Transcript Document

First and Second
Generation
Justin Champion
Room C208 - Tel: 3273
www.staffs.ac.uk/personel/engineering_and_technology/jjc1
PCS – 1G to 2G technology
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Contents
 Start
of mobile devices
 TACS
 GSM
 Technlogy
PCS – 1G to 2G technology
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History
 Earliest
Wireless Communications was Morse Code
 Then came radio
 Now we are able to carry our personal radios in the form of
mobile devices
 First Generation mobile devices
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Based on Analogue communications
First started in the UK in Jan 1985, with BT Cellnet & Vodafone
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Transmission in the UK and Italy was called Total Access Cellular
System (TACS) and was based on an American design (AMPS)
Germany adopted C-Net
France adopted Nordic Mobile Telephone (NMT)
PCS – 1G to 2G technology
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TACS
 Operated
in the 900 MHz range
 Works by the use of multiplex the traffic by the
use of Frequency Division Multiple Access
(FDMA)
The signal from these devices was not secure
 Anyone could listen into them, remember the “Squidgy
Tapes”?
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PCS – 1G to 2G technology
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FDMA
 Breaks
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Allocates a single channel to each phone call
The channel is agreed with the Base station before transmission
takes place on agreed and reserved channel
The device can then transmit and receive on this channel
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up the available frequency into 30 KHz channels
No other device can share this channel even if the person is not
talking at the time!
The voice/sound is transmitted as analogue data, which means
that a large than required channel has to be allocated.
PCS – 1G to 2G technology
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FDMA
Frequency
PCS – 1G to 2G technology
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Second Generation (2G) Technology
 Mobile
phones became popular and requirements
changed
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Users wanted more from the phones
The frequency for the phones to use was limited and better
use of this frequency was required
 Guarantee that a call was possible when needed
 Privacy was needed as the phones may be used for business
or personal conversations.
 The phones needed to be smaller for ease of carrying
 Improved battery life
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PCS – 1G to 2G technology
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Global System for Mobile Communications
(GSM)
 1982
the European Commission requested that
900 MHz be reserved for the use of GSM
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Before the use of TACS and NMT !!!!
 1989
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ETSI defined the standard which was GSM
Originally called “Groupe Spéciale Mobile” later
changed to English
PCS – 1G to 2G technology
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GSM Operates
 Using Time Division Multiplex Access (TDMA)
 This allow the frequency to be broken up into slots
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These slots are then divided into time slices
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The frequencies used are GSM 900 , GSM 1800 and GSM 1900
Separate frequencies are used for the uplink and downlink
 890-915MHz uplink, 935-960MHz downlink for example
200KHz spacing on the frequency
124 channels per frequency band
For GSM each slice is 0.577 ms
This means that there is eight times the capacity as before in one
part of the frequency
PCS – 1G to 2G technology
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TDMA
Time
Frequency
Frequencies
890 MHz - 960 MHz – Europe
1710 – 1880 MHz - Europe
1850 MHz – 1950 MHz - America
PCS – 1G to 2G technology
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GSM Operates
 Using
Time Division Multiplex Access (TDMA)
This allow the frequency to be broken up into slots
 These slots are then divided into time slices
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For GSM each slice is 0.577 ms
To allow this to happen all voice communications needs
to be converted to binary
 Synchronisation is required for the use of TDMA
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GSM System – Multiple Access
Time Division Multiple Access (TDMA)
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Guard Time: Interval between bursts used to avoid overlapping
 Preamble: First part of the burst
 Message: Part of burst that includes user data
 Postamble: Last part of burst – used to initialise following burst
Multiframe
Frame 1
Slot 1
Slot 2
Frame N
Slot i
Slot 8
……..
Slot
Guard Time
Preamble
Message
Postamble
Guard Time
Slot 1
Slot 8
PCS – 1G to 2G technology
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GSM Operates
 Using
Time Division Multiplex Access (TDMA)
 The voice is sampled using a ADC
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8KHz / second, with an 8 bit result
PCS – 1G to 2G technology
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GSM Features
 Uses encryption to make phone calls more secure
 Data networking
 Group III facsimile services
 9600 bps transmission speed
 Short Message Service (SMS) for text messages and
paging
 Call forwarding
 Caller ID
 Call waiting
 Multi-party conferencing
PCS – 1G to 2G technology
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Subscriber Identity Module (SIM) Card
 Essential
for the GSM network
 Contains
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Subscriber Authentication key
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128 bit encryption key
International Mobile Subscriber Identity
 Temporary Mobile Subscriber Identity
 Mobile Station International Service Digital Network
 PIN to secure the card
 SMS messages
 Personal data, phone numbers, Phone settings etc
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PCS – 1G to 2G technology
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SIM continued
 Each one is unique
 e-commerce
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Authentication encryption is used called the A3/A8
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Purchasing items from your phone, with certainty that your device
bought the item
This is used to authenticate your device
 A random number is sent
 The A3/A8 algorithm then works on the number and returns a 32bit response.
 If this matches the one which the network has calculated the
device is authenticated
A5 Encryption is used for the voice calls
Virgin Cola, has a vending machine where you pay via the phone
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(news.bbc.co.uk/1/hi/sci/tech/986334.stm, 2000)
PCS – 1G to 2G technology
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Short Message Service (SMS)
 Also
known as “Simple message service”
 ETSI standard for SMS is detailed in “GSM 03.40”
 Intended to allow user to replace pagers with GSM devices
 Allows the transmission of 160 Characters 7 bit characters
using a western alphabet
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The character numbers are reduce for other alphabets
 Extremely successful
 This was never expected or planned for
 1985 Vodafone in the UK was the first use of the system
PCS – 1G to 2G technology
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SMS Continued
 Transfers
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the SMS message in a single packet
Octet = 8 Bytes
SCA
Service Centre
Address
MR
Message Reference
PID
Protocol Identifier
PDU Type
Protocol Data Unit
Type
DA
Destination Address
DCS
Data Coding Scheme
VP
Validity Period
UDL
User Data Length
UD
User Data
PCS – 1G to 2G technology
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SMS Continued
 Example
SMS transmission packet saying “Hallo World”
018011000A8143372890550000A70BC82093F9045D9F522611
(www.spallared.com/nokia/smspdu/smspdu.htm#_Toc485435709, 2003)
SMSC = Short Message Service Centre
HLR = Home Location Register
Base
Station
GSM SMS Infrastructure
SMSC
HLR
Base
Station
PCS – 1G to 2G technology
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SMS Continued
 SMS
is not delay sensitive
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It is best effort to deliver the message
 The HLR for the device is requested to see if it is turned on
 If the device is turned off the SMSC will store the message for a period of
time
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This time can be defined in the PDU in the VP section or more commonly the
SMSC has a defined period to store messages for.
When the device is turned on again the HLR is informed and this then
requests the SMS message from the SMSC
GSM System – Location Management
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GSM consists of three major systems:
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The Switching System (SS)
Base-station System (BSS)
Operation and Support System (OSS)
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The Switching System performs call processing and subscriber
related functions
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The system contains the following functional units
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Home Location Register (HLR)
Mobile Switching Center (MSC)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
GSM System – Location Management
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HLR is the most important database
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Storage and management of subscriptions
Permanent data includes:
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Subscribing to a particular provider‘s service registers you in
the HLR of that provider
The MSC performs the telephony switching functions of the
network
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Controlls call to and from other telephone and data systems
Also performs functions such as
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Subscribers‘s service profile
Subscribers‘s location information
Subscriber‘s activity status
Toll ticketing
Network interfacing
Common Channel signalling
GSM System – Location Management
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VLR contains data on visiting (roaming) subscribers
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The AUC verifies the identity of the user and ensures and ensures
the confidentiality of each call
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Integrated with the MSC
When a roamer enters the service area the VLR queries the appropriate
HLR
If a roamer makes a call the VLR will already have the information it
needs for call setup
By provide authenticity and encryption parameters for every call
Protects network operators from fraud
Assures a certain level of security for the content of each call
The EIR is a database that includes info solely about the identity
mobile equipment
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Prevents calls from stolen, unauthorised or defective mobile devices
PCS – 1G to 2G technology
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GSM Infrastructure
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The specifications created by ETSI do not require any of the
following infrastructure but recommends it !
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All mobile operators have it
MSC
VLR
HLR
VLR
MSC Mobile Switching Center
VLR Visitor Location Register
HLR Home Location Register
MSC
PCS – 1G to 2G technology
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Summary
 1G
Communications
 2G GSM Communications
Physical Transmissions
 SMS Messages
 GSM Infrastructure
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