GB2594264A - Satellite communications system - Google Patents

Abstract

A method of managing data load within a gateway of a satellite telecommunications system is provided. The gateway comprises a plurality of geographically distinct ground transceiver stations 211, 212, 213 each capable of providing feeder links to a satellite 120 to enable communication with a user terminal 354-359. Attenuation data A1(t), A2(t), A3(t) is determined for signals transmitted between the satellite and the ground transceiver stations. The attenuation data is used to manage the data load within the gateway. This may involve deciding whether to switch a feeder link from one ground transceiver station to another, or adaptive channel coding. Adapting transmit power level is also mentioned. A method of processing a plurality of attenuation data time series is separately claimed. This involves “cleaning” each of the time series to correct for equipment biases (such as satellite movements or thermal effects), synchronising the time series with each other and “harmonising” the time series (e.g. using interpolation) to ensure they span identical time periods and have a common sampling interval (Fig. 12). Also claimed is a method of designing a satellite communication system by emulating such a system using attenuation data (Fig. 10).

Description

Satellite Communications System

Technical Field

This document relates to satellite communication systems. More particularly, the application relates to methods of managing data load within a gateway of a satellite communications system, designing a satellite communications system processing data relating to satellite communications systems and emulating satellite communications systems.

Background

Satellite communication systems operating with multiple transceiver stations need to apply some form of load balancing to the gateway. Such load balancing is often termed "Gateway Diversity' or "Smart Gateway Diversity" (SGD). The aim of this is to ensure availability targets for user terminals served by the gateway are met. However, most prior art SGD techniques make ideal assumptions that are not realistic for an operational system. For example, these systems often calculate a "Fade Margin" based on a maximum expected atmospheric loss.

Smart Gateway Diversity is described in the following references: 1. "Smart Gateways For Terabits/s Satellites" by N. Jeannin et al. 2. "On the Gateway Diversity For High Throughput Broadband Satellite Systems" by A. Kyrgiazos et al. 3. "Multiple Gateway Transmit Diversity in 0/V Band Feeder Links" by A.R. Gharanjik, et al. Techniques described in these references have the aim of ensuring high availability targets for the gateway are met. In doing so, a significant amount of redundancy is built in to account for drops in performance caused by rain effects (rain fade) and other adverse weather conditions at transceiver stations. As a result, systems designed according to these principals of operation can include excess levels of redundancy.

SGD exploits the geographical spatial diversity provided by interconnecting multiple OW stations in different geographic locations in order to increase network availability. Data is re-routed from one OW site to a different OW site where conditions are different. These techniques require substantial ground-based connectivity and associated satellite RE routing mechanisms.

For ensuring very high feeder link availabilities (99.9% or even 99.99%), an active OW subject to poor conditions needs to switch to another one. Such a switching event risks the loss of end user demodulator synchronization due to the land-based delay in re-routing data between GWs. The terms "switching" and "handover" may be interchangeably used for the purposes of this application.

The prior art deals with characteristics of the feeder propagation channels between the OW and the satellite by making ideal assumptions, such as perfect de-correlation of fading amid the OW locations, ideal knowledge of the fading and ideal prediction of its evolution, as well as instantaneous switching between the OW sites. In practice, the practicalities in operating SOD may play a detrimental role in the performance of prior art SOD systems in terms of offered availability.

Prior art systems do not provide robust methods of dealing with changing channel conditions. Some rely on weather predictions to determine when channel conditions are likely to be poor and react accordingly. Others rely on significant levels of system redundancy or over-specification of components (e.g. transmitter power and antenna size). Over-redundancy can result in available resources being inefficiently utilised (and can also result in significantly increased due to the capital and operating expense of installing and maintaining a transceiver station). Even with this redundancy, some prior art systems are unable to meet the service requirements when adverse weather conditions are experienced. It is an aim of the present invention to address the shortcomings of the prior art.

Summary

The present invention aims to provide a satellite communications system that operates more efficiently. One way in which the present invention addresses this objective is by determining atmospheric attenuation at each transceiver station in the gateway.

Attenuation data can be used to effectively design the size of the transceiver stations. Atmospheric attenuation values may be used to control gateway behaviour and perform load balancing to improve gateway performance (for example, by achieving better availability and leading to an overall lower cost per bit). Moreover, atmospheric attenuation data gathered over periods of time may be used to emulate satellite communications systems to determine relationships between atmospheric attenuation and gateway performance. This data may also be used to emulate proposed systems and assist with the design procedure of such systems. The design procedure may include determining tradeoffs between data rate, availability, Antenna gain, number of gateways, switching threshold, number of spot beams on a high throughput satellite systems, etc. A method of managing data load within a gateway of a satellite telecommunications system is provided. The satellite telecommunications system comprises one or more satellites. The gateway comprises a plurality of geographically distinct transceiver stations. Each of the geographically distinct transceiver stations is configured to communicate with one or more user terminals via a satellite of the one or more satellites and is subject to a data load related to a volume of data communicated between the transceiver station and the one or more user terminals. The method comprises determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations. The method further comprises managing the data load within the gateway based on the attenuation data.

Managing the data load within the gateway based on attenuation data may improve the performance of the gateway by reacting to the channel conditions and managing the gateway accordingly. This may be achieved by managing the way that the communications channels are used based on the channel conditions at that time. For example, different error-correcting coding schemes may be used depending on an expected error rate in decoding the attenuated signal. Increasing redundancy in the coding scheme may reduced the throughput of data but may also result in fewer retransmissions bring required due to uncorrectable errors. This may therefore actually increase the overall efficiency. Moreover, the modulation scheme of the signal may be chosen in a similar manner -using schemes that are more robust to errors when atmospheric attenuation is high and using schemes that provide higher data rates when atmospheric attenuation is low. In this way, the gateway may be managed to improve the utilization of available communications resources within the gateway.

Another way in which the data load may be managed within the gateway based on attenuation data may be by decreasing the relative data load on transceiver stations that are subject to high levels of atmospheric attenuation and increasing the relative data load on transceiver stations that are subject to low levels of attenuation. This may improve the performance of the gateway by leading to improved overall availability of each of the transceiver stations. Moreover, where changes to coding and/or modulation scheme have been made based on the attenuation data, the data capacity of each gateway may change. Therefore, the gateway may be managed to redistribute the data load to compensate for the changes in the data capacity of each gateway.

The methods in this application may variously be referred to as "managing the data load within a gateway", "managing a gateway", "managing the data load on the gateway" and so on.

The attenuation data may be determined concurrently with managing the data load within the gateway. In other words, the data load within the gateway is managed based on real-time attenuation data, rather than historic attenuation data.

Each of the geographically distinct transceiver stations may be configured to operate in either an active mode or a passive mode. Data may be communicated between the transceiver station and one or more user terminals via a satellite of the one or more satellites when the respective transceiver station is in the active mode. The plurality of geographically distinct transceiver stations may comprise a subset of active transceiver stations comprising a plurality of active transceiver stations and a subset of passive transceiver stations comprising one or more passive transceiver stations. The one or more transceiver stations of the plurality of geographically distinct transceiver stations may comprise a first active transceiver station. Managing the data load within the gateway based on the attenuation data may comprise initiating a handover procedure. The handover procedure may comprise switching a passive transceiver station of the one or more passive transceiver stations into the active mode to provide an activated transceiver station. The handover procedure may further comprise switching the first active transceiver station into the passive mode.

The first active transceiver station may be configured to communicate with a first group of one or more user terminals via the satellite of the one or more satellites prior to the handover procedure. The handover procedure may further comprise configuring the activated transceiver station to communicate with the first group of one or more user terminals.

Managing the data load within the gateway based on the attenuation data may comprise determining that the attenuation data indicates that atmospheric attenuation of the respective transceiver station is above an attenuation threshold or is projected to increase above the attenuation threshold and initiating a handover procedure in response.

Managing the data load within the gateway based on the attenuation data may comprise determining that the attenuation data indicates that a performance parameter of the respective transceiver station is below a performance threshold or is projected to decrease below the performance threshold and initiating a handover procedure in response.

Determining that the attenuation data indicates that the atmospheric attenuation of the respective transceiver station is projected to increase above the attenuation threshold and/or determining that the attenuation data indicates that a performance parameter of the respective transceiver station is projected to decrease below the performance threshold may comprise predicting future values of atmospheric attenuation and/or the performance parameter. Linear or non-linear extrapolation techniques may be used to predict future values of atmospheric attenuation and/or the performance parameter. Other data sets may also be used alongside the attenuation data to predict (project) the atmospheric attenuation and/or performance parameter of the one or more transceiver stations. Alternative means of projection may be used, including but not limited to machine learning and neural networks.

The attenuation threshold and/or the performance threshold may be determined based on static attenuation data corresponding to the transceiver station. The static attenuation data may comprise a plurality of attenuation values at periodic intervals over a span of time. The static attenuation data may be historic attenuation data. In other words, the attenuation threshold may be based on data collected ahead of time, rather than based on real-time attenuation data.

The performance parameter may be an availability of the transceiver station. This may be in terms of a percentage.

The predetermined threshold may be a minimum acceptable availability of the transceiver station.

Managing the data load of the gateway based on the attenuation data may comprise determining a virtual fade margin, defined as fade caused by the instantaneous atmospheric attenuation A(t) plus a predetermined fade margin based on the system specifications.

The transceiver station may be a first transceiver station of the plurality of geographically distinct transceiver stations. The determined attenuation data of the signal transmitted between the satellite and the first transceiver station may be first attenuation data. The method may further comprise determining second attenuation data of a signal transmitted between the satellite of the one or more satellites and a second transceiver station of the plurality of geographically distinct transceiver stations. Managing the data load within the gateway based on the attenuation data may comprise managing the data load within the gateway based on the first attenuation data and the second attenuation data.

Determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations may comprise determining attenuation data of a signal transmitted between a satellite of the one or more satellites and each transceiver station of the plurality of transceiver stations. Determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations may further comprise managing the data load within the gateway based on the attenuation data corresponding to each transceiver station. In other words, the system gathers attenuation data at every receiver station and manages the data load of the gateway based on attenuation data from all of the transceiver stations.

The one or more satellites may comprise one or more geostationary satellites; one or more satellites in a low earth orbit; one or more satellites in a medium earth orbit; and/or one or more earth observation satellites.

If the satellite communications system comprises a geostationary satellite then the system may only require one satellite.

Managing the data load within the gateway may comprise performing adaptive channel coding. In other words, the coding and modulation scheme used by the transceiver station may be selected (updated) based on the (concurrent) attenuation data (which provides a measure of the channel conditions).

The one or more transceiver stations may comprise three transceiver stations; four transceiver stations; six transceiver stations; two active transceiver stations and one passive transceiver station; three active transceiver stations and one passive transceiver station; four active transceiver stations and one passive transceiver station; five active transceiver stations and one passive transceiver station; or four active transceiver stations and two passive transceiver stations.

Determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations may comprise determining attenuation data of a beacon signal transmitted from the satellite of the one or more satellites received at the one or more transceiver stations of the plurality of geographically distinct transceiver stations.

Determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations may comprise determining attenuation data of a signal transmitted between the one or more user terminals and the one or more transceiver stations of the plurality of geographically distinct transceiver stations via the one or more satellites. In other words, the attenuation data may relate to a signal originating from a user terminal and transmitted to the transceiver station via a satellite.

A method of designing a satellite telecommunications system is also provided. The satellite telecommunications system comprises a gateway and one or more satellites. The gateway comprises a plurality of geographically distinct transceiver stations. The method comprises proposing one or more design characteristics of the geographically distinct transceiver stations of the gateway and/or one or more design characteristics of the one or more satellites. The method further comprises emulating the satellite telecommunications system using attenuation data of a signal transmitted between a satellite and a transceiver station to determine one or more projected performance characteristics of the satellite telecommunications system. The method further comprises designing the geographically distinct transceiver stations of the gateway and/or the one or more satellites based on the one or more projected performance characteristics.

By emulating the system using attenuation data from real sites gathered over a period of time, the method may result in design of a system that is able to effective meet the system requirements. Moreover, when the system is operated (e.g. using a method of managing the system as described above), the resources of the system provided as a result of the design procedure may be efficiently utilised.

Emulating the satellite telecommunications system using attenuation data of a signal transmitted between a satellite and a transceiver station to determine one or more projected performance characteristics of the gateway of the satellite telecommunications system may comprise using attenuation data processed according to a method as described below. Emulating the satellite telecommunications system using attenuation data of a signal transmitted between a satellite and a transceiver station to determine one or more projected performance characteristics of the gateway of the satellite telecommunications system may comprise emulating management of the gateway using a method described above.

Designing the geographically distinct transceiver stations of the gateway and/or the one or more satellites based on the one or more projected performance characteristics may comprise: designing one or more antennas of the one or more transceiver stations; designing the number of geographically distinct transceiver stations; designing the transmitter power of the one or more transceiver stations; designing the geographic locations of the transceiver stations; designing the number of satellites; and/or designing one or more orbital characteristics of the satellites. These orbital characteristics may include whether the satellites are in geostationary or low earth orbit, for example. Designing the number of geographically distinct transceiver stations may include designing the number of active and passive transceiver stations.

A method of processing attenuation data relating to a gateway of a satellite telecommunications system is also provided. The satellite telecommunications system comprises one or more satellites. The gateway comprises a plurality of geographically distinct transceiver stations. Each of the geographically distinct transceiver stations is configured to communicate with one or more user terminals via a satellite of the one or more satellites and is subject to a data load related to a volume of data communicated between the transceiver station and one or more user terminals. The attenuation data comprises a plurality of data points of atmospheric attenuation of a signal over a period of time. The method comprises cleaning the attenuation data by accounting for equipment biases present in the system. The method further comprises synchronising the attenuation data by using time measurements associated with each data point of atmospheric attenuation and accounting for offsets between time measurements at each receiver station. The method further comprises harmonising the attenuation data so that the harmonised data for each of the plurality of geographically distinct transceiver stations comprises attenuation values at regular intervals. The interval time is common between transceiver stations (common time resolution). The attenuation data for each receiver station has a common start time and a common end time. The time series may have the same validation time for all sites.

The periodic may be 30 seconds or less. The processed attenuation data may cover a period of at least 3 months. The processed attenuation data may cover a period of at least six months. The processed attenuation data may cover a period of at least one year.

Harmonising the attenuation data so that the processed data for each of the plurality of geographically distinct transceiver stations comprises attenuation values at regular intervals may comprise interpolating attenuation values at common time intervals from attenuation data (cleaned and/or synchronised).

Cleaning the attenuation data by accounting for equipment biases present in the system may comprise normalising the data points to account for one or more of: satellite movement, thermal shifts, power fluctuations, and temperature effects.

A method of processing signal power data is also provided. The method comprises determining attenuation data from the signal power data and processing the attenuation data using a method as described above.

Attenuation A(t) may be calculated as the difference between a signal reference level R(t) and the received signal S(t): A(t) = R(t) -S(t).

The signal reference level may represent the expected signal power in the absence of propagation impairments (atmospheric attenuation).

The signal reference level R(t) may be determined by iterative application of a Fourier series to the received signal S(t).

Whilst the preceding description refers to "a plurality of geographically distinct transceiver stations", these methods may also be useful more generally for a satellite telecommunications system having multiple communication channels. Accordingly, the present invention also provides a method of managing data load within a gateway of a satellite telecommunications system that comprises one or more satellites, wherein the gateway comprises one or more transceiver stations, wherein each of the one or more transceiver stations is configured to communicate with one or more user terminals via a satellite of the one or more satellites and is subject to a data load related to a volume of data communicated between the transceiver station and the user terminals, the method comprising: determining attenuation data of a signal transmitted between a satellite of the one or more satellites and a transceiver station of the one or more transceiver stations; and managing the data load within the gateway based on the attenuation data.

In one example, a transceiver station may operate on a plurality of distinct frequency channels. Each channel may exhibit different channel conditions. Attenuation data may be collected for each channel and data load may be managed based on the attenuation data.

Additionally or alternatively, a transceiver station may be configured to communicate with one or more user terminals via a plurality of distinct satellites. Each satellite may facilitate a distinct communications channel between the transceiver station and the one or more user devices. Each communications channel may exhibit different channel conditions. Attenuation data for each channel may be determined. Data load of the gateway may be managed based on the attenuation data.

Advantageously, gateway management methods as described above may allow a system to operate effectively even in systems that are subject to rain fade effects. Moreover, such methods can be applied to systems that operate in higher frequency bands that may offer higher data capacity (increased data loads and throughput) but are more prone to atmospheric attenuation. These higher frequency bands may include the K. band (26.5 to 40 GHz), the Q band (33 to 50 GHz), the V band (40 to 75 GHz) and the W band (75 to 110 GHz). The 0 and V bands are sometimes collectively referred to as the Q/V band (33 to 75 GHz).

In another example, the system may be used to communicate directly with a satellite, rather than with one or more user terminals via a satellite. Earth Observation (EO) satellites carry out imaging or sensing and transmit data to a gateway (downlink). This is termed an Earth Observation (EO) Data DownLink (DDL) system. To improve data transmission performance of these EO satellites, the one or more transceiver stations of the gateway may be managed using any of the methods described above. This may help to increase data rates on downlink.

The present invention also provides computer software comprising instructions that, when executed by a processor of a computer system, cause the computer system to perform a method as described above.

The present invention also provides an electromagnetic signal carrying computer-readable instructions that, when executed by a processor of a computer system, cause the computer system to perform a method as described above.

The present invention also provides a computer-readable medium containing computer-readable instructions that, when executed by a processor of a computer system, cause the computer system to perform a method as described above.

Brief Description of the Drawings Accompanying the Description Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a satellite telecommunications system comprising a gateway and a satellite 120.

Figure 2 illustrates a satellite telecommunications system comprising a satellite and a gateway that comprises three separate transceiver stations.

Figure 3(a) illustrates a satellite communications system comprising a satellite and a gateway that comprises three separate transceiver stations. A plurality of user terminals served by the gateway are also illustrated. Figure 3(b) illustrates a handover procedure of the system of Figure 3 (a).

Figure 4 illustrates graphs showing example attenuation data for three transceiver stations over the course of a day. Attenuation time series are shown for Chilton, Athens and Vigo on 24 May 2018. The number of switches at Chilton, Athens and Vigo is 6, 2 and 4 respectively whereas the network number of switches is 6=(12/2).

Figure 5 illustrates a system diagram for a satellite telecommunications system comprising a gateway, a satellite and a user terminal.

Figure 6 illustrates a system diagram for a satellite telecommunications system comprising a gateway, N satellites and N user terminals.

Figure 7 shows a flowchart of a method of managing data load within a gateway of a satellite communications system.

Figure 8 (a) shows a flowchart of a method of managing data load within a gateway of a satellite communications system. Figure 8 (b) shows a flowchart of another method of managing data load within a gateway of a satellite communications system.

Figure 9 shows a flowchart of a method of designing a satellite communications system.

Figure 10 shows a flowchart of an iterative method of designing a satellite communications system.

Figure 11 illustrates a schematic diagram showing data flow for emulation of a satellite communication system.

Figure 12 illustrates a flowchart of a method of processing data collected from a satellite communications system.

Figure 13 illustrates a schematic data flow diagram for how the methods described in this application may be interrelated.

Figure 14 illustrates the received signal power measured at Location A of a 400Hz signal S(t) and the derived reference signal level R(t). The data were taken on 25th of December 2017. The X-axis shows the time since midnight in seconds.

Figure 15 illustrates examples of measured attenuation values showing the effect of location and frequency. The X-axis shows the time since midnight of 25th of December 2017 in seconds.

Figure 16 illustrates annual attenuation statistics measured at 6 locations at 40 GHz.

Figure 17 illustrates measured Fading time due to fades exceeding 10dB with duration longer than x-axis value for all the locations. The fading time is normalised to the outage at 10dB.

Figure 18 illustrates measured annual fraction of time for which attenuation at both links exceeds the Y-Axis value for GWs located in the same or different climatic regions.

Figure 19 illustrates the number of network switches for the 4+2 network with SST=5dB. Figure 19(a) illustrates the number of switches per day. Figure 19(b) illustrates the distribution of the number of days with switches according to the number of switches occurred during the day.

Figure 20 illustrates the number of network switches for the 4+2 network with SST=10dB. Figure 20 (a) illustrates the number of switches per day. Figure 20 (b) illustrates the distribution of the number of days with switches according to the number of switches occurred during the day.

Figure 21(a) illustrates the network availability versus the SST for the (4+2) network. Figure 21(b) illustrates the number of required switches versus the SST for the (4+2) network.

Detailed Description of Specific Embodiments

Referring first to Figure 1, there is illustrated a satellite telecommunications system 100 comprising a gateway 110 and a satellite 120. The gateway comprises a transceiver station. The gateway 110 communicates with the satellite via electromagnetic signals. The electromagnetic signals are subject to attenuation due to atmospheric interference 130. This varies over time and is denoted as A(t). The atmospheric attenuation A(t) may be determined by the gateway and load balancing may be performed based on the atmospheric attenuation.

The carrier signal to noise density ratio equation provides a relationship between the signal to noise ratio received at the transceiver station, the transmitter power and the signal losses: C/N, = EIRP + G/T -(FSL + A(t) + L) + 228.6 (dBHz) Where C/N, is the received signal to noise density ratio, EIRP is the effective isotropic radiated power, G/T is the "figure of merit" of the receiver, FSL is the free space path loss, A(t) is the atmospheric loss, L is the other losses and 228.6 is a constant defined by 10log1o(1/k), where k is Boltzmann's constant (1.38 x 10-23 J/K).

The term relating to atmospheric losses A(t) in the equation above is of particular interest in this application. The behaviour of this term can be hard to predict and has a significant impact on the performance of the system. Other losses tend to be known or easier to estimate.

Throughout this application, reference is made to atmospheric attenuation of a signal communicated between a transceiver station and a satellite. This may be a signal transmitted by the satellite and received by the transceiver station. In this case, the transceiver station may determine the atmospheric attenuation based on the received signal power using the techniques described below. Alternatively or additionally, attenuation data may be determined for a signal transmitted by the transceiver station and received by the satellite. In this case, the satellite may determine the atmospheric attenuation based on the received signal power (as discussed below) and may transmit this data to the transceiver station. Alternatively, raw data of received signal power may be sent from the satellite to the transceiver station.

Calculation of the atmospheric attenuation may be performed at each transceiver station and this attenuation data may be sent to a gateway controller to manage the data load on the gateway based on the atmospheric attenuation data. Alternatively, raw data of received signal power may be transmitted to the gateway controller and attenuation data may be determined by the gateway controller.

Figure 2 illustrates another satellite telecommunications system comprising a gateway 210 that comprises three separate transceiver stations 211, 212 and 213. Each transceiver station communicates with satellite 120 using electromagnetic signals, which are subject to attenuation due to atmospheric effects. The transceiver stations may be separated over a large geographic area. For example, transceiver station 211 may be located in the UK, transceiver station 212 may be located in Spain and transceiver station 213 may be located in Greece. At any given time, the weather in these three locations may be different. Therefore, the atmospheric attenuation will be different for each transceiver station. The Atmospheric attenuation at the first 211, second 212 and third 213 transceiver stations is denoted as Al(t), A2(t) and A3(t) respectively. Generally, the atmospheric attenuation at the lel transceiver station may be referred to as Ak(t) Figure 3 (a) illustrates the satellite communications system of Figure 2 serving a plurality of user terminals 350. A first group of the user terminals 351 are served by a first transceiver station 211 of the gateway. A second group of user terminals 352 are served by a second transceiver station of the gateway 212. Three user terminals 354, 355 and 356 are illustrated in the first group of user terminals. Three user terminals 357, 358 and 359 are illustrated in the second group of user terminals. Each user terminal communicates with the respective serving transceiver station via the satellite 120. For example, the communication path between user terminal 354 transceiver station 211 will be via communications channel 361a and communications channel 361b. Likewise, the communication path between user terminal 357 and transceiver station 212 will be via communications channel 362a and communications channel 362b.

Transceiver station 213 is illustrated in passive mode. In passive mode, the transceiver station does not serve any user terminals. Nevertheless, the transceiver station may be in communication with the satellite 120 and the atmospheric attenuation of electromagnetic signals between the transceiver station and the satellite AO may be determined by the gateway.

In the event that channel 362a becomes subject to increased atmospheric attenuation, signals communicated between the user terminals and transceiver station 212 may exhibit lower signal-to-noise ratios. As a result, the availability of the gateway may decrease for users served by that transceiver station. In response to this, the gateway may manage the data load on the gateway to improve performance.

One way in which the data load may be managed to improve performance is by performing load balancing. Data load on transceiver stations that are experiencing high levels of rain fade (high atmospheric attenuation) may be reduced, whilst data load on transceiver stations that are not experiencing high levels of rain fade may be reduced.

Another way in which the gateway may be managed to improve performance is by increasing transmitter power in response to high levels of atmospheric attenuation. This may improve the availability of the transceiver station during periods of high rain fade.

Another way in which performance of the gateway may be improved is by applying adaptive coding techniques. For example, if channel conditions are poor between the second transceiver station and the satellite, a coding scheme that is more robust to errors may be used.

Another possibility is to manage the number of user terminals served by each gateway. For example, if the bandwidth provided by the second receiver station 212 is limited (while the first receiver station 211 has available bandwidth capacity), user terminal 357 may move from the second group of user terminals 352 to the first group of user terminals 351 and be served by the first receiver station 211 instead of the second receiver station 212.

If the system determines that the atmospheric attenuation A2(t) of signals between the second transceiver station and the satellite is below a threshold (while atmospheric attenuation Aa(t) of signals between the third transceiver station and the satellite is above a threshold), handover of the transceiver station may be initiated. As shown in Figure 3(b) Transceiver station 213 enters active mode and becomes the serving station for user terminals in the second group of user terminals. The communication path between user terminals in the second group 352 and the third transceiver station 213 will be via communications channel 363a and communications channel 362b. The second transceiver station 212 then enters passive mode but may continue to communicate with the satellite 120 via communications channel 362a.

The load balancing techniques discussed above are not mutually exclusive and a combination of techniques may be appropriate.

Whilst Figures 3(a) and 3(b) illustrate that each group of user terminals communicates with the satellite via a shared communications channel 361b and 362b, this is not necessarily the case. The user terminals may be geographically disparate and the communications channels between each user terminal and the satellite may be subject to different atmospheric conditions. Nevertheless, the user terminals in each group may share a frequency band. The channels are grouped together in these Figures for the sake of simplicity and to demonstrate handover.

Figure 4 illustrates graphs showing example attenuation data for three transceiver stations over the course of a day. As can be seen from Figure 4, transceiver stations 1 and 2 ("chilton"and "athens", respectively) are initially in an active state and transceiver station 3 ("vigo'') is in an inactive (or "standby"/"passive" state).

Shortly after the start of the data (between 0 and 10000 seconds), attenuation values at transceiver station 1 increase, prompting a handover to transceiver station 3. This handover is indicated by dashed lines labelled "1".

After between 40000 and 50000 seconds, attenuation levels at transceiver station 1 have dropped but attenuation levels at transceiver station 3 increase above a threshold. As a result, a second handover (indicated by dashed lines "2") from transceiver station 3 to transceiver station 1 is initiated.

After between 50000 and 60000 seconds, attenuation levels at transceiver station 3 have dropped but attenuation levels at transceiver station 1 increase above a threshold. As a result, a third handover (indicated by dashed lines "3") from transceiver station 1 to transceiver station 3 is initiated.

Shortly after, handover three (but before 60000 seconds), attenuation levels at transceiver station 1 have dropped but attenuation levels at transceiver station 2 increase above a threshold. As a result, a fourth handover (indicated by dashed lines 1l4") from transceiver station 2 to transceiver station 1 is initiated.

After between 60000 and 70000 seconds, attenuation levels at transceiver station 2 have dropped but attenuation levels at transceiver station 1 increase above a threshold. As a result, a fifth handover (indicated by dashed lines "5") from transceiver station 1 to transceiver station 2 is initiated.

After between 80000 seconds, attenuation levels at transceiver station 1 have dropped but attenuation levels at transceiver station 3 increase above a threshold. As a result, a sixth handover (indicated by dashed lines "6") from transceiver station 3 to transceiver station 1 is initiated.

The threshold for all stations may be 5dB. Alternatively, stations may have individual thresholds (for example, if the antenna of each transceiver station is a different size, some may be more resilient to atmospheric losses than others). Other possible attenuation thresholds include 1dB, 2dB, 3dB 4dB, 10dB, 15dB and 20dB.

Rather than using an attenuation threshold or forecast attenuation threshold, the gateway controller (or transceiver station controller) may determine (or project) a performance parameter for the transceiver based on the attenuation. For example, the system may determine the percentage availability for the transceiver station. Handover may be initiated if percentage availability of the transceiver falls (or is projected to fall) below a threshold. The threshold may be 99.9%, 99%, 95% or 90%, for example.

If an active transceiver station experiences atmospheric attenuation above the handover threshold but the passive transceiver station is also experiencing atmospheric attenuation above the threshold, the gateway controller may initiate handover based on a number of factors including: * the current atmospheric attenuation at each transceiver station; * the average atmospheric attenuation at each transceiver station over a defined time period; and * the duration each transceiver station has been experiencing attenuation above the threshold.

Figure 5 illustrates a system diagram for a satellite telecommunications system comprising a gateway, a satellite and a user terminal. The gateway comprises a gateway controller and a plurality of transceiver stations. Each transceiver station comprises a respective transceiver station controller.

The gateway controller may be configured to manage the data load on the transceiver stations. The gateway controller may manage the data load in a number of ways. The gateway controller may be configured to route the flow of data between the user terminals and the gateway through the satellite communications system. This may include specifying via which transceiver station (and satellite) data to/from a particular user terminal should be communicated. The gateway controller may also be responsible for managing handover between transceiver stations and determining which transceiver stations should be in the active mode and which should be in the passive mode. The gateway controller may also be responsible for determining at which satellite the antenna of each transceiver station is directed.

Each transceiver station controller may be configured to determine atmospheric attenuation data of the signal communicated between the transceiver station and the satellite. Each of the satellite and transceiver may be configured to measure the received signal power of the received signal and determine the atmospheric attenuation using the received signal power measurements.

Gateway controller, transceiver station controller and satellite controller elements may be provided by computer systems. A computer system may comprise a processor, memory, data input and data output. The memory of the computer system may store instructions in the form of software. When executed on the processor, the instructions may cause the computer system to perform the method steps required to implement the techniques described in this application.

Whilst certain operations are described as being performed by specific elements of the system, these operations may be performed in a distributed manner, with some elements of the operation being performed by one system element and other elements being performed by another system element.

Figure 6 illustrates a system diagram for a satellite telecommunications system comprising a gateway, N satellites and N user terminals. The gateway comprises a gateway controller and N transceiver stations. Each transceiver station comprises a respective transceiver station controller and a respective antenna. Each satellite comprises a respective satellite controller and a respective antenna.

Each satellite and transceiver station may further comprise additional components required for transmitting and receiving electromagnetic signals. For example, each transceiver station and satellite may further comprise signal amplifiers, filters (e.g. low-pass, high pass and band pass), mixers, modulators and demodulators, multiplexers and demultiplexers, analog to digital converters and digital to analogue converters, oscillators, clocks etc..

Transceivers may further comprise antenna-tracking systems so that the orientation of the antennas may be adjusted to effectively track the satellites. The satellites may further likewise comprise antenna-tracking systems. The satellites may further comprise positioning systems to adjust the orientation of the satellite and make corrections to the orbit of the satellite.

Each antenna may be a dish antenna or may be an array antenna, for example. Each antenna may comprise one or more waveguides, hyperbolic reflectors, parabolic dishes and the like.

The user terminals may be computer systems that comprise processor, memory, antenna, amplifier etc. For example, the user terminals may be mobile telephones or personal computers.

Figure 7 shows a flowchart of a method of managing data load within a gateway of a satellite communications system. The method comprises determining attenuation data at a transceiver station of the gateway and managing the data load within the gateway based on the attenuation data.

Figure 8 (a) shows a flowchart of a method of managing data load within a gateway of a satellite communications system. This method comprises determining attenuation data at each transceiver station of a gateway. The method further comprises determining whether to initiate a handover procedure based on the determined attenuation data. If the attenuation data indicates that atmospheric attenuation at a particular transceiver station is above a threshold then a handover procedure may be initiated to put that transceiver station in a passive more and switch a passive transceiver station into an active mode.

In some cases, handover may be initiated if the most recent attenuation data point exceeds a threshold. In other cases, handover may be initiated if the average of a number of most recent attenuation data points exceeds a threshold. In other cases, the system may extrapolate from the most-recent data points to predict the next attenuation data point. Handover may be initiated if the prediction of the next data point exceeds a threshold. Forecasting of attenuation data may be performed in a number of ways. Extrapolation methods such as linear or polynomial extrapolation may be used to predict future attenuation. Machine learning such as neural networks may also be used to predict future attenuation values.

If the attenuation data indicates that all active transceiver stations have atmospheric attenuation levels below a threshold (or below each of their individual thresholds), the system may wait a predetermined interval and then asses again whether a handover is required. The predetermined interval may be 1 second, 5 seconds, 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 30 minutes, or 1 hour for example.

The atmospheric attenuation at each transceiver station may be determined based on measurements of received signal power.

Figure 8 (b) shows a flowchart of another method of managing data load within a gateway of a satellite communications system. In this method, as well as using attenuation data to determine whether current attenuation is above a threshold, attenuation data is also used to forecast attenuation values. The current and forecast attenuation values may be used to manage switching as shown. This is useful because handover does not happen instantaneously. Synchronisation and handover periods between satellites and transceiver stations mean that there is a delay between initiating handover and the user terminals being served by a different transceiver station and/or via a different satellite. As well as forecasting attenuation values based on attenuation data. Additional information may be used (e.g. weather forecast data, system data etc.) to forecast and propagation impairments.

Figure 9 shows a flowchart of a method of designing a satellite communications system. The method comprises proposing design characteristics for the satellite communications system, emulating operation of the satellite communications system to determine projected performance parameters, and designing the satellite communications system based on the projected performance parameters.

Figure 10 shows a flowchart of an iterative method of designing a satellite communications system (e.g. a High Throughput Satellite System "HTS''). The method comprises proposing design characteristics for the system. These design characteristics may include number of transceiver stations, transceiver station location, antenna size, number of satellites, satellite antenna size, transmitter power, number of spot beams, and frequency sharing scheme.

The method further comprises emulating the proposed system. Emulation may be achieved by using attenuation data gathered from real transceivers at the proposed locations (or nearby). The attenuation data for the proposed transceiver station sites may be cleaned, synchronised and harmonised (according to the methods described elsewhere in this application) to ensure system performance is emulated accurately. During emulation of the system, the system under emulation may manage the data load on the gateway according to gateway management methods described in this application.

During emulation of the system, performance characteristics (performance parameters) of the system may be determined and recorded. For example, the availability of the system, the data throughput of the gateway, the throughput of the individual transceiver stations and the number of handovers between gateways may be determined.

The system may be emulated over a long period of time. For example, the emulation of the system may be performed over the same span of time as the available attenuation data. Alternatively, the emulation may be performed over a shorter period of time than that covered by the available attenuation data.

Emulation of the system may be performed so that the projected performance characteristics of the proposed system over a long period of time may be determined. However, the emulation itself may take a considerably shorter time. For example, the emulation may determine performance of the proposed system over a twelve-month period. The emulation may take only a few seconds or minutes to run.

Additionally, the performance characteristics may include utilisation efficiency of available resources. It may be desirable to ensure the transceiver stations operate at a minimum percentage of their maximum capacity. Otherwise, the system may be over-specified and the available resources may not be efficiently used.

In some examples, the performance characteristics may further include costs of building the system (including costs of building the transceiver station, costs of building and launching the satellites etc.). In some examples, the performance characteristics may further include running costs of the system.

Demand on the gateway may also be emulated using data of demand from user terminals gathered in a real satellite telecommunications system. Alternatively, demand may be generated using a random process, subject to statistical parameters.

Emulation of the satellite communications system may be performed on a computer system. The computer system may comprise memory, a processor, data input and data output. The memory of the computer system may store instructions in the form of software. When executed on the processor, the instructions may cause the computer system to perform the method steps required to emulate the satellite communications system.

The attenuation data used in the emulation may be determined by a real transceiver station controller or gateway controller. Alternatively, the attenuation data may be determined using a test network comprising receivers set up at particular geographic locations to receive a satellite signal and record attenuation data.

Following determination of a set of design characteristics for the satellite communications system, a service provider may build the transceiver stations and satellites to the proposed characteristics. The system may then be managed using the gateway management methods described elsewhere in this application. These management methods may also be used in the system emulation and therefore the performance characteristics of the real system should align with the projected performance characteristics of the emulation.

Figure 11 illustrates a schematic diagram showing data flow for emulation of a satellite communication system. As can be seen from Figure 11, the system emulation uses attenuation data from a plurality of transceiver stations along with proposed design characteristics and gateway management methods to determine projected performance characteristics. The projected performance characteristics are then used to update the proposed design characteristics and the system may be emulated again with the new characteristics. The process may be repeated until the projected performance characteristics meet a set of performance requirements for the system.

Adjustment of the design characteristics may be performed automatically. The next iteration of the emulation may then be performed automatically with the updated design characteristics, with no need for any user intervention. For example, if the emulation reveals that too many handovers are required to maintain gateway availability then the design characteristics relating to the size of the antenna on the satellite may be increased.

In some examples, the projected performance characteristics may also be used to guide modification/adjustment of the gateway management methods (SOD). This may provide further improvements to the proposed system. For example, the gateway management methods may include attenuation thresholds for the transceiver station above which the gateway controller initiates a handover between transceiver stations. These thresholds may be adjusted on the basis of the outcome of the emulation.

Figure 12 shows a flowchart of a method of processing data collected from a satellite communications system. As shown, attenuation data relating to transceiver stations at geographic locations is determined. Then, the attenuation data from the transceiver stations is cleaned to account for biases in equipment and variations in distance between satellites and transceiver stations over time. Then, the attenuation data is synchronised using timestamps associated with the data. Then, the attenuation data is harmonised by interpolating attenuation data to ensure that the start and end points of the data are aligned for each transceiver station and the resolution of the attenuation data is the same for each transceiver station.

Cleaned, synchronised and harmonised time-series attenuation data may be used in a number of ways. One use is during emulation of a satellite communication system for system design, as discussed above. Another use is to determine a relationship between atmospheric attenuation at the transceiver station and the instantaneous performance of that transceiver station. For example, the data may be used to derive a relationship between atmospheric attenuation and the percentage availability of the transceiver station. This may be useful for determining attenuation thresholds for a gateway management method. If it is a system requirement that the percentage availability of an active gateway does not fall below a certain value then the system may be managed by initiating a handover if the concurrent attenuation data indicates that the availability of an active transceiver station is (or will be) below a threshold availability.

Figure 13 illustrates a schematic data flow diagram for how the methods described in this application may be interrelated. Data from real transceiver stations may be collected and processed to provide synchronised and harmonised time-series attenuation data. This data may be used to emulate a proposed satellite communications system and arrive at design characteristics that meet performance requirements. The system emulation may also use gateway management methods that manage data load of the gateway based on concurrent (real-time) attenuation data. Emulation of the system yields projected performance characteristics that may be used to guide modification of the proposed design characteristics and/or gateway managements. The emulation may therefore provide design characteristics and gateway management methods that meet system performance requirements. These may be used to provide an improved satellite communication system.

Examples of the design characteristics may include: * antenna dimensions; * transmitter power; * number of transceiver stations; * transceiver station type; * location of transceiver stations; * number of satellites; * satellite type; * and the like.

Examples of the performance characteristics may include: * gateway availability; * transceiver station availability; * bandwidth; * data throughput; * latency; * and the like.

Examples of modifications to the gateway management method may include: * determining switching thresholds that define when to initiate handover; * determining what methods for forecasting attenuation should be used; * and the like.

The term "gateway" is used in this application to refer to the group of one or more transceiver stations that transmit and receive user data to/from user terminals via a satellite. The gateway may be connected to additional data networks such as the internet so that data may be communicated via the gateway between the user terminal and a remote location across the network. In other words, the gateway is the means by which data is converted between data communicated over a network (e.g. IF data) and data communicated in the form of electromagnetic signals to/from a satellite. When discussing the operation of a gateway, individual transceiver stations are sometimes themselves referred to as "gateways stations" (abbreviated to "GWs") or sometimes just "gateways". For clarity, when the term "gateway" is used in this application, this refers to the whole system of transceiver stations. When the terms "transceiver station", "gateway station", "ground station" or "GW" are used, this refers to an individual transceiver station of the gateway.

The term "Smart Gateway Diversity" or SGD is used in this application to refer to the methods by which a gateway may be managed.

Specific Implementation Details Data Collection Measurements of one or more signals (at one or more different frequency bands) from one or more satellites are taken at transceiver stations at multiple geographical sites. The measurements are concurrent and synchronised both at each site (for analysis of signals at different frequencies) and between all the experimental sites (for analysis of signals received at different geographic locations).

For a given space segment (i.e. satellite signal) data collection may be performed using: 1. a ground segment receiving system (which may include a receiver, antenna and antenna tracking system, etc.); and 2. a data acquisition system.

Processing of collected data For each experimental site (proposed site for a transceiver station) and satellite signal, data processing may involve: 1. removal of the space and ground segment equipment biases (e.g. movement of the satellite, drifting with temperature) from the initially collected data; and 2. extraction of the required time series propagation parameters, e.g. attenuation, and quality control of the data (e.g. identification of the valid data).

Step 1 is important for the extraction of the time series of the required radio channel parameters so that data between sites may be compared. Step 1 may be a time-consuming procedure and can be prone to errors. This is at least because the length of time covered by the measurements is ideally longer than a year. Moreover, data must be collected for multiple geographic sites. A methodology has been developed where the processing of raw data is automated. Therefore, measurements from multiple sites can be processed promptly and accurately.

At any instant t the attenuation, A(t), due to propagation impairments along the radio link is given by the equation: A(0= R(t)-S(t) where R(t) is the signal reference level, i.e. the signal in the absence of propagation impairments and S(t) the received signal.

R(t) may be established by applying iteratively a Fourier series to the received signal S(t) on a daily basis. A detailed description of the concept of the Fourier series approach can be found in "Long-term statistics of tropospheric attenuation from Ka/U band ITALSAT satellite experiment in the United Kingdom" by S.Ventouras et al..

This approach may be automated by utilising also the signal values of the previous and next day. In other words, the procedure for the extraction of the attenuation time series may be automated by utilising a moving bunch of three consecutive days.

Figure 14 shows an example of the time series of measured satellite signal S(t) and the derived signal reference level R(t).

Figure 15 shows the effect of different location and frequency on the satellite link attenuation due to propagation impairments. As can be seen from Figure 15, higher frequency signals may be more prone to atmospheric attenuation.

Harmonisation of data The use of the propagation parameters time series (time series attenuation data) for SOD analysis requires harmonisation of the data among all sites. This means that the time series data from step 2 above need to undergo the following process which: 3. generates time series with a common time resolution for all sites; and 4. generates time series with the same validation time for all sites.

In particular for step 3, there is no restriction for the sampling rates of the individual sites (e.g. to be multiples of the same number) but step 3 can be implemented for any sampling rate values.

For step 3: the common maximum time resolution of all sites, W, may be identified; and the median value of each W window may be derived for each satellite signal.

For step 4: For a satellite signal, k, the derived attenuation time series may be supplemented by the validation flag time series, VFk(t), which is a Boolean variable (e.g. 0 not valid or 1 valid); and For an analysis requiring attenuation time series from N concurrent satellite signals the common validation flag time series, VFALL(t) is given by: VFALL(t) = VF1(t) VF2(t) VEN(t) Use of time series The above-mentioned derived time series of radio channel propagation parameters (e.g. attenuation data) can be used in a wide range of aspects regarding the system design and operation. For example, for the ground segment, the utilisation of the time series ranges from the dimensioning of the individual station (Gateway, user terminal) to the managing of adaptive Fade Mitigation Techniques for both individual stations (e.g. power control, ACM) or networks (smart gateway diversity).

Time series of propagation parameters (attenuation data) from multiple sites may be utilised in the satellite systems design and operation. The approach has two sections: Fundamental Section and Smart Gateway Section.

Fundamental section The fundamental section may perform the following functions: Visualisation of the time series of satellite signal and propagation parameters for the radio paths (location, frequency) of the database according to user wishes over a period selected by the user The fundamental analysis of the radio channel characteristics -i.e. filtering, frequency scaling, spectral analysis, fade/inter-fade duration, rate of change of the satellite signal because of propagation impairments -over the period selected by the user.

The fundamental analysis statistical analysis over a specified period (annual, seasonal, monthly, daily) regarding attenuation, frequency scaling, fade slope, fade/inter-fade duration, time diversity, site diversity. In addition, there is the functionality for the predictions of the ITU-R Recommendations of series P. The fundamental section may be provided by software that allows a user to perform the above operations on the data and view the results in a graphical user interface (GUI).

Smart Gateway Diversity section The Smart Gateway Diversity section may be used in systems utilising spatial diversity techniques (e.g. site diversity or smart gateway diversity). The Smart Gateway Diversity section may be provided in a graphical user interface (GUI). The Smart Gateway Diversity section may perform the following functions: Emulation and visualisation of the performance of diversity techniques over a specified period. The user is prompted to define the observation period and to choose the system configuration -i.e. location, frequency, switching threshold, switching process delay and number of active and redundant gateways. The system performance assessment includes the achieved availability and the number of switches for both the network and the individual transceiver stations (GWs) and the history of switches.

Statistical assessment of SGD technique over a specified period (annual, seasonal, monthly). The user is prompted to define the observation period and to choose the system configuration -i.e. location, frequency, switching threshold, switching process delay and number of active and redundant gateways. The system performance assessment may include the achieved availability and the number of switches over the observation period and daily, the distribution of switches per day and the impact of the switching process delay.

A single transceiver station (GW) of the network, at a given instant t, is considered to be in outage if the attenuation experienced by this GW, A(t), is exceeding the GW fade margin FM.

A(t) L. FM (1) The above attenuation levels tolerated by the GW can be the result of several margins built into the GW's link budget, such as oversizing of HPA and reflector size.

At a given instant t, a "N active + P redundant GWs" network, is available if N (or more) GWs out of the N+P GWs are not in outage.

Equivalently, the network is out if P+1 GWs (or more) out of the N+P GWs are in outage.

For a "N active + P redundant GWs" network, its availability over the period T (e.g. day, year) is defined as follows: An instant t E [0,T) can be written as: (2) with and DT the time resolution of the data used in the emulation.

T N DT

For example: DT=1 sec, 1=365.86400 sec (one year), N=365.

Each GW is represented at the instant t by a binary variable X(t) with the value 0 if the GW is in outage and 1 if it is available. (3)

The overall system is represented then by the binary variable Y(t) with the value 0 if any N GWs are in outage and 1 if N GWs are not in outage.

with (t) (4) The probability of the overall system outage, p is estimated as the time the variable z P Y(t) is equal to 0 divided by the period T. The modelling provided by equations (2), (3) and (4) allows emulations for different system configurations, e.g. different fade margins or frequencies for each GW.

Site Switching Threshold (SST) of a GW is an attenuation threshold. When the attenuation experienced by the GW exceeds the SST, the GW switches to another GW. The SST is not necessarily equal to GW FM. For example, for a tolerated excess attenuation margin FM, the network may initiate the switching process for values smaller than FM in order to avoid network outages. The sizing of this hysteresis margin is a trade-off between availability and number of switches.

The switching mechanism may be implemented as follows: under adverse propagation conditions, an active GW1 switches its traffic to another redundant GW2 whenever its SST is exceeded for the first time. Then, GW1 becomes redundant (or standby) until the propagation conditions at another GWk require switching to GW1. A switch involves two stations: a) the Active GW which becomes Standby and b) the Standby GW which becomes Active. Therefore, the total number of Network switches is the half of the sum of the switches of each GW. Figure 4 shows an example of the switching mechanism for a (2+1) network with GWs at Chilton, Athens and Vigo with SST=5dB on 24th of May 2018.

In a "N active + P redundant GWs" network with P=1, when an active GW crosses the SST there is only one GW which might be used. However, for P>=2, there might be more than one GWs available and a decision has to be made which of the standby GWs will become active. The network availability is independent of the selection of the GW. However, the number of required switches to achieve this availability does depend on the GW choice. Therefore, for an unbiased statistical assessment of SOD performance in the emulations, a GW is selected randomly from the available GWs. Similarly, the initial selection of the standby GWs does not have an impact on the statistical assessment of SGD performance.

Assessment of Practical Smart Gateway Diversity Based on Multi-Site Measurements in Q/V band Next generations of satellite communication systems (High Throughput Satellite systems or "HTS") operating a network of gateway stations (GWs) for the gateway feeder link (e.g. in the 0/V band), may apply some form of Smart Gateway Diversity (SGD) to ensure they meet the demanding availability targets. However, most of the published research on SGD usually resorts to ideal assumptions that are not realistic for an operational system. To evaluate in more depth the performance of practical SGD, a specific non-limiting example of this application exploits multi-site propagation measurements for a network of six measurement sites (GWs) at 40 GHz. Based on this, it studies the performance of SGD in terms of feeder availability (i.e. gateway availability) and number of switches between transceiver stations (GWs) taking into account the climatic region, the switching processing delay, the clustering of GWs, and the impact of downlink versus uplink frequency in Q/V band. This example demonstrates the interplay between propagation aspects and SGD operational aspects.

For exploiting Extremely High Frequency (EHF) bands beyond 10 GHz in the RF feeder links of gateways in High Throughput Satellite (HIS) networks, the transceiver stations of the gateway may need to be managed using some form of "Smart Gateway Diversity" (SGD) method. Smart Gateway Diversity is described in the following references: 1. "Smart Gateways For Terabits/s Satellites" by N. Jeannin et al. 2. "On the Gateway Diversity For High Throughput Broadband Satellite Systems" by A. Kyrgiazos et al. 3. "Multiple Gateway Transmit Diversity in Q/V Band Feeder Links" by A.R. Gharanjik, et al. It is an object of SGD techniques to ensures that availability targets are met. The spectrum requirements resulting from HTS systems may lead to deploying multiple gateway stations (GWs) for nominal service. This may be because some prior art HTS systems which employ a traditional site diversity, where each transceiver station needs to be paired with a redundant transceiver station, which leads to a doubling of the number of transceiver stations required. In other words, a backup passive (standby) GW is provided for every active OW. For this reason, the cost of an HTS ground segment (i.e. the cost of the gateway) may represent a significant fraction of the overall cost of the satellite communication system. SGD enables the cooperation between existing transceiver stations (GWs) and improves the availability of the system by providing a smaller number of standby transceiver stations (GWs) for cold redundancy.

SGD techniques may exploit the geographical spatial diversity provided by interconnecting multiple GW stations in different feeder beams in order to increase the ground network availability of the gateway. Two possible alternative SGD techniques are "N active GWs" and "N active + P redundant GWs". Both SGD techniques operate under the same fundamental premise of re-routing data from a faded GW to a different GW site of another feeder beam (instead, with traditional site diversity, a secondary antenna is placed within the same beam kilometers away from the faded GW site). One difference between the "N active GWs" and "N active + P redundant GWs" techniques is that, in the first scheme (N), each GW is oversized in terms of resources to handle part of the traffic of a faded GW in the network, whereas, in the second scheme (N+P), the N nominal GWs are fully loaded so that when one falls in outage, one of the P redundant ones completely takes over its traffic. Both techniques require substantial ground-based connectivity and the associated satellite (spacecraft) RE routing mechanisms. As such, the choice of SGD has an impact on the satellite payload architecture. This is described in the following references: 4. "Smart Gateways Concepts For High-Capacity Multi-beam Networks" by P.Angeletti et al. 5. "Dimensioning VHTS Feeder Link Solutions For The Short to Mid-Term An Operator's Perspective" by G. Marrakchi et al. To provide very high feeder link availabilities (99.9% or even 99.99%), an active GW under heavy fading may handover to another GW. Such a switching event can risk loss of end user demodulator synchronization due to land-based delays in re-routing data between GWs. The terms "switching" and "handover" may be interchangeably used for the purposes of this application.

Spatial and temporal characteristics of the feeder propagation channels of the gateway affect the performance of the SGD technique. The effectiveness of the SGD technique in the system performance may therefore depend on both characteristics. Most of the prior-art contributions on the topic of SGD have made ideal assumptions, such as perfect de-correlation of fading amid GW locations, ideal knowledge of the fading and ideal prediction of its evolution, and instantaneous switching between the GW sites. In practice, the practicalities in operating SGD may play a detrimental role in the performance of SGD in terms of offered availability. Such practicalities include the switching/handover dynamics under practical constraints (e.g. the frequency of GW switching/handover or the criterion when to switch), the switching characteristics between GWs and the related channel estimation.

There is a clear shortcoming of prior art studies and models due also to the fact that these models make no use of existing attenuation data. For example, concurrent and synchronized time series of attenuation measured from a network of experimental sites may be used to improve SOD techniques. One example of attenuation measurements is the ALPHASAT propagation experiment:"Satellite Communication and Propagation Experiments Through the Alphasat Q/V Band Aldo Paraboni Technology Demonstration Payload" by T. Rossi et al.. The existing propagation models (ITU-R Study Group 3 Recommendations) are statistical prediction models aiming mainly at the specification of the fade margin or at the description of the fade dynamics (e.g. fade duration, fade slope etc.). These are inconclusive in determining either the performance of the real systems or how to optimize its operation.

As discussed above, it is an object of the present application to fill this gap. This specific non-limiting example aims to do so by emulating the performance of the SGD techniques employing real multi-site data (measurements) of the propagation channels in Q/V band. For easier reading of the results, the N+P variant of SOD is adopted throughout the description of this example. However, the techniques and advantages are applicable to both N+P and N techniques. Unlike anything described in the prior art, emulations according to the specific example described in this application are based on real time series attenuation data. In this specific non-limiting example, the emulations are based on measurements of the 0-band (40 GHz) propagation signal transmitted by the Aldo Paraboni payload (TDP5) from the Alphasat satellite. Although this specific set of measurements may not be appropriate for direct use for designing an HTS system, the exercise offers great insights into the SOD technique.

The measurements are the results of a joint propagation campaign at pan-European level, which was coordinated across five countries (described in "Assessment of Spatial and Temporal Properties of Ka/Q Band Earth-Space Radio Channel Across Europe Using Alphasat Aldo Paraboni Payload" by S. Ventouras et al.). Although measured data have been used in the past to assess aspects of SOD, in this example six different sites are considered. In terms of transceiver stations (GWs) of a feeder network (gateway), six GWs would correspond to a medium sized HTS system of about 100 Gbps. The experimental sites of the measurements and the climatic patterns which were found to be closely related to the SOD technique are described below. This specific example also describes SOD key parameters. The results of the emulations for different system requirements and system scenarios are also provided. These include (among others) the impact of switching delay, of payload connectivity restrictions as well as the impact of carrier frequency (downlink frequency versus uplink frequency).

Experimental And Propagation Characteristics The data used in the SOD emulations of this specific non-limiting example are collected using the 0-band experimental configuration of the ALPHASAT Propagation Experiment at the following locations: {UK: (Chilbolton, Chilton), Spain: (Vigo), Portugal: (Aveiro) and Greece: (Athens, Lavrion)) with corresponding elevation angles {UK: (26.40°,26.07°), Spain: (30.60°), Portugal:(31.80°), Greece: (45.97°,46.26°)). The observation period of the used measurements is of 12 months: from 1st January 2018 to 31th of December 2018 and the concurrent valid data availability for all locations is greater than 900/c. The distances between Chilbolton-Chilton, Vigo-Aveiro and Athens-Lavrion are 47.9Km, 173.3Km, 36.31 Km respectively. For the other pairs of the experimental sites the distances are longer than 1000Km.

The terminals of the measurement network are time synchronized (using GPS) to ensure the applicability of measurements for temporal and spatial correlation studies. The terminals measure excess attenuation of the received signal, i.e. the variation of signal that can be ascribed mainly to rain and cloud attenuation. Furthermore, the initially derived attenuation time series were further processed to make sure they are harmonized to a common time resolution of 1 second.

The experimental data derived from this experiment provide time series attenuation data for a satellite signal for a number of different geographic locations. These data may be used to emulate a satellite communication system having transceiver stations in those locations. In other words, the terminals of the experimental measurement network may be considered analogous to transceiver stations of a gateway in a satellite communication system.

This achievable coverage area is representative of the fringe of a typical satellite covering Europe and encompassing several climatic zones (from north Atlantic to the southern Mediterranean areas). The experimental sites can be clustered into 3 distinct climatic regions in terms of radio propagation: Southern UK (Chilton, Chilbolton); Spain-Portugal (Vigo, Aveiro); Greece (Athens, Lavrion). Hence, the experimental sites encompass both macro-and mid-scale diversity effects. This allows us to extrapolate also some conclusions for a feeder network (gateway) with a higher number of transceiver stations (GWs) across Europe, with a denser distribution of transceiver stations.

Figure 16 shows the annual attenuation statistics measured at the 6 locations at 39.4 GHz (for brevity, the beacon frequency carrier may be rounded to 40 GHz).

Table I lists the measured fading time and total number of fades for fades exceeding 5 dB and 10 dB. The choice of these fading margins will be motivated in the following sections.

Figure 17 shows the distribution of fading time versus the fade duration at 10 dB. The distinct propagation characteristics of the three regions are visible in the graphs shown in Figure 17. In general, the sites in Spain, Portugal and Greece experience more severe fades than in Southern UK. Regarding the number of fades, the largest numbers were observed in Vigo and the lowest were observed in Greece. This is reflected in the mean fade duration values listed in Table I (i.e. fading time over total number of fades at a given threshold). The longest mean fade duration values were observed in Greece and the shortest were observed in the UK.

Regarding the spatial characteristics of the radio channels, Table II lists the joint statistics, that is the time the attenuation at both of a pair of sites exceeds 5 dB and 10 dB. These sites may be referred to as GWs, working on the assumption that the data are used to emulate transceiver stations of a gateway managed using SGD. Of interest to the SGD technique is the fact that the time an attenuation threshold is exceeded on both OW links of a pair is not strictly related to the distance between the two GWs, but rather to meteorological characteristics of the OW locations (e.g. weather front). That is, shorter distances do not always imply higher exceedance time. As expected, for the pairs with GWs in the same climatic region the joint exceedance time is much higher than the other OW pairs, i.e. there is a stronger correlation of the propagation impairments. This is illustrated in Figure 18 which depicts annual joint attenuation statistics for 6 pairs of GWs -3 pairs with GWs from the same climatic region. For example, the joint attenuation statistics between Vigo-Aveiro is comparable to joint statistics between Chilton-Chilbolton and Athens-Lavrion, regardless of the long separation of 173.3Km between Vigo and Aveiro.

Smart Gateway Diversity Metrics And Parameters The primary metrics for the SOD assessment are the achievable feeder network availability and number of required switches over a period of interest T (e.g. a year, a day). At any instant, the feeder network is available if N (or more) GWs out of the N+P GWs are not in outage. Over a period of interest T, the feeder network availability is defined as the percentage of T the system is available.

A Smart Gateway N+P Network Configuration is at least partly defined by the following characteristics: * the required number of GWs (active and redundant); * the geographic location of the GWs; * the operational frequency (or frequencies) of the GWs; and * the available Fade Margin (FM) of each GW.

When the attenuation experienced by a GW exceeds the FM, the GW may be considered to be in "outage". It is noted that the attenuation levels tolerated by the GW (FM) can be the result of several margins built into the GW's link budget, such as oversizing of HPA and/or reflector size. Out of this oversizing, the HPA may also apply uplink power control for compensating the uplink fading and keeping under control the co-channel interference between the GWs.

Because of the required switching, two relevant parameters of the system are: a) the Site Switching Threshold (SST) and b) the switching process delay, i.e. the time required for a switching to be complete. The SST is not necessarily equal to GW FM. For example, for a tolerated excess attenuation margin FM, the network may initiate the switching process for values smaller than FM in order to avoid network outages. The size of this hysteresis margin may provide a trade-off between availability and number of switches.

The switching mechanism adopted for the emulations presented in the non-limiting example is as follows: under adverse propagation conditions, an active GW, switches its traffic to another redundant GW2 whenever its SST is exceeded for the first time. Then, GM becomes redundant (or standby) until the propagation conditions at another GWk require switching to GW1. A switch involves two stations: a) the Active GW which becomes Standby and b) the Standby GW which becomes Active. Therefore, the total number of Network switches is the half of the sum of the switches of each GW. Figure 4 shows an example of the switching mechanism for a (2+1) network with GWs at Chilton, Athens and Vigo with SST=5dB on 24th of May 2018.

In a "N active + P redundant GWs" network with P=1, when an active GW crosses the SST there is only one GW which might be used. However, for P>=2, there might be more than one GWs available and a decision has to be made which of the standby (or "passive") GWs will become active. The analysis of the data showed that the network availability is independent of the selection of the GW. However, the number of required switches to achieve this availability does depend on the GW choice. Therefore, during emulation a GW may selected randomly from the available GWs. This may provide an unbiased statistical assessment of SGD performance in the emulations. Similarly, the initial selection of the standby GWs does not have an impact on the statistical assessment of SGD performance.

SGD Assessment The 6 experimental sites enable the assessment of a 4+2 SGD technique. In addition, in order to assess the SGD technique if only one GW within the same cluster can be selected in the event of an outage, the total number of (4+2) GWs is split into two sub-sets, each containing (2+1) GWs. This situation may result from connectivity restrictions between GWs and user beams at the satellite payload or between GWs on ground. The assessment is performed for ideal switching (i.e. without considering any switching process delay), as well as for a switching process delay of 2 seconds and 30 seconds. A common dimensioning has been adopted for each GW and, hence, a common SST which is either 5 dB or 10 dB. Although this leads to a different single GW availability in each location, it is a practical hypothesis based on the assumption that all GWs will be equipped with the same equipment (antennas, HPAs). In any case, the results can be easily expanded for any choice of frequency and SST per GW.

(4+0) without SGD Deployment In general, in a N+P SGD network the number N of active GWs is determined by the required HIS system capacity whereas the deployment of P redundant GWs is to increase the network availability. In this section we discuss the availability of feeder networks consisting of 4 active GWs without deploying the SGD technique, i.e. without redundant GWs. This serves as a reference for judging both the technical need and cost effectiveness of deploying the SOD technique. The network availability is assessed for each of the 4 GWs utilising 5 dB and 10 dB of FM (as there is no switching involved), respectively.

For the selection of the 4 GWs out of 6 GWs there are 12 combinations provided that each combination has 3 GWs from different climatic regions. This selection of GWs gives the highest possible values of availabilities bearing in mind the joint exceedance time discussed earlier in Section II. Table Ill shows the measured network annual availability for each combination. The availability values range from 95.3497% to 96.9567% at 5dB and from 98.6269% to 99.0769% at 10dB with average values 96.1692% and 98.8586%, respectively. On average, the networks which include the GWs at Vigo and Aveiro have the worst availability despite the long distance: 173.3Km, between the two GWs compared to the distances between Chilton-Chilbolton and Athens-Lavrion.

In conclusion, regardless of the combination of GWs, the achieved availability cannot reach the demanding availability requirements of feeder links (e.g. 99.99%) and, consequently, the HTS systems cannot meet their service specifications.

(4+2) Without Switching Process Delay The network of this subsection consists of 4 Active and 2 Standby stations. The choice of initial combination of Active/Standby GWs makes no difference. Further, the random selection of the Active OW from the available standby GWs ensures the unbiased statistical estimation of the number of switches. Also, the network includes 3 pairs of GWs with each pair within the same climatic area. Therefore, the results are considered a worst-case scenario (see Section II).

The measured SOD performance is listed in Table IV. For SST=5dB the feeder network annual availability is 99.9645% which is achieved via 813 ideal switches (without a switching process delay) on 175 days out of the 365 days of observation. The daily network availability is 100% except for 20 days for which the availability values range from 99.1273% to 99.9965%. For SST =10 dB the network availability is 99.9992% which is achieved via 280 ideal switches on 110 days. All days have daily network availability 100% expect for two days with availabilities 99.7442% and 99.9857%. Therefore, thanks to the SOD technique, there is a significant increase from 96.1692% to 99.9645% and from 98.8586% to 99.9992% of the feeder network availability at SST=5dB and SST=10dB, respectively.

Figure 19(a) and Figure 20(a) show the daily distribution of switches for SST=5dB and SST=10dB respectively. The frequency table of the number of switches per day in the network, i.e. the number of days with 1 switch or number of switches within [2,4),[4,6), ...[38,40),... are shown in Figure 19(b) and Figure 20(b). The number of days with more than 4 switches a day drops steeply with the increasing number of switches per day. This is more apparent as the SST increases.

The number of switches for each GW for the whole observation period is given in Table V. It seems that the number of switches of each GW is related to the climatic area where it is located. As mentioned above, the lowest numbers of fades were observed in Athens and Lavrion along with the longest on average duration compared to the other locations. This results in the smaller number of switches for the GWs at these two locations.

Figure 21(a) shows the measured annual network availability versus the SST and Figure 21(b) shows the required number of switches versus the SST, which ranges from 5dB to 14dB. There is a clear increase of the feeder network availability and decrease of the number of switches respectively as the SST increases. However, beyond 10dB there is a saturation to almost 100% availability whereas the number of switches continues to decrease. This type of plot allows a ground network operator to decide how to trade between the cost of the individual GW (expressed by the SST) and the number of GWs.

For a significant fraction of the observation time, (a year in this paper), when a GW is on standby mode the attenuation on the feeder link is less that the SST. This means that the propagation impairments could be compensated by the GW's FM and the GW could be operational. This time spans from 19.90% to 39.77% and 16.03% to 44.44% at SST=5dB and SST=10dB respectively.

(2+1) Without Switching Process Delay Next, the 4+2 feeder network, i.e. 6 GWs, is split into two sub-networks each containing (2+1) GWs. The (2+1) feeder networks are structured considering the propagation dependence of the locations of the GWs and are classified into two categories: the category 1 where all the three GW pairs of the network are from different climatic regions and the category 2 where the network includes a GW pair from the same climatic area. The latter configuration may be representation of a scenario where there is a large number of GWs that can no longer be distributed in remote enough location to claim perfect weather decorrelation. However, not only the clustering of the total population of GWs into subnetworks, but also the pairing of the GWs within each sub-network may be dictated by the satellite payload connectivity between feeder beams and user beams. For example, the sites in the same climatic region may be too close to each other to be simultaneously active and still allow an adequate uplink carrier-to-co-channel interference ratio.

For the given 4+2 network there are 4 pairs of sub-networks with each containing (2+1) GWs from category 1 and 6 pairs of sub-networks containing (2+1) GWs from category 2. The performance evaluation of each pair of sub-networks is given in terms of: i) the availability and number of switches for the individual (2+1) networks of the pair and H) the pair availability and the sum of the number of switches of the two (2+1) networks. The pair availability may be defined as the average of the two (2+1) sub-networks availabilities.

Tables VI and VII reveal the measured SGD performance of the 4 pairs and 6 pairs of (2+1) sub-networks from category 1 and category 2 respectively, for SST=5dB and SST=10dB.

For all the sub-networks pairs, the availability is less than the availability of the (4+2) network. A pair of (2+1) sub-networks has, in total, an equal number of active and standby GWs, i.e. 2+2 and 1+1 respectively. However, within each sub-network there is the option of switching only to one GW compared to the option of switching to two GWs for the (4+2) network. This may result in improved availability for the (4+2) network.

The listed values in Tables VI and VII indicate that the 4 pairs of networks from category 1 are statistically similar and perform much better than the sub-networks from category 2. In particular, the availability of sub-networks from category 1 is greater than 99.9% and 99.99% for SST=5dB and SST-10dB respectively. On the other hand, the sub-networks from category 2 cannot reach availabilities greater than 99.87% and 99.986% for SST=5dB and SST=10dB respectively. This is expected based on the earlier rationale about joint exceedance statistics for GW pairs.

Regarding the number of switches of each GW for the sub-networks from category 1, similar conclusions are drawn as for the (4+2) network (see Section IV.B). However, for the sub-networks from category 2, the smaller number of GW switches occurs always at the GW that is located in a different climatic region with respect to the other two GWs.

Impact Of Switching Process Delay Let w be the time interval required for a switching from one GW to another to be completed. The following approach is adopted in the emulations of this subsection: When a switching is initiated at the time instant t, the whole network is frozen during the switching process delay window w. The network is operational, and consequently a decision for a following switch can be made, from the time instant t + w onwards. The switching delay introduces an additional network outage to fade outage, the switching outage Outswitch, which reduces further the network availability and is given by the equation: OUtswitch = Nswitches'W (1) where Nswitches is the number of required switches.

The SGD performance of the (4+2) network with switching process delay w equal to 2 s and 30s, respectively for all the GWs is shown in Table IV for SST=5dB and SST=10dB. The results can be directly compared with the SGD performance of ideal switching. The differences in the values of network fade outage, number of fades and number of switches for networks operating without and with switching process delay are rather random and due to the network freeze within the time window w. The switching characteristics, e.g. number of switches of each GW, daily distribution of switches, are similar to the switching characteristics without a processing delay discussed above. Similar conclusions are drawn for the impact of switching process delay on the (2+1) networks.

Impact Of Frequency To portray the SGD technique on the forward link (uplink) and in general to evaluate the impact of the GW operational frequency on the SGD technique, the 40 GHz measured time series of attenuation are scaled-up to their corresponding uplink frequency of 50 GHz. This is of interest because a feeder link typically carries more traffic in its uplink (forward link) than in the downlink (return link). Therefore, protocol and strategies for SOD may focus on the feeder uplink. The frequency scaling is performed by using the algorithm described in ITU-R P.618 "Propagation Data and Prediction Methods Required For the Design of Earth-Space Telecommunications Systems".

At 500Hz, the (4+2) network availability over the one-year observation period for ideal switching is 99.9932%, 99.9988% and 99.9997% for SST values equal to 10 dB, 11 dB and 12 dB respectively. The corresponding required number of switches are 454, 362 and 292. A comparison of these values with the network availability and number of switches, 99.9992% and 280, for the same (4+2) network operating at 40 GHz with SST=10 dB shows that the performance of the two (4+2) networks is similar. This can be explained by the facts that: i) The performance of SOD technique depends on the joint exceedance time of a given attenuation threshold, i.e. SST. As the frequency increases the GW links are more prone to propagation impairments. However, the strong dependence of the joint exceedance time on the spatial distribution of atmospheric phenomena significantly reduces the propagation impairments particularly if the GWs are located in different climatic regions (see above). This is also discussed in "Diversity experiments in Greece and the UK" by A.Z. Papafragkakis et al..

H) In addition, the increase of antenna gain with the increasing frequency might allow higher levels of SST with the same antenna, which reduces further the joint exceedance time. For example, the performance of the feeder network operating at 40 GHz with SST=10dB is comparable to the one operating at 50 GHz with SST=12dB.

In a practical SOD system, when a switching takes places this may be done for both the forward and the return links.

The performance of 4 active + 2 redundant SOD technique is assessed based on one-year measurements of the Q-band (40 GHz) propagation signal transmitted by the Aldo Paraboni payload (TDP5) of the Alphasat satellite in 6 European locations. This is a unique type of emulation given the wealth and quality of data from such a large number of locations.

It is found that SGD significantly improves the network availability but at the expense of the additional GWs and required number of switches. There is a steep increase of the feeder availability and decrease of number of switches, respectively as the SST increases. However, beyond 10 dB there is a saturation effect evident to almost 100% availability whereas the number of switches continues to decrease. A ground segment network design needs to take into account this information to balance the network cost between individual OW and network sizing.

For a significant fraction of the observation time, spanning on average from 16% to 45%, each OW is on standby mode with the attenuation on the feeder link less than SST. This means that during this time the propagation impairments could be compensated by the GW's FM and the OW could be operational. This fact maybe lends itself to considering reusing GWs among multiple satellite networks.

When the (4+2) network is split into two (2+1) networks, the sub-networks pair has always lesser availability than the (4+2) network.

As the switching from one OW to another cannot be ideal, i.e. without switching process delay, the network availability is reduced further by the number of switches times the switching process delay. The number of switches is a critical parameter for the implementation of the SOD, not only to reduce the switching outage, but also due to practical constraints of the system (e.g. maximum allowed number of switches a day, time spacing between consecutive switches). However, the required number of switches can be reduced by a switching management scheme, e.g. short-term prediction of the radio channel, long-term planning of switching, selection of standby OW, selection of SST, and the like. Therefore, research activities are proposed in this particular topic to secure the cost and technically effective implementation of the SOD technique.

Finally, for the impact of operation frequency on the SOD performance it seems that system dimensioning for the application of SOD technique to higher frequencies is not proportional to severity of propagation impairments at these frequencies.

Although particular embodiments of the invention have been described, the skilled person will appreciate that various modifications and variations may be made without departing from the scope of the invention.

For example, whilst the above description generally describes gateways comprising multiple transceiver stations in which the transceiver stations are separated geographically, these techniques may also be applied to gateways in which the transceivers are located at a single station. In this case, the transceivers may be configured to operate on multiple frequency bands and/or to communicate with different satellites. Where multiple satellites are contactable at different locations in the sky, different channel conditions may be observed between each satellite. Likewise, different frequency bands may exhibit different attenuation in response to atmospheric conditions. These differences in channel conditions may be managed using the techniques described in this application to perform load balancing between available channels.

Claims (22)

1. CLAIMS: 1. A method of managing data load within a gateway of a satellite telecommunications system that comprises one or more satellites, wherein the gateway comprises a plurality of geographically distinct transceiver stations, wherein each of the geographically distinct transceiver stations is configured to communicate with one or more user terminals via a satellite of the one or more satellites and is subject to a data load related to a volume of data communicated between the transceiver station and the one or more user terminals, the method comprising: determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations; and managing the data load within the gateway based on the attenuation data.
2. 2. The method of claim 1 wherein the attenuation data is determined concurrently with managing the data load within the gateway.
3. 3. The method of claim 1 or claim 2, wherein each of the geographically distinct transceiver stations is configured to operate in either an active mode or a passive mode, wherein data is communicated between the transceiver station and one or more user terminals via a satellite of the one or more satellites when the respective transceiver station is in the active mode, wherein the plurality of geographically distinct transceiver stations comprises a subset of active transceiver stations comprising a plurality of active transceiver stations and a subset of passive transceiver stations comprising one or more passive transceiver stations, wherein the one or more transceiver stations of the plurality of geographically distinct transceiver stations comprises a first active transceiver station, wherein managing the data load within the gateway based on the attenuation data comprises initiating a handover procedure comprising: switching a passive transceiver station of the one or more passive transceiver stations into the active mode to provide an activated transceiver station; and switching the first active transceiver station into the passive mode.
4. 4. The method of claim 3, wherein the first active transceiver station is configured to communicate with a first group of one or more user terminals via the satellite of the one or more satellites prior to the handover procedure, wherein the handover procedure further comprises configuring the activated transceiver station to communicate with the first group of one or more user terminals.
5. 5. The method of any preceding claim, wherein managing the data load within the gateway based on the attenuation data comprises: determining that either: the attenuation data indicates that atmospheric attenuation of the signal received by the respective transceiver station is above an attenuation threshold or is projected to increase above the attenuation threshold, or the attenuation data indicates that a performance parameter of the respective transceiver station is below a performance threshold or is projected to decrease below the performance threshold; and initiating a handover procedure in response.
6. 6. The method of claim 5, wherein determining that the atmospheric attenuation of the respective transceiver station is projected to increase above the attenuation threshold and/or determining that the attenuation data indicates that a performance parameter of the respective transceiver station is projected to decrease below the performance threshold comprises using extrapolation to predict future values of attenuation and/or the performance parameter.
7. 7. The method of claim 5 or claim 6, wherein the attenuation threshold and/or the performance threshold is determined based on static attenuation data corresponding to the transceiver station, wherein the static attenuation data comprises a plurality of attenuation values at periodic intervals over a span of time.
8. 8. The method of any preceding claim, wherein the transceiver station is a first transceiver station of the plurality of geographically distinct transceiver stations and the determined attenuation data of the signal transmitted between the satellite and the first transceiver station is first attenuation data, the method further comprising: determining second attenuation data of a signal transmitted between the satellite of the one or more satellites and a second transceiver station of the plurality of geographically distinct transceiver stations, wherein managing the data load within the gateway based on the attenuation data comprises managing the data load within the gateway based on the first attenuation data and the second attenuation data.
9. 9. The method of any preceding claim, wherein determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations comprises determining attenuation data of a signal transmitted between a satellite of the one or more satellites and each transceiver station of the plurality of transceiver stations; and managing the data load within the gateway based on the attenuation data corresponding to each transceiver station.
10. 10. The method of any preceding claim, wherein the one or more satellites comprise: one or more geostationary satellites; one or more satellites in a low earth orbit; and/or one or more satellites in a medium earth orbit.
11. 11. The method of any preceding claim, wherein managing the data load within the gateway comprises performing adaptive channel coding.
12. 12. The method of any preceding claim, wherein the one or more transceiver stations comprise: three transceiver stations; four transceiver stations; six transceiver stations; two active transceiver stations and one passive transceiver station; three active transceiver stations and one passive transceiver station; four active transceiver stations and one passive transceiver station; five active transceiver stations and one passive transceiver station; or four active transceiver stations and two passive transceiver stations.
13. 13. The method of any preceding claim, wherein determining attenuation data of a signal transmitted between a satellite of the one or more satellites and one or more transceiver stations of the plurality of geographically distinct transceiver stations comprises: determining attenuation data of a beacon signal transmitted from the satellite of the one or more satellites received at the one or more transceiver stations of the plurality of geographically distinct transceiver stations; or determining attenuation data of a signal transmitted between the one or more user terminals and the one or more transceiver stations of the plurality of geographically distinct transceiver stations via the one or more satellites.
14. 14. A method of designing a satellite telecommunications system that comprises a gateway and one or more satellites, wherein the gateway comprises a plurality of geographically distinct transceiver stations, the method comprising: proposing one or more design characteristics of the geographically distinct transceiver stations of the gateway and/or one or more design characteristics of the one or more satellites; emulating the satellite telecommunications system using attenuation data of a signal transmitted between a satellite and a transceiver station to determine one or more projected performance characteristics of the satellite telecommunications system; and designing the geographically distinct transceiver stations of the gateway and/or the one or more satellites based on the one or more projected performance characteristics.
15. 15. The method of claim 14, wherein emulating the satellite telecommunications system using attenuation data of a signal transmitted between a satellite and a transceiver station to determine one or more projected performance characteristics of the gateway of the satellite telecommunications system comprises: using attenuation data processed according to a method of any of claims 17 to 22; and/or emulating management of the gateway using a method of any of claims 1 to 13.
16. 16. The method of claim 14 or claim 15, wherein designing the geographically distinct transceiver stations of the gateway and/or the one or more satellites based on the one or more projected performance characteristics comprises: designing one or more antennas of the one or more transceiver stations; designing the number of geographically distinct transceiver stations; designing the transmitter power of the one or more transceiver stations; designing the geographic locations of the transceiver stations; designing the number of satellites; and/or designing one or more orbital characteristics of the satellites.
17. 17. A method of processing attenuation data relating to a gateway of a satellite telecommunications system that comprises one or more satellites, wherein the gateway comprises a plurality of geographically distinct transceiver stations, wherein each of the geographically distinct transceiver stations is configured to communicate with one or more user terminals via a satellite of the one or more satellites and is subject to a data load related to a volume of data communicated between the transceiver station and one or more user terminals, wherein the attenuation data comprises a plurality of data points of atmospheric attenuation of a signal over a period of time, the method comprising: cleaning the attenuation data by accounting for equipment biases present in the system; synchronising the attenuation data by using time measurements associated with each data point of atmospheric attenuation and accounting for offsets between time measurements at each receiver station; and harmonising the attenuation data so that the harmonised data for each of the plurality of geographically distinct transceiver stations comprises attenuation values at regular intervals, wherein the interval time is common between transceiver stations and wherein the attenuation data for each receiver station has a common start time and a common end time. (Method of processing signal power data)
18. 18. The method of claim 17, wherein the periodic interval is 30 seconds or less, wherein the processed attenuation data covers a period of at least 3 months preferably at least six months more preferably at least one year.
19. 19. The method of claim 17 or claim 18, wherein harmonising the attenuation data so that the harmonised data for each of the plurality of geographically distinct transceiver stations comprises attenuation values at regular intervals comprises interpolating attenuation values at common time intervals from attenuation data.
20. 20. The method of any of claims 17 to 19, wherein cleaning the attenuation data by accounting for equipment biases present in the system comprises normalising the data points to account for one or more of: satellite movement, thermal shifts, power fluctuations, and temperature effects.
21. 21. The method of any preceding claim, wherein attenuation A(t) is calculated as the difference between a signal reference level R(t) and the received signal S(t): A(t) = R(t) -S(t).
22. 22. The method of claim 21, wherein the signal reference level R(t) is determined by iterative application of a Fourier series to the received signal S(t).