Subcarrier Scheduling for Joint Data Transfer and Key Generation Schemes in Multicarrier Systems

In computational complexity and latency con- strained emerging 5G applications, e.g., autonomous vehicles, haptic communications and enhanced reality, secret key generation (SKG) at the physical layer could be considered as an alternative to currently used key agreement schemes. In this framework, we study the optimal subcarrier scheduling in multicarrier systems when a subset of the subcarriers are used for SKG and the rest for data transmission, under both security and power constraints. The amount of data that can be transmitted with a single key is determined by the cryptographic suites used, so that realistic key rate constraints can be identified. This allows us to formulate the subcarrier allocation as a subset-sum 0-1 knapsack optimization problem that we solve using i) the standard dynamic programming approach and ii) a greedy heuristic approach of linear complexity. We show that the proposed heuristic induces virtually no loss in performance. Furthermore, a comparison with a baseline scheme in which SKG and data transfer are performed sequentially, shows that the proposed parallel approach offers gains in terms of efficiency.