2 research outputs found
A Rate-Splitting Approach To Robust Multiuser MISO Transmission
For multiuser MISO systems with bounded uncertainties in the Channel State
Information (CSI), we consider two classical robust design problems: maximizing
the minimum rate subject to a transmit power constraint, and power minimization
under a rate constraint. Contrary to conventional strategies, we propose a
Rate-Splitting (RS) strategy where each message is divided into two parts, a
common part and a private part. All common parts are packed into one super
common message encoded using a shared codebook and decoded by all users, while
private parts are independently encoded and retrieved by their corresponding
users. We prove that RS-based designs achieve higher max-min Degrees of Freedom
(DoF) compared to conventional designs (NoRS) for uncertainty regions that
scale with SNR. For the special case of non-scaling uncertainty regions, RS
contrasts with NoRS and achieves a non-saturating max-min rate. In the power
minimization problem, RS is shown to combat the feasibility problem arising
from multiuser interference in NoRS. A robust design of precoders for RS is
proposed, and performance gains over NoRS are demonstrated through simulations.Comment: To appear in ICASSP 201
Robust Transmission in Downlink Multiuser MISO Systems: A Rate-Splitting Approach
We consider a downlink multiuser MISO system with bounded errors in the
Channel State Information at the Transmitter (CSIT). We first look at the
robust design problem of achieving max-min fairness amongst users (in the
worst-case sense). Contrary to the conventional approach adopted in literature,
we propose a rather unorthodox design based on a Rate-Splitting (RS) strategy.
Each user's message is split into two parts, a common part and a private part.
All common parts are packed into one super common message encoded using a
public codebook, while private parts are independently encoded. The resulting
symbol streams are linearly precoded and simultaneously transmitted, and each
receiver retrieves its intended message by decoding both the common stream and
its corresponding private stream. For CSIT uncertainty regions that scale with
SNR (e.g. by scaling the number of feedback bits), we prove that a RS-based
design achieves higher max-min (symmetric) Degrees of Freedom (DoF) compared to
conventional designs (NoRS). For the special case of non-scaling CSIT (e.g.
fixed number of feedback bits), and contrary to NoRS, RS can achieve a
non-saturating max-min rate. We propose a robust algorithm based on the
cutting-set method coupled with the Weighted Minimum Mean Square Error (WMMSE)
approach, and we demonstrate its performance gains over state-of-the art
designs. Finally, we extend the RS strategy to address the Quality of Service
(QoS) constrained power minimization problem, and we demonstrate significant
gains over NoRS-based designs.Comment: Accepted for publication in IEEE Transactions on Signal Processin