Introduction

As a result of the interest, triggered by Motorola's announcement of Iridium in 1991, in constellations of telephony satellites, several organisations have taken the concept a step further by proposing constellations of broadband satellites.

Probably the most well known of these is Teledesic which intends to use a 288 satellite constellation to provide Internet and data services world-wide in a few years time, though there are many more systems being proposed.

Typically, broadband constellations offer high data rate connections in the range of hundreds of kb/s to Mb/s. These connections are generally intended for use by very large numbers of low priced terminals. In the long term, these systems will make conventional VSATs obsolete. Over a shorter timescale, in the next few years, broadband satellite systems, with user terminals up to an order of magnitude cheaper than conventional VSAT terminals, will make significant inroads into the corporate VSAT market.

Key markets identified for broadband satellite services are:

• Internet/Intranet/Extranet connectivity for both consumers and all categories of business users
• interactive TV
• dedicated point to point connections
• shared connectivity (short term links on demand for transaction based data)
• transport (carrying telecommunications on a wholesale basis)
• fixed telephony (basic services in underdeveloped regions)

Most systems share a number of key characteristics:

• Small, very low cost user terminals will be networked in a star topology from large terrestrial gateway earth stations. Some systems may support meshed networks.
• Only a small number of gateway earth stations will be established for each system. Generally these will be owned and operated by key system investors.
• The satellites may have regenerative repeaters with on board switching and may have automatic routing between satellites using intersatellite links.
• User terminal characteristics will be standardised by the satellite operator for each system.
• User terminals for each system will be supplied by a very restricted number of manufacturers, who generally will be key system investors.

Of the twenty or so systems which will attempt to enter the market before the market stabilises in the next five to ten years, industry analysts believe that only a few systems will survive. This may not be the case, however, because the LEO/MEO systems and GEO systems address different but overlapping markets.

LEO/MEO systems are generally targeted at business users and support professional services. They are in competition with terrestrial broadband technologies such as fibre and xDSL. Wherever terrestrial broadband access is available, satellite solutions will probably not be cost effective, however, everywhere else satellite will be the only solution. The vast majority of the world, away from large concentrations of population mainly in the developed world, will not have terrestrial broadband access available for decades.

GEO systems are also targeted at business users, however there is a very large potential consumer market for interactive services, particularly Internet type services and interactive TV, which is not currently addressed by any service provider. This market will slowly begin to grow over the next few years and may eventually become the norm, virtually replacing broadcasting as we currently know it. Again, satellites will have a significant place in this market wherever a terrestrial option is not available or is not packaged by broadcasters as well as equivalent or better satellite products.

Several conclusions are forced from the market background above which will have a profound impact on the satellite service industry as a whole:

• The broadband satellite market will experience an extreme level of competition which will probably result in a price war starting perhaps in 2002 or 2003, just as most systems are beginning to establish operations.
• Although Ka band terminal technology is relatively expensive today, it will rapidly become as cheap as current consumer satellite TV technology. Economies of scale may well make Ka band SSPAs considerably cheaper than corresponding Ku band products - today the Ku band SSPA market is of the order of tens of thousands per year, within five to ten years the Ka band SSPA market could be tens of millions of units per year from domestic consumers alone.
• This competition will have a severe knock on effect on the conventional VSAT market which will face severe price competition. Unless existing equipment and service suppliers can reduce their prices significantly (by anything up to a factor of 10) they will not be able to survive.
• Investing gateway operators and user terminal suppliers in the failed broadband systems will each face losses in the range of several ten to several hundreds of millions of US$. Many of these will face bankruptcy or will become take-over targets.
• Competition in the satellite service industry will be severely restricted from about 2005 because of existing suppliers leaving the market or being absorbed by other suppliers.

return to top

Orbits

Three different orbits are proposed for these new broadband services: LEO, MEO and GEO.

return to top

GEO Broadband Satellite Systems

Most broadband satellite systems consist of high power GEO satellites. These are really extensions of current DBS/DTH technology into interactive TV, multimedia and Internet access.

The potential domestic and small business market for the services offered by these systems is very large. GEO broadband systems will make inroads into the television market providing a spread of consumer packaged products including conventional broadcasts, interactive TV (game shows, gambling, talk shows, home shopping), interactive services (banking, shopping, e-commerce, education, information services, database access) and Internet access.

The interactive services and Internet access will be particularly interesting for business users.

GEO broadband satellite systems will be capable of replacing conventional VSATs for many applications. As far as the end user is concerned, instead of using a dedicated hub or leasing space on a shared hub from a service provider, capacity will be leased from a convenient gateway operator. Whilst this will offer a certain economy of scale, a single gateway operator will replace perhaps dozens of conventional VSAT service operators reducing user choice.

User choice will be further reduced because it will become much more difficult for a large corporation to operate its own network as is done by many organisations at present. In many countries the only financially sensible route for large corporations looking for a satellite solution will be to lease gateway and space segment capacity through a regional gateway operator.

GEO gateway earth stations will be owned by the systems operator or by a regional franchisee. Gateway costs will probably be of the order of 10 MEuro plus.

GEO Broadband User Terminals

In many ways user terminals will be similar in operation and appearance to existing satellite terminals:

Interactive consumer terminals will be similar to current domestic satellite TV set top boxes and will be attached to a small dish mounted outside the house, typically on an external wall. The main differences between a broadband terminal and a current DTH/DBS system will be that the broadband terminal will also have a small SSPA integrated with the antenna feed assembly giving a transmit capability and the set top box will have some form of keyboard or mouse, possibly connected by an infra red link.

Business terminals will be practically indistinguishable from current VSAT remote terminals, though the antennas will generally be smaller than is usual today. Business terminal costs will be considerably lower than conventional VSAT terminal costs and will generally be in the range 750 to 2,000 Euro depending on performance and supplier.

return to top

LEO/MEO Broadband Satellite Systems

A few broadband systems consist of large constellations of LEO/MEO satellites. These will be sophisticated orbiting networks with ISLs (intersatellite links) to other satellites in the constellation. The constellations will be very large, sometimes numbering hundreds of satellites, with adjacent satellites interlinked by a complex mesh of optical or Ka band intersatellite links.

Broadband LEO/MEO constellations require complex and very expensive tracking gateway earth stations which are capable of maintaining contact with several satellites at any time as they track across the sky in a few minutes. Gateways will be owned by the systems operator or a regional franchisee and will cost of the order of 50 MEuro plus.

The potential business market for services is large but, being business oriented, is still very small compared to the potential consumer market available to GEO broadband systems. These systems are in direct competition with conventional VSATs, offering all the services that VSATs currently offer and more.

LEO/MEO Broadband User Terminals

LEO broadband user terminals will be considerably more complex than GEO terminals. The main reason for this is the necessity to track the rapidly moving satellites as they traverse the sky. User terminals must therefore be equipped with antennas that can lock onto a satellite and that can rapidly acquire another satellite as the satellite being used for communications passes out of view. Most systems intend to use a planar array antenna with electronic beam forming and pointing. Skybridge, however, appears to intend to use a mechanically tracked dish in a small radome as its baseline. Tracking also requires a relatively sophisticated antenna controller.

LEO systems also suffer from significant Doppler shifts which must be allowed for in both the terminals and the gateway earth stations. Whilst this is not a major problem in the gateway earth stations, the sophisticated Doppler control is a further major burden in the user terminals which adds a further level of complexity and therefore cost.

At the moment it is not clear whether it will be possible for the terminal manufacturers to meet their cost targets as well as the stringent performance requirements that are imposed by the use of LEO satellites.

return to top

Network Topologies

Irrespective of the type of orbit used, there are three main network topologies used for broadband systems. The type of orbit only affects the complexity of the physical implementation. The topology is, however, dependent on whether the satellite payload used has an on board processing and switching capability or is transparent.

Two network topologies are applicable to transparent payloads:

• bent pipe star topology
• bent pipe point top point topology

whilst one topology will be used for on board processing (OBP) payloads:

• OBP switching topology.

Bent Pipe Star Topology

This is an evolution of the interactive hubbed VSAT concept, though some operators will have reached this point by adding a return path to a high data rate broadcast from a large uplink station.

This topology is characterised by having a large gateway earth station which transmits one or more high data rate forward link broadcasts to a large number of small user terminals. These broadcasts contain address information which allows each user terminal to select those transmissions intended for it.

In the return direction, the remote user terminals transmit in bursts at low to medium data rates to the gateway.

Bent Pipe Star Topology

Bent Pipe Point to Point Topology

This is a development of the point to point VSAT concept.

In this topology a dedicated two way connection is set up between a large gateway earth station and a single user terminal.

Bent Pipe Point to Point Topology

OBP Switching Topology

This topology has the satellite being the focus of a star network instead of a gateway earth station.

The satellite is connected to the gateway earth station by one or more high data rate trunks.

In the satellite the On Board Processor (OBP) in the payload demultiplexes the uplinked trunk and splits it into downlinks intended for particular geographical areas (usually cells determined by the antenna coverage pattern). The forward downlinks produced in this fashion contain messages for large numbers of user terminals in which the destination terminal is identified by headers in the messages.

In the return direction the uplinked transmissions from user terminals in one or more cells are multiplexed together onto a downlink trunk for transmission to the gateway.

OBP Switching Topology

return to top