INDEXHABOUTHcopyright © samir amberkar

1.1
1.2
1.3
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1.6
1.7
1.8
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1.10
1.11
1.12
1.13
1.14
1.15
1.16
1.17
1.18
1.19
1.20

2.1

3.1
3.2
3.3
3.4
3.5




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LTE Allocations Explained

Requirements were:

1. system information messages (except MIB and SIB1)
2. RAR and DL RRC Connection Setup message
3. Layer 3 (NAS/RRC) signaling over SRB1/2
4. user data transmission and associated layer 2/1 signaling

Ref: [36.212:5.3.3], [36.213:7.1], [36.321:7.1]


Format RA Type
MCS
Details CRC scrambled by Requirements
0 RA Type 2
MCS index
PUSCH allocation C-RNTI UL allocations (req# 3, 4)
1 RA Type 0 or 1
MCS index
PDSCH allocation (one transport block) C-RNTI req# 2 (RRC msg3), 3, 4
1A RA Type 2
MCS index
PDSCH allocation (one transport block) SI-RNTI
P-RNTI
RA-RNTI
C-RNTI
req# 2 (RAR, RRC msg3), 3, 4
1B RA Type 2
MCS index
PDSCH allocation (one transport block) C-RNTI req# 3, 4
1C RA Type 2
TBS index1
PDSCH allocation (one transport block)
QPSK modulation2
SI-RNTI
P-RNTI
RA-RNTI
req# 1, 2 (RAR), 3 (paging, SI change4)
1D RA Type 2
MCS index
PDSCH allocation (one transport block) C-RNTI req# 3, 4
2 RA Type 0 or 1
MCS index
PDSCH allocation (two transport blocks i.e. for spatial multiplexing) C-RNTI req# 4
2A RA Type 0 or 1
MCS index
PDSCH allocation (two transport blocks i.e. for spatial multiplexing) C-RNTI req# 4
3 - PUCCH/PUSCH TPC commands TPC-PUCCH-RNTI
TPC-PUSCH-RNTI
power control
3A - PUCCH/PUSCH TPC commands TPC-PUCCH-RNTI
TPC-PUSCH-RNTI
power control

t
1: TBS index directly maps to TB size irrespective of RBs allocated [36.213:7.1.7.2.3].
2: Qm = 2 if CRC is scrambled by SI-RNTI, P-RNTI, or RA-RNTI.
3: Temporary C-RNTI.
4: System Information change notification.



Even though there are number of formats, it is not very difficult to roughly see their relative sizes as RA Type 2 is of smaller size compared to RA TYPE 0 & 1. So we can roughly say 1C < 1A, 1B, 1C, 1D < 1 < 2, 2A.

Earlier we said that CRC is scrambled by RNTI. As there are number of RNTIs, how does PHY knows which RNTI to use ? This depend on RRC and MAC procedures as RNTI is relevant to type of information or procedure as required by RRC and MAC e.g. RA-RNTI relevant to MAC random access procedure, SI-RNTI is relevant to RRC system acquisition procedure. PHY acts as a slave to MAC/RRC.



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