 Shannon Inter-layer Mobility Optimization SINR increase required to maintain throughput relative to 20 MHz 15 MHz bandwidth 10 MHz bandwidth 5 MHz bandwidth 20 MHz downlink throughput (Mbps) Figure 15.11 SINR increase required to maintain downlink throughput when reducing system band- width. Fading channel measurement result for 2x2 spatial multiplexing with a commercial UE formula or from simulation or measurement results. The interesting quantity is the required increase in SINR to maintain the same throughput. Figure 15.11 presents the additional SINR required when the source layer has 20 MHz system bandwidth and the target layer bandwidth is 15, 10 or 5 MHz. The curves are based on the measurement of a commercial UE under fading conditions. The delta SINR depends on the throughput; for low throughput the additional SINR required approaches 3 dB when the system bandwidth is halved while for high throughput the SINR difference is larger. As an example, for 10 Mbps throughput in 20 MHz system the SINR should be 5 dB higher for a 10 MHz system to reach the same 10 Mbps throughput. Similarly, 12 dB higher SINR is required for a 5 MHz system to reach 10 Mbps. When tuning the A3 handover thresholds between layers having different bandwidths the throughput difference between the layers should be taken into account using design curves similar to that shown in Figure 15.11. To make the prediction more accurate the impact of different cell overlaps and loads on SINR characteristics between layers may be included using results such as shown in Figure 15.10. 15.4.3 Inter-layer Mobility Example #1 (Non-equal Priority Non-equal Bandwidth LTE Layers) Equipped with the simple framework presented in the prequel, in this section the setting of mobility thresholds is illustrated by means of an example. The network used in the example is shown in Figure 15.12. The assumptions are Two LTE layers and one UMTS coverage layer, with priorities as shown in the figure. Minimum requirement for LTE uplink/downlink throughput at LTE1800 c