sensors Communication Dynamic Spectrum Sharing for Future LTE-NR Networks † Gordana Barb, Florin Alexa * and Marius Otesteanu Department of Communications, Politehnica University Timis, oara, 300006 Timis, oara, Romania; [email protected] (G.B.); [email protected] (M.O.) * Correspondence: fl[email protected] † This manuscript is extension version of the conference paper: Barb, Gordana, Marius Otesteanu, and Marius Roman. “Dynamic Spectrum Sharing for LTE-NR Downlink MIMO Systems.” In Proceedings of the 2020 International Symposium on Electronics and Telecommunications (ISETC), Timisoara, Romania, 5–6 November 2020; pp. 1–4. Abstract: 5G is the next mobile generation, already being deployed in some countries. It is expected to revolutionize our society, having extremely high target requirements. The use of spectrum is, therefore, tremendously important, as it is a limited and expensive resource. A solution for the spectrum efficiency consists of the use of dynamic spectrum sharing, where an operator can share the spectrum between two different technologies. In this paper, we studied the concept of dynamic spectrum sharing between LTE and 5G New Radio. We presented a solution that allows operators to offer both LTE and New Radio services using the same frequency bands, although in an interleaved mode. We evaluated the performance, in terms of throughput, of a communication system using the dynamic spectrum sharing feature. The results obtained led to the conclusion that using the dynamic spectrum sharing comes with a compromise of a maximum 25% loss on throughput. Nevertheless, the decrease is not that substantial, as the mobile network operator does not need to buy an additional 15 MHz of bandwidth, using the already existing bandwidth of LTE to offer 5G services, leading to cost reduction and an increase in spectrum efficiency. Citation: Barb, G.; Alexa, F.; Otesteanu, M. Dynamic Spectrum Keywords: dynamic spectrum sharing; LTE; 5G NR; throughput; spectrum efficiency Sharing for Future LTE-NR Networks. Sensors 2021, 21, 4215. https:// doi.org/10.3390/s21124215 1. Introduction Academic Editor: Dimitrie The next mobile generation following Long Term Evolution (LTE) that has started its C. Popescu deployment in some countries is the 5th Generation (5G). The main focus of LTE was set to increase data transfer rates, while 5G is expected to revolutionize our society, focusing Received: 10 May 2021 not only on delivering extreme mobile broadband, but also in the fields of critical machine Accepted: 16 June 2021 Published: 19 June 2021 communication and massive machine communication. New applications will emerge, and the target values and requirements proposed are extremely demanding [1]. The main Publisher’s Note: MDPI stays neutral challenges of 5G systems consist of increasing data transfer rates, reducing latency, and with regard to jurisdictional claims in increasing capacity, spectrum efficiency, and network energy efficiency, which will be published maps and institutional affil- necessary for different application scenarios [2]. iations. The current network architecture cannot sustain all the requirements and target val- ues of 5G New Radio (NR). Therefore, the 3rd Generation Partnership Project (3GPP) released two variations for the new network architecture of 5G NR communication sys- tems: Non-standalone (NSA) and Standalone (SA) [3]. The main difference between both types is that the NSA architecture is based and depends on the LTE core network, while Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. the SA architecture uses a novel next-generation core network, not depending of any This article is an open access article LTE infrastructure. distributed under the terms and The Internet of Things (IoT), mobile internet, and Cognitive Radio (CR) stand as conditions of the Creative Commons relevant driving forces for 5G development [4–7]. The IoT technology has the potential Attribution (CC BY) license (https:// ability to connect almost everything to the internet, which will lead to the massive growth creativecommons.org/licenses/by/ of devices that require network acceptance. Particularly, in 2018, there were approximately 4.0/). 22 billion connected devices, which is the equivalent of around 2.9 devices/person. It Sensors 2021, 21, 4215. https://doi.org/10.3390/s21124215 https://www.mdpi.com/journal/sensors Sensors 2021, 21, 4215 2 of 15 is expected that by 2025, the number of connected devices to be nearly 38.6 billion [8]. Simultaneously, the mobile internet has surpassed the traditional mobile communications, offering users innovative experiences. On the other hand, cognitive radio represents a technology that has evolved in order to improve the spectrum usage, exploiting both licensed and unlicensed bands. It became a promising wireless communications technology that is able to solve spectrum problems by: observation, learning, and intelligent adaptation to obtain an optimal frequency band [9]. In addition to the network architecture, another major challenge of 5G systems consists of the available frequency spectrum. Presently, the spectrum used for mobile communi- cations is located between 300 MHz and up to 6 GHz. Due to the fact that most of it is completely saturated, new frequency bands above 6 GHz need to be taken into consider- ation. Hence, it is expected that 5G NR systems will use frequency bands above 6 GHz, reaching up to 300 GHz [10]. Therefore, the main frequency spectrum to be used for 5G systems can be in licensed, shared, and unlicensed bands, see Table1. The low-band spec- trum has the goal of supporting high coverage and penetration; the mid-band spectrum provides data transfer rates up to 1 Gbps; the high-band spectrum supports peak data transfer rates up to 20 Gbps. The last group, even though it supports such high data rates, comes with the inconvenience of low coverage and penetration, being indicated to be applied in closed/indoor environments. Table 1. 5G spectrum options. Frequency Band Characteristics Spectrum Use Wide area coverage 600–2600 MHz Spectrum sharing Reframing from old technologies Mid-band mainstream for 5G 3.3–5 GHz Massive MIMO-crowded and urban areas Independent deployment Unlicensed spectrum (without old technologies) 5–6 GHz No spectrum licensed necessary Allocated mmWaves for 5G 24–39 GHz Increased data rates It is clear that the frequency spectrum is a scarce and limited resource that constitutes an important factor in mobile communication systems, as well as the related cost for the Mobile Network Operator (MNO). In this context, new spectrum explorations [11,12], higher energy efficiency [13], and dynamic spectrum usage [14–18] have become the new features of communication networks. The topic of spectrum sharing in the bands of old communication systems started drawing the attention of researchers, as it is the safest and most economical solution [19]. The standardization procedure for the spectrum sharing principles started in March 2017 by 3GPP. One of the solutions presented regarding the spectrum allocation for 5G NR systems comprises the use of the existing frequency spectrum used by the already deployed mobile generations. Spectrum sharing is based on the flexibility of the physical layer and the fact that in the LTE network, all channels are assigned in the time-frequency domain. This way, the flexibility of the 5G NR radio interface can be used for reference signals, allowing dynamic configuration and minimizing collisions between NR and LTE during simultaneous data transmission. Consequently, there is the possibility of sharing a frequency domain within the same communication channel. A comprehensive overview on the different ways of spectrum sharing that has been investigated in recent years is found in [14]. In addition, in [20,21], new schemes and algorithms for dynamic spectrum sharing between Global System for Mobile Communications (GSM) and LTE technologies were investigated. Regarding the IoT, spectrum sharing is a preferable approach to cope with the conflicts between massive Sensors 2021, 21, 4215 3 of 16 between massive IoT connections and limited spectrum resources as it was discussed in Sensors 2021, 21, 4215 [22–25]. It can also be used to solve vertical requirements and the competition3 of in 15 the ac‐ quisition of frequency bands between MNOs [26,27], as well as to improve spectrum uti‐ lization in Cognitive Radio (CR) and TV white space [28–30]. The leading mobile produc‐ ers have shown massive interest in developing solutions for dynamic spectrum sharing. IoT connections and limited spectrum resources as it was discussed in [22–25]. It can also Thesebe used are to presented solve vertical in requirementsTable 2. and the competition in the acquisition of frequency bands between MNOs [26,27], as well as to improve spectrum utilization in Cognitive TableRadio 2. (CR) Leading and TV producers white space and [ 28adopted–30]. The DSS leading solution. mobile producers have shown massive interestLeading in developing Producers solutions for dynamic spectrumName sharing. of DSS These Solution are presented in Table2. Ericsson ESS—Ericsson Spectrum Sharing Table 2. LeadingHuawei producers and adopted DSS solution. CloudAIR MediaTeck Dimensity 1000 Leading Producers Name of DSS Solution Nokia Dynamic Spectrum Sharing (DSS) Ericsson ESS—Ericsson Spectrum Sharing QualCommHuawei SnapdragonCloudAIR X60 SamsungMediaTeck DimensityDSS 1000 ZTENokia DynamicSuperDSS/Magic Spectrum Sharing Radio (DSS) Pro QualComm Snapdragon X60