## 1 Introduction  
It is widely recognized that, to be successful and meet user demands, the 5G infrastructure will be an ecosystem of networked networks, utilizing multiple different and complementary technologies [1; 2; 3]. The advanced communication functions of 5G are expected to bring enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communications (URLLC), and massive Machine Type Communications (mMTC), as shown in Figure 1.  
In 4G mobile networks, the integration of Satellite Communication (SATCOM) was based on proprietary tailored solutions at both SATCOM and mobile network level [4; 5; 6]. In the discussion of backhaul technologies, satellites were rarely considered as a cost effective solution in previous generations. The reasons for this attitude are manifold, ranging from commercial doubts to technological biases. In the latter context, various technical constraints such as throughput deficits, delay requests, or unsupported network functions are usually invoked. With the explosion of data services, Mobile Network Operator (MNO) are looking for new technologies to expand their networks and provide more capabilities to their customers. One key challenge for rural and remote 5G deployments is how to backhaul network traffic in a way that makes it affordable for MNOs to extend their services. Coverage will always remain an issue for a standalone mobile network. Satellites can extend terrestrial networks to improve coverage (see Figure 2). Moreover, satellites in the Geostationary Earth Orbit (GEO) provide efficient delivery of content across multiple sites with similar transmission delay, which is a main requirement for live broadcast to a certain area [7]. The next generation of GEO satellites can benefit of more powerful and more flexible ubiquitous coverage through a dense spot beam architecture [8; 9]. In addition to the current fleet of geostationary and Medium Earth Orbit (MEO) satellites, the next-generation MEO satellite systems, such as the O3B mPOWER constellation, will be very flexible with 30,000 fully-shapeable and steerable beams. The next generation MEO satellites will utilize more than 5000 beams per satellite to provide capacity where it is required [10; 11]. The development of a convergent satellite-terrestrial architecture, tailored to the satellite capabilities and to the targeted use cases, is one of the key challenges [12]. New technologies such as virtualization and cloud infrastructure at the edge of the cell are considered to meet the 5G requirements and use cases [13]. In contrast to the previous mobile network developments, an increasing use of testbeds implementations for experimenting and evaluating new ideas has been extended in 2018 [14; 15]. Software-Defined Radios (SDRs) and the application of software based network functions make this kind of testbeds a reality for the academics, innovative research center and new partners to verify novel approaches without relying only on simulations [16]. These testbeds are large projects that have started with 4G architectures and are moving towards 5G architectures based on the 3 rd Generation Partnership Project (3 GPP) Releases. In the past, SATCOM networks were based on proprietary hardware, that hinder the integration with future 5G networks [8]. With the virtualization paradigm, a key technology could enable new innovations for the satellite ground equipment as well as the application of new 5G protocols and algorithms. To evaluate 5G technologies over a convergent satellite-terrestrial architecture and to support the 3 GPP and the European standardization efforts, practical demonstrations by means of testbeds, as shown in [17; 18] are required. They are pioneering for this kind of architecture and provide a platform to demonstrate the 5G satellite use cases. In addition to the EU H2020 project,,Satellite and Terrestrial network for 5G\" (SaT5G) [19], the European Space Agency (ESA) funded,,Demonstrator for Satellite-Terrestrial Integration in the 5G Context\" (SATis5) [20] project has been set up.