Convolutional Encoder Option - Ce; Figure 2: Ccsds 131.0-B-1 Rendering Of Basic Convolutional Encoder Diagram - Quasonix TIMTER Installation And Operation Manual

TIMTER™ Multi-mode Dual
Telemetry Transmitter
1.3.14 Convolutional Encoder Option – CE
The CE option enables convolutional encoding and NRZ-M conversion. This encoding adds redundant information
to the transmitted data stream to help detect and correct bit errors that may occur, particularly due to predominantly
Gaussian noise. Use of convolutional encoding requires a matching Viterbi decoder in the receiver to extract the
source data. The encoded data rate will be twice the source data rate, and the occupied bandwidth will also be
doubled.
For example, the transmitter has two encoders, one for in-phase ("I") data and one for quadrature ("Q") data. Call
the input symbol stream I0/Q0, I1/Q1, ... . Each encoder outputs 2 bits for every input bit, so call the output bit
stream from the first convolutional encoder I0(1), I0(2), I1(1), I1(2), ... , and call the output bit stream from the
second convolutional encoder Q0(1), Q0(2), Q1(1), Q1(2), ... . Combining the outputs of the two encoders, then,
the output symbol stream is I0(1)/Q0(1), I0(2)/Q0(2), I1(1)/Q1(1), I1(2)/Q1(2), ... .
For modes that do not employ Quadrature modulation, such as PCM/FM, Multi-h CPM, and BPSK, only a single
encoder is used.
A single encoder is implemented exactly as described in the "Consultative Committee for Space Data Systems,
Recommendation for Space Data System Standards, TM Synchronization and Channel Coding, CCSDS 131.0-B-1,
Blue Book, September 2003, Section 3."
A basic convolutional encoder block diagram, as illustrated in CCSDS 131.0-B1, is shown in Figure 2.

Figure 2: CCSDS 131.0-B-1 Rendering of Basic Convolutional Encoder Diagram

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