무선통신망에서 처리율 개선을 위한 신호전달 부하의 저감에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 전화숙.무선통신망(wireless networks)은 무선 채널의 상태 변화에 따른 성능 저하를 줄이기 위해 링크 적응(link adaptation) 기술을 기본적으로 사용한다. 링크 적응 기술을 위해서는 채널 상태 정보를 추정하고 수집해야하기 때문에 이에 따른 신호전달 부하(signaling overhead)가 발생하게 된다. 본 논문에서는 무선통신망에서의 신호전달 부하를 줄이기 위한 두 가지 기법을 제안하였다. 먼저 협력 통신 네트워크(cooperative communication networks)에서의 적응적인 전송 기법을 제안하였다. 제안한 기법을 사용하는 협력 통신 네트워크는 ACK(positive acknowledgement)/NACK(negative ACK)와 같은 제한된 피드백 정보로부터 추정된 채널 상태에 기반을 두어 전송 속도를 조절하면서 릴레이(relay)의 사용여부도 함께 결정한다. 제한된 피드백 정보는 실제 채널 상태에 대한 부분적인 정보만을 제공하기 때문에 제안하는 기법을 불확실성 마코브 의사 결정(partially observable Markov decision process)에 따라 설계하였다. 다음으로, 셀룰러 네트워크에서의 기기 간(D2D, device-to-device) 통신을 위한 자원 관리 기법을 제안하였다. 제안한 기법은 두 단계로 구성되고 준 분산적(semi-distributed)으로 동작한다. 첫 번째 단계에서는 중앙 집중적(centralized)으로 기지국이 자원 블록을 B2D(BS-to-user device) 링크와 D2D 링크에게 할당한다. 두 번째 단계에서는 분산적(distributed)으로 기지국은 B2D 링크에 할당된 자원 블록들을 사용하여 전송 스케줄을 결정(scheduling)하고, 각 D2D 링크의 제 1 사용자 기기(primary user device)는 해당 D2D 링크에 할당된 자원 블록들에서의 링크 적응을 수행한다. 이러한 자원 관리 구조는 중앙 집중적 기법처럼 높은 네트워크 용량을 달성할 뿐 아니라 분산적 기법처럼 낮은 신호전달 및 계산(computational) 부하를 필요로 한다. 본 논문에서는 제안한 자원 관리 구조에서 주파수 자원 효율을 최대화하는 자원 블록 할당 문제들을 두 가지 서로 다른 자원 할당 정책에 대하여 만들고 이 문제들을 풀기 위해 탐욕(greedy) 알고리즘과 열 추가 기반(column generation-based) 알고리즘을 제안하였다. 또한 시뮬레이션을 통해 제안하는 기법들이 설계 목표를 달성하고 기존의 기법보다 높은 성능을 보이면서도 신호전달 부하를 줄일 수 있음을 보였다.Wireless networks usually adopt some link adaptation techniques to mitigate the performance degradation due to the time-varying characteristics of wireless channels. Since the link adaptation techniques require to estimate and collect channel state information, signaling overhead is inevitable in wireless networks. In this thesis, we propose two schemes to reduce the signaling overhead in wireless networks. First, we design an adaptive transmission scheme for cooperative communication networks. The cooperative network with the proposed scheme chooses the transmission rate and decides to involve the relay in transmission, adapting to the channel state estimated from limited feedback information (e.g., ACK/NACK feedback). Considering that the limited feedback information provides only partial knowledge about the actual channel states, we design a decision-making algorithm on cooperative transmission by using a partially observable Markov decision process (POMDP) framework. Next, we also propose a two-stage semi-distributed resource management framework for the device-to-device (D2D) communication in cellular networks. At the first stage of the framework, the base station (BS) allocates resource blocks (RBs) to BS-to-user device (B2D) links and D2D links, in a centralized manner. At the second stage, the BS schedules the transmission using the RBs allocated to B2D links, while the primary user device of each D2D link carries out link adaptation on the RBs allocated to the D2D link, in a distributed fashion. The proposed framework has the advantages of both centralized and distributed design approaches, i.e., high network capacity and low signaling/computational overhead, respectively. We formulate the problems of RB allocation to maximize the radio resources efficiency, taking account of two different policies on the spatial reuse of RBs. To solve these problems, we suggest a greedy algorithm and a column generation-based algorithm. By simulation, it is shown that the proposed schemes achieve their design goal properly and outperform existing schemes while reducing the signaling overhead.1 Introduction 1 1.1 Background and Motivation 1 1.2 Approaches to Reduce Signaling Overhead 5 1.3 Proposed Schemes 7 1.3.1 Adaptive Transmission Scheme for Cooperative Communication 7 1.3.2 Resource Management Scheme for D2D Communication in Cellular Networks 8 1.4 Organization 10 2 Adaptive Transmission Scheme for Cooperative Communication 11 2.1 System Model 11 2.2 Cooperative Networks with Limited Feedback 12 2.2.1 Operation of the Proposed Cooperative Network 12 2.2.2 Finite-State Markov Channel Model 15 2.2.3 Packet Error Probability 16 2.2.4 Channel Feedback Schemes 18 2.3 Adaptive Transmission Scheme for Cooperative Communication 19 2.3.1 POMDP Formulation 19 2.3.2 Solution to POMDP 22 3 Resource Management Scheme for D2D Communication in Cellular Networks 25 3.1 System Model 25 3.1.1 Network Model 25 3.1.2 Radio Resource Model 27 3.2 Proposed Resource Management Framework 28 3.2.1 Framework Overview 28 3.2.2 Two-Stage Resource Management 29 3.2.3 Advantages of the Proposed Framework 31 3.3 Conditions for Simultaneous Transmission of B2D and D2D Links 33 3.3.1 Analysis of Interference on B2D and D2D Links 33 3.3.2 Conditions for Simultaneous Transmission of B2D and D2D Links 36 3.4 Resource Block Allocation 38 3.4.1 Resource Block Allocation with Conservative Reuse Policy 39 3.4.2 Resource Block Allocation with Aggressive Reuse Policy 44 4 Performance Evaluation 52 4.1 Adaptive Transmission Scheme for Cooperative Communication 52 4.1.1 Simulation Model 52 4.1.2 Simulation Results 53 4.2 Resource Management Scheme for D2D Communication in Cellular Networks 62 4.2.1 Simulation Model 62 4.2.2 Simulation Results 64 5 Conclusion 75 Bibliography 77 Abstract 85Docto

NOMA based resource allocation and mobility enhancement framework for IoT in next generation cellular networks

With the unprecedented technological advances witnessed in the last two decades, more devices are connected to the internet, forming what is called internet of things (IoT). IoT devices with heterogeneous characteristics and quality of experience (QoE) requirements may engage in dynamic spectrum market due to scarcity of radio resources. We propose a framework to efficiently quantify and supply radio resources to the IoT devices by developing intelligent systems. The primary goal of the paper is to study the characteristics of the next generation of cellular networks with non-orthogonal multiple access (NOMA) to enable connectivity to clustered IoT devices. First, we demonstrate how the distribution and QoE requirements of IoT devices impact the required number of radio resources in real time. Second, we prove that using an extended auction algorithm by implementing a series of complementary functions, enhance the radio resource utilization efficiency. The results show substantial reduction in the number of sub-carriers required when compared to conventional orthogonal multiple access (OMA) and the intelligent clustering is scalable and adaptable to the cellular environment. Ability to move spectrum usages from one cluster to other clusters after borrowing when a cluster has less user or move out of the boundary is another soft feature that contributes to the reported radio resource utilization efficiency. Moreover, the proposed framework provides IoT service providers cost estimation to control their spectrum acquisition to achieve required quality of service (QoS) with guaranteed bit rate (GBR) and non-guaranteed bit rate (Non-GBR)

Separation Framework: An Enabler for Cooperative and D2D Communication for Future 5G Networks

Soaring capacity and coverage demands dictate that future cellular networks need to soon migrate towards ultra-dense networks. However, network densification comes with a host of challenges that include compromised energy efficiency, complex interference management, cumbersome mobility management, burdensome signaling overheads and higher backhaul costs. Interestingly, most of the problems, that beleaguer network densification, stem from legacy networks' one common feature i.e., tight coupling between the control and data planes regardless of their degree of heterogeneity and cell density. Consequently, in wake of 5G, control and data planes separation architecture (SARC) has recently been conceived as a promising paradigm that has potential to address most of aforementioned challenges. In this article, we review various proposals that have been presented in literature so far to enable SARC. More specifically, we analyze how and to what degree various SARC proposals address the four main challenges in network densification namely: energy efficiency, system level capacity maximization, interference management and mobility management. We then focus on two salient features of future cellular networks that have not yet been adapted in legacy networks at wide scale and thus remain a hallmark of 5G, i.e., coordinated multipoint (CoMP), and device-to-device (D2D) communications. After providing necessary background on CoMP and D2D, we analyze how SARC can particularly act as a major enabler for CoMP and D2D in context of 5G. This article thus serves as both a tutorial as well as an up to date survey on SARC, CoMP and D2D. Most importantly, the article provides an extensive outlook of challenges and opportunities that lie at the crossroads of these three mutually entangled emerging technologies.Comment: 28 pages, 11 figures, IEEE Communications Surveys & Tutorials 201

Matching Theory for Future Wireless Networks: Fundamentals and Applications

The emergence of novel wireless networking paradigms such as small cell and cognitive radio networks has forever transformed the way in which wireless systems are operated. In particular, the need for self-organizing solutions to manage the scarce spectral resources has become a prevalent theme in many emerging wireless systems. In this paper, the first comprehensive tutorial on the use of matching theory, a Nobelprize winning framework, for resource management in wireless networks is developed. To cater for the unique features of emerging wireless networks, a novel, wireless-oriented classification of matching theory is proposed. Then, the key solution concepts and algorithmic implementations of this framework are exposed. Then, the developed concepts are applied in three important wireless networking areas in order to demonstrate the usefulness of this analytical tool. Results show how matching theory can effectively improve the performance of resource allocation in all three applications discussed

A Multi-Game Framework for Harmonized LTE-U and WiFi Coexistence over Unlicensed Bands

The introduction of LTE over unlicensed bands (LTE-U) will enable LTE base stations (BSs) to boost their capacity and offload their traffic by exploiting the underused unlicensed bands. However, to reap the benefits of LTE-U, it is necessary to address various new challenges associated with LTE-U and WiFi coexistence. In particular, new resource management techniques must be developed to optimize the usage of the network resources while handling the interdependence between WiFi and LTE users and ensuring that WiFi users are not jeopardized. To this end, in this paper, a new game theoretic tool, dubbed as \emph{multi-game} framework is proposed as a promising approach for modeling resource allocation problems in LTE-U. In such a framework, multiple, co-existing and coupled games across heterogeneous channels can be formulated to capture the specific characteristics of LTE-U. Such games can be of different properties and types but their outcomes are largely interdependent. After introducing the basics of the multi-game framework, two classes of algorithms are outlined to achieve the new solution concepts of multi-games. Simulation results are then conducted to show how such a multi-game can effectively capture the specific properties of LTE-U and make of it a "friendly" neighbor to WiFi.Comment: Accepted for publication at IEEE Wireless Communications Magazine, Special Issue on LTE in Unlicensed Spectru