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Electronic Engineering George Alexander ELE 31EMT/EMC
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    Electronic Engineering George Alexander ELE 31EMT/EMC Electronic Engineering George Alexander ELE 31EMT/EMC Presentation Transcript

    • ELE 31EMT/EMC Engineering Management Mobile Cellular Telephones – an Overview Prepared by Dr Jean Armstrong with additional input from Michael Feramez 13 March, 2006
    •  
    • Cellular Generations
      • 1G
      • Basic Mobility
      • Basic Services
      • Incompatibility
      • 2G
      • Advanced Mobility (Roaming)
      • More Services (Data)
      • Towards Global Solution
      • 3G
      • Seamless Roaming
      • Service Concepts & Models
      • Global Radio Access
      • Global Solution
      1980 1990 2000
    • 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.
    • 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 -> subscribers always connected and on line
    • 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.
    • 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)
    • 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
    • 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 (<20 ) were available
      • the frequencies were not reused nearby
      cell site
    • Cellular mobile phones
      • The frequencies F1 are reused in non adjacent cells
      F1 F2 F1
    • 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
      1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5
    • 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
      1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5
    • 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
    • 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
      CE SN SN SN SN TL TL TL TL TL CE CE TL
    • Transmission
      • In POTS the transmission of voice signals is in analogue form along a pair of copper wires from the customer’s premises to the local exchange
      • Many methods of transmission are used between exchanges
        • analogue
        • digital
        • copper wire
        • optical fibre
        • microwave radio link
      CE SN SN SN SN TL TL TL TL TL CE CE TL
    • 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
    • Radio Transmission in the mobile network
      • Mobile telephones have frequency allocations around 800 - 900MHz.
      • 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
    • Signalling: H ow 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
      CE SN SN SN SN TL TL TL TL TL CE CE TL
    • 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 CEA SN1 SN2 CEB time
      • 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
      Message sequence diagram for telephone call
    • 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
    • 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
      CE SN SN SN SN TL TL TL TL TL CE CE TL
      • switching is based on switching matrices
      Switching Inlet 1 is connected to outlet 3 Inlet 2 is connected to outlet 1
    • Multistage switching
      • Most switching nodes have a series of switching stages.
    • 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
    • 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
    • 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
    • More about transmission in 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
    • Aspects of telephone system
      • transmission
      • signalling
      • switching
      • traffic
    • 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
    • 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
    • Modulation in analogue mobile phones
      • analogue mobile phones use frequency modulation
      • different carrier frequencies are used for different mobile phones within the same cell
    • 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
      analogue signal samples taken 8000 times per second each sample is converted into an eight bit binary number
    • 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
      A B C D A B C D
    • 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
    • GSM network Components BSC Base station controller BTS Base station transceiver Only Gateway MSCs have connection to other networks PSTN - public switched telephone network PLMN - public lands mobile network Mobile Station (MS) BSC BTS Base Station System (BSS) Mobile Switching Centre (MSC) PSTN and other networks
    • Relationship of network components to cells
      • Each cell has a BSS
      • A number of BSS are connected to a MSC
      1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5 1 7 2 3 6 4 5
    • Allocation of radio spectrum: Frequency 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
      frequency uplink B uplink A downlink A downlink B group of ‘channels’ each of which is 200kHz wide
    • Time Division Multiplexing: physical 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
    • 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
    • Broadcast control Channels
      • Broadcast control channels are downlink and point-to-multipoint
        • frequency correction channel carries information to allow the MS to adjust the carrier frequency accurately
        • synchronization control channel carries information for frame synchronization
        • broadcast control channel carries general information relevant to that cell e.g. which frequencies are associated with this cell
    • Common Control Channels
      • used to convey signalling information
      • shared by all the mobiles in the cell
      • point-to-point
        • Paging channel used to page the MS, downlink, point-to-point
        • random access channel used by MS to request allocation of a SDCCH, uplink, point-to-point
        • access grant channel used to allocate an SDCCH, downlink, point-to-point
      • SDCCH = stand-alone dedicated control channel
    • Dedicated Control Channels
      • point-to-point,
      • dedicated to signalling associated with one mobile
        • stand-alone dedicated control channel used for system signalling during a call set-up and before a traffic channel has been allocated. Up/downlink
        • slow associated control channel carries 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 channel steals slots from voice or data transmission. Used for example during handover
    • Additional Topics
      • Broadband
      • ADSL
      • EDGE
      • International telephone calls
      • DECT
      • Cable Modems
      • ATM
      • Bluetooth
      • VOIP
      • WLAN
    • 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.
    • 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
    • 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 (Release’99 & 2002 deployment) supports best effort packet data at speeds up to about 384 kbps
      • Phase 2 (Release’2000 & 2003 deployment) will add Voice over IP capability
      Universal Wireless Communications Consortium
    • DECT
      • Digital Enhanced Cordless Communication
      • “ A world-wide standard for short-range cordless mobility” – ETSI
      • Applications such as domestic cordless phones.
      • Cordless PABXs
    • Cable Modems
      • “ Cable modems are devices that allow high-speed access to the internet via a cable television network”.
      • International Engineering Consortium
    • 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
    • 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/
    • 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/
    • 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/
      • Thanks for your attention