For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.

For the purposes of the present document, the following symbols apply:

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905. ACB BCH DSAC EAB GANSS MOCN PPAC RLF

When the SIB repetition period is increased more SIBs can be broadcasted. But increasing the SIB repetition period goes at the expense of a longer System Information (SI) acquisition latency which could have a negative impact on some use cases, as explained in chapter 6. The MIB is broadcast with a fixed interval of 80 ms, i.e. every 4 BCH transport blocks. SIB7, which contains information that needs to be updated frequently (UL interference), is typically scheduled quite often (e.g. 80 - 160 ms). Scheduling block 1 and/or 2 could be also broadcast with a high frequency to decrease SI acquisition latency. MIB, scheduling blocks, and SIB7, which need to be send with a high frequency, require a comparatively high share of the BCH capacity. Thus the BCH capacity gain does not scale linearly with the repetition period of a single SIB.

If the System Information Block (SIB) size is too large, i.e., greater than 226 bits, it needs to be segmented into several SYSTEM INFORMATION messages. A SIB can be segmented up to maximum 16 segments (4-bit SEG_COUNT). The position of subsequent segments of a SIB is indicated by an offset SIB_OFF. The position of the first segment of a SIB is indicated by an offset SIB_POS. The counters and offsets associated with segmentation take some of the BCH capacity. Furthermore concatenation can be used to transmit two or more (smaller) SIBs in a single SYSTEM INFORMATION message to optimally use the available BCH capacity. Concatenation thus enables more efficient use of the available BCH capacity. However given the sizes of the SIBs to be broadcasted, and the possible concatenation and scheduling options, a small percentage of the BCH may remain un-used.

A longer SIB repetition period increases the SI acquisition latency. A longer SI acquisition latency has a negative effect on use cases where if the UE needs to acquire the complete system information again, e.g. CS Fallback, cell re-selection, RRC state change, cell update in case of RLC unrecoverable error or RLF, and redirection. These use cases are explained in more detail in the following paragraphs. Reception failure of a single segment of a large SIB, broadcasted with a long repetition period (e.g. neighbor cell information), further delays the SI acquisition latency. It is up to UE implementation to store the system information of one or more cells for later usage. In case the UE has stored system information for a cell (based on Cell Identity), the SI acquisition latency would be largely reduced, but the UE needs to read the MIB to check if any of the stored SIBs has changed. Furthermore it may need to check SIB3 for the Cell Identity of the cell. In case one or more SIBs have changed, the UE needs to re-acquire those. The UE may also have to re-acquire a timer based SIB, which timer has expired, or SIBs that were added. The UE shall delete any stored system information after 6 hours. The SI acquisition latency is impacted in the following use cases when the UE (re-)selects a cell for which it does not have up to date system information stored (i.e. expired or changed).