ptimization of cell dominance area reduces the inter-cell interference and improves CQI and therefore LTE network capacity and per- formance. Dominance area optimization is typically done by antenna downtilt, direction and height modifications and this is often referred to as physical layer or layer 1 optimization. The physical layer performance can be evaluated, for example, by the slope of decrease in average reported (by UE) CQI caused by increased downlink data volume per cell. The more negative this slope is the more the network suffers from inter-cell interference. Fig- ure 12.1 shows one example of cluster-level physical layer optimization results. The slope (CQI decreased due to increased downlink data volume per cell) has improved significantly from -0.009 to -0.0035 which means that network can deliver 50% more data volume during year 2 compared to year 1 with the same CQI value (based on CQI ~ 9.5). This means better end-user experience and higher network capacity. The analysis on cluster level can be extended to cell level (to find out the biggest interferers) by evaluating the slopes of cell X average CQI decrease versus data volume increase of cell Average CQI year 1 Average CQI year 2 Linear (average CQI year 1) Linear (average CQI year 2) =-0.003x+10.17 y=-0.009x+10.86 Average DL data vol (MB) per cell per 15 minutes Figure 12.1 Spectral efficiency improvement by physical layer optimization LTE Small Cell Optimization Cell E Cell 3 Cell D Cell 1 Cell A Cell 2 Cell C Cell F Cell J Cell B Cell G Cell I Cell H Figure 12.2 Analyzed network cluster X's neighbours. The analysed example cluster is shown in Figure 12.2 where the cells causing biggest interference to cell 1 are indicated with italic text box. Cell 1 is the analysed cell and cells A-I are its closest neighbours. Worst interferers are analysed based on the slopes of average reported CQI of cell 1 versus average downlink data volume for each of its neighbours. Examples are shown in Figures 12.3, 12.4, 12.5 and 12.6. Based on neighbouring cell