ECEN 478: Wireless Communications
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ECEN478, Cui
Lecture Outline
n  Course Basics
n  The Wireless History
n  Spectrum Regulation
n  Standard bodies
n  Current Wireless Systems
n  Emerging Wireless Systems
n  Technical Challenges
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ECEN478, Cui
Course Information
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Instructor: Shuguang (Robert) Cui
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Email: cui@ece.tamu.edu
Phone: 862-7957
Office: WERC 301G
Website: http://ece.tamu.edu/~cui
Office Hours: 2:00~ 2:30pm, Wed, or by appointment
Class website: http://ece.tamu.edu/~cui/ECEN478
Class time and location: MWF 11:45~12:35, BLOC 457
Prerequisite: Probability; Signal and Systems
n  Textbook: Andrea Goldsmith, Wireless Communications,
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Cambridge University Press, 2005.
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ECEN478, Cui
Course Information: policies
n  Exams and homework
n  Two exams
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Weekly homework assignments
n  Grading Policy
n  Homework 20%
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Quizzes and class participation 10%
Midterm 25%
Final 45%
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ECEN478, Cui
Course Outline
Overview of Wireless Communications
Path Loss, Shadowing, and Fading Models
Capacity of Wireless Channels
Digital Modulation and its Performance in Fading
n  Diversity
n  MIMO Systems
n  Multiuser Communications
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ECEN478, Cui
Wireless vs. Wired: why are we special?
n  No wire: more freedom, more troubles!
n  Random fading channels
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Path loss, shadowing, multipath, moving objects
n  Unwanted
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interferences
Open medium with limited spectrum
n  Don’t forget those common problems:
n  Noise
n  Finite
bandwidth: inter-symbol interferences (ISI)
n  Different link layer, different networking needed
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What is the oldest wireless system?
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Smoke signal (how to transmit more information?)
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ECEN478, Cui
Wireless History (1)
n  Ancient systems: smoke signals, semaphore flags, …
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Some are still being used: e.g., semaphore flags between
ships
n  Thousands of years without breakthrough
n  Electromagnetic wave propagation theory developed in 1860’s
and summarized by Maxwell, demonstrated later by Hertz
n  First radio transmission in the 1896 by Marconi (or 1893 by Tesla)
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Systems are of low frequency, high power, huge size,
expensive, and largely mechanical
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The development is first boosted by the invention of vacuum
tubes in 1906 by De Forest: the start of electronic age
Surprisingly, the 1st transmission is digital, and the early steps of electronic age were
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driven by the need of wireless communications, not by wired systems or computers.
ECEN478, Cui
Wireless History (2)
n  Some names to remember in the early days
(1890’s to 1930’s):
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Q1: Who invented radio?
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A1: Nikola Tesla, Guglielmo Marconi
n  Q2:
Who invented amplitude-modulated (AM)
radio?
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A2: Reginald Fessenden and Lee de Forest.
n  Q3:
Who invented frequency-modulated (FM)
radio?
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A3: Edwin H. Armstrong and Lee de Forest.
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ECEN478, Cui
Wireless History (3)
n  Systems with vacuum tubes are still huge, power hungry, and
not stable
n  The real first engine of electronic age: transistor was invented
by William Shockley et al., in the period of 1948-1951.
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Communication hardware was revolutionized for the second
time (a big one)
n  Another revolution came in the same time: information theory
initiated by Claude Shannon in 1948.
n  Golden age of information theory: 1948~1960’s, then somehow
faded: the theorems developed were far too complicated to
implement at that time
n  Many sophisticated military radio systems were developed
during and after WW2
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ECEN478, Cui
Wireless History (4)
n  The third revolution for communication hardware: integrated
circuit (IC) was invented in 1958 by Jack Kilby (independently by
Robert Noyce in 1959), developed in 1960’s and continued
exponential growth since then
n  Another driving force of wireless systems: mobile phone
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First trial was in 1915, between New York and San Francisco
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Commercial networks start at 1946
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Take off in 1980’s due to the Cellular concept, with more
than 5 Billion subscriptions today
n  Many new systems proposed in 1990s, great failures around
2000
n  Now many standards still coexist currently
n  The forth revolution: smart phones and tablets
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ECEN478, Cui
Spectrum Regulation
n  Spectral Allocation in US controlled by FCC
(commercial)
n  FCC auctions spectral blocks for set applications.
n  Some spectrum set aside for universal use
n  Worldwide spectrum controlled by ITU-R
Regulation can stunt innovation, cause economic
disasters, and delay system rollout
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Standards
n  Interacting systems require standardization
n  Companies want their systems adopted as standard
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Alternatively try for de-facto standards
n  Standards determined by TIA in US
IEEE standards often adopted
n  Process fraught with inefficiencies and conflicts
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n  Worldwide standards determined by ITU-T
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Standards for current systems are summarized in Appendix D.
ECEN478, Cui
Current Wireless Systems
n  Cellular Systems
n  Satellite Systems
WAN
n  Wireless broadband access (WiMax-compatible)
n  Radio broadcast (analog/digital audio/video)
MAN
n  Paging Systems (one way, two way)
n  Cordless phone, PHS
n  Wireless LANs (WiFi)
n  Bluetooth
n  Zigbee radios
LAN
PAN
n  Infrared wireless optical (IrDa); RFID/NFC
n  Ultra-wideband radios
n  Special purpose: Remote control, radar, sonar, missile guidance,
…,etc
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ECEN478, Cui
Cellular Systems:
Reuse channels to maximize capacity
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Geographic region divided into cells
Frequencies/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
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Cellular Phone Networks
San Francisco
BS
BS
Internet
MTSO
PSTN
New York
MTSO
BS
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ECEN478, Cui
Cellular phone: development trend (1)
n  Macrocell to microcell:
n  Macrocell: diameter ~ 1 mile
n  Microcell:
diameter ~100 meters
n  Support more users, reduce power, reduce phone
size
n  Can we shrink the size without limit?
Cost of BSs
n  Control signaling overhead
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Cellular phone: development trend (2)
n  Analog to Digital
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Digital: improve quality, increase capacity, reduce phone size,
facilitate data management (for both the network and the user),
provide security…
First generation (1G): analog
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2G: digital
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TDMA: DAMPS (IS-136, USA), GSM (Europe =>Asia, USA)
CDMA: PCS (IS-95, USA, Qualcomm)
3G: digital (another doomed ending of an universal system)
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FDMA: AMPS (USA, still being used today), TACS (Europe)
WCDMA (UMTS): Europe, Asia
CDMA2000: Qualcomm
TD-SCDMA: China (Da Tang Telecom)
3.5G: Long-Term Evolution (LTE) and WiMAX (IEEE 802.16.e)
4G (IMT-Advanced): LTE-Advanced and WirelessMAN-Advanced
(IEEE 802.16m)
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5G and beyond: no standards yet
ECEN478, Cui
Cellular phone: development trend (3)
n  Voice to Data
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1G: pure voice
2G: voice + SMS
2.5G: voice+ MMS+ Data
n  TDMA: GPRS (140kbps), EDGE (384kbps)
n  CDMA: IS-95 + EVDO
3G: voice + MMS + Data dominant
n  Date rate: 144kbps for vehicular user; 383kbps for
pedestrian user; 2Mbps for stationary user
n  WCDMA: HSPDA (up to 14 Mbps over 5MHz BW)
n  CDMA-2000: 1xEVDO Rev 0, 1xEVDO Rev A, nxEVDO
4G: all-IP traffic with peak rate 1Gbps (LTE-A)
5G and beyond: 60Ghz? Massive MIMO? C-RAN?
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ECEN478, Cui
Wireless LAN
01011011
0101
1011
Internet
Access
Point
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WLANs connect “local” computers (100m range)
Breaks data into packets
Channel access is shared (random access)
Backbone Internet provides best-effort service
¨  Poor performance in some apps (e.g., video)
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ECEN478, Cui
WLAN Standards: WiFi (current)
n  802.11b
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Standard for 2.4GHz ISM band (80 MHz)
CDMA
1.6-10 Mbps, 500 ft range
n  802.11a
Standard for 5GHz NII band (300 MHz)
OFDM
Up to 54 Mbps
Similar to HiperLAN in Europe
n  802.11g
n  Standard in 2.4 GHz, compitable with 11b
n  OFDM
n  Speeds up to 54 Mbps
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Currently
most new
WLAN
cards have all 4
standards
n  802.11n (MIMO enhancement, up to 150 Mbps)
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n  802.11ac (MU-MIMO+BW enhancement, up to several Gbps)
ECEN478, Cui
WLAN standards (extension)
n  802.11e: enhance QoS
n  802.11i: enhance security
n  802.11r: support roaming
n  802.11s: enhance MESH function
n  More working groups
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Satellite Systems
n  Motivated by Clarke’s science fiction novel
n  Different orbit heights
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GEOs (39000 Km):
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large coverage, high launching cost, large delay
Good for one-way transmission:
§  Radio (XM, DAB) and TV broadcasting
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LEOs (2000 Km)
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Small coverage, low launching cost, small delay
Ok with two-way transmission
n  Most two-way systems struggling
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Expensive alternative to terrestrial system
Famous Iridium System for Cellular (bankrupt)
Counterpart WiFi system emerging (Sat-Fi by GlobalStar)
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ECEN478, Cui
Ideal Wireless Engineering Dream:
Iridium System
n  66 cross-linked LEO satellites
n  Designed to compete with landn
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based cellular systems
Universal global coverage
Great technology vs. bad business
model
Went bankruptcy but part of the
network still working (main
customer: USA DoD)
Phones:
1616-1626.5 MHz, L-band
n  4.2 lbs
n  Now providing data modem service
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ECEN478, Cui
IEEE 802.15.1/Bluetooth
n  Named after an ancient King in Europe
n  Cable replacement RF technology (low cost)
n  Short range (10m, extendable to 100m)
n  2.4 GHz band (crowded)
n  1 Data (700 Kbps) and 3 voice channels
n  Widely supported by telecommunications, PC,
and consumer electronics companies
n  Extensions: Bluetooth 2 and Bluetooth 3
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8C32810.61-Cimini-7/98
ECEN478, Cui
IEEE 802.15.4 / ZigBee Radios
n  Low-Rate WPAN
n  Data rates of 20, 40, 250 kbps
n  Star clusters or peer-to-peer operation
n  Support for low latency devices
n  CSMA-CA channel access
n  Very low power consumption
n  Frequency of operation is in ISM bands
Focus is primarily on radio and access techniques
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ECEN478, Cui
Emerging Systems
n  Ad hoc wireless networks: infrastructure-less
n  Sensor networks (Internet of things): energy
driven
n  Distributed control networks: hard delay and
reliability requirement (automated highway)
n  Cognitive radios: new paradise of spectrum use
n  Green radios: more environment friendly
n  60GHz communication: for 5G?
n  Nano wireless systems: medical purpose
n  Wireless power/info transmissions: new
paradigm
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ECEN478, Cui
Future Wireless Paradigm
Ubiquitous Communication Among People and Devices
Wireless Internet access
Nth generation Cellular
Wireless Ad Hoc Networks
Sensor Networks
Wireless Entertainment
Smart Homes/Spaces
Automated Highways
All this and more…
• Hard Delay Constraints
• Hard Energy Constraints
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ECEN478, Cui
Design Challenges
n  Wireless channels are a difficult and capacity-limited
broadcast communications medium
n  Traffic patterns, user locations, and network conditions
are constantly changing
n  Applications are heterogeneous, some with hard
constraints that must be met by the network
n  Energy and delay constraints change design principles
across all layers of the protocol stack
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ECEN478, Cui
Key Techniques
n  Diversity techniques
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Link diversity (space, time, frequency)
Access diversity
Routing diversity
Application diversity
Content location/server diversity
n  Multiplexing
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Traditional: FDMA, TDMA, CDMA
Spatial multiplexing (MIMO, MU-MIMO/SDMA)
Frequency multiplexing (OFDM, multi-carrier)
n  Adaptive techniques
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Link, MAC, network, and application adaptation
Resource management and allocation (power control)
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