CS5984 Mobile Computing Outline : a Survey Dr. Ayman Abdel-Hamid Computer Science Department Virginia Tech An Introduction to 1 2 1/2 Advances in micro-electro-mechanical systems technology, wireless communications, and digital electronics Development of low-cost, low-power, sensor nodes (small in size) that communicate wirelessly over short distances Sensing, data processing, and communicating components Collaborative effort of a large number of nodes Improvement over traditional sensors, deployed as follows Positioned far from actual phenomenon Sensing-only sensors can be carefully positioned along with careful engineering of communications topology 3 2/2 Large number of sensor nodes inside the phenomenon or very close to it Position need not be pre-determined (random rapid deployment) Must process self-organizing capabilities Collective effort of sensor nodes Fitted with on-board processor Use processing capabilities to locally carry out simple computations and transmit only required and partially processed data Applications include: health, military, and security Realizing such applications requires wireless ad hoc networking techniques 4 1
Sensor networks vs. Ad hoc networks Number of sensor nodes several orders of magnitude higher that number of nodes in ad hoc networks Densely deployed Consume less power in multi-hop communication (neighbor nodes very close to each other) Low power transmission levels can be undetected (military) Prone to failures Very frequent topology changes Broadcast communication paradigm Limited in power (generally irreplaceable power sources), computational capabilities, and memory May not have global identification (ID) 5 Sensor Networks Applications 1/2 Different types of sensors to monitor different conditions: temperature, humidity, vehicular movement, pressure, and noise levels (among others) Used for continuous sensing, event detection, event ID, and location sensing Military applications Monitoring friendly forces, equipment and ammunition Battlefield surveillance Reconnaissance of opposing forces and terrain Targeting Battle damage assessment Nuclear, biological, and chemical attack detection and reconnaissance 6 Sensor Networks Applications 2/2 Environmental applications Tracking movement of birds, monitoring environmental conditions, chemical and biological detection, forest fire detection Health applications Providing interfaces for the disabled, integrated patient monitoring, drug administration in hospitals, and tracking and monitoring doctors and patients inside a hospital Home applications Embedded in appliances, such as vacuum cleaners, micro-waves, refrigerators, VCRs, local and remote management of home devices Other commercial applications Environmental control in office buildings, detecting and monitoring car thefts, vehicle tracking and detection, and managing inventory control Factors influencing sensor network design 1/2 Fault tolerance (may fail, blocked, or damaged. In-home deployment is different than battlefield deployment) Scalability (large number of nodes + high density) Production costs (cost of a single node has to be minimized) Hardware constraints 7 8 2
Factors influencing sensor network design 2/2 Communication Architecture 1/2 Sensor network topology Node densities may be as high as 20 nodes/m 3 Pre-deployment and deployment phase Post-deployment phase (topology changes) Re-deployment Operating Environment Transmission media (radio, infrared, or optical media) Power consumption need for power-aware protocols Multi-hop infrastructure-less architecture A node acts as a data originator and data router Power consumption: sensing, communication, and data processing 9 10 Communication Architecture 2/2 Planes needed so that sensor nodes can work together, collaboratively in a power efficient manner Power Management plane Sensor node may turn off its receiver after receiving a message from one of its neighbors When low power, broadcast inability to participate in routing messages Mobility management plane Detects and registers the movement of sensor nodes, to maintain route back to user (also knowledge of neighbors) Task management plane Balance and schedule sensing tasks given to a specific region Not all nodes might be performing sensing at all times 11 Application Layer Sensor Management Protocol (SMP) access nodes using attribute-based naming and location-based addressing introduce rules related to data aggregation, attribute-based naming, and clustering of sensor nodes Exchanging data related to location finding algorithms Turning nodes on and off authentication and key security Task Assignment and Data Advertisement Protocol (TADAP) Interest dissemination Sensor Query and Data Dissemination Protocol (SQDDP) Interfaces to issue queries, respond to queries and collect incoming replies SQTL: Sensor Query and Tasking Language 12 3
Transport Layer Needed when system is planned to be accessed through Internet or external networks Might use TCP splitting (I-TCP) TCP connections ended at sink nodes Special transport layer protocol handles communication between sink nodes and sensor nodes (UDP like protocols due to limited memory in sensor nodes) End-to-end communication schemes not based on global addressing Network Layer 1/3 Power efficiency is an important consideration T: source node sensing the phenomena, PA: available power, and α energy required to transmit a data packet through a link How to select an energy efficient route Maximum Available Power (Sink-E-F-T) Minimum Energy route (Sink-A-B-T) Minimum hop route (Sink-D-T) Maximum minimum PA node route Route along which the minimum PA is larger than the minimum PAs of other routes (Sink-D-T) 13 14 Network Layer 2/3 Data centric routing (Interest dissemination) Sinks broadcast the interest Sensor nodes broadcast an advertisement for available data and wait for a request from the interested sinks Requires attribute-based naming Data aggregation (data fusion) used to solve implosion and overlap problems Network Layer 3/3 Flooding (broadcast messages): problems of Implosion, Overlap (sensing same conditions), and resource blindness (energy un-aware) Gossiping: nodes do not broadcast but send incoming packets to a randomly selected neighbor (may take a long time to propagate a message) Sensor Protocols for information via negotiation (SPIN) Send data that describe the sensor data instead of sending the whole data 15 16 4
Data Link Layer 1/2 Data Link Layer 2/2 Multiplexing of data streams, data frame detection, medium access, and error control MAC layer Share communication resources between sensor nodes Existing MAC protocols are not suitable: no central controlling agent like the BS, network-wide synchronization not possible, and power efficiency considerations Bluetooth and MANET are closest peers but still not suitable: (Why Bluetooth not suitable?) Large number of nodes Radio range less Topology changes more frequent and can be attributed to node mobility and failure Mobility rate much lower than MANET 17 18 Research Projects 19 5