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Wireless Communications EE5131 + EE6131

Intro Lecture

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Page 1: Intro Lecture

Wireless Communications

EE5131 + EE6131

Page 2: Intro Lecture

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!

Page 3: Intro Lecture

Outline

Module overview, assessment etc

Course Syllabi

Wireless past and present:

Current Wireless Systems

Emerging Wireless Systems

Design challenges for the future

Page 4: Intro Lecture

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

Page 5: Intro Lecture

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

Page 6: Intro Lecture

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

Page 7: Intro Lecture

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)

Page 8: Intro Lecture

Makeup Class

As there was no lecture Aug 8, there is a makeup class:Monday Sept. 19

E1-06-04

Page 9: Intro Lecture

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

Page 10: Intro Lecture

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, …

Page 11: Intro Lecture

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 …

Page 12: Intro Lecture

Current Wireless Systems

Wireless LANs

Cellular Systems

Satellite Systems

Zigbee radios

Ultrawideband

Page 13: Intro Lecture

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:

Page 14: Intro Lecture

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

Page 15: Intro Lecture

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

Page 16: Intro Lecture

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)

Page 17: Intro Lecture

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

Page 18: Intro Lecture

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

Page 19: Intro Lecture

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

Page 20: Intro Lecture

Cellular Networks

BSBS

PSTN

BS

San Francisco

New YorkMTSO MTSO

Internet

Page 21: Intro Lecture

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

Page 22: Intro Lecture

Cellular development

First generation (1G):

analog,

FDMA or TDMA

Second generation (2G):

Digital

TDMA or CDMA

Third generation (3G): CDMA

Analog to digital

Page 23: Intro Lecture

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

Page 24: Intro Lecture

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?

Page 25: Intro Lecture

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

Page 26: Intro Lecture

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.

Page 27: Intro Lecture

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

Page 28: Intro Lecture

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

Page 29: Intro Lecture

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

Page 30: Intro Lecture

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

Page 31: Intro Lecture

Emerging Systems

4th generation cellular (4G)

OFDMA is the PHY layer

Ad hoc/mesh wireless networks

Sensor networks

Distributed control networks

Biomedical networks

Page 32: Intro Lecture

Ad-Hoc/Mesh Networks

Peer to peer communications

No background infrastructure

Dynamic topology

Multihop routing

Page 33: Intro Lecture

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.

Page 34: Intro Lecture

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

Page 35: Intro Lecture

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.

Page 36: Intro Lecture

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

Page 37: Intro Lecture

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

Page 38: Intro Lecture

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

Page 39: Intro Lecture

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

Page 40: Intro Lecture

Spectral Reuse

Due to its scarcity, spectrum is reused

BS

In licensed bands

eg Cellular eg Wifi

and unlicensed bands

Reuse introduces interference

Page 41: Intro Lecture

Need Better Coexistence Many devices use the same radio band

Technical Solutions:

Interference Cancellation

Smart/Cognitive Radios

Page 42: Intro Lecture

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

Page 43: Intro Lecture

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

Page 44: Intro Lecture

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

Page 45: Intro Lecture

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

Page 46: Intro Lecture

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

Page 47: Intro Lecture

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.