Provide a comprehensive technical analysis of migrating a current RSA-2048 based public key infrastructure (PKI) to a lattice-based cryptographic scheme, specifically focusing on the Learning With Errors (LWE) problem. Discuss the trade-offs regarding key size, computational overhead for encryption/decryption operations, and resistance to quantum attacks using Shor's algorithm. Include a pseudo-code implementation of a simplified key exchange mechanism based on the Ring-LWE problem.