Upload
krishpri
View
43
Download
2
Tags:
Embed Size (px)
Citation preview
Wireless Communications
EE5131 + EE6131
Acknowledgements
Modules aligned closely with textbook:
“Wireless Communications” by Andrea
Goldsmith, Stanford University
Powerpoint slides in first, intro lecture mainly by
Goldsmith (Stanford), or Cui (Texas A&M)
modified by Hanly for our syllabi
Following lectures will be on white-board – please
take notes!
Outline
Module overview, assessment etc
Course Syllabi
Wireless past and present:
Current Wireless Systems
Emerging Wireless Systems
Design challenges for the future
Module Information
Lecturer: Stephen Hanly (Part 1)
[email protected], E4-05-29
Contact: Tuesday 4-5pm
Classes: Mondays 6-9pm, E1-06-04
Two modules: EE5131, EE6131
Whats the difference?
EE5131, EE6131 share a lot of material
mainly: assessment is different!
a few topics are advanced (i.e. for EE6131). EE5131 can listen and learn something extra! There will be corresponding supplementary material for EE6131
Module Information
Prerequisites: random signals, stochastic processes
Textbook: Wireless Communications (by A. Goldsmith) Available at coop (central forum) On reserve at central library.
Class Homepage: IVLE website
All handouts, announcements, homeworks, etc. posted to website
Lecture materials regularly updated on website
Grading: EE5131: HW - 20%, Midterm – 20%, Final exam 60%
EE6131: HW- 20%, Midterm – 10%, Project 20%, Final Exam - 50%
HWs: posted on IVLE and due in class Homework loses 25% credit per day late
Must be done individually – please sign it and state that it is your own work
Exams: Midterm on Monday Sept. 12 (in class) starting at 6.20pm, 1 hour.
Midterm: not compulsory and no makeup (without midterm, your results are normalized)
Final exam is Wed Nov 30 at 5pm. Duration: 2 hours.
Module InformationAssessment
The term project (for 6131 students) involves selecting a
research paper (we will provide a list on IVLE) and writing
a report on it.
You will need to write the report in your own words, and
demonstrate a thorough understanding of the research in
the paper. You will need to do a critical analysis whereby
you identify the strong and/or weak points in the research,
identify the underlying assumptions and evaluate their generality
indicate how you think it can be used in real wireless systems.
You can do some theoretical and/or numerical explorations of your
own to illustrate/extend the results in the paper
The report is due Monday Nov 7 in class (or before)
Module InformationProject (for 6131)
Makeup Class
As there was no lecture Aug 8, there is a makeup class:Monday Sept. 19
E1-06-04
Course Syllabus
Overview of wireless communications
Wireless channel modeling
Capacity of wireless channels
Digital modulation for flat fading channels
Diversity techniques and multicarrier modulation
Multiantenna communications
Cellular Systems:
multiple access and interference management
Wireless History
Radio invented in the 1880s by Marconi
Many sophisticated military radio systems were developed during and after WW2
Cellular has enjoyed exponential growth since mid 1980s, with > 3 billion users worldwide today Ignited the wireless revolution
Voice, data, and multimedia becoming ubiquitous
Use in third world countries growing rapidly
Wifi also enjoying tremendous success and growth
3G wireless internet
Ancient Systems: Smoke Signals, Carrier Pigeons, …
Future Wireless NetworksUbiquitous Communication Among People and Devices
Next-generation Cellular
Wireless Multimedia
Sensor Networks
Smart Homes/Spaces
Automated Highways
In-Body Networks
All this and more …
Current Wireless Systems
Wireless LANs
Cellular Systems
Satellite Systems
Zigbee radios
Ultrawideband
Current Wireless Systems
Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)
Orthogonal frequency division multiplexing
(OFDMA) --- multiple carriers
Ultrawideband (UWB) --- no carrier
Systems today use one of several PHY-layer
approaches to allocate bandwidth to devices:
Current Wireless Systems
Polling/scheduling schemes
Controlled by the access point
Random access schemes like ALOHA
Carrier sense multiple access (CSMA)
Ethernet
CSMA with collision avoidance (CSMA-CA)
WiFi networks
There are also networking-layer approaches to
bandwidth allocation
Wireless Local Area Networks (WLANs)
WLANs connect “local” computers (100m range)
Breaks data into packets
Channel access is shared (random access)
Carrier sense, collision avoidance (CSMA-CA)
Backbone Internet provides best-effort service
01011011
Internet
Access
Point
0101 1011
WiFi Standards (current)
802.11b Standard for 2.4GHz ISM band (80 MHz) CDMA 1.6-10 Mbps, 500 ft range
802.11a Standard for 5GHz band (300 MHz) OFDM Up to 54 Mbps
802.11g Standard in 2.4 GHz compatible with 11b OFDM Speeds up to 54 Mbps
Many
WLAN
cards
have
all 3
(a/b/g)
WiFi Standards (future)
802.11e: enhance quality of service functions
802.11i: enhance security
802.11r: support roaming
802.11s: support MESH function
802.11n: support MIMO (multiple antennas) Standard in 2.4 GHz and 5 GHz band OFDM - MIMO in 20/40 MHz (2-4 antennas) Speeds up to 150Mbps
WiGig and Wireless HD
New standards operating in 60 GHz band
Data rates of 7-25 Gbps
Bandwidth of around 10 GHz (unregulated)
Range of around 10m (can be extended)
Uses/extends 802.11 networking layer
Applications include PC peripherals and
displays for HDTVs, monitors & projectors
Cellular Systems:Reuse channels to maximize capacity
Geographic region divided into cells Frequency/timeslots/codes/ reused at spatially-separated locations. Co-channel interference between same color cells.
Base stations/MTSOs coordinate handoff and control functions
Shrinking cell size increases capacity, as well as networking burden
BASE
STATION
MTSO
Cellular Networks
BSBS
PSTN
BS
San Francisco
New YorkMTSO MTSO
Internet
Cellular development
Macrocell: diameter ~ 1 Km
Microcell: diameter ~ 100m
Support more mobiles
Reduce power, reduce phone size
Can we shrink size indefinitely?
Cost of base stations
Signaling overhead
Macrocell to microcell
Cellular development
First generation (1G):
analog,
FDMA or TDMA
Second generation (2G):
Digital
TDMA or CDMA
Third generation (3G): CDMA
Analog to digital
Cellular development
1G: pure voice
2G: voice + SMS
2.5G: voice + MMS + data
TDMA: GPRS (140kbps), EDGE (384kbps)
CDMA: IS-95 + EVDO (Qualcomm)
3G: voice + MMS + data (dominant)
144kbps (vehicular), 383kbps (pedestrian),
2Mbps(stationary)
Voice to data
3G Cellular
Data is bursty, whereas voice is continuous Typically require different access and routing strategies Packet based switching for data (including VoIP) Circuit based switching for voice
3G “widens the data pipe”: 384 Kbps on average Standard based on wideband CDMA supports diversified applications
Evolution of existing systems Dual phone (2/3G+Wifi) use growing (iPhone, Google)
What is beyond 3G?
4G/LTE/IMT Advanced
Much higher peak data rates (50-100 Mbps)
Greater spectral efficiency (bits/s/Hz)
Flexible use of up to 100 MHz of spectrum
Low packet latency (<5ms).
Increased system capacity
Reduced cost-per-bit
Support for multimedia
Evolution of Current Systems
Wireless systems today 3G Cellular: ~200-300 Kbps. WLANs: ~450 Mbps (and growing).
Next Generation is in the works 4G Cellular: OFDM/MIMO 4G WLANs: Wide open, 3G just being finalized
Technology Enhancements Hardware: Better batteries. Better circuits/processors. Link: More bandwidth, more antennas, better modulation
and coding, adaptivity, cognition. Network: better resource allocation, cooperation, relaying,
femtocells.
Future Generations
Rate
Mobility
2G
3G
4G
802.11b WLAN
2G Cellular
Other Tradeoffs:
Rate vs. Coverage
Rate vs. Delay
Rate vs. Cost
Rate vs. Energy
802.11n
3G
Ultrawideband radio
Impulse radio: pulses of nanoseconds (10-9) or
smaller
Duty cycle a fraction of a percent
Carrier not necessarily needed
Uses a lot of bandwidth (GHz)
Low probability of detection
Multipath highly resolvable
Ultrawideband radio
Unique location and positioning properties
1cm accuracy possible
Low power CMOS transmitters
Very high data rates (500 Mbps ~ 10 feet range)
7.5 GHz free spectrum in US
Spectrum allocation overlays other uses
“Moore’s law radio”
Data rate scales with shorter pulse widths made
possible with ever faster CMOS circuits
IEEE 802.15.4/ZigBee Radios
Low-Rate wireless mesh networking
Data rates of 20, 40, 250 Kbps
Support for large mesh networking or star clusters
Support for low latency devices
CSMA-CA channel access
Very low power consumption
Frequency of operation in ISM bands
Focus is primarily on low power sensor networks
Emerging Systems
4th generation cellular (4G)
OFDMA is the PHY layer
Ad hoc/mesh wireless networks
Sensor networks
Distributed control networks
Biomedical networks
Ad-Hoc/Mesh Networks
Peer to peer communications
No background infrastructure
Dynamic topology
Multihop routing
Design Issues
Ad-hoc networks provide a flexible network infrastructure for many emerging applications.
The capacity of such networks is generally unknown.
Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.
Crosslayer design critical and very challenging.
Energy constraints impose interesting design tradeoffs for communication and networking.
Sensor Networks
Nodes powered by
Non-rechargeable batteries or environment
Data highly correlated in time and space
Data flows to fusion centre
Nodes can cooperate in:
Transmission, reception, compression, and signal processing
Fusion centre
Energy-Constrained Nodes
Each node can only send a finite number of bits. Transmit energy minimized by maximizing bit time
Circuit energy consumption increases with bit time
Introduces a delay versus energy tradeoff for each bit
Short-range networks must consider transmit, circuit, and processing energy.
Sophisticated techniques not necessarily energy-efficient.
Sleep modes save energy but complicate networking.
Changes everything about the network design: Bit allocation must be optimized across all protocols.
Delay vs. throughput vs. node/network lifetime tradeoffs.
Optimization of node cooperation.
Wireless Sensor NetworksData Collection and Distributed Control
Energy (transmit and processing) is the driving constraint
Data flows to centralized location (joint compression)
Low per-node rates but tens to thousands of nodes
Intelligence is in the network rather than in the devices
• Smart homes/buildings
• Smart structures
• Search and rescue
• Homeland security
• Event detection
• Battlefield surveillance
Distributed Control over Wireless
Interdisciplinary design approach• Control requires fast, accurate, and reliable feedback.• Wireless networks introduce delay and loss• Need reliable networks and robust controllers • Mostly open problems
Automated Vehicles
- Cars
- Airplanes/UAVs
- Insect flyers
: Many design challenges
Applications in Health,
Biomedicine and Neuroscience
Neuro/Bioscience applications- EKG signal reception/modeling- Information science- Nerve network (re)configuration- Implants to monitor/generate signals-In-body sensor networks
Recovery fromNerve Damage
Challenges
Network Challenges Scarce spectrum
Demanding/diverse applications
Reliability
Ubiquitous coverage
Seamless indoor/outdoor operation
Device Challenges Size, Power, Cost
Multiple Antennas in Silicon
Multiradio Integration
Coexistance
Cellular
AppsProcessor
BT
MediaProcessor
GPS
WLAN
Wimax
DVB-H
FM/XM
Spectral Reuse
Due to its scarcity, spectrum is reused
BS
In licensed bands
eg Cellular eg Wifi
and unlicensed bands
Reuse introduces interference
Need Better Coexistence Many devices use the same radio band
Technical Solutions:
Interference Cancellation
Smart/Cognitive Radios
Software-Defined (SD) Radio:
Wideband antennas and A/Ds span BW of desired signals
DSP programmed to process desired signal: no specialized HW
Cellular
AppsProcessor
BT
MediaProcessor
GPS
WLAN
Wimax
DVB-H
FM/XM A/D
A/D
DSPA/D
A/D
Is this the solution to the device challenges?
Today, this is not cost, size, or power efficient
Cognitive Radios
Advanced Software radio concept Programmable platform
Work with various standards (universal terminal)
Dynamic spectrum usage Seeks spectrum holes
Share spectrum with primary users
Cognitive Radios
Cognitive radios can support new wireless users in existing crowded spectrum Without degrading performance of existing users
Utilize advanced communication and signal processing techniques Coupled with novel spectrum allocation policies
Technology could Revolutionize the way spectrum is allocated worldwide
Provide sufficient bandwidth to support higher quality and higher data rate products and services
Cognitive Radio Paradigms
Underlay
Cognitive radios constrained to cause minimal interference to noncognitive radios
Interweave
Cognitive radios find and exploit spectral holes to avoid interfering with noncognitive radios
Overlay
Cognitive radios overhear and enhance noncognitive radio transmissions Knowledge
andComplexity
Crosslayer Design
Application
Network
Access
Link
Hardware
Delay Constraints
Rate Constraints
Energy Constraints
Adapt across design layers
Reduce uncertainty through scheduling
Provide robustness via diversity
Main Points
The wireless vision encompasses many exciting systems and applications
Technical challenges transcend across all layers of the system design.
Cross-layer design emerging as a key theme in wireless
communications.