Link Adaptation in Satellite LTE Networks Gbolahan Aiyetoro Dept. of Electrical, Electronic and Computer Engineering, University of KwaZulu-Natal, Durban 4041, South Africa Email: g.aiyetoro@ieee.org Giovanni Giambene Department of Information Engineering, University of Siena, Via Roma, 56, 53100 Siena, Italy Email: giambene@unisi.it Fambirai Takawira School of Electrical and Information Engineering, University of the Witwatersrand, Johannesburg, South Africa Email: fambirai.takawira@wits.ac.za Abstract—This paper investigates the impact of the Round Trip Propagation Delay (RTPD) in the satellite LTE air interface with the adoption of MIMO technology. The Satellite LTE air interface will provide global coverage and hence complement its terrestrial counterpart in the provision of LTE services to mobile users. A land mobile dual-polarized GEO satellite system has been considered for this work. The link adaption is an important module for the scheduling scheme and the satellite LTE network as a whole in order to make optimal scheduling decisions and effectively utilize the network resources respectively. However, the long RTPD experienced when Channel Quality Indicator (CQI) is reported from the User Equipment (UE) to the eNodeB via GEO satellite causes misalignment between the reported CQI at the eNodeB and the present CQI of the mobile user. The aim of this paper is to investigate the effect of the misalignment as a result of long RTPD through simulations and also investigate the effect of varying CQI reporting interval on the system performance of Satellite LTE network. The possibility of using a fixed CQI rather than an adaptive CQI is also investigated. Index Terms— CQI, RTPD, GEO satellite, LTE I. INTRODUCTION The rapid growth in mobile users and continuous increment in the demands for different types of telecommunication services, like video streaming, video conferencing, Voice over IP (VOIP), web browsing, multimedia messaging, video gaming and FTP downloads have compelled the need for new technologies able to provide high data rates and also satisfy their respective Quality of Service (QoS) requirements. It is also worth to note that the available spectrum is limited and this has made high spectrum efficiency an important target that must be addressed in the future technologies. The need to address these important challenges in future mobile networks formed the basis for ITU-R WP 8F to define the future Fourth Generation Mobile (4G). The set of transmission capacity and QoS requirements are specified which allow any technology that meets up with these requirements to be included in the IMT-Advanced family [1]. This has led to the emergence of LTE and WiMAX 802.16x. Though, these two technologies do not fulfill the requirements, they are first steps towards the 4G [2]. Advanced features are being looked into by both standards that will be included in next releases (WiMAX evolution and LTE Advanced) in order to meet up with the 4G requirements The LTE technology, which is of interest to this paper is made up of the radio access and packet core networks. The radio access network of LTE is referred to as Evolved UMTS Terrestrial Radio Access (E-UTRA) and the core network is denoted as Evolved Packet Core (EPC). LTE uses a new multiple access technology, which is Orthogonal Frequency Division Multiple Access (OFDMA) for downlink transmission and Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink. Another important technology introduced to LTE network is MIMO. It has brought a linear increase in the capacity of the network depending on the minimum of the numbers of transmit or receive antennas [3]. In order to provide seamless mobile services to users irrespective of their locations, the satellite component of 4G systems will play a vital role, since the terrestrial component will not be able to provide a global coverage due to economic and technical limitations [4]. Therefore, future satellite air interfaces need to have a high-level of commonality with the 4G terrestrial air interface. Hence, both 3GPP LTE and WiMAX air interfaces have been proposed for the satellite scenario especially for unicast communications. Though, the satellite systems have some Corresponding author: g.aiyetoro@ieee.org JOURNAL OF ADVANCES IN INFORMATION TECHNOLOGY, VOL. 5, NO. 1, FEBRUARY 2014 37 © 2014 ACADEMY PUBLISHER doi:10.4304/jait.5.1.37-43