Lecture 1: Wireless communications systems

Aliazam Abbasfar

OutlineCourse Information and policies

Course Syllabus

Communication Systems

Design Challenges

Course InformationInstructor : Aliazam Abbasfar

abbasfar@ece.ut.ac.ir Office Hours : Sa-Tu

Classes ?

Grading: HWs 10%, Midterm 60%, Project 30%

Prerequisites: Digital Communications

Class policiesExam dates are fixed (No make-up exams)

Midterm: TBDFinal: 88/11/7

Academic honestyHW should be your own work

Turn off your cell phones during lectures

Course Syllabus Overview of Wireless Communications (1) Wireless propagation (4) Diversity (6) Narrowband/Wideband Modulation (6) Spread Spectrum Techniques (4) Multiple access techniques (2) Cellular concept/standards (3) Multiple Input/output Systems (MIMO) (4) Wireless Networks and Resource Management

(1)

References David Tse and Pramod Viswanath,

Fundamentals of Wireless Communications, Cambridge University Press, 2005

Andrea Goldsmith, Wireless Communications , Cambridge University Press

Theodore S. Rappaport, Wireless communications, principles & practice, Prentice Hall, 1996

A.R.S. Bahai, B.R. Saltzberg, M. Ergen, “Multi-Carrier Digital Communications, Theory and Applications of OFDM,” 2nd Ed., Springer 2004

R. Peterson, R. Ziemer, D. Borth, Introduction to Spread Spectrum Communications, Prentice Hall, 1995.

Communication started in wireless form smoke/torch/flash signaling

Modern communication goes back to Telegraph (Morse 1837) wireline communications digital replaced old technologies

Telephone (Bell 1876) introduced telephony Analog communication wireline

Radio transmission was born decades later (Marconi 1895)

Radio technology has been growing rapidly ever since longer distances with better quality less power, and smaller, cheaper equipments

Communication systems overview

Reliable (electronic) exchange of information Voice, data, video, music, email, web pages, etc

Communication Systems Today Radio and TV broadcasting Public Switched Telephone Network (voice, fax, modem) Computer networks (LANs, WANs, and the Internet) Cellular Phones Satellite systems (TV broadcast, voice/data , pagers) Bluetooth/wireless devices Sensor networks

Communication Systems

AM radio broadcast started in 1920E. Armstrong invented super heterodyne

AM receiverFM was invented in 1933

TV broadcast Commercial TV began in London (BBC 1936)FCC authorized TV bands in 1941

Satellite broadcast servicesRapid migration to digital broadcast

Radio and TV broadcasting

Satellite types: Geosynchronous (GEO) 40,000Km Medium-earth orbit (MEO) 9000 Km Low-earth orbit (LEO) 2000 Km

GEOs first suggested in a sci-fi book (A.C. Clark 1945) First deployed satellites

No Geo Soviet Union’s Sputnik in 1957 NASA/Bell Laboratories’ Echo-1 in 1960 Telestar I was launched in 1962

Relay TV signals between US and Europe First commercial Sat (Early Bird – 1965)

GEOs Wide coverage Good for downlink broadcast no good in uplink (high power) large delay (bad for voice service)

Satellite systems

LEOs Lower power Smaller delay Need many satellites

Shift towards LEOs in 1990 Global domination Compete with cellular systems Failed miserably (Iridium )

Big, power hungry mobile terminals

Natural area for satellite systems is broadcasting Now operate in 12GHz band 100s of TV and radio channels All over the world

Global Positioning System (GPS) Satellite signals used to pinpoint location Popular in cars, cell phones, and navigation devices

Satellite systems

LAN/Ethernet technology in 1970 wireline was popular again 10 Mbps data rate far exceeded anything available

using radio

Wireless LAN was enabled by ISM band (FCC 85) No license – free band But, must have low power profile resulted in high costs ($1400 vs $200 Ethernet)

Wired Ethernets today offer data rates over 1 Gbps Performance gap between wired and wireless LANs is

likely to increase over time Additional spectrum allocation might help

WLANs are preferred due to their convenience freedom from wires

Communication networks

Provides high-speed data within a small region

1G : 26 MHz spectrum - 900 MHz ISM band Data rate : 1-2 Mbps No standard Not very successful

2G : 80 MHz spectrum - 2.4 GHz ISM band Data rate : 1.6 Mbps (raw data rates of 11 Mbps) IEEE 802.11b standard Direct sequence spread spectrum range : 150m

IEEE 802.11a wireless LAN standard operates with 300 MHz of spectrum in the 5 GHz U-NII band.

Data rate : 20-70 Mbps multicarrier modulation

European counterpart : HIPERLAN Type 1, is similar to the IEEE 802.11a wireless LAN standard

Wireless LAN overview

802.11n is the latest WLAN standard Close to finalization Operates in 2.4 and 5.0 GHz ISM bands Adaptive OFDM technology MIMO technology (2-4 antenna) Data rates up to 600 Mbps Range 60 m

Wimax (802.16) : Wide area wireless network standard System architecture similar to cellular Hopes to compete with cellular OFDM/MIMO is core link technology Operates in 2.5 and 3.5 MHz bands Different for different countries, 5.8 also used. Bandwidth is 3.5-10 MHz Fixed (802.16d) : 75 Mbps max, up to 50 mile cell radius Mobile (802.16e) : 15 Mbps max, up to 1-2 mile cell radius

Latest standards

The most successful application of wireless networking It began in 1915, wireless voice transmission between New

York and San Francisco 1946 public mobile telephone service in 25 cities across US

Initial systems used a central transmitter to cover an entire metropolitan area limited capacity

the maximum # of users was only 534 (30 years after first link)

Solution came in 50's and 60's (Bell Labs) Cellular concept Frequency reuse

First cellular system deployed in Chicago in 1983 Analog system Very popular - already saturated by 1984

Cellular systems

2nd Generation (2G)Digital communicationsHigher capacityMore services (voice, data, paging)

So many competitorsOnly 3 standards in US!GSM is most popularMulti-mode devices

3GBased on CDMA technologyWCDMA and CDMA2000

4G ?

Cellular systems

Cable replacement RF technology (low cost)Short range (10m, extendable to 100m)2.4 GHz band (crowded)1 Data (700 Kbps) and 3 voice channels, up

to 3 Mbps

Widely supported by telecommunications, PC, and consumer electronics companies

Few applications beyond cable replacement

Bluetooth

Optimized for one-way communicationsShort messagingMessage broadcast from all base

stationsSimple terminalsMostly replaced by cellular

Similar systemsElectronic shelf labels

Paging Systems

7.5 Ghz of “free spectrum” in US (underlay)

High data rates, up to 500 Mbps

UWB is an impulse radio: sends pulses of tens of picoseconds(10-12) to nanoseconds (10-9)Duty cycle of only a fraction of a percent

A carrier is not necessarily neededMultipath highly resolvable: good and bad

Limited commercial success to date

Ultra wideband Radio (UWB)

Low-Rate WPANData rates of 20, 40, 250 KbpsSupport for large mesh networking or star

clustersSupport for low latency devicesCSMA-CA channel accessVery low power consumptionFrequency of operation in ISM bands

IEEE 802.15.4 / ZigBee Radios

Information exchange between people and/or devices, anywhere, anytime home applications : new intelligent devices that

interact with each other (smart homes) connectivity between business machines; phones,

computers, servers, etc Wireless entertainment : provide wireless access to

multi-media contents Wireless internet access Wireless sensor networks Automated cars – UAVs In-body networks

Cannot pick a segment for success, but foresee a bright future for the whole industry

Wireless vision

We will have many different systems and standards Different segments have different specs

Multimedia Requirements

QoS depends on the application Rate and delay requirements Requires cross layer design

Future systems

Voice Data Video

Data rate 8-32 Kbps 1-100 Mbps 1-100 Mbps

BER 10-3 10-6 10-6

PER < 1% 0 < 1%

Delay < 100ms - <100ms

Traffic Continuous Bursty Continuous

Wireless evolution

Rate

Mobility

2G

3G

4G

802.11b WLAN

2G Cellular

Other issues:Coverage

Latency Cost Energy

802.11n

Wimax/3G

System constrains Rate, delay, energy

System optimization System adaptation (link, MAC, network, application) resource management Scheduling

Data prioritization Resource reservation Access scheduling

Achieve robustness by using diversity Link diversity (antenna, channel) Route diversity

Power control

Cross layer design

Wireless channels are a difficult and capacity-limited broadcast communications medium

Traffic patterns, user locations, and network conditions are constantly changing

Applications are heterogeneous with hard constraints that must be met by the network

Energy and delay constraints change design principles across all layers of the protocol stack

Design challenges

Ad hoc/mesh wireless networks flexible/ (robust) network infrastructure Indoor/outdoor Cellular/LAN integration

Cooperative networksMaximize network capacityRelay nodesNetwork coding

Cross layer design critical

Emerging technologies

For data collection and distributed control

Hard energy/delay constraint Each node sends only finite number of bits Energy/delay trade offs

Nodes cooperate in transmission, reception, and processing

Optimization for node/network lifetime Design nodes cooperation Completely new framework

Must consider TX, RX, and processing

Wireless sensor networks

UnderlayCognitive radios cause minimal

interference to primary users

InterweaveCognitive radios find spectral holes

OverlayCognitive radios overhear and enhance

noncognitive radio transmissions

Cognitive Radio

Spectral Allocation by ?Worldwide spectrum controlled by ITU-R

Plays a key role in communication sector growth

Allocation strategies Dedicated/public band Auction bands Overlay/Underlay Cognitive radios

Innovations are still needed

Spectrum Regulation

The wireless vision encompasses many exciting systems and applications

Technical challenges in all layers of the system

Cross-layer design emerging as a key theme in wireless

Existing and emerging systems provide excellent quality for certain applications but poor interoperability.

Standards and spectral allocation heavily impact the evolution of wireless technology

Summary

ReadingCarlson Ch. 1

Proakis Ch. 1