Question about LDPC and IR-HARQ

[quietinside123]

I noticed a passage in LDPC5GEncoder() :

    #shorten the first 2*Z positions and end after n bits
    #(remaining parity bits can be used for IR-HARQ)
    c_short = tf.slice(c_no_filler, [0, 2*self._z], [batch_size, self.n])
    #incremental redundancy could be generated by accessing the last bits

How to use this library to complete the operation of IR-HARQ?

[SebastianCa]

Hi,

HARQ is currently not supported by the Sionna API and, thus, one would need to extend the encoder/decoder. Please see Richardson for an overview of the 5G LDPC code construction.

The detailed procedure can be found in Section 5.4.2.1 of TS 38.212:

• For given redundancy version rv_id, select k_0 from Table 5.4.2.1-2 (currently k_0 is hardcoded to 0)
• Run bit selection procedure from 5.4.2.1 for given k_0
• This boils down to slicing the encoded bits from a different slice (cf. comment in the source code)
• At the decoder, one would need to re-combine the received HARQ bits before running the BP decoder

I hope that helps.