Interference management of cognitive IoT based on interference steering and alignment

In the cognitive IoT spectrum sharing process, the complex interference environment leads to a low spectral efficiency of the licensed spectrum. To solve this problem, this article allows more cognitive users (CU) to access the licensed spectrum while ensuring reliable transmission of primary users (PU) by introducing the advanced interference steering (IS) technique. Traditional IS methods are only suitable for single-user and single-data-stream scenarios. Meanwhile, these methods have many drawbacks in multi-user and multi-data-stream scenarios. To overcome these drawbacks, two IS algorithms based on time division (TD) multiple access are proposed in this article, which are TD based equivalent interference sub-channel interference steering (TD-EI-SCIS) and TD-based sub-channel interference steering (TD-SCIS), respectively. Furthermore, considering the fact that PU has the highest communication quality priority in cognitive IoT, a joint interference management (JIM) scheme based on TD-EI-SCIS, TD-SCIS, and partial interference alignment (PIA) is proposed to protect the PU. Simulation results show that the spectral efficiency (SE) of the PU in the proposed JIM scheme is not significantly improved compared with the proposed TD-EI-SCIS in the low SNR region. However, from the perspective of the total SE in the whole cognitive IoT system, TD-EI-SCIS is superior to the JIM about 3 to 4 bit/s/Hz on average. In the high SNR region, the JIM scheme significantly outperforms TD-EI-SCIS not only in terms of the SE of PU about 10 bit/s/Hz but also in the aspect of the SE in the total network about 7 bit/s/Hz on average.