HSUPA Dynamic TTI Adjustment

After an HSUPA service is set up or reconfigured, the RNC dynamically changes the TTI from 2 ms to 10 ms or from 10 ms to 2 ms to improve network performance.

Compared with the 10 ms TTI, the 2 ms TTI enables the UE to achieve a higher peak rate and a shorter scheduling delay. However, the 2 ms TTI needs to be switched to the 10 ms TTI to increase coverage and system capacity and to improve the fairness for differentiated services in the following scenarios:

1. Limited coverage

2. Insufficient resources over the Uu and Iub interfaces

3. Insufficient CE resources

4. Insufficient NodeB credit resources

If the algorithm of coverage-based BE service fallback from E-DCH to DCH is applied, the algorithm of coverage-based dynamic TTI adjustment of BE services is automatically disabled. 

The RNC can perform dynamic TTI adjustment for a single BE service only when the HSUPA dynamic channel configuration control (DCCC) function is not applied. 

The TTI adjustment principles for dual-carrier HSUPA (DC-HSUPA) UEs are the same as those for HSUPA UEs. When the TTI for a DC-HSUPA UE is changed from 2 ms to 10 ms, the UE falls back to an HSUPA one. When the TTI for an HSUPA UE capable of DC-HSUPA is changed from 10 ms to 2 ms, the UE is directly reconfigured as a DC-HSUPA one.

The dynamic TTI adjustment algorithm introduces reconfiguration signaling procedures, which may cause call drops. As a result, this algorithm may degrade key performance indicators (KPIs) such as call drop rate.