Mobile Ad Hoc Networks: Basic Concepts and Research Issues

Transcription

1 Mobile Ad Hoc s: Basic Concepts and Research Issues Ing. Alessandro Leonardi Wireless s Generations (1/3) Generation 1G 2G 2.5G 3G 4/5G Time 1980s 1990s Late1990s 2000s (2010 full deployment) 2010s Signal Type Analog Digital Digital Digital Digital Access Multiple Access FDMA/FDD TDMA/FDD CDMA/FDD EDGE, GPRS CDMA, W-CDMA, TD-SCDMA MC-CDMA, OFDM Frequency spectrum MHz MHz MHz (PCS) MHZ (varies from diff. countries) Higher frequency bands 2-8GHz Bandwidth 5-20MHz >=100MHz Antenna FEC Optimized Antenna, multiband adapter Convolutional rate, 1/2, 1/3; Smarter Antenna, Multi-band and wideband support Concatenated coding scheme 1

2 Wireless s Generations (2/3) Generation 1G 2G 2.5G 3G 4/5G Architecture Media Type Voice Mostly Voice Low speed data services via modem (10-70kbps)) Mostly Voice Higher speed data ( kbps) Voice High speed data (144kbps-2Mbps) Converged voice/data/ multimedia over IP; Ultra high speed data (2-100Mbps) Type Cellular Cellular Cellular WWAN Cell based Integrated WWAN, WMAN, WLAN (Wi- Fi,bluetooth) and WPAN (bluetooth); Structure Infrastructure based Infrastructure based Infrastructure based Infrastructure based network Hybrid of Infrastucture based and ad-hoc network Switching Circuit switched Circuit switched Circuit switched Circuit switched and packet switched Packet switched IP support N/A N/A N/A Use several air link protocol, incl. IP5.0 All IP based (IP6.0) Wireless s Generations (3/3) Generation 1G 2G 2.5G 3G 4/5G New Applications s, maps/ directions; News, shopping; e-commerce; interactive gaming, etc. Ubiquitous computing with location intelligence Example System AMPS, NMT, TACS GSM, DCS1900, IS-136, CdmaOne GPRS, EDGE UMTS IMT2000 CDMA2000 W-CDMA 2

3 Putting Wireline and Wireless Pieces Together Router VideoTel IP BACKBONE Desktop LAN Desktop Print Notebook FAX PDA PDA Notebook AP PAN 1 PAN 2 Ad Hoc definition In Latin, ad hoc literally means for this purpose only. An ad hoc network is a wireless LAN, in which some devices are part of the network only for the duration of a communication session or while in some close proximity to the rest of the network. A mobile ad hoc network (MANET) is an autonomous system of mobile routers (and associated hosts) connected by wireless links forming an arbitrary graph. Routers are free to move randomly and organize themselves arbitrarily; network topology may change rapidly and unpredictably. It may operate in a stand-alone fashion, or may be connected to the Internet. An ad hoc network can be regarded as a spontaneous network : a network that automatically emerges when nodes gather together. 3

4 Ad Hoc s Advantages " Ease of deployment " Speed of configuration (self-organization) " Decreased dependence on the infrastructure Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Applications of Ad Hoc s " Interactive applications Mobile phones and PDAs Wearable devices Outdoor Internet access Location-aware services " Cooperative applications Vehicular services Meeting and classrooms Gaming " Emergency services Infrastructure replacing Rescue data collection " Environmental monitoring Sensor networks " Military environments Tactical Operations Battlefield 4

5 Examples of Ad Hoc s 1. Personal Area s (PANs) 2. Body Area s (BANs) 3. Sensor s Personal Area s (PANs) Created when a group of people come together for some collaborative activity (e.g. exchange things and relay information). Limited extent in space and time. Nodes connected using various wireless technology (e.g., IEEE family). Authentication and trust based on first-person interaction, no administrative services. Hosts not preconfigured. Data rates: 1-10 Mbps. 5

6 Body Area s (BANs) Wireless communication between various components (earphones, microphones, sensors) attached to human body. Possible Applications: transmission of body parameters (blood pressure, pulse rate, body temperature); music entertainment. Features: transmission without interferences; licence free; low transmission power; cheap, tiny and light-weight hardware. Data rates up to 250 Kbps. Sensor s Self-configurable networks made of numerous sensors linked by a wireless medium, which perform distributed sensing tasks. Features: Frequency: variable range Bandwidth: kb/s Transmission power: ~ 1mW Access: many proposals (Aloha and CSMA-based) Sensors are very numerous. Sensors are simple and have scarse power and memory resources. Addressing done by data and area. 6

7 Characteristics and Requirements Autonomous and spontaneous nature of nodes Distributed Algorithms to support reliability, consistency and security of exchanged and stored information Time-varying network topology (no pre-existing infrastructure or central administration) Scalable routing and mobility management techniques to face network dynamics Fluctuating link capacity and network resources Enhanced functionalities to improve link layer performance, QoS network support and end-to-end efficiency Low-power devices Energy conserving techniques at all layers Possible Variations (1/3) Fully Symmetric Environment nodes have identical capabilities and responsibilities Asymmetric Capabilities transmission ranges and radios may differ battery life at different nodes may differ processing capacities may differ Asymmetric Responsibilities some nodes may act as leaders of nearby nodes (e.g., cluster head) 7

8 Possible Variations (2/3) Nodes may co-exist (and co-operate) with an infrastructure-based network Traffic characteristics may differ w.r.t. bit rate time constraints reliability requirements unicast / multicast / geocast Possible Variations (3/3) Mobility patterns may differ people sitting at an airport lounge taxi cabs kids playing military squads PAN environments Mobility characteristics speed predictability direction of movement pattern of movement 8

9 Challenges Broadcast nature of the wireless medium Limited wireless transmission range Hidden terminal problem Exposed terminal problem Capture problem Intruding terminal problem Packet losses due to transmission errors Mobility-induced route changes Mobility-induced packet losses Battery constraints Potentially frequent network partitions Ease of snooping on wireless transmissions Multihopping Data routes may traverse multiple links to reach a destination. It increases overall network capacity since the spatial domain could be reused for concurrent but physically separate sessions. It conserves transmit energy resources reduces interference. r 1 r r 3 4 r 4 9

10 QoS Mobility Management Research Issues MAC protocols Routing Multicasting QoS and Energy Efficiency Mobility Management Hot topics TCP over ad hoc networks Security Integration with cellular networks (for large coverage, high bit rates and QoS guarantee) Open Issues: Strict-Layered Approach Application 10

11 QoS QoS Mobility Management Mobility Management Open Issues: Strict-Layered Approach Directional Antennas (reduce interference at MAC level, increase range Applications by limiting energy waste in unnecessary directions, gain higher than omnidirectional antennas, number of neighbors may be greater and number of hops smaller) Open Issues: Strict-Layered Approach Broadcast and Shared Medium, Avoid Interference (Hidden Terminal, Applications Exposed Terminal), Fairness, Energy Efficiency 11

12 QoS QoS Open Issues: Strict-Layered Approach Multicast Routing, Unicast Routing, Dynamic Topology due to Mobility Management, Applications Energy Efficiency, QoS Mobility Management Open Issues: Strict-Layered Approach Multi-Hopping, Wireless Errors, Failures due to mobility, Efficiency of Routing Protocols Applications Mobility Management 12

13 QoS QoS QoS Open Issues: Strict-Layered Approach Location and Context Awareness, Resource Discovery, Smart Space Oriented Middleware, Security Application Mobility Management Routing Application Mobility Mobility Management Management 13

14 QoS Errors Application MAC Mobility Management The Biggest Issue!!! Cross-Layer Integration Theoretical Model Application Reality Application 14

15 Perspectives Application Security Scalability QoS Energy Efficiency Mobility? Multicast 15