HDLC Packet Encoder

This is a GNU Radio hierblock to construct HDLC packet. The input is raw data field message (ADDRESS field(s), CONTROL field, INFORMATION field, etc), without the FLAG(s) and FCS. The output is bitstream which already contain complete HDLC packet format (including PREAMBLE or TRAINING_SEQUENCE, HEADER_FLAG, FCS, POSTAMBLE_FLAG, and TRAILING_SEQUENCE).

Tested on GNU Radio v3.7.11 - Ubuntu.

Index

1. Installation
2. HDCL Packet Encoder in More Detail
3. Example
4. TODO

Installation

You have to have GNU Radio v3.7.10 (or newer) in your computer first.

$ cd
$ cd gr-HDLC-AFSK/hierblocks/hdlc-packet-encoder/
$ gnuradio-companion hdlc-packet-encoder.grc

• Run the flowgraph (F6).
• Reload Blocks
• Finish. Now this hierblock will appear under HDLC AFSK category as HDLC Packet Encoder block.

Detail

• Consider the following HDLC data frame, with the FLAG(s) are 0x7E character at least one byte and the FCS are CRC-16-CCITT.

• In order to be transmitted over the medium, for example using AFSK modulation, the data frame above needs to be added with training symbols or PREAMBLE. This training symbols are used as clock synchronization symbols by the receiver. Therefore, the data frame above should be packetized as the following: We can use (1,0,1,0,1,0,1,0,…) as training symbols for receiver synchonization.

• This HDLC Packet Encoder block will handle the HDLC frame construction as well as the complete packet from user-provided message input which are ADDRESS, CONTROL, and INFORMATION(optional) field.

• Moreover, the bigger picture of which happen inside this HDLC Packet Encoder blocks is the following:

NRZI coding (differential encoder) is added to make the packet compatible with the most standard. This differential coding also makes the packet practically immune to the bit polarization reversal.

Example

File:

gr-HDLC-AFSK/hierblocks/hdlc-packet-encoder/hdlc_packet_encoder-example.grc

TODO

// TODO