DiffStack: A Differentiable and Modular Control Stack for Autonomous Vehicles

Intelligent robotic systems, such as autonomous vehicles (AVs), are typically architected in a modular fashion and comprised of modules performing detection, tracking, prediction, planning, and control, among others [1, 2, 3, 4, 5, 6, 7, 8]. Modular architectures are generally desirable because of their verifiability, interpretability and generalization performance; however, they also suffer from compounding errors, information bottlenecks, and integration challenges. A promising line of work tackling these issues focuses on making AV stacks more integrated (by relaxing inter-module interfaces) and data-driven (by optimizing modules jointly with respect to their downstream task). For example, in the context of AV perception, recent work has achieved substantial performance gains by jointly training tracking models with detection [9] and prediction models [10, 11]. To extend such a joint, data-driven approach to decision making, existing approaches replace hand-engineered components, e.g., planning and control algorithms, with deep neural networks [12, 13, 14]. As neural networks are differentiable, they can be optimized end-to-end for a final control objective; however, they offer weaker generalization, little to no interpretability or safety guarantees. We introduce DiffStack, a differentiable AV stack with modules for prediction, planning, and control that combines the benefits of modular and data-driven architectures (Figure 1). The prediction module in DiffStack is a learned neural network that predicts the future motion of agents; the planning and control modules are principled, hand-engineered algorithms that produce AV actions given the current world state and motion predictions. Importantly, our hand-engineered planning and control algorithms are differentiable, enabling the training of the upstream prediction module for a downstream control objective by backpropagating gradients through the algorithms.