Connectivity of Wireless Ad hoc Networks Dr Salman
- Slides: 45
Connectivity of Wireless Ad hoc Networks Dr. Salman Durrani School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australia. http: //engnet. anu. edu. au/DEpeople/Salman. Durrani/ Dec. 2009 1
Overview • Introduction • Research Trends in Wireless Communications • Open research problems in ad hoc networks • Connectivity Analysis • Antenna & System Model • Analytical framework • Results & Conclusions 2
Canberra 3
ASP Academics • 8 Academics + 4 NICTA Adjuncts 4
ASP Research Group • The Applied Signal Processing Group conducts research in the following application areas: 1. Physical layer Communications (12 Ph. D students ) • • Telecommunications including Wireless and Mobile Communications Space-Time Signal Processing 2. Signal Processing (9 Ph. D students ) • • • Acoustic and Audio Signal Processing Broadband Near-field Sensor Arrays and Beamforming Bio-Signal Processing 3. Applied Information Theory (2 Ph. D students ) 5
My Ph. D Students • Xiangyun Zhou (EIPRS Scholarship), Channel estimation in cellular & ad hoc networks. (Jan 2008 -present) • Ali Nasir (ANU International Ph. D Scholarship), Synchronization in cooperative communication systems. (June 2009 -present) • Zubair Khalid (EIPRS Scholarship) & Rimla Javaid (ANU Ph. D Scholarship), commencing 2010. 6
Research Trends • IEEE ICC 2009 in Dresden, Germany: • 3600 paper submissions • 1046 accepted papers after peer review (29%) • Selected papers presented in oral sessions. • On average, 5 to 6 papers being presented in every session. • We looked at the number of oral sessions presented for different research topics in Globe. Comand ICC for last 3 years. 7
Research Trends Source: Internal report by Ph. D student Ali Nasir. 8
Research Trends • Research topics in steady state or decline ? Source: Internal report by Ph. D student Ali Nasir. 9
Research Trends • Research topics in steady state or decline ? Source: Internal report by Ph. D student Ali Nasir. 10
Research Trends • Other Research Topics Source: Internal report by Ph. D student Ali Nasir. 11
Research Trends: Ad Hoc Networks s k r o oc h d tw e N A 12
Basic Principles of an Ad hoc Network • • Formed by wireless nodes which may be mobile. No need (necessarily) for any pre-existing infrastructure. Decentralized operation. Multi-hop communication. 13
Applications: Sensor Networks • Networks of typically small, battery-powered, wireless devices. • Wide range of applications: • • • Environmental monitoring, Military surveillance Medical care Home appliance management Industrial monitoring 14
Applications: VANETS • Vehicular Ad Hoc Networks comprise vehicle-to-vehicle and vehicle-to-infrastructure communications based on WLAN technologies. (IEEE P 1609 WAVE Standards) Figure from Lin et. al, IEEE Comm. Mag, April 2008. 15
Applications: Telecomms Networks Ad hoc Networking 16
Research Challenges in Ad hoc Networks • Capacity • What are the fundamental performance limits (in terms of reliable data rate) for ad hoc networks? • Routing • How do you efficiently select paths in a network along which to send information? • Connectivity • If you select any pair of nodes in an ad hoc network, what is the probability they connected? • Co-operation • 3 node Source, Relay, Destination scenario. Synchronization 17
Connectivity Definitions • Connectivity from view-point of a single node: • Average Node Degree : Average no. of direct links that any given node has to other nodes. • Probability of node isolation : Probability that a randomly selected node in an ad hoc network has no connections to any other node. Average Node degree = 1. 8 2 1 3 3 2 3 1 1 2 0 Isolated node 18
Connectivity Definitions • Connectivity from view-point of an entire network: • 1 - connectivity : Probability that every node pair in the network has at least one path connecting them. • Critical Node density : Node density that yields an almost surely connected network [P (1 -con)=0. 99]. • Path Probability : Probability that two randomly chosen nodes are connected either via a single hop or a multihop path. 19
Research Challenges in Modelling Ad hoc network Connectivity • Mobility • Dynamic network topology • Realistic models for mobility • Node distribution • Uniform • Clustered • Channel • Wireless links subject to shadowing and fading • Interference from simultaneous transmissions elsewhere • Multiple Antennas • Adopted in 3 GPP (Release 6), IEEE 802. 11 n, IEEE 802. 20 • How does beamforming affect the connectivity of ad hoc networks? 20
Prior Work • Closed-form analytical results for connectivity are available for special caseof: • Node locations are Poisson, • Negligible interference, • No mobility, • Channel: Path loss & Shadowing, • Omni-directional antennas • Open Research Problem: 21
Overview • Introduction • Research Trends in Wireless Communications • Open research problems in ad hoc networks • Connectivity Analysis • Antenna & System Model • Analytical framework • Results & Conclusions 22
System Model • Nodes are distributed in 2 D according to Poisson point process. • All nodes are equipped with beamforming antennas. 23
Antenna Model • Antenna Model is characterized by associated antenna power pattern. • Uniform Linear Array or Uniform Circular Array ? 24
Power Pattern Demo (N=8) 25
Antenna Model • UCA configuration is chosen: • It has single main lobe. • 3 d. B beamwidth is constant & independent of main beam direction. • For UCA, the directivity. G is given by 26
Random Beamforming • Core Idea: Each node randomly selects a main beam direction without co-ordination with other nodes. • Advantage: • MAC is un-coordinated. • Minimal communication overhead and hardware complexity. • Disadvantage: • May not be optimal strategy 27
Channel Model • Received Signal Power Shadowing Beamforming Path Loss • Shadowing affects only the randomness and not the average value of the channel gain. 28
Communication Range • Two nodes can communicate with each other if their distance apart is smaller than a given communication range R. 29
Effective Coverage Area • With beamforming, the communication range is Random variable • Effective coverage area is Shadowing factor Beamforming factor 30
Effect of Shadowing • Shadowing factor : • Depends on: • path loss a and • Shadowing log-normal standard deviation s • Key Insight: -Shadowing reduces the effective coverage area (for a > 2). 31
Effect of Shadowing 32
Effect of Beamforming • Beamforming factor: ® 33
Effect of Beamforming • Beamforming factor: • Depends on • path loss a • Number of antenna elements in the UCA M • Does not depend on • Shadowing log-normal standard deviation s 34
Effect of Beamforming • Beamforming factor values: • Key Insight : - For a<3, random beamforming increases the effective coverage area. 35
Overview • Introduction • Research Trends in Wireless Communications • Open research problems in ad hoc networks • Connectivity Analysis • Antenna & System Model • Analytical framework • Results • Average Node degree • Probability of node isolation • 1 -connectivity • Critical node density • Path probability • Conclusions 36
Connectivity Metrics - P(iso) • Probability of node isolation Effective coverage Area • Main Result : • shadowing always increases the probability of node isolation. • beamforming, compared to omnidirectional antennas, reduces the probability of node isolation when a<3. 37
Connectivity Metrics - P(iso) • Verification (effect of shadowing, M=1): - 38
Connectivity Metrics - P(iso) • Verification (effect of beamforming, M=1, 4 & s = 4 d. B): - 39
Connectivity Metrics - rc • Critical node density: node density that yields an almost surely connected network, that is, the density at which P (1 -con) = 0. 99. • Main Result : • shadowing increases the critical node density. • rc can be reduced by using beamforming when a<3. 40
Connectivity Metrics - rc • Effect of shadowing • No of antennas M=1 41
Connectivity Metrics - rc • Effect of beamforming • No of antennas M=1, 4 42
Conclusions • We have presented an analytical model to characterize the effect of random beamforming on the network connectivity. 43
Publications • X. Zhou, S. Durraniand H. Jones, "Connectivity Analysis of Wireless Ad Hoc networks with Beamforming, " IEEE Transactions on Vehicular Technology, vol. 58, no. 9, pp. 5247 -5257, Nov. 2009. • S. Durrani, X. Zhou and H. Jones, "Connectivity of Wireless Ad Hoc Networks with Random Beamforming: An Analytical Approach, " Proc. IEEE PIMRC, Cannes, France, Sep. 15 -18, 2008. • Paper PDFs available at: http: //engnet. anu. edu. au/DEpeople/Salman. Durrani/papers. html 44
Thank you for your attention 45
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