Uplink VoIP capacity of 3GPP LTE under power control and semi-persistent scheduling

LTE-Advanced (LTE-A) standardized as Release 10 by the 3rd Generation Partnership Project (3GPP) is a packet-based 4G mobile radio system. Of specific interest is its capability to support a large number of voice calls through Voice over IP (VoIP) calls. Radio resource management for VoIP calls is challenging. Control channel limitations prevent the dynamic scheduling of every VoIP packet in each 1 ms subframe. Semi-persistent VoIP scheduling enables channel quality aware scheduling reducing load to control channels, substantially. We describe and evaluate by system level simulation a semipersistent VoIP schedulers for LTE. In addition, contributions to VoIP system capacity of power control, as applied in Soft Frequency Reuse (SFR), are evaluated. It turns out that system capacity is reduced if SFR is applied in the uplink. This unexpected result is found to be caused by performance degradation of the weakest users under SFR, limiting overall system capacity.