## -*- python -*- import numpy as np import common from digitalhf.digitalhf_swig import viterbi27 class Deinterleaver(object): "S4285 deinterleaver" def __init__(self, incr): ## incr = 12 -> L ## incr = 1 -> S self._buf = [np.zeros(incr*(31-i) + 1) for i in range(32)] def push(self, a): assert(len(a) == 32) for i in range(32): self._buf[i][0] = a[i] self._buf[i] = np.roll(self._buf[i],1) def fetch(self): return np.array([self._buf[(9*i)%32][0] for i in range(32)]) MODE_BPSK=0 MODE_QPSK=1 MODE_8PSK=2 MODES = { ## [BPS]['const'] [BPS]['punct'] [BPS]['repeat'] '2400': {'const': MODE_8PSK, 'punct': ['11', '10'] , 'repeat': 1, 'deintl_multiple': 4}, '1200': {'const': MODE_QPSK, 'punct': [ '1', '1'] , 'repeat': 1, 'deintl_multiple': 2}, '600': {'const': MODE_BPSK, 'punct': [ '1', '1'] , 'repeat': 1, 'deintl_multiple': 1}, '300': {'const': MODE_BPSK, 'punct': [ '1', '1'] , 'repeat': 2, 'deintl_multiple': 1}, '150': {'const': MODE_BPSK, 'punct': [ '1', '1'] , 'repeat': 4, 'deintl_multiple': 1}, '75': {'const': MODE_BPSK, 'punct': [ '1', '1'] , 'repeat': 8, 'deintl_multiple': 1} } DEINTERLEAVER_INCR = { 'S': 1, 'L': 12 } class PhysicalLayer(object): """Physical layer description for STANAG 4285""" def __init__(self, sps): """intialization""" self._sps = sps self._frame_counter = 0 self._is_first_frame = True self._constellations = [self.make_psk(2, [0,1]), self.make_psk(4, [0,1,3,2]), self.make_psk(8, [1,0,2,3,6,7,5,4])] self._preamble = self.get_preamble() self._data = self.get_data() self._viterbi_decoder = viterbi27(0x6d, 0x4f) self._mode_description = None def set_mode(self, mode): """set modulation and interleaver: 'BPS/S' or 'BPS/L'""" self._mode_description = mode bps,intl = mode.split('/') self._mode = MODES[bps]['const'] self._deinterleaver = Deinterleaver(DEINTERLEAVER_INCR[intl] * MODES[bps]['deintl_multiple']) self._depuncturer = common.Depuncturer(repeat = MODES[bps]['repeat'], puncture_pattern = MODES[bps]['punct']) def get_mode(self): return self._mode_description def get_constellations(self): return self._constellations def get_next_frame(self, symbols): """returns a tuple describing the frame: [0] ... known+unknown symbols and scrambling [1] ... modulation type after descrambling [2] ... a boolean indicating if the processing should continue [3] ... a boolean indicating if the soft decision for the unknown symbols are saved""" if len(symbols) == 0: ## 1st preamble self._frame_counter = 0 success,frame_description = True,[] if (self._frame_counter%2) == 0: ## current frame is a data frame frame_description = [self._preamble,MODE_BPSK,success,False] else: ## current frame is a preamble frame idx = range(30,80) z = symbols[idx]*np.conj(self._preamble['symb'][idx]) success = bool(np.sum(np.real(z)<0) < 30) frame_description = [self._data,self._mode,success,True] self._frame_counter += 1 return frame_description def get_doppler(self, iq_samples): r = {'success': False, ## -- quality flag 'doppler': 0} ## -- doppler estimate (rad/symb) if len(iq_samples) == 0: return r sps = self._sps zp = np.array([x for x in self._preamble['symb'][9:40] for _ in range(sps)], dtype=np.complex64) cc = np.correlate(iq_samples, zp) imax = np.argmax(np.abs(cc[0:18*sps])) pks = cc[(imax,imax+31*sps),] tpks = cc[imax+15*sps:imax+16*sps] r['success'] = bool(np.mean(np.abs(pks)) > 5*np.mean(np.abs(tpks))) r['doppler'] = np.diff(np.unwrap(np.angle(pks)))[0]/31/self._sps if r['success'] else 0 return r def get_preamble_z(self): """preamble symbols for preamble correlation""" a = PhysicalLayer.get_preamble() return 2,np.array([z for z in a['symb'][0:31] for _ in range(self._sps)]) def decode_soft_dec(self, soft_dec): n = len(soft_dec) r = [] for i in range(0,n,32): self._deinterleaver.push(soft_dec[i:i+32]) r.extend(self._deinterleaver.fetch().tolist()) rd = self._depuncturer.process(np.array(r, dtype=np.float32)) decoded_bits = self._viterbi_decoder.udpate(rd) quality = 100.0*self._viterbi_decoder.quality()/(2*len(decoded_bits)) return decoded_bits,quality @staticmethod def get_preamble(): """preamble symbols + scrambler(=1)""" state = np.array([1,1,0,1,0], dtype=np.bool) taps = np.array([0,0,1,0,1], dtype=np.bool) p = np.zeros(80, dtype=np.uint8) for i in range(80): p[i] = state[-1] state = np.concatenate(([np.sum(state&taps)&1], state[0:-1])) a = np.zeros(80, common.SYMB_SCRAMBLE_DTYPE) ## BPSK modulation constellation = PhysicalLayer.make_psk(2,range(2))['points'] a['symb'] = constellation[p,] a['scramble'] = 1 return a @staticmethod def get_data(): """data symbols + scrambler; for unknown symbols 'symb'=0""" state = np.array([1,1,1,1,1,1,1,1,1], dtype=np.bool) taps = np.array([0,0,0,0,1,0,0,0,1], dtype=np.bool) p = np.zeros(176, dtype=np.uint8) for i in range(176): p[i] = np.sum(state[-3:]*[4,2,1]) for _ in range(3): state = np.concatenate(([np.sum(state&taps)&1], state[0:-1])) a = np.zeros(176, common.SYMB_SCRAMBLE_DTYPE) ## 8PSK modulation constellation = PhysicalLayer.make_psk(8,range(8))['points'] a['scramble'] = constellation[p,] known_symbols = np.mod(range(176),48)>=32 a['symb'][known_symbols] = a['scramble'][known_symbols] return a @staticmethod def make_psk(n, gray_code): """generates n-PSK constellation data""" c = np.zeros(n, common.CONST_DTYPE) c['points'] = np.exp(2*np.pi*1j*np.arange(n)/n) c['symbols'] = gray_code return c