Transcript
First and Second Generation
Justin Champion
Room C208 - Tel: 3273www.staffs.ac.uk/personel/engineering_and_technology/jjc1
PCS – 1G to 2G technology
ContentsStart of mobile devicesTACSGSMTechnlogy
PCS – 1G to 2G technology 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
Based on Analogue communications First started in the UK in Jan 1985, with BT Cellnet & Vodafone
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 TACS
Operated in the 900 MHz rangeWorks 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”?
PCS – 1G to 2G technology FDMA
Breaks up the available frequency into 30 KHz channels 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
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
FDMA Frequency
PCS – 1G to 2G technology Second Generation (2G) Technology
Mobile phones became popular and requirements changed
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
PCS – 1G to 2G technology Global System for Mobile Communications
(GSM)1982 the European Commission requested that
900 MHz be reserved for the use of GSM Before the use of TACS and NMT !!!!
1989 ETSI defined the standard which was GSM Originally called “Groupe Spéciale Mobile” later
changed to English
PCS – 1G to 2G technology GSM Operates
Using Time Division Multiplex Access (TDMA) This allow the frequency to be broken up into slots
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
These slots are then divided into time slices 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
TDMA
Frequency
Time
Frequencies890 MHz - 960 MHz – Europe1710 – 1880 MHz - Europe1850 MHz – 1950 MHz - America
PCS – 1G to 2G technology 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
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
Time Division Multiple Access (TDMA)
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
Slot 1 Slot 2 Slot 8 Slot 8Slot 1
Frame 1 Frame N
Multiframe
Guard Time Preamble Message Postamble Guard Time
Slot
Slot i ……..
GSM System – Multiple Access
PCS – 1G to 2G technology GSM Operates
Using Time Division Multiplex Access (TDMA)The voice is sampled using a ADC
8KHz / second, with an 8 bit result
PCS – 1G to 2G technology 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 Subscriber Identity Module (SIM) Card
Essential for the GSM networkContains
Subscriber Authentication key 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
PCS – 1G to 2G technology SIM continued
Each one is unique e-commerce
Purchasing items from your phone, with certainty that your device bought the item
Authentication encryption is used called the A3/A8 This is used to authenticate your device
A random number is sent The A3/A8 algorithm then works on the number and returns a 32-
bit 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
(news.bbc.co.uk/1/hi/sci/tech/986334.stm, 2000)
PCS – 1G to 2G technology 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 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 SMS Continued
Transfers 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
SMS Continued Example SMS transmission packet saying “Hallo World”
018011000A8143372890550000A70BC82093F9045D9F522611(www.spallared.com/nokia/smspdu/smspdu.htm#_Toc485435709, 2003)
SMSC = Short Message Service CentreHLR = Home Location Register
SMSC
GSM SMS InfrastructureBaseStation
BaseStation
HLR
PCS – 1G to 2G technology
SMS Continued SMS is not delay sensitive 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 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 GSM consists of three major systems:
The Switching System (SS) Base-station System (BSS) Operation and Support System (OSS)
The Switching System performs call processing and subscriber related functions The system contains the following functional units
Home Location Register (HLR) Mobile Switching Center (MSC) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)
HLR is the most important database Storage and management of subscriptions Permanent data includes:
Subscribers‘s service profile Subscribers‘s location information Subscriber‘s activity status
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 Controlls call to and from other telephone and data systems Also performs functions such as
Toll ticketing Network interfacing Common Channel signalling
GSM System – Location Management
VLR contains data on visiting (roaming) subscribers 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
The AUC verifies the identity of the user and ensures and ensures the confidentiality of each call 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 Prevents calls from stolen, unauthorised or defective mobile devices
GSM System – Location Management
PCS – 1G to 2G technology
GSM Infrastructure The specifications created by ETSI do not require any of the
following infrastructure but recommends it ! All mobile operators have it
VLRMSC
VLR MSC
HLR
MSC Mobile Switching Center
VLR Visitor Location Register
HLR Home Location Register
PCS – 1G to 2G technology Summary
1G Communications2G GSM Communications
Physical Transmissions SMS Messages GSM Infrastructure