TLMN 645 Fall 2002 CLASS 4

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TLMN 645 Fall 2002CLASS 4

• CELLULAR
• PCS

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SPEECH CODERS
Source Coding
20 milliseconds frame
(260 bits)
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From Class 3 FA02Voice Codecs (A variety)
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From Class 3 FA02 CELLULAR/PCS TRANSMISSION
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CELLULAR EVOLUTION

• 1950, 1960s One antenna (Example New York City
  12 channels for telephone (no automatic trunking)
• Bell Labs proposes cellular in 1968
• not implemented because?

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PRINCIPLES OF CELLULAR

• 1.
• 2.
• 3.
• 4.
• 5.
• 6.

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How Cellular Works

• A cellular telephone system provides a wireless
  connection to the Public Switched Telephone
  Network (PSTN) for any user in the radio range of
  the system. It consists of
• mobile stations
• base stations
• the Mobile Switching Center (MSC)
• The base station is the bridge between the mobile
  users and the MSC via telephone lines or
  microwave links.
• The MSC connects the entire cellular system to
  the PSTN in the cellular system.

PSTN
MSC
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How Cellular Works

• Two-Way Cellular Communication relies on a
  variety of channels to ensure call connection and
  delivery.
• Control Channels Channels used as beacons for
  idle mobiles and access to traffic channels.
• Traffic Channels Channels used to support
  customer voice calls and messages.
• Signaling Channels Channels used to provide
  network and hand-off signals during customer
  communications.

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Cellular Power

• BASE Stations
• BSAs 100 - 500 watts
• MSAs 20 - 100 watts
• Mobiles
• .006 to 4 watts

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HANDOFF
S/N17 dB
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Handoffs

• Hard Handoffs
• Channel in current cell taken down before
  channel in new cell is established
• consequences
• loss of information

• Soft Handoff
• Simultaneous channels established at multiple
  base stations
• strongest signal utilized
• ( used with CDMA)
• Consequences
• channels not utilized most efficiently since
  multiple channels being used simultaneously for
  single message

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FREQUENCY REUSE
D/R 4.6 for S/I17 dB
N 7
R
D
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CELLULAR HISTORY

• 1983 FCC allocation
• 306 Metropolitan Statistical Areas (MSAs), 424
  Rural Statistical Areas
• A Carrier (non-wireline)
• B Carrier (local phone)

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AMPS STANDARD

• 30 kHz chs. 50 MHz spectrum
• analog voice, FDMA
• 416 channel pairs/ carrier
• mobile to base 824-849 MHz
• base to mobile 869-894 MHz

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Calculation
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Homework Problem

• Do problem 15 in Stallings p. 337.
• Doing this problem will really show you
  understand the concepts of the course thus far.

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PCS Personal Communication Service

• 2nd Generation Wireless
• FCC definition radio communication that
  encompasses mobile and fixed communications to
  individuals and businesses that can be integrated
  with a variety of computer networks
• Digital signalling
• Licensed by auction

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Sprint Block B (DC)Current Coverage
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Frequency Reuse
Analog systems require a carrier to interference
ratio (C/I) of greater then 18dB which
requires reuse factor of 1/7. Most digital
systems require a C/I of 12dB (because of error
correction), allowing a reuse factor of
1/3-1/4. CDMA however, uses the same frequency
spectrum in all cells, thus ideally allowing a
reuse factor of 1 Really 1/(1.55)
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Frequency Reuse
Frequency reuse patterns for (a) 3 frequencies
(Digital systems), (b) 7
frequencies (Analog FDMA), (c) CDMA
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Capacity Comparison
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Lattice Tower

• 60-200 feet high
• Accommodate a number of wireless industry users

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Monopole

• 25-125 feet high
• Base dia of 3 feet tapering to the top at 1.5
  feet
• Supports any combination of Whip, Panel or Dish
  antennas

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Flower Tower

• Integration of Monopoles
• into existing Light poles

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Mounting of Antennas
Building Mounted
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Microwave or Radar Towers
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Fake Trees
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Real Trees
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Diversity Techniques

• Diversity is based on the fact that individual
  channels experience independent fading events
• Space diversity techniques involving physical
  transmission path
• Frequency diversity techniques where the signal
  is spread out over a larger frequency bandwidth
  or carried on multiple frequency carriers
• Time diversity techniques aimed at spreading
  the data out over time

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Three Sector Base StationDiversity Reception
n11h/D
R1A
R1B
hheight (ft)
D distance between antennas (ft)
TA
TB
R2A
R2B
TC
R2C
R1C
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Base Station InfrastructureDiversity Reception
RECEIVER A
Transceiver
Mobile AUDIO out
RECEIVER B
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Cordless Telephone

• Analog cordless
• Power 20 microwatts
• Digital cordless
• Utilizes 32 kb/s speech (toll quality)
• operates in 902-928 MHz (moving to 2.4 GHz)
• 1 watt power
• 240 channels available
• spread spectrum frequency hopping

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Churn
Source Canners In-Stat Group
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Wireless as a Commodity

• Commodities are defined as products that are
  differentiable on price alone. They are generally
  available from a wide variety of providers who
  sporadically share market superiority when they
  find themselves offering the lowest price.
  (Shepard, 2000)
• Is this true of cellular/ PCS? What other factors
  affect the purchasers descision?