5 research outputs found
Joint Scheduling and ARQ for MU-MIMO Downlink in the Presence of Inter-Cell Interference
User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the
core of high rate data-oriented downlink schemes of the next-generation of
cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users
according to their channels vector directions and SINR levels. However, when
scheduling is applied independently in each cell, the inter-cell interference
(ICI) power at each user receiver is not known in advance since it changes at
each new scheduling slot depending on the scheduling decisions of all
interfering base stations. In order to cope with this uncertainty, we consider
the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat
reQuest (ARQ). We develop a game-theoretic framework for this problem and build
on stochastic optimization techniques in order to find optimal scheduling and
ARQ schemes. Particularizing our framework to the case of "outage service
rates", we obtain a scheme based on adaptive variable-rate coding at the
physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then,
we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ)
that is able to achieve a throughput performance arbitrarily close to the
"genie-aided service rates", with no need for a genie that provides
non-causally the ICI power levels. The novel HARQ scheme is both easier to
implement and superior in performance with respect to the conventional
combination of adaptive variable-rate coding and ARQ-LLC.Comment: Submitted to IEEE Transactions on Communications, v2: small
correction
Exploiting Hybrid Channel Information for Downlink Multi-User MIMO Scheduling
We investigate the downlink multi-user MIMO (MU-MIMO) scheduling problem in
the presence of imperfect Channel State Information at the transmitter (CSIT)
that comprises of coarse and current CSIT as well as finer but delayed CSIT.
This scheduling problem is characterized by an intricate `exploitation -
exploration tradeoff' between scheduling the users based on current CSIT for
immediate gains, and scheduling them to obtain finer albeit delayed CSIT and
potentially larger future gains. We solve this scheduling problem by
formulating a frame based joint scheduling and feedback approach, where in each
frame a policy is obtained as the solution to a Markov Decision Process. We
prove that our proposed approach can be made arbitrarily close to the optimal
and then demonstrate its significant gains over conventional MU-MIMO
scheduling.Comment: Expanded version: Accepted WiOpt 201