International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Shaped Offset QPSK (SOQPSK), as proposed and analyzed by Terrance Hill, is a family of constant envelope waveforms that is non-proprietary and exhibits excellent spectral containment and detection efficiency. Results using a conventional coherent OQPSK demodulator without any special pulse shaping to recover the SOQPSK signal have been previously presented. This paper describes a trellis detector for SOQPSK-A and SOQPSK-B that provides superior detection performance, as compared to a traditional OQPSK detector, by accounting for the pulse shaping. Analytical error performance bounds, implementation of the trellis demodulator, and computer simulation results are presented.

In a telemetry system, it has been frequently proved that multipath channels and transmission noise are the most critical sources of distortion. While equalization allows a strong limitation of the multipath effects, the noise impact can be efficiently reduced if forward error correction is used. This paper proves that the combination of blind equalization and a powerful FEC like LDPC strongly improves bit error rates for the SOQPSK modulation. We also prove that a LDPC code is able to fully correct the residual errors that may persist at the equalizer output. In other terms, the combination of equalization and LDPC code enables quasi-error free transmissions in various channel scenarios that represent the various phases of a telemetry mission.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / The optimum detector for shaped offset QPSK (SOQPSK) is a trellis detector which has high complexity (as measured by the number of detection filters and trellis states) due to the memory inherent in this modulation. In this paper we exploit the cross-correlated, trellis-coded, quadrature modulation (XTCQM) representation of SOQPSK-TG to formulate a reduced complexity detector. We show that a factor of 128 reduction in the number of trellis states of the detector can be achieved with a loss of only 0.2 dB in bit error rate performance as compared to optimum at P(b) = 10^(-5).

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 NASA Space-based Telemetry and Range Safety (STARS) program has developed and tested a low cost Ku-Band transmitter alternative for TDRSS applications based on an existing IRIG shaped offset quaternary phase shift keying (SOQPSK) transmitter. This paper presents information related to the implementation of this low cost system, as well as performance measurements of the alternative TDRSS transmitter system compared with an existing QPSK TDRSS transmitter.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Off-line software based signal analysis can be a valuable tool for detailed examination of transmitter signal characteristics. This paper describes the Advanced Range Telemetry (ARTM) Constant Envelope (CE) offset quadrature phase shift keying (OQPSK) modulation analyzer. It was developed expressly for evaluation of FQPSK-B^(1), FQPSK-JR and shaped OQPSK transmitter signals. Rationale for its creation, underlying assumptions, computation methods, and examples of its data products are presented.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper presents a method of detecting the Tier I modulation SOQPSK when it is used in a space-time coded (STC) system in which there is a non-negligible differential delay between the received signals. Space-time codes are useful to eliminate data dropouts which occur on aeronautical telemetry channels in which transmit diversity is employed. The proposed detection algorithm employs a trellis to detect the data while accounting for the offset between the in-phase and quadrature-phase components of the signals as well as the differential delay. The performance of the system is simulated and presented and it is shown that the STC eliminates the BER floor which results from the data dropouts.

ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Data-aided symbol synchronization for bursty communications utilizes a predetermined modulation sequence, i.e., a preamble, preceding the payload. For effective symbol synchronization, this preamble must be designed in accordance with the modulation format. In this paper, we analyze preambles for shaped offset quadrature phase-shift keying (SOQPSK) waveforms. We compare the performance of several preambles by deriving the Cram´er-Rao bound (CRB), and identify a desirable one for the Telemetry Group variant of SOQPSK. We also demonstrate, via simulation, that the maximum likelihood estimator with this preamble approaches the CRB at moderate signal-to-noise ratio.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Shaped Offset Quadrature Shift Keying (SOQPSK) is a spectrally efficient modulation that has been promoted in the airborne telemetry community as a more spectrally efficient alternative for legacy PCM/FM. First generation demodulators for SOQPSK use coherent detectors which achieve good bit error rates at the expense of long synchronization times. This paper examines the performance of a noncoherent SOQPSK detector which significantly improves the signal acquisition times without impacting BER performance in the AWGN environment. The two detection methods are also compared in their ability to combat other channel impairments, such as adjacent and on-channel interference.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / Shaped Offset QPSK (SOQPSK), as proposed and analyzed by Terrance Hill, is a family of constant envelope waveforms that is non-proprietary and exhibits excellent spectral containment and detection efficiency. Results for two variants, defined as SOQPSK-A and -B, have previously been presented. However, it remains to be seen whether or not even more attractive choices exist. This paper explores the bandwidth and power efficiency trade-offs of the entire SOQPSK family using computer simulations and analytical performance bounds.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / It is widely recognized that telemetry channels, particularly airborne channels, are afflicted by multipath propagation effects. It has also been shown that adaptive equalization can be highly effective in mitigating these effects. However, numerous other factors influence the behavior of adaptive equalization, and the type of modulation employed is certainly one of these factors. This is particularly true on modulations which exhibit different operating bandwidths. In this paper, we will examine the effect multipath and adaptive equalization for three modulation techniques which are either already in use, or have been proposed, for airborne telemetry.