Mobility

1
Mobility

• Anna Larmo
• Research Scientist, NomadicLab
• Oy L M Ericsson Ab

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Outline

• What is mobility?
• What does wireless mean?
• Basic vocabulary
• Wireless networks
• Wireless technologies
• How does mobility work?

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What is mobility?

• Mobility is the ability and willingness to move
  or change
• Mobility in Finnish would be according to the
  dictionary liikkuvuus

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What does wireless mean?

• Wireless is a term used to describe
  telecommunications in which electromagnetic waves
  carry the signal over an air interface
• In Finnish wireless can be translated to langaton

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Basic vocabulary

• Radio Base Station (RBS) tukiasema
• Access Point (AP) myös tukiasema esim. WLAN
• Mobile Terminal (MT) liikkuva päätelaite esim.
  kännykkä
• User Equipment (UE) myös päätelaite
• Radio Access Network (RAN) radioverkko,
  sisältää tukiaseman ja päätelaitteet
• Core Network (CN), runkoverkko, verkon ydinosa,
  johon voidaan liittää useita erilaisia
  radioverkkoja
• Vendor laitevalmistaja
• And the list goes on...

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Basic concepts
Antennas
Wireless link
Out of coverage
MT
Uplink
Downlink
RBS
Cell
MT
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Wireless networks

• Example Ad-hoc networks
• Built between terminals ad hoc with, e.g., WLAN,
  Bluetooth, infrared, or some other technology

• Example Cellular networks
• Built over large areas with core networks that
  connect to other networks, such as the Public
  Switched Telephone Network (PSTN)

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Wireless access

• Wireless networks can be divided roughly into two
  different categories
• Fixed wireless access no mobility involved
• Mobile wireless access mobility enabled in the
  network
• Independent of the terminal device as such, but
  terminal needs to support mobility to be able to
  utilize it
• There are also protocols and techniques around to
  enable mobility in fixed wireless networks

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Wireless technologies

• Several different wireless technologies exist
• Range (cell size), peak data rates, supported
  functions, etc. can vary significantly

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Examples of wireless technologies

• Long range
• HIPERLAN
• HIPERMAN
• IEEE 802.11 (WiFi)
• Ultra-wideband
• WiMAX
• xMax
• 3G (UMTS)
• GSM

• Short range
• ZigBee
• Wireless USB
• Bluetooth
• Wibree
• IrDA
• RFID

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Standardization

• Many wireless technologies, or parts of them, are
  standardized by different organizations
• Examples of such organizations
• 3rd Generation Partnership Project (3GPP)
• 3rd Generation Partnership Project 2 (3GPP2)
• Institute of Electrical and Electronics Engineers
  (IEEE)
• Standardization ensures interoperability between
  different vendors

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What is standardized?

• Examples of things standardized
• Access technology
• Radio protocols
• Retransmission timers
• Handover measurements
• Minimum delay targets
• MT states
• E.g., active, connected, paging
• Security
• Some standards are more specific than others

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3GPP Technologies

• The 3GPP technologies are part of the GSM family
  of technologies
• The GSM family is evolving
• 1G The first generation of analogue mobile phone
  technologies including AMPS, TACS and NMT
• 2G The second generation of digital mobile phone
  technologies including GSM, CDMA IS-95 and D-AMPS
  IS-136
• 2.5G The enhancement of GSM which includes
  technologies such as GPRS
• 3G The third generation of mobile phone
  technologies covered by the ITU IMT-2000 family
• http//www.3gpp.org

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3G Evolution in the future
2003/4
2005/6
2009/10
2007/8
2011/12
LTE Up to 200 Mbps DLon 20 MHz
HSPA Evolved Up to 42 Mbps DL on 5Mhz
HSUPA Up to 5 Mbps
HSDPA Up to 14 Mbps
WCDMA 0,5 Mbps
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IEEE Technologies

• 802.11 Wireless Local Area Networks (WLAN)
• Also known as Wi-Fi
• 802.16 Wireless Metropolitan Area Networks
  (WMAN)
• Also known as WiMAX
• Also standards like
• 802.15 Wireless Personal Area Networks (WPAN)
• 802.2 Ethernet
• 754 Floating point numbers
• 1003 Unix type programming standard, etc.
• http//standards.ieee.org/wireless/

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How does mobility work?

• In a cell, a terminal has a connection to the
  network
• When the terminal
• moves, the connection
• needs to move as well

Some network
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Handovers (1/5)

• Handover (or Handoff) is the action of moving a
  connection from one base station to another
• The decicion to make a handover is usually based
  on link quality measured by the terminal or the
  network
• The decision to make a handover can be made in
  the network or in the terminal, depending on what
  kind of network we are talking about

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Handovers (2/5)

• Hard handover the data transfer is moved from
  one base station to the other so that the old
  radio link is dropped and a new one is created
• Soft handover the data transfer is moved from
  one base station to the other so that there is a
  short period during which the the terminal has
  two radio links
• In UMTS there is also a Softer handover, which
  means a soft handover between cells that are in
  the same base station.
• 3G base stations often have three cells

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Handovers (3/5)

• Seamless handover means a handover during which
  the user does not have to interrupt the
  connection
• Example You are talking on the phone while
  riding a bus across the city, several seamless
  handovers happen during the ride.
• Example When you plug in your laptop to the
  Aalto-network at TKK, and later plug it in to
  some other network at home, you have basically
  done a hard handover with a long interruption
  time.

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Handovers (4/5)

• Intra-RAT handover
• A handover between two base stations of the same
  Radio Access Technology (RAT)
• Inter-RAT handover
• A handover from one RAT (e.g., UMTS) to another
  (e.g., GSM)
• Also called vertical handover

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Handovers (5/5)

• Synchronized handover
• Terminal and network negotiate a point in time
  when the handover will happen, simultaneously on
  both sides
• Non-synchronized handover
• Terminal or network decides on the handover and
  executes it without telling to the other party in
  advance

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Services and handovers

• Different services have different requirements
  for handovers regarding for example
• Interruption time
• Delay
• Packet losses

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Example FTP file download

• FTP connection uses Transmission Control Protocol
  (TCP)
• TCP tolerates short interruptions without a need
  to close the connection. Since TCP promises
  reliable transportation of data, it can recover
  from small data losses.

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Example Voice call

• Voice over IP (VoIP) uses User Datagram Protocol
  (UDP)
• UDP does not perform retransmissions, and thus
  lost packets will not be recovered. Voice data
  tolerates some delays and small interruptions.
• Voice quality may suffer if many packets are lost
  or delayed

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Velocity and handovers

• The faster a user moves, the shorter time there
  is to make the handover
• Significant difference if the user is walking (6
  km/h) or traveling in a high speed train (
  200-300 km/h)
• Note Handovers might happen also when the user
  is not moving, since the wireless link quality
  changes over time

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The Future? Seamless communication in
heterogeneous environments
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Summary

• There are several different kind of wireless
  technologies, which differ in, e.g., cell size,
  purpose, and technical details
• Mobility must be enabled either in the wireless
  system used, or in some other way in an outside
  network, and must be supported by the terminal
  device
• Moving from one BS to another is called handover
• Different services have different requirements
  for the handover duration and loss probability
• Terminal velocity has an impact on the
  successfullnes of a handover

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