There were several questions around my mind regarding MIB (Master Information Block) transmission in LTE. Here are those questions below.
We would have to get started with what MIB delivers to UE. That can be explained easily in the coming decoded message. Since MIB is broadcast all clients under a certain eNB cell, all devices should take it to understand what cell would be like during cell search procedure.
dl-Bandwidth: n50 (3)
phich-Config
phich-Duration: normal (0)
phich-Resource: one (2)
systemFrameNumber: 00 [bit length 8, 0000 0000]
spare: 0000 [bit length 10, 6 LSB pad bits, 0000 0000 00]
Let us break down MIB's contents a bit from now on.
This is straight forward and one of fundamental information UE should take care of. Since it is denoted by 3 bits, it is represented in NRB, which can be translated to real downlink cell bandwidth according to TS36.101 Table 5.6-1: Transmission bandwidth configuration NRB in E-UTRA channel bandwidths below.
UE also must take PHICH configuration of the cell in order to receive PDCCH, which allows it decode System Information Blocks or other DL control signalling or data, which are carried by PDSCH in the end.
On DL slot structure and resource grid, PCFICH indicating number of PDCCH symbols and PHICH returning ACK/NACK feedback to UL signalling or data are taken up first and second spots in a subframe (two slots). Then rest of part in symbol area indicated by PCFICH would be used or saved for PDCCH unless some of them are used for RS and PBCH or/and PSS/SSS.
Since it represents SFN in 8 bits, 256 (= 1024/4) would be maximum number UE can receive. Since MIB transport block itself is transmitted every 40 ms (4 SFNs) according to TS36.331 6.2.2 Message definitions, it uses 8-bit MSB for SFN.
I would like to describe how frequently MIB is delivered to all clients under the cell; scheduling. In LTE, MIB and SIB1 use fixed scheduling.
According to TS36.331 5.2.1.2 Scheduling, MIB is transmitted from the eNB every 40 ms, which means that whole message itself is delivered through BCCH down to BCH as a transport block every 40 ms. Periodicity term is used for this 40 ms in 3GPP specs. As a matter of fact, one BCH transport block is converted to 4 repetitive PBCH signalling, which is transmitted every 10 ms or subframe. 4 of PBCH sets have same contents and scrambling will be initialised every 40 ms. So any of 4 PBCHs would be enough for UE to read MIB contents. Repetitive term is used for this 10 ms in 3GPP specs instead.
This mapping table would explain the periodicity and repetition of MIB and SIBs altogether on physical layer perspective. Clicking this picture above would allowed to see this clearer.
Regarding how MIB goes process from BCH to BCCH, I am going to post another one. And also that would include relationship between MIB and number of antenna on eNB side.
# References
How frequently MIB is transmitted in LTE?
How frequently PBCH is transmitted in LTE? (This might sound same question or different from the one above)
What information is transmitted with MIB in LTE?
Can number of antenna information be included? If so, how would UE figure that out?
What is in Master Information Block?
We would have to get started with what MIB delivers to UE. That can be explained easily in the coming decoded message. Since MIB is broadcast all clients under a certain eNB cell, all devices should take it to understand what cell would be like during cell search procedure.
dl-Bandwidth: n50 (3)
phich-Config
phich-Duration: normal (0)
phich-Resource: one (2)
systemFrameNumber: 00 [bit length 8, 0000 0000]
spare: 0000 [bit length 10, 6 LSB pad bits, 0000 0000 00]
Let us break down MIB's contents a bit from now on.
System bandwidth (3 bits)
This is straight forward and one of fundamental information UE should take care of. Since it is denoted by 3 bits, it is represented in NRB, which can be translated to real downlink cell bandwidth according to TS36.101 Table 5.6-1: Transmission bandwidth configuration NRB in E-UTRA channel bandwidths below.
PHICH information (3 bits)
UE also must take PHICH configuration of the cell in order to receive PDCCH, which allows it decode System Information Blocks or other DL control signalling or data, which are carried by PDSCH in the end.
On DL slot structure and resource grid, PCFICH indicating number of PDCCH symbols and PHICH returning ACK/NACK feedback to UL signalling or data are taken up first and second spots in a subframe (two slots). Then rest of part in symbol area indicated by PCFICH would be used or saved for PDCCH unless some of them are used for RS and PBCH or/and PSS/SSS.
System frame number (8 bits)
Since it represents SFN in 8 bits, 256 (= 1024/4) would be maximum number UE can receive. Since MIB transport block itself is transmitted every 40 ms (4 SFNs) according to TS36.331 6.2.2 Message definitions, it uses 8-bit MSB for SFN.
How to deliver MIB?
I would like to describe how frequently MIB is delivered to all clients under the cell; scheduling. In LTE, MIB and SIB1 use fixed scheduling.
According to TS36.331 5.2.1.2 Scheduling, MIB is transmitted from the eNB every 40 ms, which means that whole message itself is delivered through BCCH down to BCH as a transport block every 40 ms. Periodicity term is used for this 40 ms in 3GPP specs. As a matter of fact, one BCH transport block is converted to 4 repetitive PBCH signalling, which is transmitted every 10 ms or subframe. 4 of PBCH sets have same contents and scrambling will be initialised every 40 ms. So any of 4 PBCHs would be enough for UE to read MIB contents. Repetitive term is used for this 10 ms in 3GPP specs instead.
This mapping table would explain the periodicity and repetition of MIB and SIBs altogether on physical layer perspective. Clicking this picture above would allowed to see this clearer.
Regarding how MIB goes process from BCH to BCCH, I am going to post another one. And also that would include relationship between MIB and number of antenna on eNB side.
# References
- TS36.101 5.6 Channel bandwidth
- TS36.331 5.2 System information
- TS36.331 6.2.2 Message definitions
- TS36.211 6.6 Physical broadcast channel
- 3G Evolution HSPA And LTE For Mobile Broadband 18.2.1 MIB and BCH transmission
- LTE, The UMTS Long Term Evolution From Theory to Practice 3.2.2 System Information