th + 12N =12(rtsink) where the subscript 'SC' emphasizes that the SINR is the average subcarrier SINR in the serving cell. RSRQ is hence related to SINR as For example, if SINR is infinite then RSRQ is 1/12/ which for y = 2/12 and y = 4/12 give RSRQ = -3 dB and RSRQ = -6 dB, which are the well-known idle cell RSRQ values for 1Tx and 2Tx cells, respectively. 12 The case of 2Tx cell requires special attention since the resource elements transmitted from the second antenna should be included in the total power measured by RSSI. With the notation in use the simplest way to do this is to let the subcarrier activity factor take values larger than 1. For the fully utilized 2Tx cell there are 20 REs carrying power in the RS symbol at 1 PRB bandwidth. This is since the resource element carrying RS in one antenna is muted in the other antenna, in order to improve reference signal SNR (and hence the downlink channel estimation accuracy). In terms of average subcarrier activity factor the own cell contribution to RSSI of a fully loaded 2Tx cell can be modelled by simply letting y = 20/12 = 5/3, while a 50% load would correspond to y = 1/2 X 20/12 = 5/6, and SO on. The mapping between SINR and RSRQ is shown in Figure 15.8. Using the above formulation it is possible to find a corresponding RSRQ value for a given SINR and own cell load. Assuming SINR = -3 dB and fully loaded 1Tx cell, s = 1, RSRQ would turn out as 1/12/(1+2) = -15.5 dB. As an application of this simple result, if an intra- frequency neighbour cell is 3 dB stronger (e.g. intra-frequency A3 RSRP offset is 3 dB), using an RSRQ trigger higher than -15.5 dB risks causing unnecessary triggering of layer change (for cell edge UEs) if both the serving and the neighbour cells become fully utilized. For a fully utilized 2Tx cell the corresponding value would be 1/12/(5/3+2) = -16.4dB. Thus the RSRQ SINR conversion rules can also be used to lend some insight into how to set RSRQ-based event triggers. 12 Throughout this section it is assumed that RS power boosting is not u