OVER VIEW OF CDMA(Code Division Multiple Access)
CDMA(Code Division Multiple Access)       Multiple users occupying the same band by having different codes is known as CDM...
Channels in CDMA        Forward Link Channels        Reverse Link Channels
Forward Link Channels Forward Pilot Channel (F-PICH)   – Shared by the mobiles   – Provide timing and phase information o...
Air Interface Forward Link               Pilot (F-PICH)              Paging (F-PCH) Base              Sync (F-SYNC)Station...
Reverse Link Channels Reverse Access Channel (R-ACH) and Reverse Common Control  Channel (R-CCCH)   – Used for communicat...
Air Interface Reverse Link              Pilot (R-PICH)          Access (R-ACH) or R-CCCH Base          Dedicated Control (...
CDMA HandoffsThe process whereby a Mobile Station moves to acquiring a new traffic channelCDMA implements various types ...
Type of CDMA Handoffs Softer Handoff: Mobile Station communicates with sectors within  the cell. Soft Handoff: “Make bef...
Power Control in CDMA CDMA goal is to maximize the number of simultaneous users Capacity is maximized by maintaining the...
Reverse Link Open Loop Power Control Mobile station adjusts its transmit power level based on received  signal quality. ...
Reverse Link Closed Loop Power                  Control Closed loop power control attempts to compensate for multipath  f...
Forward Link Power Control BTS collect FER report from the Mobile Station and makes decision  on adjusting its transmit p...
Advantage in CDMA over GSM Reduce call drop rate Improve capacity   – Path diversity allows mobile to reduce transmit po...
Book for cdma
Book for cdma
Book for cdma
Book for cdma
Book for cdma
Book for cdma
Book for cdma
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Book for cdma

  1. 1. OVER VIEW OF CDMA(Code Division Multiple Access)
  2. 2. CDMA(Code Division Multiple Access) Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system.
  3. 3. Channels in CDMA Forward Link Channels Reverse Link Channels
  4. 4. Forward Link Channels Forward Pilot Channel (F-PICH) – Shared by the mobiles – Provide timing and phase information of the cell – Used for cell acquisition and handoff by the mobile Forward Sync Channel (F-SYNC) – Used by the mobiles to acquire initial time synchronization Forward Paging Channel (F-PCH) – Used to send control information and paging messages Forward Fundamental Channel (F-FCH) – Traffic channel carrying voice and data Forward Supplemental Channel (F-SCH) – Used (but not limited) to carrying high speed data
  5. 5. Air Interface Forward Link Pilot (F-PICH) Paging (F-PCH) Base Sync (F-SYNC)Station Fundamental (F-FCH) Mobile Station Supplemental (F-SCH) Quick Paging Channel (F-QPCH)
  6. 6. Reverse Link Channels Reverse Access Channel (R-ACH) and Reverse Common Control Channel (R-CCCH) – Used for communication of layer 3 and MAC messages from the mobile to the base station Reverse Pilot Channel (R-PICH) – Time tracking – Power control measurements Reverse Dedicated Control Channel (R-DCCH) – Used for call set up Reverse Fundamental Channel (R-FCH) – Voice and data traffic channel Reverse Supplemental Channel (R-SCH) – Used for data calls – MSM5105 supports up to 78.6 kbps R-SCH rate
  7. 7. Air Interface Reverse Link Pilot (R-PICH) Access (R-ACH) or R-CCCH Base Dedicated Control (R-DCCH) MobileStation Station Fundamental (R-FCH) Supplemental (R-SCH)
  8. 8. CDMA HandoffsThe process whereby a Mobile Station moves to acquiring a new traffic channelCDMA implements various types of handoff schemes to reduce call drop rate – Soft Handoff – Softer Handoff – Soft-softer Handoff – Hard handoff
  9. 9. Type of CDMA Handoffs Softer Handoff: Mobile Station communicates with sectors within the cell. Soft Handoff: “Make before Break”. Mobile communicates with two cells. Soft-softer Handoff: Mobile Station communicates with two sectors within a cell and another sector or cell. Hard handoff ;A MS is disconnected from one BTS and is switched to another ,Break-before-make
  10. 10. Power Control in CDMA CDMA goal is to maximize the number of simultaneous users Capacity is maximized by maintaining the signal to interference ratio at the minimum acceptable Power transmitted by mobile station must be therefore controlled • Transmit power enough to achieve target BER: no less no moreTypes of Power Control Reverse Link Power Control – BTS instructs Mobile Station to raise or reduce power level based on received signal quality Forward Link Power Control – BTS raise or reduce its transmit power level based on FER reports from Mobile Stations
  11. 11. Reverse Link Open Loop Power Control Mobile station adjusts its transmit power level based on received signal quality. Mobile transmit power based on Open Loop Power Control Tx = -Rx-K+(NOM.PWR-16*NOM.PWR.EXT)+Sum of Access Probe Corrections (dBm) Rx: Mean input receive power NOM.PWR: nominal power (dB), part of system parameter NOM.PWR.EXT: nominal power for extended handoff, part of system parameter K: 76 for cellular and 73 for PCS
  12. 12. Reverse Link Closed Loop Power Control Closed loop power control attempts to compensate for multipath fading losses BTS instructs Mobile to adjust its transmit power in a 1dB step size: “0” = -1 dB, “1”=+1dB Response time: 1.25ms
  13. 13. Forward Link Power Control BTS collect FER report from the Mobile Station and makes decision on adjusting its transmit power Prevents excessive interference to other cells while maintaining a desired Frame Error Rate
  14. 14. Advantage in CDMA over GSM Reduce call drop rate Improve capacity – Path diversity allows mobile to reduce transmit power to the level only the closest cell needs – Less power means less interference – Less interference means more mobiles can access the network

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