In this letter, we propose a modified version of Fast Independent Component Analysis (FICA) algorithm to solve the self-interference cancellation (SIC) problem in In-band Full Duplex (IBFD) communication systems. The complex mixing problem is mathematically formulated to suit the real-valued blind source separation (BSS) algorithms. In addition, we propose a method to estimate the ambiguity factors associated with ICA lumped together with the channels and residual separation error. Experiments were performed on an FD platform where FICA-based BSS was applied for SIC in the frequency domain. Experimental results show superior performance compared to least squares SIC by up to 6 dB gain in the SNR.

In this paper, we propose a code‐division multiple‐access (CDMA) secondary network to operate cognitively as an underlay for a primary network. A novel interference‐minimizing code assignment (IMCA) for secondary users is proposed such that the interference from existing primary and secondary users is minimized. This is accomplished by minimizing the mean square cross‐correlations between the candidate codes and the received signal. Since the codes of the primary CDMA network are unknown to the secondary network the scheme operates blindly and the problem is formulated as a constrained optimization of a Boolean quadratic form. The solution is obtained exhaustively and we demonstrate significant performance gains compared to random code assignment (RCA). We then slightly relax the constraint on the user code space and obtain a near‐optimal solution with complexity that is linear in the spreading factor. For the secondary network, we propose a slightly modified minimum‐output energy receiver that operates semi‐blindly as a first stage followed by parallel interference cancellation. For this receiver structure, we derive improved log‐likelihood ratios for the single‐user decoders based on partial knowledge of the user codes and channel coefficients. Significant error probability performance improvements of 2 dB or more are obtained due to IMCA in the coded case. Copyright © 2008 John Wiley & Sons, Ltd.

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We propose a secondary CDMA network that operates as an underlay for a primary CDMA network where the code assignment for the secondary network is done cognitively. A code assignment criterion that minimizes interference from primary users and existing secondary users is formulated. The primary user codes as well as bit boundaries are unknown to the secondary network. The problem is initially formulated as a constrained optimization problem. Exhaustive search has complexity that is exponential in the spreading factor. The constraints are therefore relaxed to obtain a near-optimal solution with a complexity that is linear in the spreading factor and performance very close to the exhaustive search method. We consider the different cases where the primary users are bit-and chip-synchronous, chipsynchronous but bit-asynchronous, and chip-asynchronous over multi-path fading channels. We propose a method for blind epoch acquisition by processing the covariance matrix of the received signal. In all cases the performance improvement of the interference-minimizing code assignment over random code assignment is significant reaching over 3 dB for coded systems.

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