Features of cdma one
CDMA has several unique features that make it a cost-effective, high quality wireless solution. The following are the main features described of cdmaOne.
- CdmaOne uses CDMA - code division multiple access system.
- It uses both an access method and an air-interface.
- Rest of the network is very similar; Radio resource management, mobility management, security are similar.
- Power control and handoffs are different.
- It uses Discrete Sequence Spread Spectrum (DSSS) and Error Correcting code(ECC).
- Frequency reuse factor is 1
- It include 3 systems:
- IS-95 2G
- Soft capacity limit: system performance degrades for all users as number of users increase.
Wide frequency spectrum reduces fading
- Rake receiver: Separate multipath signals of different delays by Âgchiph unit.
- Cell frequency reuse 1 : No frequency planning
- Modulation is performed using DSSS.
- Employs variable rate coders.
- Powerful low rate forward error-correcting codes.
- Fast power control is employed to overcome the near-far problem.
- Soft handoff is employed.
- Qualcomm code excited linear predictive (QCELP): 13.4 kbps
- Higher capacity
- Improves voice quality (new coder)
- Less power consumption (6-7 mW)
- Choice for 3G systems
- Self-jamming – arriving transmissions from multiple users not aligned on chip boundaries
- unless users are perfectly synchronized Â„
- Near-far problem – signals closer to the receiver are received with less attenuation than signals farther away
- Soft handoff – requires that the mobile acquires the new cell before it relinquishes the old; this is more complex than hard handoff used in FDMA and TDMA schemes.
- Air-interface is the most complex
Â„ Not symmetrical (unlike TDMA)
- Forward and reverse channels are different
- Forward channel (1ÆMany) synchronized
- Forward channel uses orthogonal spreading codes
- Reverse channel transmissions are not synchronized
- Orthogonal codes are used for orthogonal waveform coding