Coexistence Analysis Between 5G NR and TVRO in C-Band

This work reports a coexistence analysis between 5G New Radio (5G NR) and Satellite Television Receive Only (TVRO) in C-Band. The coexistence experiments to detect 5G NR interference in TVRO systems are based on the two following approaches: broadcast of analog and digital TV channels, received by a 1.7 meters parabolic antenna pointed to the Star One C2 geostationary satellite from Embratel; 100 MHz-bandwidth 5G NR link at 3.55 GHz with two printed log periodic antennas. The performance analysis has been carried out as a function of the TV channel quality signal, by means of varying the 5G power level at vertical polarization. Measured spectra of either radiofrequency (RF) and intermediate frequency (IF) signals are presented for demonstrating a probable interference problem due to the installation of 5G base stations close to TVRO user homes. For instance, there are still 22 million TVRO users in Brazil and 120 million homes attended by C-Band satellites in United States for radio and TV services. Finally, two efficient technological solutions are proposed and theoretically validated, using SF.1486 ITU-R recommendation, for mitigating 5G NR interference to TVRO and their results are properly compared to other techniques reported in literature.


I. INTRODUCTION
he C-Band satellites are typically used for large coverage areas in diverse applications, including broadcasting, telemetry, tracking and command [1]. On the other hand, at higher frequencies, such as Ku-and Ka-Bands, satellite beams are focused on smaller areas to overcome the high signal attenuation due to atmospheric effects [2]. According to the International Telecommunication Union (ITU), the C-Band is vital for many countries, especially for fixed satellite services (FSS) and broadband wireless access (BWA) [3][4]. Home users use geostationary satellites to receive signals from TV broadcasts, using Satellite Television Receive Only (TVRO) systems [5][6]. C-Band satellites are mainly used to simultaneously transmit analog and digital programming from TV head-ends to the local TV broadcasters, which re-transmit the national and local contents to homes, using digital terrestrial transmissions. Those TV broadcast signals are open, thus the home users only need to point their satellite dishes to geostationary satellites. In parallel, many communications systems use TVRO adjacent channels of in C-Band, including 5G New Radio (5G NR), which is the new radio access technology (RAT) developed by the 3 rd Generation Partnership Project (3GPP) for the fifth-generation (5G) mobile network. 5G NR is going to operate over two frequency ranges, namely: Frequency range 1 (FR1) from 410 MHz to 7.125 GHz with bandwidth up to 100 MHz; Frequency range 2 (FR2) from 24.25 to 52.6 GHz with bandwidth up to 400 MHz.
Particularly the C-Band region from 3300 to 3600 MHz has been chosen for many countries to cover urban areas, aiming to ensure a trade-off between high data rate and medium coverage [7][8]. 5G NR allows multiple services for different scenarios, such as enhanced mobile broadband (eMBB), a massive number of connected Internet of Things (IoT) devices and Machine-Type Communications (MTC) [9,10].
Recently, some works on coexistence between telecom (Long Term Evolution (LTE) and 5G) and satellite (TVRO and FSS) systems have been reported in the literature [11][12][13][14][15]. Their importance are due to the interference possibility between these technologies. In 2018, Son et al. [12] presented numerical analyses in a scenario of coexistence between 5G and FSS at 3.8 GHz, resulting in a minimum distance of 15 km to obtain 95% protection against interference. In parallel, Tan et al. [13] presented numerical and experimental analyses of coexistence between 5G and satellite reception systems, operating from 3.4 to 3.6 GHz. The reception system proposed in [13]  T evaluate FSS protection, image quality and the interference origin. By means of a deterministic study, Yuan et al. [14] have analyzed the interference of the 4G / 5G signal in a mobile satellite data reception system, with the purposing of allowing a minimum protection distance between mobile communication system and FSS. Additionally, a spectrum sharing investigation has been carried out between 5G and a FSS operating at 28 GHz in the northern hemisphere [15].
TVRO systems started in the seventies and reached 1.4 million users in 1985 in the United States, mainly due to the deregulation of the telecommunications regulatory agency [16]. Currently, there are about 22 million TVRO users in Brazil [17] and 120 million homes attended by C-Band satellites in United States for radio and TV services [18], making the coexistence between TVRO and 5G a technical and social challenge, as illustrated in Fig. 1. Typically, TVRO downlink is from 3625 to 4200 MHz, which is adjacent to the main FR1 band. Therefore, depending on the power level of the 5G NR access networks and distance from its base station to the TVRO home users, there is a serious risk of interference, making coexistence analysis necessary to maintain high-quality C-band TV and radio services. In parallel, diverse groups have widely applied the ITU-R recommendations to estimate possible interferences from diverse communication systems to FSS, operating in C-Band [4] [11][12][13][14] [19][20][21][22][23][24]. The ITU-R Recommendations are approved by ITU Member States. Their implementation is not mandatory; however, as they are developed by experts from administrations, operators, the industry and other organizations dealing with radiocommunication matters from all over the world, they enjoy a high reputation and are implemented worldwide. The current work main contributions are the following ones: to the best of our knowledge, our work is the first one in literature on coexistence analysis between 5G New Radio and Satellite TVRO system published in literature; an experimental investigation of the possible 5G impact on approximately 22 million TVRO homes in Brazil, by means of varying the interference received power level and analyzing the TV image quality in analog and digital channels; an analytical analysis on the protection distance, by comparing different commercial low noise block feedhorn (LNBF); the proposal and theoretical validation of two technological solutions based on the use of RF filters and amplifiers with enhanced 1-dB compression point for mitigating the interference and, consequently, enabling a peaceful coexistence between 5G and TVRO systems.
The manuscript is structured in four sections. Section II is concerning the experiment setup, whereas experimental results and the two proposed technological solutions are presented in Section III. Conclusions and final remarks are addressed in Section IV.
II. EXPERIMENTAL SETUP Fig. 2 describes the coexistence experimental setup between TVRO and 5G NR in C-band. Two different vector signal generators from Rohde & Schwarz, SMW 200 and SMBV 100A, have been used to create a 100 MHz-bandwidth 5G NR waveform at 3550 MHz, which was radiated by a Hyperlog 6080 antenna from Aaronia using vertical polarization. All RF signals had been generated following the 3GPP TS 38.141-1 and 3GPP TS 38.141-2 base station conformance testing [25,26]. The bandwidth and modulation have been chosen in accordance to the 3GPP maximum specifications from the Release 15 for C-Band, aiming to obtain the maximum throughput using FR1 [27]. The 7-meters distance between the 5G signal generator and FSS has been chosen to guarantee a suitable dynamic range for the interference evaluation, as well as for ensuring far-field conditions. At the receiver side, a terrestrial earth station has been installed at -22.2578 0 latitude and -45.6957 0 longitude, in conjunction with a 1.7m C-Band parabolic antenna with a 65 dB-gain LNBF. The TV system has been pointed to the Embratel Star One C2 satellite, located at 70 0 W orbital position to receive the satellite transponder signals. The resultant downconverted signal from LNBF in L-Band has been divided by using 1:2 splitter. One cable was directly connected to the TV receiver and the other one to a spectrum analyzer, to evaluate the performance as a function saturation and distortion in the presence of the 5G NR signal at different power levels. An N9912A FieldFox handheld RF and microwave analyzer from Keysight has been used to monitor the 5G NR power level.

Initially, the intermediate frequency (IF) components in L-
Band, after the LNBF down-conversion, have been measured without the 5G NR signal (Fig. 3) for comparison purposes. The transponder signal in C-Band has been mixed with the 5150 MHz local oscillator from LNBF, which is responsible to downconvert the C-Band transponder frequencies to L-Band. One can clearly observe the transponder satellite frequencies without any interference. The marker 1 (Mkr 1) depicts a Globosat channel tuned at the 3720 MHz transponder, implying in IF = 1430 MHz. The frequency shift of 1.5 MHz was due to the LNBF local oscillator instability. The next step was turning the 5G NR signal generator on for experimentally evaluating its coexistence with TVRO. The 5G transmitted power has been varied from 0 to 18 dBm for obtaining the maximum power level that would not interfere in the TVRO system. The transmitting 5G antenna had been placed at 7.0 m distance to the TVRO receiving antenna, which implied in received channel power from -53 to -37.5 dBm at 3550 MHz. An example of the obtained IF spectrum in the presence of a 5G NR signal is reported in Fig. 4 for -41 dBm received channel power. One can note the impact of the spectrum persistence mode from 5G NR at 1.65 GHz (continuous green line), originally at 3550 MHz before downconversion, which implied in high-level interference to TVRO. Fig. 5 displays TV images for different power levels, including a good image without any distortion or saturation from Fig. 5a for -48 dBm channel power. The Globosat analog TV channel at 3720 MHz has been interfered by the 5G NR system for power levels higher than -46 dBm, as demonstrated in Fig. 5b. Particularly for -41 dBm, there was no discernible image on the TV screen, as shown in Fig. 5c, due to the IF signal high distortion and saturation, giving rise to a poor-quality image. As expected, this situation has been always noticed for even higher power levels.  The ITU-R SF.1486 methodology for a fixed wireless access (FWA) system in FSS [29] has been applied to sort the TVRO interference problem out due to the 5G NR system. The minimum protection distance is defined as how physically close a new entrant might be in space to an incumbent's receiver. Particularly for the 5G and TVRO coexistence analysis, the minimum protection distance represents the minimum separation between FSS (TVRO user home) and FWA (5G base station) that not results in performance degradation for TVRO users, evidenced by image distortion and blocking in analog and digital channels, respectively. Considering there is no clutter loss in our setup, due to the line-of-sight (LOS) scenario, one can calculate the required protection distance (d) by using the following equations [29]: = 92.5 + 20 log( ) + 20 log( ), where G is the reference radiation pattern gain that should be adopted for frequencies from 2 to 31 GHz [28], in (3) and (4), is the elevation position of the FSS. In (2), f is the frequency (GHz) and d is the protection distance (km). From (1), is the TVRO 1 dB compression point (P1dB), EIRP is the 5G NR effective isotropic radiated power, G = -10 dBi is the TVRO antenna gain [28] for 52 0 of elevation in our scenario, L is the free-space loss and R is the isolation protection, which might be shielding, RF filters or separation distance between stations in decibel.
We propose to use low-cost planar RF filters with low insertion loss before the low noise amplifier (LNA) stage of the LNBF for avoiding interference from 5G NR in TVRO systems. Tab. I summarize the protection distance for = 75 , L is calculated by (2), for f = 3550 MHz to find the protection distance d, R = 35 dB (RF filter rejection) and varying from -60 to -45 dBm (P1dB enhancement). As a result, the proposed filter enables to significantly reduce the required separation distance between the 5G NR base station and TVRO users from 12.02 km to 672.6 m. Additionally, the TV signal saturation can be alleviated and, consequently, the protection distance can be further lessened, by improving the LNBF P1dB, which was refereed in Tab. I as the "Proposed solution 2". As a consequence, the calculated enhanced protection distance is only 111 m, which could make the 5G deployment viable in C-band. In this way, the two important systems could coexist without imposing interference with each other.

IV. CONCLUSIONS
A coexistence analysis between the 5G NR and TVRO systems in C-band has been reported and properly discussed for different power levels and as a function of TV quality image of analog and digital channels, transmitted in horizontal polarization. Experimental results demonstrated interference problems and even image cancellation, due to the installation of 5G base stations close to TV user homes, for downconverted 5G channel powers higher than -46 dBm. Two efficient strategies have been proposed for minimizing the saturation and distortion problems and addressing the coexistence between 5G and TVRO systems. The first approach relies on adding lowcost planar RF filters with low insertion loss before the LNBF first amplification stage. Our first idea has been validated by using the ITU-R SF.1486 recommendation, which has also been applied in the references from 11 to 14 and from 19 to 29, enabling to positively reducing the required separation distance between the 5G NR base station and TVRO users from 12.02 km to 672.6 m. Furthermore, increasing the TVRO LNBF 1 dB compression point by 15 dB might further lessen the protection distance to only 111 m. Future works regard the development and implementation of the proposed RF filter, as well as carrying out new experiments based on the M.2101-0 ITU-R recommendation to experimentally validate the current theoretical predictions.