NPUSCH
The NPUSCH is used to transmit uplink data and uplink control information. The uplink subcarrier spacing is 3.75KHz and 15KHz. There are two transmission modes on the uplink: single tone transmission and multi-tone transmission, among which the single tone The subcarrier bandwidth includes 3.75KHz and 15KHz, and the Multi-tone subcarrier spacing is 15KHz, which supports transmission of 3, 6, and 12 subcarriers.
NPUSCH defines two formats: Format 1 and Format 2.
Format 1 is designed for uplink channel data on the UL-SCH. It uses the same Turbo code error correction as LTE, and its resource block size is much lower than LTE and no more than 1000 bits.
Format 2 is used for HARQ acknowledgment signaling of NPDSCH, transmits uplink control information (UCI), and uses a repetition code to correct errors.
The smallest unit mapped to the fast transmission is called a resource unit (RU), which is determined by the NPUSCH format and the subcarrier space. The uplink transmission resources are allocated in units of RU (Resource Unit), and the RU units of Single tone and Mulit-tone are defined as follows, and the number of scheduling RUs can be {1, 2, 3, 4, 5, 6, 8, 10} , indicated in NPDCCH N0.
The basic unit different from the resource allocation in the LTE system is a subframe, and the NB-IoT is used as a basic unit of resource allocation according to the number of subcarriers and the number of slots:

For NPUSCH format 1,
When the subcarrier space is 3.75 kHz, only single frequency transmission is supported. One RU includes one subcarrier in the frequency domain and 16 time slots in the time domain. Therefore, the length of one RU is 32 ms.
When the subcarrier space is 15 kHz, single-frequency transmission and multi-frequency transmission are supported. One RU contains 1 subcarrier and 16 time slots, and the length is 8 ms. When one RU contains 12 subcarriers, there are 2 time slots. The length, which is 1 ms, is just one subframe in the LTE system. The time length of the resource unit is designed to be a power of 2, in order to use resources more effectively, avoiding resource gaps and causing waste of resources.
For NPUSCH format 2,
The RU is always composed of 1 subcarrier and 4 time slots. Therefore, when the subcarrier space is 3.75 kHz, one RU duration is 8 ms; when the subcarrier space is 15 kHz, one RU duration is 2 ms.
The NPUSCH adopts the low-order modulation and coding method MCS 0`11, and the repetition times are {1, 2, 4, 8, 16, 32, 64, 128}.
DMRS
DMRS is used for channel estimation. The NPUSCH Format 1 format is the same as the LTE PUSCH slot structure, with 7 OFDM symbols per slot and one symbol in the middle as a DMRS. The Format 2 format is also 7 OFDM symbols per slot, but the middle 3 symbols are used as DMRS.
Physical channel of eMTC
The sub-frame structure of the eMTC is the same as that of the LTE. Compared with the LTE, the eMTC downlink PSS/SSS and CRS are consistent with the LTE, and the PCFICH and PHICH channels are cancelled, the LTE PBCH is compatible, and repeated transmission is added to enhance coverage. The MPDCCH is based on the LTE EPDCCH design. Supports repeated transmission, and PDSCH uses cross-subframe scheduling. The uplink PRACH, PUSCH, and PUCCH are similar to the existing LTE structure.
The eMTC can define up to four coverage levels, and each coverage level PRACH can be configured with different repetition times. The eMTC is classified into Mode A and Mode B according to the number of repetitions. Mode A has no repetition or fewer repetitions, and Mode B repeats more times.

▲ Maximum number of retransmissions of different channels of eMTC under Mode A and Mode B
Downstream:
PBCH
The eMTC PBCH is fully compatible with the LTE system with a period of 40 ms. The cell supporting the eMTC has a field indication. Repeated transmission is used to enhance coverage, and transmissions are repeated 5 times at a time.

MPDCCH
The MPDCCH (MTC Physical Downlink Control Channel) is used to transmit scheduling information. Based on the EPDCCH design of the LTE R11, the terminal receives control information based on the DMRS, and supports functions such as control information precoding and beamforming, and one EPDCCH transmits one or more ECCEs ( Enhanced Control Channel Element, enhanced control channel resource, aggregation level is {1, 2, 4, 8, 16, 32}, and each ECCE is composed of multiple EREGs (Enhanced Resource Element Group).

The MPDCCH maximum repetition number Rmax can be matched, and the value ranges from {1, 2, 4, 8, 16, 32, 64, 128, 256}.
PDSCH
The eMTC PDSCH is basically the same as the LTE PDSCH channel, but adds repetition and narrow-band frequency hopping for improving PDSCH channel coverage capability and interference averaging. The eMTC terminal can work in both ModeA and ModeB modes:
In Mode A mode, the maximum number of upstream and downstream HARQ processes is 8. In this mode, the number of PDSCH repetitions is {1, 4, 16, 32}.
In Mode B mode, the maximum number of uplink and downlink HARQ processes is 2. In this mode, the number of PDSCH repetitions is {4, 16, 64, 128, 256, 512, 1024, 2048 }
Upstream:
PRACH
The time-frequency domain resource configuration of the eACHC's PRACH follows the design of LTE and supports format 0, 1, 2, and 3. The frequency occupies 6 PRB resources, and the transmission between different repetition times supports narrowband inter-frequency hopping. Each coverage level can be configured with different PRACH parameters.
The PRACH channel obtains coverage enhancement by repetition, and the number of repetitions can be {1, 2, 4, 8, 16, 32, 64, 128, 256}.
PUCCH
The PUCCH frequency domain resource format is the same as that of LTE, and supports frequency hopping and repeated transmission.
Mode A supports the transmission of HARQ-ACK/NACK, SR, and CSI on the PUCCH, that is, supports PUCCH format 1/1a/2/2a, and the number of repetitions supported is {1, 2, 4, 8}; Mode B does not support CSI feedback. That is, only PUCCHformat 1/1a is supported, and the number of repetitions supported is {4, 8, 16, 32}.
PUSCH
The PUSCH is the same as LTE, but the maximum number of RBs that can be scheduled is limited to six. Supports Mode A and Mode B modes. The number of Mode A repetitions can be {8,16,32}, supports up to 8 processes, and the rate is higher. The ModeB coverage distance is longer. The number of repetitions can be {192,256,384,512,768,1024,1536. , 2048}, support up to 2 HARQ processes in the uplink