Improved multi-stage clustering-based blind equalisation in interference-limited CDMA environments

The improved multi-stage clustering (IMSC)-based blind equalisation algorithm proposed by Mitra and colleagues in 2011 gave rise to significant improvements in terms of performance metrics as compared with its state-of-the-art counterparts. However, the present authors´ research studies show that IMSC performance degrades significantly for multiple access interference (MAI) in code-division multiplexing access (CDMA) systems. To mitigate MAI, code filtering by orthogonal Hadamard codes is a popular practice to minimise the interference. Code-filtering techniques have been used in the past in which a de-correlating transform (inverse of an orthonormal Hadamard matrix) has been incorporated into the cost function of the parent algorithm (which can be any traditional equalisation algorithm). A hybrid equalisation scheme is suggested which combines IMSC and code-filtering, so as to mitigate interference in CDMA environments. The code-filtered IMSC shows better performance than any of the previously proposed algorithms.