Selective vector perturbation for low-power small cell MISO downlinks

A selective vector perturbation technique is introduced for low-power Small Cell downlink. In contrast to conventional vector perturbation (VP) where the search for perturbation vectors involves all users´ symbols, here the perturbation is applied to a subset of the transmitted symbols. This therefore introduces a performance-complexity tradeoff, where the complexity is greatly reduced compared to VP by limiting the dimensions of the sphere search, at the expense of a performance penalty compared to VP. By changing the size of the subset of perturbed users, the above tradeoff can be controlled. We further propose three distinct criteria for selecting which users´ symbols to perturb, each of which yields a different performance-complexity tradeoff. The presented analytical and simulation results show that the proposed is most useful in the low-power small cell scenarios where power efficiency levels improved by up to 300% compared to VP are demonstrated.