sed. Inter-layer Mobility Optimization RSRQ versus SINR 1Tx unloaded 1Tx 100% load 2Tx unloaded 2Tx 100% load RSRQ (dB) Figure 15.8 Theoretical mapping of RSRQ to SINR In the absence of other cell interference SINR = 0 dB corresponds to RSRP of about - 125 dBm, assuming UE noise figure of 7 dB. Triggering a layer change at such low received levels cannot be usually recommended since based on field experience uplink power starts to limit the performance with commercial handsets when RSRP is roughly below the rule of thumb value of -115 dBm, the actual value also depends on uplink noise rise, RS transmit power as well as UE and network capability (e.g. eNodeB receiver sensitivity and whether UE transmit antenna selection is used or not). At RSRP levels below -120 dBm the risk of an RRC connection setup failure or radio link failure tends to increase sharply. Furthermore, when RSRP is below -125 dBm the cell is not detectable in terms of neighbour cell search requirements as discussed in an earlier section. Finally, with the mapping between SINR and RSRQ, downlink throughput as a function of RSRQ can be straightforwardly approximated. For example, for a 2Tx cell where average RSRQ = -16 dB and cell load is 100%, the SINR would be about -3 dB, which based on Figure 15.7 corresponds to about 8-9 Mbps downlink throughput. Obviously, uplink through- put cannot be obtained from RSRQ and hence RSRQ can be used as purely downlink-based mobility trigger. Mapping Throughput to RSRP If there is no other cell interference the downlink SNR is simply the difference between RSRP and UE thermal noise floor at one subcarrier bandwidth, which is -125 dBm assuming a UE LTE Small Cell Optimization noise figure of 7 dB. The obtained SNR value can then be directly used to predict throughput using a performance curve similar to Figure 15.7. For the practically more important non-isolated cell case, the main problem with RSRP is that it does not contain any information about interference. Because of this, RSRP to throughput mapping is in 