Joint Satellite Gateway Placement and Routing for Integrated Satellite-Terrestrial Networks Nariman Torkzaban † , Anousheh Gholami † , Chrysa Papagianni ‡ , and John S. Baras † † Department of Electrical and Computer Engineering Institute for Systems Research University of Maryland, College Park, MD 20742, USA Email: { nariamnt | anousheh | baras} @umd.edu ‡ Nokia Bell Labs, Antwerp, Belgium Email: chrysa.papagianni@nokia-bell-labs.com Abstract—With the increasing attention to the integrated satellite-terrestrial networks (ISTNs), the satellite gateway place- ment problem becomes of paramount importance. The resulting network performance may vary depending on the different design strategies. In this paper a joint satellite gateway placement and routing strategy for the terrestrial network is proposed to minimize the overall cost of gateway deployment and traffic routing, while adhering to the average delay requirement for traffic demands. Although traffic routing and gateway placement can be solved independently, the dependence between the routing decisions for different demands makes it more realistic to solve an aggregated model instead. We develop a mixed integer linear program (MILP) formulation for the problem. We relax the integrality constraints to achieve a linear program (LP) which reduces time-complexity at the expense of a sub-optimal solution. We further propose a variant of the proposed model to balance the load between the selected gateways. Index Terms—Satellite Gateway Placement, Flow Routing, Integrated Satellite-Terrestrial Networks, Mixed Integer Pro- gramming. I. I NTRODUCTION Over the past years, the integration of satellite communi- cations with current and emerging terrestrial networks (e.g., 5G mobile networks) is gaining attention, given the growing data traffic volume which is predicted to increase by over 10,000 times in the next 20 years [1]. The trend is also supported by national directives and initiatives to support broadband connectivity in rural and remote areas, as it is considered a crucial factor for economic growth. Due to their large footprint, satellites can complement and extend terrestrial networks, both in densely populated areas and in rural zones, and provide reliable mission critical services. Standardization bodies as 3GPP, ETSI [2] and ITU [1] also recognize and promote integrated and/or hybrid satellite and terrestrial networks. The integrated satellite-terrestrial networks (ISTNs) can be a cornerstone to the realization of a heterogeneous global system to enhance the end-user experience [3]. An ISTN, as depicted in Fig. 1, is composed of satellites organized in a constellation that support routing, adaptive access control, and spot-beam management [4], whereas the terrestrial optical network consists of ground stations (gateways), switches, and servers. Delay-sensitive data services are more suitable to transport in the low earth orbit (LEO) satellite networks, Fig. 1: Example of an integrated satellite-terrestrial network. which provide inherent advantages in power consumption, pole coverage, latency, and lower cost compared with the geostationary earth orbit (GEO) satellite networks and the medium earth orbit (MEO) satellite networks [5]. However, there are multiple challenges associated with the ISTNs. Satellite networks and terrestrial networks are widely heterogeneous, supported by distinct control and management frameworks, thus their integration to date was based on pro- prietary and custom solutions. Additionally, in the integrated network, as there are multiple available paths along which data traffic can be routed, optimized path-selection is important to satisfy the Quality of Service (QoS) requirements of the traffic flows and improve the utilization of network resources [6]. Existing satellite networks employ a decentralized manage- ment architecture, scheduled link allocation and static routing strategies, which make it difficult to support flexible traffic scheduling adapting to the changes in traffic demands [7]. Complex handover mechanisms should be in place at the gate- way nodes, while their high-power consumption requirements need to be also taken into consideration. Nowadays the inclusion of plug-and-play SatCom solutions are investigated, primarily in the context of 5G. Exploiting software-defined networking (SDN) [8] and network function virtualization (NFV), ISTNs can be programmed and network arXiv:2002.03071v1 [cs.NI] 8 Feb 2020