Methods, systems, and devices for wireless communications are described. Generally, the described techniques provide for configuring group indices for uplink transmissions from a user equipment (UE) such that the UE may be able to determine whether to combine uplink transmissions scheduled on overlapping time resources. Specifically, the UE may combine uplink transmissions associated with a same group index for transmission in a single channel, and the UE may avoid combining uplink transmissions associated with different group indices. In some cases, the indication of a group index associated with an uplink transmission from a UE may be explicit (e.g., provided in a downlink control information (DCI) message), and, in other cases, the indication of a group index associated with an uplink transmission from a UE may be implicit (e.g., corresponding to a resource allocated for the uplink transmission).