L1 Developer – Paris

We are developing the Layer 1 of a cellular modem protocol stack covering 5G NR eRedCap and LTE Cat 1bis, targeting low-complexity IoT devices. The physical layer is being built from the ground up on a new embedded platform, and we are looking for L1 developers to take ownership of significant parts of it.

This is implementation work at the physical layer: turning 3GPP specifications into real-time software that drives hardware acceleration blocks, then bringing it up and making it work on target. It is not integration, test automation or system engineering around an existing stack.

You will be joining early enough to shape how the layer is structured, and you will see the code you write run on silicon.

RESPONSIBILITIES:

Depending on your background and interests, you will own one or more of the following areas:

• Uplink physical layer: Shared and control channel procedures, sounding reference signals, and the scheduling of transmission chains against hard real-time deadlines.
• L1 control: Physical layer scheduling, HARQ management, the interface to the MAC layer, and configuration handling from RRC down to the physical layer.
• Random access, power control and timing advance: Complete initial access procedures on paired spectrum, including the timing and power loops that keep a connection synchronised.
• Idle mode and low power operation: Paging reception, DRX and extended DRX, sleep and wake-up scheduling, and frame timing continuity across sleep periods — central to the power budget of an eRedCap device.
• LTE downlink control and initial access: Broadcast channel reception, downlink control region decoding, reference signal extraction, and the associated channel coding chains.

Across all areas you will work directly from the 3GPP specifications, contribute to the internal architecture and algorithm documentation, and debug on emulated and on real hardware.

REQUIRED EXPERIENCE & KNOWLEDGE:

• You know the physical layer well enough to work from the 3GPP specifications directly, and can reason about a PHY processing chain running on an embedded target under hard real-time deadlines. This is the core of the role. Having already implemented one is an advantage, but solid understanding matters more to us than a specific project history.
• Engineering degree or PhD in telecommunications, signal processing or electronics.
• Working fluency with the 3GPP physical layer specifications: you read them directly rather than relying on a summary, and you are comfortable with the 36-series, the 38-series, or both.
• Solid telecommunications fundamentals: modulation, channel coding, synchronisation, channel estimation, HARQ, and how the air interface fits together as a system.
• An awareness of what running on an embedded target implies: timing budgets, memory limits, interrupt-driven execution and the boundary between software and hardware accelerators. Hands-on experience is welcome, but we train on our development practices and tooling, so understanding the constraints matters more than having worked in this environment before.
• Fluent English, spoken and written. English is the working language of the team; French is not required.

DESIRABLE:

• Experience with UE-side rather than network-side implementation.
• Familiarity with RedCap, eRedCap, LTE-M, NB-IoT or another low-complexity device class.
• Experience bringing up a physical layer on new silicon, or on an emulated platform ahead of silicon availability.
• Exposure to MAC–PHY interface designs such as FAPI.
• Experience writing or reviewing algorithm and architecture specifications, not only consuming them.
• Background in half-duplex operation or narrowband deployment options.

WHAT WE OFFER:

• A physical layer being built rather than maintained, with real ownership of functional areas rather than tickets.
• A small, senior, English-speaking team working close to the specifications and close to the hardware.