RFGSM System Information Messages: A Detailed Overview
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This document describes the GSM System Information (SI) messages, including SI1, SI2, SI3, SI4, SI5, SI6, SI7, SI8, SI9, and SI13. These messages are transmitted on the Broadcast Control Channel (BCCH)/Standalone Dedicated Control Channel (SACCH). System information messages are broadcast either on BCCH normal, BCCH extended, or SACCH.
SI messages are transmitted in Time slot Cycle (TC) 0 to 7 in a cyclic order, repeating every eight TCs of the 51-frame multi-frame structure. TC represents the sequence number of the 51-frame multi-frame.
- SI1 to SI4: Transmitted on BCCH
- SI5 / SI6: Associated with SACCH
- SI7 / SI8: BCCH Extended
- SI-2quater and SI13: BCCH Normal or BCCH Extended
System Information Message Types
The following table outlines the different system information messages in GSM:
| System Information message type | Description |
|---|---|
| System information-1 (SI1) | Cell ARFCN, RACH parameters required to access the system by MS and hopping related information are sent in this SI message. |
| System information-2 (SI2) | Neighbour BCCH frequencies and PLMN information are sent in this SI. MS uses these frequencies for signal strength measurements required for handover. |
| System information-2bis (SI-2bis) | RACH control and BCCH extension on neighbor cells. |
| System information-2ter (SI-2ter) | Information of BCCH extended allocated on which neighbor cells are provided in this SI. Broadcasted optionally on BCCH by the network to all the MSs. |
| System information-2 Quarter (SI-2Quater) | 3G neighbor cell related information. |
| System information-3 (SI3) | Carries the following: 1. LAI of the current location area, 2. Cell identity, 3. Control channel information required to calculate paging group, 4. Cell options to achieve good performance in the cell, 5. cell selection parameters required by MS. |
| System information-4 (SI4) | CBCH and CBCH related frequency information, LAI, Cell selection parameters and RACH control information are carried by this SI4 message. |
| System information-5 (SI5) | It carries neighbor cell information. In active mode, MS sends measurement reports in the uplink and output power/timing advance information in the downlink (on SACCH). Also gets BCCH carrier related information of the neighbor cells. |
| System information-6 (SI6) | Information on LAI, cell options, Cell identity and PLMN permitted or not is transmitted on this SI. |
| System information-7 (SI7) | Cell re-selection parameters needed by MS are sent on this SI. |
| System information-8 (SI8) | Cell re-selection parameters needed by MS are sent on this SI. |
| System information-9 (SI9) | Scheduling related information is sent on this SI. |
| System information-13 (SI13) | Carries GPRS related information needed for PS call. |
This table of system information messages in GSM is helpful for analyzing GSM User Equipment (UE) related issues.
Troubleshooting SI Related Issues
In case of any issues related to the SIs mentioned above, the following should be considered:
- First, verify which SIs are transmitted by the Base Station (BS) and whether the UE has received them.
- Next, check if the SIs are decoded correctly without any Radio Frequency (RF) or physical layer (i.e., lower layer) issues.
