# On Developing Techniques for Sharing Satellite Spectrum with Indoor Small Cells in 5G +
## 1 Introduction
### Contribution and Limitation  
In this paper, we present a hybrid iSMS and aTMS by extending our previous work in [22] and by limiting the focus on assessing the performance of the only aTMSs due to sharing the satellite spectrum of iSMS with in-building small cells of the aTMS. More specifically, the main technological challenges that we aim to solve in this paper as extensions of [22] are the aforementioned issues of [22] as described in the previous section by generalizing the assumptions of the collocation of SBSs and CGC stations per apartment as well as non-orthogonal sharing of the satellite spectrum with small cells per building. In particular, the major contributions of the paper are as follows.  
* We present two spectrum sharing techniques, namely orthogonal spectrum sharing (OSS) and non-orthogonal spectrum sharing (nOSS) techniques, for a hybrid iSMS and aTMS by extending our previous work in [22]. As an extension, first, the assumptions in [22] for the collocation of all CGC stations and SBSs per apartment in each building were relaxed, resulting in the deployment of small cell base stations (BSs) and CGC stations in a building following two independent and random processes so that small cell BSs (SBSs) and CGC stations can be deployed in four ways within an apartment, assuming that the occurrence of each deployment option is equally likely. Second, in addition to an OSS in [22], we present an nOSS technique that considers non-orthogonal sharing of the satellite spectrum with SBSs per 3D cluster of SBSs per building.
* We develop an interference management strategy to address co-channel interference as well as deduce an optimal number of almost blank subframes (ABSs) per ABS pattern period (APP) to ensure a fair allocation of time resources to SBSs and CGC stations, in apartments with collocated CGC stations and small cells.
* We then derive system-level capacity, spectral efficiency, and energy efficiency performance metrics and present an algorithm for OSS and nOSS techniques.
* Finally, we carry out extensive simulation and numerical analysis to evaluate the relative outperformance of one to another for nOSS and OSS techniques and show that both techniques can meet the expected spectral efficiency and energy efficiency requirements for 5G mobile networks. We limited evaluating the performance of the proposed techniques to the following.
* The performance evaluation was limited to only aTMS (i.e., the evaluation for the iSMS was considered beyond the scope of the paper).
* Since in general, user-plane traffic is considerably higher than that of control-plane traffic, for simplicity, we assumed that the impact of control-plane traffic due to the coordination among different components of the iSMS/aTMS for sharing the satellite spectrum of iSMS with in-buildingSBSs of aTMS was negligible. In other words, we limited the scope of this paper to evaluating only the user-plane traffic capacity of aTMS when sharing the spectrum of the iSMS with indoor SBSs. The evaluation of the required control-plane traffic capacity and hence the corresponding required bandwidth needs a detailed analysis of a number of factors, which was beyond the scope of the paper.
* Satellite spectrum sharing was considered only for the in-building SBSs. Hence, the co-channel interference was considered only within buildings.
* The satellite spectrum band of 3.5 GHz for the iSMS was considered for sharing with SBSs of the aTMS following [15], and keeping the satellite frequency close to that of the aTMS (i.e., 2 GHz) so that the transceivers' frequency responses of SBSs did not deviate too high.
* The significance of the performance results of the proposed techniques was verified by comparing them with that expected for the 5G mobile networks in terms of spectral efficiency and energy efficiency.
* The performance results for the variation in the density of in-building SBSs (i.e., the number of buildings) per macrocell of the aTMS are shown, and the variation in other parameters was beyond the scope of the paper.