Differences between WCDMA and Second Generation Air Interfaces

Main differences between the third and second generation air interfaces are described. GSM and IS-95 (the standard for cdmaOne systems) are the second generation air interfaces considered here. Other second generation air interfaces are PDC in Japan and US-TDMA mainly in the Americas; these are based on TDMA (time division multiple access) and have more similarities with GSM than with IS-95. The second generation systems were built mainly to provide speech services in macro cells. To understand the background to the differences between second and third generation systems, we need to look at the new requirements of the third generation systems which are listed below:

       ·         Bit rates up to 2 Mbps;

·         Variable bit rate to offer bandwidth on demand;

·         Multiplexing of services with different quality requirements on a single connection, e.g. speech, video and packet data;

·         Delay requirements from delay-sensitive real time traffic to flexible best-effort packet data;

·         Quality requirements from 10 % frame error rate to 10_6 bit error rate;

·         Co-existence of second and third generation systems and inter-system handovers for coverage enhancements and load balancing;

·         Support of asymmetric uplink and downlink traffic, e.g. web browsing causes more loading to downlink than to uplink;

·         High spectrum efficiency;

·         Co-existence of FDD and TDD modes.

GSM also covers services and core network aspects, and this GSM platform will be used together with the WCDMA air interface: see the next section regarding core networks.