Coherent Versus Noncoherent

In this article, we investigate the design philosophies of the existing space–time (ST) block codes (STBCs) in the open literature, namely the orthogonal approach and layered method, followed by the introduction of the generalized linear dispersion architecture. We will demonstrate that the powerful linear dispersion structure is capable of unifying the entire suite of existing schemes and, as a further benefit, it offers extra design flexibility so that diverse system requirements can be satisfied. Furthermore, after characterizing the fundamental relationship between STBCs and differential STBCs (DSTBCs), we highlight the benefits of noncoherently detected schemes, which are capable of exploiting the advantages of multiple antennas, while circumventing the potentially excessive burden of multiantenna channel estimation. Additionally, the linear dispersion structure can also be applied in systems, where the multiantenna array is formed in a distributed fashion by multiple single-antenna-aided cooperating mobile stations. Hence, the design of colocated and cooperative multiple-input–multiple-output (MIMO) systems aiming for achieving diversity is linked from a linear dispersion perspective.