Topological Interference Management With Decoded Message Passing

The topological interference management (TIM) problem studies partially-connected interference networks with no channel state information except for the network topology (i.e., connectivity graph) at the transmitters. In this paper, we consider a similar problem in the uplink cellular networks, while message passing is enabled at the receivers (e.g., base stations), so that the decoded messages can be routed to other receivers via backhaul links to help further improve network performance. For this TIM problem with decoded message passing (TIM-MP), we model the interference pattern by conflict digraphs, connect orthogonal access to the acyclic set coloring on conflict digraphs, and show that one-to-one interference alignment boils down to orthogonal access because of message passing. With the aid of polyhedral combinatorics, we identify the structural properties of certain classes of network topologies where orthogonal access achieves the optimal degrees-of-freedom (DoF) region in the information-theoretic sense. The relation to the conventional index coding with simultaneous decoding is also investigated by formulating a generalized index coding problem with successive decoding as a result of decoded message passing. The properties of reducibility and criticality are also studied, by which we are able to prove the linear optimality of orthogonal access in terms of symmetric DoF for the networks up to four users with all possible network topologies (218 instances). Practical issues of the tradeoff between the overhead of message passing and the achievable symmetric DoF are also discussed, in the hope of facilitating efficient backhaul utilization

Cellular Interference Alignment

Interference alignment promises that, in Gaussian interference channels, each link can support half of a degree of freedom (DoF) per pair of transmit-receive antennas. However, in general, this result requires to precode the data bearing signals over a signal space of asymptotically large diversity, e.g., over an infinite number of dimensions for time-frequency varying fading channels, or over an infinite number of rationally independent signal levels, in the case of time-frequency invariant channels. In this work we consider a wireless cellular system scenario where the promised optimal DoFs are achieved with linear precoding in one-shot (i.e., over a single time-frequency slot). We focus on the uplink of a symmetric cellular system, where each cell is split into three sectors with orthogonal intra-sector multiple access. In our model, interference is "local", i.e., it is due to transmitters in neighboring cells only. We consider a message-passing backhaul network architecture, in which nearby sectors can exchange already decoded messages and propose an alignment solution that can achieve the optimal DoFs. To avoid signaling schemes relying on the strength of interference, we further introduce the notion of \emph{topologically robust} schemes, which are able to guarantee a minimum rate (or DoFs) irrespectively of the strength of the interfering links. Towards this end, we design an alignment scheme which is topologically robust and still achieves the same optimum DoFs

A class of index coding problems with rate 1/3

An index coding problem with $n$ messages has symmetric rate $R$ if all $n$ messages can be conveyed at rate $R$. In a recent work, a class of index coding problems for which symmetric rate $\frac{1}{3}$ is achievable was characterised using special properties of the side-information available at the receivers. In this paper, we show a larger class of index coding problems (which includes the previous class of problems) for which symmetric rate $\frac{1}{3}$ is achievable. In the process, we also obtain a stricter necessary condition for rate $\frac{1}{3}$ feasibility than what is known in literature.Comment: Shorter version submitted to ISIT 201

토폴로지 간섭관리에서 최대 토폴로지와 자유도에 관한 분석

학위논문(박사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2020. 2. 노종선.In this dissertation, four main contributions are given as i) design of maximal topology in topological interference management (TIM), ii) design of maximal topology matrix and generalized alliance construction, iii) topological interference management- treating interference as noise (TIM-TIN) decomposition, and iv) inter-cell interference coordination (ICIC) based on cell zooming are considered. First, we propose a method of alliance construction, which derives maximal topology by stipulating several conditions for message relationship in the alignment graph and conflict graph. Maximal topologies are the topologies of K-user interference channel, where any interference link cannot be added without degenerating current degrees of freedom (DoF). It is proved that a topology is maximal if and only if it is derived from the alliance construction. Through alliance construction, any maximal topologies achieving symmetric DoF 1/2 can be designed. Properties of alliance construction are derived such as the maximum number of alliances to be constructed for the given number of messages K and a method to partition messages into sub-alliances. Second, message relationship based on alliance construction is translated into topology matrix in TIM. Permutation of the topology matrix is used to demonstrate the characteristics of the alliances easily in the topology matrix. The conditions for maximal topology matrix (MTM) are characterized and the discriminant of topology matrix for maximality and transformation of non-MTM into MTM are proposed. Alliance construction is generalized by introducing generalized sub-alliances, which extends the range of topologies derived from alliance construction in the achievable DoFs. The analysis of generalized alliance construction in the topology matrix is also proposed. Third, TIM-TIN decomposition is proposed in order to handle with intermediate links in interference channel. The criterion how to separate interference links into TIM and TIN is proposed for generalized degrees of freedom (GDoF) performance. Since GDoF in TIN depends on the Hamiltonian path in graph of interference channel, it is NP-hard problem and the optimal solution is hard to be proposed for GDoF. Instead of the optimal solution, a method to derive sub-optimal solution is proposed using modified channel matrix (MCM) and simulation result will be followed to show the performance of the proposed decomposition. Lastly, ICIC for self organizing cellular network is proposed, where each base station (BS) is not able to share information through backhaul to perform conventional ICIC schemes.The proposed ICIC scheme is based on distributed cell zooming, where non-cooperative game theory is used. Further, it is shown that proposed scheme can efficiently handle inter-cell interference and coverage hole problem in self organizing network by simulation result.본 논문에서는, i) 동맹 건설을 이용한 토폴로지 간섭관리에서 최대 토폴로지 설 계, ii) 최대 토폴로지 행렬 설계 및 일반화된 동맹 건설과 이를 이용한 자유도 1/2 미만의 토폴로지 설계, iii) TIM-TIN 분리 기법 iv) 셀 간 간섭 조정 (ICIC)이 연구되었다. 먼저, 기존의 정렬 집합을 확장시켜 내적 갈등이 없고 집합 갈등을 만족하는 메세지들의 집합인 동맹 (alliance)을 정의한다. 동맹을 기반으로 상호 부분 적대를 만족하는 동맹 건설을 제안하고 이를 통해 최대 토폴로지를 생성한다. 대칭 자유도가 1/2인 모든 최대 토폴로지는 동맹 건설을 통해 설계가 된다는 것을 증명한다. 또한 동맹 건설을 이용하여 동맹의 최대 수, 동맹으로 메세지 할당 등 최대 토폴로지의 특성에 관한 내용을 제시한다. 동맹 건설을 활용하여, 최대 토폴로지 판별과 변형을 제안한다. 두 번째로, 토폴로지의 최대성을 보다 쉽게 분석하기 위해, 정렬-갈등 그래프 와 관련된 동맹 건설을 토폴로지 행렬로 변형시킨다. 최대 토폴로지 행렬 (maximal topology matrix; MTM)의 필요 충분 조건을 유도하고 MTM의 판별과 변형 역시 제안한다. 나아가, 일반화된 부분동맹을 통해 동맹 건설을 일반화하고 1/n 자유도를 얻는 토폴로지를 설계한다. 일반화된 동맹 건설도 행렬 형태로 표현되고 제안하는 기법에서 자유도 1/n을 얻는 최대 토폴로지의 조건을 제시한다. 세 번째로 일반화 자유도 합의 차선해를 위한 TIM-TIN 분리 기법을 제안한다. TIM-TIN 분리의 기초에서 시작하여, TIM과 TIN에 간섭 링크들을 분배하는 구체적 인 방법을 동맹 건설과 변형 채널 행렬 (modified channel matrix; MCM)을 활용하여 제안한다. MCM을 이용하여 각각 간섭 링크들이 각 송수신 쌍의 일반화 자유도에 대한 상대적 영향을 측정할 수 있다. 마지막으로, 자가 조직화 셀룰러 네트워크를 위한 셀 간 간섭 조정 기법이 제안 되었는데,각기지국은 종래의 셀 간 간섭 조정방식을 수행하기 위한 정보를 백홀을 통해 공유할 수 없는 상황에서 간섭조정을 수행한다. 제안된 셀 간 간섭 조정 기법은 비협조적 게임 이론이 사용되는 분산 셀 확대 기법에 기반을 두고 있다. 또한, 제안 된 기법이 자가 조직화 셀룰러 네트워크에서 셀 간 간섭 및 커버리지 공동 문제를 효율적으로 처리 할 수 있음을 모의 실험을 통하여 보인다.1 INTRODUCTION 1 1.1 Background 1 1.2 Overview of Dissertation 6 1.3 Notations 7 2 Preliminaries 9 2.1 Degrees of Freedom 9 2.2 Interference Management 11 2.3 Graph Theory 14 2.4 Treating Interference as Noise with Power Allocation 15 2.5 CellZooming 18 3 Analysis of Maximal Topologies and Their DoFs in TIM 22 3.1 Introduction 22 3.2 Alliance Construction for Maximal Topologies 23 3.2.1 System Model: K-User Interference Channel 23 3.2.2 Definitions 24 3.2.3 Alliance 24 3.2.4 AllianceConstruction 26 3.3 Properties of Alliance Constructions 39 3.3.1 Beamforming Vector Design for Alliance Construction 39 3.3.2 Maximum Number of Alliances and Partition of Messages into Alliances 40 3.4 Discriminant and Transformation of Maximal Topologies 42 3.4.1 Discriminant of Maximal Topologies 42 3.4.2 Transformation of Maximal Topology 43 4 Maximal Topology Matrix and Generalized Alliance Construction 44 4.1 Introduction 44 4.2 Conditions for Maximal Topology Matrix 44 4.3 Discriminant and Transformation of MTM 47 4.4 Generalized Alliance Construction 49 4.4.1 Generalized Sub-Alliance 49 4.4.2 Topology Matrix for Generalized Alliance Construction 51 4.5 Topology Matrix for Generalized Alliance Construction 52 5 Multi-level Topological Interference Management 55 5.1 Introduction 55 5.2 Topological Interference Management 55 5.3 Treating Interference as Noise with Power Allocation. 56 5.3.1 System Model 56 5.4 TIM-TINDecomposition 57 5.4.1 Baseline 57 5.4.2 Separation Criterion 57 6 Inter-Cell Interference Coordination Based on Game Theory by Cell Zooming for Self-Organizing Cellular Network 61 6.1 Introduction 61 6.2 Non-CooperativeGameTheory 62 6.3 Design of Utility Function Based on Neighboring Signal Power Estimation 63 6.3.1 Design of Revenue Function 63 6.3.2 Design of Cost Function 64 6.3.3 Utility Function and Nash Equilibrium 66 6.3.4 Simulation Result 69 7 Conclusion 74 Abstract (In Korean) 79Docto

Flexible backhaul design with cooperative transmission in cellular interference networks

Interference is an important factor that limits the rates that can be achieved by mobile users in a cellular network. Interference management through cooperation has emerged as a major consideration for next-generation cellular networks. In this thesis, we focus on the downlink of a sectored hexagonal cellular network, under the assumption of local interference i.e., the interference at each user is only due to transmitters in neighboring sectors. We explore the potential degrees of freedom (DoF) gain in this network under constraints on the cooperation between base-stations. The constraints that we consider are the cooperation order M, and the average backhaul load B, which denote the maximum and the average number of transmitters, respectively, that jointly transmit any message. We first study the DoF gains in a scenario where mobile receivers can be associated to any neighboring cell but no cooperative transmission is allowed, and derive bounds on the maximum achievable per user DoF for orthogonal schemes. We then show that by combining cooperative transmission with flexible message assignment to the transmitters, it is possible to achieve a per user DoF strictly greater than that without cooperation. The proposed cooperative transmission scheme does not require extra backhaul capacity, as it uses a smart assignment of messages to transmitters to meet an average backhaul load constraint of one message per transmitter. The schemes presented are simple zero-forcing beamforming schemes that require linear precoding over a single time/frequency slot (one-shot). Similar schemes are proposed which achieve a per user DoF greater than half with a minimal increase in the backhaul load. These results are derived for networks with intra-cell interference and networks without intra-cell interference

Space Shuttle/TDRSS communication and tracking systems analysis

In order to evaluate the technical and operational problem areas and provide a recommendation, the enhancements to the Tracking and Data Delay Satellite System (TDRSS) and Shuttle must be evaluated through simulation and analysis. These enhancement techniques must first be characterized, then modeled mathematically, and finally updated into LinCsim (analytical simulation package). The LinCsim package can then be used as an evaluation tool. Three areas of potential enhancements were identified: shuttle payload accommodations, TDRSS SSA and KSA services, and shuttle tracking system and navigation sensors. Recommendations for each area were discussed