Mobile Communications : Present and the Future


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Mobile communications: present and future (Part I)

Dr. Abhaya Sumanasena MSc PhD CEng MIET MIEEE

Delivered 22 January 2009 @ SLINTEC

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  • My services – anytime – anywhere – on my device Single standard in a harmonised spectrum Higher spectral efficiency Higher data rates to the user Larger capacity for the network New services at a lower cost per bit
  • 10 other different bands
  • UWC36 implemented with EDGE
  • Why spread we get gain by deliberately occupying more BW than we need Use more bandwidth to get gain and robustness Advantages disappear when spread less i.e. high data rate In a spread spectrum system, the 'processing gain' is the ratio of the spread (or RF) bandwidth to the unspread (or baseband) bandwidth. Spreading Operation transforms data symbols into chips. Thus increasing the bandwidth of the signal. The number of chips per data symbol is called the “Spreading Factor”SF”.The operation is done through multiplication with OVSF code .
  • CDMA – Meeting at UN HQ A guest at the Ambassador’s reception understands all languages (codes) in the room (cell) >Code-division She can therefore listen in on any conversation in the room >Multiple access To hear every one, she must get the people near her to talk quietly and the people far from her to talk loudly – she can then just hear every Conversation >Near-far effect As more people enter the room, the sound level increases, and so must every conversation level > Power control Eventually the people at the edge of the room are shouting as loud as they can but still can’t be Heard > Cell breathing
  • Distance= 2x > 12dB , 15 times To overcome the Near Far problem on the up link, a technique called power control is used. Power control sets the power of both mobiles 1 & 2 so that the received power at the cell site is nominally the same. The power can be set in two basic methods, firstly by the mobile using the power received from the base station secondly by the base station measuring the mobile power and explicitly telling the mobile what level to set it to.
  • innerloop via pc commands so that measured SIR fulfills the SIR target Two steps are required for power control. Estimate the minimum acceptable quality Ensure that min. power is used to maintain this quality Outer loop power control handles the first step, inner loop handles second.
  • SHO: The feature is possible because all cells use the same frequency and are separated only by codes Advantages and Disadvantages of Soft-Handover + Reducing the incidence of dropped calls due to handoff failures dramatically improving the call quality + Eliminating the audible effects of multipath fading Reducing average transmitted power (Saves handset power) + Improving Coverage of the cell. + Increasing Capacity - Requires more network resources - Increased infrastructure cost
  • Step 3 is the propagation model which converts the output of the link budget i.e. the maximum allowable path loss between the base station and a mobile at the edge of cell into a physical distance. Parameters for the propagation model include frequency, antenna height and the type of environment i.e. clutter type (dense urban, suburban, rural etc). Step 4 takes the site ranges for each clutter type as calculated from the propagation model and calculates the number of sites, by clutter type, in order to cover a certain area where this has been specified.
  • Low rate data = p rocessing gain 24 dBm=250 mW
  • capacity depends on available spectrum efficient use of the spectrum number of cells
  • HLR: A database, Master copy of users service profile, forbidden roaming areas, call forwarding infor,
  • Time varying channel Getting the base stations Different terminal implementations
  • Site sharing - sharing the mast, site, power, transmission, antennas and feeders NodeB* sharing – separate spectrum, separate RNC and separate core network, no terminal dependency RAN (Node B and RNC) sharing – No terminal dependency and no core network dependency Sharing and co-operating with a competitor is very challenging Agreeing who is doing what will be a key issues There can be two option for operations and management; Operators themselves A joint venture A neutral third party company As the neutral third party can impose strict service level agreements (SLAs) between operators, sharing deal can be implemented more successfully if the control is with a third party. In addition to the OPEX savings, one of the main benefits of network/spectrum sharing is achieving gain in radio resources known as “trunking gain” Base station, RNC and backhaul equipment cost about 50 % of the operators budget Gain achieved due to the aggregation of system resources. Probability that a voice or data session is blocked due to the lack of resources increases with the traffic load. This can be reduced by the bundling of radio resources of the multiple operators. Trunking gain can be achieved in power, base band units in the base station and in backhaul Trunking gain depends on the degree of sharing between operators and can have different gradations ranging from tight to very loose cooperation A crucial design and evaluation issue in multi-radio access scheme is the radio access selection procedure
  • Mobile Communications : Present and the Future

    1. 1. Mobile communications: present and future (Part I) Dr. Abhaya Sumanasena MSc PhD CEng MIET MIEEE 22 January 2009 Dr. Abhaya Sumanasena
    2. 2. Dr. Abhaya Sumanasena PhD CEng MIEEE MIET Dr. Abhaya Sumanasena is currently working as a Technical Policy Manager at Ofcom, the government regulator in UK. Prior to Ofocm, Abhaya has worked as a Principal Engineer in Ericsson, a global vendor, and in Hutchison 3UK, the first mobile operator dedicated to 3G services in the UK. During this period Abhaya has taken a leading role in designing, rolling out and optimization of 3G and the first HSDPA network in the UK. Before joining 3UK, Abhaya worked as a Researcher at Mitsubishi Electric research laboratory where he conducted research work for beyond 3G systems. During that period he also represented the company at IEEE standardisation meetings and European Union project consortiums. After obtaining his MSc in Radio & Communications Engineering at King's College London, Abhaya completed his Ph.D. in "Adaptive Physical layer for 3rd Generation Mobile Satellite Systems" from University of Surrey, Guildford. He has published 12 papers in international journals/major international conferences and obtained two patent rights. While pursuing his PhD, he won a special award for Research Excellence from Inmarsat. After his PhD, Abhaya has served as a Post Doctoral Research Fellow in CCSR, at University of Surrey.   At a very early stage during his academic career Abhaya has been recognized for his design skills by winning "Junior Inventor of the year award" twice in Sri Lanka and the best award for Electronics design twice in India. Abhaya has evaluated number of IET and IEEE papers in the area of mobile communications. His industry knowledge and expertise crosses a broad range of technologies, including 3G, Satellite, HSDPA, WiMAX and DVB. Abhaya has been involved in IET committee activities for about 9 years. After serving as the Chairman of the IET Surrey, he joined Berkshire area local network where he currently serves as the vice chairman.
    3. 3. <ul><ul><li>Some basics of mobile communications </li></ul></ul><ul><ul><li>Third generation (3G) mobile communication systems </li></ul></ul><ul><ul><li>High speed data transmission (HSDPA) </li></ul></ul><ul><ul><li>Practical challenges: capacity, coverage and </li></ul></ul><ul><ul><li>optimization of a mobile network </li></ul></ul><ul><ul><li>Future directions: long term evolution (LTE) </li></ul></ul><ul><ul><li>Regulatory aspects </li></ul></ul>Overview Dr. Abhaya Sumanasena
    4. 4. 3 rd Generation Mobile Communications Dr. Abhaya Sumanasena
    5. 5. Vision Dr. Abhaya Sumanasena Data rate (Mbps)
    6. 6. Spectrum Allocation WRC 92 Identified the bands 1710 - 1885 and 2500 - 2690 MHz for IMT-2000 Dr. Abhaya Sumanasena 1850 1900 1950 2000 2050 2100 2150 2200 1850 1900 1950 2000 2050 2100 2150 2200 North America MSS PCS Reserve Europe UMTS GSM 1800 DECT MSS 1880 MHz 1980 MHz Japan Korea (w/o PHS) MSS IMT 2000 PHS MSS IMT 2000 2160 MHz 1895 MHz 1918 MHz 1885 MHz ITU Allocations 1885 MHz 2025 MHz IMT 2000 2010 MHz 2110 MHz 2170 MHz China MSS IMT 2000 IMT 2000 IMT 2000 MSS UMTS 2170 MHz MSS 1885 MHz 1980 MHz A A D B E F C A A D B E F C M D S GSM 1800 1850 MHz WLL WLL
    7. 7. IMT2000 Radio Transmission Technologies UMTS OFDMA TDD WMAN WiMAX OFDMA Dr. Abhaya Sumanasena
    8. 8. What is CDMA ? Dr. Abhaya Sumanasena
    9. 9. Multiple Access Schemes
    10. 10. How does CDMA work ? <ul><li>Higher rate-of transition, causes spectral spreading </li></ul><ul><li>Higher spreading factor gives higher processing gain </li></ul>Dr. Abhaya Sumanasena
    11. 11. CDMA Receiver Dr. Abhaya Sumanasena
    12. 12. Code Division Multiple Access Dr. Abhaya Sumanasena
    13. 13. Capacity and interference Dr. Abhaya Sumanasena Situation is more complex when neighbour cells contribute to interference Hence reduce the capacity
    14. 14. Cell Breathing & soft capacity Low traffic load Cell edge C/I > required C/I for the service Loaded network C I Dr. Abhaya Sumanasena
    15. 15. “ Near far problem” <ul><li>Close mobile will cause interference to distant mobile </li></ul>Dr. Abhaya Sumanasena
    16. 16. Transmit Power control (TPC) Solution to “near far problem” <ul><li>Open-Loop </li></ul><ul><li>MS adjusts Tx level based on Received signal. </li></ul><ul><li>Reacts to Shadow signal variations (fading) </li></ul><ul><li>Slow Response time. </li></ul><ul><li>Closed-Loop </li></ul><ul><li>MS adjusts Tx level based on received control commands. </li></ul><ul><li>BS commands MS for adjustments based on Rx SNR . </li></ul><ul><li>Control frequency = 1500 Hz </li></ul>Dr. Abhaya Sumanasena
    17. 17. Node B1 Node B2 <ul><li>Macrodiversity </li></ul><ul><li>Seamless Coverage </li></ul><ul><li>Size of overlap area </li></ul><ul><li>On average 30-40% of users are expected to be in soft handover mode </li></ul>Soft Handover Dr. Abhaya Sumanasena
    18. 18. UMTS Network Architecture Dr. Abhaya Sumanasena
    19. 19. Simplified UMTS Architecture Handles switching, routing calls and data connections to external networks Dr. Abhaya Sumanasena
    20. 20. General UMTS Architecture Dr. Abhaya Sumanasena
    21. 21. UE RAB End to end services End-to-end services or Applications (i.e.Video game Internet access) MSC UMTS network External network SGSN Dr. Abhaya Sumanasena RNC
    22. 22. Signal flow Dr. Abhaya Sumanasena
    23. 23. UMTS Radio Network Planning Dr. Abhaya Sumanasena
    24. 24. “ Spreadsheet” Analysis Radio Network Planning Dr. Abhaya Sumanasena
    25. 25. Coverage <ul><li>The only way to get more coverage is to: </li></ul><ul><ul><li>- Transmit more power </li></ul></ul><ul><ul><li>- Transmit data slower </li></ul></ul><ul><ul><li>- Use bigger/higher antennas </li></ul></ul><ul><ul><li>- Use a lower frequency </li></ul></ul><ul><ul><li>- Use somebody else’s network </li></ul></ul>Dr. Abhaya Sumanasena <ul><li>Uplink transmit power likely to be the limiting factor in range </li></ul><ul><li>Downlink transmit power and peak data rate determine </li></ul><ul><li>downlink range. </li></ul><ul><li>Peak data rate then needs to be shared between users. </li></ul>
    26. 26. Terminal vs Coverage IET Vodafone lecture Dr. Abhaya Sumanasena
    27. 27. Data rate vs Coverage IET Vodafone lecture Dr. Abhaya Sumanasena
    28. 28. Capacity planning Dr. Abhaya Sumanasena
    29. 29. <ul><li>Use of enhanced technologies </li></ul><ul><ul><li>Transmit diversity: Fairly easy </li></ul></ul><ul><ul><li>Intelligent antenna: Technology not mature enough </li></ul></ul><ul><ul><li>- Multiuser Detectors: Technology not mature enough </li></ul></ul>Solutions to for capacity growth <ul><li>Reduced cell radius </li></ul><ul><ul><li>- Increased number of sites / equipment hence increased infrastructure cost </li></ul></ul><ul><li>Use of additional carrier </li></ul><ul><ul><li>- Increased number of sites / equipment hence increased infrastructure cost </li></ul></ul>Dr. Abhaya Sumanasena <ul><li>Increased Sectorisation </li></ul><ul><ul><li>- Antenna patterns are not perfect and will result in increased interference </li></ul></ul>
    30. 30. Impact on the capacity growth for network elements Dr. Abhaya Sumanasena
    31. 31. UMTS Optimization Dr. Abhaya Sumanasena
    32. 32. Some Optimisation parameters <ul><li>Cell availability </li></ul><ul><li>Call blocking probability </li></ul><ul><li>Call drop rate </li></ul><ul><li>Call completion success rate </li></ul><ul><li>Throughput at the edge of the cell (packet and voice calls) </li></ul><ul><li>End-to-end packet delay transfers </li></ul><ul><li>Cell search time </li></ul><ul><li>Call set up time </li></ul><ul><li>handover success rate </li></ul><ul><li>Measures from KPIs </li></ul>What does operator mean by “quality” Dr. Abhaya Sumanasena
    33. 33. C/I Plots Before and After Optimisation Dr. Abhaya Sumanasena Non optimised antenna tilts Poor C/I Downtilts of up to 6 ° Improved C/I Un-optimised Optimised C/I > 12 dB C/I < 12 dB C/I < 9 dB C/I < 6 dB C/I < 3 dB C/I <-6 dB C/I <-3 dB C/I < 0 dB
    34. 34. Drive tests/Walk tests Dr. Abhaya Sumanasena
    35. 35. Roaming and network sharing Dr. Abhaya Sumanasena
    36. 36. Roaming Dr. Abhaya Sumanasena
    37. 37. Network/Spectrum sharing Dr. Abhaya Sumanasena <ul><li>RAN and backhaul cost about 50 % from the budget </li></ul><ul><li>Site sharing can provide 30% cost saving for an operator [PA consulting group, LTE World Summit, Berlin, 2008] </li></ul><ul><li>Trunking gain </li></ul>