Book for cdma
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Transcript of Book for cdma
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 CDMA - Code Division Multiple Access system.
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 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
Air Interface Forward Link
Base
Station
MobileStation
Pilot (F-PICH)
Paging (F-PCH)
Sync (F-SYNC)
Fundamental (F-FCH)
Supplemental (F-SCH)
Quick Paging Channel (F-QPCH)
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
Air Interface Reverse Link
Base
Station MobileStation
Pilot (R-PICH)
Access (R-ACH) or R-CCCH
Dedicated Control (R-DCCH)
Fundamental (R-FCH)
Supplemental (R-SCH)
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
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
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
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 powerNOM.PWR: nominal power (dB), part of system parameterNOM.PWR.EXT: nominal power for extended handoff, part of
system parameterK: 76 for cellular and 73 for PCS
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
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
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