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  • 1. OVER VIEW OF CDMA(Code Division Multiple Access)
  • 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. Channels in CDMA Forward Link Channels Reverse Link Channels
  • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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