International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Shaped Offset QPSK (SOQPSK) has been shown to be nearly identical in performance to Feher-patented FQPSK, which is the Advanced Range Telemetry (ATRM) program's Tier I waveform. Multi-h CPM has been selected as the ARTM Tier II waveform, because it offers 50% better spectral efficiency than the Tier I waveform. Both the Tier I and Tier II waveforms must operate in a multipath channel in order to meet the range community's telemetry requirements. This paper presents an analytical and experimental characterization of SOQPSK and Multi-h CPM in the presence of multipath. Quantitative results are presented which demonstrate the relative robustness of the ARTM Tier I and Tier II waveforms, in channels representative of a typical range environment.

Multipath is one of the dominant causes for link loss in aeronautical telemetry. Equalizers have been studied to combat multipath interference in aeronautical telemetry. Blind equalizers are currently being used with SOQPSK-TG. The Preamble Assisted Equalization (PAQ) project studied data-aided equalizers with SOQPSK-TG. PAQ compares, side-by-side, no equalization, blind equalization, and five data-aided equalization algorithms: ZF, MMSE, MMSE-initialized CMA, and frequency domain equalization. This thesis describes the GPU implementation of data-aided equalizer algorithms. Static lab tests, performed with channel and noise emulators, showed that the MMSE, ZF, and FDE1 show the best and most consistent performance.

ITC/USA 2014 Conference Proceedings / The Fiftieth Annual International Telemetering Conference and Technical Exhibition / October 20-23, 2014 / Town and Country Resort & Convention Center, San Diego, CA / 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.

ITC/USA 2014 Conference Proceedings / The Fiftieth Annual International Telemetering Conference and Technical Exhibition / October 20-23, 2014 / Town and Country Resort & Convention Center, San Diego, CA / SOQPSK-TG is a highly bandwidth-efficient constant-envelope modulation so that it has been applied in aeronautical telemetry widely. We develop a simple detection of SOQPSK-TG which is based on a modified OQPSK detection. The simple detection has the advantages of low complexity and good performance. And it's also suitable for other varieties of SOQPSK and FQPSK.

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / Multipath interference continues to be the dominant cause of telemetry link outages in low-elevation angle reception scenarios. The most reliable and universally applicable solution to this problem is in the form of equalization. Previous work in this area has considered the Constant modulus algorithm (CMA) equalizer operating in a blind adaptive mode. To the extent that knowledge of the multipath channel improves the performance of CMA and related equalizers and permits the use of other equalization techniques, data aided equalizers are of interest. Channel knowledge is obtained by comparing the received samples with the samples corresponding to a known bit pattern (called a pilot block) periodically inserted in the telemetry data stream. The main objective of this research is to evaluate the performance of a modified CMA equalization algorithm, which has the property of automatically resolving the phase of the QPSK modulated symbol, and to determine its suitability for use with SOQPSK-TG by taking into account the capability of exploiting the presence of a periodically inserted pilot block. As an initial effort in that direction, this paper provides simulation results of the error performance of the blind linear combination of CMA and alphabet matched algorithm (AMA) equalizer as compared to that of pilot assisted equalization with SOQPSK modulation over aeronautical channel.

This paper focuses on the design of a simple Time Division Multiple Access (TDMA) signaling structure for the Link Dependent Adaptive Radio (LDAR) prototype wireless radio communication system to meet the timing requirements of the iNET standard. Built for aeronautical telemetry, LDAR adapts its modulation and coding scheme based on the channel condition in real time. In this paper, a simple protocol for transmission of Command Message and Data Message between Ground Station and Test Article is discussed. This protocol includes all analysis for the continuous adaptation of modulation scheme and coding rate to maximize throughput while ensuring a minimum level of link quality. This project was a collaborative effort between Morgan State University and Georgia Tech Research Institute and is a continuation of our previously published work on LDAR.

We demonstrate how the performance of offset quadrature phase-shift keying (OQPSK) and its variants of Feher-patented QPSK (FQPSK) and Shaped Offset QPSK (SOQPSK) (collectively known as the ARTM Tier-1 waveforms) in single input single output (SISO) system could change with the channel fading parameters. The bit error rate expression of offset QSPK and ATRM Tier-1 waveforms over the aeronautical telemetry multipath channel has been derived. Simulations show that for the case of a single multipath ray, the BER gets worse with increasing Γ for a fixed delay, and that the BER has a quasi-periodic property for fixed Γ and increasing τ. For the case of two multipath rays, the multipath component characterized by large amplitude and small delay is the main factor of the BER degradation, while the BER is not very sensitive to the change of multipath delay. Analysis of the average bit error probability shows that a relatively high error floor at approximately 10−2 occurs for |Γ1| ≥ 0.5. When offset quadrature phase-shift keying (OQPSK) is used in multiple input multiple output (MIMO) environment, orthogonal space-time block codes can be applied to waveforms to orthogonalize a space-time coded multiple-input, multiple output link. For offset QPSK, this technique has the advantage of eliminating the I/Q interference associated with simultaneous transmission of offset QPSK waveforms. In addition, orthogonalization presents uncorrelated noise samples to the space-time trellis decoder. As a consequence, a less complex space-time decoder (relative to what would be required without orthogonalization) can be used. It is demonstrated that a concatenated system based on an orthogonal space-time block code and a trellis code, optimized for single-input, single-output fading channel, outperforms a space-time trellis code for a 2x1 system. The space-time block code orthogonalizes the channel seen by the outer code and this simplifies the computations required for decoding. The advantages of orthogonalization are achieved at the expense of rate. In the examples presented, the codes were chosen to have roughly equivalent bit error rate performance and identical code rates: the complexity was compared.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / The ARTM Tier 1 waveforms include two versions of Feher patented QPSK (FQPSK-B and FQPSK-JR) and a version of shaped offset QPSK (SOQPSK-TG). In this paper we examine three common detector architectures for the ARTM Tier 1 modulations: a symbol-by-symbol detector, a cross correlated trellis coded modulation (XTCQM) detector, and a continuous phase modulation (CPM) detector. We show that when used to detect Tier 1 modulations, these detectors perform well even without knowledge of the modulation used by the transmitter. The common symbol-by-symbol detector suffers a loss of 1.5 dB for SOQPSK-TG and 1.6 dB for FQPSK-JR in bit error rate performance relative to the theoretical optimum for these modulations. The common XTCQM detector provides a bit error rate performance that is 0.1 dB worse than optimum for SOQPSK-TG and that matches optimum performance for FQPSK-JR. The common CPM detector achieves a bit error rate performance that is 0.25 dB worse than optimum for SOQPSK-TG and that approximately matches optimum for FQPSK-JR. The common XTCQM detector provides the best bit error rate performance, but this detector also has the highest complexity.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper will present the results of experiments to characterize the performance of a blind, adaptive constant modulus algorithm (CMA) equalizer in simulated telemetry multipath environments. The variables included modulation method, bit rate, received signal-to-noise ratio, delay of the indirect path relative to the direct path, amplitude of the indirect path relative to the direct path, and fade rate. The main measured parameter was bit error probability (BEP). The tests showed that the equalizer usually improved the data quality in the presence of multipath.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Improving the spectral-efficiency of aeronautical telemetry has been a principal area of research over the last several years due to the increasing demand for more data and the limitation of available spectrum. These efforts have lead to the development of the ARTM Tier 1 SOQPSK and Tier II Multi-h CPM waveforms which improve the spectral efficiency by two and three times, as compared to legacy PCM/FM, while maintaining similar detection efficiency. Now that more spectrally efficient waveform options are becoming available, another challenge is to further increase the detection performance. Better detection efficiency translates into additional link margin that can be used to extend the operating range, support higher data throughput, or significantly improve the quality of the received data. It is well known that Forward Error Correction (FEC) is one means of achieving this objective at the cost of additional overhead and increased receiver complexity. However, as mentioned above, spectral efficiency is also vitally important meaning that the FEC must also have a low amount of overhead. Unfortunately, low overhead and high coding gain are generally conflicting trades, although recent work has shown that Turbo Product Codes (TPC) are a particularly attractive candidate. Computer simulations predict that very impressive gains in detection performance are possible for a relatively small increase in bandwidth. The main drawbacks are the additional complexity of the decoding circuitry and an increase in receive side latency. This paper presents the latest simulation and hardware performance results of PCM/FM, SOQPSK, and Multi-h CPM with TPC.