In this work, we investigate the performance of cognitive multihop regenerative relaying systems in the underlay spectrum sharing scenario. The multiple relays perform detect-and-forward relaying strategy to convey a message with an order 𝑀 quadrature amplitude modulation (𝑀-QAM) from the source to the destination over independent but not necessarily identical Nakagami-𝑚 fading channels. We adopt a closed-form analysis framework based on univariate and bivariate Meijer Gfunctions to derive the end-to-end error performance (in terms of bit and symbol error rates), the outage probability, and the ergodic capacity. Various numerical examples are presented to illustrate the results with a large combination of system and fading parameters, and simulation results confirm the accuracy of our closed-form analysis.
