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What is CDMA?

Cdma means code division multiple

access.

A single cdma carrier is accessed by

multiple of users differentiated from each

other thorough their indipendent codes,

walsh codes

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Parameters to check during the

CDMA drive test.

Pilot Ec/Io.

FER

Rx level Soft and softer handovers.

Hard Handovers

Walsh Codes Pilot over shoot & Pilot Pollution

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Pilot Ec/Io

Pilot is the initial guiding signal that themobile refers to when ever it has tocommunicate with the CDMA system.

Ec/Io: Its ratio of the Energy of the carrierto the total Interference.

Ec/Io is best at -3db and its bad as it goes

down -15,-16,-17.. Normally value of Ec/Io should be between

-5db to -12db.

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FER

FER: Frame Erasure Rate

What is FER?

Answer: The mobile phone sends thespeech or data in the form of frames to the

BTS (Base Transiver Station) no of the

frames the BTS can decode the better it is.

FER is best at 0 and tolerable till 2%.

Any thing more than 2% is bad.

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Rx Level

This is the signal level that the mobile

phone receives from the BTS. Its good at

-38 dBm (just below site or in front of the

CDMA Antenna at the tower.) and is badat -98dBm (away from the site also based

on the clutter). Call drops below -102 dBm,

normally.

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Soft Handovers

Soft Handovers: Inter Site Handovers are

called soft handovers. Inter site means

between different cell sites

Cell Site A Cell Site B

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Softer Handovers

Softer Handovers: Inter cell Handovers

with in the same cell site are called softer

handovers.

Cell Site A

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Hard handovers

In CDMA we use single frequency called

the CDMA carrier. Whenever theres an

handover between different CDMA carriers

its called hard handover.

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Walsh Codes

Walsh Codes: In CDMA system each user uses the same frequency

but is differentiated through different codes called the Walsh codes.

These codes are responsible for logical channaling of CDMA.

We have 64 (0-63) walsh codes per sector.

Walsh Code 0 : This is assigned to the Pilot channel. Walsh Code 32 ; This is assigned to the Sync channel that

provides the synchronization information to the mobile station.

Walsh Code: 1 to 7 : used for Paging channel. As per the no of

users we can use either 1 or more than 1 between 1 to7

Remaing Walsh codes including the unused paging walsh codes areused for traffic channels. (user communication)

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Pilot overshoot

Whenever we are conducting a drive test, andwe see undesired pilot may be with a higherpower but coming in the coverage area ofanother cell site then that overshoot of the signalis call pilot overshoot.

Pilot Pollution: Our mobile phone is capable ofdecoding 4 pilot PNs at a time. Any no of PilotPNs more than 4 with significant strength willlead to pilot pollution that is the stage when themobile station is confused to latch to which pilotsignal.This is called Pilot Pollution.