저전력 손실 네트워크에서 대규모 응용분야를 위한 전송전력 제어기법

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 박세웅.Transmission power is an important factor which impacts on routing topology in low power and lossy networks (LLNs). LLNs have been designed for low rate traffic where use of maximum transmission power is the best choice for performance maximization since it results in reduced hop distance and transmission overhead. However, large scale applications also require LLNs to deliver very high rate traffic. In such large scale applications, the nodes which are near the root node will incur heavy traffic even though each node generates low rate traffic. As a result, it will cause severe link congestion. In this paper, we first investigate the effect of transmission power control on the performance of the routing protocol for LLNs (RPL) at heavy traffic load through testbed experiments. Our experiments show that, unlike LLNs in low rate applications, packet delivery performance at heavy load first increases and then decreases with transmission power. And we further investigate the reasons of what makes packet loss rate have a convex curve according to transmission power by per node analysis. We classify packet losses into link loss and queue loss. From the experiment results, we observe that link and queue losses are significantly unbalanced among nodes, which causes the load balancing problem of RPL. Furthermore, queue losses occur at the nodes which experience severe link loss. To solve this problem, we propose a simple power control mechanism, which allows each node to adaptively control its transmission power according to its own link and queue losses. Our proposal significantly improves the packet delivery performance by balancing the traffic load within a routing tree. We show performance improvement through experimental measurements on a real mutihop LLN testbed running RPL over IEEE 802.15.4.Contents Abstract i Contents iii List of Figures iii List of Tables v Chap 1 Introduction 1 Chap 2 Experimental Environments 4 2.1. IPv6 routing protocol for low power and lossy networks (RPL) 4 2.2. Experimental environments 5 Chap 3 Load Balancing Problem of RPL 7 3.1. Packet loss rate 7 3.2. Queue loss and link loss 8 3.3. Topology analysis 11 3.4. Per node analysis 12 Chap 4 Transmission Power Control Mechanism 15 4.1. Effect of proposed power control on load balancing 15 4.2. Power control mechanism 17 Chap 5 Experimental Results 20 5.1. Packet loss rate 20 5.2. Queue loss and link loss 22 5.3. Packet loss rate 23 Chap 6 Conclusions 25 References 26 초 록 30 감사의 글 32Maste

Comparative Analysis of Objective Functions in Routing Protocol for Low Power and Lossy Networks

Internet-of-Things (IoT), a new paradigm, has led to the extensive increase in communication among the tiny and embedded network devices. Majority of those devices are power, memory, and energy constrained and are made to work in lossy environments, thus forming an important part of Low Power and Lossy Networks (LLNs). Routing Protocol for Low Power and Lossy Networks (RPL) designed by Internet Engineering Task Force (IETF) is proved to be an effective candidate for routing in such networks. RPL defines the Objective Functions (OFs) in which a set of routing metrics (like hop count, ETX and so on) are used either in an individual or combined manner for optimal path selection between the nodes of the network in terms of various performance factors like power consumed, Packet Delivery Ratio (PDR), reliability and so on. There are two standard Objective Functions- Objective function Zero (OF0) and Minimum Rank Hysteresis Objective Function (MRHOF). The former uses the hop count and the latter uses the Expected Transmission Count (ETX) as the default routing metrics to select the optimal paths. But both of them are single metric Objective Functions (OFs) and have to face various issues regarding the energy consumed, network lifetime and so on. So a number of RPL optimizations incorporating the different routing metrics in a combined way have been proposed to enhance the performance in all respects. This paper gives the comparative analysis of existing Objective Functions that are based on different routing metrics and concludes that the use of a combination of multiple metrics will further improve the RPL performance in future

EC-CENTRIC: An Energy- and Context-Centric Perspective on IoT Systems and Protocol Design

The radio transceiver of an IoT device is often where most of the energy is consumed. For this reason, most research so far has focused on low power circuit and energy efficient physical layer designs, with the goal of reducing the average energy per information bit required for communication. While these efforts are valuable per se, their actual effectiveness can be partially neutralized by ill-designed network, processing and resource management solutions, which can become a primary factor of performance degradation, in terms of throughput, responsiveness and energy efficiency. The objective of this paper is to describe an energy-centric and context-aware optimization framework that accounts for the energy impact of the fundamental functionalities of an IoT system and that proceeds along three main technical thrusts: 1) balancing signal-dependent processing techniques (compression and feature extraction) and communication tasks; 2) jointly designing channel access and routing protocols to maximize the network lifetime; 3) providing self-adaptability to different operating conditions through the adoption of suitable learning architectures and of flexible/reconfigurable algorithms and protocols. After discussing this framework, we present some preliminary results that validate the effectiveness of our proposed line of action, and show how the use of adaptive signal processing and channel access techniques allows an IoT network to dynamically tune lifetime for signal distortion, according to the requirements dictated by the application

A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations

Driven by the special requirements of the Low-power and Lossy Networks (LLNs), the IPv6 Routing Protocol for LLNs (RPL) was standardized by the IETF some six years ago to tackle the routing issue in such networks. Since its introduction, however, numerous studies have pointed out that, in its current form, RPL suffers from issues that limit its efficiency and domain of applicability. Thus, several solutions have been proposed in the literature in an attempt to overcome these identified limitations. In this survey, we aim mainly to provide a comprehensive review of these research proposals assessing whether such proposals have succeeded in overcoming the standard reported limitations related to its core operations. Although some of RPL’s weaknesses have been addressed successfully, the study found that the proposed solutions remain deficient in overcoming several others. Hence, the study investigates where such proposals still fall short, the challenges and pitfalls to avoid, thus would help researchers formulate a clear foundation for the development of further successful extensions in future allowing the protocol to be applied more widely

Multichannel Cross-Layer Routing for Sensor Networks

Wireless Sensor Networks are ad-hoc networks that consist of sensor nodes that typically use low-power radios to connect to the Internet. The channels used by the low-power radio often suffer from interference from the other devices sharing the same frequency. By using multichannel communication in wireless networks, the effects of interference can be mitigated to enable the network to operate reliably. This thesis investigates an energy efficient multichannel protocol in Wireless Sensor Networks. It presents a new decentralised multichannel tree-building protocol with a centralised controller for ad-hoc sensor networks. The proposed protocol alleviates the effect of interference, which results in improved network efficiency, stability, and link reliability. The protocol detects the channels that suffer interference in real-time and switches the sensor nodes from those channels. It takes into account all available channels and aims to use the spectrum efficiently by transmitting on several channels. In addition to the use of multiple channels, the protocol reconstructs the topology based on the sensor nodes’ residual energy, which can prolong the network lifetime. The sensor nodes’ energy consumption is reduced because of the multichannel protocol. By using the lifetime energy spanning tree algorithm proposed in this thesis, energy consumption can be further improved by balancing the energy load in the network. This solution enables sensor nodes with less residual energy to remain functional in the network. The benefits of the proposed protocol are described in an extensive performance evaluation of different scenarios in this thesis

Efficient Routing Primitives for Low-power and Lossy Networks in Internet of Things

At the heart of the Internet of Things (IoTs) are the Low-power and Lossy networks (LLNs), a collection of interconnected battery-operated and resource-constrained tiny devices that enable the realization of a wide range of applications in multiple domains. For an efficient operation, such networks require the design of efficient protocols especially at the network layer of their communication stack. In this regards, the Routing Protocol for LLNs (RPL) has been developed and standardised by the IETF to fulfil the routing requirements in such networks. Proven efficient in tackling some major issues, RPL is still far from being optimal in addressing several other routing gaps in the context of LLNs. For instance, the RPL standard lacks in a scalable routing mechanism in the applications that require bidirectional communication. In addition, its routing maintenance mechanism suffers from relatively slow convergence time, limiting the applicability of the protocol in time-critical applications, and a high risk of incorrect configurations of its parameters, risking the creation of sub-optimal routes. Furthermore, RPL lacks in a fair load-distribution mechanism which may harm both energy and reliability of its networks. Motivated by the above-mentioned issues, this thesis aimed at overcoming the RPL’s weaknesses by developing more efficient routing solutions, paving the way towards successful deployments and operations of the LLNs at different scales. Hence, to tackle the inefficiency of RPL’s routing maintenance operations, a new routing maintenance algorithm, namely, Drizzle, has been developed characterized by an adaptive, robust and configurable nature that boosts the applicability of RPL in several applications. To address the scalability problem, a new downward routing solution has been developed rendering RPL more efficient in large-scale networks. Finally, a load-balancing objective function for RPL has been proposed that enhances both the energy efficiency and reliability of LLNs. The efficiency of the proposed solutions has been validated through extensive simulation experiments under different scenarios and operation conditions demonstrating significant performance enhancements in terms of convergence time, scalability, reliability, and power consumption