Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel
Abstract
:1. Introduction
- We propose a robust STR scheme for a GW, which is not susceptible to a large Doppler offset caused by the LEO satellite. In the GEO satellite, most conventional schemes considered limited Doppler offset and timing uncertainty environment due to the motion of UTs. On the other hand, for LEO satellites, it is not simple to maintain network synchronization between satellite and ground UTs because the UTs are used to receive a variable Network Clock Reference (NCR) signal due to the severe Doppler offsets caused by satellite motion. Thus, UTs are required to continuously estimate the differential propagation delay based on the serving satellite’s position and velocity within a beam. Furthermore, our scheme needs to consider the scenarios when UT should support high-speed vehicles such as airplanes or when UT should have a clock oscillator with low accuracy for cost-efficiency purposes [15]. Therefore, our proposed scheme can serve as a temporary solution until novel Forward Link Signaling (FLS) information, such as DVB System Information (SI), is developed to address Doppler and timing uncertainties in the DVB-RCS2 standard work for supporting LEO satellite communication [16].
- In the case of the 3GPP NTN standard, UTs are capable to compute and pre-compensate for the delay and Doppler frequency offsets due to the LEO satellite velocity and position through ephemeris information from GW’s and UT’s positions through the GNSS receiver when triggering access to GW [17,18]. Accordingly, there is a need to update the DVB-RCS2 standard, like the 3GPP NTN standard, to accommodate LEO satellite communication [16]. Until the amendment in the DVB standard, the proposed scheme can be effective as a viable option through GW receiver implementation technology within the standard. Even in the 3GPP standard, robust time and frequency synchronization enhancement based on non-GNSS operation has been required and discussed as a candidate technology for release 19. If there are situations where NTN UT is located temporarily with improper GNSS coverage or disruptions due to jamming, it may be necessary to perform initial access without the help of GNSS operations as implementation technology. The proposed scheme in this paper can contribute to improving performance in the case of the provisional non-GNSS operation when there are a large of timing and frequency offsets in initial access from UTs to GW.
2. Transmission Model Description
2.1. Transmission Structure for DVB-RCS2 Linear Modulation and Channel Model
2.2. Demodulator Structure for DVB-RCS2 Linear Modulation
3. Robust Symbol Timing Synchronization
3.1. Previous Works
3.2. The Proposed Structure
4. Numerical Results
4.1. Simulation Condition
4.2. PER Performance Assessment
4.3. Complexity and Performance Impact
5. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Abbreviations
ACI | Adjacent Channel Interference |
AVN | Absolute Value Nonlinearity |
BCT | Broadcasting Composite Table |
CPM | Continuous Phase Modulation |
CB | Control Burst |
CFO | Carrier Frequency Offset |
COTS | Commercial On-The-Shelf |
CR | Carrier Recovery |
DA | Data-Aided |
DD | Decision Directed |
DVB | Digital Video Broadcasting |
FDD | Frequency Division Duplexing |
FFT | Fast Fourier Transform |
FLS | Forward Link Signaling |
FPGA | Field Programmable Gate Array |
GEO | Geostationary Earth Orbit |
GNSS | Global Navigation Satellite System |
GPP | Generation Partnership Project |
GW | Gateway |
HGT | Half Guard Time |
IF | Intermediate Frequency |
LB | Log-on Burst |
LEO | Low Earth Orbit |
LTB | Long Traffic Burst |
MCRLB | Modified Cramer–Rao Lower Bound |
ML | Maximum Likelihood |
NCR | Network Clock Reference |
NDA | Non-Data-Aided |
NTN | Non-Terrestrial Network |
PER | Packet Error Rate |
PLL | Phase Locked Loop |
QAM | Quadrature Amplitude Modulation |
QEF | Quasi Error Free |
QPSK | Quadrature Phase Shift Keying |
RAN | Radio Access Network |
RCS | Return Channel via Satellite |
SNR | Signal-to-Noise Ratio |
SSPA | Solid State Power Amplifier |
STB | Short Traffic Burst |
STR | Symbol Timing Recovery |
TDD | Time Division Duplexing |
TDMA | Time Division Multiple Access |
ToA | Timing offset of Arrival |
UT | User Terminal |
VSAT | Very Small Aperture Terminal |
Appendix A
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Waveform ID | LB (ID#1) | CB (ID#2) | TB (ID#3, #13) |
---|---|---|---|
Maximum HGT (ToA in symbols) Uniform distribution | ±200 symbols (±20 μs in 10 Mbaud) | ±100 symbols (±10 μs in 10 Mbaud) | ±20 symbols (±2 μs in 10 Mbaud) |
Normalized maximum CFO vs. symbol rate Uniform distribution | ±0.05 (±500 kHz in 10 Mbaud) | ±0.02 (±200 kHz in 10 Mbaud) | ±0.004 (±40 kHz in 10 Mbaud) |
Waveform ID | Burst Length (Symbol) | Modulation | Code Rate | Known Symbol Length | The Ratio of Known Symbols in Burst |
---|---|---|---|---|---|
#1(LB) | 664 | QPSK | 1/3 | 208 | 31% |
#2(CB) | 262 | QPSK | 1/3 | 94 | 36% |
#3(STB3) | 536 | QPSK | 1/3 | 80 | 15% |
#13(LTB3) | 1616 | QPSK | 1/3 | 140 | 9% |
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Kim, P.; Park, H. Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel. Sensors 2023, 23, 8320. https://doi.org/10.3390/s23198320
Kim P, Park H. Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel. Sensors. 2023; 23(19):8320. https://doi.org/10.3390/s23198320
Chicago/Turabian StyleKim, Pansoo, and Hyuncheol Park. 2023. "Robust Symbol Timing Synchronization for Initial Access under LEO Satellite Channel" Sensors 23, no. 19: 8320. https://doi.org/10.3390/s23198320