A method is for controlling interleaving, within a packet for transmission, of second type symbols amongst first type symbols. The first type symbols comprise error correction encoded data modulated using a first modulation alphabet and the second type symbols are for communication parameter estimation and comprise error correction encoded data modulated using a second modulation alphabet which is smaller than the first modulation alphabet. The data modulated using the second modulation alphabet is encoded with a same error correcting code as the data modulated using the first modulation alphabet. The method comprises determining (340) one or more of: an interleaving density of the second type symbols, a type of the second modulation alphabet, and a size of the second modulation alphabet. The determination is based on one or more of: a worst case phase drift for the packet, a worst case amplitude variation for the packet, and a required signal quality for the first type symbols to meet a performance target for the packet. A method of a receiver, apparatuses for performing the methods, and a communication device are also disclosed.