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CDMA KEY TECHNOLOGY

CDMA KEY TECHNOLOGY. 2004.10.3. -- Power control in CDMA why power control how to realize -- Handoff in CDMA what is handoff CDMA’s soft handoff soft handoff procedure. Objectives. Upon completion of this lesson, the student will be able to master:.

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CDMA KEY TECHNOLOGY

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  1. CDMA KEY TECHNOLOGY 2004.10.3

  2. -- Power control in CDMA why power control how to realize -- Handoff in CDMA what is handoff CDMA’s soft handoff soft handoff procedure Objectives Upon completion of this lesson, the student will be able to master:

  3. All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators. CDMA operates by using CODES to discriminate between users. CDMA interference comes mainly from nearby users Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code. Transmit power on all users must be tightly controlled so their signals reach the base station at the same signal level and at the absolute minimum power level necessary to ensure acceptable service quality Figure of Merit: Ec/Io, Eb/No (energy per chip [bit] /interference [noise] spectral density) CDMA: Ec/Io -17 to -2 dB CDMA: Eb/No ~6to7 dB Why Power Control?

  4. The mobile station makes a coarse initial estimation of the required transmit power, based upon the total received power. Problems with Reverse Open Loop Power Control: Assumes same exact path loss in both directions; therefore, cannot account for asymmetrical path loss Estimates are based on total power received; therefore the power received from other cell sites by mobile station introduces inaccuracies Reverse Open Loop Power Control Mobile BTS Reverse Open Loop Power Control

  5. Power output level for the initial probe during open loop probing on the Access Channel (with closed loop correction inactive): mean output power (dBm) = - mean power input (dBm) + K + NOM_PWR - 16 x NOM_PWR_EXT + INIT_PWR Subsequent probes in the sequence are sent at increased power levels (each probe is incremented by a value equal to the parameter PWR_STEP) The “turn around constant” K is calculated assuminga nominal cell Effective Radiation Power (ERP) of 5 W and a nominal cell loading of 50%. Its value is -73 for cellular systems and -76 for PCS systems Estimated Reverse Open LoopOutput Power

  6. Power output level for the initial transmission on the Reverse Traffic Channel: mean output power (dBm) = - mean power input (dBm) + K + NOM_PWR - 16 x NOM_PWR_EXT + INIT_PWR + the sum of all access probe corrections (dB) Estimated Reverse Open LoopOutput Power

  7. Mobile BTS or Reverse Closed Loop Power Control Signal Strength Measurement Setpoint Reverse Closed Loop Power Control • Compensates for asymmetries between the forward and reverse paths • Consists of power up (0) & power down (1) commands sent to the mobile stations, based upon their signal strength measured at the Base Station and compared to a specified threshold • Each command requests a 1dB increase or decrease of the mobile station transmit power • Transmitted 800 times per second, always at full power • Allows to compensate for the effects of fast fading

  8. BSC Mobile BTS or Reverse Closed Loop Power Control Signal Strength Measurement Reverse Outer Loop Power Control FER Setpoint Reverse Outer Loop Power Control • Most gradual form of reverse link power control • Setpoint is varied according to the FER on the Reverse Traffic Channel (determined at the Base Station Controller) • Sampled at a rate of 50 frames per second (20 ms / frame) • Setpoint adjusted every 1-2 seconds

  9. BSC Mobile BTS Adjust Fwd. power FER Forward Link Power Control Forward Traffic Channel Power Control • The base station slowly decreases power to each mobile station. • As the FER (determined at the mobile station) increases, the mobile station requests a Forward Traffic Channel power increase.

  10. All types of power control work together to minimizes power consumption at the mobile stations, and increases the overall capacity of the system transmit power. Reverse Open Loop Power Control BSC Mobile BTS or Reverse Closed Loop Power Control Adjust Fwd. power Signal Strength Measurement FER Reverse Outer Loop Power Control FER Setpoint Forward Link Power Control Summary of All Power Control Mechanisms

  11. Handoff is the process by which a mobile station maintains communications with the Mobile Telephone Switching center(MSC), when traveling from the coverage area of one base station to that of another. Handoffs keep the call established during the following conditions: Subscriber crosses the boundaries of a cell Subscriber experiences noise or other interference above a specified threshold A base station component experiences an out-of-service condition during a call Handoffs

  12. CDMA Cell Site B Cell Site A Cell Site A Cell Site B CDMA Handoffs • CDMA Handoffs • Make-before-break • Directed by the mobile not the base station • Undetectable by user • Improves call quality • Handoffs consist of the following phases: • Initiation (trigger), Target Selection, and Completion (execution)

  13. While in the Idle State Idle Handoff Soft Handoff Softer Handoff Inter-System Soft Handoff Duringa Call CDMA-to-CDMA Handoff CDMA-to-Analog Handoff CDMA Handoffs (cont.)

  14. Cell Site B Cell Site A PSTN MSC B S C Soft Handoff • Soft Handoff: the mobile station starts communications with a target base station without interrupting communications with the current serving base station. • Can involve up to three cells simultaneously and use all signals • Mobile station combines the frames from each cell

  15. alpha beta gamma Softer Handoff • Handoff is between sectors of the same cell • Communications are maintained across both sectors until the mobile station transition has completed • May happen frequently • MSC is aware but does not participate • All activities are managed by the cell site • Signals received at both sectors can be combined for improved quality

  16. MSC E1 Links TIA/EIA-41D MSC SVBS SVBS E1 Links HIRS HIRS A f1 D f1 U f1 X f1 B f1 V f1 E f1 Y f1 C f1 W f1 F f1 Z f1 CDMA Hard Handoff ISSHO CDMA Soft Handoff Inter-System Soft Handoffs (ISSHO) • Mobile Station starts communications with a new cell controlled by a different BSC while still communicating with the cell controlled by the source BSC • Soft Handoffs over Hard Handoffs • Fewer border cell

  17. PSTN PSTN MSC MSC MSC T1 or E1 Links TIA/EIA-41D BSC BSC BSC A B A (ƒ1) B (ƒ2) CDMA-to-CDMA Hard Handoff • Between cells operating on different frequencies • Between cells that could be on the same frequency, but which are subordinated to different MSC

  18. Digital Rake Receiver Symbols Chips Traffic Correlator S PN xxx Walsh xx Symbols Receiver RF Section IF, Detector Traffic Correlator Viterbi Decoder PN xxx Walsh xx Bit Packets Traffic Correlator AGC Messages PN xxx Walsh xx Audio RF Vocoder CPU Pilot Searcher Duplexer Open Loop PN xxx Walsh 0 RF Transmit Gain Adjust Audio Messages Transmitter RF Section Transmitter Digital Section Long Code Gen. Bit Packets What’s In a Handset?

  19. Short PN Code Offsets Ec/Io Rake Fingers 1 2 3    Active Set Candidate Set Neighbor Set Remaining Set Pilots Above Searched In This Order: A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N A A A C N R Until all are scanned…then repeat Soft Handoff Key: Understand the searcher’s effect in different state --- MS power up state --- MS idle and calling state

  20. Pilot Sets 1. Active 2. Candidate 3. Neighbor 4. Remaining Pilot Sets • Pilot sets: • Active Set: Pilots associated with the forward traffic channels assigned to the mobile station (max 6 pilots) • Candidate Set: Pilots not currently in the Active Set, but received by the mobile with sufficient strength to indicate that the corresponding Traffic Channels can be successfully demodulated (max 5 pilots) • Neighbor Set: Pilots not currently on the Active or Candidate Sets, that are likely handoff candidates (at least 20 pilots) • Remaining Set: All other possible pilots in the current system on the current CDMA frequency assignment • All pilots in a set have the same frequency assignment • These sets can be updated during handoff by the base station

  21. Pilot whose Paging Channel is being monitored or associated with the assigned Forward Traffic Channel Active Candidate Empty Pilots specified in the most recently received Extended Neighbor List Message (AGE set at NGHBR_MAX_AGE) Neighbor Any other possible pilot in the system Remaining Pilot Set Initialization(While in the Idle or in an Active Call)

  22. Pilots listed the most recently received Extended Handoff Direction Msg Active Pilots whose strength exceeds T_ADD Candidate Pilots specified in the most recently received Neighbor List Update Message (or whose AGE is still less than NGHBR_MAX_AGE) Neighbor Any other possible pilot in the system Remaining Pilot Set Maintenance(While in an Active Call)

  23. A B Timing Traffic Channels C PSMM Pilot Channel Pilot Strength MeasurementMessage (PSMM) • The Pilot Strength Measurement Message is used by the mobile station to direct the base station in the handoff process. • Mobile station reports the strength of the pilots associated with forward traffic channels currently being demodulated (and whether it would like to continue to receive traffic from them), as well as pilots from the neighbor and remaining list which are being received with sufficient strength so that traffic could be demodulated from them successfully.

  24. A search window is a range of PN offsets (in chips) where the mobile station searches for usable multipath components of the pilots in a set Usable means that multipath components can be used for demodulation of an associated traffic channel Search Window for pilots in the Active and Candidate Set: SRCH_WIN_A Earliest arriving usable multipath component of the pilot Search Window for pilots in the Neighbor Set: SRCH_WIN_N pilot PN offset Search Window for pilots in the Remaining Set: SRCH_WIN_R pilot PN offset Pilot Search Windows

  25. PSMM sent (request to add) , Pilot added to Candidate Set EHOD message received, Pilot Added to Active Set, EHOC message sent, NLU message received Pilot Strength Pilot strength drops below T_DROP,Drop Timer started Pilot Strengthexceeds T_ADD Drop Timer expires T_ADD PSMM Sent (request to remove) T_DROP EHOD message received,Pilot Dropped into Neighbor Set, EHOC message sent,NLU message received T_TDROP Time (1) (2) (3) (4) (5) (6) (7) N C A N Soft Handoff Signaling • T_ADD: pilot detection threshold (Typically 26 = -13dB) • T_DROP: pilot drop threshold (Typically 30 = -15 dB) • T_TDROP: drop timer value (Typically 3 = 4 sec) • Prevents unnecessary transmissions of PSMM when a mobile station experiences a fade

  26. Length (bits) Field MSG_TYPE (‘00000001’) 8 HOME_REG 1 PWR_REP_THRESH 5 PILOT_PN 9 FOR_SID_REG 1 PWR_REP_FRAMES 4 CONFIG_MSG_SEQ 6 FOR_NID_REG 1 PWR_THRESH_ENABLE 1 SID 15 POWER_UP_REG 1 PWR_PERIOD_ENABLE 1 NID 16 POWER_DOWN_REG 1 PWR_REP_DELAY 5 REG_ZONE 12 PARAMETER_REG 1 RESCAN 1 TOTAL_ZONES 3 REG_PRD 7 T_ADD 6 ZONE_TIMER 3 BASE_LAT 22 T_DROP 6 MULT_SIDS 1 BASE_LONG 23 T_COMP 4 MULT_NIDS 1 REG_DIST 11 T_TDROP 4 BASE_ID 16 SRCH_WIN_A 4 EXT_SYS_PARAMETER 1 BASE_CLASS 4 SRCH_WIN_N 4 EXT_NGHBR_LIST 1 PAGE_CHAN 3 SRCH_WIN_R 4 GLOBAL_REDIRECT 1 MAX_SLOT_CYCLE_INDEX 3 NGHBR_MAX_AGE 4 RESERVED 1 System Parameters Message (PCH)

  27. Power Control during Soft Handoff • During soft handoff, the mobile station receives power control bits from multiple base stations. • If two or more power control subchannels are identical, their power control bits are diversity combined into one per 1.25 ms time slot. • If the mobile station receives different power control bits from different power control subchannels, it decreases its mean power output level by 1 dB. • Only if the power control bits from ALL power control subchannels request a power increase, the mobile station increases its mean power output level by 1 dB .

  28. Soft Handoff New Parameter in 1X IS-2000princinple

  29. Handoff Parameters • T_ADD • T_DROP • T_TDROP • T_COMP • SOFT_SLOPE • ADD_INTERCEPT • DROP_INTERCEPT • SRCH_WIN_A • SRCH_WIN_N • SRCH_WIN_R

  30. Prefered Parameters Setting

  31. SRCH_WIN_val Width, Chips 0 4 (±2) 1 6 (±3) 2 8 (±4) 3 10 (±5) 4 14 (±7) 5 20 (±10) 6 28 (±14) 7 40 (±20) 8 60 (±30) 9 80 (±40) 10 100 (±50) 11 130 (±65) 12 160 (±80) 13 226 (±113) 14 330 (±165) 15 452 (±226) Search Window Setting

  32. The End!

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