Dennis Lee

Bandwidth-Efficient Digital Modulation with Application to Deep Space Communications: Simon/Bandwidth-Efficient

Foreword. Preface. Chapter 1: Introduction. Chapter 2: Constant Envelope Modulations. 2.1 The Need for Constant Envelope. 2.2 Quadriphase-Shift-Keying and Offset (Staggered) Quadriphase-Shift-Keying. 2.3 Differentially Encoded QPSK and Offset (Staggered) QPSK. 2.4 /4-QPSK: A Variation of Differentially Encoded QPSK with Instantaneous Amplitude Fluctuation Halfway between That of QPSK and OQPSK. 2.5 Power Spectral Density Considerations. 2.6 Ideal Receiver Performance. 2.7 Performance in the Presence of Nonideal Transmitters. 2.7.1 Modulator Imbalance and Amplifier Nonlinearity. 2.7.2 Data Imbalance. 2.8 Continuous Phase Modulation. 2.8.1 Full Response-MSK and SFSK. 2.8.2 Partial Response-Gaussian MSK. 2.9 Simulation Performance. References. Chapter 3: Quasi-Constant Envelope Modulations. 3.1 Brief Review of IJF-QPSK and SQORC and their Relation to FQPSK. 3.2 A Symbol-by-Symbol Cross-Correlator Mapping for FQPSK. 3.3 Enhanced FQPSK. 3.4 Interpretation of FQPSK as a Trellis-Coded Modulation. 3.5 Optimum Detection. 3.6 Suboptimum Detection. 3.6.1 Symbol-by-Symbol Detection. 3.6.2 Average Bit-Error Probability Performance. 3.6.3 Further Receiver Simplifications and FQPSK-B Performance. 3.7 Cross-Correlated Trellis-Coded Quadrature Modulation. 3.7.1 Description of the Transmitter. 3.7.2 Specific Embodiments. 3.8 Other Techniques. 3.8.1 Shaped Offset QPSK. References. Chapter 4: Bandwidth-Efficient Modulations with More Envelope Fluctuation. 4.1 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Equal Signal Energie. 4.1.1 ISI-Based Transmitter Implementation. 4.1.2 Evaluation of the Power Spectral Density. 4.1.3 Optimizing the Bandwidth Efficiency. 4.2 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Unequal Signal Energies. References. Chapter 5: Strictly Bandlimited Modulations with Large Envelope Fluctuation (Nyquist Signaling). 5.1 Binary Nyquist Signaling. 5.2 Multilevel and Quadrature Nyquist Signaling. References. Chapter 6: Summary. 6.1 Throughput Performance Comparisons. References.

Uplink array concept demonstration with the EPOXI spacecraft

Uplink array technology is currently being developed for NASAs Deep Space Network (DSN), to provide greater range and data throughput for future NASA missions, including manned missions to Mars and exploratory missions to the outer planets, the Kuiper belt, and beyond. The DSN uplink arrays employ N microwave antennas transmitting at X-band to produce signals that add coherently at the spacecraft, thereby providing a power gain of N2 over a single antenna. This gain can be traded off directly for N2 higher data rate at a given distance such as Mars, providing for example HD quality video broadcast from earth to a future manned mission, or it can provide a given data-rate for commands and software uploads at a distance N times greater than possible with a single antenna. The uplink arraying concept has been recently demonstrated using the three operational 34-meter antennas of the Apollo complex at Goldstone, CA, which transmitted arrayed signals to the EPOXI spacecraft. Both two-element and three-element uplink arrays were configured, and the theoretical array gains of 6 dB and 9.5 dB, respectively, were demonstrated experimentally. This required initial phasing of the array elements, the generation of accurate frequency predicts to maintain phase from each antenna despite relative velocity components due to earth-rotation and spacecraft trajectory, and monitoring of the ground system phase for possible drifts caused by thermal effects over the 16 km fiber-optic signal distribution network. This paper provides a description of the equipment and techniques used to demonstrate the uplink arraying concept in a relevant operational environment. Data collected from the EPOXI spacecraft was analyzed to verify array calibration, array gain, and system stability over the entire 5 hour duration of this experiment.

Formulation of Forward Error Correction Coding Recommendations for Future NASA Space Communications

NASA has undertaken a study to recommend and justify coding, modulation, and link protocol (CMLP) designs for the Space Communications and Networking (SCaN) office. This paper reports on the coding part of the CMLP study, which is chartered with identifying the forward error correction (FEC) codes suitable for NASA space exploration and science missions through 2030.

Analysis of errors for uplink array of 34-m antennas for deep space applications

Although the technologies for large arrays of distributed reflector antennas with just downlink (receiving) capability have been well defined and proven for deep space applications, a similar architecture, i.e., the arraying of distributed reflector antennas for uplink (transmitting) applications has not been proven, tested, or built yet. In previous papers (Hurd, 2005) the need, feasibility, technology challenges and high-level system issues of a large array of reflector antennas with uplink capability for the future deep space network (DSN) were discussed. In particular, the primary design drivers, cost drivers, and technology challenges for uplink array phase calibration were addressed together with some preliminary test results with the 34-m antenna exciters. It is now of great interest to obtain the key requirements for the current Deep Space Network (DSN) 34-m antennas so that they can operate in an uplink array mode. The successful demonstration of the DSN 34-m antennas in uplink array mode serves as a prototype and a key milestone for the future large array development. In this paper, simulation and analysis of the current DSN 34-m antennas in an uplink array mode were discussed

GMSK modulation for deep space applications

Due to scarcity of spectrum at 8.42 GHz deep space X-band allocation, many deep space missions are now considering the use of higher order modulation schemes instead of the traditional binary phase shift keying (BPSK). One such scheme is pre-coded Gaussian minimum shift keying (GMSK). GMSK is an excellent candidate for deep space missions. GMSK is a constant envelope, bandwidth efficient modulation whose frame error rate (FER) performance with perfect carrier tracking and proper receiver structure is nearly identical to that of BPSK. There are several issues that need to be addressed with GMSK however. Specifically, we are interested in the combined effects of spectrum limitations and receiver structure on the coded performance of the X-band link using GMSK. The receivers that are typically used for GMSK demodulations are variations on offset quadrature phase shift keying (OQPSK) receivers. In this paper we consider three receivers: the standard DSN OQPSK receiver, DSN OQPSK receiver with filtered input, and an optimum OQPSK receiver with filtered input. For the DSN OQPSK receiver we show experimental results with (8920, 1/2), (8920, 1/3) and (8920, 1/6) turbo codes in terms of their error rate performance. We also consider the tracking performance of this receiver as a function of data rate, channel code and the carrier loop signal-to-noise ratio (SNR). For the other two receivers we derive theoretical results that will show that for a given loop bandwidth, a receiver structure, and a channel code, there is a lower data rate limit on the GMSK below which a higher SNR than what is required to achieve the required FER on the link is needed. These limits stem from the minimum loop signal-to-noise ratio requirements on the receivers for achieving lock. As a result of this, for a given channel code and a given FER, there could be a gap between the maximum data rate that BPSK can support without violating the spectrum limits and the minimum data rate that GMSK can support with the required FER depending on the type of GMSK receiver that is used.

Planetary radar imaging with the Deep-Space Network's 34 meter Uplink Array

A coherent Uplink Array consisting of two or three 34-meter antennas of NASAs Deep Space Network has been developed for the primary purpose of increasing EIRP at the spacecraft1. Greater EIRP ensures greater reach, higher uplink data rates for command and configuration control, as well as improved search and recovery capabilities during spacecraft emergencies2. It has been conjectured that Doppler-delay radar imaging of lunar targets can be extended to planetary imaging, where the long baseline of the uplink array can provide greater resolution than a single antenna, as well as potentially higher EIRP. However, due to the well known R4 loss in radar links, imaging of distant planets is a very challenging endeavor, requiring accurate phasing of the Uplink Array antennas, cryogenically cooled low-noise receiver amplifiers, and sophisticated processing of the received data to extract the weak echoes characteristic of planetary radar. This article describes experiments currently under way to image the planets Mercury and Venus, highlights improvements in equipment and techniques, and presents planetary images obtained to date with two 34 meter antennas configured as a coherently phased Uplink Array.

Uplink array calibration via lunar Doppler-delay imaging

Coherent arraying of transmitting antenna signals at a distant spacecraft provides an effective gain proportional to N2 , where N is the number of antennas in the array.1,2 This technology is currently being developed for NASAs Deep Space Network (DSN) to provide greater range and data throughput for future NASA missions, including manned missions to Mars and exploratory missions to the outer planets, the Kuiper belt, and beyond. However, successful uplink arraying of X-band (∼7.2 GHz) carriers transmitted by large 34 meter antennas separated by several hundred meters on the ground requires differential Doppler compensation and proper initial phasing to ensure coherent addition in the far-field of the array. This article describes a spacecraft-independent technique to phase-calibrate the array, where the calibration phases for two and three-antenna arrays are determined via lunar Doppler-delay imaging. This approach is required whenever the spacecraft range is large enough to render spacecraft-assisted calibration impractical due to long round-trip light times. The accuracy of the resulting calibration technique is evaluated, and long-term stability of the calibration phase-vector discussed in this article.

Delta-DOR and Regenerative Systems: The New CCSDS Frontier in Spacecraft Ranging

This paper presents the current Consultative Committee for Space Data Systems (CCSDS) activities aimed at improving a spacecrafts ranging accuracy and ultimately the knowledge of its orbit by developing a standard for Delta-differential one-way ranging and regenerative ranging techniques. Both techniques are explored and their expected main performance figures are given. The CCSDS work-plan is also indicated.