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CDMA Interview Questions and Answers

1
What is CDMA2000?
  • CDMA2000 is a Multi-carrier code-division multiple access version of IMT-2000 standard
  • CDMA2000 is a 3G wireless technology.
  • World’s first 3G commercial system was launched by SK Telecom of South Korea using CDMA2000 1X
  • CDMA 2000 supports mobile data communications at speeds from 144KBPS to 3MBPS
  • The versions of CDMA2000 have been developed by Qualcomm and Ericsson
  • There were 250,300,000 subscribes world for CDMA by March 2006.
2
Please differentiate between CDMA and FDMA?

CDMA

Same frequency is used by every user and simultaneous transmission occurs
Every narrowband signal is multiplied by wideband spreading signal, usually known as codeword
Every user has a separate pseudo-codeword, i.e., orthogonal to others
Only the desired codeword is detected by the receivers and others appear as noise
It is mandatory for the receivers to know about the transmitter’s codeword

FDMA

When the channel is not in use, it sits simply idle
Bandwidth of Channel is relatively narrow (30 KHz), known as narrowband system
Little or no equalization is needed for spreading symbol time
Analog links are suitable for FDMA
Framing or synchronization bits are not needed for continuous transmission
Tight filtering is needed to minimize interference
Combined with FDD for duplexing

3
Explain the following two types of hand off in CDMA system: a.) Soft handoff b.) Softer handoff

Soft handoff

  • Soft handoff is a feature in which a cellular phone is simultaneously connected to two or more cellular phones during a single call
  • It is he overlapping of repeater coverage ones, which enables every cell phone set is always well within the range of a specific repeater.
  • More than one repeater can send and receive signals to transmit signals to and from mobiles.
  • All repeaters are used with the same frequency channel for each mobile phone set.
  • Practically no dead zones and as result, the connections seldom interrupted or dropped.

Softer handoff

  • Softer handover is a significant soft handover in which the added and removed links belong to the same node
  • Macro diversity with maximum ratio combining could be performed in the same node
  • The movement of handoff, when a user can be served in another cell more efficiently (less power emission, less interference), is the most obvious cause for better performance.
4
Do you know what is the importance of CDMA in today’s cellular world?

The transition to digital radio through the process of defining standards is implementing about 90% in the cellular industry.
Smooth transition to digital standards is involved in CDMA technology.
Most often, it can be viewed as improved and replacement technology of TDMA
Moving towards 4G technology is compatible with CDMA technology .

5
What is CDMA? Explain the technology.
  • CDMA stands for Code Division Multiple Access
  • CDMA is a wireless technology used in transmission of signal from places with high Security and noise reduction.
  • The principle of Spread Spectrum is used to work with CDMA.
  • Spread signal is below the noise level noise and has no effect on the signal.
  • CDMA does not frequency specific to each user. Instead, every channel uses the full available spectrum.
    Individual conversations are encoded with a pseudo-random digital sequence.
  • CDMA always provides better capacity for voice and data communications
  • CDMA is a common platform for 3G technologies
  • Analog radio transmission technologies like Advanced Mobile Phone System were used in CDMA at the time of its inception
  • A unique code is received by all mobile network users and is allowed continuous network access instead of intermittent and timed access.
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