Module: PWN::SDR::Decoder::DSP

Defined in:
lib/pwn/sdr/decoder/dsp.rb

Overview

DSP primitives shared by every PWN::SDR::Decoder::* module.

Default path is pure Ruby operating on Array samples normalised to -1.0..1.0 (48 kHz s16le mono from GQRX UDP — no sox / multimon-ng / minimodem dependency).

When the matching system library is present the hot paths transparently accelerate via PWN::FFI::Volk,Liquid,FFTW:

unpack_s16le  → PWN::FFI::Volk   (SIMD s16→f32 convert)
unpack_cs16le → pure / Volk path (interleaved I/Q s16 → f32)
unpack_cu8    → pure path (RTL-SDR u8 I/Q → f32)
resample      → PWN::FFI::Liquid (msresamp multi-stage)
dc_block      → PWN::FFI::Liquid (firfilt DC blocker)
rms_dbfs      → PWN::FFI::Volk   (accumulate of squares)
mag_sq / fm_demod_iq → true-air I/Q paths for Base.run_iq

Each accelerated method falls back to the pure-Ruby body when the backend is missing or raises, so decoders never require a native library at install time. Force pure Ruby for testing with PWN::SDR::Decoder::DSP.native = false

Constant Summary collapse

TWO_PI = 
Math::PI * 2
BAUDOT_LTRS =

ITA2 / Baudot 5-bit → ASCII (LTRS + FIGS shift tables). Index = code.

[
  "\0", 'E', "\n", 'A', ' ', 'S', 'I', 'U',
  "\r", 'D', 'R', 'J', 'N', 'F', 'C', 'K',
  'T',  'Z', 'L',  'W', 'H', 'Y', 'P', 'Q',
  'O',  'B', 'G',  nil, 'M', 'X', 'V', nil
].freeze
BAUDOT_FIGS = 
[
  "\0", '3', "\n", '-', ' ', "'", '8', '7',
  "\r", '$', '4',  "\a", ',', '!', ':', '(',
  '5',  '+', ')',  '2', '#', '6', '0', '1',
  '9',  '?', '&',  nil, '.', '/', ';', nil
].freeze
MORSE_TABLE =

International Morse Code (dit='.', dah='-') → ASCII.

{
  '.-' => 'A', '-...' => 'B', '-.-.' => 'C', '-..' => 'D', '.' => 'E',
  '..-.' => 'F', '--.' => 'G', '....' => 'H', '..' => 'I', '.---' => 'J',
  '-.-' => 'K', '.-..' => 'L', '--' => 'M', '-.' => 'N', '---' => 'O',
  '.--.' => 'P', '--.-' => 'Q', '.-.' => 'R', '...' => 'S', '-' => 'T',
  '..-' => 'U', '...-' => 'V', '.--' => 'W', '-..-' => 'X', '-.--' => 'Y',
  '--..' => 'Z', '-----' => '0', '.----' => '1', '..---' => '2',
  '...--' => '3', '....-' => '4', '.....' => '5', '-....' => '6',
  '--...' => '7', '---..' => '8', '----.' => '9', '.-.-.-' => '.',
  '--..--' => ',', '..--..' => '?', '-..-.' => '/', '-....-' => '-',
  '-.--.' => '(', '-.--.-' => ')', '.-...' => '&', '---...' => ':',
  '-...-' => '=', '.-.-.' => '+', '.--.-.' => '@'
}.freeze

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.native ⇒ Object

Returns the value of attribute native.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 31

def native
  @native
end

Class Method Details

.authors ⇒ Object

Author(s)

0day Inc. support@0dayinc.com



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 572

public_class_method def self.authors
  "AUTHOR(S):\n  0day Inc. <support@0dayinc.com>\n"
end

.baudot_decode(opts = {}) ⇒ Object

Supported Method Parameters

txt = PWN::SDR::Decoder::DSP.baudot_decode(bits: Array<0|1>) 5-bit ITA2 with LTRS(31)/FIGS(27) shift, LSB-first per character.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 380

public_class_method def self.baudot_decode(opts = {})
  bits = opts[:bits]
  figs = false
  out  = +''
  bits.each_slice(5) do |ch|
    next if ch.length < 5

    code = ch.each_with_index.sum { |b, i| b << i }
    case code
    when 31 then figs = false
    when 27 then figs = true
    else
      tbl = figs ? BAUDOT_FIGS : BAUDOT_LTRS
      c = tbl[code]
      out << c if c
    end
  end
  out
end

.bch_31_21_syndrome(opts = {}) ⇒ Object

BCH(31,21) syndrome — generator poly 0b11101101001 (0x769). Used by POCSAG and FLEX codewords (bits 31..1 are BCH, bit 0 parity).

Supported Method Parameters

syn = PWN::SDR::Decoder::DSP.bch_31_21_syndrome(word: Integer)



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 366

public_class_method def self.bch_31_21_syndrome(opts = {})
  word = (opts[:word].to_i >> 1) & 0x7FFFFFFF
  gen  = 0x769
  reg  = word
  30.downto(10) do |i|
    reg ^= (gen << (i - 10)) if (reg >> i).odd?
  end
  reg & 0x3FF
end

.bits_to_int(opts = {}) ⇒ Object

Supported Method Parameters

int = PWN::SDR::Decoder::DSP.bits_to_int(bits: [1,0,1,...])



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 343

public_class_method def self.bits_to_int(opts = {})
  bits = opts[:bits]
  v = 0
  bits.each { |b| v = (v << 1) | (b & 1) }
  v
end

.correlate(opts = {}) ⇒ Object

Correlate a real template against magnitude-squared energy for PPM / OOK preambles. Returns best lag + score.

Supported Method Parameters

hit = PWN::SDR::Decoder::DSP.correlate( samples: 'required - Array', template: 'required - Array (same units)' ) → { lag:, score: } or nil



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 544

public_class_method def self.correlate(opts = {})
  samples  = opts[:samples]
  template = opts[:template]
  tlen = template.length
  return nil if tlen.zero? || samples.length < tlen

  best_lag = 0
  best_sc  = -Float::INFINITY
  upto = samples.length - tlen
  i = 0
  while i <= upto
    sc = 0.0
    j = 0
    while j < tlen
      sc += samples[i + j] * template[j]
      j += 1
    end
    if sc > best_sc
      best_sc = sc
      best_lag = i
    end
    i += 1
  end
  { lag: best_lag, score: best_sc }
end

.dc_block(opts = {}) ⇒ Object

Supported Method Parameters

y = PWN::SDR::Decoder::DSP.dc_block( samples: 'required - Array', alpha: 'optional - pole (default 0.995)' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 180

public_class_method def self.dc_block(opts = {})
  samples = opts[:samples]
  # Prefer liquid FIR DC blocker when caller asks for it (m:) or when
  # alpha is the default AND liquid is available — otherwise keep the
  # classic single-pole IIR so call sites that pass a custom alpha
  # stay bit-identical to pure Ruby.
  if native && opts[:m] && PWN::FFI.available?(mod: :Liquid)
    begin
      return PWN::FFI::Liquid.dc_block(
        samples: samples,
        m: opts[:m],
        as_db: opts[:as_db] || 60.0
      )
    rescue StandardError
      # fall through
    end
  end

  alpha  = (opts[:alpha] || 0.995).to_f
  y_prev = 0.0
  x_prev = 0.0
  samples.map do |x|
    y = x - x_prev + (alpha * y_prev)
    x_prev = x
    y_prev = y
    y
  end
end

.envelope(opts = {}) ⇒ Object

Supported Method Parameters

env = PWN::SDR::Decoder::DSP.envelope( samples: 'required - Array', window: 'optional - moving-average window in samples (default 32)' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 157

public_class_method def self.envelope(opts = {})
  samples = opts[:samples]
  window  = (opts[:window] || 32).to_i
  window  = 1 if window < 1
  acc = 0.0
  buf = Array.new(window, 0.0)
  out = Array.new(samples.length)
  samples.each_with_index do |x, i|
    v = x.abs
    slot = i % window
    acc += v - buf[slot]
    buf[slot] = v
    out[i] = acc / window
  end
  out
end

.envelope_signed(opts = {}) ⇒ Object

Signed moving average (like envelope but keeps sign).

Supported Method Parameters

y = PWN::SDR::Decoder::DSP.envelope_signed(samples:, window:)



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 252

public_class_method def self.envelope_signed(opts = {})
  samples = opts[:samples]
  window  = (opts[:window] || 8).to_i
  window  = 1 if window < 1
  acc = 0.0
  buf = Array.new(window, 0.0)
  out = Array.new(samples.length)
  samples.each_with_index do |x, i|
    slot = i % window
    acc += x - buf[slot]
    buf[slot] = x
    out[i] = acc / window
  end
  out
end

.even_parity_ok?(opts = {}) ⇒ Boolean

Supported Method Parameters

ok = PWN::SDR::Decoder::DSP.even_parity_ok?(word: Integer, width: 32)

Returns:

  • (Boolean) 


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# File 'lib/pwn/sdr/decoder/dsp.rb', line 353

public_class_method def self.even_parity_ok?(opts = {})
  word  = opts[:word].to_i
  width = (opts[:width] || 32).to_i
  p = 0
  width.times { |i| p ^= (word >> i) & 1 }
  p.zero?
end

.find_sync(opts = {}) ⇒ Object

Supported Method Parameters

idx = PWN::SDR::Decoder::DSP.find_sync( bits: 'required - Array<0|1>', pattern: 'required - Array<0|1> or Integer (MSB-first)', width: 'optional - bit-width when pattern is Integer', max_err: 'optional - allowed bit errors (default 0)', from: 'optional - start index (default 0)' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 309

public_class_method def self.find_sync(opts = {})
  bits    = opts[:bits]
  pattern = opts[:pattern]
  width   = opts[:width]
  max_err = (opts[:max_err] || 0).to_i
  from    = (opts[:from] || 0).to_i
  pat = if pattern.is_a?(Integer)
          w = width || pattern.bit_length
          Array.new(w) { |i| (pattern >> (w - 1 - i)) & 1 }
        else
          pattern
        end
  plen = pat.length
  upto = bits.length - plen
  i = from
  while i <= upto
    err = 0
    j = 0
    while j < plen
      err += 1 if bits[i + j] != pat[j]
      break if err > max_err

      j += 1
    end
    return i if err <= max_err

    i += 1
  end
  nil
end

.fm_demod_iq(opts = {}) ⇒ Object

Supported Method Parameters

audio = PWN::SDR::Decoder::DSP.fm_demod_iq( iq: 'required - interleaved Array [I0,Q0,…]', kf: 'optional - modulation index scale (default 1.0)' ) Polar-discriminant FM demod. Prefers PWN::FFI::Liquid.freq_demod when available; otherwise atan2 difference of consecutive samples.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 488

public_class_method def self.fm_demod_iq(opts = {})
  iq = opts[:iq]
  kf = (opts[:kf] || 1.0).to_f
  n  = iq.length / 2
  return [] if n < 2

  if native && PWN::FFI.available?(mod: :Liquid)
    begin
      return PWN::FFI::Liquid.freq_demod(iq: iq, kf: kf)
    rescue StandardError
      # fall through
    end
  end

  out = Array.new(n - 1)
  prev_re = iq[0].to_f
  prev_im = iq[1].to_f
  i = 1
  while i < n
    re = iq[i * 2].to_f
    im = iq[(i * 2) + 1].to_f
    # arg(z * conj(z_prev)) = atan2 cross/dot
    dot   = (re * prev_re) + (im * prev_im)
    cross = (im * prev_re) - (re * prev_im)
    out[i - 1] = Math.atan2(cross, dot) * kf
    prev_re = re
    prev_im = im
    i += 1
  end
  out
end

.fsk_slice(opts = {}) ⇒ Object

Supported Method Parameters

bits = PWN::SDR::Decoder::DSP.fsk_slice( samples: 'required - Array', rate: 'required - sample rate (Hz)', baud: 'required - symbol rate', mark_hz: 'required - mark tone (bit=1)', space_hz:'required - space tone (bit=0)' ) Non-coherent 2-FSK: per-symbol Goertzel on mark/space, pick the winner.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 278

public_class_method def self.fsk_slice(opts = {})
  samples  = opts[:samples]
  rate     = opts[:rate].to_f
  baud     = opts[:baud].to_f
  mark_hz  = opts[:mark_hz].to_f
  space_hz = opts[:space_hz].to_f
  spb      = rate / baud
  nsym     = (samples.length / spb).floor
  bits     = Array.new(nsym)
  i = 0
  while i < nsym
    a = (i * spb).floor
    b = ((i + 1) * spb).floor
    win = samples[a...b]
    pm = goertzel(samples: win, rate: rate, freq: mark_hz)
    ps = goertzel(samples: win, rate: rate, freq: space_hz)
    bits[i] = pm >= ps ? 1 : 0
    i += 1
  end
  bits
end

.goertzel(opts = {}) ⇒ Object

Supported Method Parameters

power = PWN::SDR::Decoder::DSP.goertzel( samples: 'required - Array', rate: 'required - sample rate (Hz)', freq: 'required - target tone frequency (Hz)' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 131

public_class_method def self.goertzel(opts = {})
  samples = opts[:samples]
  rate    = opts[:rate].to_f
  freq    = opts[:freq].to_f
  n       = samples.length
  return 0.0 if n.zero?

  k     = (0.5 + ((n * freq) / rate)).floor
  w     = (TWO_PI * k) / n
  coeff = 2.0 * Math.cos(w)
  s1 = 0.0
  s2 = 0.0
  samples.each do |x|
    s0 = x + (coeff * s1) - s2
    s2 = s1
    s1 = s0
  end
  ((s1 * s1) + (s2 * s2) - (coeff * s1 * s2)) / n
end

.help ⇒ Object

Display Usage for this Module



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 578

public_class_method def self.help
  puts "USAGE (pure-Ruby DSP + optional PWN::FFI acceleration):
    #{self}.native = true|false   # toggle VOLK/liquid/FFTW backends
    #{self}.unpack_s16le(data: raw_bytes)              # → Volk
    #{self}.unpack_cs16le(data: raw_cs16)              # I/Q s16 → f32
    #{self}.unpack_cu8(data: raw_u8)                  # RTL-SDR u8 I/Q
    #{self}.mag_sq(iq:) / #{self}.iq_rms_dbfs(iq:)
    #{self}.fm_demod_iq(iq:, kf: 1.0)                 # → Liquid
    #{self}.correlate(samples:, template:)
    #{self}.resample(samples:, src_rate:, dst_rate:)   # → Liquid
    #{self}.goertzel(samples:, rate:, freq:)
    #{self}.envelope(samples:, window: 32)
    #{self}.envelope_signed(samples:, window: 8)
    #{self}.dc_block(samples:, alpha: 0.995, m: nil)   # → Liquid if m:
    #{self}.nrz_slice(samples:, rate:, baud:, invert: false)
    #{self}.fsk_slice(samples:, rate:, baud:, mark_hz:, space_hz:)
    #{self}.find_sync(bits:, pattern:, width:, max_err: 0, from: 0)
    #{self}.bits_to_int(bits:)
    #{self}.even_parity_ok?(word:, width: 32)
    #{self}.bch_31_21_syndrome(word:)
    #{self}.baudot_decode(bits:)
    #{self}.rms_dbfs(samples:)                         # → Volk (≥64)

    Constants: MORSE_TABLE, BAUDOT_LTRS, BAUDOT_FIGS
    Backends:  PWN::FFI.backends  # { Volk: true, Liquid: true, AdalmPluto: true, … }

    #{self}.authors
  "
end

.iq_rms_dbfs(opts = {}) ⇒ Object

Supported Method Parameters

power = PWN::SDR::Decoder::DSP.iq_rms_dbfs( iq: 'required - interleaved Array [I0,Q0,…]' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 525

public_class_method def self.iq_rms_dbfs(opts = {})
  m2 = mag_sq(iq: opts[:iq])
  return -120.0 if m2.empty?

  ms = m2.sum / m2.length
  return -120.0 if ms <= 0

  10.0 * Math.log10(ms)
end

.mag_sq(opts = {}) ⇒ Object

Supported Method Parameters

m2 = PWN::SDR::Decoder::DSP.mag_sq( iq: 'required - interleaved Array [I0,Q0,I1,Q1,…]' ) Returns Array of I²+Q² per sample (length = iq.length/2).



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 466

public_class_method def self.mag_sq(opts = {})
  iq = opts[:iq]
  n  = iq.length / 2
  out = Array.new(n)
  i = 0
  while i < n
    re = iq[i * 2].to_f
    im = iq[(i * 2) + 1].to_f
    out[i] = (re * re) + (im * im)
    i += 1
  end
  out
end

.nrz_slice(opts = {}) ⇒ Object

Supported Method Parameters

bits = PWN::SDR::Decoder::DSP.nrz_slice( samples: 'required - Array (post-FM-discriminator baseband)', rate: 'required - sample rate (Hz)', baud: 'required - symbol rate', invert: 'optional - flip bit polarity (default false)' ) Simple mid-bit sampler with zero-crossing resync. Returns Array<0|1>.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 218

public_class_method def self.nrz_slice(opts = {})
  samples = opts[:samples]
  rate    = opts[:rate].to_f
  baud    = opts[:baud].to_f
  invert  = opts[:invert]
  spb     = rate / baud
  return [] if spb < 2.0 || samples.empty?

  # DC-block then low-pass via short moving average (~1/4 symbol).
  lp_win = [(spb / 4.0).round, 1].max
  filt   = envelope_signed(samples: dc_block(samples: samples), window: lp_win)

  bits  = []
  phase = spb / 2.0
  prev  = filt.first.to_f
  filt.each do |v|
    # zero-crossing → resync to mid-symbol
    phase = spb / 2.0 if (prev.negative? && v >= 0) || (prev.positive? && v.negative?)
    phase -= 1.0
    if phase <= 0
      b = v.negative? ? 0 : 1
      b ^= 1 if invert
      bits << b
      phase += spb
    end
    prev = v
  end
  bits
end

.resample(opts = {}) ⇒ Object

Supported Method Parameters

out = PWN::SDR::Decoder::DSP.resample( samples: 'required - Array', src_rate: 'required - input sample rate (Hz)', dst_rate: 'required - output sample rate (Hz)' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 90

public_class_method def self.resample(opts = {})
  samples  = opts[:samples]
  src_rate = opts[:src_rate].to_f
  dst_rate = opts[:dst_rate].to_f
  return samples.dup if (src_rate - dst_rate).abs < 1e-6

  if native && PWN::FFI.available?(mod: :Liquid)
    begin
      # liquid rate = output/input
      return PWN::FFI::Liquid.resample(
        samples: samples,
        rate: dst_rate / src_rate
      )
    rescue StandardError
      # fall through to pure Ruby
    end
  end

  ratio = src_rate / dst_rate
  out_len = (samples.length / ratio).floor
  out = Array.new(out_len)
  i = 0
  while i < out_len
    pos  = i * ratio
    idx  = pos.floor
    frac = pos - idx
    a = samples[idx] || 0.0
    b = samples[idx + 1] || a
    out[i] = a + ((b - a) * frac)
    i += 1
  end
  out
end

.rms_dbfs(opts = {}) ⇒ Object

Supported Method Parameters

dbfs = PWN::SDR::Decoder::DSP.rms_dbfs(samples: Array)



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 403

public_class_method def self.rms_dbfs(opts = {})
  samples = opts[:samples]
  return -120.0 if samples.nil? || samples.empty?

  if native && PWN::FFI.available?(mod: :Volk) && samples.length >= 64
    begin
      # Σ x² via volk: scale-square in Ruby is still the bottleneck for
      # tiny buffers so keep the pure-Ruby path under 64 samples.
      sq = samples.map { |v| v * v }
      ms = PWN::FFI::Volk.accumulate(samples: sq) / samples.length
      return -120.0 if ms <= 0

      return 10.0 * Math.log10(ms)
    rescue StandardError
      # fall through
    end
  end

  ms = samples.sum { |v| v * v } / samples.length
  return -120.0 if ms <= 0

  10.0 * Math.log10(ms)
end

.unpack_cs16le(opts = {}) ⇒ Object

Supported Method Parameters

iq = PWN::SDR::Decoder::DSP.unpack_cs16le( data: 'required - raw String of interleaved little-endian s16 I/Q' ) Returns interleaved Array [I0,Q0,I1,Q1,…] normalised ±1.0.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 435

public_class_method def self.unpack_cs16le(opts = {})
  data = opts[:data].to_s
  if native && PWN::FFI.available?(mod: :Volk)
    begin
      return PWN::FFI::Volk.unpack_s16le(data: data)
    rescue StandardError
      # fall through
    end
  end
  norm = 1.0 / 32_768.0
  data.unpack('s<*').map { |v| v * norm }
end

.unpack_cu8(opts = {}) ⇒ Object

Supported Method Parameters

iq = PWN::SDR::Decoder::DSP.unpack_cu8( data: 'required - raw String of interleaved u8 I/Q (RTL-SDR)' ) Returns interleaved Array [I0,Q0,…] centred & normalised ±1.0.



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 454

public_class_method def self.unpack_cu8(opts = {})
  data = opts[:data].to_s
  norm = 1.0 / 128.0
  data.unpack('C*').map { |v| (v - 127.5) * norm }
end

.unpack_s16le(opts = {}) ⇒ Object

Supported Method Parameters

samples = PWN::SDR::Decoder::DSP.unpack_s16le( data: 'required - raw String of little-endian signed 16-bit PCM' )



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# File 'lib/pwn/sdr/decoder/dsp.rb', line 70

public_class_method def self.unpack_s16le(opts = {})
  data = opts[:data].to_s
  if native && PWN::FFI.available?(mod: :Volk)
    begin
      return PWN::FFI::Volk.unpack_s16le(data: data)
    rescue StandardError
      # fall through to pure Ruby
    end
  end
  norm = 1.0 / 32_768.0
  data.unpack('s<*').map { |v| v * norm }
end