ICI Mitigation for OFDMA Uplink Systems

Abstract

Orthogonal frequency-division multiplexing multiple access (OFDMA) has been considered as a promising multiple access technique in OFDM-based communication systems. In an ideal OFDMA system, no intercarrier interference (ICI) occurs. However, in high-speed mobile environments, the channel may be time-variant during one OFDMA symbol period. In such a condition, the mobility-induced ICI will degrade the system performance seriously. To remove the ICI effect, the zero-forcing (ZF) method is one of the simple techniques. Unfortunately, the direct ZF method needs to invert an N x N ICI matrix, requiring a prohibitively high complexity when N is large. In this paper, we first derive a structured OFDMA uplink signal model consisting of FFTs/IFFTs. Exploring this structure and using Newton's iteration for matrix inversion, we develop a low-complexity ZF method. With our formulation, fast Fourier transforms (FFTs) can be used to reduce the complexity. Thus, the proposed method can reduce the complexity from O(N(3)) to O(N log(2) N). Simulations show that the proposed method can have the similar performance to the direct ZF method while requires much lower complexity.