A method of operation of a multi-RAT scheduler to schedule wireless communication devices in a wireless communication system that provides radio access via a first Radio Access Technology, RAT, and a second RAT, comprising: • obtaining from a first RAT system, first information comprising: o channel information regarding channels between a first plurality of wireless communication devices and at least one radio unit used by the first RAT; • obtaining from a second RAT system, second information comprising channel information regarding channels between a second plurality of wireless communication devices and at least one radio unit used by the second RAT; and • Jointly scheduling, at the multi-RAT scheduler, at least some of the first plurality of wireless communication devices on the first RAT and the at least some of the second plurality of wireless communication devices on the second RAT, characterized in that the jointly scheduling comprises o identifying a multi-RAT Multiple User- Multiple Input Multiple Output, MU-MIMO, pairing comprising a first wireless communication device from among the first plurality of wireless communication devices and a second wireless communication device from among the second plurality of wireless communication devices based on the first information and the second information; and o scheduling the at least some of the first plurality of wireless communication devices on the first RAT and the at least some of the second plurality of wireless communication devices on the second RAT such that the first wireless communication device and the second wireless communication device are scheduled on the same time-frequency resources using different spatial multiplexing layers on the first and second RATs, respectively. • obtaining from a first RAT system, first information comprising: o channel information regarding channels between a first plurality of wireless communication devices and at least one radio unit used by the first RAT; o channel information regarding channels between a first plurality of wireless communication devices and at least one radio unit used by the first RAT; • obtaining from a second RAT system, second information comprising channel information regarding channels between a second plurality of wireless communication devices and at least one radio unit used by the second RAT; and • Jointly scheduling, at the multi-RAT scheduler, at least some of the first plurality of wireless communication devices on the first RAT and the at least some of the second plurality of wireless communication devices on the second RAT, characterized in that the jointly scheduling comprises o identifying a multi-RAT Multiple User- Multiple Input Multiple Output, MU-MIMO, pairing comprising a first wireless communication device from among the first plurality of wireless communication devices and a second wireless communication device from among the second plurality of wireless communication devices based on the first information and the second information; and o scheduling the at least some of the first plurality of wireless communication devices on the first RAT and the at least some of the second plurality of wireless communication devices on the second RAT such that the first wireless communication device and the second wireless communication device are scheduled on the same time-frequency resources using different spatial multiplexing layers on the first and second RATs, respectively. o identifying a multi-RAT Multiple User- Multiple Input Multiple Output, MU-MIMO, pairing comprising a first wireless communication device from among the first plurality of wireless communication devices and a second wireless communication device from among the second plurality of wireless communication devices based on the first information and the second information; and o scheduling the at least some of the first plurality of wireless communication devices on the first RAT and the at least some of the second plurality of wireless communication devices on the second RAT such that the first wireless communication device and the second wireless communication device are scheduled on the same time-frequency resources using different spatial multiplexing layers on the first and second RATs, respectively.