Fact Sheet
Working Party:ITU-R WP 5C / Document No: USWP5C19_65_01
Ref. Annex 16,
Document 5C/410
Resolution160(WRC-15),Agenda Item 1.14 / Date:
Document Title: PROPOSED REVISIONS TO “WORKING DOCUMENT TOWARDS PRELIMINARY DRAFT NEW REPORT ITU-R F. [HAPS-21 GHZ]”
Author(s)/Contributors(s):
Michael Tseytlin
Kathryn Martin
Access Partnership / Phone: +1-703-975-6813
Email:
Phone: +1-202-503-1571
Email:
Purpose/Objective: This document offers modifications to the working document for sharing and compatibility studies for broadband HAPS in the 21.4-22 GHz frequencyranges.
Abstract: This contribution offers edits to the abovementioned working document based on comments received in the November 2017 Working Party 5C meeting as well as proposals to streamline the studies. Additionally, the contribution will offer supplemental language to support pfd masks (and/or other limits as appropriate) to protect other services.
Radiocommunication Study Groups /
Source: Annex 17, Document 5C/410 / Document 5C-XXX
XXMay 2018
English only
United States of America
PROPOSED REVISIONS TO “Working document TOWARDS PRELIMINARY DRAFT NEW REPORT ITU-R F. [HAPS-21 GHZ]”
At its November 2017 meeting, Working Party 5C (WP) developed theabove Working Document containing sharing and compatibility studies in the 21.4-22 GHz band in response to WRC-19 Agenda Item 1.14. With this contribution, the United States offers modifications to the sharing and compatibility studies presented to the ITU in November 2017 with the intention of shortening the document, providing support to the concept of using PFD masks and other limits and to further develop the working document towards the preliminary draft new report.
The attachments to this document are intended to replace “Study A” currently described in Annex 19 of Document 5C/410. Power flux density (pfd) and/or e.i.r.p density masks/limits are presented to ensure the protection of incumbent services. In addition, interference mitigation techniques and their impact on the single-entry study (i.e., MCL) are identified and assessed to maximize sharing and compatibility. For the statistical method,
- For the HAPS downlink, a statistical pfd and/or e.i.r.p density mask is presented that HAPS platform will have to comply with at the incumbent receiver versus incidence angle.
In this frequency range, the downlink HAPS Platform to Gateway and HAPS Platform to CPE links are not included to avoid interference with FSS (E-s) in-band and EESS (passive) in the adjacent band. Note that for the long-term protection criteria, nominal transmit power is assumed. Studies for short-term protection criteria, based on maximum transmit power, will be presented at later stage. The following directions are considered for the 21.4-22 GHz frequency range:
- HAPS Platform to gateway (DL)
- HAPS Platform to CPE (DL)
1
1.1Study A FS (Document 5C-330 (USA) and Document 5C- Share Folder (Mexico))
[Editor’s note: Add views, if required]
[View
HAPS DL FS
–The analysis does not facilitate the derivation of the possible requirements for the regulatory provisions to protect the considered victim system. Conclusions of the analysis are limited to the system considered. The presented analysis does not foster a conclusion that would apply to any HAPS system and a generic approach (e.g. pfd mask) could facilitate deriving generic conclusions.
–Should the study be considered further in the draft document, the following elements need to be taken into account for the enhancement of the analysis:
•The impact of the analysis is limited to the HAPS system coverage whereas all the area under HAPS visibility should be taken into account in the analysis.
•The Monte Carlo analysis does not provide sufficient number of iterations to derive a conclusion that is statistically reliable.
•Use of ATPC should be considered under relevant assumptions
HAPS UL FS
–The analysis does not facilitate the derivation of the possible conclusions of operation between HAPS GW/CPE and the considered victim system.
–The Monte Carlo analysis does not provide sufficient number of iterations to derive a conclusion that is statistically reliable.
–In HAPS UL analysis, clear impact of azimuth alignment is needed to be presented as it may have a significant impact on the result derived from the Monte Carlo analysis and may need to reconsider any need of shielding on the HAPS GW/CPE or separation distance between HAPS GW/CPE and the victim receiver.
–Use of ATPC should be considered under relevant assumptions]
1.1.1Summary
The corresponding compatibility analysis is intended to replace “Study A” currently described in Annex 16 of Document 5C/410 (Chairman’s Report).
This study investigates the coexistence between HAPS and FS. This study will first present a statistical study. Then the impact of the various mitigation techniques will be assessed.
In this frequency range, the flowing directions are considered for HAPS.
- HAPS platform to gateway (DL)
- HAPS platform to CPE (DL)
This study investigates the coexistence between HAPS and FS, considering Minimum Coupling Loss (MCL) method (deterministic), considering both full power and ATPC for HAPS.
As a second step, the probability of exceeding the protection criteria of the victim (i.e.e, a statistical Monte Carlo analysis) was performed.
1.1.2Introduction
The HAPS parameters (gateway and CPE links) used in this study is from System 6 from Annex 14 of the WP 5C Chairman’s Report (Document 5C/292410).For HAPS, a protection criterion criteria of I/N= -6 dB (may exceed 20% of the time) was assumed for this study.
Table 12The following table shows the FS (P-P) transmitter and receiver parameter used in this study. These parameters are based on the latest version of ITU-R F.758-6. in Annex 13 of the WP 5C Chairman’s Report (Document 5C/292). Note that worst case parameters are chosen for this study. Based on ITU-R F.758-6, for FS protection criteria, I/N= -10 dB was considered.
Table 1:
Table 12
FS (P-P) parameters
Parameters / FS (P-P)Maximum Gain (dBi) / 34.8
TX & RX Antenna pattern / ITU-R F.1245 (statistical approach)
ITU-R F.699 (single-entry approach) ITU-R F.1245
EIRP power spectral density (dBW/MHz) / 7.8-10.8
TX and RX Elevation angle (deg) / 0 & 5
Noise figure typical / 11
Receiver noise power density (dBW/MHz) / -133
Protection criteria / I/N = -10 dB
Knowledge of rain fade dynamics is important in the design of new HAPS systems. Adaptive Transmit Power Control (ATPC) is one of the countermeasures to address rain fade by increasing transmitted power to compensate for rain fade on the propagation path. The potential higher susceptibility to interference is successfully overcome by careful planning of link budgets and when necessary in the coordination procedure, the use of ATPC to limit transmitted power in congested networks. In this study, the results for both clear sky and rain fade (i.e., full power) conditions are presented. The following table shows the power control that was considered.
Table 13
Power control attenuation for both GW/CPE uplink and downlink
21.4-22 GHz / GW uplink / CPE uplink / GW downlink / CPE downlinkPower control attenuation (dB) / -15 / -15 / -10 / -15
This study investigates the coexistence between HAPS and FS, considering Minimum Coupling Loss (MCL) method (deterministic), for each interference scenario. Results including ATPC are also presented.
The MCL analysis determines a required separation distance. If the distance between the two interfering services is greater than the required separation distance, then these services will not interfere. However, where the separation distance is less than that calculated in the MCL analysis, there may exist cases where the protection criterion is exceeded.
To assess the probability of occurrence of those cases, a statistical Monte Carlo analysis was performed. This is a static analysis for which the long-term protection criterion is assumed to be the worst case. For this analysis, the bearing between the HAPS transmitter and the FS receiver was randomly varied over 50,000 iterations. The results of the Monte Carlo analysis provide an indication of the number ofHAPS deployments for which additional interference mitigation techniques will be required.
The following methodologies are proposed to be included in this sharing study document instead of Annex 26 of the WP 5C Chairman’s Report (Document 5C/292).
1.1.3Methodology – HAPS CPE/Gateway to Fixed Service
The methodology used for this study is as follows.
Single HAPS interference
Similar to the methodology in Recommendation ITU-R F.1609-1, the interfering power density at fixed service receiver is determined by the following equation:
I (dB(W/MHz)) = Ptx – Lf,tx + Gtx(α) – LNLOS + Grx(α) – Lf,rx
where:
Ptx: HAPS GW/CPE transmitted power spectral density (dB(W/MHz));
Gtx(α): Antenna gain of HAPS GW/CPE transmitter towards FS receiver (dBi);
Grx(α): Antenna gain of FS receiver towards HAPS GW/CPE transmitter (dBi);
LNLOS: Non-line-of-sight propagation model (Rec. ITU-R P.452-16);
Lf,tx: Feeder loss of HAPS CPE/GW (dB) (assumed 0 dB);
Lf,rx: Feeder loss of FS (dB).
The ratio of the interference power to the receiver thermal noise, I/N, is obtained by the following equation:
I/N (dB) = I – 10 log(kTB)
where:
k: Boltzmann’s constant = 1.38 x 10-23 (J/K);
T: System noise temperature of the FS receiver (K);
B: Noise bandwidth = 1 MHz.
For gateways, interference may be mitigated by taking advantage of site shielding (up to 30 dB) to reduce side lobe radiation, while maintaining system performance as mentioned in Recommendations ITU-R SF.1481 and ITU-R F.1609.
To calculate the separation distance, the propagation model is based on Recommendation ITU-R P.452-16. For every step of distance, the propagation loss and I/N for all GW/CPE elevation angles will be calculated. Therefore, for every elevation angle of the HAPS GW/CPE, the minimum separation distance will be stored when the calculated I/N meets I/N protection criterion of the FS terminal.
The Monte Carlo simulation is performed when the results of the MCL analysis do not conclusively demonstrate sharing feasibility. Note, if the MCL shows that sharing is feasible, the Monte Carlo analysis is not required.
The statistical approach (i.e., Monte Carlo) is adopted to determine the probability of interference exceeding the protection criteria (i.e., % of failure) of a fixed service receiver by randomly altering the bearing between the HAPS transmitter and fixed service receiver over 50,000 iterations. For the Monte-Carlo method, the following methodology is used.
Statistical Model
This analysis is performed when the result of the MCL analysis (described above) does not demonstrate sharing feasibility.
The following steps are performed at each Monte Carlo trial (50,000 trials)
1Define a circular area based on the size of the HAPS footprint (50 km radius)
2.Drop the FS receiver always within the HAPS footprint with a random azimuth and elevation angle. The pointing angle of the FS[1] is set fixed for the entire 50, 000 events.
3.For every trial, the HAPS CPE/gateway is randomly dropped around the FS receiver (i.e., separation distance of 0 to 50 km)
–The antenna height of the HAPS CPE/gateway is 10 m and the elevation angle is randomly set (for each trial) between 20 degrees (at the edge of the HAPS coverage) and 90 degrees (at the HAPS nadir), while the azimuth angle is randomly set between 0 and 360 degrees
4.The relative location of HAPS CPE/gateway with respect to the FS receiver is calculated in order to also calculate the path loss
5.The HAPS transmission off-axis angle and antenna gain towards the FS are calculated, which depend on the HAPS transmitter location (with respect to FS), antenna pointing angle (with respect to FS) and the antenna pattern used
6.For the GW ground terminal towards the FS scenario, a single active GW is considered per trial (based on the system characteristics). For the CPE ground terminal towards the FS scenario, four active CPEs are considered per trial (based on the system characteristics).[2]
7.At every iteration over a total of 50,000 trials, the unwanted interference is calculated. If there is more than one active interferer, the aggregate unwanted interference is calculated at each trial using the following formula:
Iaggregate = .
n is the number of interferers and Ii the unwanted interference of interferer I.
The output of the Monte Carlo simulation is given as an average of the calculated unwanted interference. It also calculates the probability of interference exceeding the FS protection criteria (i.e., % of failure).
1.1.43Methodology and results – HAPS Platform (CPE/gateway link) to Fixed Service
1.1.3.1Statistical method
This section presents the steps and results of the statistical pfd mask that HAPS downlink will have to comply with at the FS receiver versus incidence angle.
Step 1: compute the FS antenna gain towards the HAPS based on the following input parameters.
–0° is taken for the elevation angle towards the HAPS;
–0° is taken for the azimuth towards the HAPS;
–FS station antenna pointing azimuth: random variable with a uniform distribution between -180° to 180°;
–FS station antenna pointing elevation: random variable with a normal distribution (median 0.03-0.01 and standard deviation 2.682.07);
–FS maximum antenna gain: XX34.8 dBi.
Step 2: compute and store the maximum possible HAPS pfd level at the FS station using the following equation:
where:
Imax:the maximum interference level (XXX -143 dBW/MHz clear sky/long term)
Gr: the FS antenna gain towards the HAPS (see step 1);
θ:the angle between the vector FSHAPS and FS antenna main beam pointing vector.
:the gaseous attenuation (ITU-R P.676)
Step 3: redo step 1 and 2 sufficiently to obtain a stable pfd CDF curve and store it;
Step 4: redo step 1 to 3 with an increased elevation angle towards the HAPS of 1° until the elevation angle towards the HAPS is 90°.
Step 5: redo step 1 to 4 until the elevation angle towards the HAPS is 90°.
The following figure provides the results for the clear sky/long term.
Figure 1: Maximum pfd level cumulative distribution function to meet the FS protection criteria
Figure 4: Maximum pfd level cumulative distribution function to meet the FS protection criteria
Step 56: determine the pfd mask versus elevation to protect FS station receiver.
It is expected that the maximum interference level will not increase significantly even for very high amount of HAPS mainly due the low probability for an FS stations to be pointing at more than one HAPS.
The following pfd mask at the Earth surface should therefore be sufficient to protect FS station receivers under clear sky condition:
where is elevation angle in° (angles of arrival above the horizontal plane).
NOTE: THIS MASK MIGHT HAVE TO BE UPDATED FOR THE SECOND DRAFT BASED ON THE AGGREGATE STUDY RESULTS
Figure 2: Proposed pfd mask versus elevation angle
Step 67: compare with systems 2 maximum pfd level versus elevation.
The pfd is computed using the following equation:
where:
dis the distance between the HAPS and the FS station;
EIRP(el)is the nominal HAPS e.i.r.p. density level in dBW/MHz at a specific elevation angle;
Figure 3: HAPS systems 2 26 compliance with the proposed pfd mask
1.1.3.2Interference mitigation technique
The methodology used in this study is based on the following approach.
The methodology used in this study is based on the following.
Single HAPS interferer
Figure 1The following figureshows the estimated impact of the curved earth on distances.
Figure 4:
Figure 1
CCurved earth assumption impact on distances
Distance X is equal to:
which is also equal to:
hence:
and:
Finally, the distance D is approximated to:
Once the distance (D)between the HAPS platform and the fixed service terminal is calculated, the off-axis angles are determined. It is assumed that if the FS terminal is inside the HAPS coverage, the HAPS platform is pointing straight at the FS terminal with a maximum gain. However, if the FS terminal is outside the HAPS platform’s coverage area, the off-axis angle between the HAPS’ beam closest to the edge of coverage and the direction of the FS station needs to be calculated.
The following figureshows the scenario from HAPS platform to FS terminal with variables that are used in the calculation of the off-axis angles.
Figure 5:
Figure 2
HAPS platform (gateway/CPE) to FS station
The above figure Figure 2 takes into account the effect of the curved earth assumption explained above. Introducing the elevation (elev from Figure 4Figure 1) of the ground station towards the HAPS platform as a variable, the off-axis angles and is calculated as follows:
where:
- is the Earth’s radius;
- is the altitude of the HAPS platform;
- : the angle when the HAPS platform is pointing at the edge of coverage ():
where:
: is set to 0 or 5 degrees.
Knowing the two off-axis angles, the relative gains can be calculated following the associated antenna pattern for the service.
The interfering signal power density, I, at FS terminal receiver is determined by the following equation:
I (dB(W/MHz)) = Ptx - Lf,tx + Gtx() – Ls+ Grx() - Lf,rx
where:
Ptx: HAPS platform transmit power density (dB(W/MHz));
Lf,tx: Feeder loss of HAPS platform in the transmit side (dB) (assumed 0 dB);
Gtx(): Antenna gain of HAPS platform transmitter towards FS receiver (dBi);
Ls:Free space path loss between HAPS platform and FS terminal(dB) shown in the following:
Ls = 92.45 + 20 log(fGHz) + 20 log10(dkm)
dkm: Distance between FS terminal and HAPS platform (km);
fGHz: Frequency (GHz);
Grx(): Receive antenna gain of FS terminal receiver towards HAPS platform (dBi);
Lf,rx: Feeder loss of FS terminal in the receive side (dB).
The ratio of the interference power to the receiver thermal noise, I/N, is obtained by the following equation:
I/N (dB) = I – 10 log(kTB)
where:
k: Boltzmann’s constant = 1.38 x 10-23 (J/K);
T: System noise temperature of FS receiver (K);
B: Noise bandwidth = 1 MHz.
The single-entry I/N is calculated for FS terminal pointed towards the HAPS platform and located between 0 km and 500 km from HAPS platform nadir point and compared to FS I/N threshold (-10 dB) to determine mitigation techniques required for sharing feasibility.
The following figures show the calculated I/N for every distance of FS station (P-P) to HAPS nadir (both gateway and CEP downlink).