IS95 system engineering Song Pengpeng
Fundamentals of CDMA--- Orthogonal spreading sequences <ul><li>Orthogonal sequences  </li></ul><ul><ul><li>The cross-corre...
Fundamentals of CDMA---Vocoder <ul><li>Source coding </li></ul><ul><ul><li>In wireline applications: PCM, ADPCM,DM </li></...
Fundamentals of CDMA --- Power Control <ul><li>Power control on forward link : </li></ul><ul><li>Power control on reverse ...
Fundamentals of CDMA --- Power Control @ BTS <ul><li>Reverse link power control @ BTS </li></ul>
Fundamentals of CDMA --- Power Control @ MS <ul><li>Reverse link power control @ MS </li></ul>
Fundamentals of CDMA --- Soft Handoff <ul><li>Soft handoff---between different cells </li></ul><ul><ul><li>Forward link </...
Part I: IS95 system characteristics--- Layered structure <ul><li>TIA IS95 Layered Structure </li></ul>
Part I: IS95 system characteristics---Forward traffic link <ul><li>The forward traffic link is based on a design that empl...
Part I: IS95 system characteristics---Reverse traffic link <ul><li>The reverse traffic link employs long PN code for sprea...
Part I: IS95 system characteristics---Pilot Channel <ul><li>Pilot Channel is effectively the   PN sequences itself   and c...
Part I: IS95 system characteristics---Sync Channel <ul><li>The Sync Channel carries baseband information at 1.2 kbps and i...
Part I: IS95 system characteristics---Paging Channel <ul><li>Unlike the sync channel, paging channel transmits at higher r...
Part I: IS95 system characteristics---Paging Channel frame structure <ul><li>Paging channel structure and message content:...
Part I: IS95 system characteristics---Forward Traffic Channel for Rate Set 1 <ul><li>Power Control Bits are multiplexed on...
Part I: IS95 system characteristics---Forward link modulator <ul><li>The signals from pilot channel,sync channel,paging ch...
Part I: IS95 system characteristics---Access Channel <ul><li>Access channel is used by the mobile to communicate with the ...
Part I: IS95 system characteristics---Access Channel frame structure <ul><li>Access channel slots </li></ul><ul><ul><li>Ac...
Part I: IS95 system characteristics---Reverse Traffic Channel for Rate Set 1 <ul><li>Reverse traffic channel for rate set ...
Part I: IS95 system characteristics---signaling transmission <ul><li>Multiplex Option1 </li></ul><ul><ul><li>Blank and bur...
Part II: IS95 system  design engineering <ul><li>Pilot Channel </li></ul><ul><li>Forward link analysis </li></ul><ul><li>R...
Part II: IS95 system design engineering---Pilot Channel <ul><li>Ec/Io plays a prominent role in determining whether or not...
Part II: IS95 system design engineering---Forward link analysis <ul><li>Forward link Eb/No translates directly into BER </...
Part II: IS95 system design engineering---Reverse link analysis <ul><li>IS95 has no pilot on reverse link; the link Eb/No ...
Part II: IS95 system design engineering---PN offset planning <ul><li>In IS95 system, PN offset  is used to identify each B...
Part II: IS95 system design engineering---PN offset planning <ul><li>Co-PN offset management   ---the minimum required dis...
Part II: IS95 system design engineering---PN offset planning <ul><li>Adjacent PN offset management   --- the necessary con...
Part III: IS95 performance engineering <ul><li>Channel supervision </li></ul><ul><ul><li>Consecutive 12 bad frames </li></...
Part III: IS95 performance engineering <ul><li>Example: soft handoff with SRCH_WIN_A setting </li></ul>Conclusion: SRCH_WI...
Part III: IS95 performance engineering <ul><li>Field Optimization </li></ul><ul><li>Recall that   </li></ul><ul><ul><li>Pi...
Part IV: Traffic engineering <ul><li>Fundamental Concepts </li></ul><ul><ul><li>Traffic Intensity </li></ul></ul><ul><ul><...
Part IV: Traffic engineering <ul><li>Erlang B model: </li></ul><ul><ul><li>Assumes that blocked calls are cleared and trie...
Part IV: Traffic engineering <ul><li>CDMA applications: </li></ul><ul><ul><li>Hard blocking---no channel available </li></...
Part IV: Traffic engineering <ul><li>Considering the voice activity factor  and Poisson distributed active calls with mean...
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Is95 System Engineering

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An overview of IS95 radio interface rationale and system engineering aspects.

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  • Transcript of "Is95 System Engineering"

    1. 1. IS95 system engineering Song Pengpeng
    2. 2. Fundamentals of CDMA--- Orthogonal spreading sequences <ul><li>Orthogonal sequences </li></ul><ul><ul><li>The cross-correlation should be zero or very small </li></ul></ul><ul><ul><li>Each sequence in the set has an equal number of 1s and –1s, or the number of 1s differs from that of –1s by at most one </li></ul></ul><ul><ul><li>The scaled dot product of each code should equal to 1 </li></ul></ul><ul><li>Walsh codes --- Hadmard matrix </li></ul><ul><li>PN codes --- linear feedback shift registers </li></ul>
    3. 3. Fundamentals of CDMA---Vocoder <ul><li>Source coding </li></ul><ul><ul><li>In wireline applications: PCM, ADPCM,DM </li></ul></ul><ul><ul><li>In wireless applications: Vocoder </li></ul></ul><ul><ul><ul><li>PCM is not feasible in wireless applications due to limited bandwidth available </li></ul></ul></ul><ul><li>Characteristics of human speech </li></ul><ul><ul><li>Human voice is made up of voiced and unvoiced sounds </li></ul></ul><ul><ul><li>Although human voice is time varying, its spectrum is typically stationary over a period between 20 and 40 ms. That is the reason why most vocoders produce frames that have a duration on this order. </li></ul></ul>
    4. 4. Fundamentals of CDMA --- Power Control <ul><li>Power control on forward link : </li></ul><ul><li>Power control on reverse link: </li></ul><ul><ul><li>Open-loop power control: </li></ul></ul><ul><ul><li>Closed-loop power control: </li></ul></ul><ul><ul><ul><li>Inner-loop power control: </li></ul></ul></ul><ul><ul><ul><li>Outer-loop power control: </li></ul></ul></ul>BTS compares the FER on the forward link reported by MS via PMRM message and adjusts its forward link power. BTS monitors Eb/No on the reverse link and informs MS to adjust its transmission power BTS adjusts Eb/No threshold according to FER measurement Mobile adjusts its power via:
    5. 5. Fundamentals of CDMA --- Power Control @ BTS <ul><li>Reverse link power control @ BTS </li></ul>
    6. 6. Fundamentals of CDMA --- Power Control @ MS <ul><li>Reverse link power control @ MS </li></ul>
    7. 7. Fundamentals of CDMA --- Soft Handoff <ul><li>Soft handoff---between different cells </li></ul><ul><ul><li>Forward link </li></ul></ul><ul><ul><ul><li>mobile demodulates the signals from two base stations </li></ul></ul></ul><ul><ul><li>Reverse link </li></ul></ul><ul><ul><ul><li>mobile’s transmitted signal is received by both base stations and combined at MSC </li></ul></ul></ul><ul><li>Softer handoff---between different sectors </li></ul><ul><li>Hard handoff </li></ul>
    8. 8. Part I: IS95 system characteristics--- Layered structure <ul><li>TIA IS95 Layered Structure </li></ul>
    9. 9. Part I: IS95 system characteristics---Forward traffic link <ul><li>The forward traffic link is based on a design that employs a combination of FDMA,orthogonal multiple access(OMA) and CDMA techniques. </li></ul>Why use quadrature PN sequence? Why use long PN code here?
    10. 10. Part I: IS95 system characteristics---Reverse traffic link <ul><li>The reverse traffic link employs long PN code for spreading and user terminal identification purposes. </li></ul>Usage of orthogonal modulation due to the non-coherent nature of reverse link OQPSK--- this chip delay is to make sure that the QPSK signal envelope will not collapse to zero
    11. 11. Part I: IS95 system characteristics---Pilot Channel <ul><li>Pilot Channel is effectively the PN sequences itself and contains no information. </li></ul><ul><li>Pilot channel provides the mobile with timing and phase reference. </li></ul><ul><li>Pilot symbol strength is a key measurement in soft handoff. </li></ul>
    12. 12. Part I: IS95 system characteristics---Sync Channel <ul><li>The Sync Channel carries baseband information at 1.2 kbps and is spread by Walsh function 32. </li></ul>
    13. 13. Part I: IS95 system characteristics---Paging Channel <ul><li>Unlike the sync channel, paging channel transmits at higher rates at 4.8 kbps or 9.6 kbps. </li></ul>Why use a long scrambling code here?
    14. 14. Part I: IS95 system characteristics---Paging Channel frame structure <ul><li>Paging channel structure and message content: </li></ul><ul><ul><li>System parameters message </li></ul></ul><ul><ul><ul><li>hand-off parameters; </li></ul></ul></ul><ul><ul><ul><li>e.g T_ADD,SRCH_WIN_A </li></ul></ul></ul><ul><ul><ul><li>Forward power-control parameters </li></ul></ul></ul><ul><ul><ul><li>e.g PWR_REP_FRAMES </li></ul></ul></ul><ul><ul><li>Access parameters message </li></ul></ul><ul><ul><ul><li>Reverse power-control parameters </li></ul></ul></ul><ul><ul><ul><li>e.g INIT_POWER </li></ul></ul></ul><ul><ul><ul><li>Access parameters </li></ul></ul></ul><ul><ul><ul><li>e.g NUM_STEP,ACC_TMO </li></ul></ul></ul><ul><ul><ul><li>Access channel parameters </li></ul></ul></ul><ul><ul><ul><li>e.g MAX_CAP_SZ </li></ul></ul></ul><ul><ul><li>Neighbor list message </li></ul></ul><ul><ul><ul><li>PN offsets of neighbors </li></ul></ul></ul>
    15. 15. Part I: IS95 system characteristics---Forward Traffic Channel for Rate Set 1 <ul><li>Power Control Bits are multiplexed onto forward traffic channel </li></ul>the vocoder outputs variable data rate. To reduce overall interference power at a given time when lower rate are transmitted.
    16. 16. Part I: IS95 system characteristics---Forward link modulator <ul><li>The signals from pilot channel,sync channel,paging channel and forward traffic channel are coherently added to form the composite spread-spectrum signal. </li></ul>
    17. 17. Part I: IS95 system characteristics---Access Channel <ul><li>Access channel is used by the mobile to communicate with the base station when the mobile doesn’t have a traffic channel assigned. </li></ul>
    18. 18. Part I: IS95 system characteristics---Access Channel frame structure <ul><li>Access channel slots </li></ul><ul><ul><li>Access channel frames </li></ul></ul><ul><ul><ul><li>88 information bits + 8 encoder tail bits </li></ul></ul></ul>
    19. 19. Part I: IS95 system characteristics---Reverse Traffic Channel for Rate Set 1 <ul><li>Reverse traffic channel for rate set 1 </li></ul>to take advantage of voice activity factor to reduce reverse-link power during quieter periods of speech--- to randomly mask out redundant symbols produced by symbol repetition
    20. 20. Part I: IS95 system characteristics---signaling transmission <ul><li>Multiplex Option1 </li></ul><ul><ul><li>Blank and burst </li></ul></ul><ul><ul><ul><li>the entire traffic channel frame is used to send only secondary data </li></ul></ul></ul><ul><ul><li>Dim and burst </li></ul></ul><ul><ul><ul><li>The entire traffic channel frame is used to send both primary and secondary data </li></ul></ul></ul>Example: tranffic channel frame structure
    21. 21. Part II: IS95 system design engineering <ul><li>Pilot Channel </li></ul><ul><li>Forward link analysis </li></ul><ul><li>Reverse link analysis </li></ul><ul><li>PN offset planning </li></ul>System design engineering --- Whether or not the CDMA design of the cell, cluster or system will support the basic radio links? --- basic measurements: Ec/Io on pilot,Eb/No on forward traffic channel, Eb/No on reverse traffic channel.
    22. 22. Part II: IS95 system design engineering---Pilot Channel <ul><li>Ec/Io plays a prominent role in determining whether or not a mobile is within the coverage of a base station </li></ul><ul><li>--- Ec/Io effectively determines the forward coverage area of a cell or sector </li></ul>fraction of home base station overhead ERP allocated to pilot power power received at the probe mobile from overhead power emitted by home base station the total traffic channel power received at the probe mobile from the home base station thermal noise power path loss from home base station in the direction to the probe mobile a distance away home base station(sector 0) overhead ERP including pilot, paging, and sync powers in the direction to the probe mobile the total traffic channel power received at the probe mobile from all other base station sum of overhead powers from other base stations receiver antenna gain of probe mobile power received at the probe mobile from other interference of non-CDMA origins
    23. 23. Part II: IS95 system design engineering---Forward link analysis <ul><li>Forward link Eb/No translates directly into BER </li></ul><ul><li>---the concept of forward link analysis without considering the effects of diversity gain in soft/softer handoff situations </li></ul>Processing gain <ul><li>home base station(section 0) traffic channel ERP in the direction to the probe mobile 0 </li></ul>the forward traffic channel ERP intended for mobile but radiated in the direction toward the probe mobile
    24. 24. Part II: IS95 system design engineering---Reverse link analysis <ul><li>IS95 has no pilot on reverse link; the link Eb/No has implications on reverse-link voice quality </li></ul><ul><li>--- link analysis without introducing the effects </li></ul><ul><li>of diversity gain in soft/softer handoff </li></ul>reverse traffic channel ERP of the probe mobile; the transmit pattern is assumed to be omnidirectional the total interference introduced by the reverse traffic channel transmissios of all the mobiles in the home station (other than the probe mobile) total interference introduced by the reverse traffic channel transmissions of all other mobiles that are not served by the home base station
    25. 25. Part II: IS95 system design engineering---PN offset planning <ul><li>In IS95 system, PN offset is used to identify each Base Station. The length of each PN sequence is about , or 32768 chips. </li></ul>IS95 specifies usable PN sequences need to have a minimum separation of 64 chips between each other. Thus, the maximum number of usable PN sequence is 512. <ul><li>One chip lasts: </li></ul>
    26. 26. Part II: IS95 system design engineering---PN offset planning <ul><li>Co-PN offset management ---the minimum required distance between the two base stations using the same PN sequence </li></ul><ul><li>The necessary condition to avoid PN offset aliasing is: </li></ul>R is the radius of cell 2
    27. 27. Part II: IS95 system design engineering---PN offset planning <ul><li>Adjacent PN offset management --- the necessary condition for two base stations using adjacent PN offset to avoid PN offset aliasing </li></ul>In order to avoid PN 1 arrives seemingly before PN 2, the necessary condition is:
    28. 28. Part III: IS95 performance engineering <ul><li>Channel supervision </li></ul><ul><ul><li>Consecutive 12 bad frames </li></ul></ul><ul><ul><li>Fade timer– reset to 5 sec </li></ul></ul><ul><ul><li>Registration and acknowledgement </li></ul></ul><ul><li>Power control mode </li></ul><ul><ul><li>Threshold based : PWR_THRESH_ENABLE;PWER_REP_THRESH </li></ul></ul><ul><ul><li>Periodic based: PWR_PERIOD_ENABLE;PWR_REP_FRAMES;PWR_REP_DELAY </li></ul></ul><ul><li>Search-Window Sizes </li></ul><ul><ul><li>SRCH_WIN_A: large enough to capture all usable multipath components; most possible small to maximize performance </li></ul></ul><ul><ul><li>SRCH_WIN_N: typically larger than SRCH_WIN_A; but no larger than the distance between the adjacent base stations---upper bound </li></ul></ul><ul><ul><li>SRCH_WIN_R: at least as large as SRCH_WIN_N </li></ul></ul>
    29. 29. Part III: IS95 performance engineering <ul><li>Example: soft handoff with SRCH_WIN_A setting </li></ul>Conclusion: SRCH_WIN_A at least twice the maximum of the path differences
    30. 30. Part III: IS95 performance engineering <ul><li>Field Optimization </li></ul><ul><li>Recall that </li></ul><ul><ul><li>Pilot : </li></ul></ul><ul><ul><li>Forward link Eb/No : </li></ul></ul><ul><ul><li>Reverse link Eb/No : </li></ul></ul>trouble symptoms Possible reason solution High forward FER High forward FER and dropped calls; but low mobile received power Insufficient forward-link coverage due to large forward path loss or low traffic channel ERP Increase forward traffic channel ERP or add an additional BTS High forward FER High forward FER and high mobile received power Large forward link interference Reduce number of forward traffic channels; reducing pilot pollution; adjusting the antenna oritentation of neighboring BTS High reverse FER High reverse-link FER and high mobile transmit power Poor reverse-link coverage due to power control---the MT tries to increase its transmitting power moreover Add an additional BTS High reverse FER High reverse FER and high BTS received power Large reverse-link interference Reducing home cell antenna height or orientation
    31. 31. Part IV: Traffic engineering <ul><li>Fundamental Concepts </li></ul><ul><ul><li>Traffic Intensity </li></ul></ul><ul><ul><ul><li>Erlang= average number of simutaneous calls or total usage during a time interval divided by the time interval </li></ul></ul></ul><ul><li>Loads </li></ul><ul><ul><li>Offered load=the amount of traffic load offered by users to the network </li></ul></ul><ul><ul><li>Carried load=the amount of traffic load actually carried by the network </li></ul></ul><ul><ul><li>Carried load=(offered load)*(1-blocking rate) </li></ul></ul><ul><li>Grade of Service </li></ul><ul><ul><li>Blocking rate---a measured quantity for a particular base sataion </li></ul></ul><ul><ul><li>Blocking probability--- the possibility that a cell is blocked due to no channel available; a function of the desired offered load and the number of channels </li></ul></ul>
    32. 32. Part IV: Traffic engineering <ul><li>Erlang B model: </li></ul><ul><ul><li>Assumes that blocked calls are cleared and tries again later </li></ul></ul><ul><li>Erlang C model: </li></ul><ul><ul><li>Assumes that blocked calls are retried until the call is established </li></ul></ul>
    33. 33. Part IV: Traffic engineering <ul><li>CDMA applications: </li></ul><ul><ul><li>Hard blocking---no channel available </li></ul></ul><ul><ul><li>Soft blocking--- interference level increased </li></ul></ul><ul><ul><li>Total interference=(same-cell interference)+(other-cell interference)+(thermal noise) </li></ul></ul>=number of users in the same cell =energy-per-bit of the signal =baseband data rate =thermal noise power = loading factor as the ratio of interference introduced by mobiles served by other cells to interference introduced by mobiles served by the home cell Soft-blocking occurrs when the total interference level exceeds the background noise level by a predetermined amount where
    34. 34. Part IV: Traffic engineering <ul><li>Considering the voice activity factor and Poisson distributed active calls with mean and a random variable with a log-normal distribution, we get </li></ul>Dividing the above formula by yields Appoximates:
    35. 35. Thank you!

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