docs

docs/source/index.rst

@@ -3,14 +3,21 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
-|project|: Verilog Implementation of 802.11 OFDM Decoder
-========================================================
+|project|: Synthesizable, Modular Verilog Implementation of 802.11 OFDM Decoder
+===============================================================================
+
+|project| is a open source Verilog implementation of 802.11 OFDM decoder.
+Highlights are:
+
+- Supports 802.11a/g (all bit rates) and 802.11n (20MHz BW, MCS 0 - 7)
+- Modular design, easy to extend
+- Fully synthesizable, tested on USRP N210
 
 .. toctree::
    :maxdepth: 2
    :caption: Contents:
 
-   sample
+   overview
    detection
    freq_offset
    sync_long
@@ -20,11 +27,3 @@
    setting
    verilog
 
-
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`

docs/source/overview.rst

@@ -0,0 +1,129 @@
+Overview
+========
+
+Once the RF signals are captured and down-converted to baseband, the decoding
+pipeline starts, including:
+
+1. Packet detection
+#. Center frequency offset correction
+#. FFT
+#. Channel gain estimation
+#. Demodulation
+#. Deinterleaving
+#. Convolutional decoding
+#. Descrambling
+
+
+This documentation walks through the decoding pipeline and explains how each
+step is implemented in |project|.
+
+Top Level Module
+----------------
+
+.. _fig_dot11:
+.. figure:: /images/dot11.png
+    :align: center
+    :scale: 50%
+
+    Dot11 Core Schematic Symbol
+
+The top level module of |project| is :file:`dot11.v`. :numref:`fig_dot11` shows
+its input/output pins. It takes I/Q samples as input, and output 802.11 packet
+data bytes and various PHY properties.
+
+.. table:: Dot11 Module Pinout
+    :align: center
+
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | Port Name     | Port Width | Direction | Description                                                                               |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | clock         | 1          | Input     | Rising edge clock                                                                         |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | enable        | 1          | Input     | Module enable (active high)                                                               |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | reset         | 1          | Input     | Module reset (active high)                                                                |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | set_stb       | 1          | Input     | Setting register strobe                                                                   |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | set_addr      | 8          | Input     | Setting register address                                                                  |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | set_data      | 32         | Input     | Setting register value                                                                    |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | sample_in     | 32         | Input     | High 16 bit I, low 16 bit Q                                                               |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | sample_in_stb | 1          | Input     | Sample input strobe                                                                       |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | pkt_begin     | 1          | Output    | Signal begin of a packet                                                                  |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | pkt_ht        | 1          | Output    | HT (802.11n) or legacy (802.11a/g) packet                                                 |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | pkt_rate      | 8          | Output    | For HT, the lower 7 bits is MCS. For legacy, the lower 4 bits is the rate bits in SIGNAL  |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | pkt_len       | 16         | Output    | Packet length in bytes                                                                    |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | byte_out_stb  | 1          | Output    | Byte out strobe                                                                           |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | byte_out      | 8          | Output    | Byte value                                                                                |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | fcs_out_stb   | 1          | Output    | FCS output strobe                                                                         |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+    | fcs_ok        | 1          | Output    | FCS correct (high) or wrong (low)                                                         |
+    +---------------+------------+-----------+-------------------------------------------------------------------------------------------+
+
+
+Project Structure
+-----------------
+
+In the :file:`verilog` sub-directory, you will find the Verilog implementations
+of various modules. The implementations were originally targeted for the Xilinx
+Spartan 3A-DSP 3400 FPGA inside the USRP N210 device, thus there are various
+dependences to Xilinx libraries and USRP code base. In particular:
+
+- :file:`verilog/Xilinx` contains the Xilinx specific libraries
+- :file:`verilog/coregen` contains generated IP cores from Xilinx ISE
+- :file:`verilog/usrp2` contains USRP specific modules
+
+However, the project is self-contained and is ready for simulation using `Icarus
+Verilog <http://iverilog.icarus.com/>`_ tool chain, including ``iverilog`` and
+``vvp``.
+
+The :file:`scripts` directory contains various Python scripts that:
+
+- Generate look up tables (:file:`gen_atan_lut.py`, :file:`gen_rot_lut.py`,
+  :file:`gen_deinter_lut.py`)
+- Convert binary I/Q file into text format so it can be read in Verilog using
+  ``readmemh``.
+- Consolidate sample files by removing *silent* signals (:file:`condense.py`).
+- Test each step of decoding process (:file:`test.py`)
+- 802.11 decoder in Python for cross validation (:file:`decode.py`)
+
+It also contains a modified copy of the `CommPy <https://github.com/veeresht/CommPy>`_ library.
+
+The :file:`test.py` script is for cross validation between the Python decoder
+and |project| decoder. It first uses the :file:`decode.py` script to decode the
+sample file and stores the expected output of each step. It then performs
+Verilog simulation using ``vvp`` and compare the Verilog output against the
+expected output step by step.
+
+The :file:`testing_inputs` directory contains various sample files collected in
+a conducted or over the air setup. These files covers all the bit rates (legacy
+and HT) supported in |project|.
+
+.. _sec_sample:
+Sample File
+-----------
+
+Throughout this documentation we will be using a sample file that contains the
+I/Q samples of a 802.11a packet at 24 Mbps (16-QAM). It'll be helpful to use a
+interactive iPython session and exercise various steps discussed in the
+document.
+
+Download the sample file from :download:`here </files/samples.dat>`, the data
+can be loaded as follows:
+
+.. code-block:: python
+
+    import scipy
+
+    wave = scipy.fromfile('samples.dat', dtype=scipy.int16)
+    samples = [complex(i, q) for i, q in zip(wave[::2], wave[1::2])]

docs/source/sample.rst

@@ -1,19 +1 @@
-.. _sec_sample:
 
-Sample File
-===========
-
-Throughout this documentation we will be using a sample file that contains the
-I/Q samples of a 802.11a packet at 24 Mbps (16-QAM). It'll be helpful to use a
-interactive iPython session and exercise various steps discussed in the
-document.
-
-Download the sample file from :download:`here </files/samples.dat>`, the data
-can be loaded as follows:
-
-.. code-block:: python
-
-    import scipy
-
-    wave = scipy.fromfile('samples.dat', dtype=scipy.int16)
-    samples = [complex(i, q) for i, q in zip(wave[::2], wave[1::2])]

docs/source/sig.rst

@@ -102,4 +102,33 @@ in |project|:
 - Tail bits: must all be 0.
 
 
+.. _fig_ht_sig_crc:
+.. figure:: /images/ht_sig_crc.png
+    :align: center
+    :scale: 80%
 
+    CRC Calculation of HT-SIG
+
+:numref:`fig_ht_sig_crc` shows the logic to calculate the CRC in HT-SIG. The
+shift registers :math:`C_0,\ldots,C_7` are initialized with all ones. For each
+data bit :math:`m_0,\ldots,m_{33}`, the shift register is updated as:
+
+.. math:: 
+
+    C^{i+1}_7 &= C^{i}_6\\
+    C^{i+1}_6 &= C^{i}_5\\
+    C^{i+1}_5 &= C^{i}_4\\
+    C^{i+1}_4 &= C^{i}_3\\
+    C^{i+1}_3 &= C^{i}_2\\
+    C^{i+1}_2 &= C^{i}_1 \oplus C^{i}_7 \oplus m_i\\
+    C^{i+1}_1 &= C^{i}_0 \oplus C^{i}_7 \oplus m_i\\
+    C^{i+1}_0 &= C^{i}_7 \oplus m_i\\
+
+The CRC is then :math:`\overline{C^{34}_7},\ldots,\overline{C^{34}_0}`. Note the
+bits are inverted.
+
+The next OFDM symbol after HT-SIG is HT short preamble, which is skipped in
+|project|. The following OFDM symbol contains HT long training sequence, which
+replaces the legacy channel gain inside :file:`equalizer.v` module. The rest
+decoding logic is similar to 802.11a/g, except the number of data sub-carriers
+is adjusted from 48 to 52.