# Field Trials of SC-FDMA, FBMC and LP-FBMC in Indoor Sub-3.5 GHz Bands
## 4 Experiment Results
### BER Comparison According to Carrier Frequency and Distance  
Figure 10 shows the BER performance of the three waveforms, according to the distance between RX and TX (=\(D\)) and carrier frequency (=\(F\)). For the averaged performance over the area, 10 different locations in the shaded areas in Figures 5 and 6 for LoS and NLoS environments, respectively, were tested for each pair of (\(D\), \(F\)), and then the measured BERs are averaged. In general, as \(D\) increases, the TX power amplification gain (power \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Carrier frequency \(F\) & 0.6 GHz (USA), 0.7 GHz (Europe), \\  & 2.5 GHz (USA), \\  & 3.5 GHz (USA, Europe, Korea) \\ \hline Number of users \(K\) & 3 \\ \hline Number of sub-carriers per user \(N\) & 64, 128 \\ \hline Sub-carrier spacing \(\Delta f\)(=\(1/T\)) & 15 kHz, 30 kHz \\ \hline Oversampling factor & 2 \\ \hline Modulation scheme & QPSK \\ \hline Number of symbols per frame \(M\) & 20 \\ \hline Filter for FBMC & PHYDYAS pulse with \\  & overlapping factor = 4 [20] \\ \hline Cyclic prefix for SC-FDMA & T/4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Major system parameters. gain in short) should be increased in order to compensate the path loss. However, if the power gain is set too high considering only the pass loss, then the performance is degraded by the nonlinear distortions of the transceiver circuit. Figure 11 shows the received signal power versus the power gain of the employed SDR device (USRP-2901) for different distances. In order to see the overall end-to-end link nonlinearities, i.e., not only HPA in TX, but also LNA (low noise amplifier), down-conversion circuit, and analog-to-digital converter (ADC) in RX, the received signal power was measured at the ADC output of RX. Meanwhile, TX and RX were placed at the outdoor open space to exclude the channel effect in the nonlinearity measurement. The received power tends to saturate when the power gain is larger than a certain level (about 18 dB) by the nonlinear distortion, as shown in Figure 11. Except that, due to the path loss, the graphs shift vertically according to the distance, the overall nonlinear characteristics remain the same, irrespective of the distance. Note that, even with the smaller received power due to the increased distance (12 m), the received power still saturates at the identical range of power gain. This implies that the main factor for the overall non-linearity is in the TX side, i.e., HPA in the TX. Hence, we experimentally searched the optimal power gain at each location of the user. Figure 12 shows an example plot of the measured BER versus the power gain for the three waveforms in LoS environment when \(F\) is 700 MHz and distance between TX and RX is 12 m. It is shown that the BER is minimized at a gain of 16 dB for FBMC and at a gain of 17 dB for LP-FBMC and SC-FDMA. The smaller optimal power gain for FBMC when compared to those for LP-FBMC and SC-FDMA confirms the higher PAPR of FBMC as compared to those for LP-FBMC and SC-FDMA. This is because, as PAPR becomes larger, the power gain needs to be more tightly controlled to avoid nonlinear distortion. In Figure 10, commonly to the three waveforms, the BER performance deteriorates as the distance increases. This is because, as the distance increases, even optimal transmit power gain cannot fully compensate the path loss in order to avoid the unacceptable nonlinear distortion of the HPA. Hence, in the NLoS environment where the path loss is more serious as compared to LoS environment, BER degrades more rapidly as the distance increases. The BER degradations are more critical in higher carrier frequency due to higher path loss. Figure 10: BER of the SC-FDMA, FBMC, and LP-FBMC, according to the distance and carrier frequency, \(N=64\), \(\Delta f=15\) kHz. FBMC has the significantly higher BER when compared to SC-FDMA due to high PAPR. The BER gap between FBMC and SC-FDMA increases as the carrier frequency decreases with larger distance. This is because.