Here we offer a MAC-Sublayer implementation for networked control system applications.

It is based on IEEE802.15.4 implementation of Bastian Bloessl.

Development

This module uses maint-3.7 branch for development. This branch is supposed to be used with GNU Radio 3.7 branch.

Features

• Flexible slotted superframe is created by MAC-Controller block.
• Synchronization is provided by regular beacon packets, which are originated from MAC-Controller block.
• Different queuing strategies in MAC-Plant block.
• A configurable real time discrete model of an inverted pendulum as an examplary control application.
• The O-QPSK PHY encapsulated in a hierarchical block.
• A block that implements the Rime communication stack. Rime is a lightweight communication stack designed for Wireless Sensor Networks and is part of the Contiki Operating System.
• A transceiver flow graph with USRP <-> PHY <-> MAC <-> Network layer (Rime) <-> UDP Socket / APP which resembles pretty well the ISO/OSI structure.
• An IEEE 802.15.4 and Rime dissector for Wireshark.

Some interesting properties:

• Packets can be piped to Wireshark.
• The complete physical modulation is done with plain GNU Radio blocks.
• It uses a block to tag packet bursts with tx_sob and tx_eob tags. This tags are understood by the UHD blocks and allow fast switching between transmission and reception.

Dependencies

• GNU Radio

• gr-foo (Wireshark Connector, Packet Pad and Burst Tagger blocks)
  https://github.com/bastibl/gr-foo.git

• python-matplotlib (if you want to run the GUI sample application)
  sudo apt-get install python-matplotlib

Installation

Please see www.wime-project.net for installation instructions.

Usage

• The structure of the superframe can be controlled from MAC-Controller block.
• The duration of a timeslot, the number of timeslots inside a superframe are variable. They can be chosen from GRC.
• Examplary GRC flow graphs, which are compatible with inverted pendulum application, can be found inside inverted_pendulum_gui/examples folder.
• Configuration file of the control application(inverted_pendulum_gui/config.py) includes network configuration and inverted pendulum configuration variables also GUI can be activated and deactivated throug config.py. STRATEGY has no effect on the strategy of GNU Radio, but it should be chosen correctly for logging.
• Every plant application communicates with its own device, thus USRP source and USRP sink blocks should be connected with same USRP device.
• Controller application should be connected with the flowgraph with MAC-Controller block through UDP.
• Plant application should be connected with the flowgraph with MAC-Plant block through UDP.
• The number of plants should be defined correctly at MAC-Controller block in order to allocate timeslots for each plant.
• Maximum number of timeslots in a superframe is 32 and first timeslot of every superframe is reserved for beacon packet.
• The number of retransmission attempts is defined as MAX_RETRANSMISSION_ATTEMPT in mac_plant_impl.cc. If maximum retransmission number is more than 1, ACK packet will be sent by the controller.
• LOG_DIRECTORY_LOCATION definition in the mac_plant_impl.cc should be same as log directory of the application to save measurements of GNU Radio.
• The tx and rx packet format can be modified from lib/protocol.h depending on the structure of the application packets.
• The plant IDs from 1 to 4 have their predefined unicast addresses in lib/protocol.h file. If a demo uses more than 4 plants, their unicast addresses should be added to lib/protocol.h.

Open the examples/transceiver_*.grc flow graph with gnuradio-companion and check if all blocks are connected. Enable either the UHD blocks to interface with real hardware or the Packet Pad block to loop back the samples. Open some Rime connections and connect messages sources or Socket PDUs. You can easily connect to the Socket PDU blocks with netcat. Netcat can be started for example with

nc -u localhost 52001

There are also startup scripts in the apps folder.

Have fun!