Verification of Modified eNodeB Protocol for Direct-to-Cell Communication Using Real LEO Satellite and Laboratory Testbed

Direct-to-cell (D2C) communication using low earth orbit (LEO) satellites has emerged as a promising solution to extend cellular coverage in geographically challenging regions and maintain network connectivity during natural disasters. However, D2C systems face significant technical challenges, par-ticularly the large extended propagation delays may prevent the normal operation of hybrid automatic repeat request (HARQ) and random access procedures. This paper addresses these challenges by proposing protocol modifications at the eNodeB (eNB) side only to support both unmodified smartphone and narrowband internet of things (NB- IoT) systems over long term evolution (LTE) network. We develop a testbed capable of emu-lating the radio channel conditions of D2C communication links to verify the proposed eNB modifications with both smartphone and NB-IoT device in laboratory environment. Furthermore, the random access procedure between the smartphone and ground-based eNB is verified by field experiment using real LEO satellite. Our solution enables billions of legacy LTE devices to seamlessly connect to the D2C network, thereby avoiding the additional cost of purchasing new devices.