A method for communication includes configuring a communication system that includes a transmitter and a receiver with first precoding matrices for mapping up to N data streams onto N transmit antenna ports of the transmitter. Each of at least some of the first precoding matrices are derived from respective second and third precoding matrices. The second and third precoding matrices are configured for mapping data onto respective numbers of transmit antenna ports that are less than N. The data streams are mapped onto the N transmit antenna ports using a precoding scheme based on one of the first precoding matrices. The mapped data streams are transmitted over the N transmit antenna ports from the transmitter to the receiver.