Scrambling
Scrambling as a channel coding step masks transmitted bits by a pseudo-random sequence known at both receiver and transmitter in order to prevent long sequences of identical bits. Therefore, most scrambling coding operations do not introduce redundancy to the scrambled bit blocks, i.e. the code rate is usually \(R = 1\).
- class PseudoRandomGenerator(init_sequence, offset=1600)
Bases:
object
A generator for pseudo-random bit sequences.
Generators with identical initialization will output identical random sequences. Implements pseudo-random generator as described in the 3GPP standard for Physical Channels and Modulation1.
- Parameters
init_sequence (np.ndarray) – A sequence of 31 bits initializing the generator.
offset (int) – Gold sequence parameter controlling the sequence offset.
- generate()
Generate the next bit within the pseudo-random sequence.
- Returns
The generated bit.
- Return type
int
- generate_sequence(length)
Generate a new sequence of random numbers.
- Parameters
length (int) – Length of the sequence to be generated.
- Returns
A numpy array of dimension length containing a sequence of pseudo-random bits.
- Return type
np.array
- reset()
Resets the gernator to its default state.
This implies reverting the queues back to their original state (at rng position n = 0).
- Return type
None
- class Scrambler3GPP(seed=None)
Bases:
hermespy.coding.coding.Encoder
,hermespy.core.factory.Serializable
Scrambler channel coding in the physical up- and down-link standard of the 3GPP.
See section 7.3.1.1 of the respective technical standard Physical Channels and Modulation1 for details.
- Parameters
seed (np.ndarray, optional) – Seed used to initialize the scrambling sequence generation. Must contain a sequence of bits.
- yaml_tag: str = 'SCRAMBLER_3GPP'
YAML serialization tag.
- encode(data)
Encodes a single block of bits.
Bit encoding routine during data transmission, encoding a block of \(K_n\) input bits into a block of \(L_n\) code bits.
- Parameters
bits (np.ndarray) – A numpy vector of \(K_n\) bits, representing a single bit block to be encoded.
- Returns
A numpy vector of \(L_n\) bits, representing a single code block.
- Return type
np.ndarray
- Raises
ValueError – If the length of
bits
does not equalbit_block_size()
.
- decode(code)
Decodes a single block of bits.
Bit decoding routine during data reception, decoding a block of \(L_n\) code bits into a block of \(K_n\) data bits.
- Parameters
encoded_bits (np.ndarray) – A numpy vector of \(L_n\) code bits, representing a single code block to be decoded.
- Returns
A numpy vector of \(K_n\) bits, representing a single data block.
- Return type
np.ndarray
- Raises
ValueError – If the length of
encoded_bits
does not equalcode_block_size()
.
- property bit_block_size: int
Data bit block size of a single coding operation.
In other words, the number of input bits within a single code block during transmit encoding, or the number of output bits during receive decoding. Referred to as \(K_n\) within the respective equations.
- Returns
Number of bits \(K_n\).
- Return type
int
- property code_block_size: int
Code bit block size of a single coding operation.
In other words, the number of input bits within a single code block during receive decoding, or the number of output bits during transmit encoding. Referred to as \(L_n\) within the respective equations.
- Returns
Number of bits \(L_n\).
- Return type
int
- class Scrambler80211a(seed=None)
Bases:
hermespy.coding.coding.Encoder
,hermespy.core.factory.Serializable
Scrambler channel coding in the the 802.11a standard.
Refer to section 17.3.5.4 of IEEE2 for further details.
- Parameters
seed (np.ndarray, optional) – Seed used to initialize the scrambling sequence generation. Must contain a sequence of 7 bits.
- yaml_tag: str = 'SCRAMBLER_80211A'
YAML serialization tag.
- property seed: numpy.array
Random sequence generator seed.
Resets the internal register queue used to generate the scrambling sequence.
- Returns
Numpy vector containing the generator seed. Must be an array of dimension 7 containing only soft bits.
- Return type
np.ndarray
- Raises
ValueError – If seed does not contain exactly 7 bits.
- encode(data)
Encodes a single block of bits.
Bit encoding routine during data transmission, encoding a block of \(K_n\) input bits into a block of \(L_n\) code bits.
- Parameters
bits (np.ndarray) – A numpy vector of \(K_n\) bits, representing a single bit block to be encoded.
- Returns
A numpy vector of \(L_n\) bits, representing a single code block.
- Return type
np.ndarray
- Raises
ValueError – If the length of
bits
does not equalbit_block_size()
.
- decode(code)
Decodes a single block of bits.
Bit decoding routine during data reception, decoding a block of \(L_n\) code bits into a block of \(K_n\) data bits.
- Parameters
encoded_bits (np.ndarray) – A numpy vector of \(L_n\) code bits, representing a single code block to be decoded.
- Returns
A numpy vector of \(K_n\) bits, representing a single data block.
- Return type
np.ndarray
- Raises
ValueError – If the length of
encoded_bits
does not equalcode_block_size()
.
- property bit_block_size: int
Data bit block size of a single coding operation.
In other words, the number of input bits within a single code block during transmit encoding, or the number of output bits during receive decoding. Referred to as \(K_n\) within the respective equations.
- Returns
Number of bits \(K_n\).
- Return type
int
- property code_block_size: int
Code bit block size of a single coding operation.
In other words, the number of input bits within a single code block during receive decoding, or the number of output bits during transmit encoding. Referred to as \(L_n\) within the respective equations.
- Returns
Number of bits \(L_n\).
- Return type
int
- 1(1,2)
Physical Channels and Modulation. ETSI, 07 2018. Version 15.2.0 Release 15. URL: https://www.etsi.org/deliver/etsi_ts/138200_138299/138211/15.02.00_60/ts_138211v150200p.pdf.
- 2
IEEE. IEEE standard for telecommunications and information exchange between systems - LAN/MAN specific requirements - Part 11: wireless medium access control (MAC) and physical layer (PHY) specifications: high speed physical layer in the 5 GHz band. IEEE Std 802.11a-1999, 1999. doi:10.1109/IEEESTD.1999.90606.