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Mobile Communications

YEEE0004 Fall 2009

Hayden Kwok-Hay So

Early 80s

Late 90s

Around 2006

First Mobile Phone Motorola DynaTAC Year: 1979 Weight: > 2 lbs Talk Time: 30 mins Charge Time: 10 hours Cost: ~US$4000

DynaTAC 8000x (1983)

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A Brief Walk in Cell Phone History   Pre-cellular systems

•  1970s

  Analog Voice •  “1G” systems •  AMPS

  Digital Voice (and Data) •  “2G” systems •  GSM system •  GPRS

  Digital Voice and Data •  “3G” systems •  EDGE •  UMTS

Pre-Cellular Networks   Logically an extension to landline telephone service   Early systems were designed so that one radio base

station has enough power to cover a large geographical area •  Entire city •  Large rural area

PSTN

Pre-Cellular Networks   Mobile phones must transmit with high power as well

•  Larger battery is needed •  Large physical size •  Not convenient

  The collision domain is large and so only limited users are allowed

Need ways to support simultaneous users!

10km 20m

Cellular Networks   Many low-power base stations

cover the service area instead of one high-power base station

  The region covered by each station is called cell

  Individual cell sites are connected by conventional wired technology

  Number of active users in each cell is still restricted, but the area is smaller

  The first cellular telephone system (Bell Telephone System) began to deploy in 1979

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RADIO FREQUENCY Tech Brief:

Tech Brief: Radio Frequency   Wireless communications are based on

electromagnetic (EM) waves   The empty space can be divided into different

radio frequencies •  Frequency measured in Hz

  Difference communication schemes use different “chunks” of the radio frequency space so they will not interfere with each other

  Example frequency: •  Commercial Radio (881 903): 88.1 MHz, 90.3 MHz •  802.11g WiFi products: ~2.4 GHz •  Analog TV broadcast in HK: ~500 MHz •  Cell Phone: 900 MHz, 1800MHz, 2100 MHz

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Frequency Allocation in HK

  Office of the Telecommunications Authority (OFTA)

Hong Kong Frequency Allocation Chart (!"#$%&'()

Note : The frequency chart is not drawn to scale. Details can be found in Hong Kong Table of Frequency Allocations which can be obtained from OFTA website (http://www.ofta.gov.hk).

! : "#$%&'()*+,-./0123456789:;<#$=>&?8@ (http://www.ofta.gov.hk).

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Back to Cellular Network…

Cellular Networks Components   Three basic

components: •  Mobile station (MS) •  Base station (BS) •  Mobile switching center

(MSC)

  Mobile station (e.g. a cell phone) connects to a base station through a wireless link

  Base station connects to an MSC

  MSC connects to the PSTN

Handoff (Handover)   When a cell phone in conversation moves

between the coverage of a cell, call must be “handed off” to other cell

  When the signal becomes weak in the active site, central control unit will find another site

  Different cell phone systems have different handoff protocols

When a handoff is not successful, the call is dropped

Analog Voice Cellular System   Advanced Mobile Phone System (AMPS)

•  “1G” system •  One of the first commercial mobile phone system •  First available in 1984 •  Only system in US until 1997 •  Uses 800 MHz frequency band •  824–849 MHz and 869–894 MHz •  30kHz Channels

  Analog system •  The wireless link between a MS and a BS uses analog

communication •  Easy to eavesdrop •  Noise, static… •  Use FDMA to allow multiple users within a cell

Digital Voice Cellular Systems   Less prone to error/noise

  After digitization, all data can be transmitted in the same way •  E.g., we can use the Internet to transmit voice •  Very useful in 3G systems

  Can be encrypted to provide security •  Prevent eavesdropping

  Almost all modern cell phone system are digital

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2G System: GSM   Global System for Mobile communications (GSM:

originally from Groupe Spécial Mobile)   The most widely deployed “2G” system worldwide

•  Over 2 billion people across more than 212 countries and territories

  A digital communication system   Wireless frequency band:

•  900 MHz and 1800 MHz band -- Hong Kong, most of the rest of the world

•  850 MHz and 1900 MHz -- USA & Canada •  Roaming only possible when a cell phone is capable of

communication in different frequency bands

  Use Time Division Multiple Access (TDMA) to allow multiple concurrent users.

TDMA   Time Division Multiple Access   Different user communicates with the BS at

different pre-assigned time slots

Beyond Voice Calls   Basic GSM Data Service

•  Short Message Service (SMS)   General Packet Radio Service (GPRS)

•  Extension to original GSM standard •  “2.5G” system •  Packet-switched technology •  < 10 kbit/s, best effort performance •  Multimedia Messaging Service (MMS) •  Wireless Application Protocol (WAP) access •  General Internet access

  Enhanced Data rates for GSM Evolution (EDGE) •  Enhanced version of GPRS •  “2.75” system (defined in a 3G specification) •  As high as 236.8 kbit/s

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3G Networks   Voice and Data Cellular Systems   Provides much higher communication

•  Video calls •  Data communications

  Universal Mobile Telecommunications System (UMTS) •  Most deployed 3G network worldwide •  A successor to the GSM standard •  Sometimes called 3GSM •  Reuses the GSM infrastructure •  Uses a W-CDMA wireless technology

  Frequency bands •  Hong Kong and most country in Asia, Europe and Oceania

uses 2100 MHz band •  North/South America: 850/1900 MHz band

Beyond 3G…   High Speed Downlink Packet Access

(HSDPA) •  Enhanced version of the UMTS standard •  Sometimes called “3.5G” •  Up to 14 Mbit/s downlink (in theory)

  High-Speed Uplink Packet Access (HSUPA) •  Enhance the uplink transfer speed

  Both HSDPA and HSUPA are steps to move UMTS standard towards 4G •  100 Mbit/s downlink •  50 Mbit/s uplink