Senior Software Engineer - NR-NTN Protocols (L1 & L2)

Senior Software Engineer - NR-NTN Protocols (L1 & L2)

Skylo Technologies

Espoo, Finland

How You Will Impact Skylo

Skylo is seeking a highly skilled Senior Software Engineer to join our Protocol Stack team, focused on the development and optimization of 5G New Radio Non-Terrestrial Network (NR-NTN) Layer 1 and Layer 2 protocol implementations. In this role, you will design, implement, and validate PHY, MAC, FAPI, and scheduler software that runs on Skylo's NTN vRAN platform, working closely with our RF, systems, and integration teams to bring NR-NTN connectivity to market at scale.

What You’ll Do

• Design, develop, and maintain C++ implementations of 5G NR-NTN L1/L2 protocol stacks — including PHY adaptation layer, FAPI interface, MAC, and DL/UL schedulers
• Implement NTN-specific L1 adaptations: extended HARQ round-trip timers, timing advance pre-compensation, NTN-aware link adaptation, and satellite Doppler pre-compensation at the PHY layer
• Extend and optimize the MAC scheduler for NTN: HARQ retransmission management, coverage enhancement (CE) mode scheduling, and constellation-aware resource allocation
• Design and implement the FAPI interface between MAC and PHY — P5/P7 message handling, slot indication processing, DL/UL configuration, and timing/error event management for NTN-adapted slot structures
• Develop DL/UL scheduler algorithms for NTN: HARQ retransmission scheduling, CE mode resource allocation, constellation-aware policies, and QoS-aware prioritization across satellite link conditions
• Work with RF and baseband teams to validate L1/L2 protocol behaviour across lab and field NTN environments (LEO/GEO)
• Debug, root-cause, and performance-tune L1/L2 issues in Linux-based environments using GDB, Valgrind, perf, and Wireshark
• Partner with systems engineers to translate 3GPP Rel-17/18 NR-NTN specifications into software requirements and detailed L1/L2 designs
• Participate in code reviews, architecture discussions, and contribute to technical documentation
• Actively use AI coding assistants (Claude, Cursor, Codex) across the development lifecycle — from spec interpretation and test automation to code review — and help establish team best practices for AI-augmented engineering

Sound Like You? What You Bring

• 2+ years of hands-on software engineering experience in wireless/telecom protocol development, with specific depth in L1 and L2 stacks.
• Master's or PhD degree in Wireless Communications, Electrical Engineering, Telecommunications, or a closely related field.
• Strong proficiency in C++ (C++14/17) with demonstrated experience writing production-grade embedded or near-real-time protocol software.
• Deep understanding of 5G NR PHY layer: numerologies, slot/frame structure, PDSCH/PUSCH processing, HARQ operation, beamforming, and link adaptation.
• Solid understanding of 5G NR MAC layer: scheduling procedures, HARQ management, BSR/SR/PHR handling, random access procedures, and beam management.
• Strong understanding of FAPI (nFAPI or SCF FAPI): P5 configuration interface, P7 real-time slot-level messaging, and MAC-PHY synchronisation in split L1/L2 architectures.
• Hands-on experience designing or optimising DL/UL schedulers: proportional fair, round-robin, QoS-aware, and near-real-time scheduling in production RAN software.
• Experience with Linux kernel/user-space debugging tools: GDB, Valgrind, perf, tcpdump, Wireshark, and system log analysis.
• Proficiency in production-grade protocol software development: state machine design, message parsing/encoding, and multi-threaded protocol engines.