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Precoding methods for MISO broadcast channel with delayed CSIT,” arXiv preprint arXiv:1207.2103
, 2012
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Net degrees of freedom of recent schemes for the MISO BC with delayed CSIT and finite coherence time
- in Proc. WCNC
, 2013
"... ABSTRACT Most techniques designed for the multi-input single-output (MISO) Broadcast Channel (BC) require accurate current channel state information at the transmitter (CSIT) which is not a realistic assumption because of feedback delay. A novel approach by Lee and Heath, space-time interference al ..."
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Cited by 2 (1 self)
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ABSTRACT Most techniques designed for the multi-input single-output (MISO) Broadcast Channel (BC) require accurate current channel state information at the transmitter (CSIT) which is not a realistic assumption because of feedback delay. A novel approach by Lee and Heath, space-time interference alignment, proves that in the underdetermined (overloaded) MISO BC with N t transmit antennas and K = N t + 1 users N t (sum) Degrees of Freedom (DoF) are achievable if the feedback delay is not too big, thus disproving the conjecture that any delay in the feedback necessarily causes a DoF loss. We explain this approach a bit more succinctly and evaluate the net DoF that this scheme can be expected to yield in a realistic system by taking into account the cost of CSIT acquisition (training and feedback). We term the resulting scheme ST-ZF, referring to the use of Space-Time Zero Forcing precoding. The net DoF comparison with TDMA-ZF, MAT-ZF and MAT shows that ST-ZF is also of interest in practice. I. INTRODUCTION Interference is a major limitation in wireless networks and the search for efficient ways of transmitting in this context has been productive and diversified [1]- * Part of this work has been performed in the framework of the FP7 project ICT-317669 METIS, which is partly funded by the European Union. The authors would like to acknowledge the contributions of their colleagues in METIS, although the views expressed are those of the authors and do not necessarily represent the project. concerning imperfect The assumption of totally independent channel variation is overly pessimistic for numerous practical scenarios. Therefore another scheme was proposed in
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"... This is the author’s version of an article that has been published in the Proceedings of the European Conference on Networks and Communications 2015. Changes were made to this version by the publisher prior to publication. c©2015 IEEE. Personal use of this material is permitted. Permission from IEEE ..."
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This is the author’s version of an article that has been published in the Proceedings of the European Conference on Networks and Communications 2015. Changes were made to this version by the publisher prior to publication. c©2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Net DoF analysis for the K-user MISO IC with outdated and imperfect channel feedback
On the Two-User MISO Broadcast Channel With Alternating CSIT: A Topological Perspective
, 2014
"... 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 ..."
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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). I.
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"... Outage-based design of robust Tomlinson-Harashima transceivers for the MISO downlink with QoS requirementsI ..."
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Outage-based design of robust Tomlinson-Harashima transceivers for the MISO downlink with QoS requirementsI
The DoF of Network MIMO with Backhaul Delays
"... Abstract—We consider the problem of downlink precoding for Network (multi-cell) MIMO networks where Transmitters (TXs) are provided with imperfect Channel State Information (CSI). Specifically, each TX receives a delayed channel estimate with the delay being specific to each channel component. This ..."
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Abstract—We consider the problem of downlink precoding for Network (multi-cell) MIMO networks where Transmitters (TXs) are provided with imperfect Channel State Information (CSI). Specifically, each TX receives a delayed channel estimate with the delay being specific to each channel component. This model is particularly adapted to the scenarios where a user feeds back its CSI to its serving base only as it is envisioned in future LTE networks. We analyze the impact of the delay during the backhaul-based CSI exchange on the rate performance achieved by Network MIMO. We highlight how delay can dramatically degrade system performance if existing precoding methods are to be used. We propose an alternative robust beamforming strategy which achieves the maximal performance, in DoF sense. We verify by simulations that the theoretical DoF improvement translates into a performance increase at finite Signal-to-Noise Ratio (SNR) as well. I.
1 Space-Time Interference Alignment and Degrees of Freedom Regions for the MISO Broadcast Channel with Periodic CSI Feedback
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λPI2,
, 2012
"... The degrees of freedom (DoF) of the two-user multiple-input single-output (MISO) broad-cast channel (BC) are studied under the assumption that the form, Ii, i = 1, 2, of the channel state information at the transmitter (CSIT) for each user’s channel can be either perfect (P), delayed (D) or not avai ..."
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The degrees of freedom (DoF) of the two-user multiple-input single-output (MISO) broad-cast channel (BC) are studied under the assumption that the form, Ii, i = 1, 2, of the channel state information at the transmitter (CSIT) for each user’s channel can be either perfect (P), delayed (D) or not available (N), i.e., I1, I2 ∈ {P,N,D}, and therefore the overall CSIT can alternate between the 9 resulting states I1I2. The fraction of time associated with CSIT state I1I2 is denoted by the parameter λI1I2 and it is assumed throughout that λI1I2 = λI2I1, i.e., λPN = λNP, λPD = λDP, λDN = λND. Under this assumption of symmetry, the main contri-bution of this paper is a complete characterization of the DoF region of the two user MISO BC with alternating CSIT. Surprisingly, the DoF region is found to depend only on the marginal probabilities (λP, λD, λN) =
Net Degrees of Freedom of Decomposition Schemes for the MIMO IC with Delayed CSIT
"... Abstract—Most techniques designed for the multiple-input multiple-output (MIMO) Interference Channel (IC) require accu-rate current channel state information at the transmitter (CSIT) which is not a realistic assumption because of feedback delay. We evaluate the net degrees of freedom (DoF) that dif ..."
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Abstract—Most techniques designed for the multiple-input multiple-output (MIMO) Interference Channel (IC) require accu-rate current channel state information at the transmitter (CSIT) which is not a realistic assumption because of feedback delay. We evaluate the net degrees of freedom (DoF) that different schemes can be expected to reach in a realistic system by taking into account the time and the cost of CSIT acquisition (training and feedback). A recent variant of ergodic interference alignment (IA) clearly outperforms the other schemes as its robustness to feedback delays proves to be advantageous in terms of net DoF. I.
