Mumbai University > EXTC > Sem 8 > Satellite Communication and Networks

Marks: 8M

Satellite networks are used to provide two major types of service: TV services (associated withbroadcast services) and telecommunication services (associated with two-way communicationservices, symmetric—telephony—or asymmetric—Internet access).

One or more satellite networks can be deployed under the coverage of a single satellite and operated by a satellite network operator. It relies on a ground segment and utilises some satellite on-board resources (through the satellite channels that are used). The ground segment is composedof a user segment and a control and management segment. In the user segment, one finds satellite terminals (ST) connected to the end-user customer premises equipment (CPE), directly or through a LAN and hub or gateway stations, sometimes called network access terminals (NAT), connected to terrestrial networks:

—Satellite terminals are earth stations connected to CPE, sending carriers to or receiving carriers from a satellite. They constitute the satellite access points of a network; when the satellite terminals are also called Return Channel System Terminals (RCST).

CPE are also called user terminals (UT) and they include equipment such as telephone sets,television sets and personal computers. User terminals are independent of network technology and can be used for terrestrial as well as satellite networks.

The gateway earth station (GW) provides internetworking functions between the satellite network and the Internet or a terrestrial network.

The control and management segment consists of:

a mission and network management centre (MNMC) in charge of non-real-time, high-level management functions for all the satellite networks that are deployed in the coverage of a satellite.

Network management centres (NMC), also called interactive network management centres(INMC), for non-real-time management functions related to a single satellite network.

Network control centres (NCC) for real-time control of the connections and associated resources allocated to terminals that constitute one satellite network.

A satellite network (also called a satcom network) comprises a set of satellite terminals, one or more gateways and one NCC that is operated by one operator and uses a subset of the satellite resources (or capacity). Figure illustrates two satellite networks deployed under a satellite coverage and the links that can be established between their constituents

Satellite networks are characterized by their topology (meshed, star or multi-star), the types of link they support and the connectivity they offer between the earth stations.

A meshed satellite network consists of a set of earth stations which can communicate one with another by means of satellite links consisting of radio-frequency carriers.

Astar satellite network consistsof earth stations which can communicate only with a central earth station called the hub

Star network topology: (a) a single-hub star, (b) a multi-star in the abstract, and (c) an example with four earth stations and one hub