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Results for “Communication cost”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Compile-time estimation of communication costs in multicomputers

An important problem facing numerous research projects on parallelizing compilers for distributed memory machines is that of automatically determining a suitable data partitioning scheme for a program. Any strategy for automatic data partitioning needs a mechanism for estimating the performance of a program under a given partitioning scheme, the most crucial part of which involves determining the communication costs incurred by the program. A methodology is described for estimating the communication costs at compile-time as functions of the numbers of processors over which various arrays are distributed. A strategy is described along with its theoretical basis, for making program transformations that expose opportunities for combining of messages, leading to considerable savings in the communication costs. For certain loops with regular dependences, the compiler can detect the possibility of pipelining, and thus estimate communication costs more accurately than it could otherwise. These results are of great significance to any parallelization system supporting numeric applications on multicomputers. In particular, they lay down a framework for effective synthesis of communication on multicomputers from sequential program references.

Gupta, Manish↗
NASA NTRS2005

Low cost communication support of Lunar Missions

We present a concept and architecture for a low-cost communications infrastructure for these missions. There are two major elements: Earth stations and a small lunar relay constellation.

Deep Space Network (DSN) array↗
NASA NTRS1979

The critical satellite technical issues of future pervasive broadband low-cost communication networks

The critical technical issues of signal waveform design, projected spacecraft technology, satellite launch options, and satellite cost are discussed for future pervasive broadband communication networks. With DPCM video signal encoding, 32 Mb/s user-to-user data rate per channel, 10% overhead, two orthogonal polarizations, and crosstalk loss limited to 1 dB, TFM permits about 75 channels/GHz of frequency allocation. The BOM (beginning of mission) weight and power of a baseline 400-channel multibeam satellite is about 1800 kg and 5000 W. Each 35 Mb/s channel can support 1 to 10 video channels. The weight and power estimates assume hardened digital logic, composite materials for a multibeam antenna structure, high-efficiency solar cells, batteries, and amplifiers. Based on a cost model for large communication satellites, the total space segment cost of two active satellites and one spare would be about $485 M.

Harvey, R. L.↗
NASA NTRS1996

Standardized, Low Cost Communications for Planetary Mission

For Deep Space Missions, the Radio-Frequency (RF) communications link provides both communications and navigation services. In this article we discuss the increased efficiency and reduced cost that can result from the potential consolidation of the two services into one suite of equipment, and the utilization of guaranteed delivery standard protocols to improve the communications service.

Deep↗
NASA NTRS1994

Development of Low Cost Satellite Communications System for Helicopters and General Aviation

In this paper, the development of low-cost satellite communications (SATCOM) system for helicopters and General Aviation (GA) aircrafts is described. System design and standards analysis have been conducted to meet the low-cost, light-weight, small-size and low-power system requirements for helicopters and GA aircraft environments. Other specific issues investigated include coding schemes, spatial diversity, and antenna arraying techniques. Coding schemes employing Channel State Information (CSI) and inverleaving have been studied in order to mitigate severe banking angle fading and the periodic RF signal blockage due to the helicopter rotor blades. In addition, space diversity and antenna arraying techniques have been investigated to further reduce the fading effects and increase the link margin.

SATCOM helicopters general aviation satellite comm↗
NASA NTRS1993

Analysis of multigrid methods on massively parallel computers: Architectural implications

We study the potential performance of multigrid algorithms running on massively parallel computers with the intent of discovering whether presently envisioned machines will provide an efficient platform for such algorithms. We consider the domain parallel version of the standard V cycle algorithm on model problems, discretized using finite difference techniques in two and three dimensions on block structured grids of size 10(exp 6) and 10(exp 9), respectively. Our models of parallel computation were developed to reflect the computing characteristics of the current generation of massively parallel multicomputers. These models are based on an interconnection network of 256 to 16,384 message passing, 'workstation size' processors executing in an SPMD mode. The first model accomplishes interprocessor communications through a multistage permutation network. The communication cost is a logarithmic function which is similar to the costs in a variety of different topologies. The second model allows single stage communication costs only. Both models were designed with information provided by machine developers and utilize implementation derived parameters. With the medium grain parallelism of the current generation and the high fixed cost of an interprocessor communication, our analysis suggests an efficient implementation requires the machine to support the efficient transmission of long messages, (up to 1000 words) or the high initiation cost of a communication must be significantly reduced through an alternative optimization technique. Furthermore, with variable length message capability, our analysis suggests the low diameter multistage networks provide little or no advantage over a simple single stage communications network.

Matheson, Lesley R.↗
NASA NTRS2003

Abstract communication for coordinated planning

work offers evidence that distributed planning agents can greatly reduce communication costs by reasoning at abstract levels. While it is intuitive that improved search can reduce communication in such cases, there are other decisions about how to communicate plan information that greatly affect communication costs. This paper identifies cases independent of search where communicating at multiple levels of abstraction can exponentially decrease costs and where it can exponentially add costs. We conclude with a process for determining appropriate levels of communication based on characteristics of the domain.

coordination↗
NASA NTRS1994

On bottleneck partitioning k-ary n-cubes

Graph partitioning is a topic of extensive interest, with applications to parallel processing. In this context graph nodes typically represent computation, and edges represent communication. One seeks to distribute the workload by partitioning the graph so that every processor has approximately the same workload, and the communication cost (measured as a function of edges exposed by the partition) is minimized. Measures of partition quality vary; in this paper we consider a processor's cost to be the sum of its computation and communication costs, and consider the cost of a partition to be the bottleneck, or maximal processor cost induced by the partition. For a general graph the problem of finding an optimal partitioning is intractable. In this paper we restrict our attention to the class of k-art n-cube graphs with uniformly weighted nodes. Given mild restrictions on the node weight and number of processors, we identify partitions yielding the smallest bottleneck. We also demonstrate by example that some restrictions are necessary for the partitions we identify to be optimal. In particular, there exist cases where partitions that evenly partition nodes need not be optimal.

Nicol, David M.↗
NASA NTRSDate not supplied

A Flexible Low-Cost Optical Communications Ground Terminal at NASA Goddard Space Flight Center

We present the status of ongoing work at NASA-Goddard Space Flight Center (GSFC) to build a low-cost flexible ground terminal for optical communication. Previous laser communication missions at NASA have been supported by one-of-a-kind ground terminals built specifically for each mission. If NASA is to build a global network of optical terminals to enable widespread use of optical communications, then a blueprint for an economical ground terminal able to support a variety of missions is needed. With this goal in mind, NASA is constructing a ground terminal in Greenbelt, Maryland to enable testing of new ground terminal technologies from industry to academia.

Robert E Lafon↗
NASA NTRS1985

A partitioning strategy for nonuniform problems on multiprocessors

The partitioning of a problem on a domain with unequal work estimates in different subddomains is considered in a way that balances the work load across multiple processors. Such a problem arises for example in solving partial differential equations using an adaptive method that places extra grid points in certain subregions of the domain. A binary decomposition of the domain is used to partition it into rectangles requiring equal computational effort. The communication costs of mapping this partitioning onto different microprocessors: a mesh-connected array, a tree machine and a hypercube is then studied. The communication cost expressions can be used to determine the optimal depth of the above partitioning.

Berger, M. J.↗
NASA NTRS1987

A partitioning strategy for nonuniform problems on multiprocessors

The partitioning of a problem on a domain with unequal work estimates in different subdomains is considered in a way that balances the work load across multiple processors. Such a problem arises for example in solving partial differential equations using an adaptive method that places extra grid points in certain subregions of the domain. A binary decomposition of the domain is used to partition it into rectangles requiring equal computational effort. The communication costs of mapping this partitioning onto different microprocessors: a mesh-connected array, a tree machine and a hypercube is then studied. The communication cost expressions can be used to determine the optimal depth of the above partitioning.

Berger, Marsha J.↗
NASA NTRS1993

Low-cost TDRSS communications for NASA's long duration balloon project

A new transponder and RF ground support equipment for the NASA Tracking and Data Relay Satellite System (TDRSS) intended to support long duration scientific balloon flights in Antarctica are described. The new balloon class transponder features a highly integrated spread spectrum receiver design based on programmable charge coupled device (CCD) correlators and digital signal processing chips. The correlator chip is a Lincoln Labs 4ABC with four CCD channels. The balloon transponder is capable of reporting an estimate of its input bit error rate using digital signal processing. The TDRSS user RF test set is based on a set of RF ground support equipment capable of providing both the RF communications and direct control and monitoring necessary for transponder testing and a two-way RF link for preflight testing.

Israel, David J.↗
NASA NTRS2005

Large diameter refractive Fresnel lenses as low-cost optical communication ground receiver aperture

Feasibility of utilizing large diameter custom designed and fabricated Fresnel lenses as the front optical aperture for Earth-based reception of optical communication signals from remote spacecraft is investigated. This includes preliminary optical designs, investigation of stray-light effects for a particular optical design, effect of temperature variations and mechanical sag on the performance of the photon bucket, and effect of temporal dispersion on the link performance. Experimental results for several commercial off-the-shelf Fresnel lenses with diameters exceeding 1-meter are presented as well as plans for custom diamond turning fabrication of two-meter diameter Fresnel lenses.

Hemmati, Hamid↗
NASA NTRS1996

Performance Analysis and Optimization on the UCLA Parallel Atmospheric General Circulation Model Code

An analysis is presented of several factors influencing the performance of a parallel implementation of the UCLA atmospheric general circulation model (AGCM) on massively parallel computer systems. Several modificaitons to the original parallel AGCM code aimed at improving its numerical efficiency, interprocessor communication cost, load-balance and issues affecting single-node code performance are discussed.

atmospheric study optimization strategies parallel↗
NASA NTRS1977

NASA teleconferencing pilot project - An evaluation of teleconferencing as a substitute for travel

NASA conducted a Pilot Project during 1975-1976 to determine the extent to which teleconferencing could replace travel to meetings. The network consisted of approximately 34 teleconference rooms and 50 fast facsimile machines, all interconnected on private lines to a master switchboard in Huntsville, Alabama. In addition, portable conference telephones augmented the voice network and experimental video conferences were attempted. Evaluations showed that the teleconferences saved travel costs approximating 21% of the travel budget at a communications cost of 3% of this budget.

Fordyce, S. W.↗