Sang-Jo Yoo

Distributed Coordinated Spectrum Sharing MAC Protocol for Cognitive Radio

Recently, the CR (cognitive radio) technology is gathering more and more attention because it has the capacity to deal with the scarce of the precious spectrum resource. Within the domain of CR technology, channel management of CR is of utmost importance due to its key role in the performance enhancement of the transmission and the minimum interference to the primary users as well. An 802.11 WLAN based ad-hoc protocol using the cognitive radio has been proposed in this paper. It provides the detection and protection for incumbent systems around the communication pair by separating the spectrum into the data channels and common control channel. By adding the available channel list into the RTS and CTS, the communication pair can know which data sub channels are available (i.e., no incumbent signal). We proposed an ENNI (exchanging of neighbor nodes information) mechanism to deal with the hidden incumbent device problem. The simulation results show that by using our protocol the hidden incumbent device problem (HIDP) can be solved successfully.

Fast Recovery from Hidden Node Collision for IEEE 802.15.4 LR-WPANs

The IEEE 802.15.4 specification does not include RTS/CTS mechanism to avoid the hidden/exposed node problem, for the consideration of constructing the low energy consumption networks. However, based on the modified CSMA/CA algorithm in LR-WPANs, the hidden node collisions will repeat up to aMaxframeRetries (default value is 3) times until the collided packets are discarded with a high probability. Therefore, a fast recovery mechanism is proposed in this paper to achieve the fast self-healing with negligible control overheads when the networks suffer the hidden node collisions. When the coordinator recognizes the hidden node collision occurs, it will issue a group polling ACK (PACK) to indicate the priority of the collided packets retransmission. Simulation results demonstrate that the proposed PACK mechanism is able to improve the network throughput and avoid the continuous hidden node collisions efficiently.

Undetectable Primary User Transmissions in Cognitive Radio Networks

Various metrics related to the protection of primary user in cognitive radio networks, such as the detection probability and collision ratio, have been considered in recent years. In this letter, as a new metric to be used for a constraint to protect the primary user, the concept of undetectable primary user transmission (UPT) is introduced. UPT occurs when a primary user transmission only occurs between two consecutive sensing epochs. The relationship between the frequency of UPT and the sensing interval is derived and evaluated for various conditions.

Time-constrained detection probability and sensing parameter optimization in cognitive radio networks

Sensing-throughput tradeoff has widely been investigated in cognitive radio networks. Detection probability and interference ratio are usually considered the main constraints to the protection of primary signals. However, the detection probability defined during a sensing duration does not fully capture the goal of primary protection because two important factors are not taken into consideration. Neither the detection latency during the detection of the primary signal nor the unavoidable misdetection of the primary signal due to its ability to only occupy the channel between two consecutive sensing durations are considered. Motivated by these problems, we propose a new detection probability called the time-constrained detection probability (TDP) and investigate the effect of the sensing interval on the TDP. This sensing interval consists of a sensing duration and a transmission duration. Moreover, both an optimal sensing duration and an optimal sensing interval are proposed, which not only satisfy both the TDP and the interference ratio constraints for primary protection, but also maximize the achievable throughput for secondary users. Numerical analyses show the relationship between the sensing interval and the TDP and the optimal sensing parameters consisting of the optimal sensing duration and the optimal sensing interval.

QoS-Aware Channel Sensing Scheduling in Cognitive Radio Networks

Cognitive radio (CR) has been considered as the most prominent technique for flexible spectrum utilization. Protecting primary users (PUs) from any harmful interference is the most important issue in CR networks. Secondary users (SUs) periodically sense the channels in order to detect the PU’s appearance. Without a proper sensing schedule, however, sensing operation may degrade the quality of service (QoS) of SUs. In this paper, we propose the channel sensing scheduling that protects PUs by sensing the channels with a proper sensing interval as well as maintains the QoS of SUs as possible. Channel sensing intervals required for protecting PUs and sensing cycle required for guaranteeing QoS of SUs are numerically formulated. We show that our proposal outperforms the consecutive channel sensing method in terms of delay and packet loss.

Fast group scanning scheme with dynamic neighbor base station list in IEEE 802.16e networks

For handover in IEEE 802.16e, scanning procedure by mobile station is defined to find the most reliable target base station. However, the conventional scanning schemes cannot guarantee a fast target base station decision because some of the neighbor base stations of the scanning list provided by a serving base station are not actually attachable by the mobile stations. In this paper, we propose a new group-based scanning scheme, in which grouping of mobile stations by signal strength reduces the number of channels to scan so that fast scanning is achieved. To enhance the performance of the group-based scanning scheme, a dynamic neighbor base station list (DNL) management method is proposed. Simulation results show that our proposed scanning scheme is more efficient than the conventional one in terms of scanning time and accuracy of scanning channel list.

Type-2 fuzzy ontology–aided recommendation systems for IoT–based healthcare

Abstract The number of people with a chronic disease is rapidly increasing, giving the healthcare industry more challenging problems. To date, there exist several ontology and IoT-based healthcare systems to intelligently supervise the chronic patients for long-term care. The central purposes of these systems are to reduce the volume of manual work in recommendation systems. However, due to the increase of risk and uncertain factors of the diabetes patients, these healthcare systems cannot be utilized to extract precise physiological information about patient. Further, the existing ontology-based approaches cannot extract optimal membership value of risk factors; thus, it provides poor results. In this regards, this paper presents a type-2 fuzzy ontology–aided recommendation systems for IoT-based healthcare to efficiently monitor the patients body while recommending diets with specific foods and drugs. The proposed system extracts the values of patient risk factors, determines the patients health condition via wearable sensors, and then recommends diabetes-specific prescriptions for a smart medicine box and food for a smart refrigerator. The combination of type-2 Fuzzy Logic (T2FL) and the fuzzy ontology significantly increases the prediction accuracy of a patients condition and the precision rate for drug and food recommendations. Information about the patients disease history, foods consumed, and drugs prescribed is designed in the ontology to deliver decision-making knowledge using Protege Web Ontology Language (OWL)-2 tools. Semantic Web Rule Language (SWRL) rules and fuzzy logic are employed to automate the recommendation process. Moreover, Description Logic (DL) and Simple Protocol and RDF Query Language (SPARQL) queries are used to evaluate the ontology. The experimental results show that the proposed system is efficient for patient risk factors extraction and diabetes prescriptions.

Iterative Wireless Sensor Network Positioning Based on Time Synchronization

Recently, the sensor network that combines the wireless data transmission, data sinking, and information processing capacities, is a gathering more and more attentions. With the development of research on wireless sensor networks, localization – the determination of the absolute or relative position of sensor nodes is becoming an essential research issue. In this paper, we propose an iterative positioning algorithm with time synchronization (IPATS) which can enhance the positioning accuracy in wireless sensor networks. In the IPATS algorithm, we propose a new iterative distance measurement method that adapts timing synchronization information and previous ranging error. To adjust the clock skew and to compensate random delay on the signal propagation that is the main reasons of inaccurate timing synchronization and position estimation, we define a calibration parameter. Iterative corrections of positioning errors and clock differences enhance the positioning accuracy. Simulation results show that the positioning accuracy of the proposed algorithm is superior to the previous TDOA and OCLA algorithm.

Robust and Reliable Predictive Routing Strategy for Flying Ad-Hoc Networks

Ever-increasing demands for portable and flexible communications have led to rapid growth in networking between unmanned aerial vehicles often referred to as flying ad-hoc networks (FANETs). Existing mobile ad hoc routing protocols are not suitable for FANETs due to high-speed mobility, environmental conditions, and terrain structures. In order to overcome such obstacles, we propose a combined omnidirectional and directional transmission scheme, together with dynamic angle adjustment. Our proposed scheme features hybrid use of unicasting and geocasting routing using location and trajectory information. The prediction of intermediate node location using 3-D estimation and directional transmission toward the predicted location, enabling a longer transmission range, allows keeping track of a changing topology, which ensures the robustness of our protocol. In addition, the reduction in path re-establishment and service disruption time to increase the path lifetime and successful packet transmissions ensures the reliability of our proposed strategy. Simulation results verify that our proposed scheme could significantly increase the performance of flying ad hoc networks.

Enhanced Rate Division Multiple Access for Electromagnetic Nanonetworks

An electromagnetic (EM) nanonetowork is considered to be a key technology in realizing Internet of Nano-Things. However, the traditional communication schemes cannot be directly applied at nanoscale level due to extreme limitation in energy, memory, computational resources, and hardware designs. Due to unique properties of pulse-based communication in nanonetoworks, rate division time-spread ON-OFF keying is considered to be appropriate modulation and channel access mechanism. As such, a symbol in EM nanonetwork would be is represented by either a single pulse or absence of pulse. In rate division, the symbol streams transmitted by multiple users are interleaved by assigning different time periods between two symbols of each user referred as symbol interval. The symbol interval is required to be derived from prime or coprime numbers to minimize the number of collisions. In this paper, we propose a scheme to derive the symbol interval by generating unique prime number at each user node using Prime Mod algorithm. Our scheme do not require coordination between transmitter and receiver and it can be easily implemented in both infrastructure based and ad hoc nanonetworks. Moreover, we show the statistical properties of the computed prime numbers, bounds on prime numbers that can be used, collision probability, and comparison of computational complexity with conventional schemes.