326 research outputs found
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Inter Vehicle Distance based connectivity aware routing in vehicular adhoc networks
Connectivity in vehicular traffic environment has witnessed significant attention due to the direct impact on the performance of most of the traffic safety applications of intelligent transport system. Various parameters such as density, speed, direction, link quality and inter vehicle distance (IVD) have been utilized for measuring connectivity. IVD has greater impact on connectivity and controls the impact of other parameters. Usage of real time IVD for measuring connectivity has not received sufficient attention in VANETs. This paper proposes IVD based connectivity aware routing (Ivd-CAR) for enhancing connectivity aware data dissemination. IVD calculation is robust and can effectively handle instantaneous GPS failure. Two localization techniques; namely, cooperative localization and Geometry based Localization are developed. Standard deviation of real time IVDs of a forwarding path is derived. Distribution of IVDs of a forwarding path is employed for estimating connectivity. Segment vehicle based next hop vehicle selection is utilized for incorporating network load, link quality and direction into consideration while selecting forwarding path. Simulations are carried out in ns2 to evaluate the performance of Ivd-CAR in realistic traffic environment. Comparative analysis of simulation results attests the superiority of Ivd-CAR to the state-of-the-art techniques: CSR and A-CAR
Evaluating the Impact of Transmission Range on the Performance of VANET
Recently, interest in the field of Vehicular Ad-hoc Networks (VANETs) has grown among research community to improve traffic safety and efficiency on the roads. Despite the many advantages, the transmission range in vehicular network remains one of the major challenges due to the unique characteristics of VANETs such as various communication environments, highly dynamic topology, high node mobility and traffic density. The network would suffer from a broadcast-storm in high vehicular density when a fixed transmission range in VANET is used, while in sparse vehicular density the network could be disconnected frequently. In this paper, we evaluated the impact of different transmission ranges and number of flows formed between vehicles in a highway scenario using AODV as routing protocol. In order to validate the simulation of VANET, traffic and network simulators (SUMO & NS-2) have been used. The performance was evaluated in terms of packet delivery ratio and end-to-end delay. The simulation results have shown that better performance was achieved in term of higher PDR and lower end-to-end delay for less than 500 meters transmission range. On the contrary, the PDR started to decrease and end-to-end delay increased when the transmission range exceeded 500 meters. The performance degraded as the number of flows increased
QoS Variance Aware Spectrum Sensing and Allocation Strategy for Cognitive Radio Wireless Mesh Networks
QoS (Quality of Service) aware spectrum sensing and channel allocation in cognitive radio wireless mesh networks is a continuous practice due to the divergent scope of communication in wireless mesh networks. Henceforth the current research is moving in a direction to find effective solutions towards QoS aware spectrum sensing and channel allocation. But all of these solutions are specific to one or two QoS factors. According to the real-time practices the QoS assessment by one or two factors is impractical
A review of relay network on UAVS for enhanced connectivity
One of the best evolution in technology breakthroughs is the Unmanned Aerial Vehicle (UAV). This aerial system is able to perform the mission in an agile environment and can reach the hard areas to perform the tasks autonomously. UAVs can be used in post-disaster situations to estimate damages, to monitor and to respond to the victims. The Ground Control Station can also provide emergency messages and ad-hoc communication to the Mobile Users of the disaster-stricken community using this network. A wireless network can also extend its communication range using UAV as a relay. Major requirements from such networks are robustness, scalability, energy efficiency and reliability. In general, UAVs are easy to deploy, have Line of Sight options and are flexible in nature. However, their 3D mobility, energy constraints, and deployment environment introduce many challenges. This paper provides a discussion of basic UAV based multi-hop relay network architecture and analyses their benefits, applications, and tradeoffs. Key design considerations and challenges are investigated finding fundamental issues and potential research directions to exploit them. Finally, analytical tools and frameworks for performance optimizations are presented
Physical and Link Layer Implications in Vehicle Ad Hoc Networks
Vehicle Ad hoc Networks (V ANET) have been proposed to provide safety on the
road and deliver road traffic information and route guidance to drivers along with
commercial applications. However the challenges facing V ANET are numerous. Nodes
move at high speeds, road side units and basestations are scarce, the topology is
constrained by the road geometry and changes rapidly, and the number of nodes peaks
suddenly in traffic jams. In this thesis we investigate the physical and link layers of
V ANET and propose methods to achieve high data rates and high throughput.
For the physical layer, we examine the use of Vertical BLAST (VB LAST) systems
as they provide higher capacities than single antenna systems in rich fading
environments. To study the applicability of VB LAST to VANET, a channel model was
developed and verified using measurement data available in the literature. For no to
medium line of sight, VBLAST systems provide high data rates. However the
performance drops as the line of sight strength increases due to the correlation between
the antennas. Moreover, the performance of VBLAST with training based channel
estimation drops as the speed increases since the channel response changes rapidly. To
update the channel state information matrix at the receiver, a channel tracking algorithm
for flat fading channels was developed. The algorithm updates the channel matrix thus
reducing the mean square error of the estimation and improving the bit error rate (BER).
The analysis of VBLAST-OFDM systems showed they experience an error floor due to
inter-carrier interference (lCI) which increases with speed, number of antennas
transmitting and number of subcarriers used. The update algorithm was extended to
VBLAST -OFDM systems and it showed improvements in BER performance but still
experienced an error floor. An algorithm to equalise the ICI contribution of adjacent
subcarriers was then developed and evaluated. The ICI equalisation algorithm reduces
the error floor in BER as more subcarriers are equalised at the expense of more
hardware complexity.
The connectivity of V ANET was investigated and it was found that for single lane
roads, car densities of 7 cars per communication range are sufficient to achieve high
connectivity within the city whereas 12 cars per communication range are required for
highways. Multilane roads require higher densities since cars tend to cluster in groups.
Junctions and turns have lower connectivity than straight roads due to disconnections at
the turns. Although higher densities improve the connectivity and, hence, the
performance of the network layer, it leads to poor performance at the link layer. The
IEEE 802.11 p MAC layer standard under development for V ANET uses a variant of
Carrier Sense Multiple Access (CSMA). 802.11 protocols were analysed
mathematically and via simulations and the results prove the saturation throughput of
the basic access method drops as the number of nodes increases thus yielding very low
throughput in congested areas. RTS/CTS access provides higher throughput but it
applies only to unicast transmissions. To overcome the limitations of 802.11 protocols,
we designed a protocol known as SOFT MAC which combines Space, Orthogonal
Frequency and Time multiple access techniques. In SOFT MAC the road is divided into
cells and each cell is allocated a unique group of subcarriers. Within a cell, nodes share
the available subcarriers using a combination of TDMA and CSMA. The throughput
analysis of SOFT MAC showed it has superior throughput compared to the basic access
and similar to the RTS/CTS access of 802.11
Intelligent spectrum management techniques for wireless cognitive radio networks
PhD ThesisThis thesis addresses many of the unique spectrum management chal-
lenges in CR networks for the rst time. These challenges have a vital
e ect on the network performance and are particularly di cult to solve
due to the unique characteristics of CR networks. Speci cally, this thesis
proposes and investigates three intelligent spectrum management tech-
niques for CR networks. The issues investigated in this thesis have a
fundamental impact on the establishment, functionality and security of
CR networks.
First, an intelligent primary receiver-aware message exchange protocol
for CR ad hoc networks is proposed. It considers the problem of alleviat-
ing the interference collision risk to primary user communication, explic-
itly to protect primary receivers that are not detected during spectrum
sensing. The proposed protocol achieves a higher measure of safeguard-
ing. A practical scenario is considered where no global network topology
is known and no common control channel is assumed to exist.
Second, a novel CR broadcast protocol (CRBP) to reliably disseminate
the broadcast messages to all or most of the possible CR nodes in the
network is proposed. The CRBP formulates the broadcast problem as a
bipartite-graph problem. Thus, CRBP achieves a signi cant successful
delivery ratio by connecting di erent local topologies, which is a unique
feature in CR ad hoc networks.
Finally, a new defence strategy to defend against spectrum sensing data
falsi cation attacks in CR networks is proposed. In order to identify
malicious users, the proposed scheme performs multiple veri cations of
sensory data with the assistance of trusted nodes.Higher Committee For Education Devel-
opment in Iraq (HCED-Iraq
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