Adaptive Uniform Channel Decomposition in MU-MIMO-OFDM: Application to IEEE 802.11ac

This work considers the design of multiuser MIMO (MU-MIMO) schemes suitable for orthogonal frequency division multiplex (OFDM) systems such as those being currently discussed within IEEE 802.11ac. A general framework is proposed showing that the singular value decomposition (SVD), the geometric mean decomposition (GMD), and the uniform channel decomposition (UCD) are all viable mechanisms on which to lay the design. Nonetheless, some striking differences in terms of performance among these three schemes are uncovered. In particular, a novel adaptive transmission scheme based on the UCD is introduced that enables multiuser MIMO-OFDM gains to be realized, clearly outperforming those obtained using the SVD or GMD counterparts while remaining fully compliant with the latest IEEE 802.11ac specification. Relying on the UCD properties, the proposed technique takes into account the availability of a finite modulation and coding set and restrictions on transmission mode selection defined within the standard, to incorporate an optimisation step in charge of selecting the number of transmitted data streams to each user to maximise the system throughput. Comprehensive simulation results in the context of IEEE 802.11ac confirm the applicability and advantage of the adaptive UCD-based design.