Satmodem

A satmodem (for satellite modem, in English, abbreviated SM) is a modem that is used to establish a data transmission with a communications satellite.

Satellite offers the enormous advantage over terrestrial broadband connections, that it usually has much more coverage (for example, throughout the European Union) and that it is easier to change locations with the same equipment and with the same pass.

There are two different types of satellite modems:

• Unidirectional Satmodems (they are modems) DVB-IP) that use a different way to the satellite as a return channel (phone, cable, etc.).

• Bidirectional Satmodems (also called Satellite Interactive Terminal (SIT)are modems DVB-RCS) that also use the satellite as a return channel (do not need an additional connection, such as phone, cable, WiMAX, etc.). DVB-RCS is the standard ETSI EN 301 790. Most satmodems on the market include this standard and is the only open international standard.

The integrity of this can be damaged for life if it is constantly densisted, that is, cutting the signal by turning it off

Satmodem Link

A satmodem is not the only device needed to establish a communication channel. Other essential equipment for the creation of a satellite link are satellite antennas and frequency converters.

The data to be transmitted is transferred to a data terminal equipment modem (eg, a computer). The modem generally has an intermediate output frequency (IF), that is, 50 to 200 MHz, but sometimes the signal is modulated directly to L-band. In most cases the frequency is converted using an upconverter before amplification and transmission.

A modulated signal is a sequence of symbols, pieces of data represented by a corresponding signal state, eg one bit or a few bits are used, depending on the modulation scheme.

In the same way, a signal received from a satellite is first converted (this is done by a low noise blocking LNB converter), then it is demodulated by a modem, and finally it is managed by data terminal equipment. The LNB is usually powered by the modem via the signal cable with 13 or 18 V DC.

Features

The main functions of a satellite modem are modulation and demodulation. Satellite communication standards also define error correction codes and binding formats.

Popular modulation types used for satellite communications:

- Binary Phase Shift Keying (BPSK)

- Quadrature to Phase Shift (QPSK)

- Orthogonal Quadrature Phase Shift Keying (OQPSK)

-8PSK

- Quadrature Amplitude Modulation (QAM), especially 16QAM

Popular satellite error correction codes include:

The convolutional codes:

- With constraint length less than 10, usually decoded using a Viterbi algorithm (see Viterbi decoder)

- With constraint length greater than 10, usually decoded using a Fano algorithm (see sequential decoder)

Reed-Solomon codes generally contact convolutional codes with a collation.

Newer modems support error correcting codes (higher turbo codes and LDPC codes)

Frame formats that are supported by various satellite modems include:

- Service to Intelsat (SII) binding

- Intermediate Data Rate (IDR) binding

- MPEG-2 framing transport (used in DVB)

- E1 and T1 framing

High-end modems also incorporate some additional features:

- Multiple data interfaces (such as RS-232, RS-422. V.35, G.703, LVDS, Ethernet)

- Embedded Far-End Monitor and Control (Edmac), which allows monitoring of the far-end modem

- Uplink Automatic Power Control (AUPC), that is, adjusting the output power to maintain a constant signal to sound at the far end

- Drop and insert multipixelated stream function, allows to replace some channels in it.

Main manufacturers

The main manufacturers and models of DVB-RCS terminals are:

• Advantech Satellite Networks AryaSat, ASN
• Gilat Satellite Networks SkyEdge and GIL
• Informatics Services Corps (ISC)
• Newtec NEW1
• NanoTronix NAN1
• STM Norway AS SatLink and STM
• ViaSat LinkStar and VIA1

SatLabs Certification

SatLabs is an international non-profit organization for the adoption of the DVB-RCS/2 standard on a large scale. The main objective of SatLabs is to ensure inoperability between terminals (satellite modems) and DVB-RCS systems and obtain low cost solutions.

The SatLabs Qualification Program is intended to provide an independent certification process. When a terminal has successfully passed the test defined in the SatLabs Qualification Program, a Certificate of Compliance is issued and the terminal is defined as a Qualified Product (Qualified Product).

Using DVB-RCS

DVB-RCS has gained appeal in markets such as Russia, India and China, where government agencies are mandating open standards. India has even mandated DVB-RCS specifically for its Edusat distance education network, as well as its planned telemedicine system. South America is also heading decidedly in the direction of DVB-RCS.