ic birth-death traffic model is applied for generating user calls, where call arrival is according to a Poisson process with a finite payload size. Hotspot UE distribution is assumed where two-thirds of the UEs are located inside small cell hotspots while the remaining UEs are uniformly distributed within the macro cell area. For cases with non-ideal backhaul, an Small Cell Optimization CA with ideal backhaul DC with non-ideal backhaul Without CA/DC Offered traffic (Mbps) Figure 8.8 5 percentile user throughput with/without DC under different backhaul configurations X2 latency of 5 ms is assumed. The flow control between macro and small cells is performed periodically every 5 ms. The schedulers in the macro and small cells exchange information on the past average scheduled throughput for UEs that are configured with DC every 50 ms. As can be observed from Figures 8.8 and 8.9, both the 5 percentile and median user through- put performance with DC are significantly higher than without carrier aggregation or DC. Also, with non-ideal backhaul the 5 percentile and median user throughput are relatively close to the performance assuming ideal fibre-based fronthaul connection. To better quantify the gains of inter-site carrier aggregation, the system performance is compared for a target 5 percentile Ideal CA Non-ideal, 5 ms W/o CA Offered traffic (Mbps) Figure 8.9 50 percentile user throughput with/without DC under different backhaul configurations LTE Small Cell Optimization Without CA/DC DC with non-ideal backhaul CA with ideal backhaul Low load (10 Mbps High load (50 Mbps offered load) offered load) Figure 8.10 Average number of allocated PRBs per UE with and without DC under different load conditions user throughput performance of 4 Mbps. Under such requirements, the maximum tolerable offered load increases from 30 Mbps (without carrier aggregation or DC) to approximately 45 Mbps for cases with either DC or carrier aggregation, corresponding to a capacity gain of about 50%. With efficient flow control, DC with split 