On Multi-Cell Uplink-Downlink Duality with Treating Inter-Cell Interference as Noise

Joudeh, Hamdi; Yi, Xinping; Clerckx, Bruno

doi:10.1109/isit.2019.8849449

Cited by 7 publications

(6 citation statements)

References 18 publications

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“…Optimal schemes for such GDoF characterizations tend to be naturally robust schemes that require only a coarse knowledge of channel strength 2 parameters α ij at the transmitters. Aided by advances in Aligned Images (AI) bounds [7], GDoF characterizations under finite precision CSIT have been found for a variety of wireless networks in [9][10][11][12][13].The importance of simplicity is reflected in the goal of identifying parameter regimes where simple schemes are optimal in the GDoF sense [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The most relevant examples for our purpose are [14], [15] and [16].…”

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confidence: 99%

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Toward an Extremal Network Theory—Robust GDoF Gain of Transmitter Cooperation Over TIN

Chan

Wang

Jafar

2020

IEEE Trans. Inform. Theory

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Significant progress has been made recently in Generalized Degrees of Freedom (GDoF) characterizations of wireless interference channels (IC) and broadcast channels (BC) under the assumption of finite precision channel state information at the transmitters (CSIT), especially for smaller or highly symmetric network settings. A critical barrier in extending these results to larger and asymmetric networks is the inherent combinatorial complexity of such networks. Motivated by other fields such as extremal combinatorics and extremal graph theory, we explore the possibility of an extremal network theory, i.e., a study of extremal networks within particular regimes of interest. As our test application, we study the GDoF benefits of transmitter cooperation in a K user IC over the simple scheme of power control and treating interference as Gaussian noise (TIN) for three regimes of interest -a TIN regime identified by Geng et al. where TIN was shown to be GDoF optimal for the K user interference channel, a CTIN regime identified by Yi and Caire where the GDoF region achievable by TIN is convex without time-sharing, and an SLS regime identified by Davoodi and Jafar where a simple layered superposition (SLS) scheme is shown to be optimal in the K user MISO BC, albeit only for K ≤ 3. The SLS regime includes the CTIN regime, and the CTIN regime includes the TIN regime. As our first result, we show that under finite precision CSIT, TIN is GDoF optimal for the K user IC throughout the CTIN regime. Furthermore, under finite precision CSIT, appealing to extremal network theory we obtain the following results. In the TIN regime as well as the CTIN regime, we show that the extremal GDoF gain from transmitter cooperation over TIN is bounded regardless of the number of users. In fact, the gain is exactly a factor of 3/2 in the TIN regime, and 2 − 1/K in the CTIN regime, for arbitrary number of users K > 1. However, in the SLS regime, the gain is Θ(log 2 (K)), i.e., it scales logarithmically with the number of users.Finding the capacity limits of wireless networks is one of the grand challenges of network information theory. While exact capacity characterizations remain elusive, much progress has been made on this problem within the past decade through Degrees of Freedom (DoF) [1] and Generalized Degrees of Freedom (GDoF) [2] studies. This includes both new achievable schemes, including those inspired by the idea of interference alignment (IA) [3][4][5][6], and new outer bounds, such as those based on the aligned images (AI) approach [7]. With these advances as stepping stones, a worthy goal at this stage is to bring the theory closer to practice by adapting the models and metrics to increasingly incorporate practical concerns. As a step in this direction, this work is motivated by three practical concerns -robustness, simplicity, and scalability.By robustness we refer specifically to the channel state information at the transmitters (CSIT). GDoF characterizations under perfect CSIT provide important theoretical benchmarks, but often ...

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confidence: 99%

“…The importance of simplicity is reflected in the goal of identifying parameter regimes where simple schemes are optimal in the GDoF sense [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The most relevant examples for our purpose are [14], [15] and [16].…”

mentioning

confidence: 99%

Toward an Extremal Network Theory—Robust GDoF Gain of Transmitter Cooperation Over TIN

Chan

Wang

Jafar

2020

IEEE Trans. Inform. Theory

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“…Separability of parallel subchannels is a desirable attribute from a practical standpoint, as it can greatly simplify coding and multiple access in wireless networks under fading channel conditions. This desirability of, and need for, simplicity in general has fueled a number of works of late, in which the optimality of simple coding schemes has been established in broad regimes for various settings 2 [33][34][35][36][37][38][39]. Such simple schemes also tend to be more robust, as they rely less on the fine details of CSIT, making them all the more attractive for practical purposes.…”

Section: Overview Of Contribution and Organizationmentioning

confidence: 99%

On the Separability of Parallel MISO Broadcast Channels Under Partial CSIT: A Degrees of Freedom Region Perspective

Joudeh

Clerckx

2020

IEEE Trans. Inform. Theory

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We study the K-user, M -subchannel parallel multiple-input-single-output (MISO) broadcast channel (BC) under arbitrary levels of partial channel state information at the transmitter (CSIT). We show that the parallel subchannels constituting this setting are separable from a degrees-of-freedom (DoF) region perspective if and only if the partial CSIT pattern is totally ordered. This total order condition corresponds to users abiding by the same order, with respect to their CSIT uncertainty levels, in each of the parallel subchannels. In this case, the entire DoF region is achievable using simple separate coding, where a single-subchannel-type transmission scheme is employed in each subchannel. To show this separability result, we first derive an outer bound for the DoF region by extending the aligned image sets approach of Davoodi and Jafar to the considered setting. We then show that this outer bound coincides with the inner bound achieved through separate coding, given by the Minkowski sum of M single-subchannel DoF regions, under the total order condition, hence settling the if part of the main theorem. To prove the only if part of the theorem, we identify a set of DoF tuples achievable through joint coding across subchannels, yet not achievable through separate coding whenever the total order condition is violated. Moreover, we also highlight the implications of our main result on the design of CSIT feedback schemes for multi-carrier multi-antenna wireless networks.

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“…For instance, the compound TINA region in [11] is retrieved from the IBC TINA region in (21) by eliminating all messages, e.g. by setting their GDoF to zero, except for message W [π k (1)] k in each cell k, which is decoded by all users in such cell. Similarly, the opportunistic TINA region in [17] is retrieved by fixing a decoding order π a priori, and (possibly) eliminating some messages from each cell according to the criteria in [17].…”

Section: Multi-cell Tin In the Ibcmentioning

confidence: 99%

“…The signal S n 1 , which contains interference caused by cell 1 to cell 2, is given to the stronger BC user in cell 1, i.e. UE- (2,1). On the other hand, S n 2 , which contains interference caused by cell 2 to cell 1, is given to the (only) user in cell 2.…”

Section: Proof Of Outer Bound: 2-cell 3-user Examplementioning

confidence: 99%

On the Optimality of Treating Inter-Cell Interference as Noise: Downlink Cellular Networks and Uplink-Downlink Duality

Joudeh¹,

Xiao²,

Clerckx³

et al. 2019

Preprint

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We consider the information-theoretic optimality of treating inter-cell interference as noise (multi-cell TIN) in downlink cellular networks. We focus on scenarios modeled by the Gaussian interfering broadcast channel (IBC), comprising K mutually interfering Gaussian broadcast channels (BCs), each formed by a base station communicating independent messages to an arbitrary number of users. We establish a new power allocation duality between the IBC and its dual interfering multiple access channel (IMAC), which entails that the corresponding generalized degrees-of-freedom regions achieved through multi-cell TIN and power control (TINA regions) for both networks are identical. As by-products of this duality, we obtain an explicit characterization of the IBC TINA region from a previously established characterization of the IMAC TINA region; and identify a multi-cell convex-TIN regime in which the IBC TINA region is a polyhedron (hence convex) without the need for time-sharing. We then identify a smaller multi-cell TIN regime in which the IBC TINA region is optimal and multi-cell TIN achieves the entire capacity region of the IBC, up to a constant gap. This is accomplished by deriving a new genie-aided outer bound for the IBC, that reveals a novel BC-type order that holds amongst users in each constituent BC (or cell) under inter-cell interference, which in turn is not implied by previously known BC-type orders (i.e. degraded, less noisy and more capable orders). The multi-cell TIN regime that we identify for the IBC coincides with a corresponding multi-cell TIN regime previously identified for the IMAC, hence establishing a comprehensive uplink-downlink duality of multi-cell TIN in the GDoF (and approximate capacity) sense.

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On Multi-Cell Uplink-Downlink Duality with Treating Inter-Cell Interference as Noise

Cited by 7 publications

References 18 publications

Toward an Extremal Network Theory—Robust GDoF Gain of Transmitter Cooperation Over TIN

Toward an Extremal Network Theory—Robust GDoF Gain of Transmitter Cooperation Over TIN

On the Separability of Parallel MISO Broadcast Channels Under Partial CSIT: A Degrees of Freedom Region Perspective

On the Optimality of Treating Inter-Cell Interference as Noise: Downlink Cellular Networks and Uplink-Downlink Duality

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