Bs where the inter-cell interference is low. The other PRBs can be utilized for UE C because UE C does not suffer from any inter-cell interference. The FSS solution increases both cell edge data rate for UE B and the total cell capacity for Cell B. Frequency Frequency Cell A UE B UE C Cell B = Resources for UE A = Unallocated resources = Resources for UE B = Resources for UE C Figure 7.4 FSS scheduling solution in Cell B LTE Small Cell Optimization Low loaded cell High loaded cell Cell A Cell B Only slow changes in the Robust inter-cell interference frequency-domain allocation avoidance based on CQI reports Figure 7.5 Interference shaping can improve the quality of CQI reporting The quality of CQI reporting is important for the FSS performance. If the quality of CQI reporting can be improved, the FSS benefit would be higher. If Cell A in Figure 7.4 changes the allocations in the frequency domain rapidly, the CQI reporting will be delayed in Cell B and Cell A has already changed the resource allocation before Cell B had time to avoid inter-cell interference from Cell A. The combined CQI reporting and packet scheduling delay is typically 10 ms. One example solution for improving the CQI performance is called interference shaping (Figure 7.5). The idea is that the low loaded cells do not need the gain from FSS. Therefore, it is possible to keep the allocations in the frequency domain constant for tens of milliseconds in low loaded cells and avoid too fast changes. That approach improves the quality of CQI reporting in the adjacent high loaded cells. The principle is shown in Figure 7.5. The benefit of FSS can be evaluated in the simulations and in the field measurements. Figure 7.6 shows field test results with stationary UEs in different cell edge locations. There Cell edge throughput Full load in adjacent cells Partial random load in adjacent cells Partial fixed load in adjacent cells FSS OFF FSS ON Figure 7.6 Field measurements with FSS Small Cell Interference Management were in total four UEs per cell in the mea