Parallel Wireless is a U.S.-based pioneer in Open RAN innovation, transforming how mobile networks are built, optimized, and powered. Through our GreenRAN™ portfolio, we help operators deliver secure, energy-efficient, automated, and flexible connectivity across 2G, 3G, 4G, 5G, and the path toward 6G. Our software-centric, hardware-agnostic approach brings intelligence into the RAN while helping customers reduce complexity and total cost of ownership.    Parallel Wireless is looking for a hands-on wireless systems engineer to lead the development of a multi-RAT digital twin for our Open RAN solution. The digital twin will execute production RAN software-beginning with scheduler and MAC behavior-in a closed loop with PHY, channel, UE, traffic, and network models. It will allow engineering teams to design, evaluate, and compare features for LTE, 5G NR, and 2G without requiring a dedicated physical radio setup for every development cycle.  This is a senior individual-contributor role at the intersection of wireless systems, simulation, production software, and AI/ML. You will evolve an existing LTE end-to-end simulator into a scalable engineering platform for feature development, regression testing, performance optimization, and evidence-based pre-validation. Initial use cases include MAC scheduler and link-adaptation improvements, power control, mobility and interference scenarios, and neural-network-assisted channel estimation.  The successful candidate will understand that a useful digital twin must be both fast and trustworthy. You will define multiple fidelity levels-from rapid surrogate models to full PHY processing-and establish repeatable methods for calibrating the twin against lab or field reference data. The goal is to reduce dependence on continuous lab access while maintaining clear, measurable confidence in the simulation results.  WHAT YOU WILL DO: •  Own the technical architecture and roadmap for a modular, multi-RAT RAN digital twin covering LTE, 5G NR, and,     where required, 2G/GSM.  •  Integrate production MAC and scheduler software into deterministic, per-TTI/slot closed-loop simulations through      stable and maintainable interfaces.  •  Model the interaction among scheduler decisions, PHY processing, propagation channels, UE behavior, traffic,     interference, mobility, HARQ, link adaptation, and power control.  •  Extend the current LTE simulation capability and define reusable abstractions that support additional     5G NR and 2G stacks    without duplicating the platform.  •  Design a fidelity ladder that combines high-fidelity PHY execution with faster calibrated models or lookup/surrogate backends,      selecting the least expensive model that is valid for each engineering question.  •  Develop and evaluate AI/ML-based RAN capabilities, including neural channel estimation, learned link adaptation     or scheduling policies, and ML-based PHY or channel surrogates.  •  Build representative datasets and experiment pipelines; establish conventional algorithmic baselines;     measure accuracy, robustness, generalization, latency, and compute cost before recommending integration into     production software.  •  Create reproducible A/B experiments across software builds and algorithm versions, using defined scenarios,     seeds, configurations, and KPIs such as throughput, BLER/ACK-NACK behavior, MCS, resource-block allocation, SINR,     transmit power, latency, and fairness.  •  Establish simulation verification and validation practices: matched sim-vs-lab scenarios, calibration rules,     lab-repeatability baselines, divergence analysis, model-version tracking, and evidence reports.  •  Prevent overfitting the twin to a single setup by separating universal model parameters, setup-specific calibration,     and the production algorithms under test.  •  Build automated unit, component, end-to-end, regression, and performance tests and integrate them into CI/CD workflows.  •  Improve simulation speed, scale, observability, and usability so that stack, PHY, test, and AI engineers can run     repeatable experiments independently.  •  Debug discrepancies across C/C++, Python, MATLAB, PHY models, production stack behavior, configuration,     and reference measurements.  •  Document model assumptions, limitations, supported operating regions, calibration provenance,     and the validity of every simulation or ML backend.  •  Work closely with RAN stack, PHY, system architecture, AI/ML, automation,     and lab-validation teams to convert product questions into measurable simulation campaigns.    WHAT YOU BRING: •  BSc or MSc in Electrical Engineering, Computer Engineering, Computer Science, or a related field,     with substantial relevant industry experience. A PhD in wireless communications, signal processing, or a related area     is an advantage.  •  Typically 7+ years of hands-on experience in wireless systems, RAN development, modem/PHY development,     or system/link-level simulation; exceptional candidates with equivalent depth are welcome.  •  Deep knowledge of LTE and/or 5G NR L1/L2 behavior, including MAC scheduling, link adaptation,     HARQ, CQI/SINR feedback, resource allocation, and uplink power control.  •  Strong understanding of digital communications and signal processing, including channel estimation,     equalization, coding/modulation, MIMO, propagation and fading models, and performance metrics.  •  Demonstrated experience building or validating link-level, system-level, or hardware-in-the-loop simulations and     explaining where a model is-and is not-valid.  •  Strong programming skills in C or C++ and Python, including the ability to integrate production native code with     simulation and analysis tooling.  •  Practical experience with scientific computing and data analysis using tools such as NumPy, SciPy, pandas,     and visualization frameworks.  •  Hands-on experience developing or evaluating machine-learning models for communications, signal processing,     time-series data, or related domains using PyTorch, TensorFlow, or an equivalent framework.  •  Sound experimental and statistical judgment: reproducibility, baselines, error analysis, uncertainty, calibration,     controlled comparisons, and avoidance of data leakage or curve fitting.  •  Experience working in Linux development environments with Git, automated testing, containers, and CI/CD.  •  Ability to lead a technically ambiguous initiative, make architecture decisions, and communicate clearly     across research, product, development, and validation teams.  NICE TO HAVE: •  Experience with MATLAB and Communications/LTE/5G toolboxes or equivalent PHY simulation environments.  •  Direct experience with production eNodeB/gNodeB software, commercial modem stacks, or Open RAN products.  •  Knowledge of 3GPP LTE, NR, and/or GERAN specifications and experience translating standards into executable models     and test scenarios.  •  Experience with scheduler algorithms such as proportional fair, round robin, maximum C/I, QoS-aware scheduling,     or reinforcement-learning-based resource allocation.  •  Experience with neural channel estimation, learned receivers, differentiable communications, model compression,     or ML inference in latency-constrained systems.  •  Experience with multi-cell interference, mobility, carrier aggregation, massive MIMO, beam management, or realistic traffic     and UE-population modeling.  •  Experience with GPU acceleration, CUDA, distributed simulation, batch experiment orchestration, or cloud/HPC execution.  •  Familiarity with SDR, radio test equipment, lab automation, field-log analysis, or simulation-to-lab correlation.  •  Experience building internal engineering platforms, APIs, dashboards, and self-service experiment workflows.