Reliability and Throughput Enhancement in Low-power and Lossy Networks

Abstract

본 논문은 저전력 및 손실 네트워크에서 모바일 라우팅, 시간 슬롯 기반 통신, 6TiSCH 네트워크의 형성이라는 세 가지 영역에 대한 문제를 해결한다. 첫째로 모 바일 라우팅 기법, MobiRPL 은 수신 신호 세기와 주변 디바이스와의 연결성 관리 동작을 활용하여 모바일 노드가 포함된 저전력 및 손실 네트워크에서 효율적인 라 우팅이 가능하도록 한다. 시뮬레이션 및 테스트베드 실험 결과, MobiRPL 은 비교 기법에 비해 패킷 전달률을 11.3% 향상시키고 에너지 소비를 73.3% 감소시킨다. 또 한 시간 슬롯 기반 통신 시스템에서의 슬롯 내 유휴 시간으로 인한 네트워크의 통신 효율 저하를 해결하기 위해 실제 패킷 길이 분포에 따라 슬롯 크기를 동적으로 조 절하고 슬롯 사용 효율에 따라 패킷 집단 전송을 수행하는 ASAP 를 제안한다. 실제 테스트베드에서의 TSCH 기반의 연구 결과, ASAP 은 기본 TSCH에 비해 throughput 을 2.21배 향상시키고 지연 시간을 78.7% 줄인다. 세 번째로, 6TiSCH 네트워크 형성 과정의 비효율성을 개선하기 위해 TSCH 슬롯 내 전송 시작 시점에 offset을 부여함 으로써 충돌 감지 및 offset 기반 우선 순위에 따른 중요 패킷의 우선 전송을 가능케 하는 TOP 을 제안한다. 실제 테스트베드 실험 결과 TOP 는 네트워크 형성 시간을 최대 50% 감소시킨다. 이처럼 실제 구현 및 실험을 통해 입증된 제안 기법들의 성능 향상은 본 논문이 저전력 및 손실 네트워크의 전반적인 효율성 향상에 기여할 수 있음을 보여준다.

This dissertation addresses various challenges in low-power and lossy networks (LLNs) by proposing innovative solutions that improve performance and efficiency. The study explores three key aspects: mobile routing, enhancing the throughput of time-slotted communication, and accelerating network formation in LLNs. We first focus on mobile routing in LLNs. The existing IPv6 routing protocol for LLNs (RPL) lacks explicit support for mobility. To address this limitation, we design and implement an adaptive and robust mobile routing protocol called MobiRPL. MobiRPL utilizes the received signal strength indicator (RSSI) to enable efficient routing in mobile LLNs. Extensive evaluations through simulations and testbed experiments demonstrate the effectiveness of MobiRPL, with improvements in the packet delivery ratio by 11.3% compared to RPL and a 73.3% reduction in energy consumption when compared to the lightweight on-demand ad-hoc distance-vector routing protocol - next generation (LOADng). We then target the throughput enhancement of time-slotted communications in LLNs, such as the IEEE 802.15.4e time-slotted channel hopping (TSCH). In many time-slotted systems, the slot length is typically fixed to a value suited for maximum-sized packets. Consequently, time slots can be underutilized when the packet length is shorter than the maximum, leading to residue time and throughput degradation. To overcome this inefficiency, we propose a utility-based adaptation of slot size and packet aggregation called ASAP. ASAP dynamically adjusts the slot length based on the packet size distribution and employs packet aggregation to maximize time-efficiency. Experimental evaluations using real embedded devices and large-scale testbeds demonstrate a significant improvement in throughput by 2.21x and a reduction in latency by 78.7% compared to the default time-slotted communication of TSCH. Finally, we address the network formation process in IPv6 over IEEE 802.15.4e TSCH mode (6TiSCH) network, the standard LLN. The formation of the 6TiSCH network often encounters severe collisions and congestion, leading to significant delays. We identify the root cause as the synchronized transmission timing among nodes within the time slot, rendering collision avoidance ineffective. To enhance the network formation efficiency, we propose a novel offset-based collision avoidance and prioritization method named TOP. This approach assigns different transmission offsets to packets, introducing diversity in their starting points. Such diversification facilitates collision detection and enables the prioritization of formation-critical packets. Real testbed experiments validate the effectiveness of TOP, demonstrating up to a 50% reduction in network formation time. In aggregate, this dissertation presents novel approaches to address various challenges in LLNs, such as mobile routing, throughput enhancement of time-slotted communication, and network formation acceleration. The proposed solutions demonstrate significant improvements in performance, highlighting their potential to make LLNs more reliable and efficient.