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It requires at the minimum an new data indicator (NDI), a redundancy version(RV) and a HARQ process number to perform a HARQ combining for a transport block.

In Sect. 5.3.2.1 of TS36.321, it’s stated that “in case of BCCH a dedicated broadcast HARQ process is used”.
So is this “ broadcast HARQ process” also used for paging/PCCH?

Considering redundancy version, it is stated in Sect. 7.1.7.3 that the RV shall set to 0 when the DCI 1C is scrambled by P-RNTI, and that the RV is set according to SI window for DCI 1C scrambled by SI-RNTI, implying that Chase and IR combining are possible for SI-RNTI while only Chase combining is applicable for P-RNTI. For DCI 1A, eNodeB is able to set RV as needed.

For the HARQ process ID, there’s no “HARQ process number” field in DCI 1C, and for DCI 1A with P-RNTI, the “HARQ process number” field is reserved, as stated in TS36.212.

As for NDI, there’s no NDI field for DCI 1C. Though there’s NDI filed in DCI 1A, it is defined clearly that the NDI bit is reserved for P-RNTI in Sect. 5.3.3.1.3 of TS36.212. Since there’s no NDI for P-RNTI, with DCI 1C or 1A, it is not applicable for a HARQ combining for Paging.

In summary, RV is available for transport block for PCCH, but either of HARQ process ID and NDI is available for PCCH. So it is clear that HARQ combining is not applicable for Paging, under the framework of 3GPP specification.

As to system information broadcast/BCCH, HARQ process ID and NDI are also not available in the downlink control information, namely DCI 1C or 1A. However, an extra and special HARQ process is explicitly defined for BCCH in TS36.321, named broadcast HARQ process. Furthermore, the NDI for BCCH transport block is determined from the SI scheduling information. There extra settings make it possible to perform HARQ combining (even incremental redundancy!) for BCCH.