Low-Complexity SDMA User-Grouping for the CoMP-VLC Downlink

A coordinated multi-point visible light communication (CoMP-VLC) downlink is investigated, where the time-frequency (TF) resources are shared by a group of users relying on space division multiple access (SDMA). Linear zero-forcing (ZF) transmit precoding (TPC) is tailored to the CoMP-VLC system in order to eliminate the inter-user interference while accommodating the linear operating region of the light emitting diodes (LEDs). A SDMA user-group sharing the same TF has to host users having sufficiently different user-signatures, i.e. channel gains in a non-dispersive VLC channel. Hence we develop efficient resource allocation (RA) and SDMA user-grouping algorithms in the context of VLC systems that use intensity modulation and direct detection (IM/DD). Finding the optimal SDMA user-group requires an exhaustive search (ES), which has exponentially increasing complexity as the number of users increases. Therefore, a low-complexity user-grouping method is conceived and compared to three existing algorithms in terms of the attainable area spectral efficiency (ASE) and throughput fairness. Our simulation results demonstrate that the proposed algorithm gives a better performance-fairness trade-off than existing benchmarks.