constraints on the VoIP performance are addressed in the fol- lowing sections. DPCCH overhead in the uplink transmission The uplink DPCCH in 3GPP Release 6, that is, HSUPA, is used for carrying physical layer control information which mainly consists of known pilot bits to sup- port channel estimation for coherent detection and transmit power-control (TPC) commands to be used for the DL transmission. When the high capacity (in terms of users in a cell) is targeted for VoIP on HSDPA and HSUPA, the interference caused by continuously transmitted UL DPCCHs becomes the limiting factor for capacity. To illustrate this, let us calculate the UL capacity by using the following UL load formula [1]: (10.1) where p is the EbNo target after antenna combining, W is the chip rate, R is the E-DPDCH bit rate, N is the number of users, V is the equivalent activity factor, i is the other cell to own cell interference ratio, and NR is the noise rise in decibels. When the UL load formula (10.1) is used, the overhead from DPCCH, E-DPCCH, and the retransmissions are included in the equivalent activity factor V. Further, it is also possible to divide this formula into components as shown in Equation 10.2 and then have separate requirements for E/N (i.e., the signal to noise target per chip after the antenna combining) and activity factors for each channel. Here E-DCH is assumed to include both E-DPCCH and E-DPDCH, which would always be transmitted together, thus having the same activity factor: UE-DCH (5) DPCCH E-DCH DPCCH N.0+n). (10.2) HS-DPCCH N.(1+i), HS-DPCCH For DPCCH gating (see Section 10.6.1.1), it is pessimistically assumed that E-DPDCH and HS-DPCCH transmissions never overlap and thus the DPCCH activity was obtained as the sum of activities on E-DPDCH and HS-DPCCH. Thus, the noise rise (NR) contributed by inactive UEs (i.e., UEs with inactive packet transmission) can be calculated as shown in Figure 10.6, assuming that i is © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization Inactive UE number DPCCH 