Semi-blind channel estimation based on modified CMA and unitary scrambling for massive MIMO systems

Pilot contamination is one of the main impairments in multi-cell massive Multiple-Input Multiple-Output systems. In order to improve channel estimation this context, we propose use a semi-blind estimator based on constant modulus algorithm (CMA). We consider an enhanced version CMA namely Modified which modifies cost function sum functions for real and imaginary parts. Due pilot contamination, may estimate contaminating user instead that interest (the Base Station wants then data). To avoid this, scramble users sequences before transmission. different methods perform unitary scrambling rotating transmitted symbols (one Dimensional (1-D) scrambling) using matrices (two-Dimensional (2-D) scrambling). At base station, received sequence descrambled leading better convergence estimator. also case where Automatic Repeat reQuest protocol used. case, leads significant gain terms BLock Error Rate due change data from transmission another induced by scrambling.