Evaluation of LTE and Aeronautical Radionavigation Service Electromagnetic Compatibility in 694 – 790 MHz Frequency Band

In 2012 the 694-790 MHz (700 MHz) band was allocated to the International Telecommunication Union (ITU) Region 1 for mobile service (excluding aeronautical mobile), and was identified to the International Mobile Telecommunications (IMT). However, countries of Region 1 listed in Radio Regulations footnote No. 5.312 will also be able to continue using of these frequencies for their aeronautical radionavigation service (ARNS). This allocation comes into force immediately after the 2015 World Radiocommunication Conference (WRC-15). The objective of this article is to assess the electromagnetic compatibility of aeronautical radionavigation service and mobile service operating in 694 MHz–790 MHz. For interference analysis the Minimum Coupling Loss (MCL) method and Monte Carlo method simulation was used. The obtained results provide the minimum coupling distance required between ARNS and mobile service Long Term Evolution (LTE) stations to maintain the required performance level of the ARNS systems. DOI: http://dx.doi.org/10.5755/j01.eie.22.6.17231

1 Abstract-In 2012 the 694-790 MHz (700 MHz) band was allocated to the International Telecommunication Union (ITU) Region 1 for mobile service (excluding aeronautical mobile), and was identified to the International Mobile Telecommunications (IMT).However, countries of Region 1 listed in Radio Regulations footnote No. 5.312 will also be able to continue using of these frequencies for their aeronautical radionavigation service (ARNS).This allocation comes into force immediately after the 2015 World Radiocommunication Conference (WRC-15).The objective of this article is to assess the electromagnetic compatibility of aeronautical radionavigation service and mobile service operating in 694 MHz-790 MHz.For interference analysis the Minimum Coupling Loss (MCL) method and Monte Carlo method simulation was used.The obtained results provide the minimum coupling distance required between ARNS and mobile service Long Term Evolution (LTE) stations to maintain the required performance level of the ARNS systems.Index Terms-ARNS; 4G mobile communication; electromagnetic compatibility; Monte Carlo method; radiocommunication; radiofrequency interference.

I. INTRODUCTION
The 2012 World Radiocommunication Conference (WRC-12) adopted decision on the allocation of the frequency band 694 MHz-790 MHz (700 MHz) in ITU Region 1 to the mobile service, according to ITU Radio Regulations footnote 5.312A [1], [2].The 700 MHz band has allocation to the mobile service also in Regions 2 and 3.The 700 MHz band is already being described as the second digital dividend following the allocation of frequencies in the 790 MHz-862 MHz (800 MHz) band -the first digital dividend -for mobile broadband services.This part of spectrum is valuable because it provides optimum coverage for mobile service.This study focuses on compatibility assessment between the aeronautical radionavigation service and the mobile service.
This study assumes that coexistence between mobile and broadcasting service might be unlikely in a co-channel situation due to large required separation distances between stations of the services therefore the combination of both services interfering with ARNS receiving ground stations at the same time can therefore be disregarded [3].
Authors found that studies on evaluation of compatibility of LTE (4G mobile communication) with aeronautical radionavigation service operating in the 700 MHz band were performed in the ITU-R study group JTG-4-5-6-7.According to the results of the Study#A.1 of [4] (based on implementation of coordination distances) the required coordination distance for rural environment for land path is 42 km for RSBN and RLS 2 Type 2. If only RSBN ground receivers of the ARNS system are concerned then coordination distance required is 13 km.
According to the results of the Study#A.2 of [4] (based on implementation of coordination distances) the required separation distance for rural environment for land path is 18 km for RSBN ground receivers of the ARNS system and 90 km for RLS 2 Type 2. Different parameters like antenna downtilt etc. were used, as well the tropospheric scattering effect was taken into account in the Study#A.2.Study#A.1 and Study#A.2 are based on protection criteria for ARNS as the permissible aggregate threshold field strength values from a mobile service base stations (BS) according to the Recommendation ITU-R M.1830 and the GE06 Agreement.
A third study is the one in [5], where analytical calculations (MCL) showed that the required protection distance for rural environment between RSBN ground receivers of the ARNS system and the mobile service BS is 132 km.The obtained results from SEAMCAT statistical simulations showed that separation distance should be above 100 km.In the study [5] 6dB N I   interference criterion was used.Different parameters like e.i.r.p. of BS, channel bandwidth etc. were used in this study.
This article is organized as follows.The second chapter is devoted to the technical characteristics of systems.The third chapter describes the used protection criteria.The fourth chapter is devoted to the compatibility evaluation methodology.The fifth chapter represents the interference scenario.The sixth chapter is devoted to the compatibility analysis and results, and in the last one conclusions are derived.

II. TECHNICAL CHARACTERISTICS A. Parameters of LTE
The LTE parameters used in this study are taken from Guntis Ancans  The main characteristics of LTE mobile station (MS) or user equipment (UE) are provided in Table II.In this study the following frequency arrangement is assumed: 703 MHz-733 MHz (for uplink), 758 MHz-788 MHz (for downlink), and 738 MHz-758 MHz (for supplemental downlink -SDL) [9], [10].The ARNS and possible mobile service frequency utilisation is presented in Fig. 1.

B. Parameters of Aeronautical Radionavigation Service
The aeronautical radionavigation service (ARNS) parameters and technical characteristics used in this study are taken from Recommendation ITU-R M.1830 [11] and Recommendation ITU-R M.1461-1 [12].The extract of basic parameters for the 694 MHz-790 MHz band is provided in Table III.Each of them has both benefits and drawbacks [4].In this study were considered three types of coordination triggers i.e. coordination distance, coordination trigger based on N I , and aggregated field strength triggers.Three approaches were used in this paper to estimate the interference of LTE base stations operating in 738 MHz-(downlink) and 738 MHz-758 MHz (supplemental downlink) to ARNS operating in 694 MHz-790 MHz, namely Minimum Coupling Loss (MCL), Monte Carlo method simulation, and predetermined aggregate trigger field strength values for protection of ARNS.Therefore, three distant protection criteria were used to assess the interference from LTE BS to ARNS.

A. Protection Criteria Used in MCL Calculations
For calculation of interference to ARNS caused by mobile service, the interference to noise ratio ( N I ) is used.The protection criteria used in MCL calculations: I N 6 dB   [12].

B. Protection Criteria Used in Monte Carlo Simulations
In Monte Carlo simulations the protection criterion was derived from 3GPP TS 36.104, according to it the probability of interference ( PoI ) less than 5 % was considered to be a sufficient protection level.Second protection criterion used in Monte Carlo simulations of this study was I N 6 dB. 

C. Predetermined Aggregate Trigger Field Strength Values
The protected field strength values are in accordance with Recommendation ITU-R M.1830 Annex 2 Table IV (see Table III of this article), which complay also with the protection criteria of ARNS against DVB-T interference.In the GE06 Agreement the protection of ARNS against DVB-T is defined and it ensures sufficient protection of ARNS.Due to similarity with DVB-T signals the protection of ARNS interfered by mobile service (LTE) can be considered with the same criteria.

IV. COMPATIBILITY EVALUATION METHODOLOGY A. Minimum Coupling Loss Method
The Minimum Coupling Loss (MCL) method is the worst case analysis and produces a boundary result for scenarios of statistical nature.This method evaluates the required path loss level according to minimum protection criteria.

B. Monte Carlo Method
The Monte Carlo method is used in order to assess the interference from LTE BS downlink to ARNS ground receivers.Monte Carlo method is applicable to simulate mainly all possible radio communication based scenarios.This flexibility is ensured by the manner of the characterization of input parameters inside the system.The input type of each variable parameter (as horizontal and vertical antenna pattern, e.i.r.p., propagation environment etc.) is modelled like statistical distribution function.The Monte Carlo modelling provides statistical elements of real life behaviour of BS network and interference, enabling a realistic estimate of the probable interference.In this study was used SEAMCAT software tool [13].

V. INTERFERENCE SCENARIO
In this study considered LTE BS operation in 758 MHz-788 MHz (downlink) and 738 MHz-758 MHz (supplemental downlink) and its possible interference into ARNS operating in the 694 MHz-790 MHz frequency band.
Two cases are considered: RSBN receiving ground station operating at 784 MHz and RLS2 Type 2 receiving ground station operating at 740 MHz (according to Recommendation ITU-R M.1830).
The interference scenario where LTE downlink interferes ARNS (receiver) station was evaluated in this study.The SEAMCAT simulation interference scenario is presented in Fig. 3.
While there are several possible scenarios for the interference between ARNS and mobile service, this contribution focuses only on a scenario that is mostly common as shown in figure above -mobile service BS interference into fixed ARNS ground receiver.

A. Minimum Coupling Loss Method Calculation Results
For initial assessment of compatibility was used MCL method.The required path loss or isolation (MCL), where The isolation figure is further converted into a separation distance using the Recommendation ITU-R P. 1546  The SEAMCAT simulation results present that the separation distance must be more than about 112 km.The calculation results present that the required separation distance must be more than about15 km for RSBN ground receiver and about 45 km for RLS 2 Type 2 ground receiver.

VII. CONCLUSIONS
This study presents important results on the evaluation of coexistence requirements for LTE and ARNS use in the 694 MHz-790 MHz band.Electromagnetic compatibility between LTE BS downlink and ARNS ground receiver was assessed with three different methods: MCL calculations for worst case scenario and Monte Carlo method simulations for more realistic case (only RSBN ground receiver was considered), and predetermined aggregate trigger field strength values for protection of ARNS.
The minimum coupling distance required between LTE BS and RSBN ground receiver in the 700 MHz band to maintain the necessary performance level of the RSBN system is 132 km according to analytical MCL calculations.The Monte Carlo simulation results present that the required separation distance must be more than approximately 112 km with condition that the probability of interference ( PoI ) less than 5 % is considered to be a sufficient protection level using realistic ITU-R P.1546-5 propagation model.Using predetermined aggregate trigger field strength values of Recommendation ITU-R M.1830 the calculation results present that the required separation distance must be more than about15 km for RSBN ground receiver and about 45 km for RLS 2 Type 2 ground receiver.These three used calculation methods and obtained results identified that results could be verified by practical measurements.
The results of this study showed that using the selected frequency arrangement and assumptions the additional mitigation techniques, such as downtilting of antennas, antenna discrimination etc., for LTE network planning and deployment are required in order to assure the compatibility between these two services.Results of this study can be used by National Regulatory Authorities, mobile operators, equipment manufacturers when planning deployment of 700 MHz band for mobile service and ARNS in neighbouring countries.

TABLE I .
CHARACTERISTICS OF LTE BASE STATION.

TABLE II .
CHARACTERISTICS OF LTE USER EQUIPMENT.

TABLE III .
CHARACTERISTICS OF ARNS SYSTEMS OPERATING IN THE 694 MHZ-790 MHZ FREQUENCY BAND.
SEAMCAT Monte Carlo simulation results show the required separation distance between the LTE BS (downlink) and ARNS ground receiver (only RSBN was considered).The Recommendation ITU-R P.1546-5 propagation model was used in this simulation.In this study the probability of interference ( PoI ) less than 5 % was considered to be a sufficient protection level.Results of SEAMCAT results are presented in Table IV in order to verify analytical calculations results obtained in previous chapter.

TABLE V .
CALCULATION RESULTS.The protected field strength values used in this study are in accordance with Recommendation ITU-R M.1830 Annex 2 Table IV (see Table III of this article).The Recommendation ITU-R P.1546-5 propagation model was used in this evaluation.The calculation results are presented in Table V.