MIMO layer adaptation is beneficial

MIMO layer adaptation is beneficial for the UE’s power saving. Based on the current RAN4 specification [2], when the UE works in bands n7,n38,n41,n77,n78 or n79, the UE needs to be equipped with a minimum of 4 antenna ports.One remaining issue is whether the maximum number of UL MIMO layer should be adapted. In our view, the power consumption of uplink RF chains is different from that of the downlink RF chains. For the downlink, the UE needs to open sufficient number of RF chains all the time to guarantee the reception of data scheduling with the maximum number of DL MIMO layers, irrespective to whether there is actual scheduling or not. Therefore, maximum number of DL MIMO layers would be beneficial for the case of light traffic load. But for uplink, there would be transmission by the UE only when data is scheduled or other uplink transmission is triggered. For PUSCH transmission, if the UE’s channel condition is good enough, the network could schedule the UE with high uplink MIMO layer and the UE’s transmission duration may be reduced with high data rate. Therefore, there is no power waste for uplink due to large maximum number of DL MIMO layers and potentially in some case, there may be power saving with high uplink MIMO layer scheduling.Proposal 1: The maximum number of uplink MIMO layer is NOT adapted.