Method and apparatus for improving asynchronous transfer mode operation over noisy, high speed wireless links

Abstract

In an asynchronous transfer mode (ATM) system, an apparatus is used to improve the transmission and reception of encoded ATM information over a wireless link having an encoder for encoding the information, assembling the information into a frame format and interleaving of the information for transmission over the wireless link. In addition, the apparatus also has a decoder for decoding information received via the wireless link which was encoded by a similar apparatus transmitting the information over the wireless link. Further, methods utilized by the encoder and decoder to improve transmission include increasing the bandwidth efficiency by dropping a header byte from every ATM cell; assembling separate header and payload frames; utilizing and rearranging idle / unassigned cells in the payload frame for storing and, thereby, increasing error correction code in the frame; dynamically changing the coding of frame in real time from one payload frame to optimize utilization of the mumber of available idle / unassigned cells occurring in each frame; restoring the positions of all idle / unassigned cells to their original position at a receiving end in order to leave the Cell Delay Variation unaffected; interleaving the frames to reduce burst errors during transmission; preservation of overhead parity bits present in the original frames received from a wireline link; cell Header error detection and correction through the use of a generated syndrome; and a synchronization pattern detection method during decoding.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to high quality of service transmission of Asynchronous Transfer Mode (ATM) information over noisy, high speed wireless links. More specifically, the invention relates to protecting ATM cells transmitted over high speed wireless channels using framing, interleaving and forward error correction coding schemes to correct burst errors. [0002] The present application is based upon U.S. Provisional Application No. 60 / 052,359, which is incorporated herein by reference. [0003] Asynchronous Transfer Mode (ATM) is a method for transmitting information via a broadband Integrated Services Digital Network (B-ISDN). ATM is a transfer mode which-uses fixed size data units, known as cells, made up of 53 bytes; 48 of these bytes contain data (referred to as the information field or payload) and 5 contain overhead (referred to as the cell header). The data bytes correspond to the ATM Adaptation Layer (AAL) and the overhead bytes define...

AI Technical Summary

Problems solved by technology

There exist, however, a number of factors which present problems when transmitting ATM cells in SDH and PDH formats over wireless links.

However, due to the necessity of including channel coding into wireless transmissions to reduce receiving station size, such as in satellite channels for example, and thereby minimize ground segment costs, transmission bit errors in a wireless environment are likely to occur in bursts.

Furthermore, ATM protocols assume that the transmission medium has very low Bit Error Rates (10−12 or better) and that bit errors occur randomly.

Most satellite and wireless links have much worse Bit Error Rate characteristics (10−6 to 10−8) and errors tend to occur in long bursts, especially when Viterbi coding is used in the modems.

These factors have a severe effect on ATM protocols and applications that use ATM.

This feature is useless in the satellite and wireless bursty error environments, with the net result being that the cell headers of a large number of cells can get corrupted, leading to cell losses or misinsertions.

This technique, however, does not address the problem of high ATM cell error ratio (CER) characteristics present in wireless links.

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