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

QoS constrained power minimization in the MISO broadcast channel with imperfect CSI

This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/. This version of the article: González-Coma, J. P., Joham, M., Castro, P. M., & Castedo, L. (2017). 'QoS constrained power minimization in the MISO broadcast channel with imperfect CSI', has been accepted for publication in Signal Processing, 131, 447–455. The Version of Record is available online at: https://doi.org/10.1016/j.sigpro.2016.09.007.[Abstract]: In this paper we consider the design of linear precoders and receivers in a Multiple-Input Single-Output (MISO) Broadcast Channel (BC). We aim to minimize the transmit power while meeting a set of per-user Quality-of-Service (QoS) constraints expressed in terms of per-user average rate requirements. The Channel State Information (CSI) is assumed to be known perfectly at the receivers but only partially at the transmitter. To solve this problem we convert the QoS constraints into Minimum Mean Square Error (MMSE) constraints. We then leverage MSE duality between the BC and the Multiple Access Channel (MAC), as well as standard interference functions in the dual MAC, to perform power minimization by means of an Alternating Optimization (AO) algorithm. Problem feasibility is also studied to determine whether the QoS constraints can be met or not. Finally, we present an algorithm to balance the average rates and manage situations that may be unfeasible, or lead to an unacceptably high transmit power.This work was supported by Xunta de Galicia, MINECO of Spain, and FEDER funds of EU, under grants 2012/287 and TEC2013-47141-C4-1-R.Xunta de Galicia; 2012/28

QoS constrained power minimization in the multiple stream MIMO broadcast channel

This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/ licenses/by-nc-nd/4.0/. This version of the article: González-Coma, J. P., Joham, M., Castro, P. M., & Castedo, L. (2018). 'QoS constrained power minimization in the multiple stream MIMO broadcast channel', has been accepted for publication in Signal Processing, 143, 48–55. The Version of Record is available online at: https://doi.org/10.1016/ j.sigpro.2017.08.015.[Abstract]: This work addresses the design of optimal linear transmit filters for the Multiple Input-Multiple Output (MIMO) Broadcast Channel (BC) when several spatial streams are allocated to each user. We further consider that the Channel State Information (CSI) is perfect at the receivers but is only partial at the transmitter. A statistical model for the partial CSI is assumed and exploited for the filter design. The relationship between average rate and average Mean Square Error (MSE) is studied to determine the optimal way to distribute the per-user rates among the streams. Finally, the feasible average sum-MSE (sMSE) region is studied and the impact of the CSI uncertainty over the overall system performance is evaluated.This work was funded by Xunta de Galicia (ED431C 2016-045, ED341D R2016/012, ED431G/01), AEI of Spain (TEC2013-47141-C4-1-R, TEC2015-69648-REDC, TEC2016-75067-C4-1-R), and ERDF funds (AEI/FEDER, EU).Xunta de Galicia; ED431C 2016-045Xunta de Galicia; ED341D R2016/012Xunta de Galicia; ED431G/0