We propose a deception mechanism to combat a compromised station in IEEE 802.11 channel hopping systems. A compromised station can follow the hopping channels and continuously attack them, since it recognizes the channel-hopping sequence. The key concept of the deception mechanism is that an access point notifies a new hopping seed but not to the jammer, while a deception station deceives the jammer. Simulations show that the proposed scheme increases network throughput compared to conventional channel hopping schemes when they are under compromised station attacks.

We propose a new resource prediction method for the Demand Assigned Multiple Access (DAMA) scheme in satellite networks. Inaccurate prediction of future traffic causes degradation of QoS and utilization due to the long delay in satellite networks. The Dynamic Leveling Scheme (DLS) use a leveling method to modify its prediction to a discrete one to change the precision of the prediction result. This new scheme has two features: 1) It enhances the probability of successful prediction and 2) it can be applied to any type of existing prediction method. Simulations show enhanced utilization and performance of the satellite link.

We propose an outband sensing-based IEEE 802.11h protocol without a full dynamic frequency selection (DFS) test. This scheme has two features. Firstly, every station performs a cooperative outband sensing, instead of inband sensing during a quiet period. And secondly, as soon as a current channel becomes bad, every station immediately hops to a good channel using the result of outband sensing. Simulation shows the proposed scheme increases network throughput against the legacy IEEE 802.11h.

Wireless Sensor Networks (WSNs) have become a key technology for ubiquitous computing environments. In WSNs, battery recharge or replacement is impossible because sensors are left unattended after deployment. Therefore, WSNs need a networking protocol scheme to increase the life time of sensor nodes. The clustering technique is an efficient approach for reducing energy consumption in wireless sensor networks. In cluster topology, however, there is a problem which causes a large amount of energy consumption of cluster head. In addition, in the sparsely deployed sensor field, mesh topology can be more energy-efficient than cluster topology. In this paper, we propose a Hybrid Cluster Mesh (HCM) scheme, which recognizes the density of neighbor nodes and each node decides its topology itself, and HCM-RO (reorganization) scheme which reorganizes clusters. Simulation results show that the proposed hybrid topology control scheme is more energy-efficient than each topology of cluster or mesh.

In this letter, we propose an interference-aware resource allocation algorithm for the uplink of OFDMA systems. It comprises a macrocell overlaid with short range femtocells. We define the interferences that occur between a macrocell and femtocells and present the resource assignment algorithm to resolve and mitigate the cross-tier interference effect based on the defined interference factors. Simulation results show that the proposed algorithm performs well in a macrocell and femtocells.

In this letter, we propose a fast dynamic slot assignment (F-DSA) protocol to reduce timeslot access delay of a newly arrived node in ad hoc networks. As there is no central coordinator, a newly arrived node needs separate negotiation with all the neighboring nodes for assigning slots to itself. Thus, it may result in network join delay and this becomes an obstacle for nodes to dynamically join and leave networks. In order to deal with this issue better, F-DSA simplifies the slot assignment process. It provides frequent opportunities to assign slots by using mini-slots to share control packets in a short time. Numerical analysis and extensive simulation show that F-DSA can significantly reduce the timeslot access delay compared with other existing slot assignment protocols. In addition, we investigate the effect of the mini-slot overhead on the performance.

In time difference of arrival-based signal source location estimation, geometrical errors are caused by the location of multiple unmanned aerial vehicles (UAV). Herein, we propose a divide-and-conquer algorithm to determine the optimal location for each UAV. Simulations results confirm that multiple UAVs shifted to an optimal position and the location accuracy improved.

Signals transmitted by multiple stations through different multiple subchannels may arrive at a particular station, such as an access point (AP), with different time delays. If the difference in arrival time delays exceeds the cyclic prefix duration, the orthogonality among the subchannels can be broken, which leads to multiple access interference (MAI) among the stations. In this paper, we propose a multichannel slotted Aloha scheme based on an MAI-free group for a simple orthogonal frequency division multiple access (OFDMA) wireless network. Each MAI-free group consists of stations whose signals arrive at the AP within the cyclic prefix duration. The proposed scheme outperforms a conventional scheme using a fast retrial algorithm in terms of throughput due to smaller cyclic prefix duration, lower collision probability, and lower block probability. While the proposed scheme has higher delay overhead in a low arrival rate region, its delay approaches that of the conventional scheme as the arrival rate increases.

An unmanned aerial vehicle (UAV) can be used for wireless communication and localization, among many other things. When terrestrial networks are either damaged or non-existent, and the area is GPS-denied, the UAV can be quickly deployed to provide communication and localization services to ground terminals in a specific target area. In this study, we propose an UAV operation model for unified communication and localization using reinforcement learning (UCL-RL) in a suburban environment which has no cellular communication and GPS connectivity. First, the UAV flies to the target area, moves in a circular fashion with a constant turning radius and sends navigation signals from different positions to the ground terminals. This provides a dynamic environment that includes the turning radius, the navigation signal transmission points, and the height of the unmanned aerial vehicle as well as the location of the ground terminals. The proposed model applies a reinforcement learning algorithm where the UAV continuously interacts with the environment and learns the optimal height that provides the best communication and localization services to the ground terminals. To evaluate the terminal position accuracy, position dilution of precision (PDOP) is measured, whereas the maximum allowable path loss (MAPL) is measured to evaluate the communication service. The simulation result shows that the proposed model improves the localization of the ground terminals while guaranteeing the communication service.

In this letter, we emphasize the performance associated problem of the TCP protocol in the wired-wireless networks. It is shown that the increase of TCP congestion window is strongly influenced by the wireless link. To accelerate the increase of TCP congestion window regardless of wireless link conditions we adopt a fast snoop agent that sends indirect acknowledgement to the sender. Simulation results show that the proposed scheme achieves higher throughput with small data size.

We propose a control-channel-hopping scheme to mitigate scrambling attacks in orthogonal frequency division multiple access (OFDMA) systems. A scrambling attack can be realized by jamming specific frames after monitoring the control channel or by jamming the control channel itself. This letter details a situation in which the control channel is scattered among OFDMA subcarriers. The scattered control channel has a two-dimensional hopping sequence with a mixed order. Simulation results show that our scheme can prevent a jammer from monitoring the control channel and from attacking the channel itself.

When a jamming attack occurs, existing ad hoc routing protocols can experience significant throughput degradation and unnecessary control overhead due to the inclusion of unreliable links into routing paths. In this work, we identify which factors hinder establishment of reliable routing paths by the existing routing protocols in the face of jamming attacks. Our solution is Jamming-Aware Routing (JAR) based on OLSR protocol, which provides explicit route recovery procedures to counteract jamming attack. By establishing a reliable routing path, the proposed scheme achieves significant throughput gains as well as control overhead reduction.

The IEEE 802.15.4 protocol is considered a promising technology for low-cost low-power wireless personal area networks. Researchers have discussed the feasibility of voice communications over IEEE 802.15.4 networks. To this end, the personal area network (PAN) coordinator allocates guaranteed time slots (GTSs) for voice communications in the beacon-enabled mode of IEEE 802.15.4. Although IEEE 802.15.4 is capable of supporting voice communications by GTS allocation, it is impossible to accommodate voice transmission beyond two hops due to the excessive transmission delay. In this paper, we propose a GTS allocation scheme for bidirectional voice traffic in IEEE 802.15.4 multihop networks. The goal of our proposed scheme is to achieve low end-to-end delay and packet drop ratio without a complex allocation algorithm. Thus, the proposed scheme allocates GTSs to devices for successful completion of voice transmission in a superframe duration. The proposed scheme also considers transceiver switching delay. This is relatively large compared to a time slot due to the low-cost and low-gain antenna designs. We analyze and validate the proposed scheme in terms of average end-to-end delay and packet drop ratio. Our scheme has lower end-to-end delay and packet drop ratio than the basic IEEE 802.15.4 GTS allocation scheme.

This paper is concerned with the packet transmission scheduling problem for repeating all-to-all broadcasts in Underwater Sensor Networks (USN) in which there are n nodes in a transmission range. All-to-all communication is one of the most dense communication patterns. It is assumed that each node has the same size packet. Unlike the terrestrial scenarios, the propagation time in underwater communications is not negligible. We define all-to-all broadcast as the one where every node transmits packets to all the other nodes in the network except itself. So, there are in total n(n - 1) packets to be transmitted for an all-to-all broadcast. The optimal transmission scheduling is to schedule in a way that all packets can be transmitted within the minimum time. In this paper, we propose an efficient packet transmission scheduling algorithm for underwater acoustic communications using the property of long propagation delay.