Heejung Yu

A survey on routing protocols supported by the Contiki Internet of things operating system

Abstract Standardization and technology advancements have helped the realization of the Internet of things (IoT). The availability of low-cost IoT devices has also played a key role in furthering IoT research, development, and deployment. IoT operating systems (OSs) provide integration of software and hardware components. The availability of standard protocols, heterogeneous hardware support, ease of development, and simulation or emulation support are desirable features of IoT OSs. Contiki OS is one of the contenders for future IoT OSs. It was proposed in 2003, and since then, it has been continually under development and upgraded by professionals, academia, and researchers. Contiki OS supports open source, Internet standards, power awareness, dynamic module loading, and many hardware platforms. The diverse applications of IoT, including smart homes, smart health, smart cities, require efficient network connectivity and demand intelligent routing protocols that can handle heterogeneous, mobile, and diverse networks. Subsequently, designing routing protocols for memory- and central processing unit (CPU)-constrained IoT devices is a very challenging task. Therefore, this paper surveys the state-of-the-art routing protocols of Contiki OS. To the best of the authors’ knowledge, this is the first study to classify the Contiki OS routing protocol literature and list the potential challenges and future work.

Optimal sensing performance for cooperative and non-cooperative cognitive radio networks:

Spectrum sensing has gained new aspects with the advent of cognitive radio and opportunistic spectrum access techniques. Spectrum sensing plays a vital role in cognitive radio networks, and its reliability determines the success of transmission. It also enables the spectrum access for unlicensed users, enhancing the spectral utilization. The successful integration of primary users and secondary users requires the secondary users to be capable of efficient sensing and keeping precise track of the primary transmissions. There exists an inherent sensing-throughput trade-off in the time-division multiple access–based hierarchical cognitive radio networks. The sum rates of the cognitive radio networks depend on the sensing performance and can be maximized by reducing the sensing errors. In this work, we investigate the optimal sensing parameters of imperfect sensing for opportunistic spectrum access–based cognitive radio networks. The optimal sensing operating points are analyzed for different sensing durations and known primary user activities. First, the sum rate gain and sum rate loss are presented for the non-cooperative network, in terms of perfect channel sensing, and imperfect channel sensing, with and without optimal sensing pairs. Next, the trade-off between cooperative gain and cooperation overhead is examined for the multiuser cognitive radio networks. The sum rate is derived, using the optimal operating point, to investigate the cooperative sensing trade-off for different number of cooperative users in the multiuser cognitive radio network.

A cluster-based cooperative spectrum sensing in cognitive radio network using eigenvalue detection technique with superposition approach

Cognitive radio (CR) networks have been active area of research because of its ability to opportunistically share the spectrum. A cluster-based cooperative spectrum sensing (CCSS) has a tremendous impact on sensing reliability compared with cooperative spectrum sensing. The energy detection (ED) technique requires perfect knowledge of noise power. An eigenvalue-based spectrum sensing has mitigated the noise uncertainty problem. Sensing and reporting time slots are rigidly separated in the conventional ED and eigenvalue-based detection (EVD) schemes. In CCSS, more reporting time slots are required as the number of CR users (CRUs) increases. If the reporting time slots of other CRUs as sensing time slots with a superposition allocation, the more reliable channel sensing can be achieved. In this paper, we propose CCSS using EVD technique with a superposition approach scheme where the reporting time slot is properly utilized to sense the primary users (PUs) signal more accurately by rescheduling the reporting time slot for CRUs and cluster heads (CHs). Simulation result shows that the proposed EVD scheme has better detection probability than the conventional CCSS using both ED and EVD techniques.

Internet of Things (IoT): Operating System, Applications and Protocols Design, and Validation Techniques

Abstract By combining energy efficient micro-controllers, low-power radio transceivers, and sensors as well as actuators in so called smart objects, we are able to connect the digital cyber world with the physical world as in cyber physical systems. In the vision of the Internet of Things, these smart objects should be seamlessly integrated into the traditional Internet. Typically, smart objects are heavily constrained in terms of computation, memory and energy resources. Furthermore, the commonly used wireless links among smart objects or towards the Internet are typically slow and subject to high packet loss. Such characteristics pose challenges, on one hand in terms of software running on smart objects, and on the other hand in terms of network protocols which smart objects use to communicate. New operating systems, application programming interfaces, frameworks, and middleware have to be designed with consideration of such constraints. In consequence, novel validation methods and experimental tools are needed to study smart object networks in vivo, new software platforms are needed to efficiently operate smart objects, and innovative networking paradigms and protocols are required to interconnect smart objects.

An analytical approach to opportunistic transmission under Rayleigh fading channels

In cognitive radio sensor networks, the routing methods including multiple relays have been extensively studied to achieve higher throughput and lower end-to-end delay. As one of innovative approaches, the opportunistic routing scheme was proposed. In this paper, the effectiveness of the opportunistic transmission in terms of reliability and delay of transmission is verified with an analytical way. For the analysis, we establish the probabilistic model with respect to distance and the number of relay nodes under the Rayleigh fading channels including path loss effects. Under this model, we develop a generic Markov chain model to obtain the analytical results and verify the effectiveness of the statistical analysis. The results show that an opportunistic transmission approach is better than traditional multihop transmissions in terms of successful data delivery with fewer transmissions. Consequently, it can provide an energy efficient transmission mechanism for cognitive radio sensor networks.

Super-allocation and Cluster-based Cooperative Spectrum Sensing in Cognitive Radio Networks

An allocation of sensing and reporting times is proposed to improve the sensing performance by scheduling them in an efficient way for cognitive radio networks with cluster-based cooperative spectrum sensing. In the conventional cooperative sensing scheme, all secondary users (SUs) detect the primary user (PU) signal to check the availability of the spectrum during a fixed sensing time slot. The sensing results from the SUs are reported to cluster heads (CHs) during the reporting time slots of the SUs and the CHs forward them to a fusion center (FC) during the reporting time slots of the CHs through the common control channels for the global decision, respectively. However, the delivery of the local decision from SUs and CHs to a CH and FC requires a time which does not contribute to the performance of spectrum sensing and system throughput. In this paper, a super-allocation technique, which merges reporting time slots of SUs and CHs to sensing time slots of SUs by re-scheduling the reporting time slots, has been proposed to sense the spectrum more accurately. In this regard, SUs in each cluster can obtain a longer sensing duration depending on their reporting order and their clusters except for the first SU belonged to the first cluster. The proposed scheme, therefore, can achieve better sensing performance under -28 dB to -10 dB environments and will thus reduce reporting overhead.

Multiple Access Control for Cognitive Radio-Based IEEE 802.11ah Networks

The proliferation of Internet-of-Things (IoT) technology and its reliance on the license-free Industrial, Scientific, and Medical (ISM) bands have rendered radio spectrum scarce. The IoT can nevertheless obtain great advantage from Cognitive Radio (CR) technology for efficient use of a spectrum, to be implemented in IEEE 802.11af-based primary networks. However, such networks require a geolocation database and a centralized architecture to communicate white space information on channels. On the other hand, in spectrum sensing, CR presents various challenges such as the Hidden Primary Terminal (HPT) problem. To this end, we focus on the most recently released standard, i.e., IEEE 802.11ah, in which IoT stations can first be classified into multiple groups to reduce collisions and then they can periodically access the channel. Therein, both services are similarly supported by a centralized server that requires signaling overhead to control the groups of stations. In addition, more regroupings are required over time due to the frequent variations in the number of participating stations, which leads to more overhead. In this paper, we propose a new Multiple Access Control (MAC) protocol for CR-based IEEE 802.11ah systems, called Restricted Access with Collision and Interference Resolution (RACIR). We introduce a decentralized group split algorithm that distributes the participating stations into multiple groups based on a probabilistic estimation in order to resolve collisions. Furthermore, we propose a decentralized channel access procedure that avoids the HPT problem and resolves interference with the incumbent receiver. We analyze the performance of our proposed MAC protocol in terms of normalized throughput, packet delay and energy consumption with the Markov model and analytic expressions. The results are quite promising, which makes the RACIR protocol a strong candidate for the CR-based IoT environment.

Secure communication with beamforming and jamming in time-varying channels

For secured transmission over wireless channels, a beamforming technique of information and jamming signals based on channel state information is considered. By beamforming and splitting the transmission power for both sending information to the target receiver and interfering the eavesdroppers, the secured communication can be achieved. Because the beamforming vectors for information and jamming signals are calculated with channel information of the target receiver, the channel variation can cause the loss of the expected secrecy rate. In this paper, this rate loss is analyzed in high signal to noise ratio (SNR) region. It is verified that the analyzed upper bound behaves similarly the exact one with respect to both SNR and mobile speed with a constant gap.