A base station transmits a DCI comprising: an allocation of resource blocks for wireless device transmission of uplink data via a subframe of an unlicensed cell; an index indicating a starting position for the wireless device transmission of the uplink data, the index identifying one of pre-configured starting positions; and a field indicating an ending symbol for the wireless device transmission of the uplink data. The ending symbol is one of pre-configured ending symbols. The uplink data is received, based on the DCI and via the unlicensed cell, starting at the starting position in the subframe and ending before the ending symbol. The reception is based on an LBT procedure indicating a clear channel before the starting position of the subframe. The uplink data is mapped, based at least on the starting position and the ending symbol, to resource elements corresponding to the resource blocks.