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Electronic Engineering George Alexander ELE 31EMT/EMC


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Electronic Engineering George Alexander ELE 31EMT/EMC

  1. 1. ELE 31EMT/EMC Engineering Management Mobile Cellular Telephones – an Overview Prepared by Dr Jean Armstrong with additional input from Michael Feramez 12 March, 2007
  2. 3. Cellular Generations <ul><li>1G </li></ul><ul><li>Basic Mobility </li></ul><ul><li>Basic Services </li></ul><ul><li>Incompatibility </li></ul><ul><li>2G </li></ul><ul><li>Advanced Mobility (Roaming) </li></ul><ul><li>More Services (Data) </li></ul><ul><li>Towards Global Solution </li></ul><ul><li>3G </li></ul><ul><li>Seamless Roaming </li></ul><ul><li>Service Concepts & Models </li></ul><ul><li>Global Radio Access </li></ul><ul><li>Global Solution </li></ul>1980 1990 2000
  3. 4. Standardisation <ul><li>The uniform GSM standard in European countries has enabled globalisation of mobile communications. </li></ul><ul><li>ITU had a dream to specify one common global radio interface technology. </li></ul><ul><li>ITU harmonisation effort was done under the name FLPMTS (Future Public Land Mobile Telephony System) and later under IMT-2000. </li></ul><ul><li>In 1999, ITU approved an industry standard for third-generation (3G) wireless networks. </li></ul>
  4. 5. GPRS (2.5G) <ul><li>General Packet Radio Service </li></ul><ul><li>Enables high-speed wireless internet and other data communications </li></ul><ul><li>More than four times capacity of conventional GSM </li></ul><ul><li>Packet data service -> subscribers always connected and on line </li></ul>
  5. 6. 3G Key Requirements Services <ul><li>Within IMT-2000, the ITU has defined the following key requirements for 3G services: </li></ul><ul><ul><li>improved system capacity (traffic handling) , </li></ul></ul><ul><ul><li>backward compatibility with second-generation (2G) systems, </li></ul></ul><ul><ul><li>multimedia support (higher data speed) , and </li></ul></ul><ul><ul><li>high speed packet data services as shown on the next slide. </li></ul></ul>
  6. 7. High-Speed Packet Data Services <ul><li>2 Mbps in fixed or in-building environments (very short distances, in the order of metres) </li></ul><ul><li>384 kbps in pedestrian or urban environments </li></ul><ul><li>144 kbps in wide area mobile environments </li></ul><ul><li>Variable data rates in large geographic area systems (satellite) </li></ul>
  7. 8. Mobile Cellular Telephones <ul><li>Mobile phones use radio waves to transmit and receive voice signals </li></ul><ul><li>Useable electromagnetic spectrum is a limited resource with frequency allocations for broadcast television, radio, military applications etc </li></ul><ul><li>mobile phones could only have widespread application with the idea of frequency reuse </li></ul>
  8. 9. Mobile phone systems without frequency reuse <ul><li>Mobile phone systems without frequency reuse had large high powered transmitters at the cell site mounted on high towers and covered a large area. </li></ul><ul><li>Relatively few channels (<20 ) were available </li></ul><ul><li>the frequencies were not reused nearby </li></ul>cell site
  9. 10. Cellular mobile phones <ul><li>The frequencies F1 are reused in non adjacent cells </li></ul>F1 F2 F1
  10. 11. Frequency reuse schemes <ul><li>Many cellular systems are designed with the available channels divided into 7 groups </li></ul><ul><li>For equally spaced cell sites in flat terrain this results in hexagonal shaped cells </li></ul><ul><li>in practice cell shapes depend on the terrain and the distribution of users </li></ul>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
  11. 12. Cochannel interference <ul><li>A user may experience co-channel interference from users in other cells which have been allocated the same frequencies </li></ul><ul><li>For the hexagonal pattern shown below each cell has 6 interfering cells distance 4.6R away and other more distant interfering cells </li></ul>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
  12. 13. Aspects of telephone systems <ul><li>A cellular mobile phone systems has many of the same functions as the the wire based system (POTS) but these are often more complex </li></ul><ul><li>In addition it has a number of additional functions such as ‘handover’ which occurs when a user moves from one cell site to another </li></ul>
  13. 14. What do we know about the POTS network? <ul><li>CE customer equipment e.g. telephone </li></ul><ul><li>SN switching node e.g. telephone exchange </li></ul><ul><li>TL transmission link e.g. pair of copper wires from customer to local exchange </li></ul>CE SN SN SN SN TL TL TL TL TL CE CE TL
  14. 15. Transmission <ul><li>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 </li></ul><ul><li>Many methods of transmission are used between exchanges </li></ul><ul><ul><li>analogue </li></ul></ul><ul><ul><li>digital </li></ul></ul><ul><ul><li>copper wire </li></ul></ul><ul><ul><li>optical fibre </li></ul></ul><ul><ul><li>microwave radio link </li></ul></ul>CE SN SN SN SN TL TL TL TL TL CE CE TL
  15. 16. Transmission in mobile phone systems <ul><li>transmission between cell site and mobile is </li></ul><ul><ul><li>by radio </li></ul></ul><ul><ul><li>analogue or digital depending on system </li></ul></ul><ul><li>transmission from cell site through the network may use optical fibre, copper wire, or microwave radio </li></ul>
  16. 17. Radio Transmission in the mobile network <ul><li>Mobile telephones have frequency allocations around the 900MHz and 1800MHz frequencies. </li></ul><ul><li>The wavelength in free space at 900MHz is 0.33 metres </li></ul><ul><li>Multipath effects cause fading </li></ul><ul><ul><li>as well as the direct signal from the cell site to the antenna there may be a number of reflected signals </li></ul></ul><ul><ul><li>if the path lengths differ by half a wavelength they may cancel and a fade occurs </li></ul></ul><ul><ul><li>a mobile unit travelling at 24km/h in a fading environment will experience about 15 nulls per second. </li></ul></ul>reflected as well as direct signals may reach antenna
  17. 18. Signalling: H ow does the network know which phones to connect? <ul><li>When someone wishes to make a call they lift the telephone receiver which sends a signal to the exchange </li></ul>CE SN SN SN SN TL TL TL TL TL CE CE TL
  18. 19. 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
  19. 20. <ul><li>signalling between the telephone and the local exchange is customer network signalling </li></ul><ul><ul><li>transmitted along wire pair </li></ul></ul><ul><ul><li>must be easy for telephone to generate </li></ul></ul><ul><li>signalling between exchanges is network signalling </li></ul>Message sequence diagram for telephone call
  20. 21. Signalling in the mobile telephone network <ul><li>Signalling in the mobile network is much more difficult </li></ul><ul><ul><li>the customers move </li></ul></ul><ul><ul><li>a dedicated channel is not available between each telephone and a fixed local exchange </li></ul></ul>
  21. 22. Switching in POTS <ul><li>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 </li></ul>CE SN SN SN SN TL TL TL TL TL CE CE TL
  22. 23. <ul><li>switching is based on switching matrices </li></ul>Switching Inlet 1 is connected to outlet 3 Inlet 2 is connected to outlet 1
  23. 24. Multistage switching <ul><li>Most switching nodes have a series of switching stages. </li></ul>
  24. 25. Switching for the mobile network <ul><li>switching is more complex </li></ul><ul><ul><li>switching as mobile moves from one cell to another </li></ul></ul><ul><ul><li>switching from cell site into the mobile network </li></ul></ul><ul><ul><li>switching from mobile network to POTS network if required </li></ul></ul>
  25. 26. Busy hour traffic <ul><li>it would be too expensive to design the telephone network to cope with every possible traffic load </li></ul><ul><li>networks are usually designed to give a certain probability of a call being blocked during the ‘busy hour’ </li></ul><ul><li>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 </li></ul>
  26. 27. Traffic in the mobile network <ul><li>the traffic characteristics are different for the mobile network </li></ul><ul><ul><li>peak loads on arterial roads during the rush hour </li></ul></ul><ul><ul><li>peak loads in the city during the day </li></ul></ul><ul><li>need to consider the probability of a telephone moving between cells </li></ul><ul><li>sophisticated planning is required to achieve the best performance </li></ul><ul><li>channel allocations my be changed between cells so that resources are moved to t he cells which are busy at any particular time </li></ul>
  27. 28. More about transmission in the POTS <ul><li>Connection from the telephone to the local exchange is two wire </li></ul><ul><ul><li>transmission is baseband and is analogue: no modulation </li></ul></ul><ul><ul><li>the microphone generates a voltage across the two wires which is proportional to the sound input </li></ul></ul><ul><li>Connections between exchanges - separate paths for transmission in each direction </li></ul><ul><ul><li>used to be four wires - pair for each direction </li></ul></ul><ul><ul><li>now could be coaxial cable, microwave radio link, optical fibre etc, but distinct separate transmission channel for each direction </li></ul></ul>
  28. 29. Aspects of telephone system <ul><li>transmission </li></ul><ul><li>signalling </li></ul><ul><li>switching </li></ul><ul><li>traffic </li></ul>
  29. 30. Transmission: frequency range of voice signals <ul><li>Human ear can hear frequencies in range 20-16000Hz approx </li></ul><ul><li>Most of the energy is concentrated between 1KHz and 4KHz </li></ul><ul><li>International standard for telephony: only frequencies in range 300Hz to 3400Hz transmitted </li></ul>
  30. 31. Transmission: frequency division multiplexing <ul><li>when there are a number of trunks and significant distance between exchanges, a number of voice signals are multiplexed onto one carrier </li></ul><ul><li>the speech signal is bandlimited to 300Hz to 3400Hz. This signal is used to modulate a carrier. Single sideband modulation is used </li></ul>300 3400 Frequency
  31. 32. Modulation in analogue mobile phones <ul><li>analogue mobile phones use frequency modulation </li></ul><ul><li>different carrier frequencies are used for different mobile phones within the same cell </li></ul>
  32. 33. Digital transmission in POTS <ul><li>speech is transmitted in analogue form from handset to local exchange </li></ul><ul><li>usually at local exchange converted to digital form </li></ul><ul><ul><li>sampled 8000 times per second </li></ul></ul><ul><ul><li>each sample 8 bit word </li></ul></ul><ul><ul><li>resultant bit rate 64kbits/sec </li></ul></ul><ul><li>digital signals </li></ul><ul><ul><li>quality does not depend on distance </li></ul></ul><ul><ul><li>compatible with computers </li></ul></ul><ul><ul><li>more easily switched </li></ul></ul><ul><ul><li>can be multiplexed using time division multiplexing </li></ul></ul>analogue signal samples taken 8000 times per second each sample is converted into an eight bit binary number
  33. 34. Time Division Multiplexing <ul><li>Many media, such as coaxial cable and optical fibre, have the capacity to carry much more information than one telephone call. </li></ul><ul><li>In the past, frequency division multiplexing (FDM) was common. With FDM different carrier frequencies were used for different telephone channels </li></ul><ul><li>with time division multiplexing (TDM) different time slots are allocated to different calls </li></ul>A B C D A B C D
  34. 35. Multiplexing in the GSM system <ul><li>The GSM digital telephone network uses a combination of FDM and TDM </li></ul><ul><li>The available bandwidth is divided up into 200kHz bands </li></ul><ul><li>Each carrier frequency supports one direction of transmission for up to eight simultaneous telephone calls </li></ul><ul><li>These eight calls share the frequency using time division multiplexing </li></ul>
  35. 36. 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
  36. 37. Switching System (SS) Components <ul><li>MSC – Responsible for switching and supervision functions. Some act as gateway into other networks, GMSC </li></ul><ul><li>Home Location Register (HLR) contains subscriber information, subscriber number, services allowed, authentication parameters. Along with VLR, helps in locating the mobile subscriber. </li></ul><ul><li>Visitor Location Register (VLR) tracks the Location Area in which the subscriber is currently located. </li></ul><ul><li>Authentication Centre (AUC) – parameters </li></ul><ul><li>Equipment Identity Register (EIR) –equipment validation </li></ul><ul><li>Derived from some (quite old) Ericsson training material) </li></ul>
  37. 38. Relationship of network components to cells <ul><li>Each cell has a BSS </li></ul><ul><li>A number of BSS are connected to an MSC </li></ul>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
  38. 39. Allocation of radio spectrum: Frequency Division Multiplexing <ul><li>The radio spectrum available for digital mobile phones is divided up into ‘channels’ </li></ul><ul><li>signals are modulated onto carriers which are spaced at 200kHz </li></ul><ul><li>Certain frequencies are always allocated to uplinks (mobile to base station) and certain to downlinks (base station to mobile) </li></ul><ul><li>The available frequencies may be allocated to different operators </li></ul>frequency uplink B uplink A downlink A downlink B group of ‘channels’ each of which is 200kHz wide
  39. 40. Time Division Multiplexing: physical channels <ul><li>Each radio frequency carrier is modulated with a time division multiplexed signal </li></ul><ul><li>There are eight slots in a time division multiplexed frame </li></ul><ul><li>one time slot of a TDMA frame on one carrier is a physical channel </li></ul>TDMA Frame and contents when speech is being transmitted in a time slot
  40. 41. Logical Channels <ul><li>physical channels can be used for different types of logical channels </li></ul><ul><li>Traffic Channels (TCH) are used to carry encoded speech or user data </li></ul><ul><li>Control Channels are used to carry signalling and synchronization data </li></ul><ul><ul><li>broadcast control channels </li></ul></ul><ul><ul><li>common control channels </li></ul></ul><ul><ul><li>dedicated control channels </li></ul></ul>
  41. 42. Broadcast control Channels <ul><li>Broadcast control channels are downlink and point-to-multipoint </li></ul><ul><ul><li>frequency correction channel carries information to allow the MS to adjust the carrier frequency accurately </li></ul></ul><ul><ul><li>synchronization control channel carries information for frame synchronization </li></ul></ul><ul><ul><li>broadcast control channel carries general information relevant to that cell e.g. which frequencies are associated with this cell </li></ul></ul>
  42. 43. Common Control Channels <ul><li>used to convey signalling information </li></ul><ul><li>shared by all the mobiles in the cell </li></ul><ul><li>point-to-point </li></ul><ul><ul><li>Paging channel used to page the MS, downlink, point-to-point </li></ul></ul><ul><ul><li>random access channel used by MS to request allocation of a SDCCH, uplink, point-to-point </li></ul></ul><ul><ul><li>access grant channel used to allocate an SDCCH, downlink, point-to-point </li></ul></ul><ul><li>SDCCH = stand-alone dedicated control channel </li></ul>
  43. 44. Dedicated Control Channels <ul><li>point-to-point, </li></ul><ul><li>dedicated to signalling associated with one mobile </li></ul><ul><ul><li>stand-alone dedicated control channel used for system signalling during a call set-up and before a traffic channel has been allocated. Up/downlink </li></ul></ul><ul><ul><li>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 </li></ul></ul><ul><ul><li>fast associated control channel steals slots from voice or data transmission. Used for example during handover </li></ul></ul>
  44. 45. Additional Topics <ul><li>Broadband </li></ul><ul><li>ADSL </li></ul><ul><li>EDGE </li></ul><ul><li>International telephone calls </li></ul><ul><li>DECT </li></ul><ul><li>Cable Modems </li></ul><ul><li>ATM </li></ul><ul><li>Bluetooth </li></ul><ul><li>VOIP </li></ul><ul><li>WLAN </li></ul>
  45. 46. Broadband <ul><li>“ Broadband communication consists of the technologies and equipment required to deliver packet-based voice, video and data services to end users” </li></ul><ul><li>International Engineering Consortium </li></ul><ul><li>This provides much faster speeds than dial-up connections (max 56kbps) with the additional benefit of not tying up a phone line. </li></ul>
  46. 47. ADSL <ul><li>Asymmetric Digital Subscriber Line </li></ul><ul><li>“ A modem technology that converts existing twisted- pair telephone lines into access paths for high-speed communication …” </li></ul><ul><li> International Engineering Consortium </li></ul>
  47. 48. EDGE - Enhanced Data-rates for Global Communication <ul><li>Evolutionary path to 3G services for GSM and TDMA operators </li></ul><ul><li>Builds on General Packet Radio Service (GPRS) air interface and networks </li></ul><ul><li>Phase 1 (Release’99 & 2002 deployment) supports best effort packet data at speeds up to about 384 kbps </li></ul><ul><li>Phase 2 (Release’2000 & 2003 deployment) will add Voice over IP capability </li></ul>Universal Wireless Communications Consortium
  48. 49. DECT <ul><li>Digital Enhanced Cordless Communication </li></ul><ul><li>“ A world-wide standard for short-range cordless mobility” – ETSI </li></ul><ul><li>Applications such as domestic cordless phones. </li></ul><ul><li>Cordless PABXs </li></ul>
  49. 50. Cable Modems <ul><li>“ Cable modems are devices that allow high-speed access to the internet via a cable television network”. </li></ul><ul><li>International Engineering Consortium </li></ul>
  50. 51. ATM <ul><li>Asynchronous Transfer Mode </li></ul><ul><li>“ A high-performance, cell-orientated switching and multiplexing technology that utilises fixed-length packets to carry different types of traffic”. </li></ul><ul><li>International Engineering Consortium </li></ul>
  51. 52. Bluetooth <ul><li>Short range radio technology </li></ul><ul><li>Enables transmission of signals over short distances between telephones, computers and other devices. </li></ul><ul><li>Eliminates the need for wires/cables. </li></ul><ul><li>It is a global standard developed jointly by major telecommunications suppliers Intel, Nokia, Ericsson, Toshiba, IBM </li></ul><ul><li>Ref. </li></ul>
  52. 53. VOIP <ul><li>Uses internet to transmit voice </li></ul><ul><li>Is gradually replacing the traditional telephone network for transmitting voice. </li></ul><ul><li>Some initial quality problems are being addressed </li></ul><ul><li>Ref. </li></ul>
  53. 54. WLAN <ul><li>Wireless Local Area Network </li></ul><ul><li>Complements access technologies for cellular networks </li></ul><ul><li>High data rates – up to 54Mbps </li></ul><ul><li>Used in indoor ‘hotspots’ </li></ul><ul><li>Ref. </li></ul>
  54. 55. <ul><li>Thanks for your attention </li></ul>