System requirements for Ka-band Earth-satellite propagation data

Accurate estimates of the propagation impairments that affect link quality and availability and determine signal interference fields are essential for the reliable design of telecommunication systems and the efficient use of the electromagnetic spectrum. Recent announcements by commercial entities of their intent to use Ka-band spectrum to supply satellite services have heightened interest in propagation data and models for these frequencies. This paper provides a brief overview of Ka-band Earth-satellite systems and requirements in relation to the need for specific types of propagation data     

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     

Irreducible error rate in aeronautical satellite channels

The author examines the irreducible error rate in aeronautical satellite systems. It is shown that the presence of a delay in the multipath component of a Rician channel increases the irreducible error rate of the receiver     

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 NASA's 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.     

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     

An update on NASA K/sub a/-band propagation measurements

Recent and current K/sub a/-band propagation efforts are centered around two space platforms of opportunity, namely, the European Space Agency's (ESA's) Olympus,and NASA's ACTS' satellites. The US Olympus measurements were carried out by the Virginia Polytechnic Institute and State University (Virginia Tech) at Blacksburg, VA, from 1991 to 1993. The measurement phase of that experiment ended in early 1993, and the data-analysis phase was completed in December, 1993. The ACTS propagation campaign began its data-collection phase in December, 1993, at several North American sites; it will continue for two years, and may be extended to three or four years. The goal of the K/sub a/-band propagation studies at JPL is to enable the satellite-communications industry to combat propagation channel impairments in the K/sup a/-band. To define the objectives of the experimental campaigns, JPL relied on the views of the users in industry, academia, and government agencies.<>     

Phase Error Statistics in Costas Loops Due to Channel Distortion and Noise

This paper treats the problem of phase recovery loop performance loss due to a nonideal RF channel. The linear channel under consideration is assumed to suffer from a variety of impairments such as bandwidth limitation, hardware imperfections, and asymmetry of its transfer function. The phase error probability density function of a first-order Costas loop is presented. It has been determined that the phase error is biased in general, and the condition for eliminating this bias is pointed out. To avoid computational complexity and elude computer programming, a simple method is presented for hand computation of the ISI intensity in the loop. Channel bandwidth reduction also introduces phase jitter which can be controlled by proper signal spectrum shaping. For example, it is possible to communicate with a spectral efficiency of 1 bit/s/Hz without degrading the loop performance. Examples have been presented to examine a few practical problems.     

2400 bit/s DMSK modem for mobile satellite service

The letter describes the implementation of a differentially coherent receiver suitable for bursty signal transmission over fading channels. To meet the severe system phase response requirement, this implementation is conducted at baseband. Means of frequency correction (AFC) is also shown. This receiver is simple and can easily be fabricated using VLSI technology.     

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 NASA's Mars Reconnaissance Orbiter spacecraft in the 2007-2008 period, and the demonstration findings will be reported in a future publication.     

Channel Simulation to Facilitate Mobile-Satellite Communications Research

In designing a mobile satellite network, engineers and technologists are faced with wide-ranging issues for which there is no prior database. System engineers must address such issues as adequate margin to combat multipath fading, the level of adjacent channel protection required to allow transmission in narrow-band channels, the cochannel protection required to allow for frequency reuse in a multiplebeam system, and the level of intermodulation distortion tolerable for single-channel-per-carrier operation. Technologists, on the other hand, must determine the performance of various system components. For example, in the ground segment, modem and speech codec performance must be evaluated in the presence of thermal noise, fading, and other impairments. To enable system designers and technologists to optimize their design and pursue their research and development, the Jet Propulsion Laboratory has developed a mobile satellite channel simulator in hardware. This simulator has sufficient flexibility to facilitate many forms of tests and experiments.