ERGODIC CAPACITY OPTIMIZATION OF UNDERLAY COGNITIVE RADIO NETWORKS UNDER INTERFERENCE TEMPERATURE CONSTRAINTS

Summary

The rapid growth of wireless systems has increased spectrum demand, making radio resources increasingly scarce. Cognitive Radio (CR) provides a solution by enabling secondary users (SUs) to share spectrum with licensed primary users (PUs) while limiting harmful interference. This study investigates ergodic capacity optimization of underlay cognitive radio networks under interference temperature constraints. The system consists of one primary user and three secondary users, resulting in both inter-network and intra-network interference. Under the maximum interference-temperature constraint, the capacity per user increases from approximately 0.07 bpcu at −20 dB to about 6.2 bpcu at 20 dB. Under the average IT constraint, capacity also increases with SNR, while the greater flexibility in power allocation provides improved performance over the maximum IT constraint, particularly at low and moderate SNR. The sum-capacity comparison further confirms the advantage of average IT-based operation. Most importantly, at 19 dB SNR, the proposed ergodic interference-alignment approach achieves reported capacity improvements of 22.64% and 23.67% over the conventional time-division scheme under maximum and average IT constraints, respectively. The corresponding spectral-efficiency gains are 3.0094 bps/Hz and 3.1741 bps/Hz, giving an additional 0.1647 bps/Hz, or approximately 5.47%, for the average IT constraint. These results confirm that adaptive interference management and flexible power allocation can significantly improve spectral efficiency and secondary-user capacity while maintaining the required protection of the primary user.

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