NASA is involved in exploring the potential of the 20/30 GHz bands as evidenced by the propagation work in the ATS series by NASA-Goddard and, more recently, by the systems and market effort by NASA-Lewis. This paper focuses on the system and market work done by NASA-Lewis. Included are results of previous contractual and in-house studies, as well as preliminary results of on-going market and system studies. Baseline concepts for evaluating technology needs are also included.

SEASAT-1 is now an established fact. It is providing continuous sensing of the world's oceans and related meteorological phenomena from its satellite platform in space. What is the next step? This paper considers the information delivery challenges of the follow-on programs to SEASAT as they progress through the next decade. These include coping with the vast quantities of data to be transferred, fulfilling the temporal requirements on data delivery, and the trade-offs and developments needed to accomplish the various levels of processing required to convert sensor output into useful information. A need for critical development is clearly identifiable in the areas of low cost ground terminals capable of image extraction and image correlation; dynamic data assimilation to accomodate forecasters; low resolution onboard correlators; and low cost user advisory (display) terminals. The system planners for the Ocean Satellite advanced programs are utilizing an end-to-end data systems approach in meeting these challenges. The economic and scientific impact of delivering decision making information to the marine community in real time and in useful form is recognized and is potentially achievable.

The Air Force Space Laser Communications (LASERCOM) Program started with system concept and component design in the early 1970's at the Air Force Avionics Laboratory. The communications system that evolved demonstrated, in 1973, data rates up to one gigabit per second with a bit error rate of 10⁻⁶ for 40,000 kilometer simulated links. System capabilities were demonstrated during the period 1975 to present using an engineering feasibility model of a gigabit-per-second space qualifiable transmitter and a brassboard receiver. The next phase of the program started in September of this year when the LASERCOM system began operation outside of the laboratory environment at the White Sands Missile Range in New Mexico. This six-phase demonstration will include ground-to-ground links up to approximately 20 kilometers and aircraft-to-ground links up to approximately 50 kilometers. During these demonstrations, dynamic far-field acquisition, tracking, and two-way communications will be demonstrated. The performance characteristics of the LASERCOM system make its potential application to certain satellite-satellite and satellite-aircraft links unique, while other potential LASERCOM links require a detailed cost analysis of the current investment in radio frequency terminals and systems versus the cost of developing and deploying LASERCOM terminals and systems. There are also some communications links that can be most effectively satisfied by a hybrid LASERCOM and radio frequency system.

In 1979, American Satellite Corporation will be the first on-line completely all-digital communications carrier. This will be accomplished when American Satellite Corporation's major trunking earth terminals are converted to operate TDMA at data rates up to 64 Mbps.

A tandem queueing system with constant service times and threshold control is modeled and analyzed in this paper. The input to the first queue is controlled by the buffer occupancy of the second queue. When the second queue has more than No customers, the input to the first queue will be rejected. The input to the second queue consists of the output from the first queue and an external input which is assumed to be Poisson distributed. The behavior of such a queueing system is analyzed and portrayed in graphs. The threshold control rejects input traffic to the first queue and avoids congestion at the second queue. As a result, the delay for an arrival to be serviced by both of the queues is much lower than the case without threshold control. As N₀ increases, the system behavior approaches the case of the system without threshold control. Such a queueing model is motivated by congestion control in a computer network. An example is given to illustrate the applications.

Guidelines for the utilization of fiber optics transmission technology in the design of a standardized aircraft multiplex system interconnect have been difficult to establish. MILSTD-1553 is imprecise in the separation of transmission and operational functions with the result that the substitution of fiber optics for wire transmission specifications is impractical without redefinition of the 1553 word formats and data bus architecture.

It is required recently for data acquisition and supervisory system to provide transparent transmission of bit and message informations by packet or non-packet transmission method, and to provide various kinds of interface to I/O. In order to fulfill these requirements we have developed the new system called FATEC(Fujitsu Applied Telecommunication System) using microprocessor and bus technology.

We present a technique to compress M-bit data to N-bit data with a bounded error between the original and de-compressed data. The bounded error is established by quantizing the error signal of DPCM and by entropy encoding the quantized error. The fixed data rate is maintained by non-linear adaptation of the quantization interval on an intermittent basis. Examples of image data compression are given.

The currently developed theory of optimal demodulation and synchronization systems for digital data has been applied to the design of a class of programmable satellite receivers. The primary purpose is to provide flexibility in application through digital control of the important functions of the receiver. This permits the acquisition and demodulation of medium to very low data rates in widely varying communications environments and over a broad range of modulation schemes. The receiver peripherals are controlled by a digital processor which can accept external commands to reconfigure to any of a preprogrammed set of algorithms.

A demod-remod type of coherent tracking loop for conventional QPSK and staggered QPSK (SQPSK) is presented. The phase detector characteristic (S-curve) is determined. The effects of power unbalance and arm gain unbalance on the S-curve are presented. The steady state rms phase error is shown as a function of the signal-to-noise ratio at the output of the arm filters.