A wireless device receives configuration parameters of a first bandwidth part and a second bandwidth part of an unlicensed cell. An active bandwidth part is switched from the first bandwidth part to the second bandwidth part. A first contention window size determined based on the switching. Based on the first contention window size, a listen before talk procedure is performed for transmission of a transport block in one or more subbands of the second bandwidth part. A transport block is transmitted based on a listen before talk procedure indicating a clear channel.