Probe vehicle data, also known as floating car data or connected vehicle data, is the data collected from GPS-enabled sensors on vehicles. With the advancement in wireless communications and localization technologies, more and more vehicles are expected to be equipped with such sensors. Existing studies only focus on using small-scale probe vehicle data. In this paper, we are interested in developing a real-time parallel stream processing framework to extract traffic flow KPIs from large-scale probe vehicle data. The developed framework is implemented using Apache Storm on Amazon AWS, and can process one million probe vehicle messages per second. Various design considerations, such as data partition and delay processing are discussed. To evaluate the performance of stream processing framework, simulated probe vehicle data based on the actual traffic flows in Jurong Lake District (JLD) of Singapore, is generated using the microscopic simulation software VISSIM. The JLD data is replicated multiple times to represent the one million population of vehicles in Singapore. GPS errors and communication delays are added to represent the real situations before the data is fed to stream processing module. The estimated KPIs from our stream processing model are validated against the ground truth values under different penetration levels.

This paper proposes a MAC-layer timeslot allocation signaling protocol for IEEE 802.16d mesh networks. The proposed mechanism complements the three-way-handshake signaling described in the specification to achieve fair sharing of timeslots among nodes and flows. In this paper we study the case where timeslots are reserved until cancelled explicitly. This form of reservation is efficient for long sessions of data transmissions such as video streaming or interactive media applications. Since timeslots are exclusively reserved for individual flows, bandwidth starvation can occur if remaining timeslots in the wireless medium around a node are not enough to fulfill new bandwidth requests. It is thus important to design a set of mechanisms to enable sharing of network capacity across all flows fairly. A set of intra- and inter-flow fairness mechanisms is designed to work with an adaptive timeslot allocation scheme. The mechanisms and signaling are designed to efficiently integrate with the three-way-handshake signaling of the IEEE 802.16d mesh specification. Simulation results showed that the proposed schemes can prevent starvation of slot allocation and are able to maintain fairness across flows in the persistence-reservation-based IEEE 802.16d mesh network.

There is a lack of broadband wireless network in sea to meet the increasing needs of modern maritime users and we have envisaged WiMAX mesh networks for high-speed and low-cost ship-to-ship/shore communications. In such a maritime WiMAX mesh network, due to the long transmission distance and the distributed scheduling among two-hop neighbors, a single frequency channel may not be sufficient to provide the required bandwidth. An effective solution is to employ multiple frequency channels, by which the network capacity can be greatly increased. This paper presents operation of multi-channel transmission in maritime WiMAX mesh networks including allocation of minislots and frequency channels. The operation is based on a distributed adaptive time slots allocation and use of availability tables tracing minislots status. In the design, routing information is delivered in control subframe portion, and then the spreading of routing information can be speed up and less overhead in control slots can be used to describe and broadcast the availabilities of the minislots. Simulation results show that with the proposed scheme, by multi-channel transmission, the network performance can be improved in average packet delay and packets delivery ratio.

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.

We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with high speed connection to the Internet. This is achieved by forming a WiMAX-based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a wireless mesh network, routing protocol plays an important role in providing efficient and reliable communications. This paper proposes a routing protocol, called MRPT (MAC-based Routing Protocol for TRITON), that piggybacks routing information on WiMAX mesh MAC control messages. This provides proactiveness and readily available multi-path for traffic from ship to land station. For traffic from land station to ship, the proposed routing protocol uses a bitmap encoding to efficiently inform land station of the constructed routing tree. Simulation results confirm that MRPT outperforms AODV, AOMDV and OLSR in terms of delay and throughput.

We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with cost-efficient high-speed connection to the Internet. This is achieved by forming a WiMAX based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a maritime wireless mesh network, time slot allocation is an important issue as it affects the performance in terms of throughout and delay. This papers proposes a distributed adaptive time slot allocation (DATSA) scheme for WiMAX mesh MAC protocol. DATSA is a distributed scheme that allocates time slots robustly by taking into consideration difference between radio reception range and interference range, and latency in scheduling control messages. DATSA has a method to monitor reception quality of an allocated time slot, in order to detect the effect of topology changes due to ship mobility, etc. Based on the monitoring outcome, the method adaptively changes the time slot allocation if necessary. We have evaluated DATSA through random event simulation using QualNet. The simulation results confirm that DATSA outperforms the original WiMAX mesh MAC protocol that has no adaptive time slot allocation, in terms of throughput, average packet delay, and packet delivery ratio.

Unlike terrestrial networks, the received signal strength in maritime wireless networks are subjected to perturbations due to the sea movement. Surface motions at sea cause variations in antenna heights and orientations of the communicating node (e.g. ships and buoys), thus affecting the received signal strength. In order to minimize such undesirable effects, we carried out a detailed study of the relationship between sea waves and the received signal strength. The effect of antenna gain variations due to tilting of antenna masts were studied by modeling sea waves. The channel path-loss variations were studied using a two-ray path-loss model for the maritime environment. Our analysis showed that the sea wave movements affect both short and longer links. We proposed a simple scheme to avoid the use of unstable links and implemented it on the QualNet network simulator. We carried out IEEE 802.16-based mesh network simulations with sea terrain and path loss models. We observed performance improvements in packet delay and throughput when the stable link selection scheme was used.

This paper details a novel approach of developing a low-cost and high speed maritime ship-to-ship/shore mesh network to complement or replace satellite communications in narrow water channels or traffic lanes close to shorelines. To design the system, we gathered requirements from typical users of the system. We then carried out preliminary studies such as radio channel propagation over sea water, ship movement patterns, ship rocking and its effect on radio transmission and network connectivity to determine the feasibility of using a mesh network for maritime networks. We present the architecture and detail some of our routing and scheduling design considerations that address the unique challenges of the maritime environment and provide us with framework for providing fair and equal opportunity access to users.

We envisage coverage extension of the high bit rate terrestrial communication networks to the ships to reduce the cost in maritime communications. The coverage extension is achieved by forming a mobile wireless mesh network amongst neighboring ships, marine beacons and buoys. The wireless mesh network will be connected to the terrestrial networks across multiple hops via land stations at shore. In such a multi-hop wireless network, routing protocol is important. This paper compares the performance of three existing routing protocols in a maritime communication environment. The three routing protocols are OLSR, AODV and AOMDV. The performance comparison is done via simulation. In the simulation, the wireless mesh network is formed using WiMAX mesh MAC protocol. Also, the random sea surface movement and maritime communication link characteristic are simulated. From the simulation results, we found that OLSR is not as efficient as AODV and AOMDV. Also, compared to AODV, the performance of AOMDV is less affected by sea condition.

Current clustering solutions highly depend on pre-configuration by human administrators. However, these clustering solutions are not suitable for the mobile environment because the clustering configuration can be changed as the movement of the server participated in the cluster. Also, when discussing serviceability with the aspect of the quality of services, pre-configured clusters have some defects. If a process of configuration for clusters can be automated, these problems can be solved. With the self-configuration scheme, servers on a network can make clusters dynamically at any time. Any server participating in the cluster can assign its hot standby backup and can also be a backup for another server so that they can provide better services to clients. However, for making the cluster dynamically, the security issue should be considered. For realizing this scheme, the server agent and service description server, called SDS, are designed and implemented. For the security issue, a simple and lightweight authentication approach using DNS server is designed. For watching the state of the overall system, a web-based monitoring tool is also implemented

Calculations of service availability of a high-availability (HA) cluster are usually based on the assumption of load- independent machine availabilities. In this paper, we study the issues and show how the service availabilities can be calculated under the assumption that machine availabilities are load dependent. We present a Markov chain analysis to derive the steady-state service availabilities of a load-dependent machine availability HA cluster. We show that with a load-dependent machine availability, the attained service availability is now policy dependent. After formulating the problem as a Markov decision process, we proceed to determine the optimal policy to achieve the maximum service availabilities by using the method of policy iteration. Two greedy assignment algorithms are studied: least load and first derivative length (FDL) based, where least load corresponds to some load balancing algorithms. We carry out the analysis and simulations on two cases of load profiles: In the first profile, a single machine has the capacity to host all services in the HA cluster; in the second profile, a single machine does not have enough capacity to host all services. We show that the service availabilities achieved under the first load profile are the same, whereas the service availabilities achieved under the second load profile are different. Since the service availabilities achieved are different in the second load profile, we proceed to investigate how the distribution of service availabilities across the services can be controlled by adjusting the rewards vector.