packet_utils.py

这是用python语言写的一个数字广播的信号处理工具包。利用它

#
# Copyright 2005,2006,2007 Free Software Foundation, Inc.
# 
# This file is part of GNU Radio
# 
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
# 
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING.  If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
# 

import struct
import numpy
from gnuradio import gru


def conv_packed_binary_string_to_1_0_string(s):
    """
    '\xAF' --> '10101111'
    """
    r = []
    for ch in s:
        x = ord(ch)
        for i in range(7,-1,-1):
            t = (x >> i) & 0x1
            r.append(t)

    return ''.join(map(lambda x: chr(x + ord('0')), r))

def conv_1_0_string_to_packed_binary_string(s):
    """
    '10101111' -> ('\xAF', False)

    Basically the inverse of conv_packed_binary_string_to_1_0_string,
    but also returns a flag indicating if we had to pad with leading zeros
    to get to a multiple of 8.
    """
    if not is_1_0_string(s):
        raise ValueError, "Input must be a string containing only 0's and 1's"
    
    # pad to multiple of 8
    padded = False
    rem = len(s) % 8
    if rem != 0:
        npad = 8 - rem
        s = '0' * npad + s
        padded = True

    assert len(s) % 8 == 0

    r = []
    i = 0
    while i < len(s):
        t = 0
        for j in range(8):
            t = (t << 1) | (ord(s[i + j]) - ord('0'))
        r.append(chr(t))
        i += 8
    return (''.join(r), padded)
        

default_access_code = \
  conv_packed_binary_string_to_1_0_string('\xAC\xDD\xA4\xE2\xF2\x8C\x20\xFC')
preamble = \
  conv_packed_binary_string_to_1_0_string('\xA4\xF2')

def is_1_0_string(s):
    if not isinstance(s, str):
        return False
    for ch in s:
        if not ch in ('0', '1'):
            return False
    return True

def string_to_hex_list(s):
    return map(lambda x: hex(ord(x)), s)


def whiten(s, o):
    sa = numpy.fromstring(s, numpy.uint8)
    z = sa ^ random_mask_vec8[o:len(sa)+o]
    return z.tostring()

def dewhiten(s, o):
    return whiten(s, o)        # self inverse


def make_header(payload_len, whitener_offset=0):
    # Upper nibble is offset, lower 12 bits is len
    val = ((whitener_offset & 0xf) << 12) | (payload_len & 0x0fff)
    #print "offset =", whitener_offset, " len =", payload_len, " val=", val
    return struct.pack('!HH', val, val)

def make_packet(payload, samples_per_symbol, bits_per_symbol,
                access_code=default_access_code, pad_for_usrp=True,
                whitener_offset=0, whitening=True):
    """
    Build a packet, given access code, payload, and whitener offset

    @param payload:               packet payload, len [0, 4096]
    @param samples_per_symbol:    samples per symbol (needed for padding calculation)
    @type  samples_per_symbol:    int
    @param bits_per_symbol:       (needed for padding calculation)
    @type bits_per_symbol:        int
    @param access_code:           string of ascii 0's and 1's
    @param whitener_offset        offset into whitener string to use [0-16)
    
    Packet will have access code at the beginning, followed by length, payload
    and finally CRC-32.
    """
    if not is_1_0_string(access_code):
        raise ValueError, "access_code must be a string containing only 0's and 1's (%r)" % (access_code,)

    if not whitener_offset >=0 and whitener_offset < 16:
        raise ValueError, "whitener_offset must be between 0 and 15, inclusive (%i)" % (whitener_offset,)

    (packed_access_code, padded) = conv_1_0_string_to_packed_binary_string(access_code)
    (packed_preamble, ignore) = conv_1_0_string_to_packed_binary_string(preamble)
    
    payload_with_crc = gru.gen_and_append_crc32(payload)
    #print "outbound crc =", string_to_hex_list(payload_with_crc[-4:])

    L = len(payload_with_crc)
    MAXLEN = len(random_mask_tuple)
    if L > MAXLEN:
        raise ValueError, "len(payload) must be in [0, %d]" % (MAXLEN,)

    if whitening:
        pkt = ''.join((packed_preamble, packed_access_code, make_header(L, whitener_offset),
                       whiten(payload_with_crc, whitener_offset), '\x55'))
    else:
        pkt = ''.join((packed_preamble, packed_access_code, make_header(L, whitener_offset),
                       (payload_with_crc), '\x55'))

    if pad_for_usrp:
        pkt = pkt + (_npadding_bytes(len(pkt), samples_per_symbol, bits_per_symbol) * '\x55')

    #print "make_packet: len(pkt) =", len(pkt)
    return pkt

def _npadding_bytes(pkt_byte_len, samples_per_symbol, bits_per_symbol):
    """
    Generate sufficient padding such that each packet ultimately ends
    up being a multiple of 512 bytes when sent across the USB.  We
    send 4-byte samples across the USB (16-bit I and 16-bit Q), thus
    we want to pad so that after modulation the resulting packet
    is a multiple of 128 samples.

    @param ptk_byte_len: len in bytes of packet, not including padding.
    @param samples_per_symbol: samples per bit (1 bit / symbolwidth GMSK)
    @type samples_per_symbol: int
    @param bits_per_symbol: bits per symbol (log2(modulation order))
    @type bits_per_symbol: int

    @returns number of bytes of padding to append.
    """
    modulus = 128
    byte_modulus = gru.lcm(modulus/8, samples_per_symbol) * bits_per_symbol / samples_per_symbol
    r = pkt_byte_len % byte_modulus
    if r == 0:
        return 0
    return byte_modulus - r
    

def unmake_packet(whitened_payload_with_crc, whitener_offset=0, dewhitening=True):
    """
    Return (ok, payload)

    @param whitened_payload_with_crc: string
    """

    if dewhitening:
        payload_with_crc = dewhiten(whitened_payload_with_crc, whitener_offset)
    else:
        payload_with_crc = (whitened_payload_with_crc)

    ok, payload = gru.check_crc32(payload_with_crc)

    if 0:
        print "payload_with_crc =", string_to_hex_list(payload_with_crc)
        print "ok = %r, len(payload) = %d" % (ok, len(payload))
        print "payload =", string_to_hex_list(payload)

    return ok, payload


# FYI, this PN code is the output of a 15-bit LFSR
random_mask_tuple = (
  255,  63,   0,  16,   0,  12,   0,   5, 192,   3,  16,   1, 204,   0,  85, 192, 
   63,  16,  16,  12,  12,   5, 197, 195,  19,  17, 205, 204,  85, 149, 255,  47, 
    0,  28,   0,   9, 192,   6, 208,   2, 220,   1, 153, 192, 106, 208,  47,  28, 
   28,   9, 201, 198, 214, 210, 222, 221, 152,  89, 170, 186, 255,  51,   0,  21, 
  192,  15,  16,   4,  12,   3,  69, 193, 243,  16,  69, 204,  51,  21, 213, 207, 
   31,  20,   8,  15,  70, 132,  50, 227,  85, 137, 255,  38, 192,  26, 208,  11, 
   28,   7,  73, 194, 182, 209, 182, 220, 118, 217, 230, 218, 202, 219,  23,  27, 
   78, 139, 116, 103, 103, 106, 170, 175,  63,  60,  16,  17, 204,  12,  85, 197, 
  255,  19,   0,  13, 192,   5, 144,   3,  44,   1, 221, 192,  89, 144,  58, 236, 
   19,  13, 205, 197, 149, 147,  47,  45, 220,  29, 153, 201, 170, 214, 255,  30, 
  192,   8,  80,   6, 188,   2, 241, 193, 132,  80,  99, 124,  41, 225, 222, 200, 
   88,  86, 186, 190, 243,  48,  69, 212,  51,  31,  85, 200,  63,  22, 144,  14, 
  236,   4,  77, 195, 117, 145, 231,  44,  74, 157, 247,  41, 134, 158, 226, 232, 
   73, 142, 182, 228, 118, 203, 102, 215, 106, 222, 175,  24, 124,  10, 161, 199, 
   56,  82, 146, 189, 173, 177, 189, 180, 113, 183, 100, 118, 171, 102, 255, 106, 
  192,  47,  16,  28,  12,   9, 197, 198, 211,  18, 221, 205, 153, 149, 170, 239, 
   63,  12,  16,   5, 204,   3,  21, 193, 207,  16,  84,  12,  63,  69, 208,  51, 
   28,  21, 201, 207,  22, 212,  14, 223,  68,  88,  51, 122, 149, 227,  47,   9, 
  220,   6, 217, 194, 218, 209, 155,  28, 107,  73, 239, 118, 204,  38, 213, 218, 
  223,  27,  24,  11,  74, 135, 119,  34, 166, 153, 186, 234, 243,  15,   5, 196, 
    3,  19,  65, 205, 240,  85, 132,  63,  35,  80,  25, 252,  10, 193, 199,  16, 
   82, 140,  61, 165, 209, 187,  28, 115,  73, 229, 246, 203,   6, 215,  66, 222, 
  177, 152, 116, 106, 167, 111,  58, 172,  19,  61, 205, 209, 149, 156, 111,  41, 
  236,  30, 205, 200,  85, 150, 191,  46, 240,  28,  68,   9, 243,  70, 197, 242, 
  211,   5, 157, 195,  41, 145, 222, 236,  88,  77, 250, 181, 131,  55,  33, 214, 
  152,  94, 234, 184,  79,  50, 180,  21, 183,  79,  54, 180,  22, 247,  78, 198, 
  180,  82, 247, 125, 134, 161, 162, 248, 121, 130, 162, 225, 185, 136, 114, 230, 
  165, 138, 251,  39,   3,  90, 129, 251,  32,  67,  88,  49, 250, 148,  67,  47, 
  113, 220,  36,  89, 219, 122, 219,  99,  27, 105, 203, 110, 215, 108,  94, 173, 
  248, 125, 130, 161, 161, 184, 120, 114, 162, 165, 185, 187,  50, 243,  85, 133, 
  255,  35,   0,  25, 192,  10, 208,   7,  28,   2, 137, 193, 166, 208, 122, 220,