Jae-Kark Choi

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.

Optimal Sensing Interval Considering Per-primary Transmission Protection in Cognitive Radio Networks

Sufficient protection of primary user is a challenging issue in cognitive radio networks. The probability of detection and the interference ratio (probability of collision) have been considered as the main constraints for primary protection in the literature. Based on the sensing parameters designed to comply with these constraints, secondary users are often considered to be able to use licensed bands without giving harmful interference to primary users. However, satisfying these constraints might not guarantee that each primary transmission (i.e., each busy period) is sufficiently protected. Obviously, if a large fraction of a busy period is interfered, the busy period may be subject to the useless transmission potentially degrading the quality of service of primary users. We suggest that the busy period impaired more than a certain ratio of so-called required per-transmission interference ratio (PTIR) is subject to the primary transmission failure (PTF), which has not been considered in the literature. As the first attempt, with the assumption of perfect sensing, the effect of sensing interval on the PTIR and PTF is investigated. The probability of PTF is derived as a function of sensing interval given the required PTIR. Then, given the required PTIR and probability of PTF, the optimal sensing interval that maximizes the throughput for secondary users is derived. Performance evaluation shows that primary users can be more protected with the optimal sensing interval obtained by using the proposed constraint.

Iterative path-loss exponent estimation-based positioning scheme in WSNs

In wireless sensor networks, the positioning scheme using the received signal strength (RSS) has been widely considered due to its simplicity. Appropriate estimation of path-loss exponent (PLE) between a sensor node and an anchor node plays a key role in reducing position error in this RSS-based positioning. In the conventional researches, a sensor node directly uses the PLEs given by its neighboring anchor nodes, e.g., its nearest anchor node, to calculate its position. However, the PLE between a sensor node and an anchor node is usually different from those given by the anchor nodes, and accordingly results in the distance error in sensor nodes positioning. In this paper, we propose the method how a sensor node estimates PLEs from the anchor nodes of interest by itself and calculates its position based on these self-estimated PLEs. In the proposed scheme, a sensor node recalculates PLEs depending on the estimated distances between itself and anchor nodes, and reproduces its position based on the recalculated PLEs. Through simulations, we show that our proposed positioning scheme outperforms the traditional scheme in terms of position error.

Group Node Contention Algorithm for Avoiding Continuous Collisions in LR-WPAN

In this paper, we proposed a group node contention algorithm for avoiding continuous collisions in LR-WPAN. The purpose of IEEE 802.15.4 is to achieve low speed, low cost and low power consumption. Recently, as applications of LR-WPAN have been extended, there is a high probability of collision as well. There are two types of collisions in LR-WPAN: i) contended collision: nodes are transmitting data concurrently at CCA starting point, ii) hidden node collision: collisions happened due to the hidden node problem. While the CSMA/CA mechanism can solve the contended collision, the hidden node collision can not be solved. Moreover, if the collision continuously occurs due to hidden node collision, network performance could be extremely decreased. Nowadays, a few papers have been proposed to address hidden node collision. One of the solutions is making use of PACK in WPAN which formed groups, but this algorithm wastes channel resource if continuous collisions frequently occur. In this paper, we assume that PAN has already formed groups, and by using pulse signal, coordinator allocates channel and orders, and then, nodes in the allocated group can compete with each other. Hence, contention nodes can be decreased significantly, channel wastage caused by collision can be reduced, and data transmission rate can be improved. On the whole, this algorithm can protect the network from disruption caused by frequent collisions and simulation result shows that the performance can be improved by using the algorithm.

Group scanning scheme for fast target channel decision in seamless handover of wireless networks

In wireless networks, when a mobile roaming station decides to initiate a handover, it should scan multiple channels operated by neighboring base stations (BSs) (or access points (APs)) in order to find an appropriate target base station before the actual handover. In some wireless networks, the active base station is able to provide a list of channels operated by neighboring base stations. However, some of these candidate channels may not be accessible to the mobile station (MS); nonetheless, the MS scans the candidate channels consecutively. For this reason, it may take a relatively long time for the MS to select an adequate target base station channel. This process can degrade the quality of service (QoS) during handovers. To shorten the scanning latency efficiently, in this paper we propose a cooperative channel scanning method whereby groups of MSs scan candidate channels using a dispersive schedule. They then share the scanning results amongst themselves, which results in a fast handover channel decision. To apply the proposed method to a real network environment, we present a group scanning architecture and detailed application scenarios appropriate for IEEE 802.16e worldwide interoperability for microwave access (WiMAX) networks. Numerical analyses and simulation results show that our proposed method achieves a shorter target channel scanning latency. Our method is thus more efficient in terms of scanning time and channel selection accuracy. Copyright

The Coexistence Solution using Transmission Schedule and User`s Position Information in Cognitive Radio Networks

In cognitive radio networks, a secondary user opportunistically accesses an empty channel based on periodic sensing results for avoiding possible interference to the primary users. However, local sensing does not guarantee the full protection of the primary users because hidden primary receivers may exist within the interference range of the secondary transmitter. To protect primary systems and simultaneously to maximize utilization of the secondary users, we need to derive carefully designed coexistence solutions for various network scenarios. In this paper, we propose coexistence conditions without any harmful interference in accordance with the uplink/downlink schedule and user position. We have classified the coexistence conditions into four different scenario cases depending on the provided information to the secondary network basestations. Computer simulation results demonstrated that the proposed method can be applied to the real cognitive radio system to improve the communication probability of CR devices.

Zone-Based Sharable Sensing Scheme in Decentralized Cognitive Radio Networks

In cognitive radio networks, secondary users conduct local sensing to use underutilized spectrum bands. However, every secondary user’s local sensing usually gives rise to much sensing overhead, and it requires the proper quiet period. Moreover, a secondary user should keep the quiet periods when the secondary users within its interference range perform spectrum sensing. As a result, both the local sensing overhead and quiet periods may reduce the channel utilization of a secondary user. To cope with these problems, in this paper, we propose a zone-based sharable sensing scheme, in which multiple secondary users alternate in local sensing and share the sensing results with others. We defined a certain area, so-called sensing zone, in which the sensing result by one secondary user is valid for others within the given area. The secondary user in charge of sensing in a sensing zone is elected in a distributed way. Each of the other secondary users can determine its quiet period schedules in accordance with the distance between itself and the elected sensing node. Numerical analyses and computer simulations show that our proposed sensing achieves a significantly reduced sensing overhead as well as an improved channel access opportunity.