Joint user association and BS on-off scheduling in heterogeneous networks

Heterogeneous wireless networks (HetNets) provide a means to increase network capacity by introducing small cells and adopting a layered architecture. HetNets can allocate resources flexibly through time sharing, on-off scheduling and cell range expansion/contraction. As shown in [1] such networks are constrained to a capacity limit in terms of the maximum number of downloads per second which can be achieved for a given offered traffic density. This capacity can be obtained as the solution to a continuous linear program (LP) (see [1]). Using the above results we investigate the scope for capacity extension in a single macro cell network. In particular it is shown that multiple pico cells per hot spot can significantly extend capacity but the gains can only be realized in conjunction with on-off scheduling of the picocells. We further show that scheduling according to a small number of on-off modes is sufficient to realise this gain. We also develop tight capacity bounds which can be used to investigate larger networks in cases where the size of the LP is too large for direct solution.