Ming-Tuo Zhou

A method to deliver AODV routing messages using WiMAX mesh MAC control messages in maritime wireless networks

We envisage extending the coverage of existing terrestrial wireless broadband wireless networks to the sea so that cost-efficient wireless access is available to the ships near the shore. The coverage extension is achieved through a multi-hop WiMAX wireless mesh networks where ships, maritime beacons and buoys are the nodes. In such a multi-hop network, routing protocol plays an important role in ensuring reliable end-to-end packet delivery. Compared to AOMDV and OLSR, AODV has been found as a more suitable routing protocol in terms of average packet delay, packet delivery ratio, and implementation complexity. AODV requires route request messages being broadcast during route discovery process. However, WiMAX mesh MAC protocol is not efficient in supporting broadcast of data packets that carry the route request. This inefficiency is due to need of performing the three-way-handshaking process in reserving a data slot before transmitting each route request. As a result, AODV suffers from large initial packet delay and average packet delay. In view of the problem, this paper proposes a method to efficiently deliver the AODV routing messages by piggybacking them on the existing WiMAX mesh MAC control messages. As such, the three-way-handshaking is avoided leading to a faster transmission of routing messages. Simulation results confirm that the proposed scheme can lead to an improvement in initial packet delay, weighted average delay, and packet delivery ratio.

An analysis model of DoA in maritime environment for ship-to-ship/shore wireless communications

Wireless mesh ad hoc network is envisaged by us recently for maritime communications because of the lack of high-speed and low-cost communication systems in sea. A maritime simulator is developed for the purpose to simulate the sea environment and evaluate designs and protocols used in maritime mesh networks. In maritime simulator, modeling direction of arrival (DoA) of radio signal is critical since it determines antenna gain and received radio signal power at a receiver. In this paper, we propose an analysis model of DoA in maritime environment based on modeling sea wave movement as Trochoid wave and analyzing orientations of ships in various sea states. Simulations have been carried out and the results match very well with measured. The model can be used in simulation of wireless ship-to-ship/shore communications, and in finding maximum loss of antenna gain due to sea wave movement, which needs being considered in link budget when do network planning.

A cluster-free MAC protocol for cognitive IEEE 802.16 Mesh networks

Recently, various wireless networks are emerging and it leads to spectrum congestions. Cognitive radio, which allows users of the emerging wireless networks to opportunistically utilize the unused bands of the existing primary systems, can alleviate this problem. As one of the emerging wireless networks, 802.16 networks are suggested to explore TV “White Space” and then it is necessary to study cognitive operations of this network. In this paper, we propose enhanced frame structure and new channel accessing algorithms to enable cognitive operation of the WiMAX Mesh networks. With the novel algorithms for dynamically accessing the frequency channels for the control messages transmissions, no extra common control channels and operations of mesh clusters are needed, thus the spectrum resource can be saved and the network operation becomes simpler. The performance of the algorithms and the MAC protocol are analyzed theoretically and evaluated numerically. Results show that our algorithms can achieve, e.g., 3 times gain, in getting control messages received by neighbors, when compared to the scheme of mesh clusters. It also shows that with the parameter values presented, the normalized saturation throughput can be, e.g., as high as 75%.

Multi-channel WiMAX Mesh networking and its practice in sea

WiMAX Mesh networking is of many advantages for intelligent transportation systems (ITS) applications. In long-hop-distance ITS networks, multi-channel transmission may alleviate problem of insufficiency of bandwidth when a network uses single frequency channel. This paper presents algorithm of multi-channel bandwidth allocation in WiMAX mesh networks. Simulation is carried out with a maritime simulator, by which performance of multi-channel WiMAX mesh transmission is evaluated for high-speed ship-to-ship/shore communications in sea. Simulated results show that with multi-channel operations, in terms of packet delivery ratio and average end-to-end delay, the network performance is improved, in both sea state 3.0 and 6.0. In more rough sea and with more heavy traffic load, the improvement is observed clearer.

Energy/bandwidth-Saving Cooperative Spectrum Sensing for Two-hopWRAN

A two-hop wireless regional area network (WRAN) providing monitoring services using Television White Space (TVWS), i.e., IEEE p802.22b, is now under development. A great number of subscriber customer-premises equipments (S-CPEs) may be connected to a base station with relaying of a relay CPE (R-CPE) in p802.22b. Cost-effective and power-saving S-CPEs are needed due to the its large volume and the possibility of absence of main power supply. This paper proposes cooperative spectrum sensing (CSS) employing energy detection to IEEE p802.22b. With the proposal, a number of S-CPEs are instructed to cooperatively sense TV channels and a R-CPE serves as fusion center. We further propose that when an S-CPE without upstream detects the presence of primary users it does not report to the R-CPE if it detects a signal-to-noise ratio (SNR) less than a pre-defined threshold, for purpose of saving energy and bandwidth consumption. Numerical results show that with the proposed energy/bandwidth-saving scheme the fused error probability changes very little while the fused miss-detection probability and false alarm probability are lower than 10% that is required by 802.22. With 10 S-CPEs participating CSS, it is possible to save more than 40% of the energy/bandwidth in a Rayleigh fading channel.

Performance and Noise Analysis of VCSEL ROF Using Spherical-ended Multimode Fiber Coupling

A low cost radio-over-fiber (ROF) transmitter has been built based on extremely low cost 850 nm vertical-cavity surface-emitting laser (VCSEL) diode using spherical-ended multimode fiber (MMF) coupling technique. This technique has been shown to deliver excellent light launching characteristics for VCSEL lasers in short haul ROF applications. Transmission distance of more than 600 m has been demonstrated experimentally with consistent performance highly desired for transmitting WLAN RF signals in both 2.45 and 5.25 GHz in a directly modulated MMF VCSEL short haul ROF link. Various coupling methods and the bonding process of mating the VCSEL to MM fiber have been investigated to optimize the optical power coupling for cost reduction and low complexity. The results show that the transmitter coupled by spherical-ended MMF provides 30% more optical coupling efficiency and enhanced noise figure performance than the lens-less flat cleaved alternative