Browse Prior Art Database

Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-30
Document File: 3 page(s) / 176K

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A proposal for a novel G.728 synchronization scheme using the Auto-Correlation Function (ACF) of a Pseudo-Random Binary Sequence (PRBS) and bit-stealing to allow in-band sychronization.

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MOTOROLA Technical Developments


  A proposal for a novel G.728 synchronization scheme using the Auto-Correlation Function (ACF) of a Pseudo-Random Binary Sequence (PRBS) and bit-stealing to allow in-band sychronization.


Frame Synchronization, G. 728, Autocorrela- tion, Pseudo-Random Binary Sequence (PRBS)


ACF- Auto-Correlation Function. CCITT- International Telegraph and Telephone

  Consultative Committee. CELP-Cod Excited Linear Prediction. El-CCI'IT ISDN channel @ 2.048 MBPS. GSM - Global System for Mobile Communication.
G.728-ITU Recommendation G.728 [Ref. 11. ISDN- Integrated Services Digital Network. ITU- International Telecommunication Union. LD- Low Delay.

MBPS- Mega (Million) bits per second. PRBS- Pseudo-Random Binary Sequence. Tl- CCITT ISDN channel @ 1.544 MBPS.


  This proposal addresses the problem of frame synchronization for G.728 data that is sent over an Elm1 (2.048/1.544 MBPS) span line. Each G.728 data stream will be sent as 2 bits of an g-bit El/I1 timeslot. Once the data stream is extracted from the ISDN channel, it must by ensured that both ends of the span are synchronized. There are "elastic" buffers at each end of the link. This allows for the timing difference at each end of a non-synchronised network link with free-running clocks. Occasional- ly, due to excessive timing differences, the elastic buffers are flushed without sending their contents or send the same frame twice. Consequently, a com- plete El/T1 frame is lost or repeated. This would result in the loss or gain of 2 bits in a G.728 stream.

  A synchronization sequence would allow re-syn- chronization following a frame slippage. Since there are four G.728 data streams per timeslot (each
G.728 stream using the full 16 KBPS rate of these sub-channels), there is no spare capacity for syn- chronization sequences. To circumvent this prob- lem, in-band signaling can be used. With in-band signaling the signaling information is inserted into the data stream. Prior knowledge of the scheme at the receiving end allows this signaling information to be extracted. Once the synchronization sequence bits are extracted, they can be used to synchronize the framing of the data.


  The author is unaware of similar synchroniza- tion schemes using the novelties listed. However, synchronization schemes exist that use a PRBS sequence. For example, the GSM system uses blocks of 16- and 41-bit PRBS as a means of chan- nel sounding and timing synchronization. The dif- ference with this scheme is that the sequence is dis- tributed throughout the data stream.


  It is proposed that a method of in-band signaling may be used that involves "bit stealing" a number of data bits to include the synchronization sequence. The G.728 recommendation suggests a bit-stealing scheme based on using one bit from every 16 output vectors [see ref. Error! Reference source not found., section 3.111...