3G technology is intended for the true multimedia cell phone -- typically called smartphones --
and features increased bandwidth and transfer rates to accommodate Web-based applications and
phone-based audio and video files. 3G comprises several cellular access technologies as follows:
1. CDMA2000 : based on 2-G Code Division Multiple Access
2. Wideband Code Division Multiple Access-UMTS (WCDMA-UMTS) : In W-CDMA
interface different users can simultaneously transmit at different data rates and data rates
can even vary in time. UMTS networks need to support all current second generation
services and numerous new applications and services.
3. Time Division Synchronous Code Division Multiple Access (TD-SCDMA) :
TD-SCDMA uses the Time Division Duplex (TDD) mode, which transmits uplink
traffic (traffic from the mobile terminal to the base station) and downlink traffic (traffic
from the base station to the terminal) in the same frame in different time slots. That
means that the uplink and downlink spectrum is assigned flexibly, dependent on the type
of information being transmitted. When asymmetrical data like e-mail and internet are
transmitted from the base station, more time slots are used for downlink than for uplink.
A symmetrical split in the unlink and down link takes place with symmetrical services
like telephony.
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