Y. Elgholb Satellite Communication: Key Enabling Technologies 1 Satellite Communication: Key Enabling Technologies Youssef El Gholb Digicomm Group, Department of Electronic, Telecommunications and Information Technologies University of Bologna, Bologna, Italy. Abstract—Satellites have proven to be access for public and private networks. Moreover, indispensable for universal communication national borders do not affect transmission via networking in support of a variety of personal, satellite and its cost is not distance-related. commercial,and security applications. In an For business, users the attraction is the ability to attempt and effort to remain competitive with establish a network specifically dimensioned for the terrestrial systems, in the context of increasing required service in terms of demand, performance, requirement for the future communication and geographical distribution, with the capability to systems. The rapid increase of capacity of add growth where the market dictates. Moreover, terrestrial link in terms of generations (1G to 5G satellite terminals are more transportable than fixed in 2020) can be analogous to satellite links and they lend themselves to mobile services communications. The first generation (1G) such as those required by ships and other forms of having a capacity of 5-50 Gbps per satellite, transport and can be installed quickly without any 2010-2020; the second generation (2G) satellite existing telecommunication infrastructure, and are 50-500 Gbps, and 2020-2030; as the needs thus a viable means of providing service to a increase, for instance, as far future needs of the remote location, whether this is a construction site communication for Mars human community, or a small island. Their independence from other this can be considered as third generation (3G) networks may make them more secure and offer satellite 0.5-5 Tbps. SatCom are trying to follow unrivaled back-up possibilities. the progress in terrestrial in such as: Multicarrier waveforms use, Full Duplex,SDN, In an effort to remain competitive with terrestrial MmWave, MIMO technologyand profit from the systems, SatCom are trying to follow the progress significant research achievements in the area of in terrestrial technology and profit from the multiple antenna techniques. This work presents significant research achievements in the area of an overview of technologies that revolution Waveforms, MIMO, MmWave, fullduplex terrestrial communication systems and techniques. Hence the question to answer is, are considered as key technologies for 5G with the these techniques applicable to SatCom? since they possibility of its application in satellite exhibit distinct characteristics compared to communication. terrestrial systems, with regard to service coverage, link geometry, propagation delay, channel Keywords —5G, modulation, satellite communications, impairments, interference scenarios and physical SDSN, Massive MIMO, Mm wave, Full Duplex layer interface. Moreover, we can distinguish between different SatCom systems variants 1. Introduction depending on [1]: the choice of orbit (GSO vs. NGSO), user mobility (fixed vs. mobile), operating Satellites have the advantage of coverage frequency band group size of intended users nationally, internationally, and between continents. (broadcast, multicast, unicast), multiplexing scheme The coverage can be tailored for specific regions, (single carrier TDM vs. multicarrier OFDM), type and the capacity can be partitioned to provide of application (delay tolerant vs. delay intolerant), Mediterranean Telecommunications Journal Vol. 7, N° 1, January 2017 ISSN: 2458-6765 Y. Elgholb Satellite Communication: Key Enabling Technologies 2 availability of FMTs (CCM vs. ACM) and so on. One major drawback of multicarrier systems is the This work presents an overview of technologies increase of the PAPR compared to single carrier that revolution terrestrial communication systems systems. This increase is the result of the and considered as key technologies for 5G with the superposition of a large number of statistically possibility of its application in satellite independent sub-channels, which are able to communication. constructively sum up to high peaks [5]. The problem is that practical transmission systems are 2. Waveforms peak-power limited and show nonlinear characteristics which cause spectral widening of the Multiple access schemes, the most fundamental transmit signal. Clipping is a good, example among aspect of the physical layer, to a large extent, are several existing PAPR reduction techniques[6,7], considered as the defining technical feature of each for the reduction of PAPR but not always because wireless communication generation[2]. As some part of signal clipped that threshold should everyone knows that Machine Type have to be chosen properly which is generally not Communications (MTC) and the Internet of Things chosen properly and Clipping causes in-band noise, (IoT) will be significantly important application for which causes a degradation in the BER 5G. It is obviously that a new waveform study is performance [8]. [9] gives a comprehensive required to support multiple access technology, or overview of the used techniques.The economical requires the joint design of waveforms and multiple and efficient offerings from the terrestrial networks access technologies. Multicarrier systems provide have strongly motivated the satellite community optimum adaptability to the time and frequency towards devising economical missions and use of selectivity of propagation channels, which waveforms with improved spectrally efficiency.The simplifies their equalization. This is very attractive time domain OFDM signal is a sum of a large for mobile communication channels, which are number of complex sinusoids, which means that, subject to multipath propagation and vary according to the central limit theorem, the frequently with time. They also allow for an amplitude distribution will be Gaussian, leading to adaptation to the frequency response of the channel a large PAPR of the signal. Hence, a power by using different modulation alphabets and power amplifier with a relatively large linear range is allocation for the respective subcarriers. In this way required, otherwise non-linear effects will severely an approximation to the water-filling solution can degrade the system performance, which one major be achieved and the available bandwidth can be problems in satellite communications where the used very efficiently.OFDM is a well-known power amplifier has to operate close to saturation multicarrier, thoroughly studied, and heavily region or applied a back off to bring it to linear applied waveform design principle. For instance, region causing a loss in power amplification both 4G (LTE and its evolutions so far), worldwide efficiency. But there are methods like DFT- interoperability for microwave access (WiMAX), precoding used in conjunction with CP-OFDM to [3] DVB-T and IEEE 802.11 (WiFi) use OFDM as build up single-carrier FDMA for bringing down basic signal format for carrying the data. While PAPR [10 ], Fig1. having many nice aspects, OFDM has a fundamental characteristic making it less attractive for the cellular communication system to come as it carries critical importance due to shortcomings of OFDM such as cyclic prefix (CP) overhead, high side lobes, susceptibility to carrier frequency offset (CFO) and doubly dispersive channels, and larger peak-to-average-power ratio (PAPR) [4]. Mediterranean Telecommunications Journal Vol. 7, N° 1, January 2017 ISSN: 2458-6765 Y. Elgholb Satellite Communication: Key Enabling Technologies 3 applied when the amplifier is operated in multicarrier mode. Fig2. Satellite Channel At the satellite transponder, the carriers are channelized through an input multiplexing (IMUX) Fig1. OFDM&SC-FDMA(additional stages in dash) filter and further amplified by a non-linear HPA. transceiver scheme Additionally, the combination of HPA non-linearity with the onboard channelizing filters, introduces non-linear inter-symbol interference (ISI) and multiple carrier power amplification introduces However, sharing the on-board high power further impairments in the form of severe non- amplifier among different uplinked carriers (links) linear adjacent channel interference (ACI) due to is attractive since it provides for economical and the generated intermodulation terms [12 ].An sustainable satellite missions. However, the non- output-multiplexing (OMUX) filter is used to linear characteristic of the satellite amplifier suppress the undesired spectral regrowth (out-of- introduces intermodulation products leading to band) caused by the non-linear amplification to Adjacent Channel Interference (ACI), thereby some extent. The desire of an improvement in degrading performance, more so for the spectrally power and spectral efficiencies triggered the efficient modulations. development of on-ground mitigation techniques including predistortion (PD) at transmitter and A typical satellite resource-sharing scenario is the equalization at receiver This is because on- joint amplification of multiple channels/ carriers [13,14]. board processing increases mass/ power using a single wideband HPA (High Power Amplifier) onboard a transparent satellite instead of consumption and is less amenable to enhancements. dedicated HPAs per channel. This allows for a With the shortcomings of OFDM, other alternatives relaxation of the payload-critical requirements on were proposed such as: F-OFDM, BFMC, GFDM mass/