Kai-Ten Feng

LMA: Location- and Mobility-Aware Medium-Access Control Protocols for Vehicular Ad Hoc Networks Using Directional Antennas

In recent years, the incorporation of the directional antennas within mobile devices has been studied in many areas. The usage of directional antennas can greatly reduce the radio interference, which results in improved utilization of the wireless medium. It becomes practical to exploit the directional antennas in the medium-access control (MAC) protocol design. In this paper, a location- and mobility-aware (LMA) MAC protocol is developed for vehicular ad hoc networks (VANETs). The predictive location and mobility of the vehicles are adopted to provide robust communication links while using the directional beams. The deafness problem is also alleviated using the directional-listen mechanism in the proposed algorithm. Moreover, the exploitation of the directional beacons within the scheme can enhance the reliability of the communication linkages, even when the moving directions and speeds of the vehicles have been changed. Under dynamic moving scenarios, both the spatial reuse and the routing efficiency are preserved using the proposed LMA MAC scheme. The performance of the proposed algorithm is evaluated and compared with other existing MAC protocols in simulations.

A queueing-theoretical framework for QoS-enhanced spectrum management in cognitive radio networks

This article outlines the fundamental modeling issues of opportunistic spectrum access in cognitive radio networks. In particular, we identify the effects of connection-based channel usage on the QoS performance of spectrum management techniques. During the transmission period of a secondary users connection, the phenomenon of multiple spectrum handoffs due to interruptions of primary users arises quite often. In addition to multiple interruptions, the connection-based channel usage behaviors are also affected by spectrum sensing time, switching between different channels, generally distributed service time, and channel contention between multiple secondary users. An analytical framework based on the preemptive resumption priority M/G/1 queueing theory is introduced to characterize the effects of the above factors simultaneously. The proposed generalized analytical framework can incorporate various system parameters into the design of very broad spectrum management techniques, including spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. The applications of this analytical framework on spectrum decision as well as spectrum mobility are discussed, and some open issues using this framework are suggested in this article.

Velocity-Assisted Predictive Mobility and Location-Aware Routing Protocols for Mobile Ad Hoc Networks

In recent years, many location-aware routing protocols have been proposed for mobile ad hoc networks. The efficiency of the routing protocols can be improved by considering the location information of the mobile nodes (MNs). However, the mobility characteristics of the MNs have not been taken into account in most of the related work. In this paper, the proposed velocity-aided routing (VAR) algorithm determines its packet forwarding scheme based on the relative velocity between the intended forwarding node and the destination node. The routing performance can further be improved by the proposed predictive mobility and location-aware routing (PMLAR) algorithm, which incorporates the predictive moving behaviors of MNs in protocol design. The region for packet forwarding is determined by predicting the future trajectory of the destination node. The routing performance can be effectively enhanced by adopting both the proactive maintenance and the VAR mechanisms within the proposed PMLAR scheme. Simulation results show that the PMLAR protocol associated with its derivative schemes outperforms other routing protocols under different network topologies.

Hybrid location estimation and tracking system for mobile devices

Mobile location estimation has attracted lots of attention in recent years. The location algorithms for the mobile devices can generally be categorized into the network-based and the satellite-based systems. Both types of system have their advantages and limitations under different environments (i.e. urban, suburban, or rural area). In order to provide adaptation to various scenarios for location estimation, a hybrid location scheme, which combines both the satellite-based and the network-based signals, is proposed in this paper. The proposed scheme utilizes the two-step least square method for estimating the three-dimensional position (i.e. the longitude, latitude, and altitude) of the mobile devices. The Kalman filtering technique is exploited to both eliminate the measurement noises and to track the trajectories of the mobile devices. A fusion algorithm is employed to obtain the final location estimation from both the satellite-based and the network-based systems. Numerical results demonstrate that the proposed hybrid location scheme provides accurate location estimation by adapting itself under different environments

Greedy Routing with Anti-Void Traversal for Wireless Sensor Networks

The unreachability problem (i.e., the so-called void problem) that exists in the greedy routing algorithms has been studied for the wireless sensor networks. Some of the current research work cannot fully resolve the void problem, while there exist other schemes that can guarantee the delivery of packets with the excessive consumption of control overheads. In this paper, a greedy anti-void routing (GAR) protocol is proposed to solve the void problem with increased routing efficiency by exploiting the boundary finding technique for the unit disk graph (UDG). The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node under the UDG network. The boundary map (BM) and the indirect map searching (IMS) scheme are proposed as efficient algorithms for the realization of the RUT technique. Moreover, the hop count reduction (HCR) scheme is utilized as a short-cutting technique to reduce the routing hops by listening to the neighbors traffic, while the intersection navigation (IN) mechanism is proposed to obtain the best rolling direction for boundary traversal with the adoption of shortest path criterion. In order to maintain the network requirement of the proposed RUT scheme under the non-UDG networks, the partial UDG construction (PUC) mechanism is proposed to transform the non-UDG into UDG setting for a portion of nodes that facilitate boundary traversal. These three schemes are incorporated within the GAR protocol to further enhance the routing performance with reduced communication overhead. The proofs of correctness for the GAR scheme are also given in this paper. Comparing with the existing localized routing algorithms, the simulation results show that the proposed GAR-based protocols can provide better routing efficiency.

An efficient geometry-constrained location estimation algorithm for NLOS environments

Mobile location estimation has attracted a significant amount of attention in recent years. The network-based location estimation schemes have been widely adopted based on the radio signals between the mobile device and the base stations. The two-step least square (LS) method has been studied in related research to provide efficient location estimation of the mobile devices. However, the algorithm results in inaccurate location estimation with the existence of the non-line-of-sight (NLOS) errors. A geometry-constrained location estimation (GLE) algorithm is proposed in this paper with the consideration of different geometric layouts between the mobile device and its associated base stations. In order to enhance the precision of the location estimate, the GLE scheme is designed to incorporate the geometric constraints within the formulation of the two-step LS method. The proposed GLE scheme can both preserve the computational efficiency from the two-step LS algorithm and obtain precise location estimation under NLOS environments. Numerical results demonstrate that the proposed GLE algorithm can achieve better accuracy, comparing with other existing schemes, in mobile location estimation.

Green transmission technologies for balancing the energy efficiency and spectrum efficiency trade-off

As 4G wireless networks are vastly and rapidly deployed worldwide, 5G with its advanced vision of all connected world and zero distance communications is already at the corner. Along with the super quality of user experience brought by these new networks, the shockingly increasing energy consumption of wireless networks has become a worrying economic issue for operators and a big challenge for sustainable development. Green Transmission Technologies (GTT) is a project focusing on the energy-efficient design of physical-layer transmission technologies and MAC-layer radio resource management in wireless networks. In particular, fundamental tradeoffs between spectrum efficiency and energy efficiency have been identified and explored for energy-efficiency-oriented design and optimization. In this article, four selected GTT solutions are introduced, focusing on how they utilize the degrees of freedom in different resource domains, as well as how they balance the tradeoff between energy and spectrum efficiency. On top of the elaboration of separated solutions, the GTT toolbox is introduced as a systematic tool and unified simulation platform to integrate the proposed GTT solutions together.

A POMDP-Based Spectrum Handoff Protocol for Partially Observable Cognitive Radio Networks

Recent studies have been conducted to indicate the ineffective usage of licensed bands due to the static spectrum allocation. In order to improve the spectrum utilization, the cognitive radio (CR) is therefore suggested to dynamically exploit the opportunistic primary frequency spectrums. How to provide efficient spectrum handoff has been considered a crucial issue in the CR networks. Existing spectrum handoff algorithms assume that all the channels within the network can be correctly sensed by the CR users in order to perform appropriate spectrum hand-off process. However, this assumption is considered impracticable in realistic circumstances primarily due to the excessive time required for the CR user to sense the entire spectrum space. In this paper, the partially observable Markov decision process (POMDP) is exploited to estimate the network information by partially sensing the frequency spectrums. A POMDP-based spectrum handoff (POSH) scheme is proposed to determine the optimal target channel for spectrum handoff according to the partially observable channel state information. By adopting the policy resulted from the POSH algorithm for target channel selection, minimal waiting time at each occurrence of spectrum handoff can be achieved. Numerical results illustrate that the proposed POSH scheme can effectively minimize the required waiting time for spectrum handoff in the CR networks.

Wireless Location Tracking Algorithms for Environments with Insufficient Signal Sources

Location estimation and tracking for the mobile devices have attracted a significant amount of attention in recent years. The network-based location estimation schemes have been widely adopted based on the radio signals between the mobile device and the base stations. The location estimators associated with the Kalman filtering techniques are exploited to both acquire location estimation and trajectory tracking for the mobile devices. However, most of the existing schemes become inapplicable for location tracking due to the deficiency of signal sources. In this paper, two predictive location tracking algorithms are proposed to alleviate this problem. The predictive location tracking (PLT) scheme utilizes the predictive information obtained from the Kalman filter in order to provide the additional signal inputs for the location estimator. Furthermore, the geometric-assisted PLT (GPLT) scheme incorporates the geometric dilution of precision (GDOP) information into the algorithm design. Persistent accuracy for location tracking can be achieved by adopting the proposed GPLT scheme, especially with inadequate signal sources. Numerical results demonstrate that the GPLT algorithm can achieve better precision in comparison with other network-based location tracking schemes.

GALE: An Enhanced Geometry-Assisted Location Estimation Algorithm for NLOS Environments

Mobile location estimation has attracted a significant amount of attention in recent years. The network-based location estimation schemes have been widely adopted based on the radio signals between the mobile device and the base stations. The two-step Least-Squares (LS) method has been studied in related research to provide efficient location estimation of the mobile devices. However, the algorithm results in insufficient accuracy for location estimation with the existence of Non-Line-Of-Sight (NLOS) errors. A Geometry-Assisted Location Estimation (GALE) algorithm is proposed in this paper with the consideration of different geometric layouts between the mobile device and its associated base stations. In order to enhance the precision of the location estimate, the GALE scheme is designed to incorporate the geometric constraints within the formulation of the two-step LS method. The algorithm can be utilized to estimate both the two-dimensional and the three-dimensional positions of a mobile device. The proposed GALE scheme can both preserve the computational efficiency from the two-step LS algorithm and obtain a precise location estimation under NLOS environments. Moreover, the Cramer-Rao Lower Bound (CRLB) for various types of measurement signals is derived to facilitate the performance comparison between different location estimation schemes. Numerical results illustrate that the proposed GALE algorithm can achieve better accuracy compared with other existing network-based location estimation schemes.