Paper presentation – Ultra-Portable Devices Outline – Overview of ad hoc wireless networks Paper: Paper: – Application with emphasis on energy constraints – Cross-layer design Design Challenges for Energy-Constrained Ad Hoc Wireless Networks – Link layer design issues Andrea J. Goldsmith, Stephen B. Wicker – MAC layer design issues IEEE Wireless Communication IEEE Wireless Communication – Networking design issues August 2002, pages 8-27 – Application design issues – Summary and conclusions Presented by: Nafiseh Mazloum 2009-08-20 Paper Presentation - Ultra Portable Devices 1 2009-08-20 Paper Presentation - Ultra Portable Devices 2 Overview of ad hoc wireless networks (I) Overview of ad hoc wireless networks (II) • Definition • Two design issues of ad hoc networks – Ad hoc : for the particular purpose in hand or in view – Mobility – Ah hoc wireless networks : Self-configured wireless mobile nodes – Energy efficiency without established infrastructure • Characteristics – Nodes handle control and networking tasks g – Peer-to-peer communication – Multihop routing p g – Not flat depending on design requirement 2009-08-20 Paper Presentation - Ultra Portable Devices 3 2009-08-20 Paper Presentation - Ultra Portable Devices 4
Applications (I) Applications (II) • Data networks • Device networks – Data exchange between devices like laptops, palmtops, PDAs – Short-range wireless connection between devices – Challenges are high data rate and cost – Challenge is energy – 802.11a and 802.11b standards – Bluetooth standard • Home networks Home networks • Sensor networks Sensor networks – Communication between electronics in and around home – Large number of sensors used to sense, detect and track – Challenges: varied QoS cost standardization and energy Challenges: varied QoS, cost, standardization and energy – Challenges are energy, size and cost Ch ll i d t – 802.11a and 802.11b standards – PicoRadio 2009-08-20 Paper Presentation - Ultra Portable Devices 5 2009-08-20 Paper Presentation - Ultra Portable Devices 6 Cross layer design (I) Cross layer design (II) • Why cross-layer design? • To design an adaptive cross-layer protocol stack Inflexibility, suboptimality and – What information should be exchanged and how that information should be adapted to? poor performance of layered approach – How should global system constraints and characteristics be factored into protocol design at each layer? • How it can be done? • How it can be done? – Information exchange across all layers in protocol stack all layers in protocol stack – Adaptivity and optimization with respect to global system respect to global system constraints and characteristics 2009-08-20 Paper Presentation - Ultra Portable Devices 7 2009-08-20 Paper Presentation - Ultra Portable Devices 8
Link layer design issues (I) Link layer design issues (II) • Max. data rate • Multiple antennas – The goal is to reach fundamental capacity limit – Techniques: � Diversity – Due to energy constraints, it is not possible to reach this max.data rate � Beamsteering – We need a new definition for capacity limit which proposed as capacity � MIMO per unit energy or capacity in bits – Trade-off between multiple antennas and energy consumption T d ff b t lti l t d ti – Energy constraints nodes can transmit finite no. of bits • Power control • Coding – Key role on enery-efficient cross-layer design Error control coding techniques • Adaptive resource allocation can reduce transmit power p adapts link transmission scheme to experienced channel, interference and data characteristics 2009-08-20 Paper Presentation - Ultra Portable Devices 9 2009-08-20 Paper Presentation - Ultra Portable Devices 10 MAC layer design issues (I) MAC layer design issues (II) • Medium access control (MAC) protocol Channelization Methods determines how different user share available spectrum – Frequency division � System bandwidth divided into nonoverlapping channels � Simple to implement, inflexible, limited no. of users – Time division • Two components of spectrum allocation • Two components of spectrum allocation � Ti � Time divided into orthogonal time slot di id d i t th l ti l t � Difficult to implement, flexible, limited no. of users – Channelization: How to divide spectrum into different channels – Code division Code division – Channel access: How to assign different channels to different users Ch l H t i diff t h l t diff t � Data modulated by orthogonal or semi-orthogonal spreading code � Complex, flexible Co p e , e b e – Hybrid combinations of these methods – Trade-off between frequency, time and code channelization Trade off between frequency, time and code channelization 2009-08-20 Paper Presentation - Ultra Portable Devices 11 2009-08-20 Paper Presentation - Ultra Portable Devices 12
MAC layer design issues (III) Network layer design issues (I) Channel access • Neighbor discovery – Process of determining number and identity of network nodes with which direct – Random access communication can be established given max. power level and min. link requirements � Channels are allocated to users that need them � Techniques: o aloha, slotted aloha, o CSMA, aloha with CSMA, four-way handshake (802.11) y ( ) • Network connectivity N t k ti it o RX and TX busy tone transmission � Issues: collision, hidden terminals, exposed terminals – Ad hoc networks assume a fully-connected network � Energy efficient technique: limit transmitting and receiving time period � Energy efficient technique: limit transmitting and receiving time period – Connectivity gets influenced by C ti it t i fl d b � Node mobility � Link layer parameters – Scheduling Scheduling Link layer parameters � Power efficiency � Channels are assigned to users to avoid conflicts � Scheduled access and aloha combination for ad hoc networks (PRMA) � Energy efficient technique: schedule optimization 2009-08-20 Paper Presentation - Ultra Portable Devices 13 2009-08-20 Paper Presentation - Ultra Portable Devices 14 Network layer design issues (II) Network layer design issues (III) Routing Routing – Flooding – Distributed routing � Highly robust to changing network topology � Little routing overheads � Little routing overhead � Adapts quickly to changes � Wasting bandwidth and battery power � Suboptimal � Proper for small networks � Proper for small networks – Reactive routing R ti ti – Centralized routing � Globally efficient � Efficient due to optimality � Efficient due to optimality � Little overhead � Little overhead � Cannot adapt to fast changes � Significant delay � combination of proactive and reactive � Requires much overhead � Proper for small networks – Multi-hop routing gets influenced by � Mobility � Energy efficiency 2009-08-20 Paper Presentation - Ultra Portable Devices 15 2009-08-20 Paper Presentation - Ultra Portable Devices 16
Network layer design issues (IV) Application design issues • Scalability and distributed protocols • Application must adapt to time-varying QoS due to dynamic characteristics of network – How scalable the distributed control network algorithm are • Application must adapt itself to offered QoS • Network capacity – How to improve per-user rates in a large network 2009-08-20 Paper Presentation - Ultra Portable Devices 17 2009-08-20 Paper Presentation - Ultra Portable Devices 18 Summary List of interesting papers • In energy constraints systems – Applications (Picoradio): [27] J. Rabaey et al., “PicoRadio Supports Ad Hoc ultra low Power Wireless Networking ” IEEE Comp July 2000 pp 42 48 low Power Wireless Networking, IEEE Comp., July 2000, pp. 42–48. – Cross-layer design saves energy across entire protocol stack – Link layer (fundamental capacity limit): [41] H. Mandyam and A. J. Goldsmith, – Adaptivite solutions and optimized algorithms based on design “Capacity of Finite Energy Channels,” Proc. Allerton Conf. Commun. Cntl. Comp., Oct. 2001. requirements improve performance and minimize energy consumption – MAC layer (scheduling): [91] E. Uysal-Biyikoglu, B. Prabhakar and A. El Gamal , – Trade-off between local algorithm and global system energy saving “Energy-Efficient Transmission of Packets in a Wireless Network ” to appear IEEE Energy Efficient Transmission of Packets in a Wireless Network, to appear IEEE Trans. Net., also Proc. IEEE INFOCOM, Mar. 2002. – [15] J. M. Kahn, R. H. Katz, and K. S. Pister, “Emerging Challenges: Mobile N t Networking for “Smart Dust,” J. Commun. Net., Aug. 2000, pp. 188–96. ki f “S t D t ” J C N t A 2000 188 96 2009-08-20 Paper Presentation - Ultra Portable Devices 19 2009-08-20 Paper Presentation - Ultra Portable Devices 20
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