Personal Communications Services, PCS Architecture

1. Personal Communications
Services

2. PCS (Personal Communications Services)
 Personal communications services (PCS) refers to a wide
variety of wireless access and personal mobility services
provided through a small terminal, with the goal of enabling
communications at any time, at any place, and in any form.
 Business opportunities for such services are tremendous, since
every person (not just every home) could be equipped, as long
as the service is fairly inexpensive.
 Several PCS systems have been developed to meet rapid
growth prompted by heavy market demand.
 Meet of them are connected to the public Switched telephone
network (PSTN) to provide access to wire-line telephones.

3. Examples
High-tier digital cellular systems (mobile phone systems) far widespread vehicular
and pedestrian services.
• Global System for Mobile Communication (GSM)
• IS-136 TDMA based Digital Advanced Mobile Phone Service (DAMPS)
• Personal Digital Cellular (PDC)
• IS-95(CDMA-based cdma One System)
Low-tier telecommunication system standards for residential, business, and public
cordless access applications:
• Cordless Telephone 2 (CT2)
• Digital Enhanced Cordless Telephone (DECT)
• Personal Access Communications Systems (PACS)
• Personal Handy Phone System (PHS)
Wideband wireless systems have been developed to accommodate Internet and
multimedia services. Examples include:
• cdma2000, evolved from cdmaOne
• W-CDMA, proposed by Europe
• SCDMA, proposed by China/Europe

4. The PCS umbrella also includes:
• Special data systems such as Cellular Digital Packet Data, RAM
Mobile Data, and Advanced Radio Data Information System
(ARDIS)
• Paging system
• Specialized mobile radio (SMR) access technologies
• Mobile-satellite systems such as the existing American Mobile
– Satellite Company (AMSC), as well as numerous proposed mobile satellite
systems, including S-band, L-band, low-earth orbit (LEO), mid-earth orbit
(MEO), geosynchronous orbit, and geostationary earth orbit (GEO), for
both data and voice applications.
• Unlicensed industrial, scientific, and medical (ISM) band
technologies, as well as wireless local area networks (LANs)
should also be thrown into the PCS mix

5. Goal
• This book describes network management, protocols, and services
for PCS systems.
• Besides the mobile telecommunications issues, we also cover
wireless Internet.
• We attack this problem from the telecommunication aspect.
• And because this book is designed for readers without a radio
background, we try to avoid the details of the physical radio
technologies.

6. PCS Architecture
• PCS technologies have grown rapidly in the telecommunications
industry.
• Two of the most popular are:
– High-Tier Cellular telephony
– Cordless and low-Tier PCS telephony
• These technologies have similar architectures, as shown in
Figure 1.1.

7. PCS Architecture
Wireline Transport Network
Radio Network

8. 8
Historical Development …
Switch
SwitchPSTN/ISDN
Isolated Mobile Systems Basic Cellular System
Historical Background

9. PCS Architecture
• Basic architecture consists of two parts:
– Radio Network.
– Wireline Transport Network.

10. PCS Architecture
• Radio Network
– PCS use mobile stations (MSs) to communicate with the base
stations (BSs) in a PCS network.
– MS is also referred to as handset, mobile phone, subscriber unit, or
portable.
– For example,
• subscriber unit : wireless local loop;
• Portable : low-tier systems (PACS); and
• mobile station : GSM system.

11. PCS Architecture
• Modern MS technology allows the air interface to be updated
(e.g., from DECT to GSM) over the air remotely
• The MS can also be remotely monitored by the system
maintenance and diagnostic capabilities.
• Different types of MSs have various power ranges and radio
coverage.
– hand-held MSs have a lower output power (where the maximum output
power can be as low as 0.8 watts for GSM 900) and shorter range
compared with vehicle-installed MSs with roof-mounted antennas (where
the maximum output power can be as high as 8 watts in GSM900).

12. PCS Architecture
• The radio coverage of a base station, or a sector in the base
station, is called a cell.
• For systems such as GSM, cdmaOne, and PACS, the base
station system is partitioned into
– a controller (base station controller in GSM and radio port control
unit in PACS) and
– radio transmitters/receivers (base transceiver stations in GSM and
radio ports in PACS).
• The base stations usually reach the wireline transport
network (core or backbone network) via land links or
dedicated microwave links.

13. PCS Architecture
• Wire-line Transport Network.
• The mobile switching center (MSC) connected to the base
station is a special switch tailored to mobile applications.
– For example, the Lucent 5ESS MSC 2000 is an MSC modified from
Lucent Technologies' 5ESS switching system.
– The Siemens' D900/1800/1900 GSM switch platform is based on its
EWSD (Digital Electronic Switching System) platform.
– The Ericsson MSC is based on its AXE switching platform.
• The MSC is connected to the PSTN to provide services between
the PCS users and the wire-line users.
• The MSC also communicates with mobility databases to track
the locations of mobile stations.

14.  This section gives an overview of four popular cellular
telephony networks:
 AMPS,
 GSM,
 DAMPS (IS-136)
 CDMA (IS-95).
Cellular Telephony

15. • First generation cellular mobile communications: (1980)
 Technology: FDMA and Analog Technology.
 Systems: AMPS(USA), NMT-900(Sweden), HCMTS(Japan)
 Shortages: Low capacity, poor Security, Low quality, voice
only (no data)
 Advantages: enough for the time
Historical Development

16. 16
Historical Development …
• Second generation, 2G : (1992)
 Technology : TDMA, TDMA hybrid FDMA
 Systems : DAMPS(USA, IS-54), GSM
 Advantages : Higher Capacity, good Security, good speech
quality
 Technology : CDMA (Qualcomm)
 Systems : CDMA(IS-95)
 Advantages : Good Security, Higher & Soft Capacity,
Speech Activity, Multipath Diversity Rx., good speech quality
 Shortages : Mainly Voice Service & low data rate Services

17. 17
Historical Development …
• 2.5 Generation, 2.5 G: (1996-2000)
 GPRS in Europe: Higher data rate (up ~ 150 kbps),
Packet Switched Data, compatible with GSM
 IS-95 B in US: Higher Data rate (up to ~114 kbps),
Packet or Switched Data, compatible with IS-95

18. 18
Historical Development …
• The third generation 3G: (2001-2005)
 Support Multimedia Service, especially Internet Service,
144kb/s ( Outdoor and higher velocity ), 384kb/s ( from Outdoor
to indoor, lower velocity), 2Mb/s (indoor).
 Better Speech Quality and other services.
 New Technologies like Tx Diversity, Turbo coding, Multiuser
Detection and Interference Cancellation, Beam forming and
Smart Antennas.

19. Comparison
Gen TECHNOLOGY FEATURES
1-G
Late 1970’s,
early 1980’s
AMPS Advanced Mobile Phone
Service
• Analog voice service
• No data service
2-G
1990’s
CDMA Code Division Multiple Access
TDMA Time Division Multiple Access
GSM Global System for Mobile
Communications
PDC Personal digital cellular
Digital voice service
• 9.6K to 14.4K bit/sec.
• CDMA, TDMA and PDC offer one-
way data transmissions only
• Enhanced calling features like caller
ID
• No always-on data connection
3-G
2000 and
beyond
W-CDMA Wide-band Code Division
Multiple Access
CDMA-2000 Based on the Interim
Standard-95 CDMA standard
TD-SCDMA Time-division
synchronous CDMA
• Superior voice quality
• Up to 2M bit/sec. always-on data
• Broadband data services like video
and multimedia
• Enhanced roaming

21. 21
System Components
• Mobile Stations (MS)
– Transceiver
– Antenna
– Control circuitry
– Moves at pedestrian or vehicle speeds
• Base Transceiver Station (BTS)
– Several transmitters and receivers
– Tower that supports several transmitting and receiving antennas
• Base Station Controller (BSC)
– Control BTS
– Bridge between all mobile users of the BTSs and a Mobile switching center
• Mobile Switching Center (MSC)
– Connects MSs to the PSTN (public-switched telephone network)
– Coordinates activities of all BSCs
– Controls all billing and system maintenance functions
– Several MSCs in large cities

22. 22
System Components …
Public Switched
Telephone Network
1 2 3
4 5 6
7 8 9
* 8 #
1 2 3
4 5 6
7 8 9
* 8 #
MSC
BSC BSC
BTS BTS
BTS
BTS
MS
MS
MS
MS
MS

23. 23
Cellular Concept
• Idea: replace high power transmitter with several lower power
transmitters to create small “cells”
• Multiple cells cover a geographic area
• Each cell assigned a set of frequencies
• Neighboring cells assigned different group of frequencies to
reduce adjacent-cell interference
• Enables spatial frequency reuse
• Increase capacity by increasing number of transmitters and
decreasing transmit power
• Enables fixed bandwidth to serve arbitrarily large number of
subscribers
• Users within a cell communicate with the cell BS

24. 24
Cellular Concept…
• As users move between cells, calls go through “hand-off” when
switching to new cell BS
• Large-radius cells for large coverage area with small number of
users
• Evolve into small-radius cells when number of users increase
using cell-splitting
• Main ideas of cellular systems
– Small coverage areas (cells)
– Frequency reuse
– Handoff
– Cell splitting to increase capacity

25. Cellular Telephony
 Characterized by
 High mobility provision
 Wide-range
 Two-way voice communication
 Handoff and roaming support
 Integrated with sophisticated public switched
telephone network (PSTN)
 When mobile is turned on and not engaged in a call
• monitors the control channel for strongest BS.

26. Cellular Telephony
 Mobile users and handsets
 Very complex circuitry and design
 Base stations
 Provides gateway functionality between wireless
and wire line links
 Mobile switching centers
 Connect cellular system to the terrestrial
telephone network

27. Cellular System

28. Cellular Concept

29. Cellular Concept