Abstract: A system for use in transmitting digital data includes a modulation element that receives block of digital data and modulates each block using one of at least two modulation types, such as QPSK and k-QAM, where k is a power of 2. The system also includes an automatic power control element that applies a selected gain value to each of the blocks of data before transmission. The automatic power control element selects each of the gain values from a group of at least two predetermined gain values, each of which corresponds to one of the modulation types. In general, the modulation types have different associated average power levels, and the power control element selects the gain values to maintain substantially constant average transmission power level among all of the blocks of data.

Abstract: Digital data are communicated from a transmitter to a terrestrial receiver by encoding the data into first and second 1/2 rate convolutional encoded signals during different periods. During the different periods, the convolutional signals are encoded into first and second forward error correction convolutional encoded signals having 2/3 and 6/7 punctured codes transmitted to the receiver via a satellite. Power emitted from the satellite during the first period is 3 db lower than that emitted during the second period. An antenna dish having a diameter no greater than about 1 meter is at the receiver responsive to both signals emitted from the satellite. The encoded signals include sequential bits P.sub.1 (0), P.sub.1 (1), etc. and P.sub.2 (0), P.sub.2 (1), etc. At the 2/3 rate, parallel punctured bit streams respectively including sequential bits P.sub.1 (0), P.sub.2 (1), P.sub.2 (2), P.sub.1 (4) and P.sub.2 (0), P.sub.1 (2), P.sub.2 (3), P.sub.2 (4) are derived.

Abstract: A variable digital filter employs a variable rate sample clock with combinations of various digital filter elements such as an efficient implementation of decimation to achieve various filter realizations allowing a selectable output bandwidth. More specifically, a digital filter apparatus is coupled to receive input analog signals from a fixed anti-aliasing analog filter and optionally includes one or several stages of digital decimation filters, a low-pass filter, an optional equalizer, and an optional high-pass filter each of which may be programmed so as to configure the device with a variety of transfer characteristics. The filter device employs an input sample clock in the range of F-K*F, where, in a specific embodiment K is selected to be 2. The selectable combination of elements and stages used to form the filter needed is operative at a broad range of sample rates over a predetermined bandwidth range without loss of resolution.