Aeronautical telemetry was supported by a standard set of tools for the last 40 years of the 20th century. Some of these legacy tools are still in use today, but they do not come close to matching the performance available now. New technologies, introduced in the past few years, have revolutionized the way telemetry is done, and the dramatically improved the quality of the flight test data thereby delivered. This overview describes these technologies, and the leadership role that Quasonix has taken in their introduction.
- Spectrally Efficient Modulations – Shaped Offset QPSK (SOQPSK) has become the de facto standard for telemetry because it uses less than half the bandwidth of the legacy PCM/FM waveform. SOQPSK was invented, introduced, and developed by the founder and president of Quasonix. With over 7,500 transmitters and 1,500 receivers in the field today, no other vendor has more experience in delivering SOQPSK systems than Quasonix.
- Trellis Demodulation – While not explicitly addressed in the RFI, any upgrade to telemetry systems being considered today should certainly include trellis demodulation, which provides dramatic improvements in bit error rate and synchronization performance, compared to traditional single-symbol detection. The founder and president of Quasonix led the team that first introduced trellis demodulators in the early 2000’s, and today Quasonix is the only vendor who offers trellis demodulation for PCM/FM, SOQPSK, and multi-h CPM waveforms.
- Adaptive Equalization – Multipath has always been a major cause of data dropouts in telemetry, and for about 50 years, there was no solution. Then, in mid-2015, Quasonix introduced the 3rdGeneration RDMS telemetry receiver with adaptive equalization, which largely eliminates multipath effects. The telemetry community immediately recognized this as a breakthrough, and nearly 400 units are now fielded, fixing multipath every day.
- Space-Time Coding (STC) – The traditional antenna installation on high-dynamic aircraft requires two antennas to provide reception from any aircraft attitude. This approach creates a “porcupine” antenna pattern for the aircraft, with inter-antenna interference creating nulls as deep as 30 dB in some directions. Space-Time Coding was introduced by Quasonix to solve this problem, and the field results are unambiguous: it simply works. STC eliminates the dropouts created by using two antennas on the aircraft, and therefore improves link margin. Instead of designing the link to tolerate the 20 to 30 dB antenna nulls, the TM engineer can assume that the aircraft antennas actually deliver the antenna gain specified by the manufacturer. This represents a link margin improvement of 20 dB or more. Quasonix has published the STC waveform details, and the Range Commanders Council incorporated STC into IRIG 106 in 2015. While this opens the door for our competitors to introduce their own STC transmitters and receivers, only Quasonix has actually delivered this ground-breaking technology.
- Low Density Parity Check Coding (LDPC) – Forward error correction in the telemetry channel has historically been problematic because the decoders have taken too long to synchronize. When Quasonix introduced LDPC error correction in 2013, we designed the signal to have very fast, very robust synchronization. This approach was quickly recognized as a breakthrough, which is why the Range Commanders Council adopted our LDPC technique in IRIG 106-15. The RCC has subsequently expanded the LDPC family to include a total of six codes. LDPC offers as much as 10 dB of additional link margin, to help close the longest links. Quasonix is the only vendor who can offer telemetry transmitters and receiver with even a single LDPC code, let alone all six.
- Time-aligning Diversity Combiner – Diversity combining is virtually ubiquitous in the telemetry market, because it simply works – most of the time. Conventional combiners require that the two signals being combined (two receive polarization, two frequencies, etc.) be aligned in time. If this assumption breaks down (a dual-transmitter frequency diversity system with widely separated transmit antennas, for example), then the conventional combiner fails because the waveforms being combined are not the same data. Only Quasonix offers a time-aligning diversity combiner, with the ability to time shift the two signals up to 1300 ns, so that the combiner can operate even with very large spacing between the two transmit antenna. This technique essentially improves link margin by allowing the combiner to always deliver the expected gain.
- Data Quality Metrics (DQM) – Many telemetry systems rely upon very primitive measures of signal quality, signal strength being the most common example. In today’s highly congested spectrum, this can lead to severe telemetry breakdowns, because “big” signals may not be “good” signals. In 2015, Quasonix developed a calibrated Data Quality Metric (DQM), which allows the receiver to determine the bit error probability (BEP) of the signal in real time – without knowing any of the data in the TM stream. This technique, which will be added to IRIG 106 in the 2017 edition, gives a Quasonix TM system the ability to stay locked on the desired signal, not just the biggest signal. This plays a key role in HyperTrack™ (see below).
- Data Quality Encapsulation (DQE) – For TM systems that utilize multiple receiving sites, correlating best source selection (BSS) is a powerful technique for bridging any gaps in coverage that might be encountered at a single site. However, until Quasonix introduced Data Quality Metrics, the BSS had no mathematically sound way of knowing which signal was “best”. When Quasonix introduced our DQM approach, we packaged this information into a Data Quality Encapsulation (DQE) format. Modern best source selectors use this information to make rock-solid decisions about how to utilize the data from multiple receiving sites. In one recent test using low-flying helicopters in he very rugged terrain of Yuma Proving Grounds in Arizona, STC, LDPC, DQE, DQM, and BSS combined to yield 34 minutes of absolutely error-free telemetry, a feat that had never been accomplished before. Only Quasonix offers all these key building blocks of 21st century telemetry systems.
- Telemetry over IP (TMoIP) – As telemetry resources become more widely deployed, the task of moving the data around on the ground becomes more significant. The cost effective approach to “publishing” TM data for use by multiple flight test consumers is to put the data onto an IP network. IRIG 218 defines how to do this, and Only Quasonix offers built-in TMoIP in our RDMS™ receivers. While this does not offer any improvement in link margin, or tracking accuracy, it does greatly streamline the ground infrastructure for distributing the received data.
- Multi-band Operation – The traditional L and S band allocations for aeronautical telemetry are slowly being reassigned to other end uses, worldwide. The migration to C band has already begun, and will continue for the next several years. During this transition period, multiband operation (covering L, S, and C bands) will be essential. Only Quasonix can offer the complete multi-band system solution, including transmitters, antennas, and receivers.
- Target Simulator – Verifying that a tracking antenna is working correctly is an important part of system checkout. The Quasonix Target Simulator (QTS) is a innovative package of software and hardware that exercises the antenna tracking loop by creating a synthetic AM and top dead center (TDC) signal. The user loads a hypothetical target trajectory into the QTS, and the QTS compares the current azimuth and elevation of the simulated target to the reported azimuth and elevation of the pedestal. Based on the position error, the QTS creates an AM signal at the amplitude and phase that would be created with a real target at that position. The tracking loop then acts to correct the position error, and the QTS captures the track of both the simulated target and the pedestal. This simulation capability is a powerful tool in the configuration, maintenance, and test of the tracking loop. Again, only Quasonix offers this capability. See Appendix D for more details.
- HyperTrack™ - Auto-tracking antennas have operated by the same basic principle since the 1960s: design the antenna to scan a small area around the target, and use the amplitude modulation (AM) thereby induced to steer the antenna toward the target. The specific implementations of this scheme have improved over the years, but there has been no fundamental change to the basic control mechanism – until now. Starting in mid 2017, Quasonix will begin shipping all 3rd Generation RDMS™ telemetry receivers with HyperTrack™, which revolutionizes the way auto-tracking antennas function. See Appendix D for the ground-breaking HyperTrack™ features.
- Ground Station Analyzer – Combining the QTS with HyperTrack™, Quasonix is able to offer the revolutionary Ground Station Analyzer (GSA). The QTS generates the AM signal as described above, but instead of injecting this waveform directly into the ACU, it is used to modulate an RF signal that is synthesized in the GSA. An amplitude modulator imposes the synthesized AM onto the RF signal, and then the amplitude and phase modulated signal is transmitted via a test dipole that’s installed facing the feed. This injects the test signal exactly as a real test article would, thereby testing the entire ground station. When driven by the QTS, the antenna will follow the synthetic target across the synthetic sky, and the receivers will demodulate the ARTM waveforms, for downstream processing by the decommutators. If there are dropouts caused by any limitations in the ground station, including tracking errors, the GSA will produce them. Once again, Quasonix leads the way.
- Commercial off the Shelf, Non-ITAR – While many of these technologies were once included on the United States Munitions List (USML), and therefore covered by ITAR, Quasonix has taken the initiative to have our entire catalog reclassified by the US Department of Commerce (DoC). Applying the new rules introduced under the US Export Control Reform Initiative, the DoC has determined that our entire catalog is no longer on the USML, but instead is on the Commerce Control List (CCL). This means that everything we have described above is a Commercial off the Shelf (COTS) item, and can be exported without an export license.
Taken together, the advanced technologies summarized above provide a level of telemetry data quality and operator insight that was not even remotely possible just ten years ago. Quasonix has not only played a leading role in the development of all these technologies, but is the only vendor in the telemetry market who can offer the complete end-to-end solution that leverages these advances, including transmitters, receivers, and tracking antennas. No one else can provide the whole system.