Digital Communications Corporation

M/a-Com Dcc, Inc.

Pradman P Kaul

Ova Gene Gabbard

Anders A Eklof

Pradeep Kaul

John M Husted

Deepak Muzumdar

Time Division Multiple Access (TDMA) is being utilized widely in domestic and international communication networks. The types of TDMA networks in operation fall into two categories: Wideband and Narrowband. In the past few years, a number of Wideband and Narrowband TDMA networks have gone into operation. However, these networks have typically operated as independent nets. As the existing Wideband TDMA networks expand into cities with a smaller amount of originating traffic, a major economic problem occurs. It becomes difficult to justify the cost of a Wideband TDMA station for the smaller amount of traffic. This invention presents an approach that solves the above problem by providing an integrated network with Wideband TDMA for the large cities and Narrowband TDMA for the smaller cities.

Integrated narrowband and wideband TDMA networks

A TDMA multiplexer-demultiplexer includes a plurality of input/output ports and common control equipment. Each input port is capable of accepting information asynchronous to the TDMA clock and at typical terrestrial clock rates. The input/output ports perform all the necessary signal processing for a TDMA terminal including pulse stuffing, changing continuous asynchronous low rate information to high bit rate burst form as well as forward acting error correcting encoding, if desirable. By incorporating all the signal processing in the multiplexer-demultiplexer, much equipment duplication is eliminated along with eliminating a requirement for multiple high frequency control and timing signal line drivers and buffers. More particularly, the transmit side of each port includes a separate elastic buffer to raise the input rate to a synchronous common higher rate. In addition, on the receive side, clocking on the low speed side of the expansion buffer is derived from the station's transmit clock.

TDMA Multiplexer-demultiplexer with multiple ports

A communication terminal interface accepts, on different channels, information in a plurality of formats for communication purposes over a communication link which may be a TDMA satellite link. Each channel is accepted by a different interface unit which serves to format the information for communication over the system. This unit includes a compression-expansion buffer memory for allowing information received at a receive rate R.sub.s to be multiplexed and transmitted at a transmission rate T.sub.s which may be many times higher than the receive rate. In addition some units may include forward acting error correcting coding selected to provide the necessary corrected bit error rate for the type of information accepted by the unit and the capacity of the communication link over which the information is to be transmitted. The transmitter may employ differential encoding. To avoid increasing the error rate, which would normally result from this type of encoding, the encoded data is interleaved at the transmit side such that adjacent errors, after de-interleaving, on the receive side, are sufficiently displaced such that they may be corrected by the error decoding.

Error coding communication terminal interface

A TDMA system in which each station times its respective data burst from a reference sync burst transmitted by a designated primary reference station over the satellite link. Another station transmits a secondary sync burst timed from the primary stations sync burst. To maintain synchronism at the satellite each station has a burst synchronizer operated by receipt of the primary reference sync burst. The secondary sync burst is also received by each of the stations and is capable of ensuring synchronization in case of failure of the primary stations's sync burst.

Double sync burst TDMA system

A frame synchronizer is disclosed for searching for the framing bits of an N bit frame in a stream of binary signals. Means are provided to compare, bit by bit, the signals in different bit positions of two adjacent frames. When only a single bit position indicates an alternating pattern of binary signals, it is considered the framing bit and a framing pulse is provided in that bit position. Apparatus is also provided to detect loss of synchronization including a pair of counters, one counting framing pulses and the other counting alternating signals in that bit position. To reduce the likelihood of false out-of-synchronization signals, the second of these counters can be pre-set. Only when the count of the first counter exceeds the number of signals counted by the second counter by this pre-set quantity will out-of-synchronization be declared.

Growing community of inventors

Gaithersburg, MD, United States of America

Pradman P Kaul