International Mobile Satellite Organization

Inmarsat Limited

Inmarsat Global Limited

Howard Ray Feldman

Eyal Trachtman

Hok Shuen Wong

Siu Wah Wong

Francois-Arnaud Remael

Louis Mimis Christodoulides

Nobuyuki Kawai

Joan Obradors

Thomas Francis Harold McHugh

Richard Douglas Lane Smith

Louis Christodoulides

A set of formats and protocols is proposed for a satellite communications system. In these formats, a pilot signal (PS) is inserted after every 25 or 29 data symbols. The formats consist of SCPC frames (F) which may contain either data (D) and in-band signaling information (SU), or only signaling information (SU). In either case, the contents of each frame (F) are error-correction coded before transmission with the same coding rate. Each data frame (F) carries the data content of an integral number of input user data frames (M), each of which comprises four subframes. Different symbol transmission rates are used for different input data rates, the symbol transmission rates being selected so that their different synchronizing clock rates can easily be obtained from a common clock. Data bursts may be preceded by a constant power level preamble (P). The formats and protocols satisfy the requirements of a high data rate satellite communications system.

Communication method and apparatus

A set of formats and protocols is proposed for a satellite communications system. In these formats, a pilot signal (PS) is inserted after every 25 or 29 data symbols. The formats consist of SCPC frames (F) which may contain either data (D) and in-band signalling information (SU), or only signalling information (SU). In either case, the contents of each frame (F) are error-correction coded before transmission with the same coding rate. Each data frame (F) carries the data content of an integral number of input user data frames (M), each of which comprises four subframes. Different symbol transmission rates are used for different input data rates, the symbol transmission rates being selected so that their different synchronizing clock rates can easily be obtained from a common clock. Data bursts may be preceded by a constant power level preamble (P). The formats and protocols satisfy the requirements of a high data rate satellite communications system.

Data interface apparatus and method

A network station receives a principal signal and data. When the principal signal is present or contains information it is transmitted to a receiving station through a communications channel. When the principal signal is absent or does not have a significant information content, the network station transmits the data through the same communications channel in a format such that the data is received and output by a further receiving station.

Communication method and apparatus with transmission of a second signal during absence of a first one

An interface between a data terminal and a digital communications link implements protocols and frame formats designed to reduce delays in a data communication with a remote terminal. The interface overcomes the need to send or receive an HDLC SABME or UA control signal for establishing an asynchronous balanced mode, and allows data to be sent over the digital communications link as soon as the communication parameters are established. In a non-ARQ (error correction) mode, the interface sends control signals and data over the communications link in frames subdivided into many small subframes of fixed length, each subframe having a length code indicating an amount of valid information but without CRC, address or control information. The interface, when arranged for connection to the data terminal through a telephone network, encodes call progress signals from the telephone network for sending over the digital communications link. The interface encodes and decodes interrupt signals for sending between the data terminal and the digital communications link when an interrupt signal is detected.

A communications link for data communication via satellite includes interface apparatus comprising a satellite link interface for connection to a satellite link and a PSTN interface for connection to a PSTN. The interface apparatus supports different data compression modes in the communication link. Mode A allows data compression over the PSTN but not over the satellite link. Mode B allows data compression over the PSTN and over the satellite link, but enables decompression and recompression of data flowing in each direction through the interface apparatus. Mode C allows compressed data to pass transparently between the PSTN and the satellite link, while the interface apparatus performs error correction on the satellite link and on the PSTN.

Communication method and apparatus using data compression

Method and apparatus for determining direction

A facsimile interface unit, which encodes signals from a facsimile terminal for transmission by satellite, can only encode signals which conform to the Group 3 standard. The interface unit intercepts signals which identify non-standard features supported by the terminal and replaces them by a modified signal of the same format which does not identify any non-standard features. Another facsimile terminal receiving the modified signal is prevented from enabling any non-standard features and signals to the first facsimile terminal that the Group 3 standard is to be followed. Therefore, the facsimile interface unit is able to encode and decode signals successfully during the subsequent transmission.

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Middlesex, United Kingdom

Howard Ray Feldman