Nec Corporation

Yasuhito Isoe

Toshinori Hotta

Tomoyuki Ooi

In a satellite communications system, satellite channels are divided into groups of successively adjacent channels which are covered by a range of frequency drifts caused by a satellite transponder and the channels of each group are assigned unique words of different bit patterns. Modulation systems of an earth station are associated respectively with demodulation systems of distant earth station via the respective satellite channels. A unique word is transmitted from each modulation system together with an information signal and received by an associated demodulation system of the distant earth station. A variable frequency carrier is synthesized in the demodulation system to demodulate the received signal to recover the information signal and the unique word. The recovered unique word is used to establish the frame start timing and the variable frequency carrier is controlled in response to the unique word to tune in the demodulation system to the desired satellite channel.

Transponder frequency offset compensation with recurrently assigned

In a communications system, a multiframe data signal is sent from a transmit end to a receive end of the system. The multiframe is composed of a series of submultiframes each containing a series of frames. Each frame in turn comprises a sync word for establishing the start timing of the frame, an identifier for uniquely identifying the submultiframe in which the frame is contained, and a specified number of data bits. A pseudo-random scrambling bit pattern, which repeats at intervals of multiframe and varies from one pattern to another at frame intervals, is generated as a scrambling bit pattern with which the data bits of each frame are scrambled prior to transmission. At the receive end, the sync word of each frame is detected to establish frame synchronization. A memory stores initial bit patterns each of which is identical to the pattern which was generated at the beginning of each submultiframe. The identifier is detected when frame sync is established and applied as a read address to the memory. The initial bit pattern of the submultiframe which is next to a one in which the establishment of frame sync occurred is read out of the memory into a pseudo-random sequence generator. The latter is activated at the beginning of the next submultiframe to generate a pseudo-random sequence, which successively varies at frame intervals and repeats the same pattern at multiframe intervals, for descrambling received data bits.

Scrambling/descrambling method using a memory for storing initial

A DAMA control system for an SCPC satellite communication system includes first and second control stations which can independently perform centralized DAMA control through corresponding common signaling channels, a large number of slave stations capable of receiving data through either common signaling channel, and a satellite station. While one control station performs DAMA control, the other control station performs a backup operation. When one control station loses a control function, the other control station takes over centralized DAMA control.

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Tokyo, Japan

Yasuhito Isoe