On-board Switching Research Articles

The optical crossbar switch for signal routeing on board communication satellites

A switch matrix operating on baseband or microwave signals is a critical element of communications satellites employing multiple beam antennas and on-board switching. Optical switching by spatial light modulators (SLMs) offers a means of implementing large and highly flexible switch arrays capable of routeing signals at baseband or microwave frequencies. This approach offers potential mass, power and size advantages compared to alternative technologies. The paper reviews the essential features of optical crossbar switch architectures based on SLMs and discusses options for the lasers, SLMs, interface optics and photodetectors. Proof-of-concept demonstrators for optical crossbar switches operating on both baseband and microwave signals are described. Finally, an outline design for a compact switch module is described and the critical component developments needed to realize this are identified.

An advanced satellite communication system with on‐board fast packet switching capabilities

AbstractThis paper is focused on a satellite communication system having on‐board fast packet switching capabilities. Different alternatives for the up‐link access technique and for the architecture of the onboard switching fabric are considered. In particular an efficient time division multiple access technique with slots assigned on demand and a novel switching approach are proposed. Performances in terms of mean access delay and mean on‐board switching delay are derived by analytical approaches and computer simulations.

Computer-aided planning of SS/TDMA network operation

A computer-aided approach to the planning of SS/TDMA network operation is proposed. SS/TDMA is a sophisticated satellite communication network based on an onboard switch matrix, whose operation planning is formulated as a large-scale scheduling problem. An overall planning and scheduling model is presented to deal with practical SS/TDMA systems, such as a two-frequency channel network and nondisjoint beam coverage. For systematic planning suitable for a computer-aided approach, the entire scheduling process is divided into several steps, for each of which an efficient mathematical model is proposed. A linear programming model is used for distribution of traffic on a beam-to-beam basis and the generated switching sequence is further refined by a model using the traveling salesman problem. Burst scheduling is carried out by the Bin packing algorithm and scheduling models for practical networks allowing transponder hopping and multidestination bursts. An algorithm called enhanced rescheduling is presented to further improve the scheduling capability of the existing methods. The performance of the proposed methods is demonstrated by simulation results. >

Communications satellites: orbiting into the 90s

Engineering advances in satellite communications are discussed. These include sophisticated switchboards, narrow beams, source coding for higher capacity, larger networks, and the use of higher and lower frequency bands and lower orbits. One of the most popular new 14/11-14/12 GHz commercial services has been time-division multiplexing of multiple carriers operating at low to medium bit rates. Multiple-carrier, low-burst-rate TDMA (time-division multiple access), in which several TDMA carriers are shared among ground terminals, is widely used with very small-aperture terminals (VSAT) on the customer's premises. NASA's (US National Aeronautic and Space Administration) ACTS and Italy's Italsat both plan to use signal regeneration at 30/20 GHz. Onboard switching and multiplexing will not only minimize noise and boost power, but also trim the cost of the entire satellite network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On-board switching and processing

Findings from NASA's space electronics division's (SED's) advanced systems studies related to future communications satellite services that will require onboard switching and processing technology are reviewed. SED's digital signal switching and processing technology program is reviewed. This program responds to specific systems technology development needs for enabling commercial development of future satellite services. The technologies include: modulators, demodulators, and forward error-correction hardware for space- and ground-based applications; onboard information switching and processing, onboard network control, and health monitoring; and cost-efficient ground terminals. The in-house systems integration, test, and evaluation (SITE) project, which includes a laboratory testbed for evaluating technology in a simulated systems environment, is reviewed. >

Demand assignment in the ACTS LBR system

The advanced communications technology satellite (ACTS) is an experimental communications satellite being developed by NASA's Lewis Research Center. Low burst rate (LBR) traffic stations will access the ACTS multibeam communications package (MCP) through two hopping beams that can be directed at certain cities and areas in the continental United States. An onboard baseband processor (BBP) demodulates uplink traffic received via two up-link (30 GHz) hopping beams, switches the traffic between uplink and downlink beams at baseband, and then remodulates the traffic for retransmission at 20 GHz via two downlink hopping beams. This study concentrates on the demand assigned operation of the ACTS LBR system where the onboard switch is remote from both the traffic stations and the centralized master control station (MCS). Network control uses inbound and outbound orderwire channels and a BBP control channel thereby allowing the MCS to coordinate assignment of individual 64-kb/s channels in the spacecraft. Models are developed to simulate the dynamics of the demand assignment process in order to verify call blocking behavior, to predict control channel loads, and to evaluate alternative algorithms for burst time plan rearrangement that becomes necessary to minimize blocking under conditions of high-traffic intensity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

VSAT networking concepts and new applications development

The authors present some innovative very small aperture terminal (VSAT) technology that can be used to support new applications. The first of these applications explores the possibility of realizing a VSAT-based satellite wide area network (SWAN) to provide flexible interconnection between local area networks (LANs) and metropolitan area networks (MANs) as well as gateway access to centralized information databases and computing services. A second application deals with the potential provision of ISDN-compatible services via VSATs in conjunction with existing satellites as well as future advanced satellites (ADSATs) having onboard switching and processing capabilities. The use of VSATs to solve backhaul interconnection/internetworking problems associated with evolving mobile satellite (MSAT) communication networks is discussed. >

Advanced architectures and the required technologies for next-generation communications satellite systems

To be competitive with other modes of information-transport systems, the next-generation communications satellites will use new technologies including multiple-beam antennas, and onboard processing and switching. This paper discusses these technologies and illustrates their use by providing a description of three satellite systems currently under development. The paper is organized in three sections: Section 1 describes advanced architectures for future satellite systems and the required technologies to enable these systems; Section 2 gives examples of such systems by briefly describing the American ACTS, the Japanese ETS-VI, and the Italian ITALSAT; and finally Section 3 provides some simplified design equations that relate some of the key top-level parameters involved in the design of such systems.

Criteria for approval of mining equipment incorporating on-board switching of high-voltage circuits

The US Mine Safety and Health Administration (MSHA) recently developed criteria to modify the current regulation prohibiting the on-board switching of high-voltage circuits (>1000 V AC). Extensive research conducted by the US Bureau of Mines and MSHA provided the basis for the development of safe and viable criteria. Under the provisions of Title 30 Code of Federal Regulations, Section 18.82, experimental permits were issued to high-voltage continuous miners and longwall systems incorporating this new technology. The information gathered from the operation of this equipment in the field along with industry concerns and recommendations were considered during the finalization of these criteria. >

Channel reallocatable onboard baseband switch

The letter proposes a novel single-buffer single-stage time switch architecture enabling channel reallocation with no bit dropout for onboard baseband switches. By applying dedicated LSIs to the breadboard model, a baseband switch having 104 channels, a scale of 30 × 30 × 30cm, a weight of 25kg and a power consumption level of 30W can be achieved.

Minimizing the Number of Switchings in an SS/TDMA System

In this paper, we investigate the problem of constructing a TDMA frame for a multibeam satellite system. Our objective is to permit the transmission of a given pattern of traffic, while ensuring that the number of times that the on-board switch needs to be reconfigured is minimized. We find that the underlying optimization problem is computationally intractable, but go on to suggest an efficient heuristic algorithm which we validate through experiments on randomly generated traffic patterns.

Communications Satellites: Countdown for INTELSAT VI

Since the formation of COMSAT 20 years ago, the number of international telephone circuits made through satellites has grown 400 times and the cost of a telephone call has decreased by 12,000 percent. Worldwide communications linking 109 nations are achieved with 14 satellites in earth-synchronous orbit. Advances in microwave technology have expanded the transmission bandwidth per satellite from 50 to more than 3000 megahertz. Improvements in solar cell, battery, stationkeeping, and microwave amplification technology have increased satellite lifetime from 1.5 years to 10. The sixth generation of INTELSAT satellites, now being manufactured, will be introduced into the system in 1986, and each satellite will carry more than 40,000 telephone channels plus two television programs. The next generation of satellites, now under design for expanded capacity, will be needed by the middle 1990's to meet the traffic demand. These satellites are likely to add new frequencies (20 and 30 gigahertz), onboard signal processing and switching, and more bandwidth-efficient modulation, to achieve larger communication capacity at each orbital location.

Satellite communications networks

The evolution of satellite communication systems over the past two decades from simple point-to-point links with unique subcarrier-defined paths between points to today's multipoint, satellite-switched, multi-satellite networks tying together hundreds of earth stations, and transmitting voice and data increasingly in the time domain is considered. Examples of the methods used to manage network resources efficiently through terrestrial control and monitoring of information flow together with on-board switching are given. These examples are choosen mostly from the INTELSAT experience which will soon include a sixth generation of space segment. The paper concludes with a discussion of the future directions of satellite network development made possible by the technology being planned for NASA's Advanced Communications Technology Satellite. This design anticipates the needs of both high-volume trunking and thin-route service.

An integrated voice and data multiple-access scheme for a land-mobile satellite system

A Land-Mobile Satellite System (LMSS) is a satellite-based communications network which provides voice and data communications to mobile users in a vast geographical area. By placing a "relay tower" at a height of 22300 mi, an LMSS can provide ubiquitous radio communication to vehicles roaming in remote or thinly populated area. LMSS is capable of supporting a variety of services, such as two-way alphanumeric service, paging service, full-duplex voice service, and half-duplex dispatch service. A Network Management Center (NMC) will handle the channel requests, channel assignments, and in general the network control functions. A pool of channels is managed at the NMC to be shared by all mobile users. An integrated demand-assigned multiple-access protocol has been developed for the experimental LMSS. The pool of channels is divided into reservation channels and information channels. The information channels can be assigned by the NMC to be either voice channels or data channels. Each mobile user must send a request through one of the reservation channels to the NMC via the ALOHA random-access scheme. Once the request is received and processed, the NMC will examine the current traffic condition and assign an information channel to the user. NMC will periodically update the partitions between the reservation channels, voice channels, and data channels to optimize system performance. Data channel requests are queued at the NMC while voice channel requests are blocked calls cleared. Various operational scenarios have been investigated. Tradeoffs between the data and voice users for a given delay requirement and a given voice call blocking probability have been studied. In addition, performance impacts of such technological advancements as satellite on-board switching and variable bandwidth assignment are discussed.

Advanced Communications Satellite Systems

Demand for in-orbit capacity through the use of satellite systems will continue throughout the next two decades. The potential of the 30/20 GHz frequency band for fixed satellite services will be exploited. However, many technology questions must be answered if the band is to be used commercially because of the high rain fades that can occur at these high frequencies. NASA has conducted a technology development program in high gain antenna and on-board switching and processing systems which can be combined such that cost competitive services are possible at acceptable rain outage percentages. Other supporting technologies have also been pursued including transmitters, both tube type and solid state, and low noise receivers. The critical technologies have been combined into an experimental satellite payload; an experimental flight is planned to verify these technologies and enable development of operational systems. Implementation of such systems would be by commercial carriers and could occur in the early 1990's, depending on the demand for additional or bit capacity. The high capacity systems that can be made possible through the use of the 30/20 GHz band and the employment of frequency reuse technology will contribute to the continued downward trend in circuit costs and may allow new and innovative satellite services.

Efficient Packet Satellite Communications

This paper gives an extensive analysis of a Packet satellite (PACSAT) communications system that uses a digital processing satellite in a packet data network. It is shown that multiple uplinks coupled with on-board switching and storage can provide significant gains in throughput, efficiency, and margin against instability. Design tradeoffs are presented and the theoretical results are verified by extensive computer simulations.

Switching in space

Dynamic connection of beams on board a satellite raises the prospect of “central offices” in the sky that could route signals to their destinations on earth via separate spacecraft antenna beams. On-board switching would eliminate almost all of the terrestrial transmission and switching now needed.

Satellite communications in the 1980s and after

The second decade of satellite communications which we are now entering should show as rapid progress as the first, which saw the creation of a global network of satellites and Earth stations connecting eighty countries on six continents. Domestic systems are providing many types of services to small and large communities, and maritime systems to ships at sea. Future satellite communications systems will have higher capacity and provide varied services to small users. Increased transmission of television, graphics, and computer data will be provided, interconnecting individual users with ‘rooftop’ and mobile terminals. Technological advancements in this second decade will involve the use of new frequency bands (30/20 and 14/11 GHz), and frequency reuse through spatial separation and polarization discrimination. Digital transmission techniques will find widespread use. The third decade will see the application of very large multibeam, multifrequency antenna systems, beam shaping, and satellite onboard switching and processing. The use of the space shuttle with high-energy upper stage propulsion units will allow the deployment of very large, permanent geostationary platforms for providing economical multiple communications service.