Satellite block transmission using wideband fiber optic links

#The present invention is directed to a system for transmitting one or more blocks of information signals from a satellite antenna to a remote receiver using wideband fiber optic links.

#Conventional television-receive-only (TVRO) earth station systems consist of a TVRO antenna which receives one or more high frequency signals directly from a telecommunications satellite, low noise amplifiers (LNAs) which amplify the signals, and coaxial cables which transmit the amplified signals to headend equipment containing a receiver which extracts baseband video and audio signals from the high frequency satellite signals for transmission to subscribers.

#Multiple TV channels are transmitted from a satellite in blocks of twelve frequency division multiplexed signals, typically over a 3.7-4.2 GHz band. Current satellites are capable of transmitting twenty-four TV channels in two blocks--a twelve channel, horizontally polarized block and a twelve channel vertically polarized block. Each block is separately received by the satellite antenna, amplified by a LNA and transmitted over coaxial cable to headend equipment comprising the receiver(s) and "on channel" modulators.

#FIG. 1 is a block diagram of a conventional satellite transmission system.

#FIG. 2 is a block diagram of a satellite transmission system designed in accordance with the invention.

#FIG. 3 is a block diagram of a block down-converter for use in the system of the invention.

#Referring to FIG. 1, a conventional satellite transmission system for television receive only (TVRO) is illustrated in block form. The system includes satellite antenna 1 which receives one or more blocks of high frequency signals, typically in the frequency band of 3.7-4.2 GHz, from a telecommunications satellite. Present technology permits such satellites to transmit a maximum of twenty-four video channels in two blocks of twelve frequency division multiplexed channels. Of course, smaller numbers of signals can also be transmitted. The blocks are transmitted as vertically and horizontally polarized signals to keep them distinct. The blocks of horizontally and vertically polarized signals are received by the antenna and separately detected and amplified by low noise amplifiers (LNA) 3 and 5, respectively. Power feeds 7 and 9 drive the LNAs. The amplified signal blocks are transmitted over high frequency low loss coaxial cable 11 and 13 to satellite receivers 15 and 17, respectively. The receivers convert the high frequency signals to the appropriate video and audio signals which can be processed for reception by subscribers.

#FIG. 2 illustrates the satellite transmission system of the invention. This system includes satellite antenna 19, which is identical to the satellite antenna used in the conventional system. Low noise amplifiers 21 and 23 also correspond to the conventional LNAs used to amplify the vertically and horizontally polarized signal blocks. However, unlike the conventional systems, the system of the invention contains first block conversion means 25 and 27 which down-convert each block of high frequency signals to an intermediate frequency band of 0.6-1.1 GHz.

#The down-converted signals are then used to modulate the output of optical transmitters 29 and 31 in the fiber optic links. While any type of optical transmitter which is capable of transmitting the intermediate frequencies over an optical waveguide approximately 1 km in length may be employed in the system of the invention, injection laser diode (ILD) transmitters which launch intensity modulated signals are most preferred. ILD's with the following specifications have demonstrated adequate performance in model systems: