In the recent releases 3GPP has focused on enhancing the efficiency of high speed channels leading to significant network data capacity gain. It is also widely beneficial for operators to enhance the link efficiency of DCH for certain services leading to a further improvement in network data capacity. For example the DCH is still a very attractive option to serve CS voice. The ability to configure soft handover on both downlink and uplink improves the reliability of signaling and voice delivery at cell edge, and minimizes call drop ratio. Furthermore, a superior uplink link budget can be achieved for CS voice services when mapped on 20ms TTI DCH.
New 3GPP study proposed to investigate enhancements to the efficiency of DCH channels on both the uplink and downlink. These enhancements could provide significant data throughput gains in scenarios involving a mix of voice and data transfer when CS voice is carried over DCH. Furthermore, these enhancements could significantly increase the UE battery life or talk time as well.
Uplink performance of DCH in UMTS system can be improved in several ways. A basic enhancement to UL DCH would be introduction of Frame Early Termination (FET). Since in UMTS R99 Circuit-Switched (CS) traffic, the target BLER for speech service is usually 1%, it is not always necessary to receive all slots within the TTI for a successful block decoding. Once the receiver successfully decodes the data (i.e. CRC passes), it may ask the transmitter to stop transmission immediately, i.e., even before the TTI ends, which reduces transmit power consumption without impact to the reception quality. A number of modifications in UL improve the chance of FET and UE’s battery consumption. These modifications include for example changes to UL DPCCH slot format to maintain ILPC timeline, changes to TPC rate to accommodate ACK signalling, or compression/repetition in UL.
Read more about DCH Enhancement for UMTS from this 3GPP study Item.