Lecture 1: Introduction
Chapter 1
Introduction to Wireless
Communication Systems
Introduction
 “It is dangerous to put limits on wireless.” Guglielmo Marconi, 1932
 There has been tremendous growth in wireless
in the past 10 years. Even more in Europe and
Asia than North America
 Driven by technological advances – digital and
RF circuit fabrication improvements, large scale
circuit integration, miniaturization technologies,
digital switching
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 Driven by business investment – although
overinvestment has created bad profitability
recently.
 Driven by consumer demand – Regardless of
current business profitability, the growth rate in
terms of numbers of customers is substantial. The
ability to communicate wirelessly is of obvious
benefit to many. What are some of the benefits?
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I. History
 Wired Communications
 1834 - Gauss and Weber build telegraph system in
Germany
 1844 - Morse connects Baltimore and Washington by
telegraph
 1858 - First transatlantic telegraph cable laid
 1876 - Alexander Bell demonstrates telephone
 1911 - New York can telephone Denver
 Wireless Communications --Not so “new”
 Had slow growth at first compared to other inventions.
 But now is growing very rapidly.
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1899 - Marconi sends first radio message across Atlantic
1905 - Hulsmeyer detects ships with radar
1927 - US & Europe telephones linked by HF radio
1934 - AM mobile police radios for public safety widely
used
1935 - Edwin Armstrong demonstrates FM radio system,
became the primary modulation technique.
1940 - First microwave radar
1965 - First commercial communication satellite
1968 - AT&T proposes cellular phone system to Federal
Communications Commission (FCC)
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 1983 - FCC allocates spectrum for analog cellular service
(AMPS)
 1990 - GSM digital cellular service introduced in Europe
 1995 - FCC auctions new Personal Communication Service
(PCS) licenses in U.S. for digital services
 1998 - 40 million cellular phone users in U.S.
 2000 - In some countries, mobile users outnumber
conventional wireline customers.
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 2001 - 630 million subscribers worldwide (as compared
to 1 billion wired phone lines.
 2001 - Over 1% of worldwide wireless subscribers have
abandoned wired telephone service for home use.
 2005 − Over 130 million cellular phone users in U.S.
(out of population of 300 million including children).
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II. Frequencies
 RF - Radio Frequency
 1 MHz to 1 GHz - general classification, not absolute
 100 MHz to 1 GHz - more widely used definition
 Microwave
 1 GHz to 300 GHz - general
 1 GHz to 100 GHz - more widely used
 Trends towards use of higher frequencies
 greater signal bandwidth (BW) per channel
 more users and/or higher data rates
 but more difficult to design - more $$, more
engineering required
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III. Wireless Applications
 Mature
 Home Appliances - What devices are used that are
wireless?
 Communications
 fixed microwave (point-to-point or Line Of Sight) nearly 20,000 in U.S
 satellite to fixed ground stations (TV, phone, defense,
etc.)
 analog cellular : AMPS (FM) since 1980's
 paging
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 Emerging
 WLAN: Wireless Local Area Networks
 Mobile computers/email
 Wireless Local Loop (WLL)
 local phone service via wireless connection
 prominent in non-industrialized nations
 cheaper to install than wired lines
 new IEEE 802.16 standard has been developed for WLL.
 Wireless-enabled Personal Digital Assistants (PDAs)
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 Wireless Device Connectivity between computer
peripherals (printers, monitors, keyboards, etc.) Bluetooth
 Satellite to mobile ground units - Land Mobile
Satellite (LMS)
 Motorola/Iridium
 Digital Cellular/PCS
 PCS = Personal Communication Services
 Several types of services and capabilities are
offered
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 Radio Frequency Identification Tags (RFID’s) on
merchandize in warehouses and stores.
 Sensor networks – small devices wirelessly
communicating among themselves to monitor
environments using a variety of sensors.
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 FCC controls all usable Radio Spectrum allocates specific frequency bands for specific
uses
 Military
 Public safety and public service - Police, fire,
utilities, medical
 Commercial - To customers, between commercial
mobiles
 Unlicensed
 Amateur
 Etc.
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 SMR Bands - Specialized Mobile Radio
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Three 20 MHz bands from 800-900 MHz
Large number of radio system licenses nationwide
paging/messaging
voice dispatch - taxi, Police/Fire/Ambulance
data (UPS/Fedex)
 Extended SMR
 Nextel/Motorola partnership
 Nationwide coverage providing digital cellular/data
service
 Created by buying SMR licenses from a large
number of private radio service providers
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 ISM Bands - Industrial/Scientific/Medical
 902-928 MHz, 2400-2484 MHz, & 5725-5850 MHz
 “Garbage” bands
 spread spectrum modulation
 Transmit (Tx) power level < 1 W
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Remote meter reading
Wireless medical monitors
Digital cordless telephones
Big new application: Wireless Local Area Networks
(WLAN’s)
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 Cellular Phone
 AMPS: Advanced Mobile Phone System
 824-849 MHz
 Reverse Channel: Transmit from mobile to fixed
base station
 869-894 MHz
 Forward Channel: Transmit from base station to
mobile
 FCC mandated duopoly in Major Trading Areas (MTAs)
 MTA = 51 largest U.S. cities
 two providers per MTA
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 PCS Band
 1.8-1.9 GHz
 FCC Spectrum Auctions - $10 Billion!!
 1st time spectrum sold for $$ in U.S.
 It is has been hard for companies to recover this investment
 A & B blocks for Major Trading Areas (MTAs)
 duopoly like AMPS
 C, D, E, & F blocks - Basic Trading Areas (BTAs)
 BTA = 492 large rural areas (includes MTAs)
 Digital cellular phone service + PCS
 PCS = special services like messaging, caller ID, voice mail,
FAX, data, etc.
 Compete with analog cellular and SMR services combined
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V. Mobile Radiotelephony
 The focus of this course: mobile wireless
communications.
 Our predominant focus will be on mobile cellular
communications
 Historically voice communications, but also
incorporating data into newer generation systems.
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 But we will also take a substantial look at Wireless LAN’s
 Have grown quickly over the past couple of years.
 Are an important replacement opportunity for traditional
wiring in buildings.
 Some are trying to make them a competitor to cellular for
data communications.
 Cellular can or will provide 10’s to 100’s of kilobits
per second.
 But if one can connect to a Wireless LAN (either at
home/office or in public “hot spot” areas), 10’s of
Megabits per second are readily available
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 And below all of these technologies are important
radio transmission issues we need to study
 Radio signal propagation – signal strengths varies with
distance from the transmitter, but may also vary by large
amounts over a few centimeters
 Digital modulation – putting data on analog wireless signals.
 Compensation for fading – making channels more reliable
 Frequency reuse and sharing (multiple access techniques) –
making best use of spectrum to support multiple users.
 Sharing in the time, frequency, and code domains.
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 Early mobile phone systems used a high power
Tx to cover a large spatial area (R = 50 km)
 Half-duplex (HDX) operation
 two-way communication using same radio channel
 transmit or receive only at a given time (HDX)
 “push-to-talk” system - CB radio
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 Allocated spectrum determines maximum # of
simultaneous users
 e.g., 10 MHz allocated BW with 100 kHz channels
= 100 simultaneous users/market
 Demand was great in large cities and this led to
poor service (many blocked calls)
 Spectrally inefficient system
 allocated spectrum supports small # of users
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 In 1976, Bell Mobile Phone Service only had
12 channels for all of New York City (10
million people), which could acceptably only
support 543 customers.
 Acceptable service - Certain probability of not
being able to make a call (i.e., be "blocked")
 Given the # of customers, average calling load per
customer, # of channels → can compute blocking
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 Cellular Concept - break coverage area (market) into
many small cell (many transmitters) where each nonadjacent cell will reuse different portions (not all) of
allocated spectrum
 Increase spectrum efficiency
 many users share same channels
 Increase in required system infrastructure (base stations)
 more capital costs to provide adequate coverage
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BASE
STATION
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 Advanced Mobile Phone System (AMPS) spectrum
allocated by FCC in 1983
 Full duplex (FDX) operation : simultaneous two-way
communication
 two 30 kHz channels (forward & reverse)
 Two providers for each market - duopoly
 limited competition
 Analog frequency modulation (FM) used exclusively
 Frequency Division Multiple Access (FDMA)
 one channel per pair of users
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 USDC: U.S. Digital Cellular proposed in 1991
(D-AMPS or IS-54)
 Replace single user analog channel with digital
channels that support 3 users/30 kHz channel BW
 User capacity is 3 times greater than AMPS - more
provider revenue ($$)
 Digital modulation & speech coding allow Time
Division Multiple Access (TDMA)
 3 users share one channel by using different time slots
 This service is provided under the title "Digital
Cellular"
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VI. Mobile Radio Terminology
 Table 1.4, pg. 10 - everyone is responsible for these
definitions
 Mobile: high speed motion (e.g. cell phone in car)
 Portable: low speed motion (cordless phone in home,
walking)
 Mobile Unit = subscriber unit = user communication device
 Transmitter (Tx) and Receiver (Rx)
 Base Station: Tx/Rx on tower at center of cell that provides
service to group of mobile users
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 Forward/Reverse Channels (a.k.a. downlink/uplink)
 Forward: From base station to mobile
 Reverse: From mobile to base station
 Simplex (SX), Half Duplex (HDX), & Full Duplex
(FDX)
 Frequency Division Duplexing (FDD) - Using two
separate frequency bands to provide both sides of the
duplex operation
 Example: AMPS uses 824-849 MHz for reverse channel
and 869-894MHz for forward channel
 PSTN: Public Switched Telephone Network
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VII. Paging Systems
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One-way communication (SX)
Send short message to mobile unit (pager)
Wide area coverage
Page broadcast from many base stations
simultaneously to remote units
 no information as to user location
 Reliable communication everywhere (need good
Signal to Noise performance)
 Requires large Tx power and low data rate (~ 2-8 kbps)
 Noise has less of an effect when the data rate is lower.
 Coverage needed even inside buildings w/ 20-30 dB signal
attenuation
 Needs an extensive network of transmitters to transmit the
signal everywhere
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VIII. Cordless Telephone Systems
 Primarily in-home use
 Use ISM bands – 900 MHz most popular for a while, now
2.4 GHz is common and 5.8 GHz is available.
 Low power, limited range (~ 100 m) and coverage, and
limited mobility
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IX. Cellular Telephone Systems
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 Large geographic coverage
 Limited frequency spectrum – a surprisingly
low amount of spectrum has been allocated for
a service with such popularity.
 High user mobility
 High system capacity - Large # of simultaneous
users
 obtained by limiting coverage of each base station
to small area (cell)
 frequency spectrum can be reused by other nonadjacent cells in network
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 Base station
 serves mobile users in each cell
 bridge between mobile unit and MSC
 connected to MSC via phone line (for example,
T1 of 24 channels or T3 of 672 channels) or
Line of Sight microwave link
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 MSC: Mobile Switching Center
 controls base stations, call initiation & routing, handoffs, etc.
 connects cellular system to Public Switched Telephone
Network (PSTN)
 cellular network brains:
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call initiation/setup
base station handoffs
controlling power levels in mobile units
billing information
roaming user ID and verification
 Typically handles 5000 simultaneous calls supporting
100,000 cellular subscribers (at most 5% of subscribers are
assumed to be active at anyone time)
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 Common Air Interface (CAI)
 Standard mechanism used by all mobiles.
 Defines 4 different channels to be used by a mobile
unit
 Forward/reverse voice channels - FVC/RVC
 Full Duplex communication
 Forward/reverse control channels - FCC/RCC
 call initiation & setup
 makes up 5% of total # of available channels
 One cell contains 10 to 60 voice channels and only
1 to 3 control channel pairs (F+R)
 MSC broadcasts call request from PSTN over all
FCC's of all base stations – to find the mobile user
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 There are two ways to keep mobiles “connected” to the
best base station
1. Mobile unit monitors FCC's looking for strongest base
station (closest) and incoming call
 if FCC signal < acceptable level - mobile looks for
another base station
 neighboring base stations must use same frequencies for
FCC/RCC
 handoff from one base station to another occurs when
FCC signal is less than an acceptable level
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2. Base stations (current server + adjacent stations) monitor
RCC and report mobile unit signal strength to MSC
(analog AMPS system)
 if RCC signal < acceptable level - MSC initiates handoff
to one of neighboring base stations
 neighboring base stations must use different frequencies
for FCC/RCC
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 Cellular Phone Call Timing
 Mobile Identification Number (MIN) is the
subscriber's telephone number
 Electronic Serial Number (ESN) is device identifier.
 Station Class Mark (SCM) identifies the class of the
device, based on its maximum transmit power level.
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