Uplink and downlink use different modulation formats: while the downlink employs “classical” OFDM, the uplink uses a format that can be interpreted as single-carrier transmission, but in LTE can be better characterized as DFT-precoded OFDM .

The implementation of the downlink transmission is straightforward: the modulation is OFDM with 15-kHz subcarrier spacing. Data intended for different MSs are multiplexed onto the different RBs; each RB can employ a different modulation format. For each OFDM symbol, the overall signal is then subjected to an Inverse Fast Fourier Transform (IFFT) transformation; the cyclic prefix is prepended, and the signal is upconverted to passband for transmission (the more complicated case of multiantenna transmission.

For the uplink, an MS has a number of contiguous subcarriers available for signaling. The MS maps the symbols onto the input of a DFT whose size equals the number of subcarriers.

The output of this DFT is then mapped onto the subcarriers, which are processed like in the downlink (IFFT, cyclic prefix, upconversion to passband). The combination of the DFT with the IFFT inherent in the OFDM implementation results in a single-carrier signal with cyclic prefix, which can be effectively equalized by frequency domain equalization.

The bandwidth of the signal corresponds to the number of subcarriers used in the transmission, multiplied with the subcarrier spacing of 15 kHz (i.e., the same as for the uplink).