Use Case: Telecom Network Holdover with BRIDZA STW-AS600 During GNSS Outage

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Customer Profile

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The Challenge: GNSS Vulnerability and Network-Wide Synchronization Risk

Modern telecom networks are fundamentally dependent on precise timing. With the rollout of 5G NR using Time Division Duplex (TDD) architecture, every cell site requires synchronization to a common time reference accurate to within ±1.5 μs. This timing is typically derived from GNSS receivers locked to GPS, Galileo, or BeiDou constellations.

However, GNSS is not infallible. The operator identified multiple scenarios where GNSS signals were degraded or lost entirely:

• Solar storms and ionospheric disturbances causing widespread signal degradation across entire regions for hours at a time.
• Intentional and unintentional jamming, particularly near military installations, airports, and national borders, where RF interference routinely disrupted GPS L1 signals.
• Spoofing events in contested or urban environments, where false GNSS signals introduced timing errors that cascaded through the synchronization network.
• Physical obstructions at small cell and indoor DAS (Distributed Antenna System) sites, where rooftop access was unavailable and GNSS antennas suffered persistent multipath and signal attenuation.

During a documented 18-hour GNSS outage affecting 1,200 cell sites in a metropolitan region — caused by a combination of severe space weather and localized jamming — the operator's legacy holdover oscillators (standard TCXOs) drifted beyond acceptable thresholds within 4 to 6 hours. The result: inter-cell handover failures, degraded VoNR call quality, reduced downlink throughput due to timing misalignment in carrier aggregation, and ultimately, a measurable increase in customer complaints and churn risk.

The operator needed a solution that could maintain sub-1.5 μs time accuracy for a minimum of 24 hours without any GNSS input — the so-called "holdover" requirement defined by ITU-T G.8273.2 for boundary clocks and by 3GPP specifications for 5G TDD networks.

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The Solution: BRIDZA STW-AS600 with High-Performance OCXO Holdover

After evaluating multiple GNSS-disciplined timing modules, the operator selected the BRIDZA STW-AS600 as the core timing engine for a network-wide upgrade program. The STW-AS600 was deployed at each cell site as part of an integrated small-form-factor timing card within the site's grandmaster clock.

The STW-AS600 offered several critical advantages: 1. Multi-Constellation, Multi-Frequency GNSS Reception The STW-AS600 simultaneously tracks GPS L1/L5, Galileo E1/E5a, BeiDou B1C/B2a, and GLONASS L1 signals across multiple constellations. This multi-frequency capability provided inherent resilience against single-constellation outages and enabled real-time ionospheric error correction, ensuring the oscillator was disciplined to the highest possible accuracy while GNSS was available. 2. Advanced OCXO Holdover Engine The heart of the holdover solution is the STW-AS600's integrated OCXO (Oven-Controlled Crystal Oscillator), calibrated and continuously disciplined using an adaptive aging compensation algorithm. While locked to GNSS, the module characterizes the OCXO's frequency offset, aging rate, and temperature sensitivity in real time, building a predictive model of oscillator behavior. Upon GNSS signal loss, the module seamlessly transitions to holdover mode, using this model to predict and correct frequency drift autonomously. 3. Intelligent Jamming and Spoofing Detection The STW-AS600 incorporates multi-layer interference detection, including signal-to-noise ratio monitoring, receiver autonomous integrity monitoring (RAIM), and consistency checks across constellations. When jamming or spoofing is detected, the module proactively enters holdover before corrupted timing data can discipline the oscillator — preserving the integrity of the holdover model. 4. Seamless Hitless Switching The transition from locked mode to holdover is entirely seamless, with no phase discontinuity or timing step. This "hitless" behavior ensured that downstream network elements experienced no synchronization disturbance during the switchover.

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Results

Following a six-month field trial across 300 sites in the affected metropolitan region, the operator measured the following performance during controlled and natural GNSS outages:

Across the 300-site trial, zero synchronization-related service degradation events were recorded during multiple GNSS disruptions totaling over 120 cumulative outage hours. Inter-cell handover success rates remained above 99.7%, and VoNR call drop rates showed no statistically significant increase compared to GNSS-locked operation.

The operator calculated an estimated annual avoided cost of $2.4 million in reduced truck rolls, avoided SLA penalties, and prevented customer churn attributable to synchronization-related outages.

Based on these results, the operator initiated a full network-wide deployment of the BRIDZA STW-AS600 across all 4,500+ sites, with completion targeted within 12 months.

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Conclusion

The BRIDZA STW-AS600 demonstrated that precision OCXO holdover, guided by intelligent GNSS discipline and predictive aging compensation, can reliably sustain telecom-grade timing accuracy well beyond the 24-hour holdover window mandated by international standards. For operators facing growing GNSS vulnerability — from space weather, jamming, spoofing, or site-level obstruction — the STW-AS600 provides a robust, field-proven path to synchronization resilience.