Second Generation

1
Second Generation

• Justin Champion
• Room C203 - Tel 3292
• jjc1_at_staffs.ac.uk

2
FMC 2nd Gen

• Contents
• Why was this needed
• GSM
• Technology

3
FMC 2nd Gen

• Why was 2G needed
• The number of phones users increased
• The user base which was originally mostly
  business related started to change to include
  other groups
• This increased the number of users which were on
  the networks
• Became a supply and demand problem
• If current providers could not provide for the
  demand users would move away from the technology.
• As the user base increased in size users in peak
  areas would find that they could not connect to
  the network

4
FMC 2nd Gen

• 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

5
FMC 2nd Gen

• 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
• European Telecommunication Standards Institute
  (ETSI)
• Originally called Groupe Spéciale Mobile later
  changed to English

6
FMC 2nd Generation World

• There was a recognition of the problems with 1G
  and compatibility issues
• To deal with this 2 approaches were taken
• Force adoption of a standard
• European Commission decided that all member
  countries should use one system GSM
• Market forces dictating
• United States of America adopted this approach
• In the US the 2G system had to use the same
  spectrum as 1G
• AMPS became DAMPS Digital AMPS - TDMA
• Code division Multiple access (CDMA) (also know
  as IS-95) was introduced

7
FMC 2nd Generation World

• GSM due to its standards based approach
• Now dominates the cellular market
• 80.79 of all mobile phones operate on the GSM
  standards
• Just under 3 Billion users
• http//www.gsmworld.com/news/statistics/pdf/gsma_s
  tats_q2_08.pdf
• Although a slow down is now being seen in the
  number of phones being sold
• http//www.vnunet.com/vnunet/news/2226669/per-cent
  -world-mobile-2011
• This is most likely due to saturation of the
  market
• In some countries there are now more phones than
  people
• Users having more than one phone for each of
  there roles
• http//www.guardian.co.uk/world/2008/feb/27/nokia.
  mobilephones
• More phones than people in the UK and Italy

8
FMC 2nd Generation World

• Subscriber statistics end Q2 2008
• World 3,665,389,343
• cdmaOne 7,919,081 0.22
• CDMA2000 1X 292,479,194 7.98
• CDMA2000 1xEV-DO 101,171,640 2.76
• CDMA2000 1xEV-DO Rev. A 2,349,544 0.06
• GSM 2,961,292,242 80.79
• WCDMA 216,434,662 5.90
• WCDMA HSPA 43,416,405 1.18
• TDMA 3,042,671 0.08
• PDC 9,150,409 0.25
• iDEN 27,610,798 0.75
• Analog 522,697 0.01

http//www.gsmworld.com/news/statistics/pdf/gsma_s
tats_q2_08.pdf
9
FMC 2nd Gen

• GSM Services
• Intended primarily as a voice service
• Although now we can see the benefit of data, the
  increasing use of voice calls was the issue
  addressed by this standard
• GSM does support some limited data services
• Three services are offered by GSM
• Teleservices
• Bearer Services
• Supplementary Service

10
FMC GSM

• Teleservices
• Telephony
• Codecs for voice and data
• Encryption of voice data
• Emergency Calls
• These calls must have the highest priority
• Directing you to the nearest connection point
• Voice Mail
• Fax Mail
• Facsimile Group 3
• Short Messaging Service (SMS)
• Including the SMS Cell Broadcast (SMS-CB)

11
FMC GSM

• Bearer Services
• Bearer services are for the transport of data
• 9600 bits per second maximum
• Synchronous and asynchronous
• Alternate data and speech
• Transparent
• Fixed delay in data transfer
• No guarantees of data integrity
• Non transparent
• Variable Delay
• Guaranteed data integrity via Automatic repeat
  request (ARQ)

12
FMC GSM

• Supplementary Services
• User Identification
• Call Redirection
• Call Hold
• Advice of Charge
• Call Barring
• Call Forwarding
• Multiparty calls

13
FMC 2nd Gen

• GSM Operates
• Using Time Division Multiplex Access (TDMA)
  FDMA
• This allow the frequency to be broken up into
  slots
• The frequencies used are GSM 900 , GSM 1800 and
  GSM 1900
• Possible selling off though of the 900 Mhz range
• http//www.theinquirer.net/en/inquirer/news/2007/0
  9/21/ofcom-wants-to-sell-900-mhz-bandwidth
• Separate frequencies are used for the uplink and
  downlink
• 890-915MHz uplink, 935-960MHz downlink for
  example
• Uplink and Downlink are 45 MHz apart
• 200KHz spacing on the frequency
• 124 pairs of channels
• These channels are then divided into 8 time
  slices
• For GSM each slice is 577 ns (0.000000577
  seconds)
• Total channels available is 8 124 992 (in a
  theoretical context)
• This means that there is eight times the capacity
  as before in one part of the frequency
• Assuming the same rate is used

14
FMC 2nd Gen

• TDMA FDMA

Time
Frequency
Frequencies 890 MHz - 960 MHz Europe 1710
1880 MHz - Europe 1850 MHz 1950 MHz - America
15
FMC 2nd Gen

• TDMA FDMA
• Same diagram in a different view
• Four devices all communicating at an exact time
• All of the devices will act as though they are
  the only device transmitting/receiving

Time
Frequency Uplink
16
FMC 2nd Gen

• GSM Operates
• One of the features which allowed the increase in
  the number of users is digitisation of voice
• The voice is sampled using a (analogue to Digital
  Converter) ADC
• 8KHz / second, with an 8 bit result
• The voice information is then transferred using
  one of these methods
• Enhanced Full Rate
• Best quality speech
• Uses a full slot
• Marginal increase in processor overhead
• Full Rate
• Improved speech quality
• Takes a full slot to transfer
• Half Rate
• This mode allows for a doubling of capacity to a
  base station
• Loss in speech quality, but not significant
• Half a slot to transfer

17
FMC 2nd Gen

• Analogue to Digital Convertor (ADC)
• Regular samples are taken from the analogue
  signal and converted into a digital value
• The more samples you take with a higher level of
  precision the more accurate the representation of
  the original signal
• 8Khz with a 8 bit result
• 8000 samples taken per second with a value of 0
  to 255

255
0
Time
18
FMC 2nd Gen

• Digitisation
• Of voice allows for a number of features
• Takes less bandwidth to transfer the voice
• The data once digital
• Can be encrypted
• Can be recovered even with the attenuation
  effects
• Additional bits can be added to allow for errors
  within transport
• Without the need for retransmission Forward
  Error Checking (FEC)
• The digital voice data can then be place inside
  of a packet for transport

19
GSM System Multiple Access

• 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

Multiframe
Frame 1
Frame 26
..
Slot 1
Slot 2
Slot 8
Slot 8
Slot 1
Slot i
Slot
Guard Time
Preamble
Message
Postamble
Guard Time
20
FMC 2nd Gen - SIM

• Subscriber Identity Module (SIM) Card
• Essential for the GSM network
• The SIM is located within the Mobile station (MS)
• Basically the phone handset you use
• Contains
• Subscriber Authentication key
• 128 bit encryption key
• International Mobile Subscriber Identity (IMSI)
• A unique international none dialable number which
  is attached to your device
• Temporary Mobile Subscriber Identity
• Mobile Station Integrated Service Digital Network
  (MSISDN)
• Basically this is YOUR phone number
• PIN to secure the card
• SMS messages
• Personal data, phone numbers, Phone settings etc

21
FMC 2nd Gen

• 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 using
  challenge/response
• 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
• http//www.gsmworld.com/using/algorithms/index.sht
  ml
• Using your mobile as an electronic wallet
• http//technology.timesonline.co.uk/tol/news/tech_
  and_web/the_web/article2631026.ece

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FMC Location

• GSM consists of three major systems
• Base-Station System (BSS)
• Network Switiching Sub-System (NSS)
• 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)

23
FMC BSS

• Base Station System (BSS)
• This is the part of the network which connects
  the MS to the network via the radio interface
• Base Station (BS)
• Know as (Base Transceiver Station (BTS) ) in
  official GSM documentation
• This is the radio transceiver the area of
  transmission is referred to as the cell

Theory
Reality
BS
BS
Transmission distance
24
FMC 2nd Gen

• Base station controller
• This node takes overall control of a number of
  base stations a point of control for the BS
• Other functionality
• Traffic concentration
• Switching operations
• Data based and voice
• Network management to all BS attached
• Radio channel management for all BS attached
• Conversion of air interface rates to network
  applicable rates
• 13 Kbps to 64 Kbps
• Handover control
• This is for base stations which it has control of

25
FMC BSS

• Base station Controller

Base Station Controller
26
FMC GSM - NSS

• Network Switching Sub-System (NSS)
• Responsible for the transfer of information from
  the handsets to the correct part of the
  infrastructure
• Functions
• Handovers between BSCs
• Allow communication between mobile and PSTN
  networks
• Allows for roaming between networks
• A number of nodes are a part of the NSS

27
FMC GSM - NSS

• NSS nodes consist of
• Mobile Switching Centre (MSC)
• Home Location Register (HLR)
• Visitor Location Register (VLR)
• Authentication Centre (AuC)
• Equipment Identity Register (EIR)

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FMC GSM - NSS

• HLR is the most important database
• Storage and management of subscriptions
• Permanent data includes
• Subscriber's service profile
• Subscriber's location information
• Subscribers activity status
• Subscribing to a particular providers service
  registers you in the HLR of that provider
• The MSC performs the telephony switching
  functions of the network
• Controls call to and from other telephone and
  data systems
• Also performs functions such as
• Toll ticketing
• Network interfacing
• Common Channel signalling

29
FMC GSM - NSS

• 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
• Since 2002 all UK based operators have shared the
  contents of the EIR database
• This is also true for countries which have
  roaming agreements with UK operators
• If a phone is stolen anywhere in the world, it
  can now be registered as stolen and traced within
  24 hours

30
FMC GSM - OSS

• Operation and Support System
• This part of the network allows monitoring of the
  network
• Ensures the smooth running and involves
  management tasks
• Accounting and Billing
• Status Reports
• Traffic monitoring
• In addition if a BSC can not carry out all of its
  tasks the OSS will take control of the BSCs
  tasks
• The OSS is logically connected to all equipment
  in the infrastructure

31
FMC 2nd Gen

• GSM Infrastructure
• The specifications created by ETSI do not require
  any of the following infrastructure but
  recommends it !
• All mobile operators have it

AUC
OSS
VLR
MSC
HLR
VLR
MSC
MSC Mobile Switching Center VLR Visitor Location
Register HLR Home Location Register
32
FMC GSM

• The infrastructure which has been discussed
• Is ever expanding
• As new functionality is required this is built
  into the infrastructure
• This gives GSM the ability to remain future proof
  without large investment in new infrastructure
  when new technology becomes available
• This will be seen more in the future lectures
  when we can see that new technology uses GSM as a
  basis and essential part
• Even for 3G/4G communications

33
FMC 2nd Gen

• Summary
• 2G GSM Communications
• Physical Transmissions
• GSM Infrastructure