 for which PRB utilization is above 20% per 15-minute sample. It should be noted that the carriers are not deployed on the same sites and optimization is performed on carrier basis trying to achieve highest possible performance per carrier. As can be seen from Figure 13.36 the low band (700, 800 or 900 MHz) 10 MHz cells provide slightly worse average user throughput compared to the high band (1800, 2100 or 2600 MHz) 10 MHz cells. The highest average user throughput can be achieved by the high band (1800, 2100 or 2600 MHz) 20 MHz cells. Low band (10 MHz) High band (10 MHz) High band (20 MHz) Power (low band (10 MHz)) Power (high band (10 MHz)) Power (high band MHz)) 10,000 456563x-0.9 y = 85784x-0.935 Average number of RRC connected users Figure 13.36 Average downlink throughput per user (kbps) as a function of the number of RRC- connected users per FD LTE cell. Highest loaded cell 15-minute statistics are used LTE Small Cell Optimization High band (20 MHz) Low band (10 MHz) High band (10 MHz) Linear (high band (20 MHz)) Linear (low band (10 MHz)) Linear (high band (10 MHz)) -0.714x 11.495 -1.1392x 11.842 -1.1841x 11.057 Average DL data volume (GB) per cell per 15 min Figure 13.37 Spectral efficiency per carrier as a function of downlink data volume If downlink throughput limit is set to, for example, 1 mbps per user then that means that on an average analysed cells can support the following amount of RRC-connected users: 20 MHz high band FD LTE can support 392 RRC-connected users per cell 10 MHz high band FD LTE can support 186 RRC-connected users 10 MHz low band FD LTE can support 117 RRC-connected users The throughput difference between 10 MHz low band and high band allocations comes from radio quality difference between the bands, that is, high band is in general easier to optimize and therefore high band can provide better spectral efficiency as can be seen from Figure 13.37. The higher the carrier frequency the less the CQI decreases while the downlink data volume per cell increases. Also the more the bandwi