On the Two-User MISO Broadcast Channel With Alternating CSIT: A Topological Perspective

Abstract

Abstract-In many wireless networks, link strengths are affected by many topological factors, such as different distances, shadowing, and intercell interference, thus resulting in some links being generally stronger than other links. From an information theoretic point of view, accounting for such topological aspects is still a novel approach, that has been recently fueled by strong indications that such aspects can crucially affect transceiver and feedback design, as well as the overall performance. This paper here takes a step in exploring this interplay between topology, feedback, and performance. This is done for the two user broadcast channel with random fading, in the presence of a simple two-state topological setting of statistically strong versus weaker links, and in the presence of a practical ternary feedback setting of alternating channel state information at the transmitter [alternating channel state information at the transmitter (CSIT)] where for each channel realization, this CSIT can be perfect, delayed, or not available. In this setting, the work derives generalized degrees-of-freedom bounds and exact expressions, that capture performance as a function of feedback statistics and topology statistics. The results are based on novel topological signal management schemes that account for topology in order to fully utilize feedback. This is achieved for different classes of feedback mechanisms of practical importance, from which we identify specific feedback mechanisms that are best suited for different topologies. This approach offers further insight on how to split the effort-of channel learning and feeding back CSIT-for the strong versus for the weaker link. Further intuition is provided on the possible gains from topological spatio-temporal diversity, where topology changes in time and across users.Index Terms-Broadcast channel, channel with state, feedback, network topology, channel state information at the transmitter (CSIT), degrees-of-freedom (DoF).

The Generalized Degrees of Freedom Region of the MIMO Z-Interference Channel With Delayed CSIT

“…where inequality (a) is obtained by using (7) and substituting (12) in (6), and the second inequality (b) is obtained by using (9), after substituting the asymptotic approximations from (10) and (11). As shown below in Lemma 2, the expression in (13) is maximized for both weak and strong interference when r = 0, and thus, we substitute r = 0 to obtain the inequality in (c).…”

“…More recently, [12] studied the GDoF region of the two-user MISO BC with fixed and alternating topologies (link strengths) under alternating CSIT, where the CSIT state of each link can be either perfect and instantaneous (P), delayed (D) or not known (N). Inner and outer bounds on the GDoF under delayed CSIT were obtained therein, which are, however, not tight, so that the characterization of the GDoF region of even a two-user MISO BC with a static topology and delayed CSIT remains an open problem.…”

A Survey on Robust Interference Management in Wireless Networks

“…For instance, Figure 7a illustrates the system model for state (I 1,t , I 2,t ) T = (D, N) T . When considering an entire transmission interval spanning multiple channel uses, the transmitters are interested in knowing the fraction of the transmission time (a) β I 1 ,I 2 during which the CSIT state is given by any pair (I 1 , I 2 ) T ∈ {P, D, N} × {P, D, N} [9] and (b) β A 1 ,A 2 during which the topology state is given by any pair (A 1 , A 2 ) T ∈ {γ, 1} × {γ, 1} [62,63]. Thus, effectively, β I 1 ,I 2 and β A 1 ,A 2 correspond to two-dimensional probability mass functions that depend on the pair of random variables (I 1 , I 2 ) and (A 1 , A 2 ), respectively [64].…”

A Partition-based Scheme for IRS-aided MIMO Fading Channels: Outage and DMT Analysis

“…Furthermore, an opportunistic rate splitting scheme was proposed in [19] for an RIS-aided two-user MISO system. In particular, by utilizing the RIS to modify the channel characteristics through an alternating CSI formulation, which was inspired by the information theoretic framework presented in [20], it was shown that the achievable rate of such systems can be improved.…”