bit errors due to noise FEC (Forward Error Correction) -Adds check to the bitstream Typically 8 channels at varying bit rates Satellite Communication Systems Signal to Noise Ratio (SNR per bit) Eb/N0 Eb/N0 energy per bit / noise power spectral density what does Eb/N0 identify? -modulation effectiveness Max bit rate = 19 Mbps satellite TV transponder -Bandwidth = 36 MHz ATSC audio bit rate: 448 kbps bitrate is dependent on compression and bandwidth Over the Air TV -Bandwidth = 6 MHz Backwards compatible with 2 channel stereo Non-Backwards compatible with Part 3 What is the encoder / decoder protocol that controls compression called? CODEC What kind of MPEG2 Systems (container format) is designed to be used for a live broadcast? transport stream What does Part 2 of MPEG 2 describe? video (H.262) dolby digital (AC-3) -ATSC Audio Compression standard backwards compatible MPEG-2 part 7: AAC (advanced audio coding) -Same bit rate as mp3, better quality Uses MPEG-1 Coding with additions MPEG multichannel 5.1 surround Profiles are split into Levels Profiles compression algorithm, chroma format levels bit rate, frame size MPEG-2 Part 3: Audio -Compression layers based on bit rate Identifies file data for MUX & DEMUX transport stream live broadcast, transmissions program stream media storage (hard disk, flash drives, etc) MPEG- 2 Part 2: video (H.262) -Flexible format, split into Profiles Computer Graphics, streaming media, internet, Broadcast & satellite TV (DISH, DirecTV) MPEG-2 part 1: SYSTEMS -container format multi-channel audio MPEG-4 -Absorbs MPEG-1 & MPEG-2 standards Signal is then reconstructed CODEC encoder/decoder What does MPEG stand for? Moving Picture Experts Group MPEG-2 -International video standard adjust tilt angle to match skew What is the function of a transponder? receives uplink, amplifies, and down-converts to downlink frequency, relay the signal compression -Allows for large amounts of data at a fraction of the size 36 MHz Bandwidth Ku-Band Transponders vary in number and bandwidth Co-polarized (earth-based transmitters and receivers must be "co-polarized" each stations and satellites must match polarizations carrier frequencies are staggered C-Band Transponders -24 per "bird" polarize different signals at right angles (horizontal or vertical) relays the signal downconverting the uplink frequency helps to prevent interference with downlink What is the international standard for Digital TV developed by the Moving Picture's Expert Group? MPEG-2 Frequency Re-use Bandwidth= $$ less than 3dB= digital cliff satellite transponders-receives uplink EIRP peaks at center, then rolls off (similar to contour lines) EIRP- downlink power measurement EIRP Effective Isotropic Radiated Power more about satellite footprint -can cover a specific region one satellite can provide continuous coverage satellite footprint -area covered by downlink orbits every 24 hours Geostationary Orbit (GEO) is used for television broadcasting, communications Geostationary Orbit - maintains a constant relative position to the surface of the earth orbits every 12 hours Medium Earth Orbit (MEO) is used for Navigation (GPS) Both LEO and MEO require multiple satellites for continuous coverage Geostationary Orbit (GEO) - 22,300 miles above earth orbits every 90 minutes Low Earth Orbit (LEO) are used for cellular phones, observation satellites Medium Earth Orbit (MEO) - 5,000-10,000 miles above earth High frequency loss what is the Ku-band reserved for? satellite communications what do the frequencies of the C band and the Ku band have in common? the uplink is always a higher frequency than the downlink What type of EM Radiation are Satellite Signals? microwaves higher orbits = larger coverage circular orbit regular interval time elliptical orbit more time on one side of earth during apogee Low Earth Orbit (LEO) -200-930 miles above earth Lower equipment cost disadvantages of Ku-band satellites -Affected by rain fade, requires more power What is rain fade caused by? moisture in the air that can absorb microwaves and attenuate signals the Ku-band uplink frequency range is 14 - 14.5 GHz the Ku-band downlink frequency range is 11.7 - 12.2 GHz advantages of Ku-band satellites -Reserved band, less terrestrial interference
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