ELE 31EMTEMC Engineering Management

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ELE 31EMT/EMC Engineering Management

• Mobile Cellular Telephones an Overview
• Prepared by Dr Jean Armstrong with additional
  input from Michael Feramez

12 March, 2007
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(No Transcript)
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Cellular Generations

• 3G
• Seamless Roaming
• Service Concepts Models
• Global Radio Access
• Global Solution

• 2G
• Advanced Mobility (Roaming)
• More Services (Data)
• Towards Global Solution

• 1G
• Basic Mobility
• Basic Services
• Incompatibility

1980
1990
2000
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Standardisation

• The uniform GSM standard in European countries
  has enabled globalisation of mobile
  communications.
• ITU had a dream to specify one common global
  radio interface technology.
• ITU harmonisation effort was done under the name
  FLPMTS (Future Public Land Mobile Telephony
  System) and later under IMT-2000.
• In 1999, ITU approved an industry standard for
  third-generation (3G) wireless networks.

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GPRS (2.5G)

• General Packet Radio Service
• Enables high-speed wireless internet and other
  data communications
• More than four times capacity of conventional GSM
• Packet data service -gt subscribers always
  connected and on line

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3G Key Requirements Services

• Within IMT-2000, the ITU has defined the
  following key requirements for 3G services
• improved system capacity (traffic handling),
• backward compatibility with second-generation
  (2G) systems,
• multimedia support (higher data speed), and
• high speed packet data services as shown on the
  next slide.

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High-Speed Packet Data Services

• 2 Mbps in fixed or in-building environments (very
  short distances, in the order of metres)
• 384 kbps in pedestrian or urban environments
• 144 kbps in wide area mobile environments
• Variable data rates in large geographic area
  systems (satellite)

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Mobile Cellular Telephones

• Mobile phones use radio waves to transmit and
  receive voice signals
• Useable electromagnetic spectrum is a limited
  resource with frequency allocations for broadcast
  television, radio, military applications etc
• mobile phones could only have widespread
  application with the idea of frequency reuse

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Mobile phone systems without frequency reuse

• Mobile phone systems without frequency reuse had
  large high powered transmitters at the cell site
  mounted on high towers and covered a large area.
  
• Relatively few channels (lt20 ) were available
• the frequencies were not reused nearby

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Cellular mobile phones

• The frequencies F1 are reused in non adjacent
  cells

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Frequency reuse schemes

• Many cellular systems are designed with the
  available channels divided into 7 groups
• For equally spaced cell sites in flat terrain
  this results in hexagonal shaped cells
• in practice cell shapes depend on the terrain and
  the distribution of users

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Cochannel interference

• A user may experience co-channel interference
  from users in other cells which have been
  allocated the same frequencies
• For the hexagonal pattern shown below each cell
  has 6 interfering cells distance 4.6R away and
  other more distant interfering cells

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Aspects of telephone systems

• A cellular mobile phone systems has many of the
  same functions as the the wire based system
  (POTS) but these are often more complex
• In addition it has a number of additional
  functions such as handover which occurs when a
  user moves from one cell site to another

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What do we know about the POTS network?

• CE customer equipment e.g. telephone
• SN switching node e.g. telephone exchange
• TL transmission link e.g. pair of copper wires
  from customer to local exchange

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Transmission

• In POTS the transmission of voice signals is in
  analogue form along a pair of copper wires from
  the customers premises to the local exchange
• Many methods of transmission are used between
  exchanges
• analogue
• digital
• copper wire
• optical fibre
• microwave radio link

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Transmission in mobile phone systems

• transmission between cell site and mobile is
• by radio
• analogue or digital depending on system
• transmission from cell site through the network
  may use optical fibre, copper wire, or microwave
  radio

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Radio Transmission in the mobile network

• Mobile telephones have frequency allocations
  around the 900MHz and 1800MHz frequencies.
• The wavelength in free space at 900MHz is 0.33
  metres
• Multipath effects cause fading
• as well as the direct signal from the cell site
  to the antenna there may be a number of reflected
  signals
• if the path lengths differ by half a wavelength
  they may cancel and a fade occurs
• a mobile unit travelling at 24km/h in a fading
  environment will experience about 15 nulls per
  second.

reflected as well as direct signals may reach
antenna
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SignallingHow does the network know which
phones to connect?

• When someone wishes to make a call they lift the
  telephone receiver which sends a signal to the
  exchange

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Establishing a call between two phones on
different local exchanges
The calling party is often called the A party and
the called party the B party
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Message sequence diagram for telephone call

• signalling between the telephone and the local
  exchange is customer network signalling
• transmitted along wire pair
• must be easy for telephone to generate
• signalling between exchanges is network signalling

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Signalling in the mobile telephone network

• Signalling in the mobile network is much more
  difficult
• the customers move
• a dedicated channel is not available between each
  telephone and a fixed local exchange

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Switching in POTS

• In response to the signalling sequence a
  connection is made between the calling (A) party
  and the called (B) party this requires switching
  of the call

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Switching
Inlet 1 is connected to outlet 3 Inlet 2 is
connected to outlet 1

• switching is based on switching matrices

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Multistage switching

• Most switching nodes have a series of switching
  stages.

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Switching for the mobile network

• switching is more complex
• switching as mobile moves from one cell to
  another
• switching from cell site into the mobile network
• switching from mobile network to POTS network if
  required

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Busy hour traffic

• it would be too expensive to design the telephone
  network to cope with every possible traffic load
• networks are usually designed to give a certain
  probability of a call being blocked during the
  busy hour
• the usual design rule for the fixed telephone
  network is that there should be a probability of
  0.02 of blocking of a call during busy hour

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Traffic in the mobile network

• the traffic characteristics are different for the
  mobile network
• peak loads on arterial roads during the rush hour
• peak loads in the city during the day
• need to consider the probability of a telephone
  moving between cells
• sophisticated planning is required to achieve the
  best performance
• channel allocations my be changed between cells
  so that resources are moved to t he cells which
  are busy at any particular time

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More about transmissionin the POTS

• Connection from the telephone to the local
  exchange is two wire
• transmission is baseband and is analogue no
  modulation
• the microphone generates a voltage across the two
  wires which is proportional to the sound input
• Connections between exchanges - separate paths
  for transmission in each direction
• used to be four wires - pair for each direction
• now could be coaxial cable, microwave radio link,
  optical fibre etc, but distinct separate
  transmission channel for each direction

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Aspects of telephone system

• transmission
• signalling
• switching
• traffic

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Transmission frequency range of voice signals

• Human ear can hear frequencies in range
  20-16000Hz approx
• Most of the energy is concentrated between 1KHz
  and 4KHz
• International standard for telephony only
  frequencies in range 300Hz to 3400Hz transmitted

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Transmission frequency division multiplexing

• when there are a number of trunks and significant
  distance between exchanges, a number of voice
  signals are multiplexed onto one carrier
• the speech signal is bandlimited to 300Hz to
  3400Hz. This signal is used to modulate a
  carrier. Single sideband modulation is used

300 3400 Frequency
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Modulation in analogue mobile phones

• analogue mobile phones use frequency modulation
• different carrier frequencies are used for
  different mobile phones within the same cell

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Digital transmission in POTS

• speech is transmitted in analogue form from
  handset to local exchange
• usually at local exchange converted to digital
  form
• sampled 8000 times per second
• each sample 8 bit word
• resultant bit rate 64kbits/sec
• digital signals
• quality does not depend on distance
• compatible with computers
• more easily switched
• can be multiplexed using time division
  multiplexing

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Time Division Multiplexing

• Many media, such as coaxial cable and optical
  fibre, have the capacity to carry much more
  information than one telephone call.
• In the past, frequency division multiplexing
  (FDM) was common. With FDM different carrier
  frequencies were used for different telephone
  channels
• with time division multiplexing (TDM) different
  time slots are allocated to different calls

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Multiplexing in the GSM system

• The GSM digital telephone network uses a
  combination of FDM and TDM
• The available bandwidth is divided up into 200kHz
  bands
• Each carrier frequency supports one direction of
  transmission for up to eight simultaneous
  telephone calls
• These eight calls share the frequency using time
  division multiplexing

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GSM network Components
Only Gateway MSCs have connection to other
networks
BSC Base station controller BTS Base station
transceiver
PSTN - public switched telephone network PLMN -
public lands mobile network
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Switching System (SS) Components

• MSC Responsible for switching and supervision
  functions. Some act as gateway into other
  networks, GMSC
• Home Location Register (HLR) contains subscriber
  information, subscriber number, services allowed,
  authentication parameters. Along with VLR, helps
  in locating the mobile subscriber.
• Visitor Location Register (VLR) tracks the
  Location Area in which the subscriber is
  currently located.
• Authentication Centre (AUC) parameters
• Equipment Identity Register (EIR) equipment
  validation
• Derived from some (quite old) Ericsson training
  material)

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Relationship of network components to cells

• Each cell has a BSS
• A number of BSS are connected to an MSC

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Allocation of radio spectrumFrequency Division
Multiplexing

• The radio spectrum available for digital mobile
  phones is divided up into channels
• signals are modulated onto carriers which are
  spaced at 200kHz
• Certain frequencies are always allocated to
  uplinks (mobile to base station) and certain to
  downlinks (base station to mobile)
• The available frequencies may be allocated to
  different operators

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Time Division Multiplexingphysical channels

• Each radio frequency carrier is modulated with a
  time division multiplexed signal
• There are eight slots in a time division
  multiplexed frame
• one time slot of a TDMA frame on one carrier is a
  physical channel

TDMA Frame and contents when speech is being
transmitted in a time slot
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Logical Channels

• physical channels can be used for different types
  of logical channels
• Traffic Channels (TCH) are used to carry encoded
  speech or user data
• Control Channels are used to carry signalling and
  synchronization data
• broadcast control channels
• common control channels
• dedicated control channels

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Broadcast control Channels

• Broadcast control channels are downlink and
  point-to-multipoint
• frequency correction channelcarries information
  to allow the MS to adjust the carrier frequency
  accurately
• synchronization control channelcarries
  information for frame synchronization
• broadcast control channelcarries general
  information relevant to that cell e.g. which
  frequencies are associated with this cell

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Common Control Channels

• used to convey signalling information
• shared by all the mobiles in the cell
• point-to-point
• Paging channelused to page the MS, downlink,
  point-to-point
• random access channelused by MS to request
  allocation of a SDCCH, uplink, point-to-point
• access grant channelused to allocate an SDCCH,
  downlink, point-to-point
• SDCCH stand-alone dedicated control channel

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Dedicated Control Channels

• point-to-point,
• dedicated to signalling associated with one
  mobile
• stand-alone dedicated control channelused for
  system signalling during a call set-up and before
  a traffic channel has been allocated. Up/downlink
• slow associated control channelcarries
  information such as measurement reports from the
  mobile about received signal strengths from
  adjacent cells. Is carried in control slots of
  multiframe. up/downlink
• fast associated control channelsteals slots from
  voice or data transmission. Used for example
  during handover

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Additional Topics

• Broadband
• ADSL
• EDGE
• International telephone calls
• DECT
• Cable Modems
• ATM
• Bluetooth
• VOIP
• WLAN

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Broadband

• Broadband communication consists of the
  technologies and equipment required to deliver
  packet-based voice, video and data services to
  end users
• International Engineering Consortium
• This provides much faster speeds than dial-up
  connections (max 56kbps) with the additional
  benefit of not tying up a phone line.

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ADSL

• Asymmetric Digital Subscriber Line
• A modem technology that converts existing
  twisted- pair telephone lines into access paths
  for high-speed communication
• International Engineering Consortium

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EDGE - Enhanced Data-rates for Global
Communication

• Evolutionary path to 3G services for GSM and TDMA
  operators
• Builds on General Packet Radio Service (GPRS)
  air interface and networks
• Phase 1 (Release99 2002 deployment) supports
  best effort packet data at speeds up to about 384
  kbps
• Phase 2 (Release2000 2003 deployment) will add
  Voice over IP capability

Universal Wireless Communications Consortium
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DECT

• Digital Enhanced Cordless Communication
• A world-wide standard for short-range cordless
  mobility ETSI
• Applications such as domestic cordless phones.
• Cordless PABXs

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Cable Modems

• Cable modems are devices that allow high-speed
  access to the internet via a cable television
  network.
• International Engineering Consortium

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ATM

• Asynchronous Transfer Mode
• A high-performance, cell-orientated switching
  and multiplexing technology that utilises
  fixed-length packets to carry different types of
  traffic.
• International Engineering Consortium

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Bluetooth

• Short range radio technology
• Enables transmission of signals over short
  distances between telephones, computers and other
  devices.
• Eliminates the need for wires/cables.
• It is a global standard developed jointly by
  major telecommunications suppliers Intel, Nokia,
  Ericsson, Toshiba, IBM
• Ref. http//www.ericsson.com/technology/

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VOIP

• Uses internet to transmit voice
• Is gradually replacing the traditional telephone
  network for transmitting voice.
• Some initial quality problems are being addressed
• Ref. http//www.budde.com.au/

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WLAN

• Wireless Local Area Network
• Complements access technologies for cellular
  networks
• High data rates up to 54Mbps
• Used in indoor hotspots
• Ref. http//www.ericsson.com/technology/

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• Thanks for your attention