introduction to embedded and real-time systems – w14: an ... · systems perspective): – basics...
TRANSCRIPT
Introduction to Embedded and Real-Time Systems – W14:
An Introduction to Communication Systems and
Final Course Conclusions
What communication systems do you know?
Outline
• Wired Communication– Communication model– Modulation, demodulation
• Wireless Communication– Sharing the medium– Throughput limits (Shannon-Hartley)– Link budget, free space path loss
• Available Technologies– Example: dam monitoring
Wired Communication
Communication Model
Transmitterchannel
Receiver
Communication Model
Transmitterchannel
Receiver
Noise
DistortionFilteringFrequency shift...
ModulationCoding(Compression)
DemodulationDecoding(Decompression)
RS-232 (serial port)
• Hardware:– 3 wires: TxD, RxD, Ground
RxD
Transceiver1
Transceiver2
TxD
Ground
TxD
RxD
Ground
Transceiver = Transmitter + Receiver
RS-232 (serial port)
• Signal: between RxD/TxD and Ground
RxD
Transceiver1
Transceiver2
TxD
Ground
TxD
RxD
Ground
RS-232 Modulation
RS-232 Demodulation
RS-232 Delay
• Packet-based– 1 byte / packet– 8 data bits + 2 control bits = 10 bits
• Transmission speed– max. 115'200 bits/s (bps)
• Propagation speed:– approx. c (speed of light)
RS-232 Delay
• Transmission delay– 10 bits / 115'200 bps = 86.8 us
• Signal propagation delay (2 m cable)– 2 m / c = 6.6712819 ns
• Processing delay:– ~ 1 us (modulation, demodulation, processing)
• Total: ~ 90 us = 0.09 ms
Wireless Communication
Transmitterchannel =
ElectroMagneticwaves in air
Receiver
Noise
ReflectionsFadingInterferenceOther EM sources...
Communication Model
Communication Model
Transmitterchannel =
ElectroMagneticwaves in air
Receiver
Noise
ReflectionsFadingInterferenceOther EM sources...
Channel estimationAdvanced modulation typesCoding and error correction
Sharing the Medium
2
1
3
Sharing the Medium
• TDMA– Time-Division Multiple Access– “You shut up while I talk“– Time allocation
• Fixed, synchronizede.g. mobile phones (GSM)
• Dynamic (check if channel is free)e.g. Wireless LAN (802.11b/g/n)
1 2 3 2 3 time
Sharing the Medium
• FDMA– Frequency-Division MA– e.g. FM radio channels– Frequency regulation
• BAKOM (CH)
1 2 3
frequencyallocated by BAKOM
bandwidth
Sharing the Medium
• CDMA (spread spectrum)– Code-Division MA– Using different transmission codes– e.g. GPS– Interesting properties
• Wide channels (fading)• Concurrent communication
– More complex demodulation
Throughput (bits/s)
• TDMA, FDMA, CDMA can be combined• Total throughput is shared
TDMA
CDMA
FDMA
Shannon-Hartley Limit
• Hard theoretical limit on throughput– More bandwidth = higher throughput– More power (SNR) = higher throughput
C: capacity (throughput)B: bandwidthS: signal power (W)N: noise power (W)
Power
• Increased power– higher throughput– mobile systems: shorter battery life– increased health risk (?)
• Regulation– CH: BAKOM– e.g. WLAN: 100 mW
Power
• Unit: W (Watt)– Often written in dBm (decibels mW)
• Gain / loss: factors– Often written in dB (decibels)
Link Budget
TX powerTX lossesTX antenna gainFree space path lossRX antenna gainRX losses
RX power
RX sensitivity
100 mW0.51.61.0106e81.60.5
20 dBm-3 dB2 dB-80 dB2 dB-3 dB
-85 dBm
-62 dBm
Margin 23 dB200
Typical WLAN link budget (100 m, dipole antennas):
Free Space Path Loss
• Signal power decay in air:
• Proportional to the square of the distance d• Proportional to the square of the frequency f
– high frequency = high loss– low frequency = low bandwidth
Available Technologies
Dam MonitoringVibrations Temperature
A few wired technologies:Copper line (8 Mbps)Analog phone line (56 kbps)ADSL (8 Mbps)USB (< 15 m, 480 Mbps) Ethernet (< 200 m, 1 Gbps)RS-232 / RS-485 (< 100 m, 115 kbps)SATA (< 1 m, 6 Gbps)
A few wireless technologies:Satellite link (long delay, 2 Mbps)Bluetooth (< 10 m, 1 Mbps)WLAN (< 100 m, 54 Mbps)Mobile phone (100 kbps, subscription)Wireless link (1 Mbps)Packet radio (9.6 kbps)HQ
Some Pointers for Embedded System
Technology in Civil/Environmental
Engineering
Civil Engineering Applications• Structural Health Monitoring (SMH)
– Embedded Networks Laboratory, USC, Los Angeles, U.S.A., Prof. R. Govindan: http://enl.usc.edu/projects/shm/index.html
– Structural Engineering Laboratory, EMPA, Duebendorf, Prof. M. Motavalli, Dr. G. Feltrinhttp://www.empa.ch/plugin/template/empa/93/*/---/l=2
- Prof. D. Culler, EECS department, UCB, Berkeley, U.S.A.:http://www.eecs.berkeley.edu/~binetude/ggb/
- Prof. J. Wallace and B. Kaiser, CENS, UCLA, Los Angeles, U.S.A. http://research.cens.ucla.edu/projects/2007/Seismic/Tall_Special/
Civil Engineering Applications• (Decentralized) Structural Control
– Laboratory for Smart Structural systems, Prof. Y. Wang, GaTech, Atlanta, U.S.A.http://people.ce.gatech.edu/~ywang/research.htm#_WirelessControl
- Prof. Ian Smith, EPFL, IMAC (active structures) http://imacwww.epfl.ch/Common/research-en.jsp
- DISAL (Smart bridge project, in collaboration with EMPA): http://www5.epfl.ch/swis/page26715.html
- Laboratory for Intelligent Structural Technology, Prof. J. P. Lynch, University of Michigan: http://www-personal.umich.edu/~jerlynch/index.html
Environmental Engineering Applications• Environmental Monitoring using sensor networks
- http://research.cens.ucla.edu/research/, Prof. D. Estrin (UCLA, Los Angeles, U.S.A.), Director; work on urban sensing, animal and plants, aquatic environment, contaminant transport
- Profs. M. Vetterli, M. Parlange, K. Aberer and DISAL (EPFL)http://sensorscope.epfl.ch/index.php/Main_Page
- Swiss Experiment (several Swiss institutions, Dr. M. Lehning, WSL Davos, Principal Investigator): http://lsir-swissex.epfl.ch/index.php/Main_Page
- Prof. Paul Flikkema (NAU, Flagstaff, U.S.A), Prof. J. Clark (Duke University, U.S.A) http://wisardnet.nau.edu/
Environmental Engineering Applications• Waste treatment process using (wired) sensor networks:
– EAWAG innovative sensing technology (Prof. H. Sigrist)http://www.eawag.ch/organisation/abteilungen/eng/schwerpunkte/abwasser/msr_konzept/index_EN
• Env. monitoring using distributed robotic systems:– Aquatic microbic observing systems (Prof. G. Sukhatme,
USC Los Angeles, U.S.A.) http://robotics.usc.edu/~namos/index.html
– Adapting sampling of oceans (Prof. N. E. Leonard, Princeton, U.S.A.): http://www.princeton.edu/~dcsl/asap/
Course Take Home Messages
What is an Embedded System?
From Wikipedia: An embedded system is a special-purpose computersystem designed to perform one or a few dedicated functions often with real-time computing constraints. It is usually embedded as part of a complete device including hardware and mechanical parts. In contrast, a general-purpose computer, such as a personal computer, can do many different tasks depending on programming.
Consumer Market Devices
Digital Watch
Weather station
Digital video camera
Digital camera
Niche Market – Scientific Equipment Commercially Available
Sensorscopestation, 2nd generation
Mica-Z
e-puck
Handheld Airborne Mapping System
What is Challenging in Designing Embedded Systems?
• Computation is subject to physical and resource constraints such as timing, deadlines, memory restrictions, and power consumption requirements.
• The traditional abstraction of separating software from the hardware is more difficult. Hardware and software are integrally intertwined.
What we did cover• Fundamentals of signal processing:
– Analog/Digital signals, Time/Frequency domains, Filters, Converters
• Fundamentals of computer science (from an embedded systems perspective):– Basics of computer architecture– UNIX (crash course)– C programming (vs Java, Matlab)
• Fundamentals of embedded and real-time systems:– Microprocessors, microcontrollers, memory– Sensors and actuators– Basic control techniques and concepts– Communication systems
Our Main Objectives for Civil and Environmental Engineers
• This course should allow you to become a power user of the key instruments in civil and environmental engineering used nowadays (sensor networks, meteorological stations, data loggers, etc.) and in the future (exploratory and cleaning robots, robotics sensor networks, etc.)
• This course should allow you to collaborate more efficiently with electrical and computer engineers in general and, in particular, to give you sufficient background to attend, if any interest, the follow-up master course on distributed intelligent systems
Why is this objective realistic?• Off-the-shelf hardware components are becoming more and
more flexible, cheap, small, and standardized. The design complexity is continuously shifting to software!
• You have domain knowledge which can be translated to code: as long as you can program in the appropriate language you can contribute to design embedded systems for applications in your area!
• However, since in embedded systems hardware and software are more intertwined than in other computer systems because of hardware resources constraints, you need to have an idea of what these constraints are and be ready to analyze the specifications of a given hardware system or component.
Next Iteration• 5 ECTS, i.e. 150 h workload• Breakdown:
– 2 ECTS lecture (attendance, preparation, exam)– 2 ECTS lab+hwk (probably 10 labs @ 6 h each)– 1 ECTS course project (30 h work)
• Full in English• SSIE compulsory, SGC optional• Remain at BS 6th semester for the time being
for both sections• All your valuable will back will be considered
A Note for SGC Students
• Optional courses = motivated students• The content is clear and will remain about the
same (with more problem domain examples), do not come to this course if not motivated
• 27/40 ECTS (available 23 WS, 17 SS) this year; next year 28/45 ECTS (available 26 WS, 19 SS): do your planning well (i.e. have backup if you do not like the course in the first weeks)!
• If not enough optional courses, ask for more at SGC!
Master Course on Distributed Intelligent Systems
We focused in giving you some understanding of one device
The reality is however that most of the civil/environmental applications requires a network of devices …
Thank you for your attention and valuable feedback!