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21
The degrees of freedom region of twouser and certain threeuser MIMO broadcast channel with delayed CSI
 IEEE Trans. Inf. Theory
"... The degrees of freedom (DoF) region of the fastfading MIMO (multipleinput multipleoutput) Gaussian broadcast channel (BC) is studied when there is delayed channel state information at the transmitter (CSIT). In this setting, the channel matrices are assumed to vary independently across time and t ..."
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The degrees of freedom (DoF) region of the fastfading MIMO (multipleinput multipleoutput) Gaussian broadcast channel (BC) is studied when there is delayed channel state information at the transmitter (CSIT). In this setting, the channel matrices are assumed to vary independently across time and the transmitter is assumed to know the channel matrices with some arbitrary finite delay. An outerbound to the DoF region of the general Kuser MIMO BC (with an arbitrary number of antennas at each terminal) is derived. This outerbound is then shown to be tight for two classes of MIMO BCs, namely, (a) the twouser MIMO BC with arbitrary number of antennas at all terminals, and (b) for certain threeuser MIMO BCs where all three receivers have an equal number of antennas and the transmitter has no more than twice the number of antennas present at each receivers. The achievability results are obtained by developing an interference alignment scheme that optimally accounts for multiple, and possibly distinct, number of antennas at the receivers. Index Terms Broadcast channel, degrees of freedom, delayed CSIT, interference alignment, outer bound.
The Capacity Region of the MIMO Interference Channel and its Reciprocity to Within a Constant Gap
, 2011
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Structured Lattice Codes for Some TwoUser Gaussian Networks with Cognition, Coordination and Two Hops,” submitted to
 IEEE Transactions on Information Theory
, 2013
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On two unicast wireless networks with destinationtosource feedback
, 2012
"... Abstract—In this paper we study the role of feedback in layered two unicast wireless networks with arbitrary number of nodes and connectivity. The feedback model allows destinations to feedback their received signals to their respective sources. In the case of linear deterministic networks, we fully ..."
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Cited by 3 (0 self)
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Abstract—In this paper we study the role of feedback in layered two unicast wireless networks with arbitrary number of nodes and connectivity. The feedback model allows destinations to feedback their received signals to their respective sources. In the case of linear deterministic networks, we fully characterize the capacity region when the two individual minimum cut values are equal to 1 and show that feedback only helps increase capacity whenever the capacity region without feedback has (1, 1/2) or (1/2, 1) as its corner point but not both. Therefore, feedback helps balance the resource utilization of the two users, similar to the role of feedback in the twouser interference channel [1]. I.
On the Optimality of Treating Interference as Noise for K user Parallel Gaussian Interference Networks
"... It has been shown recently by Geng et al. that in a K user Gaussian interference network, if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all signal strengths measured in ..."
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Cited by 2 (2 self)
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It has been shown recently by Geng et al. that in a K user Gaussian interference network, if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all signal strengths measured in dB scale), then power control and treating interference as noise (TIN) is sufficient to achieve the entire generalized degrees of freedom (GDoF) region. Motivated by the intuition that the deterministic model of Avestimehr et al. (ADT deterministic model) is particularly suited for exploring the optimality of TIN, the results of Geng et al. are first revisited under the ADT deterministic model, and are shown to directly translate between the Gaussian and deterministic settings. Next, we focus on the extension of these results to parallel interference networks, from a sumcapacity/sumGDoF perspective. To this end, we interpret the explicit characterization of the sumcapacity/sumGDoF of a TIN optimal network (without parallel channels) as a minimum weighted matching problem in combinatorial optimization, and obtain a simple characterization in terms of a partition of the interference network into vertexdisjoint cycles. Aided by insights from the cyclic partition, the sumcapacity optimality of TIN for K user parallel interference networks is characterized for the ADT deterministic model, leading ultimately to corresponding GDoF results for the Gaussian setting. In both cases, subject to a mild invertibility condition the optimality of TIN is shown to extend to parallel networks in a separable fashion.
On the Optimality of Treating Interference as Noise: General Message Sets
"... Abstract — In a Kuser Gaussian interference channel, it has been shown that if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all values in decibel scale), then treating int ..."
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Abstract — In a Kuser Gaussian interference channel, it has been shown that if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all values in decibel scale), then treating interference as noise (TIN) is optimal from the perspective of generalized degrees of freedom (GDoF) and achieves the entire channel capacity region to within a constant gap. In this paper, we show that for such TINoptimal interference channels, even if the message set is expanded to include an independent message from each transmitter to each receiver, operating the new channel as the original interference channel and treating interference as noise is still optimal for the sum capacity up to a constant gap. Furthermore, we extend the result to the sumGDoF optimality of TIN in the general setting of X channels with arbitrary numbers of transmitters and receivers. Index Terms — Gaussian networks, generalized degrees of freedom (GDoF), sum capacity, treating interference as noise (TIN), X channels. I.
Approximate Capacity of the TwoUser MISO Broadcast Channel with Delayed CSIT
"... Abstract—We consider the problem of the twouser multipleinput singleoutput complex Gaussian Broadcast Channel where the transmitter has access to delayed knowledge of the channel state information. We characterize the capacity region of this channel to within a constant number of bits for all val ..."
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Abstract—We consider the problem of the twouser multipleinput singleoutput complex Gaussian Broadcast Channel where the transmitter has access to delayed knowledge of the channel state information. We characterize the capacity region of this channel to within a constant number of bits for all values of the transmit power. The proposed signaling strategy utilizes the delayed knowledge of the channel state information and the previously transmitted signals, in order to create a signal of common interest for both receivers. This signal is the quantized version of the summation of the previously transmitted signals. To guarantee the independence of quantization noise and signal, we extend the framework of lattice quantizers with dither, together with an interleaving step. For converse, we use the fact that the capacity region of this problem is upperbounded by the capacity region of a physically degraded broadcast channel with no channel state information where one receiver has two antennas. We then derive an outerbound on the capacity region of this degraded broadcast channel which in turn provides an outerbound on the capacity region of the twouser multipleinput singleoutput complex Gaussian broadcast channel with delayed knowledge of the channel state information. By careful examination, we show that the achievable rate region and the outerbound are within 1.81 bits/sec/Hz per user. I.
On the Optimality of Treating Interference as Noise for Parallel Deterministic Interference Networks
"... Abstract—It has been shown recently by Geng et al. that in a K user Gaussian interference network, if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all signal strengths meas ..."
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Abstract—It has been shown recently by Geng et al. that in a K user Gaussian interference network, if for each user the desired signal strength is no less than the sum of the strengths of the strongest interference from this user and the strongest interference to this user (all signal strengths measured in dB scale), then power control and treating interference as noise (TIN) is sufficient to achieve the entire generalized degrees of freedom (GDoF) region. Motivated by the intuition that the deterministic model of Avestimehr et al. (ADT deterministic model) is particularly suited for exploring the optimality of TIN, the results of Geng et al. are first revisited under the ADT deterministic model, and corresponding TIN optimality results are obtained. Next, we focus on the extension of these results to ADT deterministic parallel interference networks, from a sumcapacity perspective. To this end, we interpret the explicit characterization of the sumcapacity of a TIN optimal network (without parallel channels) as a minimum weighted matching problem in combinatorial optimization, and obtain a simple characterization in terms of a partition of the interference network into vertexdisjoint cycles. Aided by insights from the cyclic partition, the sumcapacity optimality of TIN for K user parallel interference networks is characterized for the ADT deterministic model. Subject to a mild invertibility condition the optimality of TIN is shown to extend to parallel networks in a separable fashion. I.
On the TwoUser 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 twostate 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 degreesoffreedom 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 spatiotemporal 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), degreesoffreedom (DoF). I.