 as it considers the delay requirements of VoIP traffic by prioritizing urgent transmissions and retransmissions. Moreover, SCS makes Table 10.2 Relative Capacity Gain with Different Scheduler Improvements Compared to Round Robin Scheduler with 80 ms Delay Budget Scheduler Capacity gain (%) Proportional fair (PF) PF I SCS Dynamic resource allocation (PF + SCS + RA) Source: P. Lundén and M. Kuusela, "Enhancing performance of VolP over HSDPA," VTC 2007 Spring. C 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology the packet bundling more likely, thus improving the overall efficiency. The capacity gain of dynamic resource allocation (PF + SCS + RA) over even-share resource allocation is approximately 20% to 30% for the PF + SCS scheduler. 10.4.3.3 RNC Controlled Nonscheduled Transmission in the Uplink for VolP over HSUPA There are two scheduling schemes defined for HSUPA: Node B controlled scheduled transmission and RNC controlled nonscheduled transmission. The former scheme does not guarantee a minimum bit rate since the scheduling algorithm decides whether to allocate any power to the user or not. The latter scheme (nonscheduled transmission) defines a minimum data rate at which the UE can transmit without prior request. When nonscheduled transmission is configured by the serving RNC (SRNC), the UE is allowed to send E-DCH data at any time, up to a configured bitrate, without receiving any scheduling command from Node B. Thus, signaling overhead and scheduling delay are minimized. Therefore, RNC controlled non- scheduled transmission is the most suitable choice for VoIP traffic. 10.4.4 Advanced Receivers By using advanced receiver techniques at UE, the performance of VoIP can be sig- nificantly improved. The following advanced receiver techniques were introduced to HSDPA terminals: 2-antenna Rake receiver with Maximum Ratio Combining (MRC) and 1-antenna LMMSE time domain chip level equalizer were adopted by 3GPP Release 6 onwards, and 2-antenna LMMSE chip level equalizer