Hi,

this an IEEE 802.11 a/g/p transceiver for GNU Radio v3.7. Over the air, I tested it with the Ettus USRP N210 with XCVR2450 and CBX daughterboards. For interoperability tests I use mainly an Atheros (ath5k) WiFi card. The code can also be used for packet error rate simulations.

# Installation


## Dependencies

Please note that ```apt-get``` is the package manager of Debian/Ubuntu based systems, while ```port``` is one package manager for OSX. So use either (not both) according to your needs.


### log4cpp

I use the new [logging feature](http://gnuradio.org/doc/doxygen/page_logger.html) of GNU Radio which relies on log4cpp. This should be an optional dependency some day, but currently it is required. You can install it with

    sudo apt-get install liblog4cpp5-dev
    sudo port install log4cpp


### GNU Radio v3.7

You need at least version 3.7.3.

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

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


### IT++

I use the Viterbi decoder of IT++.

    sudo apt-get install libitpp-dev
    sudo port install itpp


### 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


### 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/uhd_docs/manual/html/calibration.html).



# Checking you 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.


## RX frames from a WiFi card

TBD


## TX frames to a WiFi card

TBD


## Transceiver (SDR <-> SDR)

TBD


## 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

- 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?


# Asking for help

In order to help you it is crucial that you provide enough information about what is going wrong and what you are actually trying to do. So if you write me please include at least the following

- OS (Ubuntu, OSX...)
- hardware (SDR and daughterboard)
- GNU Radio version
- What are you trying to do
- What is you setup, i.e. are you transmitting between SDRs or with WiFi cards.
- Bandwidth and frequency
- What did you already do to debug?
- Where exactly does it break, i.e. is frame detection working? Is the signal field decoded correctly?).


# Further information

For further information please checkout our project page
[http://www.ccs-labs.org/projects/wime/](http://www.ccs-labs.org/projects/wime/)
