Faramaz Davarian

Mobile digital communications via tone calibration

A new digital signaling technique that is particularly suited for channels impaired by multipath fading is presented. The proposed modulation scheme employs a continuous-wave (CW) tone to calibrate the mobile channel against the multipath-induced phase uncertainties. This technique is applicable to quaternary phase shift keying as well as to more complicated signal constellations such as M-ary phase shift keyed schemes. The advantages of tone calibration are: 1) robustness of the receiver and 2) elimination of the link dependent error floor. Furthermore, since the CW tone can also be used for coherent signal demodulation, carrier phase acquisition can be achieved within a bit time. This property is particularly attractive when a burst of data with a short burst length has to be detected. This radio technique is useful for both the terrestrial mobile and the newer satellite-aided mobile communication (SAMC) services.

Deep Space Ka-Band Link Management and Mars Reconnaissance Orbiter: Long-Term Weather Statistics Versus Forecasting

During the last 40 years, deep space radio communication systems have experienced a move toward shorter wavelengths. In the 1960s, a transition from L- to S-band occurred, which was followed by a transition from S- to X-band in the 1970s. Both these transitions provided deep space links with wider bandwidths and improved radio metrics capability. Now, in the 2000s, a new change is taking place: namely, a move to the Ka-band region of the radio frequency spectrum. Ka-band will soon replace X-band as the frequency of choice for deep space communications, providing ample spectrum for the high data rate requirements of future missions. The low-noise receivers of deep space networks have a great need for link management techniques that can mitigate weather effects. In this paper, three approaches for managing Ka-band Earth-space links are investigated. The first approach uses aggregate annual statistics, the second one uses monthly statistics, and the third is based on the short-term forecasting of the local weather. An example of weather forecasting for Ka-band link performance prediction is presented. Furthermore, spacecraft commanding schemes suitable for Ka-band link management are investigated. Theses schemes will be demonstrated using NASAs Mars Reconnaissance Orbiter spacecraft in the 2007-2008 period, and the demonstration findings will be reported in a future publication.

Uplink Arrays for the Deep Space Network

Deep-space communication and navigation is faced with two challenges in the future: (1) the potential retirement of the largest antennas of NASAs Deep Space Network and (2) an anticipated need for increasing ground system capacity so as to support higher data rates to and from missions operating at remote locations in the solar system, as well as in anticipation of a larger number of simultaneously flying missions. In the transmitting, or uplink, direction, one approach to increasing the effective transmitted power is to array multiple antennas. This is attractive mainly because it promises a lower construction cost than equivalent (large) single antenna systems. In addition, it has the potential for increasing the reliability of the uplink and reducing maintenance costs. This paper introduces the concept of uplink arraying by examining technological challenges and possible solutions to them. Arraying principles are presented and error sources described. The main challenge is to maintain carrier phase alignment among the antennas, and this must be done by periodic calibration. Presently, two calibration methods are being developed at the Jet Propulsion Laboratory as part of an uplink arraying demonstration effort. These methods are briefly discussed.

Link design and planning for Mars Reconnaissance Orbiter (MRO) Ka-band (32 GHz) telecom demonstration

NASA is planning a Ka-band (32 GHz) engineering telemetry demonstration with Mars Reconnaissance Orbiter (MRO). Capabilities of Ka-band for use with deep space mission are demonstrated using the link optimization algorithms and weather forecasting. Furthermore, based on the performance of previous deep space missions with Ka-band downlink capabilities, experiment plans are developed for telemetry operations during superior solar conjunction. A general overview of the demonstration is given followed by a description of the experiment planning during cruise, the primary science mission and superior conjunction. As part of the primary science mission planning the expected data return for various data optimization methods is calculated. These results indicate that, given MROs data rates, a link optimized to use of at most two data rates, subject to a minimum availability of 90%, performs almost as well as a link with no limits on the number of data rates with the same minimum availability requirement. Furthermore, the effects of forecasting on these link design algorithms are discussed

The Ka-band propagation measurements campaign at JPL

OLYMPUS, the NASA sponsored, JPL-managed, Ka-band propagation measurement campaign carried out at Virginia Tech and many European sites, is discussed. The basic physics involved, the OLYMPUS experiment itself, and the advanced communications technology satellite (ACTS) program, the purpose of which is to demonstrate the feasibility of the Ka-band (20 and 30 GHz) spectrum for satellite communications, as well as to help maintain US leadership in satellite communications. are described.<<ETX>>

Comments on "BPSK system with sounder to combat Rayleigh fading in mobile radio communication"

M. Yokoyama describes a binary phase shift keying (BPSK) system that by utilizing a sounder removes the error floor associated with Rayleigh faded signals. This correspondence shows that the analysis provided by Yokoyama can be drastically simplified.

A multiple digital modulator

A highly versatile modulator that uses digital signal processing methods is described. The scheme can realize most known modulations exhibiting diverse forms of signal spectrum and eye diagram, and it can realize a given modulation with extreme precision. A single modulator unit can be host to many forms of modulation, i.e. many forms of signal constellations and spectral shapes. The technique also tends itself very well to very large-scale integration (VLSI) and mass production.<<ETX>>

In Search of Earth-Like Planets [Point of View]

The question “are we alone in the Universe?” has more of a philosophical flavor than pure science. First, its underlying concept may be too complex to approach scientifically. In this article the author concern himself with the scientific aspect of the question and examine recent science-based findings.

Special Issue on Technical Advances in Deep-Space Communications and Tracking

The twelve articles in this special issue are devoted to the topic of deep space communication.

Forecasting of weather effects for the deep space network

The paper presents a proposed approach for Ka-band link management for deep space applications using daily weather forecasts and discusses the tools that will be employed for operations. Performance metrics are also presented. The proposed approach will be tested in a two-year experiment campaign.