The Cell Phone Moves on

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The Cell Phone Moves on

• Justin Champion
• 3292 JJC1_at_staffs.ac.uk

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Content

• What we will look at
• Where from

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Handover - Cellular

• The term of handover is used regularly within
  cellular networks
• A mobile phone can be thought of as an advanced
  walkie talkie
• What makes the mobile phone different is the
  ability that once it is out of range of the
  transmitter this can be recognised and a
  mechanism will be employed to find another
  transmitter
• Because both of the transmitters are attached to
  the same infrastructure there will be no break in
  the communications
• Hopefully !

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Handover - Cellular

• Handover as it is logically seen
• Each of the hexagons is referred to as a cell
• At the centre of the cell is a transmitter
  referred to as a base station in the 2G
  communications
• These cells then cover a geographic area
• i.e. Stafford

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Handover - Cellular

• Example of a person walking through some cells

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Handover - Cellular

• The Hexago shape is a theoretical shape used for
  planning purposes
• The reality is that the shape actually changes
  for the transmitter

Actual Transmission Distance
Theoretical Transmission Distance
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Handover - Cellular

• The perfect circle will never be achieved
• Unless the ground is flat
• And there is nothing anywhere within range of the
  transmission
• Including trees, which have a varying effect on
  the signal during the year
• The reality is
• Everything has an effect on the transmission
• Think of it as someone talking, instead of a
  radio signal
• If a wall no matter how thin is in between the
  talker and receiver there will be some loss of
  sound
• As the wall get more dense this reduction will
  get worse
• The faculty has this issue with the safety glass
  which is used in the labs
• This has a large effect on the quality of the
  signal

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Signal Quality

• When dealing with voice the quality of the signal
  is not as important
• Your own brain and hearing will adjust for the
  lowering of the quality
• You can interpret what was said based on what you
  can hear
• You can request more information
• Can you say that again?
• In computer terms though
• Though this is not good
• If the application is using TCP then the data can
  be requested again
• If UDP is being used then the data is lost
• Your application can not say can you please speak
  up I am not quite hearing you
• There are a large number of research papers
  discussing the issue of TCP across a wireless
  Link, if you look on the Internet
• TCP was not designed for this type of environment
  and as such it is not the perfect mechanism,
  blocking the air interface when it is not
  required

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Roaming

• We have already introduced handover and what this
  has given to cellular communications
• The extension of this is roaming
• Remember one of the problems of 1G was the fact
  that you had to use a different phone for each of
  the European countries
• What roaming allows you to do is take the same
  GSM phone from ANY GSM based company and use it
  to attach to another country
• In reality this will be companies in another
  country as there has to have been a roaming
  agreement between the companies
• Here is a list of the global roaming agreements
• http//www.gsmworld.com/roaming/gsminfo/index.shtm
  l
• The more interesting thing is to find a country
  without one

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Roaming Considerations

• Roaming has a number of considerations
• There must be a roaming agreement
• Both of the operators must have the correct parts
  of the GSM standard installed
• These are
• Home Location Register (HLR)
• Visitor Location Register (VLR)
• Remember although GSM is a standard it can be
  interpreted differently by different operators
• Although these two servers are pretty well
  compulsory based on what they do
• Before you can use your phone agreement will be
  reached with your home operator
• As to what you can do on the network you have
  roamed to

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2.5G communications

• There was a recognition quite earlier on in the
  use of GSM of how much money could be made beyond
  the traditional service
• This being voice communications
• The big driver for this was the massive growth
  seen in text messaging
• Short Messaging Service (SMS)
• Operators were then getting a new stream of
  revenue for little outlay
• In the case of SMS very little outlay in terms of
  a single class of server being attached to the
  network
• Short Messaging Service Centre (SMSC)

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2.5G communications

• In addition the growth of the information age was
  continuing
• This would give the operators an opportunity to
  attach mobile devices to any packet switched
  network
• Most commonly the Internet
• This would then allow for
• Access to Information from Anyplace, Anytime
• This would then be a new stream of revenue for
  the operators
• The users would get an improved experienced
  though from there devices with the ability to get
  access to Internet based data in a format which
  they were used to from the home PC

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2.5G communications

• This increase in data services was good in a
  number of ways from the operator point of view
• Charge for every byte of data received and sent
• Charge for the applications which use this data
• Provide new data based services to the user
• At the moment widely discussed is the films/music
  to your mobile
• Handset manufacturers selling new devices which
  were better at using the new applications
• Selling software from third party providers which
  is hosted on the companies servers
• This was though an opportunity for both
  developers and users as well
• This is a whole new field of possible users
  wanting services which companies can provide and
  developers can create for
• The drivers in this were probably going to be
  different from the desktop ones

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2.5G communications

• The cost of upgrading any infrastructure
  completely is quite considerable
• Particularly in the UK a lot of money had been
  spent on just the purchasing of the frequency
• The solution was a stepped approach towards 3G
  communications
• Upgrade part of the infrastructure in a way which
  could be built upon at a later stage to give full
  3G communications.

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3G Frequency UK

• 3G spectrum auction
• License shows the size of the spectrum with A
  being the largest
• Part of the auction rules was a new company in
  the UK won the License type A
• Auction closed on the 27th April 2000
• Original estimates were for a total selling value
  of 1.5 billion (http//www.3gnewsroom.com/html/wh
  itepapers/nao_3g_report.zip)
• The license is allocated until the 31st December
  2021
• The operators must have 80 uk coverage by the
  31st December 2007 otherwise they will be fined
• The UK phone companies in June, 2003 said that
  they would claim the VAT back on the license
  purchases! About 3.3 Billion pounds
• European Court case started in 2004
• This claim though was dismissed though in June
  2007 (http//www.theregister.co.uk/2007/06/26/no_v
  at_on_3g/)

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2.5G communications

• The 2.5G technology which was developed was GPRS
• General Packet Radio Service (GPRS)
• This standard was developed by ETSI
• It was agreed in March 1998
• Basically what it gave was
• It allowed faster data communications while still
  using the original GSM infrastructure
• The data communications were based on a packet
  driven architecture rather than circuit switched
  as with GSM
• Only some upgrade to Base stations and additional
  servers to deal with the packets were required
• This all meant that the upgrade can be done
  quickly in addition to being done cheaply
• Quick return on the investment, if people used
  the technology

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2.5G communications

• Computer based elements
• In theory GPRS will allow communications at the
  rate of 171Kbps
• The reality of this though as with most mobile
  computing technologies is that it does operate a
  lot slower than this
• A lot will effect how fast it actually operates
• It would have to have perfect conditions to
  operate at this rate and this will never happen
  outside of a laboratory environment
• Actually speeds with conditions taken into
  account is theoretically a maximum of 53.6 Kbps
• Studies have shown the average is usually about
  30 40 Kbps
• This though is a considerable improvements upon
  the standard GSM

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2.5G communications

• GPRS only effects the data communications !
• If you make a voice call it is still on GSM

GSM
GPRS
GPRS Enabled Device
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2.5G communications

• Packet switched communications
• These are what is commonly now used in any
  computer network
• Ethernet relies on this technology
• It is a relatively simple technology, where when
  a medium is free anyone who needs to transmit can
• This allows for more efficient use of the medium
  with no prior reservations needed
• It is not all advantages though as with Ethernet
• If you have a application which needs some sort
  of guarantee
• Commonly these are games or video streams
• Pure packet switched can not give these
• It may be that a lot of people are transferring
  data at a time

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2.5G communications

• Packet switched communications
• The data that needs sending is then transferred
  into the data part of a packet
• The issue with packet switched communications is
  that assuming that your data is split into three
  packets
• Each of these may take a different route to get
  to the destination
• As Internet based communications usually generate
  a larger response than sending this problem is
  magnified
• i.e. the command HTTP GET http//www.fcet.staffs.
  ac.uk/index.html
• A few bytes are sent but 94 KiloBytes are
  returned
• The TCP/IP protocol which is widely used on every
  network will put the packets back into sequence,
  but this all takes time
• Some packets will never actually arrive but again
  TCP will deal with this but at the expense of
  delays in the communications

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2.5G communications

• Packet switched communications

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2.5G communications

• The GSM infrastructure only needed the most minor
  update to the infrastructure to allow these data
  communications
• The base stations had to have new software
  installed
• This was to deal with the fact that data packets
  now had to be forwarded differently to the voice
  communications
• And the fact that everything is now in packets
• This update can take place overnight as normal
  update
• In the same way that your home PC installs
  updates
• The actual hardware did not need a upgrade as the
  modulation technique which was used did not
  change
• New Servers
• Serving GPRS Supporting Node (SGSN)
• Keeps records of packets to be charged for
• Acts as the VLR for data communications
• Router for packets which are mislaid during a
  handover

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2.5G communications

• Packet Control Unit
• Responsible for the packet delivery at the base
  station
• Although this has a separate name it is actually
  a part of the base station
• It is just a different piece of software
• Gateway GPRS Support Node (GGSN)
• Although a fancy title this is effectively a
  proxy server and a firewall
• This node is the point at which the packet
  switched network attaches to the cellular network
• Any translation which is needed on the packets
  will also be done at this point
• Packets needing changing between formats, or a
  private IP address being changed a public version

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2.5G Benefits

• This change then might seem quite small
• Effectively all that ETSI with GPRS was to give
  an increased data rate to the actual devices
• This increased data rate though in combination
  with the increasing power of the devices opens up
  a whole new area of communications
• These are for both business and personal usage
• The communications for GPRS are always on
• In this respect there is no delay in the actual
  communications
• In reality there is a small delay whilst the
  first packets are arriving
• But this is considerably less than the GSM
  communications where a number had to be dialled
• Similar to your PC a application which needed the
  network would just need to be started to make the
  connection
• When your device is first started the details of
  the network communications are agree at this
  stage before you actually need to use them

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2.5G Benefits

• GPRS supports both the IP and X25
• X25 you are unlikely to use any more
• Most commonly is the travel agent terminals, but
  again this is changing away to IP addressing
• The fact that you have an IP address allows for
  communications with the Internet
• Depending on what you have paid for this can also
  mean that the Internet can communicate with you
• The same as your Internet Service Provider (ISP)
  connection you will usually get a temporary IP
  address
• This can be changed though the same as your PC so
  that you get a permanent IP address on your
  device
• This allows for two way communications without
  having to wait for the phone to start the
  connection

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2.5G Benefits

• All of these data services open up the
  opportunity on the phones
• But in addition other devices can make use of the
  technology
• Laptop users, who want data access away from the
  major town areas can install a data card
• Gaining access anywhere
• Delivery drivers can have a device in the truck
• Allowing for real-time updates as in
• Collect from this location now
• I have delivered the following parcel
• Linking this into the company servers, this give
  instant updates as to status

http//www.commerce.com.tw/datas/1/d/c/C0011591/sh
owroom/2/1135004933c.jpg
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2.5G Benefits

• By linking multiple technologies we can benefit
  further
• Tracking of vehicles using the Global Positioning
  System (GPS)
• This is a one way system for working out a
  position of a device, using timing
• By receiving this data and then have the device
  send the location back to a central point via
  GPRS a company could keep track of a vehicle
• http//www.gsm-modem.de/vehicle-tracking.html

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Conclusion

• Although the intention was always to go straight
  to 3G communications
• Due to the expense and difficulty an intermediate
  technology was required
• Which based on the GSM standard was GPRS
• This gave the GSM user base the same
  infrastructure for voice communications
• But allowed them to use enhanced data services
• This then gave the users an introduction to data
  services and to see the benefits