## 6 Conclusions  
In this paper, four time sources (GPS, LEO satellites, pulsar signals, and WWVB) and four distribution mechanisms (NTP, PTP, White Rabbit, and 5G) were systematically evaluated, and their characteristics, performance, and suitability for power grid scenarios were compared. While traditional methods like GPS remain widely adopted due to their balance of accuracy and flexibility, emerging technologies such as LEO constellations and 5G are redefining synchronization paradigms with enhanced coverage and scalability. The analysis underscores that no single method is universally optimal. Instead, the selection hinges on aligning the method's strengths with the application's priorities. For instance,  
* High-precision applications: Phasor measurement units (PMUs) and substation automation necessitate sub-microsecond accuracy and deterministic performance, making White Rabbit or PTP with 5G the preferred choices. These methods leverage optical synchronization or ultra-reliable low-latency communication (URLLC) to meet stringent timing requirements. * Wide-area monitoring and fault detection systems: These prioritize resilience alongside precision. Here, GPS/LEO serves as a viable primary source if augmented with anti-jamming measures, while pulsar signals offer a niche backup for GNSS-denied environments due to their inherent spoofing resistance. * Cost-sensitive deployments: Applications such as smart metering and demand response favor scalable solutions like 5G network timing or LEO satellites, which minimize per-device costs while achieving millisecond-level accuracy sufficient for non-critical tasks. * Legacy systems: Systems like SCADA require compatibility with existing infrastructure, positioning PTP with hardware timestamping as a pragmatic upgrade path that balances accuracy with interoperability. Security emerges as a critical cross-cutting concern. While GPS and NTP are vulnerable to cyberattacks and signal interference, methods like quantum-secured PTP or hybrid architectures combining GNSS with terrestrial PTP mitigate risks through encryption and multi-source validation. Meanwhile, WWVB and pulsar-based systems, though limited in accuracy, provide low-complexity alternatives for non-critical or remote applications. Looking ahead, the integration of emerging technologies--such as LEO constellations for global coverage, 5G for scalable synchronization, and AI-driven error correction--will enable hybrid frameworks that maximize robustness. However, interoperability standards and cybersecurity protocols must evolve in parallel to address the growing complexity of grid infrastructure. Future research should prioritize harmonizing these technologies while exploring pulsar-based timing and quantum encryption to future-proof power grids against both technical and threat-related disruptions. In conclusion, the optimal synchronization strategy for power grids lies in a context-aware approach that rigorously evaluates accuracy, security, cost, and coverage against operational needs. By judiciously selecting and combining methods--such as pairing GNSS with terrestrial PTP or deploying 5G for distributed assets--grid operators can achieve a resilient, future-ready synchronization ecosystem that supports the transition to smart, decentralized energy systems. Conceptualization, Y.L. ([PERSON]) and B.S. ; methodology, Y.W. ; investigation, Y.Z. and W.W.; original draft preparation, Y.L. ([PERSON]) and J.Y. ; review and editing, N.L.T. and Q.L. ; supervision, Y.L. ([PERSON]). All authors have read and agreed to the published version of the manuscript. This work was supported by the National Science Foundation under NSF Award Number EEC-1920025. No new data were created or analyzed in this study. Data sharing is not applicable to this article. The authors declare no conflicts of interest.