mobile and sensor systems - university of cambridge
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Mobile and Sensor Systems
Lecture 1: Introduction to Mobile Systems
Prof Cecilia Mascolo
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About Me
time
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In this course
• The course will include aspects related to general understanding of – Mobile and ubiquitous systems and networks
– Sensor systems and networks
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List of Lectures
• Lecture 1: Introduction to Mobile Systems.• Lecture 2: Mobile Medium Access Control and
Wireless Systems.• Lecture 3: Infrastructure, Ad-hoc and Delay Tolerant
Mobile Networks.• Lecture 4: Sensor Systems and MAC Layer Protocols.• Lecture 5: Sensor Networking Routing Protocols.• Lecture 6: Sensor Systems Reprogramming and Mobile
Sensing.• Lecture 7: Mobile Phone Sensing.• Lecture 8: Practical: Mobile Phone Programming.
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Teaching Material
• No required textbook.• Some suggested readings:– Schiller, J. (2003). Mobile communications. Pearson
(2nd ed.). – Karl, H. & Willig, A. (2005). Protocols and
architectures for wireless sensor networks. Wiley. – Agrawal, D. & Zheng, Q. (2006). Introduction to
wireless and mobile systems. Thomson.
• Specific lectures will reference research papers which can be used for additional reading.
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In this lecture
• We will describe mobile systems and their applications and challenges.
• We will start talking about wireless networks.
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Smart Phones: ���the Computing Platform of the Future
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Smart Phones: ��� the Computing Platform
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Some Numbers
• 7 billion mobile subscriptions worldwide, estimates The International Telecommunication Union (May 2014). This is equivalent to 95.5 percent of the world population.
• A billion extra mobile subscriptions in three years, but growth is slowing – 2011: 5.9 billion; 2012: 6.2 billion; 2013: 6.7 billion; 2014: 6.9 billion.
• The number of cellular subscribers surpasses the number of wired phone lines.
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Mobile Users (Millions)
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Video Traffic
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Which App…
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Location-based ���Social Network Systems
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Geographic Recommender Systems
Mirco Musolesi
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Credit: CNet
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Fundamental Challenges ���in Mobile Computing
• Mobile devices are resource-constrained.• Mobile connectivity is highly variable in
performance and reliability.• Mobile devices are inherently less secure.
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Mobile Devices are Inherently Resource Constrained
• Mobile devices rely on batteries. • Energy consumption due to:– Computation (CPU, co-processors)– Display
– Communication– Sensing
• Energy-efficient algorithms are needed.
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Mobile Devices are Inherently Resource Constrained
• Computational constraints– But, for example, in the Samsung
Galaxy SIII you have1.4 GhZ quad-core Cortex A-9 +GPU
• Memory constraints– But, for example, in the Samsung
Galaxy SIII you have1GB or 2GB of RAM
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Mobile Connectivity is Highly Variable in Performance and Reliability���
• Various types of connectivity:– Cellular (GSM, 3G, 4G, etc.)– WiFi– Bluetooth– Near Field Communication (NFC)– …
• Constraints related to:– Coverage issues– Trade-offs: energy consumption, throughput, costs
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Mobile Devices are Inherently��� Less Secure���
• Wireless not wired communication:– Eavesdropping.– Need for encrypted communication.
• Devices can be stolen:– Devices might also be accessible by everyone (for
example, sensors).
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Ubiquitous and Mobile Computing
“The most profound technologies are those that disappear.”
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Mark Weiser (1952-‐1999)
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Mirco Musolesi 24
Copyright: PARC
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Mirco Musolesi 25
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Issues in Designing ���Mobile Computing Systems
• Distributed systems issues:– Remote communication– Fault tolerance
– Remote information access– Distributed security
• Networking issues:– Wireless communication
– Transport layer for wireless channel
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Issues in Designing ���Mobile Computing Systems
• Databases issues:– Disconnected operations– Weak consistency
• Energy issues:– Adaptation in terms of communication– Intelligent uploading of data– Hardware aspects
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Issues in Designing ���Mobile Computing Systems
• HCI issues:– Limited interface– Interaction with the devices (input, etc.)– Ergonomics
• Privacy issues:– Location sharing– Activity recognition
• Security issues:– Encrypted communication
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Wireless and Mobile Networks
• Two important (but different) challenges– wireless: communication over wireless link
– mobility: handling the mobile user who changes point of attachment to network
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Elements of a wireless network
network infrastructure
wireless hosts v laptop, PDA, IP phone v run applicaMons v may be staMonary (non-‐
mobile) or mobile § wireless does not always
mean mobility
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Elements of a wireless network
network infrastructure
base staMon v typically connected to
wired network v relay -‐ responsible for
sending packets between wired network and wireless host(s) in its “area” § e.g., cell towers,
802.11 access points
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Elements of a wireless network
network infrastructure
wireless link v typically used to connect
mobile(s) to base staMon v also used as backbone
link v mulMple access protocol
coordinates link access v various data rates,
transmission distance
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Wireless rate vs distance
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Elements of a wireless network
network infrastructure
infrastructure mode v base staMon connects
mobiles into wired network
v handoff: mobile changes base staMon providing connecMon into wired network
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Elements of a wireless network
ad hoc mode v no base staMons v nodes can only transmit
to other nodes within link coverage
v nodes organize themselves into a network: route among themselves
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Wireless network taxonomy
single hop mulMple hops
infrastructure (e.g., APs)
no infrastructure
host connects to base staMon (WiFi, WiMAX, cellular) which connects to larger Internet
no base staMon, no connecMon to larger Internet (Bluetooth,
ad hoc nets)
host may have to relay through several wireless nodes to connect to larger Internet: mesh net
no base staMon, no connecMon to larger Internet. May have to relay to reach other a given wireless node
MANET, VANET
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Suggested Readings
• Mark Weiser. The Computer for the 21th Century. Scientific American. September 1991.
• Mark Weiser. Some Computer Issues in Ubiquitous Computing. Communications of the ACM. Vol. 36. Issue 7. July 1993.
• M. Satyanarayanan. Pervasive Computing: Vision and Challenges. IEEE Personal Communications. Vol. 8 Issue 4. August 2001.
• Chapter 6 of James F. Kurose and Keith W. RossComputer Networking. A Top Down Approach. 6th Edition. Pearson 2012.
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Acks
• Some material for the slides of this course has been contributed by:
• Dr Christos Efstratiou,
• Dr Nicholas Lane, • Dr Mirco Musolesi,
• Dr Sarfraz Nawaz.
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