A radio terminal comprising: a wireless transceiver configured to transmit signals to a base station and receive signals from the base station; and at least one processor configured to: receive beam configuration information from the base station; measure a first plurality of transmission beams transmitted from the base station in accordance with the beam configuration information, each of the first plurality of transmission beams using a first carrier and carrying a beamformed reference signal to be measured by the radio terminal, the beam configuration information including reference signal configuration indicating a radio resource used on each beam for transmitting the beamformed reference signal; use, as a first serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the first plurality of transmission beams based on a measurement result of the first plurality of transmission beams; measure a second plurality of transmission beams transmitted from the base station, the second plurality of transmission beams using a second carrier; use, as a second serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the second plurality of transmission beams based on a measurement result of the second plurality of transmission beams; perform aggregation of the first carrier and the second carrier; and provide a single Medium Access Control, MAC, entity that performs downlink reception on both the first serving beam belonging to the first carrier and the second serving beam belonging to the second carrier, wherein the MAC entity is configured to, when switching of a serving beam in the first carrier is performed, suspend or stop at least part of MAC layer processing for the first carrier but to continue MAC layer processing for the second carrier. a wireless transceiver configured to transmit signals to a base station and receive signals from the base station; and at least one processor configured to: receive beam configuration information from the base station; measure a first plurality of transmission beams transmitted from the base station in accordance with the beam configuration information, each of the first plurality of transmission beams using a first carrier and carrying a beamformed reference signal to be measured by the radio terminal, the beam configuration information including reference signal configuration indicating a radio resource used on each beam for transmitting the beamformed reference signal; use, as a first serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the first plurality of transmission beams based on a measurement result of the first plurality of transmission beams; measure a second plurality of transmission beams transmitted from the base station, the second plurality of transmission beams using a second carrier; use, as a second serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the second plurality of transmission beams based on a measurement result of the second plurality of transmission beams; perform aggregation of the first carrier and the second carrier; and provide a single Medium Access Control, MAC, entity that performs downlink reception on both the first serving beam belonging to the first carrier and the second serving beam belonging to the second carrier, receive beam configuration information from the base station; measure a first plurality of transmission beams transmitted from the base station in accordance with the beam configuration information, each of the first plurality of transmission beams using a first carrier and carrying a beamformed reference signal to be measured by the radio terminal, the beam configuration information including reference signal configuration indicating a radio resource used on each beam for transmitting the beamformed reference signal; use, as a first serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the first plurality of transmission beams based on a measurement result of the first plurality of transmission beams; measure a second plurality of transmission beams transmitted from the base station, the second plurality of transmission beams using a second carrier; use, as a second serving beam for transmission from the base station to the radio terminal, one or more beams selected from among the second plurality of transmission beams based on a measurement result of the second plurality of transmission beams; perform aggregation of the first carrier and the second carrier; and provide a single Medium Access Control, MAC, entity that performs downlink reception on both the first serving beam belonging to the first carrier and the second serving beam belonging to the second carrier, wherein the MAC entity is configured to, when switching of a serving beam in the first carrier is performed, suspend or stop at least part of MAC layer processing for the first carrier but to continue MAC layer processing for the second carrier.