Performance analysis and resource allocation of heterogeneous cognitive gaussian relay channels

Motivated by the deployment of cognitive radio (CR) based relays in cellular networks, this paper studies the fundamental limits of heterogeneous cognitive Gaussian relay channels (HCGRCs). Unlike conventional relay channels, in HCGRC a source transmits to a relay in a licensed band, while the relay transmits to a destination in an unlicensed cognitive spectrum band. The licensed and unlicensed bands are characterized by different power, bandwidth and reliability constraints. Taking an information-theoretic perspective, the fundamental properties of the HCGRC are analyzed thoroughly in terms of capacity, spectral efficiency (SE), and energy efficiency (EE). With regard to each metric, we derive the optimal resource allocation strategy and discuss the impacts of CR spectrum reliability and relay location on the metric. We find that in HCGRC, improving the SE and EE are not necessarily conflicting objectives. Instead, both metrics can be optimized simultaneously with proper resource allocation.