Apparatus comprises a memory configured to store a matrix of transmit data; a multi-element antenna; and a transmitter configured to transmit a signal from a multi-element antenna as part of a packet within a transmit period in a switching interval by: switching between different elements of the multi-element antenna in a sequence of transmit intervals within the transmit period; and deriving the signal for transmission in different transmit intervals from different ones of the transmit data in the matrix. Also, apparatus comprises a receiver configured to receive plural packets; and an accumulator configured, for each packet, to accumulate signals received in a switching interval of the packet. The apparatus is configured to: derive a correlation metric for each of the packets from the accumulated signals for the packets; identify a packet with the best correlation metric; identify a direction associated with the packet identified as having the best correlation metric; and provide the direction as an output.