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......@@ -13,7 +13,7 @@ found in the `gr-elen90089` git repo.
3. [Packet PHY Tx](#packet-phy-tx)
- [Header Format CDC](#header-format-cdc)
- [CDC Symbol Mapper](#cdc-symbol-mapper)
4. [Packet PHY Rx](#packet-phy_rx)
4. [Packet PHY Rx](#packet-phy-rx)
- [CDC TS Correlator](#cdc-ts-correlator)
- [CDC Costas Loop](#cdc-costas-loop)
- [CDC Constellation Decoder](#cdc-constellation-decoder)
......@@ -41,13 +41,13 @@ demonstrate how to create and configure the link.
The CDC link is composed of three main functional blocks that implement a single
carrier pulse modulation PHY and skeleton MAC layer.
- [CDC Packet MAC Tx](packet-mac-tx)
- [CDC Packet PHY Tx](packet-phy-tx)
- [CDC Packet PHY Rx](packet-phy-rx)
- [CDC Packet MAC Tx](#packet-mac-tx)
- [CDC Packet PHY Tx](#packet-phy-tx)
- [CDC Packet PHY Rx](#packet-phy-rx)
The Tx/Rx PHY blocks are hierarchical blocks composed of standard GNU Radio C++
signal processing blocks along with some custom C++ blocks in the `gr-elen90089`
OOT. The custom blocks are modified versions of existing GNU Radio block.
OOT. The custom blocks are modified versions of existing GNU Radio blocks.
- [Header Format CDC](#header-format-cdc)
- [CDC Symbol Mapper](#cdc-symbol-mapper)
......@@ -57,11 +57,12 @@ OOT. The custom blocks are modified versions of existing GNU Radio block.
> **Note**: This page provides a basic overview of individual blocks in the CDC
> link. Additional information can be found in documentation of the
> `gr-elen90089` OOT. To view this documentation, open a web browser on the
> CDC Ubuntu VM and navigate to the following location:
> `gr-elen90089` OOT. To view this documentation after building and installing
> the OOT, open a web browser on the CDC Ubuntu VM and navigate to the
> following location:
> [file:///usr/local/share/doc/gr-elen90089/html/index.html]()
## CDC Packet MAC Tx
## Packet MAC Tx
The *Packet MAC Tx* is implemented as a python block found at the following
location:
......@@ -89,12 +90,12 @@ These metadata entries will be converted to stream tags within *Packet PHY Tx*.
The `bps` parameter is then used by downstream blocks to configure the payload
modulation constellation (BPSK, QPSK, etc.). The `freq` and `gain` parameters
will prompt the bladeRF to update its transmit frequency and gain just prior to
transmitting this packet. See bladeRF's
transmitting this packet. See `gr-bladeRF-cdc`'s
[Stream Tag Interface](stream-tag-interface)
for more information on how this process works.
The *Packet MAC Tx* is a very basic skeleton of a MAC layer which you can
update for your particular application.
update for your DSA application.
## Packet PHY Tx
......@@ -113,9 +114,9 @@ The block has the following configuration parameters.
The hierarchical block is composed of the following subblock arrangement.
```
pdu > [Async CRC32] > [Protocol Formatter] > [FEC Async Encoder]
pdu in > [Async CRC32] > [Protocol Formatter] > [FEC Async Encoder]
> [CDC Symbol Mapper] > [Burst Shaper] > [Polyphase Arbitrary Resampler] > iq
> [CDC Symbol Mapper] > [Burst Shaper] > [Polyphase Arbitrary Resampler] > iq out
```
Functionality for these subblock is as follows.
......@@ -135,7 +136,7 @@ independent constellations for the header and payload. See
[CDC Symbol Mapper](#cdc-symbol-mapper) below.
**Burst Shaper**: Prepends phasing symbols to the beginning of the transmit
burst along with a amplitude ramp up and ramp down. See
burst along with an amplitude ramp up and ramp down. See
[Burst Shaper](https://wiki.gnuradio.org/index.php/Burst_Shaper).
**Polyphase Arbitrary Resampler**: upsamples symbol stream and applies RRC
......@@ -158,13 +159,14 @@ following fields.
transmission burst.
- counter (16 bits): Packet sequence number incremented for each newly
transmitted packet
- pkt_len (16 bits): Payload length in number of bytes. Used along with bps by
- pktlen (16 bits): Payload length in number of bytes. Used along with bps by
receiver to determine how many payload symbols are present in a burst.
- bps (8 bits): bits-per-symbol of payload constellation
- crc (8 bits): cyclic redundancy check over header fields (counter, pkt_len,
- bps (8 bits): Bits-per-symbol of payload constellation
- crc (8 bits): Cyclic redundancy check over header fields (counter, pktlen,
bps) used by the receiver to check integrity of decoded header
```
# Mapping of fields in CDC Header Format
| 0 - 7 | 8 - 15 | 16 - 23 | 24 - 31 |
| access code |
| access code |
......@@ -192,9 +194,9 @@ to be changed on a per packet basis.
## Packet PHY Rx
The *Packet PHY Rx* block is a GRC hierarchical block that implements packet-
based pulse demodulation. The GRC file for this block can be found at the
following location.
The *Packet PHY Rx* block is a GRC hierarchical block that implements
packet-based pulse demodulation. The GRC file for this block can be found
at the following location.
- `./examples/packet_phy_rx.grc`
......@@ -207,12 +209,12 @@ The block has the following configuration parameters.
The hierarchical block is composed of the following subblock arrangement.
```
[CDC TS Correlator] > [Mult Tag Value] > [Symbol Sync] > [Header/Payload Demux]
iq in > [CDC TS Correlator] > [Mult Tag Value] > [Symbol Sync] > [Header/Payload Demux]
hdr: > [CDC Costas Loop] > [Constellation Decoder] > [Protocol Parser]
hdr > [CDC Costas Loop] > [Constellation Decoder] > [Protocol Parser]
pld: > [CDC Costas Loop] > [CDC Constellation Decoder] > [FEC Async Decoder]
> [Async CRC32] > phy_sdu
pld > [CDC Costas Loop] > [CDC Constellation Decoder] > [FEC Async Decoder]
> [Async CRC32] > phy_sdu out
```
The first common portion of the receive chain includes the following.
......@@ -244,7 +246,8 @@ approach removes any phase ambiguity at the start of each packet burst. See
[CDC Costas Loop](#cdc-costas-loop) below.
**Constellation Decoder**: Performs hard decision slicing of the header symbols
to the header constellation and then demaps symbols to bits.
to the header constellation and then demaps symbols to bits. See
[Constellation Decoder](https://wiki.gnuradio.org/index.php?title=Constellation_Decoder).
**Protocol Parser**: Searches for access code/training sequence within received
header bits and parses header fields once found. *Threshold* determines the
......@@ -258,13 +261,13 @@ used to determine the phase error of each symbol is updated by `bps` tags found
in the symbol stream. See [CDC Costas Loop](#cdc-costas-loop) below.
**CDC Constellation Decoder**: Slices received payload symbols to constellation
points where the constellation used is updated by `'bps` tags found in the
points where the constellation used is updated by `bps` tags found in the
received symbol stream. This is needed to support changing payload modulation
on a packet-by-packet basis.
**FEC Async Decoder**: Dummy FEC decoding of received payload bits. This block
is currently present to covert the output format of the *CDC Constellation
Decoder* block from soft bits (values between +/-1) to packed bytes. With
is currently present to convert the output format of the *CDC Constellation
Decoder* block from soft bits (real valued) to packed bytes. With
appropriate modifications to the transmitter it could also be used to implement
FEC for the payload data.
......@@ -299,7 +302,7 @@ This block has the following configuration parameters.
| ------------ | ------------------------------------------------------------- |
| symbols | Samples of the modulate training sequence. |
| threshold | Normalized correlation value required to declare training sequence found.<br>Values typicially in range [0.0, 1.0] |
| mark delay | Offset between peak correlation sample and where output stream is tagged with various parameters. Used to account for delays introduced by the matched filtering performed in the *Symbol Sync* block. |
| mark delay | Offset between peak correlation sample and where output stream is tagged with various parameter estimates. Used to account for delays introduced by the matched filtering performed in the *Symbol Sync* block. |
Once found, this block adds the following tags to the output stream.
......@@ -307,28 +310,29 @@ Once found, this block adds the following tags to the output stream.
| ------------ | ------------------------------------------------------------- |
| `corr_start` | Marks starting sample of access code in sample stream. |
| `corr_est` | Marks starting sample of access code offset by *mark delay*. Value of tag is the normalized correlation result. |
| `chan_est` | Inverse LLS channel estimate from training sequence. |
| `phase_est` | Hardcoded to zero. This tag is used to reset the phase accumulation of the downstream Costas Loop block. Initial carrier phase offset is included in `chan_est`. |
| `time_est` | Estimate of fractional symbol timing offset based on correlation result. This is used to initialize *Symbol Sync's* interpolation at the beginning of each packet. |
| `chan_est` | Value of tag is *inverse* LLS channel estimate from training sequence and is used in single-tap equalisation. |
| `phase_est` | Value of tag is hardcoded to zero. This tag is used to reset the phase accumulation of the downstream Costas Loop block. Initial carrier phase offset is incorporated in the `chan_est` parameter estimate instead. |
| `time_est` | Value of tag is estimate of fractional symbol timing offset based on correlation result. This is used to initialize *Symbol Sync's* interpolation at the beginning of each packet. |
The channel estimate is a linear least squares (LLS) estimate using the detected
training sequence.
The channel estimate is a linear least squares (LLS) estimate based on the received
training sequence samples.
```math
\hat{h}_\text{LLS} = \frac{t^*}{tt^*} y
```
The value of the $\hat{h}_\text{LLS}$ is inverted in the `chan_est` tag to allow
for inversting the channel at the downstream *Multiply by Tag Value* block.
The value of $\hat{h}_\text{LLS}$ is inverted in the `chan_est` tag to allow
for inverting the channel at the downstream *Multiply by Tag Value* block.
The fractional symbol timing offset is calculated based on the peak correlation
value and its two neighbouring samples.
The fractional symbol timing offset of `time_est` is calculated based on the
peak correlation value and its two neighbouring samples.
```math
\eta = \frac{R[n-1] + 2*R[n] + 3*R[n+1]}{R[n-1] + R[n] + R[n+1]} - 2
\epsilon = \frac{R[n-1] + 2*R[n] + 3*R[n+1]}{R[n-1] + R[n] + R[n+1]} - 2
```
See the block's `work()` method for further algorithmic details.
See the block's `work()` method for further algorithmic implementation
details.
### CDC Costas Loop
......@@ -345,6 +349,9 @@ update the constellation used for determining the current phase error. This is
only used for payload symbols and allows the payload constellation to be
changed on a packet-by-packet basis.
See [Costas Loop](https://wiki.gnuradio.org/index.php?title=Costas_Loop) for
details of the GNU Radio implementation.
### CDC Constellation Decoder
<div align="center">
......@@ -356,5 +363,13 @@ changed on a packet-by-packet basis.
The *CDC Constellation Decoder* slices received symbols to constellation points
and then maps these points to their corresponding bit values. These bit values
can either be soft bits (real valued) or hard bits (0 or 1). The key
functionality of this block is that it can adapt the constellation used in
functionality of this block is that it can adapt the constellation used for
slicing based on `bps` tags encountered in the received symbols stream.
This block has the following configuration parameters.
| Parameter | Description |
| --------------- | ---------------------------------------- |
| Bits per Symb | Sets default symbol constellation used for slicing if no `bps` tag is encountered. |
| Soft Decisions | Generate soft (real valued) or hard (0 or 1) bit decisions. |
| Length Tag Name | Stream tag indicating start and length a packet's payload symbols. This block will update all tag offsets appropriately based on the bits per symbol of the constellation. |
\ No newline at end of file