Source: http://www.patentgenius.com/patent/8655270.html
Timestamp: 2018-10-17 12:57:30
Document Index: 745965506

Matched Legal Cases: ['Application No. 09734884', 'Application No. 09734930', 'Application No. 08737942', 'Application No. 08737942', 'Application No. 08737942', 'Application No. 2', 'Application No. 10', 'Application No. 208816', 'Application No. 10', 'Application No. 08737942', 'Application No. 208817']

Method and apparatus for compensation for weather-based attenuation in a satellite link - Patent # 8655270 - PatentGenius
8655270 Method and apparatus for compensation for weather-based attenuation in a satellite link
U.S. Class: 455/13.4; 455/127.1; 455/127.5; 455/177.1; 455/200.1; 455/266; 455/452.2; 455/522; 455/574
Foreign Patent Documents: 1137198; 1906578; WO 2005/027373; WO 2008/129509; WO 2009/130700; WO 2009/130701
Other References: Official Action Dated Mar. 14, 2011 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/081,850. cited by applicant.
Response Dated Feb. 13, 2011 to International Search Report and the Written Opinion of Aug. 4, 2009 From the International Searching Authority Re.: Application No. PCT/IL2009/000440. cited by applicant.
International Preliminary Report on Patentability Dated Nov. 4, 2010 From International Bureau of WIPO Re. PCT/IL2009/000439. cited by applicant.
International Preliminary Report on Patentability Dated Nov. 4, 2010 From the International Bureau of WIPO Re. Application No. PCT/IL2009/000440. cited by applicant.
Communication Pursuant to Article 94(3) EPC Dated Jun. 4, 2012 From the European Patent Office Re. Application No. 09734884.1. cited by applicant.
Communication Pursuant to Article 94(3) EPC Dated Jun. 4, 2012 From the European Patent Office Re. Application No. 09734930.2. cited by applicant.
Response Dated Jun. 14, 2011 to Official Action of Mar. 14, 2011 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/081,850. cited by applicant.
Notice of Allowance Dated Jul. 20, 2011 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/081,850. cited by applicant.
Communication Pursuant to Article 94(3) EPC Dated Apr. 14, 2010 From the European Patent Office Re. Application No. 08737942.6. cited by applicant.
International Preliminary Report on Patentability Dated Nov. 5, 2009 From the International Bureau of WIPO Re.: Application No. PCT/IB2008/051537. cited by applicant.
International Search Report Dated Sep. 2, 2009 From the International Searching Authority Re.: Application No. PCT/IL2009/000439. cited by applicant.
International Search Report Dated Aug. 4, 2009 From the International Searching Authority Re.: Application No. PCT/IL2009/000440. cited by applicant.
International Search Report Dated Sep. 4, 2008 From the International Searching Authority Re.: Application No. PCT/IB2008/051537. cited by applicant.
Response Dated Aug. 11, 2010 to Communication Pursuant to Article 94(3) EPC of Apr. 14, 2010 From the European Patent Office Re. Application No. 08737942.6. cited by applicant.
Written Opinion Dated Sep. 2, 2009 From the International Searching Authority Re.: Application No. PCT/IL2009/000439. cited by applicant.
Written Opinion Dated Aug. 4, 2009 From the International Searching Authority Re.: Application No. PCT/IL2009/000440. cited by applicant.
Written Opinion Dated Sep. 4, 2008 From the International Searching Authority Re.: Application No. PCT/IB2008/051537. cited by applicant.
Alberty et al. "Adaptive Coding and Modulation for the DVB-S2 Standard Interactive Applications: Capacity Assessment and Key System Issues", IEEE Wireless Communications, XP011191780, 14(4): 61-69, Aug. 1, 2007. p. 61-62. cited by applicant.
ETSI "Digital Video Broadcasting (DVB). User Guidelines for the Second Generation System for Broadcasting, Interactive Services. News Gathering and Other Broadband Satellite Applications (DVB-S2); ETSI TR 102 376", ETSI Standards, Technical Report,XP014027139, BC(V1.1.1): 1-104, Feb. 1, 2005. cited by applicant.
ETSI "Digital Video Broadcasting (DVB); Second Generation Framing Structure, Channel Coding and Modulation Systems for Broadcasting, Interactive Services, News Gathering and Other Broadband Satellite Applications", European Broadcasting Union, ETSIStandards, XP014034070, ETSI EN 302 307, BC(V1.1.2), 2006. .sctn. [5.5.2.2], [OH.4], Figs.H.5, H.7, H.8. cited by applicant.
Maral et al. "Satelllite Communications Systems", STI, 1986. cited by applicant.
Maurutschek et al. "DiffServ-Based Service-Specific VCM in DVB-S2", 16th IST Mobile and Wireless Communications Summit, 2007 IEEE, XP031132465, p. 1-5, Jul. 1, 2007. .sctn. [0III], [00IV], Figs.1, 3, 4, Tables II, V. cited by applicant.
Morello et al. "DVB-S2: The Second Generation Standard for Satellite Broad-Band Services", Proceedings of the IEEE, 94(1): 210-227, Jan. 2006. cited by applicant.
Saam et al. "Uplink Power Control Technique for VSAT Networks", Energy and Information Technologies in the Southeast, Proceedings of the Southeast Conference, Southeastcon '89, IEEE, XP00007682, 1(of 3) 96-100, Apr. 9, 1989. cited by applicant.
Maurutschek et al. "DiffServ-Based Service-Specific VCM in DVB-S2", 16th IST Mobile and Wireless Communications Summit, 2007 IEEE, XP031132465, p .1-5, Jul. 1, 2007. .sctn. [0III], [00IV], Figs.1, 3, 4, Tables II, V. cited by applicant.
Communication Pursuant to Article 94(3) EPC Dated Nov. 23, 2011 From the European Patent Office Re. Application No. 08737942.6. cited by applicant.
Notice of Allowance Dated Sep. 15, 2011 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/081,850. cited by applicant.
Official Action Dated Jul. 5, 2013 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/920,619. cited by applicant.
Requisition by Examiner Dated Jun. 4, 2013 From the Canadian Intellectual Property Office Re. Application No. 2,684,854. cited by applicant.
Translation of Notice of the Reason for Rejection Dated May 8, 2013 From the Korean Intellectual Property Office Re. Application No. 10-2009-7024239. cited by applicant.
Official Action Dated Feb. 26, 2013 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/920,619. cited by applicant.
Office Action Dated Jul. 22, 2013 From the Israel Patent Office Re. Application No. 208816 and Its Translation Into English. cited by applicant.
Translation of Notice of the Reason for Rejection Dated Sep. 5, 2013 From the Korean Intellectual Property Office Re. Application No. 10-2009-7024239. cited by applicant.
Communication Pursuant to Article 94(3) EPC Dated Oct. 30, 2013 From the European Patent Office Re. Application No. 08737942.6. cited by applicant.
Notice of Allowance Dated Nov. 25, 2013 From the US Patent and Trademark Office Re. U.S. Appl. No. 12/920,619. cited by applicant.
Office Action Dated Dec. 4, 2013 From the Israel Patent Office Re. Application No. 208817 and Its Translation Into English. cited by applicant.
Abstract: Method for managing power and bandwidth resources in operation over a plurality of links from a hub, said power and bandwidth resources being limited, the method comprising: initially assigning power and bandwidth combinations to individual links according to current conditions pertaining to respective links, each combination having a corresponding resource cost; and controllably changing said initially assigned combinations at respective ones of said links to reduce respective resource costs, thereby to controllably balance an overall resource cost of said plurality of links to lie within available overall power and bandwidth resource limitations.
1. Apparatus for managing resources of a communication hub providing communication links, the apparatus comprising: a link manager configured for initially assigningpower and bandwidth combinations to individual links according to current conditions pertaining to respective links, each power and bandwidth combination having a corresponding resource cost in said communication hub; a controller, configured to receiverequests from respective ones of said links and to determine if said requests are allowable, each of said requests having a corresponding resource cost; and a resource optimizer associated with said link manager and said controller, configured to changea respective power and bandwidth combination of a requesting link in accordance with at least one of said allowed requests, and for controllably selecting alternative combinations at selected others of said links so as to adjust resource usage in view ofsaid changed combination, thereby to controllably balance respective resource usage of said plurality of links such that an overall resource cost in said communication hub lies within available overall power and bandwidth resource limitations, wherein arequest comprises a request to change MODCOD, and wherein said balancing comprises selecting among a set of MODCODs, each of said MODCODs having a respective assigned ratio of inbound traffic, such that a total of said inbound traffic remains within saidassigned ratios, said MODCODs being ordered from high to low, wherein higher MODCODs of said set consume more power equivalent bandwidth (PEB) than bandwidth, while lower MODCODs of said set consume more bandwidth than PEB.
2. The apparatus of claim 1, wherein the hub is a satellite hub and the plurality of links are to ground stations.
3. The apparatus of claim 1, wherein the conditions comprise atmospheric conditions.
4. The apparatus of claim 1, wherein said initially assigning power bandwidth combinations further comprises maintaining information rate in the presence of available power resource costs through managing at least one member of the groupcomprising power control, Transmission Rate Control (TRC) and ACM.
5. The apparatus of claim 4, wherein the information rate is a committed information rate (CIR).
6. The apparatus of claim 4, wherein the information rate is an actual information rate.
7. The apparatus of claim 1, wherein said hub comprises a plurality of transponders and said available overall power and bandwidth resource limitations are calculated per transponder, thereby to provide balanced transponder resourceutilization.
8. The apparatus of claim 4, wherein said hub comprises a plurality of transponders and said available overall power and bandwidth resource limitations are calculated per transponder, thereby to provide balanced transponder resourceutilization.
9. The apparatus of claim 7, wherein at least one of said transponders includes a forward link and a corresponding return link, such that said balancing is between respectively corresponding forward and return links.
10. The apparatus of claim 9, wherein said balancing within a transponder comprises presetting an outbound link and then setting an incoming link in balance therewith.
11. Method for managing power and bandwidth resources in operation over a plurality of links from a hub, said power and bandwidth resources being limited, the method comprising: initially assigning power and bandwidth combinations to individuallinks according to current conditions pertaining to respective links, each combination having a corresponding resource cost of resources in said communication hub; receiving requests from respective links, each of said requests having a correspondingresource cost; identifying allowable ones of said requests; and changing a respective assigned combination of a requesting link in accordance with at least one of said allowable requests, and controllably changing respective assigned combinations ofothers of said links in accordance with said changed respective assigned combination so as to controllably balance respective resource usage of said plurality of links such that an overall resource cost in said communication hub of said plurality oflinks lies within available overall power and bandwidth resource limitations, wherein a request comprises a request to change MODCOD, and wherein said balancing comprises selecting among a set of MODCODs, each of said MODCODs having a respective assignedratio of inbound traffic, such that a total of said inbound traffic remains within said assigned ratios, said MODCODs being ordered from high to low, wherein higher MODCODs of said set consume more power equivalent bandwidth (PEB) than bandwidth, whilelower MODCODs of said set consume more bandwidth than PEB.
12. The method of claim 11, wherein the plurality of links are to ground stations.
13. The method of claim 11, wherein the conditions comprise atmospheric conditions.
14. The method of claim 11, wherein said initially assigning power bandwidth combinations further comprises maintaining information rate (CIR) with available power resources by balancing through at least one member of the group comprising powercontrol, transmission Rate Control (TRC) and ACM.
15. The method of claim 11, wherein said hub comprises a plurality of transponders and said available overall power and bandwidth resource limitations are calculated per transponder, thereby to provide balanced transponder resource utilization.
16. The method of claim 15, wherein at least one of said transponders includes a forward link and a corresponding return link, such that said balancing is between respectively corresponding forward and return links.
17. The method of claim 16, wherein said balancing within a transponder comprises presetting an outbound link and then setting an incoming link in balance therewith.
18. A communication system comprising a communication hub with limitations on power and bandwidth resources, wherein the communications hub is the center for a plurality of communication links, each link having an information rate to bemaintained; the hub comprising: a link manager configured for initially assigning a power bandwidth combination to each link at a corresponding resource cost of resources in said communication hub; a controller, configured to receive requests fromrespective ones of said links and to determine if said requests are allowable, each of said requests having a corresponding resource cost; and a resource optimizer associated with said link manager and said controller, configured to change a respectivepower and bandwidth combination of a requesting link in accordance with said allowed requests, and to balance the resource costs of respective resource usage amongst others of said plurality of links so as to adjust resource usage in view said changedcombination and of a total available resource at said hub in order to maintain respective information rates, wherein a request comprises a request to change MODCOD, and wherein said balancing comprises selecting among a set of MODCODs, each of saidMODCODs having a respective assigned ratio of inbound traffic, such that a total of said inbound traffic remains within said assigned ratios, said MODCODs being ordered from high to low, wherein higher MODCODs of said set consume more power equivalentbandwidth (PEB) than bandwidth, while lower MODCODs of said set consume more bandwidth than PEB.
19. The apparatus of claim 2, wherein said requests originate from respective ground stations.
20. The method of claim 11, wherein at least one of said links operates with a respective fixed assigned bandwidth, said fixed-bandwidth links cooperatively releasing unnecessary power, said releasing comprising: reducing a fixed-bandwidthlink's respective MODCOD to a minimum enabling actual traffic within said link's respective assigned bandwidth; reducing said fixed-bandwidth link's respective assigned power to a minimum possible level for said reduced MODCOD; and freeing unused powerfor usage by other links.
21. The method of claim 20, wherein said releasing is in accordance with at least one of climate changes and varying traffic loads.
22. The apparatus of claim 1, wherein said adjusting is further in view of respective traffic loads of said links.
23. The apparatus of claim 1, wherein at least one of said links operates with a respective fixed assigned bandwidth and said resource optimizer is operable to adjust said fixed-bandwidth link's respective MODCOD so as to support a requiredtraffic load while remaining within said fixed bandwidth.
24. The apparatus of claim 1, wherein at least one of said links operates with a respective fixed assigned bandwidth and said resource optimizer is operable to increase said fixed-bandwidth link's MODCOD when a respective traffic load increasesand to reduce said fixed-bandwidth link's MODCOD when said traffic load decreases, so as to support a required traffic load while remaining within said fixed bandwidth.
25. The system of claim 18, said optimizer carrying out said balancing by managing at least one member of the group comprising power control, Transmission Rate Control (TRC) and ACM.
The present invention relates to a system for compensation for weather-based attenuation in a satellite link and, more particularly, but not exclusively to such compensation wherein a range of modulation levels can be selected. The presentmethods can be used in either one direction, that is forward or return links, or in both directions (forward and return links).
Weather can cause attenuation to the signal on a satellite communication link. Furthermore the ground to satellite leg may experience different weather conditions from the satellite to ground leg. Furthermore, in a broadcast system, differentsatellite to ground legs may experience different weather conditions, so that the overall attenuation in the link may not only change rapidly but may differ between different receiving stations at the same instant.
A number of solutions have been used in the past. One popular solution involves designing the satellite communication system at the outset for the worst case weather conditions. Such a solution is particularly wasteful of power although itrarely fails. Another solution involves using climatology to estimate weather parameters of concern, and then setting the transmission power for the estimated conditions. Further solutions use empirical models based on climatological data and longbaseline observations of signal strength to model RF attenuation and compensate accordingly.
A recent proposal involves operating the link based on expected daily weather conditions for the specific geographical region in which the link operates. However even in this case transmission power is wasted since the system operates on thebasis of the worst case within the time and geographical frame of the estimate.
It is known to provide automatic uplink power control (AUPC), that is, adjusting the output power on the uplink, with the general aim of maintaining a constant signal to noise ratio at the remote end. This is however inexact as the control overthe downlink is indirect.
Adaptive coding and modulation (ACM) is known to keep the SNR of the channel constant in the face of changing noise levels. The modulation pattern is changed between a high capacity modulation at low noise and a low capacity but highly robustmodulation when the noise increases.
However attempts to dynamically change the modulation based on the requirements of the system as a whole lead to problems with individual links. Likewise attempts to dynamically change individual links lead to imbalances in the system as awhole.
Thomas J. Saam, "Uplink Power Control Technique for VSAT Networks", in Proceedings of Souteastcon 89, pp. 96-101, April 1989.
Thomas J. Saam, "Uplink power control mechanism for maintaining constant output power from satellite transponder", U.S. Pat. No. 4,941,199, Filed Apr. 6, 1989.
Lawrence W. Krebs et al., "Methods and Apparatus For Mitigating Rain Fading Over Satcom Links Via Information Throughput Adaptation, U.S. Pat. No. 7,174,179, Filed Feb. 6, 2007.
ETSI EN 302 307 V1.1.1 (2004-01):"Digital Video Broadcasting (DVB) Second generation framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications".
Alberto Morello, Vittoria Mignone, "DVB-S2: The Second Generation Standard for Satellite Broad-band Services", Proceedings of the IEEE, vol. 94, no. 1, pp. 210-227, January 2006
The changing levels of attenuation in the system can be compensated for dynamically by changing the modulation level in the link between the hub and the end user. However over the system as a whole rules are set to ensure that the hub remainswithin its resources.
The present embodiments provide what may be termed a multi-ACM controller to balance resource usage between links in view of the overall resources available in the hub.
The current art carries out mobilization of bandwidth in a process known as bandwidth on demand (BOD) and this is provided within an overall bandwidth limitation. The present embodiments carry out a wider mobilization of resources withinoverall power and bandwidth limitations.
According to a first aspect of the present invention there is provided apparatus for managing resources of a communication hub providing communication links, the apparatus comprising:
a link manager configured for initially assigning power and bandwidth combinations to individual links according to current conditions pertaining to respective links, each power and bandwidth combination having a corresponding resource cost; and
a resource optimizer configured for controllably selecting alternative combinations at selected ones of the links to reduce resource usage in view of usage of resources at others of the links, thereby to controllably balance the plurality oflinks such that an overall resource costs lies within available overall power and bandwidth resource limitations.
In an embodiment, the hub is a satellite hub and the plurality of links are to ground stations.
In an embodiment, the conditions comprise atmospheric conditions.
In an embodiment, the initially assigning power bandwidth combinations further comprises maintaining information rate in the presence of available power resource costs through managing at least one member of the group comprising power control,Transmission Rate Control (TRC) and ACM.
In an embodiment, the information rate is a committed information rate (CIR).
In an embodiment, the information rate is an actual information rate.
In an embodiment, the hub comprises a plurality of transponders and the available overall power and bandwidth resource limitations are calculated per transponder, thereby to provide balanced transponder resource utilization.
In an embodiment, at least one of the transponders includes a forward link and a corresponding return link, such that the balancing is between respectively corresponding forward and return links.
In an embodiment, the balancing within a transponder comprises presetting an outbound link and then setting an incoming link in balance therewith.
In an embodiment, the balancing comprises selecting among a set of MODCODs ordered from high to low, for the return links, wherein higher MODCODs of the set consume more power equivalent bandwidth (PEB) than bandwidth, while lower MODCODs of theset consume more bandwidth than PEB.
According to a second aspect of the present invention there is provided a method for managing power and bandwidth resources in operation over a plurality of links from a hub, the power and bandwidth resources being limited, the methodcomprising:
initially assigning power and bandwidth combinations to individual links according to current conditions pertaining to respective links, each combination having a corresponding resource cost; and
controllably changing the initially assigned combinations at respective ones of the links to reduce respective resource costs, thereby to controllably balance an overall resource cost of the plurality of links to lie within available overallpower and bandwidth resource limitations.
According to a third aspect of the present invention there is provided a communication system comprising a communication hub with limitations on power and bandwidth resources, wherein the communications hub is the center for a plurality ofcommunication links, each link having an information rate to be maintained; the hub comprising:
a link manager configured for initially assigning a power bandwidth combination to each link at a corresponding resource cost; and
a resource optimizer to balance the resource costs amongst the plurality of links in the presence of a total available resource at the hub in order to maintain respective information rates, the optimizer carrying out the balancing by managing atleast one member of the group comprising power control, Transmission Rate Control (TRC) and ACM.
Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalentto those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.
Implementation of the method and/or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment ofembodiments of the method and/or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. The description taken with the drawings makes apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In an embodiment the weather-related attenuation on the uplink, meaning the link from the originating ground station to the satellite, is measured, or more accurately estimated from a measure of the overall attenuation, and the uplink power iscontrolled accordingly to achieve a substantially constant received uplink power. In the same embodiment the weather related attenuation on the downlink, meaning the link from the satellite to the receiving station, is measured, or more accuratelyestimated from the same measurement as before, and the downlink modulation and coding parameters are modified to compensate for the attenuation and provide a substantially constant receive quality at the receiving station.
The present embodiments further modify the transmission on the link between the hub and the home, not by modifying the transmission power since this is often not possible, but rather by modifying the MODCOD, that is to say modifying themodulation so that at low attenuation (good weather) high level modulation is used to obtain a high bandwidth channel. At greater attenuations lower level modulation is used to compensate for the greater attenuation and still provide correct reception,but at the cost of bandwidth. The hub or part of the hub involved in the particular transmission however does not operate using endless MODCODS for all of its links. Rather, according to the present embodiments the total number of MODCODs in use at anygiven time is limited, and the limitation follows a scheme which looks for the best efficiency from the MODCODs chosen.
In the present embodiments, an ACM controller at the hub sends commands to the various terminals to control the transmission speed, transmission power, and MODCOD for Inbound links. The control is provided with the aim of achieving balancedresource consumption namely balancing Bandwidth and Power Equivalent Bandwidth, while taking into account the individual limitations of the terminals in terms of EIRP, the individual instantaneous traffic load, and the individual climate conditions atthe remote site of each terminal.
The estimation of the climate conditions can be based on the same measurements that are used for the Outbound link or separate measurements performed by the return links receiver at the Hub. In other words, the ACM of the hub at the return linkis concerned with balancing of resources. This contrasts with control at the terminal which has different aims and resources. At the terminal there is no issue of sharing fixed resources. The terminal's only limitation is transmission power to thesatellite. At the down link, that is to the earth station, the receiver antenna is so large that attenuation is not really an issue. The only issue for the terminal using the return link is to change the rate of transmission in accordance with theweather, and use the highest MODCOD that the weather based attenuation allows.
However from the point of view of the system, bandwidth relates to power, and the power available at the satellite is limited. Thus it is desirable to use all available power over the system as a whole but no more. Individual terminals attimes of low overall traffic may of course be assigned the highest MODCOD. However once power availability does not meet requirements a lower MODCOD is assigned even if the weather does not require it.
Also, for the system as a whole, even in the case of low traffic and good weather, the satellite may still wish to limit the user of high MODCODs, because of issues with the power equivalent bandwidth. The present embodiments provide a policyfor all users, not just those in crisis due to weather etc to assign MODCODs.
More specifically, the present embodiments involve enhancing a VSAT star network based on a single carrier time multiplexed outbound channel (e.g. DVB-S2), with combined AUPC (Automatic Uplink Power Control) and ACM (Adaptive Coding andModulation) capabilities in order to optimize satellite resources utilization. The AUPC is designed to maintain constant satellite transmitted power in all weather conditions by dynamically adapting the transmitted carrier level to the uplink rainattenuation. The ACM capability is designed to maintain constant received signal quality at each terminal by dynamically adapting the modulation and coding assigned to the packets transmitted to each terminal to the downlink rain degradation affectingthis terminal.
The following abbreviations are used throughout this specification: AUPC--Automatic Uplink Power Control ACM--Adaptive Coding and Modulation CNR--Carrier to Noise Ratio SIGL--Signal Level NBW--Noise Bandwidth HPA--High Power Amplifier LNB--LowNoise Block SCPC--Single Channel Per Carrier PEB--Power Equivalent Bandwidth
In the following description and claims, the terms adapt and compensate are used synonymously. In general the concept of compensation is used for power whereas the concept of adaptation is used for modulation and encoding. In the presentembodiments however, modification of the power and of the modulation and encoding parameters are carried out in an integrated fashion so that the two terms become synonymous.
As explained in greater detail below in relation to FIG. 1, there is provided apparatus for managing resources of a communication hub providing communication links. The apparatus comprises a link manager which initially assigns power andbandwidth combinations, to individual links according to current conditions pertaining to the particular links. The combinations may involve different ranges of bandwidth, different levels of modulation, different carriers, different MODCODS, or thelike. Each power and bandwidth combination has a corresponding resource cost in terms of resources in the communication hub. Power may be limited, as may computing resources for calculating error correction codes etc.
The initially assigned combinations may add up to more than the resources available in the hub. Thus there is additionally provided a resource optimizer, which attempts to balance resource usage between the various links. Rather than justassign resources arbitrarily or on a first come first served basis, the optimizer controllably selects alternative combinations at some of the links to reduce resource usage at these particular links in view of usage of resources at other links. Theidea is to controllably balance the plurality of links so that overall resource costs lie within available overall power and bandwidth resource limitations, but that the needs of each link are considered in the overall balancing process.
The hub may be a satellite hub and the links may be independent or dependent links, typically to ground stations. The overall system described herein is a star formation but other communications architectures are relevant as well.
The conditions at the individual links may relate to atmospheric conditions, or to load or to any other variable pertainable to links.
The task of initially assigning power bandwidth combinations may further comprise maintaining information rate in the presence of available power resource costs. Such may be achieved via managing power control, or Transmission Rate Control(TRC) or ACM.
The information rate to be maintained may be a committed information rate (CIR) or an actual information rate.
The hub may comprise separate transponders. The overall resources, including available overall power and bandwidth resource limitations may be calculated and balanced per transponder, thereby to provide balanced transponder resourceutilization.
When the hub comprises a plurality of transponders and the available overall power and bandwidth resource limitations are calculated per transponder, the result is balanced transponder resource utilization.
One or more transponders may include a forward link and a corresponding return link, such that balancing is between respectively corresponding forward and return links.
Balancing within a transponder may involve presetting an outbound link and then setting an incoming link in balance therewith.
In an embodiment, balancing comprises selecting among a set of MODCODs ordered from high to low, for the return links, wherein higher MODCODs of the set consume more power equivalent bandwidth (PEB) than bandwidth, while lower MODCODs of the setconsume more bandwidth than PEB.
The present embodiments may further comprise a method for managing power and bandwidth resources in operation over a plurality of links from a hub, the power and bandwidth resources being limited.
The method includes initially assigning power and bandwidth combinations to individual links according to current conditions on the links. As mentioned, each combination has its own resource cost.
The method further includes controllably changing the initially assigned combinations at certain links in order to reduce resource costs, thereby to controllably balance an overall resource cost of the plurality of links to lie within availableoverall power and bandwidth resource limitations.
In the case of bandwidth being fixed, so that only power can be changed, a cooperative mode may be provided in which each individual link releases unnecessary resources when traffic load reduces. Release is provided as follows:
Reduce MODCOD to minimum that enables the actual traffic within the fixed assigned bandwidth for this link, and then
reduce the power to the minimum possible level for this MODCOD. Finally free the unused power for other links.
More particularly, the individual link combination may be changed as follows. The embodiment applies to the same case as above where the bandwidth assigned to each of the multiple links is fixed. Each link may adapt its combinations not onlyto climate changes but also to varying traffic loads. When traffic load increases the link may be expected to consume more power, thereby leading to an increased level of MODCOD and power to allow more bps/Hz at the same original BW. When the trafficload reduces the link consumes correspondingly less power, thus a decrease in MODCOD and power for lower bps/Hz at the same BW. As above this releases satellite transponder power that can be used by the other links. The system controller may manage allthe requirements so that overall power and bandwidth constraints are met, and if necessary the controller forces certain individual links to use less power than they request in order to comply with the requirements and allow overall balance of thesystem.
It was noted above that the communications configurations may include star configurations. There may also be provided multiple star VSAT networks whose hubs may be located at different sites. Again bandwidth is fixed but power is variable. The networks share the same satellite resource. The controller mobilizes satellite resources as the traffic load changes, say an increase in one network and a decrease in another network, in the following way: The Outbound links are managed as in theabove paragraph as their bandwidth is fixed. Inbound links can be also managed as above but they are more flexible, namely they can have varying bandwidth. As the Inbound links can have varying bandwidth so the controller can shift bandwidth from onenetwork to another so that each network may utilize available resources according to actual traffic load. When the bandwidth dedicated for Inbound links of a network increases, the hub of this network can assign more bandwidth to the Inbound links up tothe total assigned bandwidth to all Inbound links of the multi-star network.
Reference is now made to FIG. 1 which illustrates a controlled satellite link, according to a first preferred embodiment of the present invention. A hub 10 transmits a signal to a satellite 12 over an uplink 14. The uplink encounters rain andclouds 16 which cause weather-related attenuation of the signal. It will be appreciated that weather conditions can change rapidly so that the overall attenuation of the uplink is itself liable to change rapidly.
The satellite 12 relays the signal it has received on the uplink to one or more ground-based receiving stations 18 via a downlink 20. The downlink 20 is also liable to weather based attenuation, which may be brought about by rain and clouds 22. It will be appreciated that the dynamic variation in attenuation on the downlink tends to add to any attenuation on the uplink and also tends to vary independently. It is noted that the uplink attenuation is present in all received signals since thereis only one uplink in the present embodiment, but the downlink attenuation varies.
Thus in a first embodiment of the present invention a reference unit 24 is inserted at a receiving station for measuring signal attenuation over the link. The measured attenuation is transmitted back to the hub 10 where a control unit 26,controls a link transmission parameter to dynamically compensate for changes in the measured signal attenuation. Thus as the signal attenuation increases the reference unit 24 informs the control unit, which then either strengthens the signal or makesthe coding or modulation or both more robust so that the received signal remains readable.
In FIG. 1, only a single ground-based receiving station is shown, although it will be appreciated that most satellites relay to multiple ground stations. In fact the satellite link may be a broadcast link, and there may therefore be numerousground-based receiving stations spread over a substantial region. In any event different weather conditions may apply to different receiving stations.
Reference is now made to FIG. 2, which illustrates a further embodiment of the present invention in which the link of FIG. 1 is modified to provide separate control over the uplink and the different down links. Parts shown in hashed lines maybe regarded as theoretical since the ability to make modifications to the satellite 12 is limited and practical implementations are explained below. Specifically items shown in dashed lines indicate features which one would like to include at thesatellite, but in practice this is not possible and a system of indirect measurement is discussed below. Separate reference units are provided for the uplink and all or some of the different down links. Reference unit 28 is theoretically provided atthe satellite for independent measuring of attenuation at the uplink, and control unit 26 independently compensates for uplink attenuation. Reference unit 24 measures attenuation on the downlink and control unit 30 at the satellite independentlycompensates for changes in the measured attenuation at the downlink. In practice reference unit 24 is all that is available, so that uplink attenuation is derived from the measurements at reference unit 24, as will be described in greater detailhereinbelow.
It is noted that in satellite communication there is a beacon transmitted at a different frequency with constant power towards the earth. Based on received beacon signal level the uplink attenuation can be estimated after taking into accountthe frequency difference between the beacon and the signal transmission.
In one embodiment a reference unit is provided at each receiving station and the signal to each ground-based receiving station is independently controlled. However, in the case of television or like broadcasting there may be hundreds ofthousands or even millions of receiving stations so, in an alternative embodiment, it is possible to aggregate the various downlinks on a regional basis. That is all downlinks in a certain geographical area may be compensated together based on localweather as measured at one or two of the receiving stations in the region. In an embodiment, only certain receiving stations, judiciously distributed, are used as references. Certain variations in attenuation may be dealt with by attention to theuplink alone, whereas other variations may require changes to the downlink. Stations that are reference stations may report all attenuation changes, but those stations which are not reference stations need only report if the downlink needs attention. More particularly, in order to reduce the number of interrupt signals, each individual VSAT can calculate the current downlink attenuation or an indicator for zero downlink attenuation and determine if variation that it measures in its CNR correspondsalso to downlink attenuation variation or only to uplink attenuation variation. In the latter case a VSAT, which is not a reference terminal, need not issue an interrupt with a request for MODCOD change but rather may simply wait for the AUPC tocompensate for the uplink attenuation variation.
Parameters used in transmission channels are numerous and many such parameters can be adjusted to overcome attenuation. One such parameter is transmitted power. In case of severe attenuation the transmission power can be increased. Increasedtransmission power is generally only available from the hub 10 however. The satellite has only limited power resources and thus increases in transmission power for the down link are not really practical. Other parameters that can be modified are codingand modulation parameters. The complexity or robustness of the coding and/or modulation of the signal can be adjusted to maintain received signal quality.
Reference is now made to FIG. 3, which is a simplified diagram showing an uplink 32 in which the controlled transmission parameter is transmission power. A downlink 34 is shown in which adaptive coding and modulation are provided to ensure thequality of the received signal is maintained. It will be appreciated that compensation for attenuation by modifying the coding and modulation parameters to make the coding and modulation more robust leads to a reduction in the signal rate. Thus picturequality may have to be degraded, and say high definition television HDTV quality may be lost over the duration of a bad weather episode. However as long as the degradation is restricted to the bad weather episode due to dynamic measuring of the signalthen the disruption to the customer is minimized. Alternatively, if the satellite beam covers a large territory with many regions of independent climatic conditions, the throughput of a site can be maintained even in varying rain conditions andaccordingly varying modulation and coding parameters. The network design may take into account a distribution of modulation and coding parameters according to climate statistics over the region. When a specific site uses more robust parameters it doesnot have to reduce throughput but it can consume a larger fraction of the total carrier, while other sites may use less robust parameters at the same time and therefore consume a smaller fraction of the carrier. For a large network the actual aggregatedthroughput may be similar to the calculated average throughput with very small variance.
Reference is now made to FIG. 4, which shows in greater detail how the invention may be applied in practice to a broadcast type satellite link with a single hub and multiple receiving stations in which modifications to the satellite are notpossible. In FIG. 4 hub 10 broadcasts to satellite 12 which relays the signal to ground-based receiving stations 18.1 . . . 18.n. Each ground-based receiving station has different weather conditions. The SNR at each receiving station is measured by ameasurement unit 24.1 . . . 24.n. The measurements are then fed via return links, which are typically satellite links or ground links 38, say ADSL over a telephone network, to AUPC and ACM controller 40. The AUPC and ACM controller then interacts withACM modulator 42 and both the controller 40 and modulator 42 interact with traffic shaper 44 to modify the signal that is sent over the link.
Two independent measurements of SNR and received signal level are performed by a reference ground station or alternatively measurements of forward link and return link SNR of a reference ground station. The two measurements are consideredtogether and enable estimations of the uplink and the downlink attenuation separately. Thus the inability to measure at the satellite is compensated for. The measurements from different ground stations are also considered together. Uplink attenuationcan be used to average the uplink result and downlink attenuation is attributed to the different downlinks.
The present embodiments provide for coordination between the mechanisms that compensate for uplink and downlink variations in the attenuation. Compensation for the uplink by changing the transmitted power affects the measurements performed bythe ground station and the selection of modulation and coding parameters. Thus lack of coordination may result in the repeating of transmissions of requests to change the current selection from any of the ground stations before and after uplink powercompensation, so that the ground stations ask for a change that has already been provided. Furthermore the present embodiments require time for achieving stable selection of parameters. The object of the coordination is that different parts of thenetworks are not working against each other and therefore preventing stability from being attained. Failure to coordinate may lead to a need for increased margins, namely wasting satellite resources.
The presently derived approach may also be used for other ACM capable Outbound signals and also for point-to-point SCPC (Single Channel Per Carrier) satellite links. The embodiments use communication channel measurements, to allow location andbeam independent, real time operation, of the combined AUPC and ACM processes. The channel measurements are used for estimating dependent or independent uplink and downlink rain attenuation and degradation. These estimations are then used for makingthe decisions on the compensations required in the uplink and in the downlink.
As will be explained in greater detail below, several principle implementations are discussed. A first implementation, hereinafter Case I, involves a reference terminal installed at the teleport. A second implementation, Case II involvesreference terminals anywhere, namely either at the teleport or other locations in the same beam, or at other locations in a different beam. A third implementation, Case III involves a return link via the satellite. This contrasts with FIG. 4 above,where the return link was terrestrial. In case III the return link provides measurements that are used together with forward link measurements for estimating the uplink and downlink attenuation. In case II the return link can be either via satellite orterrestrial and is used for forwarding the measurements made by the ground station relating to the link from the ground station to the hub.
The present embodiments may be used for AUPC only, for example where ACM is not supported by terminals or not activated. Alternatively the embodiments may be used for ACM only, for example where a beacon receiver is used for uplink powercontrol, or uplink is transmitted via C band beam, or the transponder operates at ALC--Automatic Level Control mode. As a further alternative the embodiments may involve combined AUPC and ACM operating together to achieve optimal utilization oftransponder resources.
The present embodiments provide a controller that compensates in real time for independent atmospheric and other variations in both uplink and downlink of a satellite communications link. Such a link may be either the multiplexed Outboundcarrier of a star VSAT network, or a point-to-point SCPC satellite link. The compensation is performed for the uplink by controlling the transmitted power in order to maintain constant satellite transmitted power at all weather conditions. For thedownlink the compensation is based on assigning appropriate modulation constellation and code rate which can provide the maximal throughput for the actual weather conditions. The controller algorithm uses channel measurements performed by the receivingstations that are sent back to the controller. The receiving stations are standard stations that provide service and can be anywhere, under any beam of the satellite. Measurements performed by several or all stations can be used for improving thechannel estimations. The uplink control is designed to maintain constant satellite transmitted power at all weather conditions by adapting the transmitted carrier level to the uplink rain attenuation. The adaptation of coding and modulation is designedto maintain constant received signal quality at each terminal according to the downlink rain degradation affecting this terminal. The adjustment for each terminal is implemented by the modulator by transmitting, using time-division multiplexing, asequence of frames, where the coding and modulation format may change frame-by-frame. Each frame may carry traffic to terminals that expect the coding and modulation levels assigned to that frame.
The uplink and down link adaptation are based on the same channel measurements. The present embodiments may separate the effects of the uplink and down link as reflected from the channel measurements performed by the receiving stations. As theuplink control influences the downlink performance, the present embodiments perform combined control of uplink and downlink by deducting the effect of the uplink control from the current channel measurements in order to allow for computing the downlinkcontrol stage using the same current measurements. Such a technique reduces the control cycle time and the number of modulation and coding corrections as there is no need to wait for the next updated measurements that would be affected by the uplinkupdate for correctly updating the downlink modulation and coding.
The above approach avoids repeating transmissions from all ground stations requesting to change selection of modulation and coding before and after uplink power modification, and saves time for achieving stable selection. Consequently smallermargins are required and satellite resources are saved.
The channel estimations produced by the above process, namely uplink and down link attenuations can be used, after appropriate correction according to up/down frequency ratios, to additionally control the return links of a star VSAT network (orthe return link of the SCPC link). The controller instructs each VSAT to increase/decrease its power level in order to compensate for changes in the estimates of the Return link uplink attenuation. If the VSAT EIRP is already fully exploited and theuplink rain-linked fading is not fully compensated, then compensation may be achieved by a reduction in transmission rate and/or modulation and coding, and the spare power may then be assigned to other more powerful VSATs, so that the total powerconsumed from any transponder is maintained at a constant level. The controller may also instruct a modification of the transmission rate, modulation and coding in order to compensate the changes in downlink rain attenuation. Compensation may be basedon either the already estimated downlink rain degradation or the measured return link signal to noise ratio. Compensation should be after deduction of the uplink power compensation.
Another consideration that may be taken into account by the controller is to achieve balanced resource utilization, namely appropriate selection of modulation codes or MODCODs for the return links. That is to say the controller may wish tobalance the consumed power and bandwidth resources from a transponder which contains the return links with or without the Outbound link. Balancing is based on having a selection of a few MODCODs for the return links where the higher MODCODs consume morepower equivalent bandwidth (PEB) than bandwidth, while the lower MODCODs consume more bandwidth than PEB. In the case that the Outbound link is in the same transponder it might be more efficient to make the Outbound unbalanced, to allow a higherOutbound MODCOD, and to balance it with appropriate selection of MODCODs for the return links residing in the same transponder. In the case of a band (or full transponder) assigned only for return links the controller may assign MODCODs according totraffic requirements, weather conditions, satellite coverage, and balancing requirements so that overall balancing may be achieved. Such operation of the controller enables to use all available resources in an efficient way. FIG. 6 is a graph showingthe result of such balancing. The controller takes into account that generally the return links are sensitive mainly to uplink fading and not to downlink fading as the CNR in the downlink is generally much larger that in the uplink due to the use of alarge teleport antenna. Therefore in the design of the balanced operation the assignment of MODCODs is mainly according to overall network traffic in the return links that may be delivered with specific MODCOD. The controller uses ACM and TRC(Transmission Rate Control) to compensate for the limitation of the remote terminal in terms of EIRP for severe rain conditions at the terminal site and for increasing the transmission rate beyond the committed rate to best effort based rates. Such aconcept not only optimizes the satellite transponder resources utilization but also allows minimizing of the required EIRP of the terminals and a reduction in their cost.
The concept is applicable to any form of modulation that the return channel may use. In particular it is applicable for both FDMA and TDMA type return channels, where for TDMA the terminals may have to be moved among carriers with differentMODCODs or instantaneous transmission rate when the controller decides to change their MODCOD or their instantaneous transmission rate. In some TDMA implementations the MODCOD can be changed in the same carrier. The controller algorithm is as followsfor three active MODCODs, but can be extended to any number of MODCODs: 1. Design in advance the ratios of overall network Inbound traffic that may use High MODCOD, Medium MODCOD, and Low MODCOD respectively to achieve balanced resource consumption. Balance should be in terms of bandwidth and PEB in the frequency band assigned to all the network carriers within given a transponder, and may include the presence of an unbalanced Outbound carrier in the same transponder, or may not. 2. Assign theHigh MODCOD to all terminals with low data rates and good climate conditions until the maximum aggregated traffic allowed to work in such MODCOD is reached, according to the designed balance. 3. Assign Medium MODCOD to the rest of the terminals. Theseare terminals which can survive at this time with the High MODCOD, but are not far from exhausting their EIRP, add those terminals where the CNR is such that they cannot use the High MODCOD and thus could not otherwise deliver the actual requiredtransmission rate in their climate conditions. Add also those terminals which can survive at this time with a higher MODCOD, but are not far from exhausting their EIRP, until the designed aggregated traffic for this MODCOD is reached. 4. Assign LowMODCOD to the rest of the terminals. 5. When traffic requirements or climate conditions change the controller may change the assignments accordingly to maintain the designed ratio for balanced resources consumption, while taking into account theterminal limitations in terms of EIRP. At the individual control stage the terminal tries to maintain committed information rate (CIR) with its available EIRP resources through power control, TRC (transmission Rate Control) and ACM. When rain fadingstarts the VSAT initially requests increasing its power. If all VSAT EIRP is exploited, and it is above CIR, and still need more power to achieve the desired Eb/No for its current MODCOD, it will reduce data rate down to CIR, and then if furthercompensation is required it will reduce the MODCOD. Power adjustment is performed per all changes in data rate or MODCOD for achieving the desired Eb/No for such MODCOD. Further compensation can be done by further reduction of data rate below CIR, inorder to maintain the link rather than let it to break, thus increasing availability significantly beyond the required availability, though with data rates below CIR. Generally the design supports CIR for the required availability with a certain MODCOD. When the rain fading decreases, if the data rate is below CR and it requests to increase data rate, the controller will increase its data rate (TRC) until it reaches CR and if there is still available EIRP to support a jump due to changing MODCOD, theMODCOD will be increased for saving bandwidth. If there is still available power the controller can either increase again the MODCOD or allow increasing the data rate above CIR based on best effort. After the individual stage where each VSAT adapts itspower, data rate, and MODCOD to the traffic requirements, and actual rain conditions, the controller performs the system wise adjustments of MODCOD assignments in order to achieve balanced transponder resources utilization. At this stage VSATs thatcould use high MODCOD may be switched to a lower one for the purpose of balancing. Based on this higher level decision on MODCOD the VSAT then adjusts it power accordingly to achieve the desired Eb/No level. It might occur that an individual request tochange MODCOD is allowed by the controller, since this is the only way to support CR in requested availability, but then the controller will command one or few other VSATs to change their MODCODs in order to maintain balance.
We define the following parameters: BW=Bandwidth in Hz .alpha.=Roll Off Factor COD=Code Rate of the FEC (Forward Error Correcting) Code MOD=log.sub.2( ) of modulation constellation size (e.g. 2 for QPSK, 3 for 8PSK) R.sub.s=Symbol Rate in sps(symbols per second) R.sub.b=Bit Rate in bps (bits per second), R.sub.b=R.sub.s(MODCOD) C=Carrier Power in Watts [(C) in dBW], after the receiver matched filter N=Noise Power in Watts [(N) in dBW], after the receiver matched filter NBW=Noise Bandwidth inHz N.sub.o=Noise Spectral Density in Watts/Hz, i.e. Noise Power per 1 Hz, N.sub.o=N/NBW E.sub.s=Energy per symbol in Joules, E.sub.s=C/R.sub.s E.sub.b=Energy per bit in Joules, E.sub.b=C/R.sub.b CNR=Carrier to Noise Ratio [(CNR) in dB], CNR=C/NSIGL=Received Signal Level in Watts [(SIGL) in dBW] (G/T) (dB/K) is the figure of merit of a receiving terminal L.sub.fs,dn (dB) is the free space loss between the satellite and the reference VSAT at frequency f.sub.dn (Hz) A.sub.dn (dB) is the downlinkrain attenuation A.sub.up (dB) is the uplink rain attenuation M.sub.CS (dB) required clear sky margin (CNR).sub.HMC (dB) the lower CNR threshold for the highest MODCOD (see Table 3) T.sub.antenna (K) Antenna noise temperature T.sub.LNB (K) LNB noisetemperature HMC highest MODCOD allowed for clear sky conditions
We describe the algorithm for maintaining constant satellite transmitted power EIRP.sub.sat at all weather conditions by adapting the transmitted Outbound carrier level Tx_PWL to the uplink rain attenuation A.sub.up, where a reference VSAT, withantenna diameter D.sub.ref is installed at the teleport, and the same satellite beam covers both teleport and all other VSATs in the network, so that the carrier transmitted from the teleport may be received at the teleport. In Case I the referenceterminal is installed at the uplink teleport, thus having dependent uplink and downlink rain attenuation. CNR measurements and G/T corrections are used as proposed by Thomas J. Saam, "Uplink Power Control Technique for VSAT Networks", in Proceedings ofSoutheastcon 89, pp. 96-101, April 1989, and Thomas J. Saam, "Uplink power control mechanism for maintaining constant output power from satellite transponder", U.S. Pat. No. 4,941,199, Filed Apr. 6, 1989.
where L.sub.fs,dn (dB) is the free space loss between the satellite and the reference VSAT at frequency f.sub.dn (Hz) transmitted from the satellite, A.sub.dn (dB) is the downlink rain attenuation, (G/T).sub.ref (dB/K) is the figure of merit ofthe receiving reference terminal, and k.sub.B=-228.6 dBW/HzK is the Boltzmann constant. The rain attenuation in the uplink is related to the rain attenuation in the downlink as follows: A.sub.up=K+A.sub.dn (dB) (1.2)
The relation between C/N.sub.o and E.sub.b/N.sub.o is as follows:
where R.sub.s is the symbol rate, MOD is log.sub.2( ) of the modulation constellation size, and COD is the code rate.
In the following algorithm, the term `linkbudget` refers to the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system. Itaccounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline and miscellaneous losses.
A simple link budget equation may be as follows: Received Power (dBm)=Transmitted Power (dBm)+Gains (dB)-Losses (dB) It is noted that decibels are logarithmic measurements, so adding decibels is equivalent to multiplying the actual numericratios. A more sophisticated listing of linkbudget components with exemplary measurements is given in table 1 below:
TABLE-US-00001 TABLE 1 A LinkBudget for a typical Satellite link. Tx BUC Rx Antenna BUC OBO Antenna Data Rate FEC Link Tx Location size (m) (Watt) (dB) size (m) (Kbps) Modulation FEC TYPE BER Outbound Best Teleport 9.10 400.00 18.16 1.2052000.00 6APSK 0.667 LDPC 1.- E-08 MODCOD Outbound Req. Teleport 9.10 400.00 18.16 1.20 26000.00 QPSK 0.667 LDPC 1.E- -08 Avlblty Inbound R1A VSAT 1.20 2.00 3.54 9.10 32.00 8PSK 0.889 Turbo 1.E-08 Best MODCOD Inbound R1B VSAT 1.20 2.00 7.34 9.10 32.008PSK 0.667 Turbo 1.E-08 Req. Avlblty Space Clear Sky Segment Rain Margin % Power % BW of Margin Link Tx Location (KHz) Availability (dB) of transponder transponder (dB) Outbound Best Teleport 23400.00 91.00% 2.03 71.68 65.00 2.46 MODCOD Outbound Req. Teleport 23400.00 99.70% 2.23 71.68 65.00 Avlblty Inbound R1A VSAT 14.64 99.70% 2.00 0.08 0.04 Best MODCOD Inbound R1B VSAT 19.52 99.70% 2.00 0.03 0.05 Req. Avlblty
Algorithm steps for Case I. (1) Determine from the linkbudget the highest MODCOD (denoted by HMC) allowed for clear sky conditions so that a predefined requirement for clear sky margin M.sub.CS of e.g. 1 dB is met. The required (C/N.sub.o) forclear sky conditions (C/N.sub.o).sub.cs, at the reference terminal, is calculated as follows: (C/N.sub.o).sub.cs=(CNR).sub.HMC+10log(R.sub.S)+M.sub.CS+M.sub.ref (dB Hz), where (CNR).sub.HMC is the lower CNR threshold for the highest MODCOD (see Table 3). If the diameter of the reference terminal is different from the diameter of a typical VSAT antenna in this network the difference M.sub.ref in the clear sky margin obtained should be compensated accordingly. This value can be obtained from linkbudgettool by calculating the margin for the standard antenna and for the reference antenna. (2) Make calibration at clear sky conditions and determine the Tx_PWL required to obtain the desired (C/No).sub.cs. This is the Tx_PWL.sub.cs that obtains thedesired EIRP.sub.sat at clear sky conditions. Calculate Tx_PWL.sub.max by adding the uplink rain fade as found by linkbudget tool for the desired uplink availability. Measure the resulting (C/No).sub.cs for this operating point and use the measuredvalues in all calculations rather than the linkbudget calculated value. This reduces sensitivity to fixed measurement errors. (Note that calibration can be in any MODCOD lower or equal to HMC). (3) Measure (C/No) at predefined time intervals andperform averaging over predefined number of measurements to obtain (C/No).sub.i for the i-th interval. Search the solution for uplink power control gain required at the i+1 time interval G.sub.upc,i+1 satisfying the following expression
Where typically T.sub.rain=278K, and T.sub.ref=T.sub.antenna/1.12+290*0.11+T.sub.LNB (K) [6, pp. 191-192]. This expression can be solved through numerical methods. It was found by simulation that five iterations provide good accuracy. Theiterations can be started by substituting as initial guess G.sub.upc,i in G.sub.upc,i+1, and generating through five iterations the G.sub.upc,i+1 for the receiver quality (C/No).sub.i+1. (4) The new power level will then beTx.sub.--PWL.sub.i+1=Tx.sub.--PWL.sub.cs+G.sub.upc,i+1 (dBW) (1.5)
In this Section we describe the algorithm for maintaining constant satellite transmitted power EIRP.sub.sat at all weather conditions by adapting the transmitted Outbound carrier level Tx_PWL to the uplink rain attenuation A.sub.up, where areference VSAT, with antenna diameter D.sub.ref is installed either (1) at the teleport, and the same satellite beam covers both teleport and all other VSATs in the network, or (2) at another location, and the same satellite beam covers both teleport andall other VSATs in the network, or (3) at another location, and different satellite beams cover the teleport and all other VSATs in the network.
The solution for Case II is based on using measurements performed at the reference VSAT of both CNR (Carrier to Noise Ratio) and SIGL, the received signal level. The measurements can be reported either through a return link or any othercommunication link.
Typically the CNR is measured after the received signal is filtered by a square root raised-cosine matched filter with equivalent noise bandwidth NBW=R.sub.s, where R.sub.s is the carrier symbol rate. Consequently
C/N.sub.o can be expressed as a function of CNR and the symbol rate R.sub.s
The received signal level SIGL is measured at the tuner IF input with bandwidth IFBW which is typically larger than the signal 3 dB bandwidth, Rs, in order to allow initial frequency error during acquisition stage. Consequently SIGL can beexpressed as follows: SIGL=C(1+.beta.)+N(IFBW/Rs)(Watts) (1.9)
where (1+.beta.) is the ratio between signal power before and after the matched filter.
.function..beta..times..times. ##EQU00006##
resulting in the following expression for the carrier power C as a function of the measured CNR and SIGL, the receiver filter bandwidth IFBW, and the matched filter factor (1+.beta.)
.times..beta..times..times. ##EQU00007##
(1) Determine from the linkbudget the highest MODCOD (denoted by HMC) allowed for clear sky conditions so that a predefined requirement for clear sky margin M.sub.CS of e.g. 1 dB is met. The required (C/N.sub.o) for clear sky conditions(C/N.sub.o).sub.cs, at the reference terminal, is calculated as follows: (C/N.sub.o).sub.cs=(CNR).sub.HMC+10log(R.sub.S)+M.sub.CS+M.sub.ref (dB Hz), where (CNR).sub.HMC is the lower CNR threshold for the highest MODCOD (see Table 3). If the diameter ofthe reference terminal is different from the diameter of a typical VSAT antenna in this network the difference M.sub.ref in the clear sky margin obtained should be compensated accordingly. This value can be obtained from linkbudget tool by calculatingthe margin for the standard antenna and for the reference antenna.
(2) Make calibration at clear sky conditions and determine the Tx_PWL required to obtain the desired (C/No).sub.cs. This is the Tx_PWL.sub.cs that obtains the desired EIRP.sub.sat at clear sky conditions. Calculate Tx_PWL.sub.max by adding theuplink rain fade as found by linkbudget tool for the desired uplink availability. Measure the resulting (C/No).sub.cs and (C).sub.cs for this operating point and use the measured values in all calculations rather than the linkbudget calculated value. This reduces sensitivity to fixed measurements errors. (Note that calibration can be in any MODCOD lower or equal to HMC).
(3) Measure (C/N.sub.o) and (C) at predefined time intervals and perform averaging over predefined number of measurements to obtain (C/No).sub.i+1 and (C).sub.i+1. Solve the following expression for G.sub.upc,i+1, the uplink power control gainrequired at the i+1 iteration
Where typically T.sub.rain=278K, and T.sub.ref=T.sub.antenna/1.12+290*0.11+T.sub.LNB (K). All other values in this expression are in dB.
The new transmitter power level will then be Tx.sub.--PWL.sub.i+1=Tx.sub.--PWL.sub.cs+G.sub.upc,i+1 (dBW). (1.13)
(4) Optionally measurements can be performed by several reference terminals, or by all terminals, for achieving more reliable decision for the power control gain. Measurements that have large variance can be filtered out while the resultingpower control gain per terminal from the other reference terminals can be averaged. Alternatively weighted average can be used where the weights are proportional to the CNR. Therefore after Polling, that is after requesting measurements from allreference terminals, a weighted average calculation may be performed where the weights are proportional to the CNR
After Interrupt, that is after a terminal pushes its measurements when it measures a significant change between Pollings, a weighted update of the last result may be performed G.sub.upc,i+1=(1-.gamma.) G.sub.upc,i+.gamma.G.sub.upc,i+1 (dB),0<.gamma.<1 (1.15)
The last step of the algorithm is useful also for reducing the effect of reference VSAT pointing loss. The algorithm cannot distinguish between rain and variations in pointing loss. Therefore, such variations in pointing loss of the teleportantenna or the reference terminals may be interpreted erroneously as uplink rain attenuation as they do not affect the VSAT noise level. The weighted average step can reduce the VSAT pointing loss effect as the pointing loss varies independently fromVSAT to VSAT.
It is additionally noted that in order to reduce the number of interrupts, each individual VSAT can calculate the current downlink attenuation or an indicator for zero downlink attenuation and to determine if variation it measured in its CNRcorresponds also to downlink attenuation variation or only to uplink attenuation variation. In the latter case a VSAT, which is not a reference terminal, will not issue an interrupt with a request for MODCOD change but will wait for the AUPC tocompensate for the uplink attenuation variation.
The solution for Case III is based on using measurements performed at both ends of the link, e.g. at the Teleport and at the reference VSAT (or at both ends of SCPC link) of received CNR (Carrier to Noise Ratio) for both Forward and Returnlinks. The measurements can be reported either through the return link or any other communication link.
The CNR equation that is shown by (B.14) can be used for both Forward and Return links with appropriate indication of all parameters, where "F" stands for Forward link and "R" stands for Return link. For the Forward link the expression is asfollows:
The rain attenuation in the uplink is related to the rain attenuation in the downlink, with a factor K.sub.T for the teleport side and a factor K.sub.V for the VSAT side, as follows: .sub.FA.sub.up=K.sub.T+.sub.RA.sub.dn (dB) (2.18).sub.RA.sub.up=K.sub.V+.sub.FA.sub.dn (dB) (2.19)
Substituting for A.sub.dn in the above CNR equations produces the following two
These two equations can be solved with cross iterations, namely initially substituting guesses for both .sub.FA.sub.up and .sub.RA.sub.up in the first equation. N iterations are then performed for .sub.RA.sub.up, and then the result issubstituted in the second equation. Now N iterations are performed for .sub.FA.sub.up, and then the cross iterations are repeated N times. Alternatively a look up table could be used.
The ACM mechanism can be operated to compensate for both uplink and down link fades, or for downlink compensation independently, see Lawrence W. Krebs et al., "Methods and Apparatus For Mitigating Rain Fading Over Satcom Links Via InformationThroughput Adaptation", US Patent Application Publication 2003/0054816, Filed Aug. 8, 2002; ETSI EN 302 307 V1.1.1 (2004-01):"Digital Video Broadcasting (DVB) Second generation framing structure, channel coding and modulation systems for Broadcasting,Interactive Services, News Gathering and other broadband satellite applications"; and Alberto Morello, Vittoria Mignone, "DVB-S2: The Second Generation Standard for Satellite Broad-band Services", Proceedings of the IEEE, vol. 94, no. 1, pp. 210-227,January 2006. In the latter a beacon receiver is used for uplink power control, or uplink is transmitted via a C band beam, or the transponder operates at ALC--Automatic Level Control mode. The ACM mechanism can alternatively be combined with AUPC.
The present embodiments provide a combined AUPC and ACM controller designed to achieve overall optimization based on allowed usage of satellite resources. The controller algorithm uses channel measurements performed by the receiving stationsthat are sent back to the controller. The receiving stations are standard stations that provide service and can be located anywhere, under any beam of the satellite. Measurements performed by several or all stations can be used for improving the uplinkchannel estimations. The uplink control is designed to maintain constant satellite transmitted power at all weather conditions by adapting the transmitted carrier level to the uplink rain attenuation. The adaptation of coding and modulation is designedto maintain constant received signal quality at each terminal according to the downlink rain degradation affecting this terminal. The adjustment for each terminal is implemented by the modulator by transmitting, in time-division multiplex, a sequence offrames, where the coding and modulation format may change frame-by-frame. The traffic of a terminal that was assigned a specific MODOCD--see table 2 below, may be transmitted in the appropriate frame.
The uplink and down link adaptation are based on the same channel measurements. The present embodiments may separate the effects of the uplink and down link as reflected from the channel measurements performed by the receiving stations. As theuplink control influences the downlink performance, the present embodiments perform combined control of uplink and downlink by deducting the effect of the uplink control from the current channel measurements in order to allow for computing of thedownlink control stage using the same current set of measurements. This reduces the control cycle time and the number of modulation and coding corrections as there is no need to wait for the next updated measurements that would be affected by the uplinkupdate for correctly updating the downlink modulation and coding.
FIG. 4, already referred to above shows the scheme of an AUPC & ACM Management system, comprising the AUPC & ACM Controller 40, the ACM modulator 42, which includes the upconverter and the HPA--High Power Amplifier, the Earth station 10, and thesatellite 12. The satellite terminals (VSAT) 18.1 . . . 18.n are connected to the AUPC & ACM Controller via return links. The terminals submit the CNR and SIGL measurements to the Controller. The ACM modulator operates at constant symbol rate, sincethe available transponder bandwidth is assumed to be constant. ACM is implemented by the modulator by transmitting, in time-division multiplex, a sequence of frames, where the coding and modulation format may change frame-by-frame. Each frame can carrytraffic to terminals that know to expect the coding and modulation levels assigned to that frame. Therefore, service continuity is achieved, during rain fades, by reducing user bits while increasing, at the same time, the FEC redundancy and/ormodulation ruggedness. Physical layer adaptation is achieved as follows.
3) In order to avoid information overflow during fades, traffic shaping may be implemented, using traffic shaper 44 to adapt the offered traffic to the available channel capacity. Thus for example during fades, television image quality may bedegraded.
The importance of making the correction phase within a combined AUPC and ACM cycle is as follows: Both AUPC and ACM update can be performed on the same set of channel measurements thus reducing the cycle period. Shortening the cycle periodallows the required margin to be decreased. That is more efficient use is made of the scarce satellite resources allocated for compensating for fast rain fading. Otherwise if only AUPC is performed initially, ACM may be performed on a later measurementof channel status taken after the AUPC update already affected the measurements.
The channel measurement correction can be expressed by ( CNR.sub.i+1)=(CNR.sub.i+1)+G.sub.upc,i+1 (dBHz). (2.22)
See equations (2.7) and (2.8) above for the relations between (E.sub.b/N.sub.o) and (CNR) and between (C/N.sub.o) and (CNR).
A typical table with selection of MODCODs for DVB-S2 is shown as Table 2 below. A typical example for a MODCOD threshold table showing the upper and lower thresholds for selecting a MODCOD is given in Table 3 below. The (CNR) ranges forneighbor MODCODs are partly superposed in order to reduce number of MODCOD switching when (CNR) is near the border between two MODCODs. The combined process of AUPC and ACM is shown in the flow chart of FIG. 5. Periodic polling is carried out of allVSATs (receiving stations). On periodical Polling of all VSATs. Interrupts are generated by individual VSATs and occur between Polling events when the particular VSAT needs to correct its MODCOD for maintaining its received signal quality. In order toreduce the number of interrupts, each individual VSAT can calculate the current downlink attenuation based on expression (B.16) and determine if the variation it has measured in its CNR corresponds also to downlink attenuation variation or only to uplinkattenuation variation. In the latter case a VSAT, which is not a reference terminal, will not issue an interrupt with a request for MODCOD change but will wait for the AUPC to compensate for the uplink attenuation variation. We can thus define thefollowing expression
.times..times. ##EQU00013## as an indicator for downlink attenuation as if it equals zero (or close to zero with predefined accuracy) the downlink attenuation in expression (B.16) is also zero.
TABLE-US-00002 MODCOD Table 2 from ETSI EN302307 reference above. MOD Mode COD QPSK 1/4 1.sub.o QPSK 1/3 2.sub.o QPSK 2/5 3.sub.o QPSK 1/2 4.sub.o QPSK 3/5 5.sub.o QPSK 2/3 6.sub.o QPSK 3/4 7.sub.o QPSK 4/5 8.sub.o QPSK 5/6 9.sub.o QPSK 8/910.sub.o QPSK 9/10 11.sub.o 8PSK 3/5 12.sub.o 8PSK 2/3 13.sub.o 8PSK 3/4 14.sub.o 8PSK 5/8 15.sub.o 8PSK 8/9 16.sub.o 8PSK 9/10 17.sub.o 16APSK 2/3 18.sub.o 16APSK 3/4 19.sub.o 16APSK 4/5 20.sub.o 16APSK 5/8 21.sub.o 16APSK 8/9 22.sub.o 16APSK 9/1023.sub.o 32APSK 3/4 24.sub.o 32APSK 4/5 25.sub.o 32APSK 5/6 26.sub.o 32APSK 6/9 27.sub.o 32APSK 9/10 28.sub.o Reserved 29.sub.o Reserved 30.sub.o Reserved 31.sub.o DUMMY 0.sub.o PLFRAME
TABLE-US-00003 TABLE 3 Example for MODCOD Thresholds Table CNR CNR Spetral Ideal Lower Upper Ideal Efficiency Recommended Allowed Lists MODCOD Modulation MOD Code Rate CNR Threshold Threshold Eb/No bps/Hz Pilots QPSK Q/8PSK Q/8/16 Q/8/1- 6/32 1QPSK 2 0.250 -2.35 -infinity -0.44 0.7 0.42 Off v v v v 2 QPSK 2 0.333 -1.24 -0.64 0.50 0.5 0.56 Off v v v v 3 QPSK 2 0.400 -0.30 0.30 1.80 0.7 0.67 Off v v v v 4 QPSK 2 0.500 1.00 1.60 2.80 1.0 0.83 Off v v v v 5 QPSK 2 0.600 2.23 2.60 3.50 1.4 1.00 Offv v v v 6 QPSK 2 0.667 3.10 3.30 4.40 1.9 1.11 Off v v v v 7 QPSK 2 0.750 4.03 4.20 5.00 2.3 1.25 Off v v v v 8 QPSK 2 0.800 4.68 4.80 5.60 2.6 1.33 Off v v v v 9 QPSK 2 0.833 5.18 5.40 6.50 3.0 1.39 Off v v v v 10 QPSK 2 0.889 6.20 6.40 6.90 3.7 1.48Off v 11 QPSK 2 0.900 6.42 6.70 +infinity 3.9 1.50 Off v 12 8PSK 3 0.600 5.50 6.00 7.10 2.9 1.50 On v v v 13 8PSK 3 0.667 6.62 6.90 8.40 3.6 1.67 On v v v 14 8PSK 3 0.750 7.91 8.20 9.80 4.4 1.88 On v v v 15 8PSK 3 0.833 9.35 9.70 11.30 5.4 2.08 On v 168PSK 3 0.889 10.69 11.10 11.60 6.4 2.22 On v 17 8PSK 3 0.900 10.98 11.40 +infinity 6.7 2.25 On v 18 16APSK 4 0.667 8.97 9.47 10.91 4.7 2.22 On v v 19 16APSK 4 0.750 10.21 10.71 11.73 5.4 2.50 On v v 20 16APSK 4 0.800 11.03 11.53 12.31 6.0 2.67 On v v 2116APSK 4 0.833 11.61 12.11 13.50 6.4 2.78 On v v 22 16APSK 4 0.889 12.89 13.39 13.83 7.4 2.96 On v 23 16APSK 4 0.900 13.13 13.63 +infinity 7.6 3.00 On v 24 32APSK 5 0.750 12.73 13.23 14.34 7.0 3.13 On v 25 32APSK 5 0.800 13.64 14.14 14.98 7.6 3.33 On v26 32APSK 5 0.833 14.28 14.78 16.39 8.1 3.47 On v 27 32APSK 5 0.889 15.69 16.19 16.75 9.2 3.70 On v 28 32APSK 5 0.900 16.05 16.55 +infinity 9.5 3.75 On v Note if the lower threshold is crossed going downward, the MODCOD will be reduced If the upperthreshold is crossed going upward, the MODCOD will be increased
In other words the combined process of AUPC and ACM, as shown in FIG. 5 is based on periodical Polling of all VSATs and obtaining interrupts generated by individual VSATs between Polling events when the VSAT needs to correct its MODCOD formaintaining its received signal quality.
Reference is now made to FIG. 7, which is a simplified diagram illustrating MODCOD and bandwidth relationships. For the purpose of analysis and efficient operation it is desirable to simplify the scenario. We propose here two stages ofreducing the number of operational MODCODs.
Stage 1: Partition the service territory into regions characterized by significantly different satellite coverage strength and/or climate conditions. Select two MODCODs per each such region by assuming two modes of operation, Mode 1: "HighestMODCOD" (HMC) which can be used in the region based on the satellite EIRP and earth stations capabilities, for near to clear sky conditions, and the availability that corresponds to such a MODCOD, called "Derived Availability" (A.sub.HMC). Typically theavailability that reflects near to clear sky conditions will be about 95%. Mode 2: "Required Availability" (A.sub.RQ) and the corresponding "Derived MODCOD" (DMC) that can satisfy such availability. Such two modes with appropriate MODCODs prevail ineach region. We can use efficiency in terms of bps/Hz (bps stands for bit per second) as an indication of the achieved throughput or consumed bandwidth per each MODCOD. The efficiency per MODCOD is give by g=MOD*COD/(1+.alpha.) The total efficiency perregion is defined by g.sub.i=g.sub.HMCA.sub.HMC+g.sub.DMC(A.sub.RQ-A.sub.HMC) The system efficiency G is calculated using the traffic distribution as follows:
.times..times. ##EQU00014## Where Traffic.sub.i is the aggregate traffic for region i. The following table 4 describes a case study based on the above method. For example in Region 2, HMC is 16APSK 0.833 and is active A.sub.HMC=96.0% of thetime, and DMC is 8PSK 0.75 and is active A.sub.RQ-A.sub.HMC=99.7%-96.0%=3.7% of the time, achieving as result the required availability of 99.7%.
TABLE-US-00004 TABLE 4 Case study for analysis based on partitioning to regions and two MODCODs per region. Region 1 Region 2 Region 3 Region 4 Best MODCOD Throughput, Mbps 105,000 100,000 80,000 105,000 MOD 16APSK 16APSK 16APSK 16APSK COD0.875 0.833 0.667 0.875 Availability % A.sub.HMC 99.30 96.00 94.00 98.45 Efficiency bps/Hz 2.92 2.78 2.22 2.92 Req. Availability Throughput, Mbps 90,000 67,500 36,000 80,000 MOD 16APSK 8PSK QPSK 16APSK COD 0.750 0.750 0.600 0.667 Availability % A.sub.RQ99.70 99.70 99.70 99.70 Delta Availability % 0.40 3.70 5.70 1.25 Efficiency bps/Hz 2.50 1.88 1.00 2.22 Total Outbound Total efficiency 2.91 2.74 2.15 2.90 performance bps/Hz Traffic Distribution % 52.7 4.2 37.1 6.0 System efficiency 2.62 bps/Hz ACM gain162%
For the purpose of operation it is also desirable to reduce the number of instantaneously operational MODCODs. The ACM based carrier (e.g. DVB-S2) is built from blocks of coded traffic. Each block has a fixed MODCOD for the traffic carried init. The traffic that waits for transmission in the buffer is waiting for a block with the appropriate MODCOD. If the number of MODCODs is large there are many queues of traffic waiting for a turn to be transmitted. Traffic with a rarely used MODCODmay indeed have to wait a long time until their turn comes. There will be large variations in the delay which are not suitable for interactive applications. For the above case study, FIG. 8 describes the distribution of MODCODs. This distribution isgenerated by weighing each MODCOD with its activity factor (availability for HMC or Delta availability for DMC) and with the traffic fraction using it, namely the traffic per that region scaled by the total traffic. Actually we can reduce at this stagethe number of MODCODs to those selected in the analysis described above and achieve the performance obtained by the analysis. In the case study shown here six different MODCODs are needed.
A method for further reduction in the number of MODCODs can be based on using the set of MODCODs selected in Stage 1 and eliminating those of low utilization, e.g. less than 1% of the time. The rule is that traffic that needs a certain MODCODmay fall to the next low allowed MODCOD. In such a method the lowest MODCOD should be kept in the allowed list. In the case study shown here two of the six MODCODs that remained after Stage 1 may be eliminated with insignificant degradation in thesystem efficiency. FIG. 9 illustrates a series of MODCODs each with different levels of traffic.
Rules for adjusting the MODCOD table (Table 3): When few of the MODCODs are disabled, the thresholds will be calculated as follows: 1. The lower Threshold of the lowest allowed MODCOD is unlimited (-infinity). 2. The lower thresholds ofallowed MODCODs (other than the lowest allowed MODCOD) are in force. 3. The upper thresholds of allowed MODCODs are recalculated: Upper_Threshold(Any_MODCOD)=Lower_Threshold(NEXT_higher_allowed MODCOD)+Margin, where the margin is typically 0.2 dB. 4. The upper threshold of the highest allowed MODCOD is unlimited (+infinity)
In the following we provide the detailed derivation of the expression for the uplink power control gain required at the i+1 iteration G.sub.upc,i+1 for case 1 above.
The received C/N.sub.o can be expressed as follows:
At the i+1 iteration the transmitted EIRP becomes: EIRP.sub.i+1=EIRP.sub.sat-A.sub.up,i+1+G.sub.upc,i (dBW) (A.2)
Where EIRP.sub.sat is the EIRP that should be maintained constant, A.sub.up,i+1 is the rain attenuation at the i+1 iteration, and G.sub.upc,i is the control gain applied at the i-th iteration. Consequently the received C/N.sub.o will become:
Substituting (A.1) at clear sky (A.sub.dn=0) into (A.2) and the result in (A.3), and also using the relation A.sub.up=K+A.sub.dn, the following expression is obtained
Where typically T.sub.rain=278K, and T.sub.ref=T.sub.antenna/1.12+290*0.11+T.sub.LNB (K) See Maral and Bousquet pp. 191-192.
The received carrier power can be expressed by (C)=EIRP.sub.sat-L.sub.fs,dn-A.sub.dn+G.sub.ref-A.sub.Rx (dBW) (B.1)
where L.sub.fs,dn (dB) is the free space loss between the satellite and the reference VSAT at frequency f.sub.dn (Hz) transmitted from the satellite, A.sub.dn (dB) is the downlink rain attenuation, G.sub.ref (dB) is the gain of the referenceterminal antenna, and A.sub.Rx is the receiver RF/IF chain loss. It is assumed that the CNR at the uplink is high and all the EIRP.sub.sat transmitted by the satellite is used only by the desired signal.
At the i+1 iteration the transmitted EIRP becomes EIRP.sub.i+1=EIRP.sub.sat-A.sub.up,i+1+G.sub.upc,i(dBW). (B.2)
Where EIRP.sub.sat is the EIRP that should be maintained constant, A.sub.up,i+1 is the rain attenuation at the i+1 iteration, and G.sub.upc,i is the control gain applied at the i-th iteration. Consequently the received carrier power (C) willbecome: (C.sub.i+1)=EIRP.sub.i+1-L.sub.fs,dn-A.sub.dn,i+1+G.sub.ref-A.sub.Rx(dBW)- . (B.3)
Substituting (B.1) at clear sky (A.sub.dn=0) into (B.2) and the result in (B.3), the following expression is obtained: (C.sub.i+1)=(C.sub.cs)+L.sub.fs,dn-G.sub.ref+A.sub.Rx-A.sub.up,i+1+G.sub.-upc,i-L.sub.fs,dn-A.sub.dn,i+1+G.sub.ref-A.sub.Rx(dBW) (B.4)
where (C.sub.cs) is the received carrier power at clear sky. After simplification it becomes the Carrier Power equation: (C.sub.i+1)=(C.sub.cs)+G.sub.upc,i=A.sub.up,i+1-A.sub.dn,i+1(dBW), (B.5)
At the i+1 iteration the transmitted EIRP becomes: EIRP.sub.i+1=EIRP.sub.sat-A.sub.up,i+1+G.sub.upc,i(dBW). (B.7)
Where EIRP.sub.sat is the satellite EIRP that should be maintained constant, A.sub.up,i+1 is the rain attenuation at the i+1 iteration, and G.sub.upc,i is the control gain applied at the i-th iteration. Consequently the received (C/N.sub.o)will become:
.times..times..times. ##EQU00022##
Substituting (B.6) at clear sky (A.sub.dn=0) into (B.7) and the result in (B.8), the following expression is obtained:
.times..times..times. ##EQU00023##
As per Maral and Bousquet page 31, the difference in received noise temperature can be expressed by: .DELTA.T=T.sub.ref,i+1-T.sub.ref,cs=T.sub.rain(1-10.sup.-A.sup.dn,i+1.sup- ./10)(K). (B.11)
.times..times..times..times..times..times..DELTA..times..times..times..ti- mes..times. ##EQU00025##
By substituting .DELTA.T from equation (B.11) the following expression is obtained
.times..times..times..times..times..times. ##EQU00026##
.times..times..times..times..times..times. ##EQU00027##
Now by combining the Carrier Power Equation (B.5) and the CNR Equation (B.14) through equating G.sub.upc,i-A.sub.up,i+1-A.sub.dn,i+1 the following expression is obtained
.times..times..times..times..times..times. ##EQU00029##
Consequently by using the Carrier Power Equation (B.5) the uplink rain attenuation can be expressed by A.sub.up,i+1=(C.sub.cs)-(C.sub.i+1)+G.sub.upc,i-A.sub.dn,i+1 (dB) (B.17)
where the gain control G.sub.upc,i at the i-th iteration can be expressed by the transmitter power level at the i-th iteration with respect to power level at clear sky G.sub.upc,i=Tx.sub.--PWL.sub.i-Tx.sub.--PWL.sub.cs (dB). (B.18)
Finally the Control Gain Applied at the i+1 Iteration G.sub.upc,i+1 should be Equal to A.sub.up,i+1 in order to maintain EIPR.sub.sat constant as required G.sub.upc,i+1=A.sub.up,i+1=(C.sub.cs)-(C.sub.i+1)+G.sub.upc,i-A.sub.dn,i+- 1 (dB) (B.19)
where A.sub.dn,i+1 is given by (B.16).
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