A wireless device receives configuration parameters of cells grouped into timing advance groups (TAGs). The cells comprise: downlink-uplink cells, each of the downlink-uplink cells having a configured uplink and a configured downlink; and at least one downlink-only cell, each of the at least one downlink-only cell having a configured downlink with no configured uplink. A TAG is configurable to consist of one or more downlink-only cells in response to the wireless device having a first capability, otherwise each TAG comprises one or more downlink-uplink cells in the downlink-uplink cells. At least one timing advance command (TAC) for a first TAG is received. The TAC is applied to uplink transmission timing of at least one downlink-uplink cell in the first TAG.