CDMA allows multiple users to occupy the same frequency band using unique codes. It uses various channels for communication between base stations and mobile stations, including pilot, paging, sync, fundamental, and supplemental channels. CDMA implements soft handoff which allows communication between a mobile and multiple base stations for a smooth transition. Power control is important in CDMA to maximize capacity by maintaining the minimum required signal to interference ratio through open and closed loop adjustments between base stations and mobiles.

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.

8. Channels in CDMA
Forward Link Channels
Reverse Link Channels

9. 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

10. 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)

11. 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

12. Air Interface Reverse Link
Pilot (R-PICH)
Access (R-ACH) or R-CCCH
Base
Dedicated Control (R-DCCH) Mobile
Station
Station
Fundamental (R-FCH)
Supplemental (R-SCH)

14. 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

16. 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

17. 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
more
Types 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

18. 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

19. 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

20. 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

21. 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