Mitigating Radio Interference in Large IoT Networks through Dynamic CCA Adjustment

The performance of low-power wireless sensor networks used to build Internet of Things applications often suffers from radio interference generated by co-located wireless devices or from jammers maliciously placed in their proximity. As IoT devices typically operate in unsupervised large-scale installations, and as radio interference is typically localized and hence affects only a portion of the nodes in the network, it is important to give low-power wireless sensors and actuators the ability to autonomously mitigate the impact of surrounding interference. In this paper we present our approach DynCCA, which dynamically adapts the clear channel assessment threshold of IoT devices to minimize the impact of malicious or unintentional interference on both network reliability and energy efficiency. First, we describe how varying the clear channel assessment threshold at run-time using only information computed locally can help to minimize the impact of unintentional interference from surrounding devices and to escape jamming attacks. We then present the design and implementation of DynCCA on top of ContikiMAC and evaluate its performance on wireless sensor nodes equipped with IEEE 802.15.4 radios. Our experimental investigation shows that the use of DynCCA in dense IoT networks can increase the packet reception rate by up to 50% and reduce the energy consumption by a factor of 4

Adaptive parameters adjustment in WBAN to mitigate Wi-Fi interferences

Wireless Body Area Network (WBAN), called also Wireless Body Sensor Network (WBSN), is composed of a set of tiny wireless devices (sensors) attached, implanted or ingested into the body. It offers real time and ubiquitous applications thanks to the small form, the lightness, and the wireless interface of sensors. WBAN performance is expected to be considerably degraded in the presence of Wi-Fi networks. Their operating channels overlap in the 2.4 GHz Industrial Scientific and Medical (ISM) band which produces interference when they transmit data, accompanied by data losses and quick battery exhaustion. Therefore, it is crucial to mitigate the interference between WBAN and Wi-Fi networks in order to maintain the efficiency and the reliability of the WBAN system. Proposals in the literature use an added complex hardware in WBAN system, or perform the exchange of additional information, or establish expensive communications, or affect the quality of service of the WBAN. Unlike previous researches, we proposed simple, low cost and dynamic method that adaptively adjusts specific parameters in the Medium Access Control (MAC) layer. We have proved the effectiveness of our approach based on theoretical analysis and simulation using MiXiM framework of OMNet++ simulato

Towards Scalable Design of Future Wireless Networks

Wireless operators face an ever-growing challenge to meet the throughput and processing requirements of billions of devices that are getting connected. In current wireless networks, such as LTE and WiFi, these requirements are addressed by provisioning more resources: spectrum, transmitters, and baseband processors. However, this simple add-on approach to scale system performance is expensive and often results in resource underutilization. What are, then, the ways to efficiently scale the throughput and operational efficiency of these wireless networks? To answer this question, this thesis explores several potential designs: utilizing unlicensed spectrum to augment the bandwidth of a licensed network; coordinating transmitters to increase system throughput; and finally, centralizing wireless processing to reduce computing costs. First, we propose a solution that allows LTE, a licensed wireless standard, to co-exist with WiFi in the unlicensed spectrum. The proposed solution bridges the incompatibility between the fixed access of LTE, and the random access of WiFi, through channel reservation. It achieves a fair LTE-WiFi co-existence despite the transmission gaps and unequal frame durations. Second, we consider a system where different MIMO transmitters coordinate to transmit data of multiple users. We present an adaptive design of the channel feedback protocol that mitigates interference resulting from the imperfect channel information. Finally, we consider a Cloud-RAN architecture where a datacenter or a cloud resource processes wireless frames. We introduce a tree-based design for real-time transport of baseband samples and provide its end-to-end schedulability and capacity analysis. We also present a processing framework that combines real-time scheduling with fine-grained parallelism. The framework reduces processing times by migrating parallelizable tasks to idle compute resources, and thus, decreases the processing deadline-misses at no additional cost. We implement and evaluate the above solutions using software-radio platforms and off-the-shelf radios, and confirm their applicability in real-world settings.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133358/1/gkchai_1.pd

Towards the efficient use of LoRa for wireless sensor networks

Since their inception in 1998 with the Smart Dust Project from University of Berkeley, Wireless Sensor Networks (WSNs) had a tremendous impact on both science and society, influencing many (new) research fields, like Cyber-physical System (CPS), Machine to Machine (M2M), and Internet of Things (IoT). In over two decades, WSN researchers have delivered a wide-range of hardware, communication protocols, operating systems, and applications, to deal with the now classic problems of resourceconstrained devices, limited energy sources, and harsh communication environments. However, WSN research happened mostly on the same kind of hardware. With wireless communication and embedded hardware evolving, there are new opportunities to resolve the long standing issues of scaling, deploying, and maintaining a WSN. To this end, we explore in this work the most recent advances in low-power, longrange wireless communication, and the new challenges these new wireless communication techniques introduce. Specifically, we focus on the most promising such technology: LoRa. LoRa is a novel low-power, long-range communication technology, which promises a single-hop network with millions of sensor nodes. Using practical experiments, we evaluate the unique properties of LoRa, like orthogonal spreading factors, nondestructive concurrent transmissions, and carrier activity detection. Utilising these unique properties, we build a novel TDMA-style multi-hop Medium Access Control (MAC) protocol called LoRaBlink. Based on empirical results, we develop a communication model and simulator called LoRaSim to explore the scalability of a LoRa network. We conclude that, in its current deployment, LoRa cannot support the scale it is envisioned to operate at. One way to improve this scalability issue is Adaptive Data Rate (ADR). We develop two ADR protocols, Probing and Optimistic Probing, and compare them with the de facto standard ADR protocol used in the crowdsourced TTN LoRaWAN network. We demonstrate that our algorithms are much more responsive, energy efficient, and able to reach a more efficient configuration quicker, though reaching a suboptimal configuration for poor links, which is offset by the savings caused by the convergence speed. Overall, this work provides theoretical and empirical proofs that LoRa can tackle some of the long standing problems within WSN. We envision that future work, in particular on ADR and MAC protocols for LoRa and other low-power, long-range communication technologies, will help push these new communication technologies to main-stream status in WSNs

간섭 환경에서 저전력 무선 센서 네트워킹에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 이용환.The demand for commercial deployment of large-scale wireless sensor networks (WSNs) has rapidly been increasing over the past decade. However, conventional WSN technologies may not be feasible for commercial deployment of large-scale WSNs because of their technical flaws, including limited network scalability, susceptibility to co-channel interference and large signaling overhead. In practice, low-power WSNs seriously suffer from interference generated by coexisting radio systems such as IEEE 802.11 wireless local area networks (WLANs). This interference problem seriously hampers commercial deployment of low-power WSNs. Few commercial WSN chips can provide secure and reliable networking performance in practical operation environments. In this dissertation, we consider performance improvement of low-power WSNs in the presence of co-channel interference. We first investigate the effect of co-channel interference on the transmission of low-power WSN signal, and then design a low-power WSN transceiver that can provide stable performance even in the presence of severe co-channel interference, while providing the backward compatibility with IEEE 802.15.4. We also consider the network connectivity in the presence of co-channel interference. The connectivity of low-power WSNs can be improved by transmitting synchronization signal and making channel hand-off in a channel-aware manner. A beacon signal for the network synchronization is repeatedly transmitted in consideration of channel condition and signaling overhead. Moreover, when the channel is severely interfered, all devices in a cluster network make communications by means of temporary channel hopping and then seamlessly make channel hand-off to the best one among the temporary hopping channels. The performance improvement is verified by computer simulation and experiment using IEEE 802.15.4 motes in real operation environments. Finally, we consider the signal transmission in the presence of co-channel interference. The throughput performance of low-power WSN transceivers can be improved by adjusting the transmission rate and the payload size according to the interference condition. We estimate the probability of transmission failure and the data throughput, and then determine the payload size to maximize the throughput performance. It is shown that the transmission time maximizing the normalized throughput is little affected by the transmission rate, but rather by the interference condition. The transmission rate and the transmission time can independently be adjusted in response to the change of channel and interference condition, respectively. The performance improvement is verified by computer simulation.Chapter 1 1 Chapter 2 11 2.1. ZigBee/IEEE 802.15.4-based cluster-tree networks 11 2.2. Performance of IEEE 802.15.4 transceiver 14 Chapter 3 17 3.1. System model 18 3.2. Previous works 21 3.3. Proposed interference management scheme 28 3.4. Performance evaluation 37 Chapter 4 51 4.1. System model 52 4.2. Transmission in the presence of interference 56 4.3. Proposed transmission scheme 60 4.4. Performance evaluation 65 Chapter 5 82 Appendix 85 A. Average synchronization time during frequency hopping 85 B. Derivation of (4.2) 86 References 88 Korean Abstract 97Docto

RF Integrated Circuits for Energy Autonomous Sensor Nodes.

The exponential growth in the semiconductor industry has enabled computers to pervade our everyday lives, and as we move forward many of these computers will have form factors much smaller than a typical laptop or smartphone. Sensor nodes will soon be deployed ubiquitously, capable of capturing information of their surrounding environment. The next step is to connect all these different nodes together into an entire interconnected system. This “Internet of Things” (IoT) vision has incredible potential to change our lives commercially, societally, and personally. The backbone of IoT is the wireless sensor node, many of which will operate under very rigorous energy constraints with small batteries or no batteries at all. It has been shown that in sensor nodes, radio communication is one of the biggest bottlenecks to ultra-low power design. This research explores ways to reduce energy consumption in radios for wireless sensor networks, allowing them to run off harvested energy, while maintaining qualities that will allow them to function in a real world, multi-user environment. Three different prototypes have been designed demonstrating these techniques. The first is a sensitivity-reduced nanowatt wake-up radio which allows a sensor node to actively listen for packets even when the rest of the node is asleep. CDMA codes and interference rejection reduce the potential for energy-costly false wake-ups. The second prototype is a full transceiver for a body-worn EKG sensor node. This transceiver is designed to have low instantaneous power and is able to receive 802.15.6 Wireless Body Area Network compliant packets. It uses asymmetric communication including a wake-up receiver based on the previous design, UWB transmitter and a communication receiver. The communication receiver has 10 physical channels to avoid interference and demodulates coherent packets which is uncommon for low power radios, but dictated by the 802.15.6 standard. The third prototype is a long range transceiver capable of >1km communication range in the 433MHz band and able to interface with an existing commercial radio. A digitally assisted baseband demodulator was designed which enables the ability to perform bit-level as well as packet-level duty cycling which increases the radio's energy efficiency.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110432/1/nerobert_1.pd