sell Catv Stb Dvd

The selected DVB-T modulation scheme has the following characteristics: - OFDM (Orthogonal Frequency Devision Multiplex) In this technique, a fast fourier transform is used to generate a broadcast signal with thousands of mutually orthogonal QAM modulated carriers. A single symbol carries therefore several kilobits of information. A guard interval between symbols allows echos to pass by before the receiver starts the detection of the next symbol - 8192 or 2048 carrier frequencies, each modulated using a QAM with between 4 and 64 Symbols - 8 MHz bandwidth - outer FEC: Reed Solomon FEC RS(204, 188, T=8) - outer convolutional interleaving. - inner FEC: Convolutional Co (1/2, ..., 7/8) - inner interleaving Satellite transmission (DVB-S) Channel properties of satellite transmission are: - relatively low signal/noise ratio - large bandwidths available - amplifier tubes in the satellites are operated in a very non-linear mode for maximum power efficiency The selected satellite modulation system is a 2 bit/symbol QPSK(quaternary phase shift keying)modulation. This modulation system is defined in the DVB-S standard ETS 300421. Some characteristics are (this is only for interested modem experts): - scrambling applied for spectral formation - outer FEC: Reed Solomon Forward Error Correction RS(204, 188, T=8) - convolutional interleaving (Forney) - inner FEC: convolutional Code - 35% half-Nyquist filtering - flexible symbol rate