PORTABLE AND MOBILE TERMINALS FOR MULTIMEDIA & BUSINESS USE

Introduction

Satellite-based multimedia service for the consumer is an important part of the business plans of many of the Ka-band systems now under construction. This has developed as an important activity since the 1992/1993 study. Research programs like ACTS, Japan's program in highly intelligent communications, Italy's ITALSAT, and the European DIGISAT, ISIS and MMIS projects, demonstrate that the feasibility of satellite-based interactive multimedia services, are laying the necessary groundwork. The development of portable and mobile terminals for these applications should proceed rapidly along an evolutionary path since--except for reducing terminal size and cost--few hardware innovations are involved.

Japanese Activities

Mobile multimedia satellite service is an important research area in Japan. Japanese researchers are looking at all aspects of networked multimedia communications, of which satellites and satellite terminals are but one part (Figure 4.5). Japanese research includes both direct satellite systems (Figure 4.6) and cellular systems supported by satellites (Figure 4.7).



Fig. 4.5. Japanese concept of a multimedia network.



Fig. 4.6 Japanese concept of a satellite-based multimedia network.



Fig. 4.7. Japanese concept of a cellular multimedia network supported by satellites.

One of the missions of the Japanese ETS-VIII satellite (2002 launch) is to provide Internet services for mobile users. Planned experiments will test e-mail, file transfer, World Wide Web, and videoconferencing between mobile users and network computers. Figure 4.8 and Table 4.1 indicate the general concept of the program and indicate some of the parameters, respectively. The terminals will transmit approximately 20 W and operate with 10 m class antennas on the spacecraft.


Fig. 4.8. Planned multimedia experiments with ETS-VIII.

Table 4.1
Link Parameters for ETS-VIII Mobile Multimedia Experiments

Modulation

[pi]/4 - shift QPSK

Demodulation

Coherent detection

Information rate

512 kbps (forward error correction (FEC) on) or 1024 kbps (FEC off)

Error correction

FEC (convolutional coding (k=7, R=1/2), Viterbi decoding)

Selective repeat ARQ

Error detection

32 bits CRC error detection

Link access method

Modified slot ALOHA (random access + reserved access)

Collision detection

Announce from satellite

Slot length

8 msec

Frame format

Multi-frame

Minor frame: 128 msec

Major frame: 1.024 sec

Super frame: 8.192 sec

Switching port

2 feeder links, 2 mobile links

Routing protocol

First phase: bridge (addressing in datalink layer)

Second phase: TBD

Download function

Download from base station through feeder link

MPU

RAD6000 (10 MHz)

OS

VxWorks

Multiple access is a key issue in satellite multimedia terminal development since the earth stations cannot hear each other's uplink transmissions and the network cannot rely on the carrier sense multiple access (CSMA) protocols commonly used in terrestrial local area networks (LANs). The ETS-VIII experimental terminals will be able to select both random and reserved ALOHA schemes.

Large Japanese companies like Fujitsu are aware of the commercial possibilities of satellite multimedia delivery and already offer integrated voice, data, and image in their VSAT systems. (These probably will be extended to mobile and portable applications. Fujitsu's 1996 annual report describes the company as aggressively developing its network based multimedia business.)

KDD is developing an ultra small Ku-band USAT antenna targeted for multimedia services, coming to Japan early in 1998. PerfecTV has already introduced digital DBS; DirecPC also has been introduced, but it uses the PSTN for the return path. A bi-directional (all satellite) multimedia service is envisioned with a 46 cm aperture. A 27 MHz transponder will support a 40 Mbps QPSK time division multiplex (TDM) wave form transmitted by a 7 meter hub. The return link (from user to hub) would be 128 kbps, using a chirped binary phase shift keying (BPSK) wave form. The chirp is used to spread the energy over a 500 kHz bandwidth and is sufficient to prevent interference, allowing for a 0.5 pointing error for a home installation, with 3 orbit spacing. A 1 W transmitter will be integral to the outdoor unit, designed for continuous transmission in 20C air. Use of TDM multiple access is anticipated and will produce a low duty cycle.

European Activities

European companies and laboratories are also developing multimedia satellite systems and planning portable and mobile services. The SECOMS/ABATE projects, described to the panel by Alenia Aerospazio, have as their objectives "to manufacture...vehicular land-mobile and aeronautical terminal prototypes...using electronically steered array antennas...[and] to demonstrate the feasibility of broadband multimedia satellite services...for mobile users with flexible data-rate assignment." SECOMS/ABATE will "define an advanced satellite system configuration, envisaging portable/mobile terminals to cope with various environments and for individual/collective use." Figure 4.9 illustrates the proposed network architecture and indicates some of the anticipated data rates.



Fig. 4.9. Proposed European multimedia network architecture from SECOMS/ABATE projects.

Airborne and Ship Borne Terminals

Airborne and shipborne terminals have continued to grow in population at an increasing rate. These terminals might be considered an intermediate class between "personal" (individual, single user) and the more traditional larger FSS terminals not associated with a particular user or group of users. In any case, airborne and shipborne terminals are both important in themselves and possibly as indicators or precursors to the larger market included within the category of mobile systems (MSS).

Inmarsat maintains a record of commercial aircraft having terminals installed. As of the end of 1997, there were 856 installations. The majority of these are 5 channel units on large aircraft that allow passenger telephone service. Inmarsat type qualifies terminals and there are a number of certified terminal providers.

Inmarsat also maintains records of ship terminal commissions. As of the end of 1997, there were 50,687 Inmarsat shipboard terminals in service. Improved, lower cost technology and competition have both helped to lower the cost of Inmarsat airborne and shipborne terminals. It is perhaps significant to note that the service provider originally ordered 200 ship terminals on speculation, partly with the intention that a large order would encourage tooling for quantity and other cost saving approaches for terminals. This decision not only made a terminal product available but also held the initial price to $50,000. This is an historical example of a creative exploitation of the cost versus quantity relationship.

The more important development in airborne terminals is the successful production of phased arrays at Ku-band for aircraft, by Boeing. A photograph of the low profile Boeing Ku-band phased array is shown in Figure 4.10, which also includes a few examples of other airborne and satellite phased array antennas from around the world. This set is by no means exhaustive. An overlooked aspect of phased array antennas is their use in synthetic aperture radars being flown on satellites. The activity for earth observation is synergistic with communications satellite applications (e.g., requiring manufacture of large numbers of efficient, small, and reliable array elements).



Fig. 4.10. New aircraft and mobile antenna designs.

The communications antennas allow reception of DBS where satellite coverage permits (i.e., currently, there is not a lot of coverage over oceans where it might be most useful to airlines). Current systems would suggest two way airborne terminals at Ka-band; however, the cost associated with current technology may slow the spread of such terminals. The alternative is to employ lower gain arrays either made possible by lower altitude systems (e.g., Teledesic) or enabled by still higher effective radiated powers (EIRP) GEO satellites. In any case, development of airborne arrays will be an important area of future development.

Hubs and Gateways

A "hub" is a large aperture terminal that is used as a central network control of smaller terminals (e.g.,VSATs). The hub assigns transmit and receive channels, monitors traffic for billing purposes, relays messages between VSATs (if required) and connects the VSATs to other media. When the other medium is the public telephone system or another satellite system, the hub is functioning as a "gateway."

Gateway terminals have been inherently designed into the fabric of nearly all personal/mobile and little LEO data/messaging satellite systems. The rationale for this is to allow country by country connection to the local responsible government post and telegraph (PT&T) authority or independent carrier. The assumption is that calls or messages will likely originate or terminate at telephones, with a mobile terminal at the other end of the link. The gateway therefore provides both a telephone interface and a central point for traffic monitoring for local billing. This rationale also applies when a mobile terminal is at both ends of the link. The possibility of revenue generation also creates globally distributed interest and potential participation in financing the overall system.

Since the Inmarsat consortium has 81 participating countries and INTELSAT has 165 signatories, each personal/mobile system has the potential of about one hundred gateway stations. Since the personal and mobile systems use low and medium orbits, multiple satellites may be in view and each gateway station may have multiple terminals. An Iridium gateway station toured by the WTEC panel had five antennas. It was determined by analysis that for Globalstar gateway locations, 3.1 antennas were needed on average, so usually four antennas were provided. Gateways are under construction around the world for Iridium, Globalstar and Orbcomm. Gateway technology is no problem, and no major initiatives are needed. Most of the gateways employ U.S. technology.

Multimedia Ka-band systems may employ hubs (e.g., for intranets) and gateways for enriched connectivity. Although typically regional in geographic focus, these systems have multiple country coverage and the same rationale for gateways as the global systems.

Hubs and gateways typically employ 4 to 10 m antennas. The antennas and all other radio frequency components are available as existing products (feeds, LNAs, HPAs, frequency converters). One distinction is the requirement to track moving satellites for systems using lower orbits. This has not been typical for geostationary satellite systems and places a new mechanical design/reliability requirement on the gateway terminals, which must be ultra-reliable due to the central role they perform in communications. Radar antennas provide some useful experience and technology; and redundant backup or a single spare antenna per gateway will allow high gateway availability.

Military Terminals

An important recent change of direction in U.S. military satellite communications has been the congressional direction to emphasize the use of commercial systems. Changes in the world situation and evolving defense roles have resulted in review of terminal performance characteristics. A significant investment exists in the form of UHF (300/250 MHz), SHF (8/7 GHz), and EHF (44/20 GHz) military terminals, making a sudden shift to commercial use both difficult and costly. "Use of commercial systems" would seem to imply use of commercial terminals (L/S, C, Ku-band). In particular, commercial systems can not be viewed as "in place," since locations of military operations are uncertain and maneuvering of forces requires either transportable or mobile terminals.

For ground terminals, an alternative concept is to provide terminals capable of operation in any of several frequency bands (e.g., C, X, Ku). The operational advantage is the ability to employ multiple satellites in any location due to the high population of commercial satellites. Advanced versions of such "tri-band" terminals have lower weight, volume and cost than the single band terminals they are to replace. An important development achieved by L3 Communications is an antenna feed capable of operating across the C through Ku-bands without adjustment or change of components. A photograph of an antenna with this feed is shown in Figure 4.11.

Introduction of a global broadcast system at Ka-band will result in a need for receive-only terminals for ground, aircraft and ship applications. The quantity of such terminals will depend on the use of the broadcast channel and consequent organizational levels using the broadcast information. The success of direct broadcast satellite television and low cost receive-only terminals will likely lead ultimately to broad use and a large population of terminals. Plans now call for receive-only terminals; specific information must be requested via other communications systems (i.e., rather than via a direct satellite uplink from the receive terminal).

A need to address satellite replenishment for SHF and severe budget constraints has led to planning studies suggesting the possible future use of Ka-band. A Ka-band system would make possible a two way terminal that might closely resemble the Ka-band multimedia VSAT. Proximity of commercial and military or government Ka-band frequency allocations suggests the possibility of a shared technology and production base, thus offering a promise of cost savings.



Fig. 4.11. L3 Communications antenna incorporating proprietary very wideband feed.

Government needs, particularly military applications, require mobile and airborne capability. Presently planned Ka-band commercial systems have two potential problems in this regard, namely coverage and adaptability for such mobile users. The commercial systems are aimed at population centers of highly developed countries, whereas humanitarian and military operations historically have been most often in undeveloped areas, precisely where coverage is not planned. This apparent disconnect between the commercial plans and government needs is discussed in two papers presented at the 1997 Third Ka-band Utilization Conference (see site report, Appendix B).

A cutting edge issue will be airborne terminals. A variety of considerations point to phased arrays as the appropriate choice but current gain requirements demand large numbers of array elements resulting in high costs. Further evolution of systems to allow lower cost antennas and to facilitate mobile terminals was independently suggested in two papers at the Third Ka-band Utilization Conference.

Technology Assessment and Challenges

The major challenge for commercial systems is the achievement of low cost of production to encourage rapid market development. This applies to both mobile/personal systems and to multimedia VSATs. In particular at Ka-band, low cost microwave components such as solid state amplifiers (1 to 5 W rf power) have to be developed before market success is likely.

A major challenge is to achieve high performance airborne antennas at reduced cost. Progress in receive arrays for Ku-band GEO systems is encouraging. However, extension to low cost transmit and receive arrays for Ka-band airborne applications needed for both commercial airlines and government/military uses remains a challenge.

A similar airborne terminal challenge (high performance/low cost) will exist for LEO/MEO systems.

Since systems design can in principle bundle many combinations of services and data, determining the associated combination or set of terminal features that can both be produced within cost goals and achieve the required market appeal may prove the critical challenge determining the economic success of many systems.

A general challenge to government/military terminals is interoperability with allies. Introduction of the use of commercial bands will not ease the dimensions of this long standing interoperability problem. A specific challenge for military terminals is to provide the required features without extensive redevelopment of commercial products. The advent of consumer oriented satellite communications together with reduced defense budgets greatly diminishes opportunities for technology leadership through innovation for military terminals. Innovation is expected to come for the commercial terminals; however, there will remain military features and requirements that may not be satisfied without targeted or focused development.

Interoperability features of handheld terminals are important. Terminals having several modes, such as one satellite and one terrestrial cellular standard, are expected. But more diverse functionality may be both highly useful and a market differentiator (for handset providers). "More diverse functionality" refers to the possibility of being able to operate in more than one satellite system and/or more than one cellular system.

The continuing improvement of digital components (reduced feature size, lower voltage operation, processing power, software libraries) due to advances in the computer industry will offer much of the raw material needed for handset innovation and multi-mode functionality. Of course, selection of particular technologies and adaptation and specific development for terminals will be required. Improved and innovative visual displays will suggest changes in services (and increases in link data rates) and again challenge terminal designers to achieve low cost, even with the addition of displays or other media features.


Published: December 1998; WTEC Hyper-Librarian