ation voice over DCH (about 65 voice users per sector) [3] with continuous DPCCH, and gating gives 40-50% further gain. Otherwise, fewer transmissions can increase the DPCCH gating gain in the capacity from 50% to 77% with 10 ms TTI because of the increasing opportunities for DPCCH gating from fewer transmissions on E-DCH. (For more results and simulation assumptions, see, e.g., [3,12,30,37].) VolP performance in HSDPA VoIP system performance in HSDPA achieved with the best mode scheduling alter- native ("PF + SCS + RA" described in Section 10.4.3.2 ) is shown in Figure 10.17 for both Release 6 and Release 7. Release 6 results are achieved with a 1-antenna LMMSE chip equalizer, whereas Release 7 results are achieved with a 2-antenna RAKE with MRC combining. Corresponding UL capacities for Release 6 and 7 are also presented in the figure for comparison. As the results show, receive diversity provides superior perfor- mance compared to the 1-antenna LMMSE chip equalizer. Furthermore, results indicate that HSPA capacity is uplink limited. Effect of the mobility on the performance In the real world, the UE is always moving at a varying speed. Therefore, it makes sense to understand the effect of UE velocity and handover delay in practice. VoIP AMR 12.2 kbps Uplink Downlink HSPA R6 VolP HSPA R7 VolP Figure 10.17 VolP HSPA capacity comparison between downlink and uplink. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 100 ms 200 ms 400 ms UE velocity (km/h) Figure 10.18 Average VolP cell capacity with different UE velocities and handover delays. (Source: P. Lundén, J. Aijänen, K. Aho, and T. Ristaniemi, "Performance of VolP over HSDPA in mobility scenarios," VTC 2008 Spring. With permission.) cell capacities are presented in Figure 10.18. The figure shows the achieved capaci- ties for 100 ms, 200 ms, and 400 ms handover delays. From the results it can be seen that the VoIP capacity is highly sensitive to UE velocity. Higher velocities lead to lowered VoIP capacity: the 