MIMO Downlink Scheduling in LTE and LTE-Advanced Systems

[dietcha]

LTE and LTE-Advanced (LTE-A) broadband wire-less data networks are characterized by their use of Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple InputandMultipleOutput(MIMO)techniques.Schedulingplays a vital role in such systems in exploiting multi-user, multi-channel and spatial diversity. We consider the downlink (DL) scheduling problem at the base station (BS) over such networks under a variety of practical constraints mandated by the 3GPP standards.Defininganewconstructcalled“transmissionmode”, which denotes a particular choice of MIMO operational mode, precoding matrix, transmission rank, as well as the modulation andcodingschemes(MCSs)ofuptotwocodewords,weshowthat both LTE and LTE-A systems require that in every scheduling interval, each scheduleduserbeserved usingonlyonetransmis-sionmode.Wethenprovethattheresultingschedulingproblems
are NP-hard under both backlogged and finite queue traffic
models. In each case, we re-formulate the scheduling problem
as the maximization of a monotonic submodular function under
a matroid constraint. This enables us to develop a unified low-complexity greedy algorithm that yields solutions guaranteed to
be within1/2 of the respective optima. Extensive performance
evaluation in realistic settings reveals near-optimal performance
of our proposed algorithm and that it significantly outperforms
the state of the art, especially for the finite queue model.

http://www.nec-labs.com/~honghai/TR/lte-scheduling.pdf

[rajaganesh]

some more on mimo in LTE