Satellite on-board RFI detection

In one embodiment there are provided systems and methods for detecting radio frequency interference (RFI) on a satellite that implements on-board processing. The system leverages an on-board programmable modem complex, and in some cases reprograms portions thereof, to function as an RF spectrum analyzer sensor element that captures and relays received RF information as meta-data to a ground-based system where that information can then be used, on the ground, to generate a spectral display of a received signal at the satellite.

TECHNICAL FIELD

The present disclosure relates to satellite communications, particularly satellite communications that employ satellites with advanced on-board processing capabilities.

BACKGROUND

An important task of a satellite operator is to ensure that the Radio Frequency (RF) signals transmitted by earth-bound satellite antennas do not interfere with each other as they are received at the satellite. Normally, resulting Radio Frequency Interference (RFI) at the satellite is easily detectable because, in a traditional “bent pipe” configuration, all transmissions to the satellite are shifted in frequency and, for all practical purposes, immediately transmitted back to the ground. The received RF emissions can then be analyzed using, e.g., a ground based spectrum analyzer and any interference can be uncovered.

With the advent of satellite architectures employing on-board processing, where the uplink transmissions are terminated at the satellite, uplink RFI cannot be seen on the ground. That is, in an on-board processing system, the uplink signal is demodulated on the satellite, and converted into digital data using a modem complex. The modem complex passes the data to a computer system or processor that operates on the data and then passes new downlink data back to the modem complex. The modem complex then synthesizes and modulates the downlink data for downlink transmission. Thus, the nature of any RFI present in a signal received at the satellite is lost by the time the modem complex has finished its receive processing. This makes detection of RFI nearly impossible and can result in undetected poor received signal quality at the satellite.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

Described herein are systems and methods for detecting RFI on a satellite that implements on-board processing. The system uses an on-board programmable modem complex, and in some cases reprograms portions thereof, to function as an RF spectrum analyzer sensor element that captures and relays received RF information as meta-data to a ground-based system where that information is then used to generate a spectral display.

Example Embodiments

FIG. 1shows components on-board a satellite100that perform, at least partially, spectrum analysis of received signals. As shown, there is on-board satellite100, a receiver110(e.g., a transponder) that receives uplink signals from, e.g., a satellite antenna167that is fed an uplink signal168from satellite terminal A165. The original data, typically in digital form, may be supplied by a computer160that is itself connected to a network (not shown). The network may be of any type, including, e.g., an Ethernet network that handles packetized data.

Referring again to the elements on-board the satellite, the receiver110outputs a signal111that is passed to a frequency conversion module112that converts the signal111, e.g., in the form of a radio frequency (RF), to an intermediate frequency (IF) that can be more easily processed by subsequent processing modules. More specifically, in the case of a satellite with on-board processing, a modem complex120is provided and receives the IF output113of the frequency conversion module112. The IF output113is then demodulated by demodulation module122to provide original, e.g., packetized digital data123originally provided by computer160(or network connected thereto).

The packetized data123is then passed to at least one on-board processing element140. On-board processing element140may be a routing complex that is configured to, among other things, route individual packets in a stream of packets to one or more other routers or other downstream network devices. An advantage of such space-based routing is that the need to “double hop” network traffic from the satellite to a ground gateway hub (for routing) and then back again to the satellite is eliminated. This, in turn, reduces latency by shortening the end-to-end path of a given communication channel. Furthermore, on-board demodulation of satellite signals separates the uplink and downlink to enable support of multiple selectable satellite antennas. Further still, Quality of Service can be applied to different streams of a demodulated signal such that, e.g., audio and video conferencing applications are provided higher bandwidth than, perhaps, a generic file download.

In any event, once packets are processed by on-board processing element140, the output124thereof is passed back to the modem complex120in which a modulation module125modulates the packetized data to an IF. The thus-modulated data126is passed to frequency conversion module114, which converts the IF modulated data126output from the modulation module125to an RF signal115. RF signal115is then passed to a selected travelling wave tube amplifier (TWTA)116for transmission from the satellite via a downlink channel (transponder).

The downlink signal176from TWTA116is received by a satellite ground station antenna177and passed to satellite terminal B175for demodulation, etc. Resulting data may be passed to one of two locations: computer170(and associated network (not shown)) or spectrum analyzer display172.

Spectrum analyzer display172operates in conjunction with spectrum analyzer sensor element130that is on-board the satellite100. In order to troubleshoot RFI in a system employing on-board processing, spectrum analysis of the received signal168is implemented before the demodulation function. In this regard, spectrum analyzer sensor element130captures the IF signal113from the frequency conversion module112before that signal is processed by demodulation module122. The resulting frequency analysis data135is passed to on-board processing element140for, e.g., packetization, and then sent, similarly to other packetized data, to modulation module125, frequency conversion module114and TWTA116for downlink to satellite terminal B175. The frequency analysis data can then be passed to spectrum analyzer display172for viewing by a user.

FIG. 2shows space segment210and ground segment250for performing spectrum analysis on the received signal168. Analog-to-digital conversion (ADC) module220receives analog IF signal113and converts it to digital “chunks” that are sent for processing by the demodulation module122and, in this case, also are sent to digital down converter (DDC)230within spectrum analyzer sensor element130. The output of DDC230is down-sampled time domain signal meta-data (also referred to as “metadata”), which can be stored in, or passed through, a buffer or memory240. This meta-data comprises actual sampled data along with context information such as time that together enable a display to graphically present a radio spectrum. The down-sampled time domain signal meta-data is then passed to on-board processing element140as shown inFIG. 1, so as to be processed for downlink to the satellite terminal B175.

FIG. 2also depicts a ground segment250that receives the meta-data, and that performs a fast Fourier transform on that data as indicated by module260. The results are then passed to display module172that is configured to present a graphical frequency spectrum based on that data.

FIG. 3shows an example implementation of the modem complex120that can be configured to perform partial spectrum analysis of a received signal at the satellite100. The modem complex120(and spectrum analysis sensor element) may be implemented as one or more hardware components, one or more software components, or combinations thereof. More specifically, the modem complex120/sensor element130may be implemented as a programmable processor (microprocessor or microcontroller) or a fixed-logic processor360. In the case of a programmable processor, any associated memory370may be of any type of tangible processor readable memory (e.g., random access, read-only, etc.) that is encoded with or stores instructions, such as sensor/modem logic380that may employed to effect the modem complex120/sensor element130of the space segment210. Alternatively, the modem complex120of the space segment210may be comprised of a fixed-logic processing device, such as an application specific integrated circuit (ASIC) or digital signal processor that is configured with firmware comprised of instructions or logic (e.g., modem/sensor logic380) that cause the processor360to perform the functions described herein. Thus, the modem complex120of the space segment210may take any of a variety of forms, so as to be encoded in one or more tangible media for execution, such as with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and any processor may be a programmable processor, programmable digital logic (e.g., field programmable gate array) or an ASIC that comprises fixed digital logic, or a combination thereof. In general, any process logic may be embodied in a processor (or computer) readable medium that is encoded with instructions for execution by a processor that, when executed by the processor, are operable to cause the processor to perform the functions described herein. To enable connectivity with, e.g., frequency converter module112and on-board processor element140, an interface unit390may also be provided to effect connectivity with an on-board bus and/or other connection approaches.

Thus, as explained, a digital spectrum analyzer is implemented between a receive transponder (e.g., receiver110) and a programmable satellite modem (e.g., modem complex120) on-board the satellite100. The up-link signal of interest (e.g., signal168along with any interfering signal) is converted to the frequency domain via the digital down converter230and the generated digital spectrum is relayed either in-band (via the same transponder or a different one) or out-of-band to an earth station (e.g., satellite terminal B175) for analysis.

In one implementation, the space segment sensor function210is configured to be controlled via out-of-band communication. This provides the ability to investigate the frequency spectrum for RFI without having to disrupt service, as any disruption is often fatal to the system being observed, or before service is established.

In an embodiment, the modem complex120comprises several re-programmable elements and, in one configuration, one modem in the array supports each transponder on the satellite100to which the system connects. In one actual implementation, the modem complex120employs three active modems (with one held in an inactive state as a redundant spare) that connect with three transponders.FIGS. 4-7depict several modem card embodiments400,500,600,700a,700bthat support the spectrum analyzer functionality. These re-programmable modems cards allow for a single waveform algorithm to evolve using updated code loads. In addition, they allow new waveforms to be added to the system. While in some systems, the entire modem array operates using the same waveform algorithm software, in the embodiments described herein one modem may be programmed differently from the others, namely to function as a spectrum analysis sensor.

Under normal operating conditions, the re-programmable signal processors (e.g., processor360) in the modem array process the incoming and outgoing streams using the waveform code corresponding to the ground terminals sending and receiving the RF emissions. If RF interference were suspected on one of the transponders, the corresponding modem can be reloaded (e.g., re-programmed) with code to perform the digital down converting. Whereas a standard spectrum analyzer would take the output samples from the DDC, convert the samples to the frequency domain and plot the resulting data on a display screen, the down-converted data samples on the satellite generated by such a re-programmed modem are transported down to earth via modem complex120where they form the input to a remote spectrum analyzer (e.g., ground segment250).

For satellite modem complexes with multiple modems, the meta-data output from the modem running the spectrum analyzer code is itself packetized and sent out via one of the other modems to ground systems using, e.g., TCP/IP or whatever networking protocol supported by the system. Alternately, if the system only possessed one transponder/modem combination, the meta-data from the spectrum analyzer code could be stored on the system (e.g., in memory370) and transported to the ground once the waveform code (modem code) was once again loaded into the re-programmable processor360.

During satellite troubleshooting it is possible to be in a situation where in-band communication is not available through the transponder under investigation. For this reason, satellite command and control operations may be performed through a very robust transponder channel. This channel enables very basic out-of-band management to be performed on the components of the satellite without regard to the status of the other transponders. In one embodiment, this robust transponder channel/out-of-band interface is used to control the spectrum analyzer settings and to download the spectrum analysis data samples.

It is possible that when a given modem is re-programmed with spectrum analyzer code, waveform processing for all terminals under the effected modem/transponder combination may be disrupted. Assuming there were sufficient resources within the re-programmable processor360, it is possible to insert the spectrum analyzer/digital down converter code as a shim layer. The shim layer receives the raw input (already analog-to-digitally converted) and passes that to the spectrum analyzer code. It would also duplicate the received digital raw input and pass it to the waveform code. Still another possibility exists for systems that employ redundant modem cards. Assuming the bus structure and power budgets allow, a redundant modem card could be pressed into service as the spectrum analyzer. The redundant modem card could perform analysis operations on the received stream, but also duplicate the stream to the modem that normally processes the waveform in an attempt to reduce the impact to users on the analyzed transponder.

Thus, there are a number of possible configurations for the modem complex120to support the space segment sensor function210. Several of these configurations are explained next with reference toFIGS. 4-7.

In a first configuration depicted byFIG. 4, there is a limited capacity modem processing element420on modem card400. That is, the modem card400can either handle waveform processing or DDC processing, but not both. In this configuration out-of-band (OOB) configuration commands may be used to re-program the modem card400with the DDC function code230. The duration of the DDC processing and other tunable parameters may also be supplied via OOB commands. The resulting DDC meta-data135is passed to the on-board processing element140and stored for later retrieval (storage could also occur within the modem complex120). At the end of the sampling duration, the waveform modem code is re-programmed back into the modem card400. Finally, the stored meta-data is retrieved by the ground segment for display.FIG. 4also shows how the modem card can communicate via a bus410, and that a digital to analog converter221is used to generate an analog signal for downlink transmission.

In a second configuration depicted byFIG. 5, a larger capacity modem card500is provided that can handle both waveform processing and DDC processing, simultaneously. That is, the re-programmable processing element520handling the modem functions for the waveform has sufficient capacity to perform both waveform processing and DDC processing. Thus, in this embodiment, an in-band configuration command may be used to enable the DDC function code230within the modem card500. Likewise, duration and other tunable parameters may also be supplied in-band. In one implementation, original digital chunks from the ADC220are duplicated by the DDC module230with one chunk passed untouched to the demodulation module122and one chunk processed by the DDC module230. DDC meta-data is passed to the on-board processing element140and then, e.g., in-band to the ground segment. Normal network communication processing proceeds under this configuration.

In a third configuration depicted byFIG. 6, multiple limited capacity modem processing elements on a single modem card600are implemented for, e.g., radiation robustness. One of the processing elements620acan be employed for DDC processing allowing the others620b,620cto perform waveform processing in a reduced robustness capacity. Thus, in this configuration, the modem card600has multiple re-programmable modem processing elements620a-cto aid in radiation robustness, each of which has insufficient capacity to handle both waveform processing and DDC processing. In-band configuration commands may be used to re-program one of the modem processing elements (620a) with the DDC function code. The duration and other tunable parameters may also be supplied in-band. The other processing elements620b,620ccontinue to perform their modem functions but in a degraded state. The DDC meta-data135is passed to the on-board processing element and then, e.g., in-band to the ground segment. As with the second configuration, normal network communication processing proceeds. At the end of the sampling duration, the DDC element230is re-programmed with the waveform modem function.

Finally, in a fourth possible configuration, depicted byFIG. 7, an active701and warm-standby702modem card employing limited capacity modem processing elements720a,720bwhere the warm-standby modem card402can be selected for service for DDC processing while the active modem card continues waveform processing. In-band configuration commands may be used to re-program the modem processing element720aon the warm-standby modem card702with the DDC function code230. The duration and other tunable parameters may also be supplied in-band. The active modem card701continues communication processing, while DDC meta-data135is passed to the on-board processing element140and then, e.g., in-band to the ground. At the end of the sampling duration, the warm-standby modem card702is re-programmed with waveform code and returned to a warm-standby state.

It is noted that in the embodiments ofFIGS. 5-7user traffic can continue to flow through the satellite while troubleshooting the communications link.

FIG. 8depicts an example series of steps that may be performed to obtain spectral analysis in connection with a satellite that conducts on-board processing of received uplink signals.

Beginning at step810, a processor (within, e.g., modem complex120) is re-programmed to perform digital down converting of a received digital signal. At step812, a satellite receives an analog signal. That signal will likely include a desired uplink signal, but may also include one or more interfering signals that might increase the noise associated with the desired uplink signal. At step814, the received analog signal is analog-to-digitally converted on-board the satellite. At this point, the resulting digital signal is provided to, e.g., digital down converter module230(e.g., the re-programmed processor) so that at step816the resulting digital signal is digitally down converted. The result of this conversion is down-sampled time-domain signal meta-data. This meta-data, at step818, is processed for transmission to a ground station. Processing may include packetization of the meta-data, as well as digital-to-analog conversion. At step820, the processed meta-data is transmitted to ground. The processed meta data can be transmitted in real time, namely substantially at the same time as it is generated, or it may instead stored in memory for subsequent transmission, after, e.g., step822wherein the processor is re-programmed back to an original functionality, such modem functionality.

Although not shown inFIG. 8, the meta-data transmitted, or downlinked, to ground is then retrieved and processed for presentation as a spectrum analysis graphical display. The spectrum analysis can be compared to a spectrum analysis of an uplink analog signal to detect the presence of radio frequency interference (RFI) at a receive antenna of the satellite.

As part of the downlink transmission and as a result of on-board processing capabilities, it is possible in accordance with one possible implementation to select a downlink channel (or transponder) from among a plurality of downlink channels (or transponders) via which to send the down-sampled time-domain signal meta-data. This provides flexibility to satellite operators to select an appropriate downlink channel to, e.g., least impact satellite operations, or to ensure robustness of the downlink by using, e.g., an out of band control channel.

In an embodiment, re-programming of a processor to perform the digital down converting function lasts only for a predetermined amount of time. That amount of time is selectable by the satellite operator, but should be sufficient to capture and analyze enough received data to provide useful spectrum analysis to a ground based user.

Although the system and method are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the scope of the apparatus, system, and method and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the apparatus, system, and method, as set forth in the following.