Orthogonal Complex Hadamard Spreading Codes for I/Q Imbalance Mitigation in MC-CDMA Systems

Zero-IF (direct conversion) receivers are very sensitive to non-linearities of analog hardware. A phase and/or amplitude imbalance between the inphase and quadrature signal branch results in a base band signal deterioration known as I/Q imbalance. Especially OFDM and the OFDM-based MC-CDMA modulation technique are affected by this error. This paper proposes a novel orthogonal quaternary MC-CDMA spreading code scheme that uses the inherent mathematical symmetry to mitigate I/Q imbalance without additional computational cost.