Comsat Corporation

Communications Satellite Corporation

Intelsat Global Service Corporation

Farhad Hemmati

Spiros S Dimolitsas

Roderick James Ragland

Lin-Nan Lee

Bangalor Ramachandra Bhaskar

A decoding method and apparatus, using the Viterbi algorithm for selecting survivor paths terminating on each trellis state, applied for realization of a shared channel decoder (SCD). The shared channel decoder include a branch metric calculator for calculating branch metrics B , a plurality of ACS units for computing and exchanging new path metrics &Ggr; and survivor paths E , a memory (RAM) for storing new path metrics &Ggr; and survivor paths E , and a memory (RAM) for storing previous path metrics &Ggr; and previous survivor paths E . The branch metrics B is the set of branch metrics for decoding step t (e.g., for a code rate of &frac12;, B &equals;&lcub;B , B , B , B &rcub;), the path metrics &Ggr; is the set of S survivor metrics &lcub;&ggr; , &ggr; , . . . , &ggr; &rcub; at decoding step t and the survivor paths E is the set of S survivor metrics &lcub;E ,E , . . . , E &rcub; where S is the number of decoder states. In one embodiment, the shared channel decoder includes a branch metric queue for storing branch metrics B , a tentative path metric memory for storing tentative path metrics &Ggr; , and a multiplexer (selector) for selecting the previous path metrics &Ggr; when t&ne;T&plus;cD, and selecting the tentative path metrics &Ggr; when t&equals;T&plus;cD. In an alternative embodiment, the size of required RAM is traded off against the decoder BER performance, but tentative path metrics are not stored when t&equals;(c&plus;1)D. Instead, when t&equals;T&plus;cD, the state j having best path metric is selected and the contents of the survivor register, denoted by E , are output as the D decoded bits.

Method for implementing shared channel decoder for onboard processing satellites

A communication network, comprising data transmission and data receiving systems and operations, for carrying reliable voice communications, particularly for mobile communications applications involving land-mobile, aeronautical and maritime systems. Because the quality of the links in such systems may vary, the present invention combines a nested codec with a channel coder at the transmission side of the link and a decoder at the reception side. The nested codec will transmit at a constant rate, which is the highest bit rate possible in the system, but according to channel conditions, will reconstruct voice at different bit rates. Thus, for example, transmission will always occur at a rate of 3600, but the reconstruction of the transmitted signal will be at 2400 or 1200 bps, depending on the quality of the signal. Notably, the lower two rates are subsets of the higher rate, thus defining their 'nested' characteristic. Moreover, the rate reductions from the constant maximum rate occur automatically at the receiver, without transmitter control, based on the detected degraded conditions at the receiver. Because the rates are nested, they are a known multiple of the lowest rate.

Communication systems using nested coder and compatible channel coding

A communication system including: a first secure communication terminal for providing analog voiceband data; a first processing circuit connected to receive the secure data from the first secure communication terminal and for converting the received data into secure baseband data, the first processing circuit transmitting the baseband data; a second processing circuit connected to receive--the transmitted baseband data from the first processing circuit, and for converting the received baseband data into analog voiceband data; and a second secure communication terminal for receiving the analog voiceband data from the second processing circuit. The communication system is especially applicable for handling secure data transmitted by a STU-III.

Secure communication system

A block code decoding method finds the highest path metric path in a forward direction of a trellis diagram from an initial state of the trellis diagram to a final state. Next, the highest path metric path is found in a backward direction from the final state back to the initial state. The metrics of these two highest path metric paths are compared and the path having the absolute highest metric, in either direction, is chosen as a most likely path through the trellis diagram.

Bidirectional trellis coding

Interference from other users in a CDMA Spread Spectrum system is cancelled by constructing a single reference sequence which is representative of the spreading sequences of all users in the system. Interference from the other users can be cancelled without each receiver employing a separate decorrelator for every other user in the system and having an accurate estimate of the received power level of every transmitted signal.

Method and apparatus for simple and efficient interference cancellation

A communication system including: a first secure communication terminal for providing analog voiceband data; a first processing circuit connected to receive the secure data from the first secure communication terminal and for converting the received data into secure baseband data, the first processing circuit transmitting the baseband data; a second processing circuit connected to receive the transmitted baseband data from the first processing circuit, and for converting the received baseband data into analog voiceband data; and a second secure communication terminal for receiving the analog voiceband data from the second processing circuit. The communication system is especially applicable for handling secure data transmitted by a STU-III.

A modem/codec is designed for a digital signal transmission system using a single satellite transponder. The system is capable of transmitting data of a rate of 155.52 Mbps, and is thus compatible with the BISDN rate. A codec of rate 13/15 is used, and an octal phase shift keying modem is also used. In this way, the digital signal transmission system is capable of receiving data at a rate of 155.52 Mbps over a single INTELSAT V/VA transponder with a usable bandwidth of 72 MHz.

Bisdn compatible modem codec for digital information communication system

Linear and nonlinear bits are logically combined to form each of at least three sequences, one of which is selectively used to couple either one of the others to the output of the sequence generator.

Growing community of inventors

Darnestown, MD, United States of America

Farhad Hemmati