ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / High data rate communication between airborne vehicles and ground stations over the bandwidth constrained Aeronautical Telemetry channel is attributed to the development of bandwidth efficient Advanced Range Telemetry (ARTM) waveforms. This communication takes place over a multipath channel consisting of two components - a line of sight and one or more ground reflected paths which result in frequency selective fading. We concentrate on the ARTM SOQPSKTG transmit waveform suite and decode information bits using the reduced complexity Viterbi algorithm. Two different methodologies are proposed to implement reduced complexity Viterbi decoders in multipath channels. The first method jointly equalizes the channel and decodes the information bits using the reduced complexity Viterbi algorithm while the second method utilizes the minimum mean square error equalizer prior to applying the Viterbi decoder. An extensive numerical study is performed in comparing the performance of the above methodologies. We also demonstrate the performance gain offered by our reduced complexity Viterbi decoders over the existing linear receiver. In the numerical study, both perfect and estimated channel state information are considered.

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 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper will present equations for calculating the minimum recommended frequency separation of two digital telemetry signals. The signals can be filtered continuous phase frequency shift keying (CPFSK), multi-h continuous phase modulation (CPM) [1], shaped offset quadrature phase shift keying-Telemetry Group (SOQPSK-TG, aka SOQPSK-A*) [2], or Feher’s patented quadrature phase shift keying FQPSK-B (or FQPSK-JR [3]). The equations are based on measured data in an adjacent channel interference (ACI) environment for filtered CPFSK (aka PCM/FM), multi-h CPM (or CPM for short), SOQPSK-TG, FQPSK-JR, and FQPSK-B. This paper is an extension of my 2001 and 2002 International Telemetering Conference papers on this topic [4, 5]. The quantity measured was bit error probability (BEP) versus frequency separation at a given signal energy per bit to noise power spectral density ratio (Eb/No). The interferers were CPFSK, CPM, SOQPSK-TG or FQPSK-B (-JR) signals. The results presented in this paper will be for a desired signal bit rate of 1 to 20 Mb/s, one interferer 20 dB larger than the desired signal (a few tests included two interferers), and various center frequency spacings, interfering signals, receivers, and demodulators. The overall ACI test effort has collected data sets at several bit rates and with one and two interferers. The results will be useful to system designers and range operators as they attempt to maximize the number of Mb/s that can be simultaneously transmitted with minimal interference in the telemetry bands.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / This paper will present measured data in an adjacent channel interference (ACI) environment for filtered continuous phase frequency shift keying (CPFSK or FM), multi-h continuous phase modulation (multi-h CPM or CPM for short) [1] and Feher’s patented quadrature phase shift keying (FQPSK-B) [2]. This paper is an extension of my 2001 International Telemetering Conference paper on this topic [3]. The quantity measured was bit error probability (BEP) versus signal energy per bit to noise power spectral density ratio (E(b)/N(o)). The interferers were CPFSK, CPM, or FQPSK-B signals. The results presented in this paper will be for a desired signal bit rate of 5 Mb/s, one interferer 20 dB larger than desired signal (a few tests included two interferers), and various center frequency spacings, interfering signals, receivers, and demodulators. The overall ACI test effort will collect data sets at several bit rates and with one and two interferers. The results will be useful to system designers and range operators as they attempt to maximize the number of Mb/s that can be simultaneously transmitted with minimal interference in the telemetry bands.

Aeronautical telemetry suffers from multipath interference, which can be resolved through the use of equalizers at the receiver. The coefficients of data-aided equalizers are computed from a channel estimate. Most channels seen in aeronautical telemetry are sparse, meaning that most of the coefficients of the channel are zero or nearly zero. The maximum likelihood (ML) estimate does not always produce a sparse channel estimate. This thesis surveys a number of sparse estimation algorithms that produce a sparse channel estimate and compares the post-equalizer bit error rates (BER) using these sparse estimates with the post-equalizer BER using the ML estimate. I show that the generalized Orthogonal Matching Pursuit (GOMP) performs the best followed by the Sparse Estimation based on Validation Re-estimated Least Squares (SPARSEVA-RE) and the Least Absolute Shrinkage and Selection Operator (LASSO).

Wireless sensor networks have become a rapidly growing research field in recent years. They are envisioned to have a wide range of applications in military, environmental and many other fields. We examine the performance of wireless sensor network applications to aeronautical telemetry. To date, test ranges have relied on a single telemetry ground station for the reception of packets from all air borne transmitters. We researched an alternate means of achieving this same goal with fewer resources. It is a well known fact that communication power and bandwidth are the most expensive commodities in wireless communications. The telemetry world is ever in need of ways and means to reduce power requirements of its networks while maximizing the use of available bandwidth. In our alternate method, packets will be reliably transported to a centrally located monitoring station in a series of hops. We will effectively reduce the power requirements of the network by minimizing the distance coverage of the sensor nodes. We will also explore different network topologies with a view to maximizing the use of available bandwidth. The alternate method will present a less expensive way to implement telemetry networks. Currently, telemetry networks make use of a single, huge and expensive base station receiving packets from all airplanes in test. Affordable sensor nodes placed strategically on the range and configured properly will achieve the same goal in a cost effective, power saving and bandwidth considerate manner.

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 / A rocket launch, as high dynamics target, was used to demonstrate X-band tracking and also to verify high bit rate frequency planning while demonstrating significant bandwidth reduction with IRIG standard advanced modulation methods. X-band tracking by a modified 8-foot mobile telemetry antenna was excellent. Three separate S-band transmitters with three separate wraparound antennas were launched as a piggyback payload on an Enhanced Orion sounding rocket at White Sands Missile Range (WSMR) to compare the performance of 10 Mbs and 20 Mbs bit error rate (BER) pattern data transmission from CPFSK, FQPSK-JR and ARTM CPM modulation formats under high dynamic conditions. The test is more remarkable in that another S-band wideband spread spectrum signal was also transmitted with good success. These results show that all three modulation methods performed well during ignition and liftoff, low aspect angle (receiving through the rocket motor plume during ascent from a tracker near the launch pad), spin stabilization antenna lobe fades and payload tumbling. Spectrum pictures are provided to show the dramatic reduction in transmission bandwidth from CPFSK to FQPSK-JR to ARTM CPM. Confirmation of the preflight RF adjacent channel interference planning procedures from IRIG 106-05 is described by spectrum pictures and data quality measurements.

Aeronautical telemetry systems have historically been implemented with constant envelope modulations like CPM. Shifts in system constraints including reduced available bandwidth and increased throughput demands have caused many in the field to reevaluate traditional methods and design practices. This work examines the costs and benefits of using APSK for aeronautical telemetry instead of CPM. Variable rate turbo codes are used to improve the power efficiency of 16- and 32-APSK. Spectral regrowth in nonlinear power amplifiers when driven by non-constant envelope modulation is also considered. Simulation results show the improved spectral efficiency of this modulation scheme over those currently defined in telemetry standards. Additionally, the impact of transitioning from continuous transmission to burst-mode is considered. Synchronization loops are ineffective in burst-mode communication. Data-aided feed forward algorithms can be used to estimate offsets in carrier phase, frequency, and symbol timing between the transmitter and the receiver. If a data-aided algorithm is used, a portion of the transmitted signal is devoted to a known sequence of pilot symbols. Optimum pilot sequences for the three synchronization parameters are obtained analytically and numerically for different system constraints. The alternating sequence is shown to be optimal given a peak power constraint. Alternatively, synchronization can be accomplished using blind algorithms that do not rely on a priori knowledge of a pilot sequence. If blind algorithms are used, the observation interval can be longer than for data-aided algorithms. There are combinations of pilot sequence length and packet length where data-aided algorithms perform better than blind algorithms and vice versa. The conclusion is that a sequential arrangement of blind algorithms operating over an entire burst performs better than a CRB-achieving data-aided algorithm operating over a short pilot sequence.

Mathematical optimization is applicable to nearly every scientific discipline. This thesis specifically focuses on optimization applications to digital communications and signal processing. Within the digital communications framework, the channel encoder attempts to encode a message from a source (the sender) in such a way that the channel decoder can utilize the encoding to correct errors in the message caused by the transmission over the channel. Low-density parity-check (LDPC) codes are an especially popular code for this purpose. Following the channel encoder in the digital communications framework, the modulator converts the encoded message bits to a physical waveform, which is sent over the channel and converted back to bits at the demodulator. The modulator and demodulator present special challenges for what is known as the two-antenna problem. The main results of this work are two algorithms related to the development of optimization methods for LDPC codes and the two-antenna problem. Current methods for optimization of LDPC codes analyze the degree distribution pair asymptotically as block length approaches infinity. This effectively ignores the discrete nature of the space of valid degree distribution pairs for LDPC codes of finite block length. While large codes are likely to conform reasonably well to the infinite block length analysis, shorter codes have no such guarantee. Chapter 2 more thoroughly introduces LDPC codes, and Chapter 3 presents and analyzes an algorithm for completely enumerating the space of all valid degree distribution pairs for a given block length, code rate, maximum variable node degree, and maximum check node degree. This algorithm is then demonstrated on an example LDPC code of finite block length. Finally, we discuss how the result of this algorithm can be utilized by discrete optimization routines to form novel methods for the optimization of small block length LDPC codes. In order to solve the two-antenna problem, which is introduced in greater detail in Chapter 2, it is necessary to obtain reliable estimates of the timing offset and channel gains caused by the transmission of the signal through the channel. The timing offset estimator can be formulated as an optimization problem, and an optimization method used to solve it was previously developed. However, this optimization method does not utilize gradient information, and as a result is inefficient. Chapter 4 presents and analyzes an improved gradient-based optimization method that solves the two-antenna problem much more efficiently.