gr-ieee802-11/README.md

Hi!

This an IEEE 802.11 a/g/p transceiver for GNU Radio that is fitted for operation
with Ettus N210s and B210s. Interoperability was tested with many off-the-shelf
WiFi cards and IEEE 802.11p prototypes. The code can also be used in
simulations.


# Development

Like GNU Radio, this module uses *master* and *maint* branches for development.
These branches are supposed to be used with the corresponding GNU Radio
branches. This means: the *maint-3.7* branch is compatible with GNU Radio 3.7,
*maint-3.8* is compatible with GNU Radio 3.8, and *master* is compatible with
GNU Radio master, which tracks the development towards GNU Radio 3.9.


# Installation


## Dependencies


### GNU Radio

There are several ways to install GNU Radio. You can use

- [pybombs](http://gnuradio.org/redmine/projects/pybombs/wiki)
- [pre-compiled binaries](http://gnuradio.org/redmine/projects/gnuradio/wiki/BinaryPackages)
- [from source](http://gnuradio.org/redmine/projects/gnuradio/wiki/InstallingGRFromSource)


### gr-foo

I have some non project specific GNU Radio blocks in my gr-foo repo that are
needed. For example the Wireshark connector. You can find these blocks at
[https://github.com/bastibl/gr-foo](https://github.com/bastibl/gr-foo). They are
installed with the typical command sequence:

    git clone https://github.com/bastibl/gr-foo.git
    cd gr-foo
    mkdir build
    cd build
    cmake ..
    make
    sudo make install
    sudo ldconfig


## Installation of gr-ieee802-11

To actually install the blocks do

    git clone git://github.com/bastibl/gr-ieee802-11.git
    cd gr-ieee802-11
    mkdir build
    cd build
    cmake ..
    make
    sudo make install
    sudo ldconfig

### Adjust Maximum Shared Memory
Since the transmitter is using the Tagged Stream blocks it has to store a
complete frame in the buffer before processing it. The default maximum shared
memory might not be enough on most Linux systems. It can be increased with

    sudo sysctl -w kernel.shmmax=2147483648


### OFDM PHY

The physical layer is encapsulated in a hierarchical block to allow for a
clearer transceiver structure in GNU Radio Companion. This hierarchical block is
not included in the installation process. You have to open
```/examples/wifi_phy_hier.grc``` with GNU Radio Companion and build it. This
will install the block in ```~/.grc_gnuradio/```.


### Check message port connections

Sometime the connections between the message ports (the gray ones in GNU Radio
Companion) break. Therefore, please open the flow graphs and assert that
everything is connected. It should be pretty obvious how the blocks are supposed
to be wired. Actually this should not happen anymore, so if your ports are still
unconnected please drop me a mail.


### Python OpenGL

If you want to run the receive demo (the one that plots the subcarrier
constellations), please assert that you have python-opengl installed. The nongl
version of the plot does not work for me.


### Run volk_profile

volk_profile is part of GNU Radio. It benchmarks different SIMD implementations
on your PC and creates a configuration file that stores the fastest version of
every function. This can speed up the computation considerably and is required
in order to deal with the high rate of incoming samples.


### Calibrate your daughterboard

If you have a WBX, SBX, or CBX daughterboard you should calibrate it in order to
minimize IQ imbalance and TX DC offsets. See the [application
notes](http://files.ettus.com/manual/page_calibration.html).


# Checking your installation

As a first step I recommend to test the ```wifi_loopback.grc``` flow graph. This
flow graph does not need any hardware and allows you to ensure that the software
part is installed correctly. So open the flow graph and run it. If everything
works as intended you should see some decoded 'Hello World' packets in the
console.


## Troubleshooting

If GRC complains that it can't find some blocks (other than performance counters
and hierarchical blocks) like

    >>> Error: Block key "ieee802_11_ofdm_mac" not found in Platform - grc(GNU Radio Companion)
    >>> Error: Block key "foo_packet_pad" not found in Platform - grc(GNU Radio Companion)

Most likely you used a different ```CMAKE_INSTALL_PREFIX``` for the module than
for GNU Radio. Therefore, the blocks of the module ended up in a different
directory and GRC can't find them. You have to tell GRC where these blocks are
by creating/adding to your ```~/.gnuradio/config.conf``` something like

    [grc]
    global_blocks_path = /opt/local/share/gnuradio/grc/blocks
    local_blocks_path = /Users/basti/usr/share/gnuradio/grc/blocks

But with the directories that match your installation.


# Usage


## Simulation

The loopback flow graph should give you an idea of how simulations can be
conducted. To ease use, most blocks have debugging and logging capabilities that
can generate traces of the simulation. You can read about the logging feature
and how to use it on the [GNU Radio
Wiki](http://gnuradio.org/doc/doxygen/page_logger.html).


## Unidirectional communication

As first over the air test I recommend to try ```wifi_rx.grc``` and
```wifi_tx.grc```. Just open the flow graphs in GNU Radio companion and execute
them. If it does not work out of the box, try to play around with the gain. If
everything works as intended you should see similar output as in the
```wifi_loopback.grc``` example.


## Ad Hoc Network with WiFi card

- The transceiver is currently connected to a TAP device, i.e. is a virtual
  Ethernet interface. Therefore, we have no WiFi signaling like association
  requests and hence, the transceiver can not "join" an ad hoc network. You have
  to make some small changes to the kernel in order to convince you WiFi card to
  send to this hosts nevertheless.
- The transceiver can not respond to ACKs in time. This is kind of an
  architectural limitation of USRP + GNU Radio since Ethernet and computations
  on a normal CPU introduce some latency. You can set the number of ACK retries
  to zero and handle retransmits on higher layers (-> TCP).
- RTS/CTS is not working for the same reason. You can however just disable this
  mechanism.
- Currently, there is no CSMA/CA mechanism, but this can be implemented on the
  FPGA.


# Troubleshooting

- Please check compile and installation logs. They might contain interesting
  information.
- Did you calibrate your daughterboard?
- Did you run volk_profile?
- Did you try different gain settings?
- Did you close the case of the devices?
- Did you try real-time priority?
- Did you compile GNU Radio and gr-ieee802-11 in release mode?
- If you see warnings that ```blocks_ctrlport_monitor_performance``` is missing
  that means that you installed GNU Radio without control port or performance
  counters. These blocks allow you to monitor the performance of the transceiver
  while it is running, but are not required. You can just delete them from the
  flow graph.
- The message

    You must now use ifconfig to set its IP address. E.g.,
    $ sudo ifconfig tap0 192.168.200.1

is normal and is output by the TUN/Tap Block during startup. The configuration
of the TUN/TAP interface is handled by the scripts in the ```apps``` folder.
- Did you try to tune the RF frequency out of the band of interest (i.e. used
  the LO offset menu of the flow graphs)?
- If 'D's appear, it might be related to your Ethernet card. Assert that you
  made the sysconf changes recommended by Ettus. Did you try to connect you PC
  directly to the USRP without a switch in between?


# Further information

For further information please checkout our project page
[https://www.wime-project.net](https://www.wime-project.net)