and allocated bandwidth per cell. Figure 13.34 shows example per different bands and bandwidths. As can be seen from Figure 13.34 the 3GPP-simulated spectral efficiency of 1.7 bit/s/Hz [6] per cell for 100% load can be met and exceeded provided that the reported CQI is 9 or better. It should also be noted that this high spectral efficiency can be achieved by low band and high band with 10 and 20 MHz bandwidths. The 3GPP simulations for spectral efficiency are using full buffer traffic model which means that each cell is having 100% DL PRB utilization at the same time. The own cell DL PRB utilization and its neighbours' DL PRB utilization are hardly ever at 100% at the same time in real live networks as shown in the Figure 13.35. Low band (10 MHz) High band (10 MHz) High band (20 MHz) Spectral efficiency per cell per hour (bit/s/Hz) Figure 13.34 Downlink spectral efficiency as a function of average reported CQI for cells having 80% and above downlink PRB utilization over the measurement period LTE Small Cell Optimization DL PRB utilization <15% DL PRB utilization <30% DL PRB utilization <50% DL PRB utilization <80% Own cell DL PRB utilization Figure 13.35 Own cell DL PRB utilization as a function of neighbouring cell DL PRB utilization Figure 13.35 shows that when the own cell DL PRB utilization increases the share of its neighbours which are having the same or higher DL PRB utilization slightly increases as well. For example, when own cell DL PRB utilization reaches 90-95% then 35% of its neighbours are having DL PRB utilization less than or equal to 15%. Or at the same 90-95% DL PRB utilization for own cell, only 5% of its neighbours have higher than 80% DL PRB utilization at the same time. This means that in real networks the spectral efficiency can exceed the 3GPP limits due to the unbalanced load between the cells. Throughput per User The downlink throughput per user depends on the bandwidth allocation, spectral efficiency and the number of users simultaneously receiving data from a cell. As explained in the 