ary 0.79% 1.78% 2.19%¹0 1.34% 11 95.11% ¹2 86.93% Sample Size 11997 Call setup failure rate Delay 2.19% 95th perc. 6.34 sec. (Alerting) 3G RADIO NETWORK PLANNING AND OPTIMISATION can be improved (as the transmitted power requirement would be less). This is possible only for NRT data (which are less delay-critical) and for voice signals, which have lower bit rates. However, Eb/No cannot be lowered below the requirements of the requested service. Another way to improve the Eb/No ratio is to increase the multipath diversity. Two signals arriving at two antennas instead of one can be combined coherently, while the receiver noise can be combined non-coherently. This technique not only provides better gain, it also gives protection against fast fading etc. Concepts like antenna tilts are also used in WCDMA radio networks to improve the coverage area. A typical example is shown in Figure 7.9. Actual tilt angle Proposed tilt angle Site ID Sector Scrambling Code E tilt M tit E tilt M tilt Plot Strength Canic 132000 127.000 dim 127,000 122000 dilm 2122000 117000 dBm -117000 112000 dim 112000 107 000 dim -107.000 102.000 Bm 102000 97000 Bm 97000 32 000 Bm 92 000 87 000 dBm 07 000 92 000 dam 02000 77.000 dBm 77 000 72000 Figure 7.9 Typical coverage plans after antenna tilts in a WCDMA network Capacity Enhancements As noted earlier, capacity and coverage are heavily inter-dependent in WCDMA networks. The higher the uplink coverage, the lower is the uplink capacity, and vice versa. This is WCDMA RADIO NETWORK OPTIMISATION because lower capacity means fewer mobile subscribers, which means less interference. Moreover, the uplink power budget is used to calculate the cell range, which is further used to calculate the downlink power budget. The load factor along with the link budget calculations can be used to study the capacity in the network. The load factor is used for capacity analysis for both the uplink and downlink directions. The load factor is dependent upon Eb/No, processing gain, interference, activity factor, etc. Orth