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West Chester, OH, United States

Geoghegan M.,Quasonix | Boucher L.,Bombardier
Proceedings of the International Telemetering Conference

In order to provide reliable line-of-sight communications, test aircraft typically use two transmit antennas to create top and bottom hemispherical patterns that cover the full range of possible aircraft orientations. The two transmit signals are normally generated by a single transmitter with the power being split between the two antennas. Although this configuration is straightforward and easy to implement, problems can arise due to the two signals constructively and destructively interfering with each other. This can result in the composite antenna pattern having periodic nulls with a depth and geometric spacing dependent upon the amplitude and phase differences of the two transmitted signals. This problem is usually addressed by either unevenly splitting the transmit power between the two antennas, or by using two separate transmitters at different frequencies. Unfortunately, these methods have drawbacks that require either system performance or cost trade-offs. This paper discusses the use of Space-Time Coding to eliminate this antenna interaction by transmitting modified waveforms that simultaneously allow for both full power transmission and single-channel operation. This approach effectively restores the nominal antenna performance, thereby resulting in better overall coverage and less pattern-induced dropouts. Telemetry performance results from recent flight testing are presented to validate the benefits of this approach. Source

Schultz M.,Quasonix
Proceedings of the International Telemetering Conference

This article defines the system design for translating burst Ethernet packetized data into a constant rate serial data stream suitable for transmission over standard telemetry hardware physical links. The system supports both unidirectional (UDP) and bidirectional (TCP/IP, etc.) communications. This paper will evaluate the capabilities and limitations of the established fielded hardware, as well as possibilities for system growth (IRIG Chapter 10 compatibility). Source

Hill T.,Quasonix
Proceedings of the International Telemetering Conference

There is great potential in using Best Source Selectors (BSS) to improve link availability in aeronautical telemetry applications. While the general notion that diverse data sources can be used to construct a consolidated stream of "better" data is well founded, there is no standardized means of determining the quality of the data streams being merged together. Absent this uniform quality data, the BSS has no analytically sound way of knowing which streams are better, or best. This problem is further exacerbated when one imagines that multiple vendors are developing data quality estimation schemes, with no standard definition of how to measure data quality. In this paper, we present measured performance for a specific Data Quality Metric (DQM) implementation, demonstrating that the signals present in the demodulator can be used to quickly and accurately measure the data quality, and we propose test methods for calibrating DQM over a wide variety of channel impairments. We also propose an efficient means of encapsulating this DQM information with the data, to simplify processing by the BSS. This work leads toward a potential standardization that would allow data quality estimators and best source selectors from multiple vendors to interoperate. Source

Hill T.,Quasonix | Uetrecht J.,Quasonix
Proceedings of the International Telemetering Conference

Over the past decade, SOQPSK has been widely adopted by the flight test community, and the low density parity check (LDPC) codes are now in widespread use in many applictions. This paper defines the waveform and presents the bit error rate (BER) performance of SOQPSK coupled with a rate 2/3 LDPC code. The scheme described here expands the transmission bandwidth by approximately 56% (which is still 22% less than the legacy PCM/FM modulation), for the benefit of improving link margin by over 10 dB at BER = 10-6. Source

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