RLS-adaptive parallel interference cancellation assisted decision-directed channel estimation for OFDM

OFDM systems employing multiple transmit antennas have recently drawn wide interest in the context of both space-time coded- and multi-user space-division multiple access (SDMA) arrangements. A prerequisite for using coherent detection at the receiver is the availability of reliable channel transfer factor estimates. Robust parallel interference cancellation (PIC) assisted decision-directed channel estimation (DDCE) has been shown in the literature to be also applicable to scenarios, where the number of users is in excess of the number of OFDM subcarriers - normalized to the number of Channel Impulse Response (CIR) related taps to be estimated - which imposed a limitation in the context of least-squares assisted DDCE techniques invoked in conjunction with multiple transmit antennas. In this paper we will demonstrate that the Recursive Least-Squares (RLS) algorithm is applicable to optimizing the predictors' coefficients on a CIR-related tap-by-tap basis. Compared to 'robust', non-adaptive approaches the proposed solution has the advantage of a potentially lower estimation MSE and a higher resilience to erroneous subcarrier symbol decisions.