Techniques for performing inter-frequency and/or inter-radio access technology (RAT) measurements are disclosed. A multi-receiver wireless transmit/receive unit (WTRU) may receive downlink transmissions via a plurality of downlink carriers simultaneously. The WTRU may perform inter-frequency and/or inter-RAT measurements using an inactive receiver without measurement gaps if at least one receiver is inactive. If the WTRU receives a measurement order on a disabled carrier, the WTRU may perform measurements on the disabled carrier without measurement gaps using an inactive receiver while maintaining a status of the disabled carrier as disabled. The WTRU may perform the measurements autonomously if a trigger condition is met and at least one receiver is inactive. If all receivers are active, the WTRU may perform the measurements using measurement gaps, that may be configured on a downlink carrier, or alternatively, on an unpaired downlink carrier, or alternatively, on a subset of associated downlink uplink carrier pairs.