Scrambling#

Scrambler([seed, keep_batch_constant, ...])

Randomly flips the state/sign of a sequence of bits or LLRs, respectively.

Descrambler(scrambler[, binary, precision, ...])

Descrambler for a given scrambler.

TB5GScrambler([n_rnti, n_id, binary, ...])

5G NR Scrambler for PUSCH and PDSCH channel.

The Scrambler module allows to (pseudo) randomly flip bits in a binary sequence or the signs of a real-valued sequence, respectively. The Descrambler implement the corresponding descrambling operation.

To simplify distributed graph execution (e.g., by running scrambler and descrambler in a different sub-graph/device), the scramblers are implemented stateless. Thus, the internal seed cannot be update on runtime and does not change after the initialization. However, if required an explicit random seed can be passed as additional input the scrambler/descrambler pair when calling the layer.

Further, the TB5GScrambler enables 5G NR compliant scrambling as specified in [3GPPTS38211].

The following code snippet shows how to setup and use an instance of the scrambler:

# set-up system
scrambler = Scrambler(seed=1234, # an explicit seed can be provided
                     binary=True) # indicate if bits shall be flipped

descrambler = Descrambler(scrambler=scrambler) # connect scrambler and descrambler

# --- simplified usage with fixed seed ---
# c has arbitrary shape and contains 0s and 1s (otherwise set binary=False)
c_scr = scrambler(c)
# descramble to reconstruct the original order
c_descr = descrambler(c_scr)

# --- advanced usage ---
# provide explicite seed if a new random seed should be used for each call
s = torch.randint(0, 12345678, ())

c_scr = scrambler([c, s])
c_descr = descrambler([c_scr, s])

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