Design and performance evaluation of a novel ranging signal based on an LEO satellite communication constellation

Figures & data

Table 1. Iridium STL signal system.

Channel	Frequency band (MHz)	Function	Multiple access
Bidirectional channel	1616.0–1626.0	Broadcast, synchronization, voice and data services	TDMA
Unidirectional channel	1626.0–1626.5	Bell alarm and broadcast messages	FDMA

Figure 1. Block diagram of the OFDM system.

Figure 2. Block diagram of LSCC-BPR signal generation.

Figure 3. LSCC-BPR signal time-frequency structure.

Figure 4. Schematic diagram of the LSCC-BPR signal structure. (a) Partial insertion of a pilot in front of the subcarrier. (b) Partial insertion of a pilot in the middle of the subcarrier. (c) Partial insertion of a pilot behind the subcarrier.

Figure 5. Block diagram of the traditional OFDM ranging system.

Figure 6. Ranging system of the LSCC-BPR signal.

Figure 7. Ranging algorithm flow based on the LSCC-BPR signal.

Figure 8. Time delay estimation based on fractional sampling. (a) When the number of carriers is 512. (b) When the number of carriers is 1024. (c) When the number of carriers is 2048. (d) When the number of carriers is 4096.

Figure 9. Simulation of time-domain delay estimation for different SNRs.(a) When the SNR is −5 dB. (b) When the SNR is −10 dB. (c) When the SNR is −15 dB. (d) When the SNR is −20 dB.

Figure 10. Relationship between L/N and ranging error.

Figure 11. Relationship between ranging error and SNR for different numbers of subcarriers.

Figure 12. Relationship between ranging error and SNR when the ranging pilots are inserted in the front.

Figure 13. Relationship between ranging error and SNR when the pilots are inserted in the middle.

Figure 14. Relationship between ranging error and SNR when the pilots are inserted in the back.

Figure 15. Relationship between the ranging error and SNR at different positions with 2048 pilots.

Figure 16. Relationship between the ranging error and SNR at different positions with 1024 pilots.

Figure 17. Relationship between the ranging error and SNR at different positions with 512 pilots.

Figure 18. Effect of the Doppler shift on ranging accuracy.

Figure 19. Ranging accuracy simulation based on the traditional OFDM signal and the LSCC-BPR signal.

Figure 20. CSS signal time delay estimation with the SNR of 0 dB.

Table 2. Comparison of ranging performances of the CSS and LSCC-BPR signals.

Ranging signal	Integer delay true value	Integer delay estimate value	Fractional delay estimate value	Fractional delay estimate value	Advantages	Disadvantages
CSS signal	50 μs	50 μs	0.02 μs	No fractional delay estimate value	Doppler shift has less effect; performance is more pronounced at large bandwidths	Time resolution is affected by bandwidth; not easy to generalize
LSCC-BPR signal	50 μs	50 μs	0.02 μs	1.02 μs	Save frequency resources; can measure more accurately; easy to generalize	The ranging accuracy will be affected by the Doppler shift

Figure 21. Proportions of pilots, information, and subcarriers.

Table 3. Ranging accuracy for different numbers of pilots at an SNR of 0 dB.

Number of subcarriers	Number of pilots	Quantity of information	Ranging accuracy (m)	Carrier occupancy
4096	512	3584	2.66	12.5%
4096	1024	3072	1.00	25%
4096	2048	2048	0.80	50%
4096	4096	0	0.80	100%

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.