to different types of links such as uplink and downlink, while preserving performances.
