A network node receives a first signal in a first grant-free transmission from a client device, wherein the first signal comprises data having a first redundancy version and having a corresponding first transmission attempt number, in a first resource unit; determines an identity of the client device based on the first signal, establishes that a data decoding error associated with the first grant-free transmission has occurred if the data in the first signal cannot be decoded correctly; receives a second signal in a second transmission from the client device, wherein the second signal comprises the data having a second redundancy version and having a corresponding second transmission attempt number, in a second resource unit; and establishes that a data decoding error associated with the second transmission has occurred if the data in the second signal cannot be decoded correctly.