An apparatus comprising: means for generating a plurality of pilot sequences (P i (k)) for a plurality of transmit antennas based on frequency-domain code division multiplexing, FD-CDM, of a Chu sequence (c N (n)) defined by a transmitter-specific value; and means for generating a plurality of pilot transmissions based on the plurality of pilot sequences (P i (k)); wherein the means for generating the plurality of pilot sequences (P i (k)) comprises means for generating the Chu sequence (c N (n)) with the transmitter-specific value, and means for generating the plurality of pilot sequences (P i (k)) based on the Chu sequence (c N (n)); characterised in that the means for generating the Chu sequence (c N (n)) comprises means for generating the Chu sequence (c N (n)), for even N, as follows: c n = e j πλ n 2 N where c(n) is the Chu sequence (c N (n)), N is length of the Chu sequence (c N (n)), λ is the transmitter-specific value, and n is time index; wherein the means for generating the plurality of pilot sequences (P i (k)) based on the Chu sequence (c N (n)) comprises: means for generating a frequency-domain base sequence (B N (k)) based on the Chu sequence (c N (n)) or the IDFT of the Chu sequence (c N (n)), means for multiplying the frequency-domain base sequence (B N (k)) with a plurality of orthogonal sequences (W i (k)) to obtain a plurality of intermediate sequences, and means for generating the plurality of pilot sequences (P i (k)) based on the plurality of intermediate sequences; wherein the orthogonal sequences (W i (k)) are defined as follows: W i k = e j 2 πik T, for k = 0,..., N − 1 and i = 0,..., T − 1 T being the number of antennas. means for generating a plurality of pilot sequences (P i (k)) for a plurality of transmit antennas based on frequency-domain code division multiplexing, FD-CDM, of a Chu sequence (c N (n)) defined by a transmitter-specific value; and means for generating a plurality of pilot transmissions based on the plurality of pilot sequences (P i (k)); wherein the means for generating the plurality of pilot sequences (P i (k)) comprises means for generating the Chu sequence (c N (n)) with the transmitter-specific value, and means for generating the plurality of pilot sequences (P i (k)) based on the Chu sequence (c N (n)); characterised in that the means for generating the Chu sequence (c N (n)) comprises means for generating the Chu sequence (c N (n)), for even N, as follows: c n = e j πλ n 2 N where c(n) is the Chu sequence (c N (n)), N is length of the Chu sequence (c N (n)), λ is the transmitter-specific value, and n is time index; wherein the means for generating the plurality of pilot sequences (P i (k)) based on the Chu sequence (c N (n)) comprises: means for generating a frequency-domain base sequence (B N (k)) based on the Chu sequence (c N (n)) or the IDFT of the Chu sequence (c N (n)), means for multiplying the frequency-domain base sequence (B N (k)) with a plurality of orthogonal sequences (W i (k)) to obtain a plurality of intermediate sequences, and means for generating the plurality of pilot sequences (P i (k)) based on the plurality of intermediate sequences; means for generating a frequency-domain base sequence (B N (k)) based on the Chu sequence (c N (n)) or the IDFT of the Chu sequence (c N (n)), means for multiplying the frequency-domain base sequence (B N (k)) with a plurality of orthogonal sequences (W i (k)) to obtain a plurality of intermediate sequences, and means for generating the plurality of pilot sequences (P i (k)) based on the plurality of intermediate sequences; wherein the orthogonal sequences (W i (k)) are defined as follows: W i k = e j 2 πik T, for k = 0,..., N − 1 and i = 0,..., T − 1 T being the number of antennas.