COD: Blind path separation with limited antenna size

This paper proposes a generalized multipath separability condition for subspace processing and derives a novel COD (Combined Oversampling and Displacement) algorithm to utilize both spatial and temporal diversities for path separation and DOA estimation. A unique advantage lies in its ability to cope with the situation where the number of multipaths is much larger than that of antenna elements, which arises in many practical situations. The traditional data matrix or any of its horizontally expanded versions cannot yield a sufficient matrix rank to satisfy the condition, when there is antenna deficiency. Neither can a vertical expansion via oversampling, except when there is no overlapping among intra-user paths (a much stronger condition than the asynchrony condition). The COD strategy solves the antenna deficiency problem by combining vertical expansion with temporal oversampling and horizontal expansion with spatial displacement. Another unique advantage of COD is its multiplicity of eigenvalues which greatly facilitates the later signal recovery processing [5]. The paper first analyzes the theoretical footings for COD and follows with some illustrative simulation results in noisy channels.