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Interference into radio broadcast satellite uplinks
Acta Astronautica 166 (2020) 413–416
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
Interference into radio broadcast satellite uplinks a,∗
b
Robert Briskman , Riza Akturan a b
T
Sirius XM, 1221 Avenue of the Americas, New York, NY 10020, USA Sirius XM, Signal Delivery, 989 Lenox, Lawrenceville, NJ 08648, USA
ARTICLE INFO
ABSTRACT
Keywords: Transmission interference Satellite broadcasting Spectrum frequency planning
Radio frequency interference into satellite transmission channels is a matter of concern. There have been many studies of this subject by the ITU (International Telecommunications Union) particularly to mobile user receivers in the satellite radio broadcasting services by IMT (International Mobile Telecommunications) transmitters, since such receivers have high sensitivities (e.g., downlink channel system noise temperatures of under 100 deg. Kelvin) and provide Satellite Digital Audio Radio Service (SDARS) quality using relatively low satellite signal levels on the ground. Recently, proposals have been made by future low orbit satellite constellations, IMT and terrestrial interconnection systems to share radio frequency bands used by the transmission uplinks to radio broadcasting satellites. The broadcasting satellite uplink transmission channel at 7 GHz has typical system noise temperatures of 900 deg. Kelvin followed by very high electronic and antenna amplification. The overall system transmission design is generally set so the satellite broadcast uplink C/N does not appreciably degrade the downlink C/N, since the downlink simultaneously serves than 35 million mobile users with satellite radio service in North America. This paper describes the effect of potential interference into a satellite radio broadcast service from in-band and adjacent band transmissions and from associated intermodulation products by sharing uplink frequency spectrum transmitters. The analysis shows that such sharing services should be carefully arranged in the radio frequencies utilized and limited in flux densities impinging the geostationary orbital arc so harmful interference to radio broadcast satellite services does not occur.
1. Introduction
2. Satellite system configuration
There has been much analysis of interference into satellite communications and broadcast mobile receiving terminals, particularly by the International Telecommunications Union (ITU). Most of these analyses have centered on the interference to proper reception at such terminals which is normally termed the “downlink” (the desired radio transmission from the satellite to the mobile receiving terminals). All broadcast and communications satellites also have an “uplink” (the desired radio transmission from central earth stations to the satellite containing the signal(s) that the satellite is to retransmit). There are a wide variety of communications and broadcast satellite systems operating in many different radio frequency bands. For simplicity, the following will use as its technical model the satellite parameters of the Sirius XM radio broadcasting system. This system has operated for more than a decade and provides satellite radio service to over 35 million mobile subscribers throughout North America [1]. The satellite uplink radio frequency band for the system is 7025–7075 MHz referred to hereafter as the 7 GHz band.
Fig. 1 shows the model satellite broadcasting system which includes the “uplink” which is the radio transmission from the system's ground stations to the satellite for retransmission by the satellite to the mobile receiving terminals. There are 6 uplink carrier frequencies used continuously plus 4 command carriers at radio frequencies around 7 GHz to the four active satellites in the constellation. There is a fifth satellite which is an on-orbit spare and will not be further discussed. The subsequent discussion deals with interference into the 4 uplink carriers; the command carriers are also vulnerable to interference but will not be discussed for proprietary reasons. The satellite up-link radio frequency configuration is simple. Basically, the up-link transmission from the central earth station is amplified by the satellite receive antenna and coupled to a 7 GHz receiver. The satellite receiver further amplifies the transmission and sends it to a frequency translator converting it to 2.3 GHz. The 2.3 GHz transmission is then amplified by paralleled TWTAs and transmitted by the satellite transmit antenna to the mobile subscriber receiving terminals on earth. The satellite receive system noise temperature is
∗
Corresponding author. E-mail addresses: [email protected] (R. Briskman), [email protected] (R. Akturan).
https://doi.org/10.1016/j.actaastro.2019.07.040 Received 7 December 2018; Received in revised form 22 February 2019; Accepted 14 July 2019 Available online 16 October 2019 0094-5765/ © 2019 Published by Elsevier Ltd on behalf of IAA.
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
density will be dictated by the antenna's levels of the sidelobes which point towards the satellite. Besides terrestrial interferers, there have been many recent ITU filings for satellite constellations in low earth orbits. A few of these specify use of the satellite radio broadcast 7 GHz uplink radio frequency band which could be a future source of interference [2]. 4.2. Adjacent-band interference The selectivity of the satellite uplink radio frequency filtering is not perfect at band edge. Interferers close to the band edge can provide interference levels almost equivalent to in-band interferers. This interference source can be avoided by either making adjacent frequency allocations with a small guard band at the satellite's uplink band edges or by ensuring the adjacent frequency allocated transmissions have low interference potential.
Fig. 1. SiriusXM satellite radio transmission system.
4.3. Intermodulation
typically 900 deg. Kelvin including earth noise seen by the satellite receive antenna. The widest uplink transmission bandwidth is 4.2 MHz resulting in a satellite receiving thermal noise floor of – 132.5 dBW. The following deals with uplink interference which simply means an increase in this noise floor (or a corresponding decrease in the uplink carrier to noise ratio C/Nup).
It is possible that intermodulation products can fall in-band causing interference. Practically, the major contributors would create intermodulation interference at a frequency of 2A-B (or 2B-A) where A and B are the frequencies of each contributor. Strong radio frequency carriers in the 5–9 GHz range can combine to create intermodulation interference in the frequency bands used by SiriusXM. This can be addressed through allocation coordination. The main concern here is high powered military surveillance radars because radar power output far exceeds normal wireless communication transmit levels.
3. Interference The sources of uplink interference can be categorized as those within the uplink transmission bandwidth (“in-band”), those adjacent to the band and intermodulation products. The primary sources are from transmitters on the earth's surface but, as described later, there are proposals to share the 7 GHz broadcast uplink band by low orbit satellite constellations. There are two characteristics which distinguish uplink interference from downlink interference. The first is that most broadcast and many communications satellite systems are located in geostationary orbits. This means that terrestrial interfering transmissions will be attenuated by the path loss to the satellite which, at 7 GHz, is typically 201.2 dB. The second is that the satellite receiving antenna generally views a significant portion of the earth's surface. All terrestrial transmitters using in-band frequencies within this portion of the earth will cause interference. The interference from such transmitters is additive to each other and is received and amplified by the satellite's receive (uplink) antenna gain. Fig. 2 shows the typical Sirius XM satellite receive antenna coverage and directionality. The antenna coverage includes most of the United States and adjacent portions of Canada, Mexico and the Caribbean. Any interfering flux density from in-band earth-based transmitters throughout this area of the earth will be amplified by the satellite receive antenna by a factor of approximately 800 (29 dBi).
5. Existing in-band interference There are several terrestrial services currently sharing the 7 GHz uplink band in the United States. They are the Fixed Service (FS) microwave links, television Broadcast Auxiliary Service (BAS), Cable Television Relay Service (CARS) and Local Television Transmission Service (LTTS). Generally the transmitters are not high powered and use directive antennas. The FS has approximately 100,000 transmitters in the 5.913–7.125 GHz band and plans to increase the number of transmitters [3]. Sirius XM satellite radio's licensed uplink frequencies are contained within 7025–7075 GHz bands. The resulting aggregate uplink interference from these sharing services is tolerable as later discussed. 6. Proposed new terrestrial uplink interferers There have been filings at the USA Federal Communications Commission (FCC) to authorize unlicensed Radio Local Area Network (RLAN) devices in the radio frequency region including the subject 7 GHz satellite uplink band [4]. The proponents provided an engineering study by RKF Engineering LLC which purported to show the RLANs would not interfere with the subject 7 GHz uplinks. Table 1 shows an interference analysis of the RKF study. The study estimates 958 million RLAN devices by 2025 of both indoor and outdoor types. For simplicity, the analysis modeled the outdoor RLANs as a 1-W transmitter of a 20 MHz wide Wi-Fi signal feeding an omnidirectional antenna. The analysis uses the RKF harmful interference to satellite noise floor ratio criterion of −21.9 dB. Based on estimates of other parties, such as the CEPT ECC report dealing with a similar proposed European wide system, one can assume a 5.3% outdoor use factor and 0.4% usage activity rate for the proposed RLAN devices.1 This would result in 2,623 simultaneous active outdoor
4. Types of interference 4.1. In-band interference Any transmitter at in-band frequencies within view of the satellite is an interferer. Even if an individual transmitter causes low interference, if there are sufficient number of them, the aggregate can create a harmful interference level. An illustration of this is provided subsequently. Currently all known in-band interferers are terrestrial. Most potentially interfering terrestrial transmitters at 7 GHz can use directive antennas pointed towards the horizon on the earth surface. If the antennas are directed at or near the geostationary arc where the satellite is located, a high interference flux density will result. If the terrestrial antennas are not pointed there, the magnitude of the interfering flux
1 RKF presumed a low 2% outdoor use factor and 0.04% usage activity rate that would not be realistic and cannot be supported with future internet and application growth projections.
414
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
Fig. 2. Typical SXM satellite uplink receive antenna pattern. Table 1 Calculation of interference levels to SDARS uplinks from projected RLAN transmissions. #
Parameter
Value
Calculation
1 2 3 4
Tolerable carrier power at SDARS satellite receiver Thermal noise power at SDARS satellite receiver Tolerable RLAN interference to noise ratio RLAN interference at SDARS satellite receiver
−117.4 dBW −132.5 dBW −21.9 dB −154.4 dBW
5 6 7
SDARS satellite uplink receive antenna gain Uplink path loss Aggregate RLAN interference at ground level
8 9
Aggregate RLAN interference ground power density Single RLAN interferer power level density
29.0 dBi 201.2 dB 17.8 dBW, or 60.4 W −48.7 dBW/Hz −73.0 dBW/Hz
Satellite manufacturer specification Calculated per satellite manufacturer specification RKF claimed maximum interference threshold [2] + [3] No interference from FS, BAS, CARS or LTTS considered Satellite manufacturer specification Geostationary SDARS satellite path loss to earth surface [4,5] + [6]
10 11
Number of RLAN devices to reach the tolerable aggregate interference level Estimated number of RLAN transmitters operating within the SDARS band
268 2,623
12
Exceedance level of RKF-proposed interference Ratio
9.8 dB
a b
1200 MHz: total proposed 6 GHz bandwith allocation for RLAN devices. 15.5 MHz: spectrum fully effecting the 4.5 MHz SDARS uplink band from 20 MHz RLAN emissions.
transmitters in North America out of the total RFK projected 958 million RLAN devices projected in the early to mid-time frame.2 The analysis result shows the interference into the satellite uplink from the proposed RLAN system would exceed RKF's proposed harmful 2
[7] - 10*log10(4.5 MHz) 10*log10(1 W/20 MHz) For an example WiFi device emitting 1 Watt power in 20 MHz bandwidth 10^(([8] - [9])/10) 958 M total users *(15.5MHz/1200 MHz)*0.4% *5.3% 0.4%: Activity rate 5.3%: Outdoor rate Seea for 1200 MHz Seeb for 15.5 MHz 10*log([11]/[10])
interference criterion by an order of magnitude (9.8 dB or ∼10 times the number of devices) very harmfully impacting SDARS. It is also noted that the RKF study did not account for the existing or other potential future uplink interference previously described which would further increase the excessive and harmful interference levels.
Not including any additional interference from such indoor transmitters. 415
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
7. Real life interference
that the C/Nup does not significantly increase C/Ntotal. Therefore, it would be reasonable to assign C/Nup no more than a sixth (i.e., 1%) of the total allowed interference criterion for the aggregate uplink interference since there are multiple individual interferers that the satellite system has to deal with. Although increase in the noise floor by interference is a good criterion, it is noted that there may also be C/Ntotal and signal availability impact requirements. In the model system herein, the C/Ntotal must be sufficient to overcome foliage attenuation [6] and, in some communications/broadcast systems operating at higher radio frequencies than the model, to overcome rain attenuation.
It is important to note that, while the above RLAN is currently hypothetical, uplink satellite interference occurs. A communications satellite operator offering Mobile Satellite Service (MSS), Globalstar, Inc. has experienced substantial satellite uplink interference [5]. The uplink satellite radio frequency band in this case is 5150–5250 MHz. Several years ago, the FCC authorized unlicensed use in this frequency band of devices similar to RLANs called U-Nll with restriction to indoor use. A few years ago, over the potential uplink interference arguments of Globalstar, the FCC authorized their outdoor use. As detailed in Ref. [5], Globalstar has recently measured an increase in the noise floor level of its satellite uplink receiver over the United States of 2 dB during the day and 1 dB at night.
9. Conclusions Significant interference into uplinks of broadcast and communications satellites must be avoided. Although limited sharing of the frequency bands used by these satellites with other services is possible, such sharing cases must be limited in the total tolerable amount of interfering power it causes as seen by the satellite's receiving antenna to keep within the system's aggregate interference tolerance requirement.
8. Interference criteria A universally agreed interference criterion is the ITU one specifying a rise in the noise floor by interference of more than 6% called Delta T/ T where Delta T is the rise in the noise floor and T is the total receiving system noise temperature including aggregate interference from all types of interferers. This is generally measured at the satellite downlink user receiver. It includes all transmission interference such as in-band uplink and downlink, adjacent channel and intermodulation products. As earlier stated in this paper, the C/Nup is automatically combined with the C/Ndown for satellite repeaters of transmissions (reflecting the design of most communications/broadcast satellites) which results in C/Ntotal. C/Ndown is generally interference critical so a high interference allowance is desirable. For the model system of this paper, the downlink is to subscriber mobile terminals of high sensitivity (terminal receiver noise temperatures of 80 deg. Kelvin) and there is a need to provide subscriber signal availability at least 99.9% of the time. The model system must also cope with other ground-based interference from the Wireless Communications Service (WCS) in both adjacent downlink radio frequency bands. Also, as previously mentioned, the system link budget design in most communications/broadcast satellites is done so
Acknowledgements The authors thank the many members of the Sirius XM Engineering Division who contributed to this paper. References [1] R. Akturan, An overview of the Sirius satellite radio system, Int. J. Satell. Commun. Netw. 26 (5) (2008). [2] ITU IFIC 2849, 2864. [3] AT&T Letter from Stacey Black to Marlene H. Dortch of the FCC, March 19, 2018. [4] Frequency Sharing for Radio Local Area Networks in the 6 GHz Band, prepared by RKF Engineering Services LLC, GN Docket No. 17-183, filed Jan. 25 2018. [5] Globalstar Inc, Petition for Notice of Inquiry, RM-11808, (May 21 2018). [6] Dr.J. Goldhirsh, Dr.W. Vogel, Propagation Effects for Land Mobile Satellite Systems: Overview of Experimental Modeling Results vol. 1274, NASA Reference Publication, 1992.
416
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
Interference into radio broadcast satellite uplinks a,∗
b
Robert Briskman , Riza Akturan a b
T
Sirius XM, 1221 Avenue of the Americas, New York, NY 10020, USA Sirius XM, Signal Delivery, 989 Lenox, Lawrenceville, NJ 08648, USA
ARTICLE INFO
ABSTRACT
Keywords: Transmission interference Satellite broadcasting Spectrum frequency planning
Radio frequency interference into satellite transmission channels is a matter of concern. There have been many studies of this subject by the ITU (International Telecommunications Union) particularly to mobile user receivers in the satellite radio broadcasting services by IMT (International Mobile Telecommunications) transmitters, since such receivers have high sensitivities (e.g., downlink channel system noise temperatures of under 100 deg. Kelvin) and provide Satellite Digital Audio Radio Service (SDARS) quality using relatively low satellite signal levels on the ground. Recently, proposals have been made by future low orbit satellite constellations, IMT and terrestrial interconnection systems to share radio frequency bands used by the transmission uplinks to radio broadcasting satellites. The broadcasting satellite uplink transmission channel at 7 GHz has typical system noise temperatures of 900 deg. Kelvin followed by very high electronic and antenna amplification. The overall system transmission design is generally set so the satellite broadcast uplink C/N does not appreciably degrade the downlink C/N, since the downlink simultaneously serves than 35 million mobile users with satellite radio service in North America. This paper describes the effect of potential interference into a satellite radio broadcast service from in-band and adjacent band transmissions and from associated intermodulation products by sharing uplink frequency spectrum transmitters. The analysis shows that such sharing services should be carefully arranged in the radio frequencies utilized and limited in flux densities impinging the geostationary orbital arc so harmful interference to radio broadcast satellite services does not occur.
1. Introduction
2. Satellite system configuration
There has been much analysis of interference into satellite communications and broadcast mobile receiving terminals, particularly by the International Telecommunications Union (ITU). Most of these analyses have centered on the interference to proper reception at such terminals which is normally termed the “downlink” (the desired radio transmission from the satellite to the mobile receiving terminals). All broadcast and communications satellites also have an “uplink” (the desired radio transmission from central earth stations to the satellite containing the signal(s) that the satellite is to retransmit). There are a wide variety of communications and broadcast satellite systems operating in many different radio frequency bands. For simplicity, the following will use as its technical model the satellite parameters of the Sirius XM radio broadcasting system. This system has operated for more than a decade and provides satellite radio service to over 35 million mobile subscribers throughout North America [1]. The satellite uplink radio frequency band for the system is 7025–7075 MHz referred to hereafter as the 7 GHz band.
Fig. 1 shows the model satellite broadcasting system which includes the “uplink” which is the radio transmission from the system's ground stations to the satellite for retransmission by the satellite to the mobile receiving terminals. There are 6 uplink carrier frequencies used continuously plus 4 command carriers at radio frequencies around 7 GHz to the four active satellites in the constellation. There is a fifth satellite which is an on-orbit spare and will not be further discussed. The subsequent discussion deals with interference into the 4 uplink carriers; the command carriers are also vulnerable to interference but will not be discussed for proprietary reasons. The satellite up-link radio frequency configuration is simple. Basically, the up-link transmission from the central earth station is amplified by the satellite receive antenna and coupled to a 7 GHz receiver. The satellite receiver further amplifies the transmission and sends it to a frequency translator converting it to 2.3 GHz. The 2.3 GHz transmission is then amplified by paralleled TWTAs and transmitted by the satellite transmit antenna to the mobile subscriber receiving terminals on earth. The satellite receive system noise temperature is
∗
Corresponding author. E-mail addresses: [email protected] (R. Briskman), [email protected] (R. Akturan).
https://doi.org/10.1016/j.actaastro.2019.07.040 Received 7 December 2018; Received in revised form 22 February 2019; Accepted 14 July 2019 Available online 16 October 2019 0094-5765/ © 2019 Published by Elsevier Ltd on behalf of IAA.
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
density will be dictated by the antenna's levels of the sidelobes which point towards the satellite. Besides terrestrial interferers, there have been many recent ITU filings for satellite constellations in low earth orbits. A few of these specify use of the satellite radio broadcast 7 GHz uplink radio frequency band which could be a future source of interference [2]. 4.2. Adjacent-band interference The selectivity of the satellite uplink radio frequency filtering is not perfect at band edge. Interferers close to the band edge can provide interference levels almost equivalent to in-band interferers. This interference source can be avoided by either making adjacent frequency allocations with a small guard band at the satellite's uplink band edges or by ensuring the adjacent frequency allocated transmissions have low interference potential.
Fig. 1. SiriusXM satellite radio transmission system.
4.3. Intermodulation
typically 900 deg. Kelvin including earth noise seen by the satellite receive antenna. The widest uplink transmission bandwidth is 4.2 MHz resulting in a satellite receiving thermal noise floor of – 132.5 dBW. The following deals with uplink interference which simply means an increase in this noise floor (or a corresponding decrease in the uplink carrier to noise ratio C/Nup).
It is possible that intermodulation products can fall in-band causing interference. Practically, the major contributors would create intermodulation interference at a frequency of 2A-B (or 2B-A) where A and B are the frequencies of each contributor. Strong radio frequency carriers in the 5–9 GHz range can combine to create intermodulation interference in the frequency bands used by SiriusXM. This can be addressed through allocation coordination. The main concern here is high powered military surveillance radars because radar power output far exceeds normal wireless communication transmit levels.
3. Interference The sources of uplink interference can be categorized as those within the uplink transmission bandwidth (“in-band”), those adjacent to the band and intermodulation products. The primary sources are from transmitters on the earth's surface but, as described later, there are proposals to share the 7 GHz broadcast uplink band by low orbit satellite constellations. There are two characteristics which distinguish uplink interference from downlink interference. The first is that most broadcast and many communications satellite systems are located in geostationary orbits. This means that terrestrial interfering transmissions will be attenuated by the path loss to the satellite which, at 7 GHz, is typically 201.2 dB. The second is that the satellite receiving antenna generally views a significant portion of the earth's surface. All terrestrial transmitters using in-band frequencies within this portion of the earth will cause interference. The interference from such transmitters is additive to each other and is received and amplified by the satellite's receive (uplink) antenna gain. Fig. 2 shows the typical Sirius XM satellite receive antenna coverage and directionality. The antenna coverage includes most of the United States and adjacent portions of Canada, Mexico and the Caribbean. Any interfering flux density from in-band earth-based transmitters throughout this area of the earth will be amplified by the satellite receive antenna by a factor of approximately 800 (29 dBi).
5. Existing in-band interference There are several terrestrial services currently sharing the 7 GHz uplink band in the United States. They are the Fixed Service (FS) microwave links, television Broadcast Auxiliary Service (BAS), Cable Television Relay Service (CARS) and Local Television Transmission Service (LTTS). Generally the transmitters are not high powered and use directive antennas. The FS has approximately 100,000 transmitters in the 5.913–7.125 GHz band and plans to increase the number of transmitters [3]. Sirius XM satellite radio's licensed uplink frequencies are contained within 7025–7075 GHz bands. The resulting aggregate uplink interference from these sharing services is tolerable as later discussed. 6. Proposed new terrestrial uplink interferers There have been filings at the USA Federal Communications Commission (FCC) to authorize unlicensed Radio Local Area Network (RLAN) devices in the radio frequency region including the subject 7 GHz satellite uplink band [4]. The proponents provided an engineering study by RKF Engineering LLC which purported to show the RLANs would not interfere with the subject 7 GHz uplinks. Table 1 shows an interference analysis of the RKF study. The study estimates 958 million RLAN devices by 2025 of both indoor and outdoor types. For simplicity, the analysis modeled the outdoor RLANs as a 1-W transmitter of a 20 MHz wide Wi-Fi signal feeding an omnidirectional antenna. The analysis uses the RKF harmful interference to satellite noise floor ratio criterion of −21.9 dB. Based on estimates of other parties, such as the CEPT ECC report dealing with a similar proposed European wide system, one can assume a 5.3% outdoor use factor and 0.4% usage activity rate for the proposed RLAN devices.1 This would result in 2,623 simultaneous active outdoor
4. Types of interference 4.1. In-band interference Any transmitter at in-band frequencies within view of the satellite is an interferer. Even if an individual transmitter causes low interference, if there are sufficient number of them, the aggregate can create a harmful interference level. An illustration of this is provided subsequently. Currently all known in-band interferers are terrestrial. Most potentially interfering terrestrial transmitters at 7 GHz can use directive antennas pointed towards the horizon on the earth surface. If the antennas are directed at or near the geostationary arc where the satellite is located, a high interference flux density will result. If the terrestrial antennas are not pointed there, the magnitude of the interfering flux
1 RKF presumed a low 2% outdoor use factor and 0.04% usage activity rate that would not be realistic and cannot be supported with future internet and application growth projections.
414
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
Fig. 2. Typical SXM satellite uplink receive antenna pattern. Table 1 Calculation of interference levels to SDARS uplinks from projected RLAN transmissions. #
Parameter
Value
Calculation
1 2 3 4
Tolerable carrier power at SDARS satellite receiver Thermal noise power at SDARS satellite receiver Tolerable RLAN interference to noise ratio RLAN interference at SDARS satellite receiver
−117.4 dBW −132.5 dBW −21.9 dB −154.4 dBW
5 6 7
SDARS satellite uplink receive antenna gain Uplink path loss Aggregate RLAN interference at ground level
8 9
Aggregate RLAN interference ground power density Single RLAN interferer power level density
29.0 dBi 201.2 dB 17.8 dBW, or 60.4 W −48.7 dBW/Hz −73.0 dBW/Hz
Satellite manufacturer specification Calculated per satellite manufacturer specification RKF claimed maximum interference threshold [2] + [3] No interference from FS, BAS, CARS or LTTS considered Satellite manufacturer specification Geostationary SDARS satellite path loss to earth surface [4,5] + [6]
10 11
Number of RLAN devices to reach the tolerable aggregate interference level Estimated number of RLAN transmitters operating within the SDARS band
268 2,623
12
Exceedance level of RKF-proposed interference Ratio
9.8 dB
a b
1200 MHz: total proposed 6 GHz bandwith allocation for RLAN devices. 15.5 MHz: spectrum fully effecting the 4.5 MHz SDARS uplink band from 20 MHz RLAN emissions.
transmitters in North America out of the total RFK projected 958 million RLAN devices projected in the early to mid-time frame.2 The analysis result shows the interference into the satellite uplink from the proposed RLAN system would exceed RKF's proposed harmful 2
[7] - 10*log10(4.5 MHz) 10*log10(1 W/20 MHz) For an example WiFi device emitting 1 Watt power in 20 MHz bandwidth 10^(([8] - [9])/10) 958 M total users *(15.5MHz/1200 MHz)*0.4% *5.3% 0.4%: Activity rate 5.3%: Outdoor rate Seea for 1200 MHz Seeb for 15.5 MHz 10*log([11]/[10])
interference criterion by an order of magnitude (9.8 dB or ∼10 times the number of devices) very harmfully impacting SDARS. It is also noted that the RKF study did not account for the existing or other potential future uplink interference previously described which would further increase the excessive and harmful interference levels.
Not including any additional interference from such indoor transmitters. 415
Acta Astronautica 166 (2020) 413–416
R. Briskman and R. Akturan
7. Real life interference
that the C/Nup does not significantly increase C/Ntotal. Therefore, it would be reasonable to assign C/Nup no more than a sixth (i.e., 1%) of the total allowed interference criterion for the aggregate uplink interference since there are multiple individual interferers that the satellite system has to deal with. Although increase in the noise floor by interference is a good criterion, it is noted that there may also be C/Ntotal and signal availability impact requirements. In the model system herein, the C/Ntotal must be sufficient to overcome foliage attenuation [6] and, in some communications/broadcast systems operating at higher radio frequencies than the model, to overcome rain attenuation.
It is important to note that, while the above RLAN is currently hypothetical, uplink satellite interference occurs. A communications satellite operator offering Mobile Satellite Service (MSS), Globalstar, Inc. has experienced substantial satellite uplink interference [5]. The uplink satellite radio frequency band in this case is 5150–5250 MHz. Several years ago, the FCC authorized unlicensed use in this frequency band of devices similar to RLANs called U-Nll with restriction to indoor use. A few years ago, over the potential uplink interference arguments of Globalstar, the FCC authorized their outdoor use. As detailed in Ref. [5], Globalstar has recently measured an increase in the noise floor level of its satellite uplink receiver over the United States of 2 dB during the day and 1 dB at night.
9. Conclusions Significant interference into uplinks of broadcast and communications satellites must be avoided. Although limited sharing of the frequency bands used by these satellites with other services is possible, such sharing cases must be limited in the total tolerable amount of interfering power it causes as seen by the satellite's receiving antenna to keep within the system's aggregate interference tolerance requirement.
8. Interference criteria A universally agreed interference criterion is the ITU one specifying a rise in the noise floor by interference of more than 6% called Delta T/ T where Delta T is the rise in the noise floor and T is the total receiving system noise temperature including aggregate interference from all types of interferers. This is generally measured at the satellite downlink user receiver. It includes all transmission interference such as in-band uplink and downlink, adjacent channel and intermodulation products. As earlier stated in this paper, the C/Nup is automatically combined with the C/Ndown for satellite repeaters of transmissions (reflecting the design of most communications/broadcast satellites) which results in C/Ntotal. C/Ndown is generally interference critical so a high interference allowance is desirable. For the model system of this paper, the downlink is to subscriber mobile terminals of high sensitivity (terminal receiver noise temperatures of 80 deg. Kelvin) and there is a need to provide subscriber signal availability at least 99.9% of the time. The model system must also cope with other ground-based interference from the Wireless Communications Service (WCS) in both adjacent downlink radio frequency bands. Also, as previously mentioned, the system link budget design in most communications/broadcast satellites is done so
Acknowledgements The authors thank the many members of the Sirius XM Engineering Division who contributed to this paper. References [1] R. Akturan, An overview of the Sirius satellite radio system, Int. J. Satell. Commun. Netw. 26 (5) (2008). [2] ITU IFIC 2849, 2864. [3] AT&T Letter from Stacey Black to Marlene H. Dortch of the FCC, March 19, 2018. [4] Frequency Sharing for Radio Local Area Networks in the 6 GHz Band, prepared by RKF Engineering Services LLC, GN Docket No. 17-183, filed Jan. 25 2018. [5] Globalstar Inc, Petition for Notice of Inquiry, RM-11808, (May 21 2018). [6] Dr.J. Goldhirsh, Dr.W. Vogel, Propagation Effects for Land Mobile Satellite Systems: Overview of Experimental Modeling Results vol. 1274, NASA Reference Publication, 1992.
416