|Saturday, 12 August 2006|
Direct broadcast satellite service (DSS or DBS) refers to satellite transmission of television signals directly for use by individual households or subscribers having the proper signal receiving equipment. The digital satellite service (DSS) allows viewers in sparsely populated or mountainous areas high quality access to television programs from around the world. Direct broadcast satellite services include Pay-TV, tele-conferencing, tele-seminar, and private broadcast networks. Digital direct-to-home satellite systems broadcast hundreds of programming channels to a very wide geographical area. Broadcast satellite systems can provide many channels due to their efficient use of bandwidth. A digital satellite television system for direct television broadcasting includes a transmitter for transmitting television signals including video and audio components to a geostationary satellite. Modern digital satellite communication systems typically employ a ground-based transmitter that beams an uplink signal to a satellite positioned in geosynchronous orbit. These systems permit the household or business subscribing to the system to receive audio, data and video signals directly from the satellite by means of a relatively small directional receiver antenna. Television transmitters operating in the digital satellite service system provide coded digital signals via a satellite to receivers located within the field of view of the satellite. The satellite or satellites in the DSS system retransmit a signal from one or more earth stations to a large number of receiving earth stations.
Satellite television signals may be received from a satellite positioned in geosynchronous orbit in which it is stationary with respect to a geographic receiving area. Television signals are transmitted from one earth location to another earth location via geostationary satellites that all orbit in a defined belt and with a defined altitude above the earth. The satellite broadcasting system transmits a broadcast signal of frequency in the range of 11.7-12.2 GHz having a number of channel signals. The satellites receive the signals from the different television stations in the frequency range and modulate these signals with a carrier signal having a suitable frequency such as a frequency in the range of approximately 950 MHz to approximately 2150 MHz. The satellites then transmit the modulated carrier signals to television receivers on the ground. Reception of satellite broadcasting which is broadcast making use of a communications satellite requires a down converter for converting a frequency of radio waves of satellite broadcasting received, for example, by way of a parabola antenna, and a satellite broadcasting tuner for selecting a desired broadcasting channel from within an output of the down converter and demodulating a video signal of the selected broadcasting channel.
A satellite television broadcasting receiver is used for the purpose of receiving pictures and television broadcasting programs offered by utilizing satellites. The satellite receiving arrangement is generally composed of an outdoor unit generally associated with the antenna and an indoor unit generally associated with the television set or the like. The outdoor and indoor units are coupled via a coaxial cable. Satellite television receiving systems usually comprise a dish-like receiving antenna and a block converter, and an indoor unit including a tuner and a signal processing section. The block converter converts the entire range of relatively high frequency RF signals transmitted by a satellite to a more manageable, lower range of frequencies. Satellite television receivers decode satellite broadcast television signals for display by a television monitor. These receivers are widely used in earth stations by homeowners in connection with an antenna to directly receive satellite broadcast television signals from one of a number of satellites in geosynchronous orbit about the equator. The satellite broadcast signal transmitted is received by a block converter mounted in a parabolic antenna and the satellite broadcast signal is converted to a radio frequency (RF) signal in the range of 950-2050 MHz to allow following signal process, e.g., tuning a certain channel signal. The television signals produced by the block converter are connected via a coaxial cable to an indoor satellite receiver coupled to a TV set. The satellite receiver includes the componentry for controlling the position of the antenna so that a selected television signal can be received from the appropriate one of the plurality of geostationary satellites. The satellite receiver also includes circuitry for processing the received signal, i.e., descrambling, filtering, and otherwise conditioning the received signal, and then providing the post-processed signal to the user's television.
Satellite receiver tunes, demodulates and otherwise processes the received television signals to provide video and audio signals with a NTSC, PAL or SECAM format suitable for processing by the TV set that produces an image on a display screen in response to the video signals, and an audible response by means of speakers in response to the audio signals. A direct broadcast satellite system transmits compressed television and other ancillary signals in compressed and packet form. Within the transmitter, analog video and audio signals are converted to respective digital signals compressed according to the motion picture expert group (MPEG) encoding standard. MPEG-2 video compression is one particular method of efficient bandwidth usage employed by broadcast satellite systems. The information for broadcast is converted into digital signals that are divided into packets. Each packet is assigned a header that is used to identify the information for a particular television service.
A satellite broadcast system decoder is provided between the receiving dish and a user's television. This decoder takes the incoming data stream, demodulates and decodes the incoming data, and converts the data into analog form. The satellite receiver comprises a tuner for selecting the appropriate carrier signal retransmitted by the satellite and for converting the frequency of the selected carrier to an intermediate frequency (IF) signal. A TV set top receiver translates the DSS stream into an analog signal fed to the television receiver. For pay-per-view and automatic billing services the receiver is connected to a telephone jack connected to the local exchange telephone network. Satellite broadcasting tuner receives a signal having a frequency of 1 GHz obtained by down-conversion by a down converter and frequency converts the received signal to form an intermediate frequency in which video signals of several channels are included. Satellite broadcasting tuner has an automatic fine tuning (AFT) function wherein a local oscillation frequency supplied to a frequency converter is controlled in accordance with a level of a demodulated video signal.
The use of satellite antennas to receive satellite television transmissions has provided these households with access to hundreds of television channels. Direct broadcast satellite service receivers generally are parabolic antennas that consumers mount on a residential rooftop or recreational vehicle. Digital television is digitally modulated when broadcast over satellite systems using phase shift keyed modulation schemes. The signals are typically received at Ku-band or C-band via a satellite dish antenna. A typical antenna constructed to receive satellite signals comprises a dish-shaped reflector that has a support arm protruding outward from the front surface of the reflector. The dish-like antenna directs the received television signals to the block converter that converts the frequencies of the received television signals to respective lower frequencies. For home satellite TV reception, the disk antenna is usually permanently positioned on a concrete pad in the yard or occasionally on the roof of the home. To obtain an optimum signal, the antenna must be installed such that the centerline axis of the reflector, also known as the "bore site" or "pointing axis", is accurately aligned with the satellite. The receiver and antenna are usually provided as one assembly having an outdoor unit and an indoor unit.