Blind array channel division multiple access (AChDMA) for mobile communications

The paper introduces array channel division multiple access (AChDMA), which is a new blind algorithm for advanced SDMA in mobile communications systems. As an SDMA technique, AChDMA increases the system capacity by improving its time and frequency reuse. Being a blind algorithm, it requires no training sequences, previously known directions of arrival, or user codes, AChDMA separates the moving sources by tracking their multipath configuration and resolving their distinct generalized steering vectors. It maximizes a finite mixture log-likelihood function, combining an efficient initialization procedure with an EM-based algorithm that provides fast convergence to the global maximum. AChDMA reconstructs the mobile data sequences using only internal variables of the EM algorithm. These characteristics and its parallel structure make AChDMA suitable for real-time mobile communications. We test AChDMA with synthetic data in a number of different scenarios, illustrating the ability of the blind algorithm to separate and track in time the moving sources, and showing its good performance in a variety of practical situations.