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Below are types of MPDCCH search spaces:
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Type-2 common search space
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RACH procedure, RAR/MSG4 allocations
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UE-specific search space
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DL/UL allocations in connected mode
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Type-1 common search space
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Paging procedure, Paging message allocation
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Type-0 common search space
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FFS
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MPDCCH narrowband for common search spaces is noted in eMTC SIB2.
MPDCCH narrowband for UE specific search space is part of EPDCCH/MPDCCH configuration in RRC Connection Setup message.
Refer 36.36.213:9.1.5 [9] for more details on MPDCCH search spaces and assignment.
In principle, eMTC UE follow same - RRC/MAC/PHY - procedures as LTE UE with certain differences.
These differences bring in low complexity, effectively leading to low cost, low power consumption devices.
After acquisition on eMTC SIBs, eMTC UE start RACH procedure with eMTC RACH preambles.
Further DL/UL allocations happen via MPDCCH/PDSCH procedures.
Higher the cell bandwidth, higher the number of narrowbands, higher the number of eMTC UEs that can be allocated in a subframe.
However, this has to be weighed against allocations for LTE UEs.
Cross-subframe scheduling and HD-FDD operation of eMTC makes resource scheduling at eNB tricky
if it has to service both LTE and eMTC UEs.
Similar to HARQ retransmissions, repetitions improves the coverage.
Repetitions are supported for all types of information - System (MIB, SIB1-BR), Control (MPDCCH, PUCCH), and Data (PDSCH, PUSCH).
MPDCCH repetitions can be controlled separately based on search space.
PDSCH and PUSCH repetition information is contained in DCI transmitted over MPDCCH.
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MIB (PBCH)
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36.211:6.6 [8]
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SIB1-BR
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36.211:6.4.1 [8]
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MPDCCH
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36.213:9.1.5 [9]
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PUCCH
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36.213:10.1 [9]
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PDSCH
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36.213:7.1.11 [9]
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PUSCH
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36.213:8.0 [9]
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Refer 36.212:5.3.3.1 [10] for more details on DCI formats - 6.1 (for DL), 6.0 (for UL), and 6.2 (for Paging).
As repetitions reduce the capacity of the cell, it may have to be minimally used based on field requirements and field trials.
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