The resulting discrete multi-tone (DMT) signal is real-valued, even if symbols are complex. xn Figure - Carrier mapping for standalone link IFFT The time-domain signal is given by X(k) where denotes the sample index, the complex-valued baseband signals in the frequency k xn domain and the block size of the IFFT. 2N Cyclic prefix At the output of the IFFT, in the serial of 2N samples, the last CP samples are copied as a sub-block being repeated and appended at the beginning of the block of samples, see Figure 6. By adding the CP at the transmitter, and removing it at the receiver, the multipath channel matrix can be transformed from Toeplitz-shape into a circulant shape, which allows the use of IFFT at the transmitter and FFT at the receiver to obtain a diagonal channel, so that a simple equalizer (FDE) can be used. Figure - Cyclic Prefix insertion Single-carrier modulation (optional) Optional precoding infront of the OFDM modulator can be used to reduce the probability of clipping and enhance efficiency while sacrificing no or minor spectral efficiency see [2, 3]. For single-carrier (SC) transnmission, precoding, together with an OFDM “outer” “inner” transmitter is used to emulate SC transmitter inside the OFDM concept. These schemes require little more advanced signal processing, and the same minor increase of sophistication can be expected at the receiver, i.e. the decoding is straightforward. The schemes are shown in principle in Figure 5. More details can be found in [2, 3]. Pure DFT precoded SC The well-known SC-FDMA transmitter from 3GPP LTE is shown in Figure 5, row A. First, the symbol sequence is passed through the N-DFT and then mapped directly onto the desired
The resulting discrete multi-tone (DMT) signal is real-valued, even if symbols xn are complex. Figure - Carrier mapping for standalone link IFFT The time-domain signal X(k) is given by where k denotes the sample index, xn the complex-valued baseband signals in the frequency domain and 2N the block size of the IFFT. Cyclic prefix At the output of the IFFT, in the serial of 2N samples, the last CP samples are copied as a sub-block being repeated and appended at the beginning of the block of samples, see Figure 6. By adding the CP at the transmitter, and removing it at the receiver, the multipath channel matrix can be transformed from Toeplitz-shape into a circulant shape, which allows the use of IFFT at the transmitter and FFT at the receiver to obtain a diagonal channel, so that a simple equalizer (FDE) can be used. Figure - Cyclic Prefix insertion Single-carrier modulation (optional) Optional precoding infront of the OFDM modulator can be used to reduce the probability of clipping and enhance efficiency while sacrificing no or minor spectral efficiency see [2, 3]. For single-carrier (SC) transnmission, “outer” precoding, together with an “inner” OFDM transmitter is used to emulate SC transmitter inside the OFDM concept. These schemes require little more advanced signal processing, and the same minor increase of sophistication can be expected at the receiver, i.e. the decoding is straightforward. The schemes are shown in principle in Figure 5. More details can be found in [2, 3]. Pure DFT precoded SC The well-known SC-FDMA transmitter from 3GPP LTE is shown in Figure 5, row A. First, the symbol sequence is passed through the N-DFT and then mapped directly onto the desired