Further Development of Synchronous Array Method for Ad Hoc Wireless Networks

Based on the bridge health monitoring data, the traffic-load effect model for arch bridge suspender was set up using direct statistical method. Firstly, the Bridge Health Monitoring System (BSHM) set up on the Ebian Dadu River Bridge in Sichuan province to obtain daily traffic-load effect of suspenders was introduced. Secondly, the section distribution of suspender traffic-load effect was researched by statistical approach using monitoring data. Finally, the probability distribution of maximum traffic-load effect during design period was given. The statistical result shows that the section distribution of suspender traffic-load effect follows lognormal distribution and the probability distribution of maximum traffic-load effect during design period follows generalized extreme-value distribution. The traffic-load effect model of suspender was different with the design code given which may underestimates the real load effect level. It's the first time in China to determine the traffic-load effect probability model for arch bridge suspenders based on actual acquired monitoring data using statistical and probabilistic approach.

In wireless mobile ad-hoc networks, data packets have to be relayed hop by hop from a given source node to a destination node. This means that some or all of the mobile nodes must accept to forward information for the benefit of other nodes. It has been shown by F. Nait-Abdesselam, et al., (2003) that this ability of forwarding packets leads to a new unfairness problem in wireless ad-hoc networks, where a node which is forwarding other node's packets gets less bandwidth, for its own use, than a node which is not participating to the routing service. The proposed RAMAC scheme by F. Nait-Abdesselam, et al., (2003), has shown all its effectiveness to cope with this unfairness problem. However, an extra bandwidth is sometimes allowed to the routing node's own traffic comparing to other nonrouting node's own traffics, and the routing node's routed traffic gets much less bandwidth. This is explained by the fact that at the upper layer (for instance the IP layer) does not differentiate between the routing and the own traffics, and that the multiplicative factor used to compute the new contention window is too aggressive. In this paper, an enhanced RAMAC scheme is proposed, by taking into account the differentiation on top of the MAC layer, between the and routed traffics within a routing node, and by smoothing the multiplicative factor used to compute the new contention window. The simulation results obtained showed a good improvement of the original RAMAC scheme, leading to better approximate equal bandwidth share among all the mobile nodes in the wireless ad-hoc network.

Geographic routing protocols establish scalable and robust routes for multi-hop trsdansmission in wireless mobile ad-hoc networks, where accurate location information of the mobile nodes is needed. Aiming to alleviate the influence of location errors, existing works focus on modifying routing protocols through modeling the error sources and mobility prediction. In this paper, we propose a cooperative cluster based geographic routing (CCGR) protocol, which views the cooperative cluster as one virtual relay node, and lessens the impact of location errors through opportunistic receiving and cooperative radio range extension. Opportunistic receiving achieves the link diversity and radio range extension enlarges the transmission distance of one hop. The performance of CCGR is analyzed under scenarios of both static and mobility location errors in terms of reliability index, which is defined to represent the link stability. Further more, numerical results demonstrate that our proposed transmission scheme CCGR outperforms non-cooperative routing schemes in terms of link error probability with location errors.

In many networks there is a necessity to transmit data packets flows, the intensity of which exceeds the throughput of one channel SpaceWire, GigaSpaceWire, SpaceFibre. This flow can be a packet flow from a single source to a single destination, for example, from a camera to a monitor. Also, a packet flow can include packets from different sources to different destinations that goes via two neighboring routers. An example is transmission of packets between two routers located on the boundaries of neighboring regions. The packets, belonging to one flow can have almost same length (transmission of uncompressed video), or quite different length (transmission of compressed video, transmission of packets with different content between two regions). The adaptive routing can be used for transmission of such packet flows. This mechanism includes in SpaceWire standard. A set of alternative output ports (a group of ports) can be determined in routing table for the logical (or regional address). Any output port from this group (if connection for this port is established and port is not occupied by other packet) may be used for transmission of packet with this address. Thus, the summary throughput of all ports belongs to the group can be used for transmission of data packets with this address. However, the possibility of parallel transmission of packets from this flow to different output ports belongs to the group is required for effective utilization of this summary throughput. If the length of packets may be different or if the quantity of input ports for considered flows is not equal to the quantity of output ports in the group, the router should include special mechanisms to ensure efficient parallel transmission of packets to all ports belongs to the group. Adaptive routing for intensive data flows transmission can be implemented not only in SpaceWire/GigaSpaceWire networks, but also in SpaceFibre networks. We consider the specific of its implementation taking into account the features of data link layer (virtual channels with a fairly large buffers, retry mechanism) In this paper we discuss possible implementations of these mechanisms for SpaceWire, GigaSpaceWire and SpaceFibre, estimate achievable bandwidth utilization of port's group, the overhead of the implementation of these mechanisms for packets flows with different characteristics. A side effect of adaptive routing is a possible mismatch of the order in which packets are sent to the network form the source and the order of their receipt by destination. We evaluate the packet's window size that required in the destination node for recovery order of packets and the associated delays. The ports of router belonging to the same group may be connected to one or several different routers (according to the standard). In the first case all packets from the flow will be transmitted via one chain of routers (via one path via network). In the second case, they will be transmitted through the network in different ways. The reordering of packets is possible in both cases. However, in the first case, the mechanisms, that prevent the packets reordering, can be implement in routers. But its implementation can lead to decrease of throughput utilization, to additional hardware costs and to increase of packet's transmission time. In the paper we estimate these overheads for data packets flows with different parameters.

Exploring the effects of directional antennas on the secure connectivity and hop count of secure multi-hop ad-hoc wireless networks

A mobile ad-hoc network comprises of a number of low power wireless nodes. Each of these participating nodes endeavours to pass packets for other nodes based upon a preagreed protocol. The dynamic source routing (DSR) protocol is one of the most commonly used protocols in ad-hoc wireless networks. In a DSR based network, each transmitted data packet contains the complete list of node addresses that the packet has to traverse in order to reach its final destination. Intermediate nodes blindly forward these packets as per the attached list without taking into consideration the behavioural pattern of the subsequent nodes. In this paper, we present a variant of the DSR protocol in which intermediary nodes act as trust gateways. These gateways take into account the contemporary trust levels of the network nodes and thus facilitate in detecting and evading malicious nodes. With the help of extensive simulations, we demonstrate that the proposed DSR protocol augments the performance of the standard DSR protocol by up to 30% in a network where 40% of the nodes act maliciously. The proposed scheme is also independent of cryptographic mechanisms and does not impose any superfluous conditions upon the network establishment and operation phase.

In this work we consider incremental redundancy hybrid ARQ (HARQ) transmission of data packets over independent block-fading channels. In HARQ, the transmitter, upon request (NACK), resends the NACKed packet in the next available block. Conventionally, the original and retransmitted packets occupy one block, each. In our approach, we allow the transmitter to share the resources between the new and the retransmitted packets. To implement such a multi-packet transmission we consider the superposition coding and the timesharing modulation as possible encoding schemes for simultaneous transmission of both packets. Targeting the maximization of the throughput, we cast the problem into the framework of Markov decision process (MDP), where the decisions about the optimal transmission strategy are taken using information about the state of the receiver in the previous transmissions. Numerical examples obtained in a Rayleigh block-fading channel show that proposed transmission strategy provides notable gains over a conventional HARQ.

A wireless ad-hoc network is a self-organized wireless network without fixed or backbone infrastructure. All nodes have routing capability and use peer-to-peer packet transmission or forward packets to other node using multi hop communication. Now days mobile ad-hoc networks are being used for different applications and traffics, so it require quality of service (QoS) support in routing protocol. In this paper, a modified QoS routing protocol using directional antenna has been proposed. High and normal priority can be assigned based on type of traffic. All the nodes in the path used by high priority flow are reserved as high priority flow for that flow and normal priority flow will avoid the paths used by high priority flows. If no disjoint paths are available, there may be two possibilities: Normal priority flows are blocked and other is, normal priority flows are allow using the coupled path with high priority flow. Blocking the normal priority flow, QoS routing protocol improves the performance of high priority flow. This concept may be use in emergency communication. Simulation results show that by assigning the priorities to flows, performance of high priority flows are improved and it will further improved by blocking the normal priority flow.

To provide benefit for design, rating, evaluation and management of signature bridges, site-specific extreme wind speeds, structural temperatures, and traffic load effects of a long-span cable-stayed bridge were estimated using relatively long-term structural health monitoring (SHM) data and compared with respective design values in this paper. The generalized Pareto distribution was adopted and briefly introduced to predict the extreme values in consideration of its advantage in making full use of limited measurement data available. The configuration and characteristics of the 3rd Nanjing Yangtze River Bridge and its SHM system were then presented. The extreme wind speed at the deck level and the four extreme temperatures of the bridge were estimated and compared with the corresponding design values. After a brief introduction to the simulation of traffic load effects, five extreme traffic load effects were finally estimated and compared with the design ones. The comparative results showed that the site-specific extreme wind speed, uniform girder temperature change, and five traffic load effects are all lower than the respective design values. The site-specific extreme vertical and transverse girder temperature differences and the site-specific extreme tower temperature difference were, however, larger than the respective design values.

Performance Analysis of Wireless Adhoc Networks in Flat Fading and Frequency Selective Fading channels

Neighbors of both the transmitter and the receiver must keep quiet in a 802.11 wireless network as it requires bidirectional exchange, i.e., nodes reverse their roles as transmitters and receivers, for transmitting a single DATA frame. To reduce role reversals and to improve spatial reuse, a piggybacked acknowledgment based approach has been proposed to enable concurrent transmissions. Recent findings on physical layer capture show that it is possible to capture a frame of interest in the presence of concurrent interference and that the SINR threshold is dependent on the relative order in which the frame and the interference arrive at the receiver. In this paper, we show that it is possible to exploit capture and increase concurrent transmissions in wireless adhoc networks. We develop a distributed channel access scheme and demonstrate that it offers significant throughput gain particularly at lower data rates.

Collaborative last-hop scheduling strategy for large-scale LEO constellation routing

2008 14th IEEE International Conference on Parallel and Distributed Systems, ICPADS'08, Melbourne, VIC, 8-10 December 2008

This paper introduces a Non-Orthogonal Multiple Access (NOMA) scheme to support concurrent transmission of multiple IEEE 802.15.4 packets. Unlike collision avoidance Multiple Access Control (MAC), concurrent transmission supports Concurrent-MAC (C-MAC) where packet collision is allowed. The communication latency can be reduced by C-MAC because a user can transmit immediately without waiting for the completion of other users' transmission. The big challenge of concurrent transmission is that error free demodulation of multiple collided packets hardly can be achieved due to severe Multiple Access Interference (MAI). To improve the demodulation performance with MAI presented, we introduce an architecture with multiple switching antennas sharing a single analog transceiver to capture spatial character of different users. Successive Interference Cancellation (SIC) algorithm is designed to separate collided packets by utilizing the spatial character. Simulation shows that at least five users can transmit concurrently to the SIC receiver equipped with eight antennas without sacrificing Packet Error Rate.

Eighteen certified flight instructors from the University of Illinois Institute of Aviation participated in an experiment exploring the design of the Cockpit Display of Traffic Information (CDTI) for free flight. Pilots flew a sequence of flight scenarios to compare the effects of traffic load, dimensionality, and a vertical profile orientation on maneuver frequency, safety, and maneuver efficiency. Climbs and descents were found to be more frequent than other maneuvers. Both the rear-view and 3D displays were safer in terms of predicted conflict avoidance than the side-view display. Climbing maneuvers were more safely implemented with the rear-view and 3D displays than with the side-view display. The lateral efficiency of climbing maneuvers was highest with the rear-view display. Altitude maintenance of lateral/vertical maneuvers was highest with the side-view, then the rear-view, and then lowest with the 3D display. Airspeed efficiency of airspeed maneuvers was highest with the rear-view display. These findings suggest that a rear-view coplanar CDTI may be preferable to either a side-view coplanar or 3D display.