7] the CQI reports from the UEs can be used to decide the needed CCEs, that is, coding rate, for successful resource allocation grant delivery per UE. Therefore, the worse the UE-reported CQI is the more CCEs, that is, lower coding rate, are needed from PDCCH and the lower amount of UEs can be scheduled per single TTI. This applies for the UE-specific search space resource allocation grants but as the common search space resource allocation grants are targeted for all the UEs under the cell the coding rates are typically fixed to 4 or 8. Figure 13.38 shows the impact of average CQI on average aggregation level and the worse the CQI the higher the aggregation level. Note that Figure 13.38 contains DCIs for both UE- specific and common search space and the common search space resource allocation grants are all using fixed aggregation level of four. The higher the traffic the more the UEs needed to be scheduled per TTI and the more CCEs are therefore needed but the higher the traffic the higher the inter-cell interference and therefore per UE the required amount of CCEs increases. Therefore, in terms of PDCCH usage the control of inter-cell interference increase due to the traffic increase is crucial. The low-frequency band cells are having higher average aggregation Low band (10 MHz) High band (10 MHz) High band (20 MHz) Average CQI Figure 13.38 Average aggregation level as a function of average CQI, reported by the UEs, per cell using 15-minute statistics samples LTE Small Cell Optimization level due to the lower average CQI compared to the high-frequency band cells. The carrier bandwidth does not seem to have strong impact on average aggregation level or CQI. As explained in [7] due to the UE decoding cost reduction, the blind decoding attempts a UE shall monitor on every TTI is reduced by hashing function. Hashing function defines the starting positions of each aggregation level (1, 2, 4 or 8) based on the UE identification e.g. cell radio network temporary identifier (C-RNTI) for UE-specific search space and sy