# Performance Evaluation of the New Compound-Carrier-Modulated Signal for Future Navigation Signals
## 2 NSCC and Its Properties
### ACF and PSD
With the increment to 10 MHz, the ACF profiles of BOC(1,1) become steeper, but the MBOC modulation doesn't appear to have any advantage compared with BOC(1,1) resulting in the loss of high-frequency components. Note that the NSCC modulation presents superior tracking performance with the narrowest ACF profiles in comparison with legacy navigation signals, and the NSCC ACF become increasingly steep as the pre-filtering bandwidth increases, closely followed by the BPSK(5) at 10 MHz bandwidth and BPSK(10) at 20 MHz bandwidth. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Modulation Scheme** & **Main Lobe (dBW/Hz)** & **First Side Lobe (dBW/Hz)** & **Power Attenuation (dBW/Hz)** \\ \hline BPSK(1) & \(-\)60.10 & \(-\)73.36 & 13.26 \\ BPSK(5) & \(-\)67.09 & \(-\)80.35 & 13.26 \\ BPSK(10) & \(-\)70.10 & \(-\)83.36 & 13.26 \\ QPSK(10) & \(-\)67.09 & \(-\)80.35 & 13.26 \\ BOC(10,5) & \(-\)70.07 & \(-\)78.64 & 7.94 \\ BOC(15,2.5) & \(-\)67.96 & \(-\)79.32 & 11.36 \\ BOC(14,2) & \(-\)67.00 & \(-\)78.61 & 11.61 \\ BOC(6,1,1/11) & \(-\)63.31 & \(-\)73.87 & 10.56 \\ AltBOC(15,10) & \(-\)64.99 & \(-\)74.87 & 9.88 \\ MSK & \(-\)61.01 & \(-\)84.01 & 23.00 \\ NSCC & \(-\)70.10 & \(-\)82.05 & 12.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The relative power attenuations between the first side lobe and the main lobe. We further investigate the ACFs for NSCCs with different parameter configurations including the number of sub-carriers, the subcarrier chip rate, the subcarrier spacing and the power distribution. The results are shown in Figures 4 and 5. Figure 4 illustrates the ACFs for monomodal NSCCs within 20 MHz pre-filtering bandwidth. The NSCCs are allocated constant power distribution. The code rate is 1.023 Mcps for NSCC(19), 2.046 Mcps for NSCC(9), 4.092 Mcps for NSCC(4), 5.115 Mcps for NSCC(3), 10.23 Mcps for BPSK(10). The number of sub-carriers are set up in conjunction with the chip rate to adapt the finite bandwidth. It can be seen that as the number of sub-carriers increases and the chip rate reduces, the sharpness of the main peaks of the NSCCs is enhanced slightly and the locations of side-lobes move gradually far away from the main peaks. Figure 4: ACFs for monomodal NSCCs with different sub-carriers in 20 MHz bandwidth. Figure 3: ACFs for NSCC modulation and legacy navigation modulations with: (**a**) 2 MHz, (**b**) 4 MHz, (**c**) 10 MHz, (**d**) 20 MHz pre-filtering bandwidths. Figure 5 shows the ACFs for NSCC(19), NSCC(9) monomodal and NSCC(8) bimodal. These signals all adopt 1.023 MHz chip rate, 1.023 MHz sub-carrier spacing and constant power distribution. The main-lobes of the two baselines have no overlap with each other in the frequency domain. Note that the largest proportions of high-frequency component enhance the second order moment of the spectrum, rendering the NSCC signal to process sharpest peaks, while it also brings to the highest secondary lobes and these locations are closest to main peak. Besides, the NSCC has an obvious drawback due to its multi-peak ACF. Its characteristic ACF relates to the frequency information contained within the NSCC baseband signal, and the secondary lobes far to the zero delay are associated with the superposition of NSCC subcarriers' ACFs. The abovementioned feature implies possible false acquisition or biased tracking, resulting in ambiguous measurements if no special care is taken. Since the NSCC is essentially the superposition of subcarriers with BPSK modulation, the conventional BPSK techniques can be utilized to avoid the ambiguity, and above all, be combined with the NSCC subcarrier information to promote their performance [24; 25]. Another solution is the bump and jump (BJ) technique, proposed by [PERSON] and [PERSON] in [26], which uses extra correlators referred to as very early (VE) and very late (VL) correlators to monitor the amplitudes of the suspicious side peaks.