MISO Networks With Imperfect CSIT: A Topological Rate-Splitting Approach

Abstract

Recently, the Degrees-of-Freedom (DoF) region of multiple-input-single-output (MISO) networks with imperfect channel state information at the transmitter (CSIT) has attracted significant attentions.An achievable scheme is known as rate-splitting (RS) that integrates common-message-multicasting and private-message-unicasting. In this paper, focusing on the general K-cell MISO IC where the CSIT of each interference link has an arbitrary quality of imperfectness, we firstly identify the DoF region achieved by RS. Secondly, we introduce a novel scheme, so called Topological RS (TRS), whose novelties compared to RS lie in a multi-layer structure and transmitting multiple common messages to be decoded by groups of users rather than all users. The design of TRS is motivated by a novel interpretation of the K-cell IC with imperfect CSIT as a weighted-sum of a series of partially connected networks. We show that the DoF region achieved by TRS covers that achieved by RS. Also, we find the maximal sum DoF achieved by TRS via hypergraph fractional packing, which yields the best sum DoF so far. Lastly, for a realistic scenario where each user is connected to three dominant transmitters, we identify the sufficient condition where TRS strictly outperforms conventional schemes.

Rate-splitting multiple access for downlink communication systems: bridging, generalizing, and outperforming SDMA and NOMA

“…Finally, the performance benefits of the power-partitioning strategy relying on RS in the overloaded MISO BC with heterogeneous CSIT was confirmed using simulations at finite SNR in the presence of a diversity of channel strengths [35]. In particular, in contrast to the RS used in [13], [19], [30], [31], [34], [35], [39], [41], [42] that relies on a single common message, [40] (as well as [32]) showed the benefits in the finite SNR regime of a multi-layer (hierarchical) RS relying on multiple common messages decoded by various groups of users.…”

“…Second, we provide a general framework of multi-layer RS design that encompasses existing RS schemes as special cases. In particular, the single-layer RS of [19], [30], [31], [34], [35], [39], [41], [42] and the multi-layer (hierarchical and topological) RS of [32], [40] are special instances of the generalized RS strategy developed here. Moreover the use of RS was primarily motivated by multi-antenna deployments subject to multi-user interference due to imperfect CSIT in those works.…”

“…By keeping 1-order, K-order and l-order streams, where l is selected from {2, · · · , K − 1}, the problem becomes the 2layer HRS originally proposed in [40] with two-layers of common messages to be transmitted. Another example of such a multi-layer RS has also appeared in the topological RS for MISO networks of [32]. Therefore, the formulated Kuser RS problem is a more general problem.…”

Multiuser Millimeter Wave Beamforming Strategies With Quantized and Statistical CSIT

“…By contrast, the achievable sum DoF of RS is 1+(K −1)δ, which is strictly larger than Kδ achieved with ZF. In subsequent works, RS has been shown to be a very promising strategy in a wide range of scenarios, namely future PHY layer strategy [14], massive MIMO [15], MIMO networks [16], [17], multi-group multicast [18] and under various performance metric, namely sum-rate maximization [19], max-min fairness [20]. However, the benefit of RS in the context of multiuser mmWave systems with hybrid precoding has never been investigated.…”

Tomlinson-Harashima Precoded Rate-Splitting for Multiuser Multiple-Antenna Systems

“…RS has also been considered for robust transmissions under bounded CSIT errors in [8]. Studies of massive MIMO and MISO networks using RS strategies have been reported in [9] and [10], respectively. RS has so far been studied and optimized using a linear precoding framework.…”