LTE Advanced: 3GPP Solution for IMT-Advanced

14.5 Small Packet Efficiency

Much of the discussion has been allocated for improving the peak data rates and practical user data rates. Those data rate capabilities are important for large file transfer but further system features are required to support efficiently the transmission of small packets. HSPA in Releases 5 and 6 improved packet efficiency considerably by bringing fast scheduling and resource allocation to the base station. There are still some limitations in HSPA – mainly the continuous transmission of physical control channel DPCCH. Let's consider small packet sizes of 0.5–10 kB which are typical with smartphone applications. Those packet sizes are too large for RACH which can carry maximum a few hundred bytes by using multiple RACH messages. Therefore, HSPA channel need to be allocated often for smartphone traffic. The transmission time of 1 kB with 1 Mbps HSPA data rate is less than 10 ms. The allocation of HSPA channel takes several 100 ms, the inactivity release timer is a few seconds but the actual transmission time is just a few milliseconds, which is highly inefficient. The problem here is that the interference caused by the continuous DPCCH is relatively high, especially in uplink. The network resource consumption is high when the channel is occupied for a long time compared to the actual usage, and the UE power consumption increases when running DPCCH. The delay in setting up the channel impacts end user performance and the relative signalling overhead is ...