## 2 Related Work
The focus of research in [17] is uplink communication in Ka-band where FSS satellite terminals try to reuse frequency bands of FS terrestrial microwave (MW) links which represent the incumbent users. Three different power allocation algorithms are used to control the transmit power of the FSS satellite terminals, thus keeping the aggregated interference caused at the FS system below some acceptable threshold. We can see from the presented papers on satellite-terrestrial coexistence that various cognitive techniques are applied in different frequency bands. However, all techniques focus on the static use casewhere the satellite segment consists only of GSO satellites and FSS to static ESs, and they cannot be applied to dynamic systems that, in addition to GSO satellites and terrestrial networks, may consist of NGSO satellites and mobile ESIMs. Reference [18] proposes an adaptive power control technique for the coexistence of an NGSO satellite link with another NGSO/GSO satellite link for both downlink and uplink scenarios. The proposed technique is used to provide the required signal-to-noise ratio (SINR) at the receiver and mitigate the in-line interference between the GSO and NGSO systems. In [19], the cognitive power control from [18] was enhanced based on the distance between the NGSO satellite and the NGSO earth terminal. The focus of this study is on the mitigation of downlink in-line interference from the NGSO satellite to the static GSO earth terminal in Ka-band and improving link quality for the NGSO system. In [20], the operation of the cognitive network with GSO and low earth orbit (LEO) broadband systems is studied in the downlink Ka-band, where LEO satellites are incumbent users, whereas GSO satellites are secondary users. To enhance spectral efficiency and protect the incumbent system, an optimization algorithm based on beam hopping and adaptive power control techniques is proposed. While the proposed solutions offer coexistence for dual satellite systems, none of them can be applied to simultaneously improve spectrum utilization, mitigate interference, and enable coexistence in the most complex scenario where GSO and NGSO satellite systems (with static or mobile ESs) and terrestrial networks operate in the same frequency bands. Reference [21] analyzes the case where interference is caused to GSO systems by terrestrial cellular systems and NGSO systems, respectively, both in the downlink and uplink Ka-band. The protection area is calculated where no cognitive users (terrestrial system or NGSO system) are allowed to transmit, whereas, outside the protection area, the cognitive users are allowed to transmit concurrently with GSO systems. However, it is worth noting that this paper analyzes two separate scenarios. In the first one, GSO is protected against NGSO interference, while in the other, against terrestrial interference. Therefore, coexistence is again not analyzed for the complex scenario where GSO, NGSO, and terrestrial systems operate together in the same frequency band. Authors in [22] address the cognitive GSO uplink in the Ka-band where satellite terminals reuse frequency bands of FS terrestrial MW links which are the incumbent users. For the interference impact of GSO satellite on FS links to stay within the regulatory interference limitations, a joint power and carrier allocation strategy was proposed, which requires the existence of a complete and reliable FS database. Further extension of study in [22] can be found in [23], where a joint power and carrier allocation technique was proposed for uplink coexistence of GSO satellite with terrestrial FS in Ka-band. This technique was enhanced with a bandwidth allocation scheme that allocates bandwidth according to the user rate demands. This paper also analyzed the downlink coexistence of GSO and FS links in the Ka-band, where a joint beam-forming and carrier allocation was introduced. Availability of the FS database is assumed, which consists of FS antenna location and pointing directions.