Significance of Satcom Modem in Data Transferring

Satellite Modem

A device used to transmit and receive signals from a satellite transponder. For transmission, it modulates digital data signals (can be from a multiplexing device) into a modulated carrier (BPSK, QPSK, 8PSK, 16PSK/QAM etc) frequency for delivery to an up converter, amplifier or BUC (Block Up converter) and antenna. For receiving, it converts the frequencies from the downconverter via an LNB (Low Noise Block Downconverter) via a demodulator and error correction decoding.

How does it work?

The original DVB-S system, on which DVB-S2 is based, specifies the use of QPSK modulation along with various tools for channel coding and error correction. Further additions were made with the emergence of DVB-DSNG (Digital Satellite News Gathering), for example allowing the use of 8PSK and 16QAM modulation. DVB-S2 benefits from more recent developments and has the following key technical characteristics:

• There are four modulation modes available, with QPSK and 8PSK intended for broadcast applications in nonlinear satellite transponders driven close to saturation. 16APSK and 32APSK, requiring a higher level of C/N, are mainly targeted at professional applications such as news gathering and interactive services.

• DVB-S2 uses a very powerful Forward Error Correction scheme (FEC), a key factor in allowing the achievement of excellent performance in the presence of high levels of noise and interference. The FEC system is based on concatenation of BCH (Bose-Chaudhuri-Hcquengham) with LDPC (Low Density Parity Check) inner coding.

• Adaptive Coding and Modulation (ACM) allows the transmission parameters to be changed on a frame by frame basis depending on the particular conditions of the delivery path for each individual user. It is mainly targeted to unicasting interactive services and to point-to-point professional applications.

• DVB-S2 offers optional backwards compatible modes that use hierarchical modulation to allow legacy DVB-S receivers to continue to operate, whilst providing additional capacity and services to newer receivers.

DVB-S2 delivers excellent performance, coming close to the Shannon limit, the theoretical maximum information transfer rate in a channel for a given noise level. It can operate at very low carrier-to-noise ratios with QPSK, through to +16dB using 32APSK. The table overleaf (Figure 1) shows the improvements in efficiency that DVB-S2 delivers when compared to DVB-S with typical TV broadcast parameters, with gains in the useful bitrate of more than 30% in each case.

Various modes for modem test procedure:

1. Continuous mode

2. Burst mode

Types of satcom modems employing digital video broadcasting standard:

1. DVB-S/S2 is a broadcast-satellite modem, An IRD (integrated receiver demodulator) is usually at the remote, receiving end.

2. DVB- RCS uses a satellite based return channel.

What else is in the typical satellite modem?

• DC linear regulated power supply

• Bit Error Rate tester (DTE)

• AWGN adder

• Spectrum analyzer

DVB is short for Digital Video Broad-casting and S2 stands for Second Generation. DVB-S2 is a digital TV broadcast standard that designs as a successor for the popular DVB system. Dvb-s2 modulatoris using satellite serving every possible continent of the world.

Features of DVB-S/S2 modulator:

DVB-S2 (EN 302 307) is a digital satellite transmission system

• Modulation- single- carrier QPSK and higher with multiple streams.

• Input interface- Multiple transport stream and (GSE) generic stream encapsulation.

• Modulation schemes- BPSK, QPSK, 8PSK to 256QAM

• Interleaving- Bit- interleaving.

• Interior coding

• Modes- VCM: Variable coding & modulation, ACM: Adaptive coding & modulation

• Pilots- Pilot symbols.

• Input stream management to minimize end-to-end delay.

• Automatic uplink power control

Market Deployment

Having been formally published as an ETSI standard in March 2005, DVB-S2 was quickly adopted by the industry for the delivery of new services. In Europe and the USA a number of major satellite broadcasters use DVB-S2, in conjunction with MPEG-4 advanced video coding, for the delivery of HDTV services (e.g., BSkyB in the UK and Ireland, Premiere in Germany, Sky in Italy, DirecTV in the USA). DVB-S2 has also been deployed by DTH operators elsewhere in the Americas, in Asia, the Middle East and Africa, creating a global deployment base of more than 250 million DVB-S/S2 receivers. Two significant factors have contributed to the success of DVB-S2. Firstly, in August of 2006 the ITU’s (International Telecommunications Union) study group on satellite delivery issued a recommendation that DVB-S2 alone be adapted as the preferred option for a “Digital Satellite Broadcasting System with Flexible Configuration (Television, Sound and Data)” (ITU recommendation number BO.1784). Secondly, late in 2006, an announcement from the holders of key DVB-S2 intellectual property rights indicated that licensing costs for manufacturers of DVB-S2 equipment would not exceed $1.00 per consumer device, or $0.50 for quantities exceeding 500,000. The certainty granted by this announcement fostered the rapid adoption of DVB-S2 by the global satellite broadcasting and telecommunications industries. DVB-S2 has also been adopted for professional applications. The EBU’s Eurovision network, one of the world’s largest contribution networks, has been fully upgraded from DVB-S to DVB-S2. Testing of the new systems in spring 2005 revealed a 20% increase in throughput, a result which encouraged the EBU to upgrade the network in time to distribute, for example, the 2006 FIFA World Cup over DVB-S2.