PCS

Introduction to Personal
Communications Systems (PCS):
What’s PCS and its Principles

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 What’s PCS

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 What is Personal
Communication?

 A PCS provides people with

wireless access to information
service
• e.g. Cordless, cellular, mobile data
networks and etc.
 Mobility is the heart of PCS

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 Characteristics of PCS

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 Characteristics of PCS
 Personal Information Machine (PIM)
• Information device carried by the person
such as PDA, Notebook, Cellular Phone
 Personal Address
• Associated with the person as he or she
changes location
 Personal Profile
• Contains details of services selected by the
subscriber
 Ubiquitous:
• Services will be available anywhere &
anytime

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 Dimensions of PCS

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 Examples of Two Telephone Calls
 Conventional Call
• A pair of wires connects each telephone
to the switching system
• Each pair of wires has its own
telephone number
 Cellular Call
• Wireless: Signals travel through the air
• Each host associates with a telephone
number regardless of location

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 Conventional Phone Call:
Network Elements

Public Switched
Telephone Network

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 Conventional Phone Call:
Information Flow

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 Cellular Phone Call:
Handoff (Hard and Soft)

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 A Cellular System
 A cellular system includes:
• Telephone sets, radio channels, base
stations, a switch, and connections
linking to the switch
 Cellular systems are more complex
than conventional telephone systems

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 Network Elements

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 Information Flow

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 Technical Challenges
 Mobility: Roaming
• Location management and Handoff
 Ether: Radio signals
• Access technology: FDMA, TDMA, CDMA
• Channel impairments: fading and noise
• Bandwidth: channel reuse, signal compression,
an efficient modulation and coding
• Privacy and Security: Encryption and
Authentication
 Energy: Power control

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 Evolution of PCS
 Four stepping-stones to PCS
• Cellular Networks
• Cordless Telephones
• Mobile Computing
• Paging

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 Cellular Networks
 Four major trends in cellular
technologies:
• Analog systems ® Digital systems
• Signaling and network control
technologies ® Standard
• Vehicle-mounted ® Small portable units
• Expanding the scope of services such as
caller ID, transmit text message, direct
access to internet and WWW

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 Standards
 AMPS (Advanced Mobile Phone
System)
• Used in the US and Canada
• Frequency bands: 850 MHz
• Access: FDMA
• More than 700 service areas (two
companies/each area)
 GSM (Global System for Mobile
Communications)
• Used in Europe
• Frequency bands: 900 MHz &1800 MHz
• Access: TDMA
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 Cordless Phones
 Limited distance from a single residential
BS
 Standards: CT2 (Cordless Telephone,
Second Generation), DECT (Digital
European Cordless Telecommunications)
and CT2Plus
• To interconnect many different base stations
such as residential BSs, BSs connected to
business telephone systems (PBX), and
telepoint BSs (BS in public area)

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 Mobile Computing and Paging
 Mobile Computing = Portable
Computers + Internet
 Paging is the oldest of PCS and the

cheapest one
 The most advanced pagers also

receive voice email

 Two-way paging services are

supported since 1995 in USA

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 Current PCS
 Europe: The term of PCS originated in
1989 in the United Kingdom
• Spectrum is assigned around 1800 MHz
 North America:
• Spectrum is assigned around 1900 MHz
• High-tier systems: High transmission power
serving at vehicle speed such as NA-TDMA,
NA-CDMA, GSM
 Low-tier systems: PACS (Personal
Access Communications system), DECT
 Japan: A low-tier system PHS (Personal
Handyphone System) operated in 1995
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 Frequency Bands

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 Other Wireless
Communications Systems
 Four important systems to serve
special needs
• Mobile communication satellites: low-
bit-rate, global coverage area
• Wireless local area networks: high-
bit-rate, limited coverage area
• Wireless local loops: higher spectrum
efficiency
• Wireless data networks: diversity

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 Mobile Satellite Systems

 A major trends since 1990:

• Broadcast satellite TV industry
• Two-way communication between
satellites and vehicles, ships
• One-way GPS

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 Categories of Satellite
Systems
 GEO (geosynchronous orbits) at 35,800
km above the equator
• Advantage: simple network configuration (3
satellites are enough to cover the earth)
• Disadvantages: high transmission power,
long propagation path delay, poor radio
coverage at high latitudes
 MEO (Medium Earth Orbits) at 10,000
km above the earth

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 Categories of Satellite
Systems
 LEO (Low Earth Orbits) on the order
of 500 to 2,000 km above the earth
 Both the MEO and LEO satellite

systems required handoff in satellites

 Channel Transmission rates:

2.4Kbps ~ 2 Mbps

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 Principles of PCS

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 Information Services for People
 Telephone Services
 Short Message Services (SMS)
 Voice-band Data and Facsimile
 Direct Digital Access
• Transparent data transmission: using FEC
• Non-transparent data transmission: using
ARQ
 Closed User Groups
 Telemetry
 Wireless Local Loops
 Video and Other Broadband Services

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 Voice-band Data and Facsimile

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 Figures of Merit (Design Goals)
 Subscribing to a system:
• Terminal price,Terminal size and weight,
Service price, Range of services, Coverage
area, Roaming
 Using a system:
• User interface, Call blocking, Setup time,
Transmission quality, Privacy,Mobility, Call
dropping, Battery life, Modes of operation
 Operating company:
• Infrastructure cost, Cell radius, Spectrum
efficiency, Network security, Early deployment
and adaptability
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 System Operations

 User Information Transport

 Mobility Management

 Authentication and Encryption

 Call Management

 Radio Resources Management

 Operations, Administration and

Maintenance (OA&M)

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 Radio Resources
Management
 Resources assigned by the system to
a terminal includes:
• A base station
• A physical channel depends on the
access technology
• The power of the signal transmitted by
the terminal
• The power of the signal transmitted to
the terminal by the base station
 RRM is an combination optimization
problem
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 Four Separate Tasks
 Call Admission
• Determine whether the system accepts a
request to set up a new communication
 Base Station and Channel Assignment
• Fixed channel allocation
• Dynamic channel allocation
 Power Control
• Reduce system interference
• Promote battery life
 Handoff Criteria

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 PCS Architecture:
Network Elements

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Examples: Cellular - Centralized

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 Cordless - Distributed

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 Air Interfaces

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 Obstacles of Radio
Transmission
 Limited spectrum that must be shared
efficiently
 Transmission impairments that can change
abruptly with time, location and frequency
band
 Interrupted connections associated with
handoff procedures
 Limited power available to portable
terminals

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 How to Conquer the Obstacles
 Modulation
 Source coding

 Channel coding

 Interleaving

 Diversity reception

 Channel equalization

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 Media Access
 Three frequently used access
techniques:
• FDMA
• TDMA
• CDMA
 Two multiplexing methods:
• TDM
• FDM

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 Review Exercise
1. Why do cellular phone systems require handoff
procedures?
2. What are some advantages and disadvantages
of using communications satellites to provide
wireless personal communications?
3. Why does a terminal register its location with a
network? What is the advantage of frequent
registration? What is the disadvantage?
4. Compare fixed channel allocation with dynamic
channel allocation. What are some advantages
and disadvantages of the two approaches?

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