A source node may send a first data unit to a destination node. To send the first data unit, the source node may transmit a modulation pattern over a transmission medium. In some cases, particular data units may correspond to modulation patterns with features that cause errors in transmission. The source node may receive an indication of an error from the destination node. To avoid repeated errors the retransmission, coding circuitry at the source node may alter data within the first data unit to generate a retransmission data unit. The alteration may result in the retransmission data unit corresponding to a modulation pattern different from that of the first data unit. The new modulation pattern may lack the error causing features and reduce the chance of repeated errors.