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Ch. 13: Wireless Networks


The Big Picture Is is widely believed that wireless networking is inevitable and the payoff could be fantastic The convenience of mobility is just too ... – PowerPoint PPT presentation

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Title: Ch. 13: Wireless Networks

Ch. 13 Wireless Networks
The Big Picture
  • Is is widely believed that wireless networking is
    inevitable and the payoff could be fantastic
  • The convenience of mobility is just too
  • The big issue is timing when will wireless pay
  • The technology problems can be daunting
  • How good is your wireless service right here in
    the Broomfield campus?
  • Only 95 of cell calls are successfully connected
    in the UK
  • Imagine trying to run a high-speed network using
    the same technology

Why Wireless?
  • We are increasingly mobile!
  • Terrain may not allow wired
  • Quick deployment
  • But
  • Low data rates
  • Interference, signal loss, noise, sniffing
  • Frequency reuse

What is Wireless?
  • When most IT professionals speak of wireless
    technologies today they are referring to mobile
    technologies that involve a cellular phone or
    some similar device (but.)
  • These can run over many different kind of
    cellular technologies (involving G3, GSM, GPRS,
    C/TDMA, MMDS, etc)

Wireless Networks
  • Terrestrial
  • Infrared, Packet radio networks
  • Terrestrial Cellular
  • Analog and Digital Cellular (AMPS, GSM), TDMA and
    CDMA and CDPD, PCS
  • Satellite
  • GPS, narrowband, broadband Geostationary, LEO

Wireless Transmission
  • transmission and reception are achieved by means
    of an antenna
  • directional
  • transmitting antenna puts out focused beam
  • transmitter and receiver must be aligned
  • omnidirectional
  • signal spreads out in all directions
  • can be received by many antennas

  • Modulation of incoherent infrared light
  • Wavelength 900 nm
  • Up to 2 Mbps
  • Does not penetrate walls

  • Omnidirectional and easily received
  • Broadcast radio
  • 30 MHz to 1 GHz - FM, UHF, VHF television
  • Mobile telephony
  • several bands below 1GHz
  • Wireless LAN
  • 2.4 GHz range for 11 MB to 525 (800) ft.

  • AMPS North and Latin America, China
  • Advanced Mobil Phone Service
  • First generation analog, ATT, 1970s
  • Second generation TDMA 31 channel gain
  • Third generation various tricks may get 101
  • GSM European standard spreading
  • Global System for Mobile Communications
  • Started as digital TDMA, 1990
  • Open standard, spreading, security features
    built-in (smart-card), including PCS bands, no
    modem data comm at 9.6kbps

  • Mobile
  • Base Transceiver
  • Mobile Switching Center
  • Spectral Allocation
  • Outbound (869-894 MHz)
  • Inbound (824-849 MHz)
  • 12.5MHz each direction/operator (30KHz apart)
  • 2 operators per market (to encourage competition)
  • 395 voice channels / operator (freq. Modulation)
  • used for bursts of control data
  • 21 channels for control / operator (10 kbps)

Spatial Allocation
  • Hexagonal tessellation (cells)
  • 6.5 to 13 km in size
  • Power limited
  • With only 395 channels, must reuse!
  • 10-50 frequencies used per cell
  • n7 is smallest pattern for isolation
  • N 395 / n 7 ? ? 57 frequencies / cell on
  • As you move handoffs

Frequency Reuse Patterns
Mobile Units
  • Frequency agile
  • ESN
  • Electronic Serial Number
  • 32-bit ID (oem assigned)
  • SIN
  • System ID Number
  • 15-bit ID (system assigned)
  • Can deduce roamer
  • MIN
  • Mobile ID Number
  • 34-bit ID (10-digit phone number)

Mobile Switching Center
  • Logon
  • Monitoring
  • Handling calls
  • Handoffs

  • Global System for Mobile communications
  • Not just a European Standard
  • In over 200 countries with 270 carriers
  • http//
  • http//

  • Generic handset/device
  • Subscriber Identity Module (smart card)
  • SIN, authorized networks, encryption, etc.
  • Transmissions are encrypted private! (Through
    the air, but not once it gets to land-lines!)

  • Subscriber
  • Base Transceiver
  • Base Station Controllers
  • handoffs, power levels, freq. assignments
  • Mobile Services Switching Center
  • H Home location register database
  • V Visitor location register database
  • A Authentication center database
  • E Equipment identity register database

GSM Layout
Spectral Allocation
  • 25MHz
  • (935-960MHz) base
  • (890-915MHz) mobile
  • Other similar systems use 1800 and 1900 MHz
  • But US uses DCS-1900 (1900MHz spectrum)
  • FDMA and TDMA
  • Traffic channels voice (13Kbps) or data
  • Slotted ALOHA protocol for control
  • FDM (124 carriers), TDM (8 parts)

  • Personal Communications Services
  • Frequencies auctioned by FCC (early 1995)
  • The biggest spenders were Wireless Co, L.P. (the
    alliance between Sprint and cable MSOs, including
    TCI, Cox, and Comcast), spending over 2.1B on 29
    licenses ATT Wireless PCS Inc., spending nearly
    1.7B on 21 licenses and PCS PRIMECO, L.P. (the
    alliance between RBOCsBell Atlantic, NYNEX, US
    West, and AirTouch), spending over 1.1B for 11
    licenses, total 7.1Billion
  • Smaller, cheaper, smarter, much lower power

  • Code Division Multiple Access initially a
    military technology for robustness, security
  • Gets at least 101 over AMPS FDMA

Code Division Multiplexing
  • Synchronized Communication
  • Convert messages using
  • Spreading Factor typically gt 100
  • Users Code
  • Filters simultaneous broadcasts
  • Qualcomm claims 10X over AMPS

Pre-CDMA cellular re-use
No similarly colored cells are adjacent, and
therefore there are no adjacent cells using the
same channel. While real systems do not ever look
like these idealized hexagonal tilings of a
plane, the seven-way reuse is typical of that
achieved in practice. The capacity of a K-way
reuse pattern is simply the total number of
available channels divided by K. With K7 and 416
channels, there are approximately 57 channels
available per cell. At a typical offered load of
0.05 Erlangs per subscriber, each site supports
about 1140 subscribers.
cdmaOne Cells
144 kbps packet data 1.25 MHz channel Moving
to 2 Mbps on 10MHz
Activity factor of voice is 35 !
CDMA Transmitted Data
CDMA Conventional Receiver
1-bit represented by subscribers code 1 1 1
1 1 1.
0-bit represented by inverse of subscribers
code -1 1 1 -1 1 1.
CDMA Example
  • Base Station Receiver decodes spread spectrum
    chip bits
  • Su(d) d1xc1 d2xc2 d3xc3
  • Su(d) large (absolute) value if d (data) came
    from subscriber u
  • Receiver receives 1-bit from A
  • dA(1) 1 1 1 1 1 1
  • dA(0) -1 1 1 -1 1 -1
  • As code is cA 1 1 1 1 1 1
  • SA(dA(1)) 1x1 -1x-1 -1x-1 1x1 -1x-1
  • 1 1 1 1 1 1 6
  • SA(dA(0)) -1x1 1x-1 1x-1 -1x1 1x-1
  • -1 -1 -1 -1 -1 -1 -6

Second CDMA Example
  • Receiver receives 1-bit from A
  • dA(1) 1 1 1 1 1 1
  • dA(0) -1 1 1 -1 1 -1
  • Attempt to decode with Bs code cB 1 1 -1 -1 1
  • SB(dA(1)) 1x1 -1x1 -1x-1 1x-1 -1x1
  • 1 -1 1 -1 -1 1 0
  • SB(dA(0)) -1x1 1x1 1x-1 -1x-1 1x1
  • -1 1 -1 1 1 -1 0
  • We know that the data is not from B

CDMA Forward Channels
Pilot Channel The pilot channel is used by the
mobile unit to obtain initial system
synchronization and to provide time, frequency,
and phase tracking of signals from the cell site.
Sync Channel This channel provides cell site
identification, pilot transmit power, and the
cell site pilot pseudo-random (PN) phase offset
information. With this information the mobile
units can establish the System Time as well as
the proper transmit power level to use to
initiate a call. Paging Channel The mobile unit
will begin monitoring the paging channel after it
has set its timing to the System Time provided by
the sync channel. Once a mobile unit has been
paged and acknowledges that page, call setup and
traffic channel assignment information is then
passed on this channel to the mobile unit.
Forward Traffic Channel This channel carries
the actual phone call and carries the voice and
mobile power control information from the base
station to the mobile unit.
CDMA Reverse Channels
Access Channel When the mobile unit is not active
on a traffic channel, it will communicate to the
base station over the access channel. This
communication includes registration requests,
responses to pages, and call originations. The
access channels are paired with a corresponding
paging channel. Reverse Traffic Channel This
channel carries the other half of the actual
phone call and carries the voice and mobile power
control information from the mobile unit to the
base station.
The information in a CDMA transmission is
digitally mixed with unique coding and spread out
over the entire 1.25 MHz carrier. Other
transmissions on the same frequency get the same
treatment, but with different codes. The effect
is that the carrier doesn't appear to be carrying
discrete transmissions at all - it's just filling
up with a kind of noise. This is what originally
made CDMA attractive to the military it's
difficult to intercept or jam wide-bandwidth
noise. (By comparison, an analog signal occupies
only 30KHz, but each call requires a separate
30KHz channel.) At the receiving end, the codes
are detected and removed, leaving the original
intelligible data bits. These ultimately become
sound (in the case of a voice call). When this
set of codes is applied to all the other spread
data present in the carrier, no translation takes
place (wrong code!) so that data is simply
ignored.The success of this call then becomes a
function of the signal-to-noise ratio. As more
calls are added to the carrier, the
signal-to-noise ratio changes, but interference
does not result... CDMA receivers convert the
desired (decoded) signal to digital frames which
can be carefully checked for errors, resulting in
clear, static-free call quality. The rest is
ignored. To stay synchronized, CDMA stations
need very accurate time signals, which they get
from the Global Positioning System (GPS).
While GSM divides up its frequency allotments
into small channels, and then time-shares those
channels, Code Division Multiple Access (CDMA)
lets everybody in the area use the same piece of
spectrum and separates the calls by encoding each
one uniquely. The analogy often used is the
international cocktail party - dozens of people
are in the room, all talking at once, and all
talking in different languages that you don't
understand. Suddenly, from across the room, you
hear a voice speaking in your own familiar
language, and your brain tunes out all the
background gibberish and locks onto to that one
person. Your brain understands the "code" being
used by the other person, and vice versa.CDMA
uses coding unique to your call and allows your
phone to disregard other transmissions on the
same frequency. CDMA base stations tell each
phone to adjust their volume to help hear these
Cellular Data Communications
  • Cell phone modems
  • Operate at 9.6kbps up to 14.4 -- sometimes!
  • Are not entirely compatible with ordinary modems
  • Are not necessarily standard and may not
    interoperate with other brands

Cell Phone Modem Use
  • Cellular Digital Packet Data
  • Standard packet architecture for North American
    cellular industry
  • Best for bursty data like E-mail, Credit card
    verification, ATMs, Query applications
  • Uses gaps in voice cellular network
  • CDPD channel is shared among all users in the

Example CDPD Network
Other Wireless Networking Technlogies
  • Fixed Wireless
  • 802.11b
  • Bluetooth
  • There are others, but these three are getting
    most of the big news

Fixed Wireless
  • Competes for the last mile customer
  • Operates in the 2.4 GHz range
  • Can provide DSL-like connectivity
  • Subject to bad weather and radio interference
  • Customer must be line-of-sight
  • May hit 2 million users by 2002

  • IEEE 802.11b is the current standard for
    11M-bit/sec business wireless LANs that operates
    in the 2.4-GHz spectrum range.
  • Used to replace or extend existing copper-based
    local networking
  • In an open cube environment with no walls range
    can be 200-500 feet.
  • With walls, 60-100 feet is realistic
  • Only uses 40-bit encryption (easy for Jr. next
    door to hack)

802.11? The Next Gen
  • IEEE 802.11g basically doubles the current speed
    to 22M bit/sec.
  • IEEE 802.11a, which will run in the 5-GHz band,
    will offer 20M to 24M bit/sec at 802.11b's
    current ranges.
  • HiperLAN/2, an international favorite, is also
    slated to run at 54M bit/sec speeds

Bluetooth Wireless Glue?
  • The PAN (personal area network)
  • Multiple devices share a single internet
    connection through a Bluetooth gateway
  • Could be your wrist watch
  • Serious security issues
  • Will your PDA need its own firewall?
  • Business model is very iffy at this point

  • http//
  • http//
  • Microchip with radio transceiver
  • 2.4 GHz band (doesnt require line-of-sight)
  • Frequency Hopping Spread Spectrum (1600/s?)
  • Built into digital devices
  • Eliminates need for cable connections
  • Creates pico network
  • 10m distance normal, 100m possible
  • Automatically adapts power usage (normal 1 mW)
  • Error correction, encryption, authentication
  • Gross data rate 1 Mbit/s, max data transfer 721
    56 kbit/3 voice channels, full-duplex data wrate
    within multiple piconet structure with 10 fully
    loaded independent piconets gt 6 Mb/s
  • 1300 mfgs on board (including Microsoft, 3Com,
    Intel, IBM, Lucent, Motorola, Nokia, Ericsson,
    and Toshiba)

  • Most of the US players use WAP (Wireless
    Application Protocol) for organizing and
    presenting the data
  • WAP is Open Standard
  • WML (Wireless Markup Language) is the lingua
    franca for WAP
  • iMode is a proprietary competitor to WAP
  • Developed by NTT DoCoMo in Japan
  • WAP is how the data is packaged, GSM (or
    whatever) is how the data is transported

Wireless Application Protocol
  • WAP Specifications include
  • Programming model
  • Based on WWW programming model
  • WML
  • Markup language, adheres to XML
  • Browser specification
  • Suitable for small, mobile terminals
  • Lightweight comm protocol stack
  • Framework for wireless telephony apps (WTAs)

WAP End-to-End Communication
IETF protocols for Internet Communications
WAP for Wireless Communications
Wireless Infrastructure
Requires WAP Gateway to manage the protocol
WAP Web Sites
  • http//
  • http//
  • http//

The J2ME Play
  • Java 2 micro edition (J2ME)
  • Targeted at consumer electronics and embedded
  • Consists of a virtual machine and a set of APIs
  • In wireless space the kvm is designed to work
    with devices in with 128-512 K of memory
  • Think Java Phone

(No Transcript)
  • Invented by Mari Matsunaga, considered by many to
    be amongst the most powerful women in business
  • Her degree was in French Literature
  • She had never used the Internet prior to 1997 and
    disliked cell phones prior to being hired by NTT
    in July 1997
  • She fought McKinsey consultants in a battle of
    heroic proportions
  • Her point Content is king make on traffic
    she hand-picked vendors
  • Their point logic trees charging everyone for
    everything open to all
  • She won. Big time. She left NTT last year and
    is now editor-in-chief of E-woman
  • No users on 2/99, 16,000,000 subscribers on
  • She is a hero in Japan her biography sold
    180,000 copies in 6 months
  • No one else has figure out how to make money on
    wireless yet!!!!

WAP vs. iMode
  • Open standards vs. Proprietary standard
  • Circuit switched (dial-up) vs. packet switched
    (always on)
  • Connection time charge vs. packet charge
  • 14.4 kbps vs. 9.6 kbps
  • WML vs. cHTML cute special characters

Terrestrial Radio Networks
  • Advanced Radio Data Information Systems
  • Joint enterprise of IBM and Motorola
  • 1,400 base stations (US), 90 of businesses
  • Interconnected via leased private network
  • RAM (BellSouth Wireless Data)
  • Uses Mobitex, an International radio packet data
  • 1,000 base stations in US, Intl connections
  • Interconnected in 6-level hierarchy in US

  • Global Positioning System
  • US Government system of 24 satellites
  • Receiver triangulates from 3 or 4 satellites
  • Government degrades standard signal to 15-25
    meter accuracy
  • Accurate to within about 1 centimeter with
    differential GPS -- compares with nearby fixed
    ground station (or now installed in orbit!)
  • See for a GPS tutorial.