composites/ertreceiver: add ERTReceiver

radio/composites/ertreceiver.lua

@@ -0,0 +1,88 @@
+---
+-- Demodulate and decode ERT frames from an OOK modulated complex-valued
+-- signal. IDM, SCM, SCM+ protocols are supported.
+--
+-- This receiver is based on rtlamr's excellent description:
+-- <https://github.com/bemasher/rtlamr/wiki/Signal-Processing>
+--
+-- @category Receivers
+-- @block ERTReceiver
+-- @tparam[opt={'idm','scm','scm+'}] array protocols Protocols to decode,
+--                                                   choice of 'idm', 'scm',
+--                                                   'scm+'. Default is all
+--                                                   three.
+-- @tparam[opt={}] table options Additional options, specifying:
+--                               * `decimation` Downsampling factor (int, default 6)
+--
+-- @signature in:ComplexFloat32 > out1:IDMFrameType, out2:SCMFrameType, ...
+--
+-- @usage
+-- local receiver = radio.ERTReceiver({'scm', 'scm+'})
+-- local scm_sink = radio.PrintSink()
+-- local scm_plus_sink = radio.PrintSink()
+-- top:connect(src, receiver)
+-- top:connect(receiver, 'out1', scm_sink, 'in')
+-- top:connect(receiver, 'out2', scm_plus_sink, 'in')
+
+local block = require('radio.core.block')
+local types = require('radio.types')
+local blocks = require('radio.blocks')
+
+local ERTReceiver = block.factory("ERTReceiver", blocks.CompositeBlock)
+
+function ERTReceiver:instantiate(protocols, options)
+    blocks.CompositeBlock.instantiate(self)
+
+    options = options or {}
+
+    local symbol_rate = 32768
+    local decimation = options.decimation or 6
+
+    local magnitude = blocks.ComplexMagnitudeBlock()
+    local data_filter = blocks.LowpassFilterBlock(128, symbol_rate * 4)
+    local downsampler = blocks.DownsamplerBlock(decimation)
+    local matched_filter = blocks.ManchesterMatchedFilterBlock(symbol_rate)
+
+    self:connect(magnitude, data_filter, downsampler, matched_filter)
+
+    local framer_blocks = {}
+    local outputs = {}
+
+    for i, protocol in ipairs(protocols) do
+        local sampler, slicer, framer, frame_type
+
+        if protocol == 'idm' then
+            sampler = blocks.PreambleSamplerBlock(symbol_rate / 2, blocks.IDMFramerBlock.IDM_PREAMBLE, blocks.IDMFramerBlock.IDM_FRAME_LEN)
+            slicer = blocks.SlicerBlock()
+            framer = blocks.IDMFramerBlock()
+            frame_type = blocks.IDMFramerBlock.IDMFrameType
+        elseif protocol == 'scm' then
+            sampler = blocks.PreambleSamplerBlock(symbol_rate / 2, blocks.SCMFramerBlock.SCM_PREAMBLE, blocks.SCMFramerBlock.SCM_FRAME_LEN)
+            slicer = blocks.SlicerBlock()
+            framer = blocks.SCMFramerBlock()
+            frame_type = blocks.SCMFramerBlock.SCMFrameType
+        elseif protocol == 'scm+' then
+            sampler = blocks.PreambleSamplerBlock(symbol_rate / 2, blocks.SCMPlusFramerBlock.SCM_PLUS_PREAMBLE, blocks.SCMPlusFramerBlock.SCM_PLUS_FRAME_LEN)
+            slicer = blocks.SlicerBlock()
+            framer = blocks.SCMPlusFramerBlock()
+            frame_type = blocks.SCMPlusFramerBlock.SCMPlusFrameType
+        else
+            error("Unsupported protocol \"" .. protocol .. "\"")
+        end
+
+        self:connect(matched_filter, sampler, slicer, framer)
+        framer_blocks[#framer_blocks + 1] = framer
+        outputs[#outputs + 1] = block.Output("out" .. i, frame_type)
+    end
+
+    self:add_type_signature({block.Input("in", types.ComplexFloat32)}, outputs)
+
+    self:connect(self, "in", magnitude, "in")
+
+    -- Connect last block of each protocol decoding chain to an aliased output
+    for i, _ in ipairs(outputs) do
+        self:connect(self, "out" .. i, framer_blocks[i], "out")
+    end
+end
+
+return ERTReceiver

radio/composites/init.lua

@@ -23,4 +23,5 @@ return {
     AX25Receiver = require('radio.composites.ax25receiver'),
     POCSAGReceiver = require('radio.composites.pocsagreceiver'),
     BPSK31Receiver = require('radio.composites.bpsk31receiver'),
+    ERTReceiver = require('radio.composites.ertreceiver'),
 }