Frame synchronization of digital telemetry information

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FRAME SYNCHRONIZATION OF DIGITAL TELEMETRY INFORMATION
I.M. Sidyakin , M.A. Elshafey
Bauman Moscow State Technical University, Moscow, Russian Federation
e-mail: ;
Frame synchronization algorithm plays an important role in the recovery process
of telemetry data transmitted over a communication channel with noise, and it
significantly affects the entire process efficiency. In particular, frame synchronization
is important in the case when the nature of noise in the communication channel and
methods of processing the transmitted information allow for both omission of the
reliable messages and insertion of the false ones into the telemetry data stream, as
well as interruption and resuming transmission at irregular intervals. In general,
the frame synchronization process provides a decommutation ability of telemetry
information parameters in the stream. A necessary theoretical description of the
frame synchronization system model is given, as well as techniques for selecting
basic parameters of the synchronizer. The selection criteria for these parameters are
defined. In the experiments with real telemetry data of IRIG-106 format, the model of
a communication channel with noise allowing for both inversion and bit omissions
is used. The obtained experimental results are compared with theoretical estimations
of the synchronizer parameters.
Keywords: telemetry information, frame synchronization, synchronization code,
synchronization threshold, Search mode, Test mode, Capture modes, IRIG-106
standard, symmetric binary channel with missing bits.
Data synchronization is a detection of a cycling group of characters
in a stream of digital telemetry information (TMI). A synchronizer can be
represented as a finite state machine with three modes [1–4]:
• “Search” mode — is a state in which the synchronizer scans the entire
input data stream to detect a synchronization code;
• “Test” mode — is a state in which the synchronizer confirms the initial
detection of the synchronization code using a predetermined number
of successful checking detections of the synchronization code;
• “Capture” mode — is a synchronizer operation condition in which
the synchronization code is detected with a high degree of accuracy
based on the initial detection and a sufficient number of checks.
Theoretical calculation of the frame synchronization system parameters
introduced in well-known publications [1–7] is based on the fact that
an information component of the frames is filled with random values
distributed according to the normal law. The frames in the stream are
divided by bit sequences of the synchronization codes. Transmission of TMI
stream through a signal channel distorts both the information component of
the frame and the synchronization codes due to noise. In general, this leads
to a loss of the real synchronization codes and emerging of the false ones in
the stream. The probability of the false synchronization codes occurrence
depends on the structure and the content of an information part of the
frame and it may differ from the one theoretically calculated. This paper
ISSN 0236-3933. HERALD of the BMSTU. Series Instrument Engineering. 2015. No. 2 117