# Suitability of NB-IoT for Indoor Industrial Environment: A Survey and Insights
## 2 Technical Background of NB-IoT
### The Standardization and Technology of NB-IoT
#### 2.3.2 NB-IoT and Its Features  
Some of the main features of NB-IoT are enhanced coverage range, low energy consumption rate meaning long battery life, capacity to connect a massive number of devices per cell, increased reliability, low cost of the terminal and various deployment modes. These features are briefly explained below. _Coverage and Latency_: NB-IoT gives better coverage as compared to the legacy LTE with 20 dB performance. This allows it to deliver to areas that are difficult to reach, such as basements, making it suitable for use in underground car parks. NB-IoT can achieve this coverage either by in-band, stand-alone, or guard band deployment modes. The 20 dB coverage enhancement is supported by retransmission and low-frequency modulation mechanisms. With the two retransmission tones (3.7 and 15 kHz) available for use, NB-IoT can retransmit using up to 128 bits for uplink and 2048 bits for downlink. The latency budget of NB-IoT is 10 s, but a lower latency of 6 s can be achieved for maximal coupling losses as simulated and specified in TR45.820 [1, 17]. Figure 8: A unique representation of the NB-IoT standardization process. The transmission tone feature, which enhances the coverage capability of NB-IoT is presented uniquely in a block diagram in Figure 10. The diagram presents the operational bandwidths of NB-IoT, 200 kHz for stand-alone deployment and 180 kHz for both in-bound and guard-band deployments. For the uplink transmission, NB-IoT uses a Single Carrier Frequency-Division Multiplexing Access (SC-FDMA) modulation scheme. With this modulation scheme, it operates at 3.75 or 15 kHz sub-carrier intervals. These single-tone carriers are at 32 and 8 ms, respectively. The transmission rates used are from 160 to 200 kb/s to achieve a large coverage range that is powered by its high spectral density. The downlink transmission, however, uses an OFDMA modulation scheme with only a 15 kHz sub-carrier interval. It also utilizes multi-tone carriers of 3, 6, and 12 ms that support 160 to 250 kb/s transmission rates. The coverage enhancement of NB-IoT to achieve a 20 dB was evaluated in [80], and it was shown that this is true as compared to the legacy LTE. _Low energy consumption_: The standardization process of the NB-IoT introduced the PSM and eDRX mechanisms for low energy consumption. In the PSM, the device remains registered to the network of transmission but usually enters a deep sleep mode and completely switches off most of its circuitry; at this stage, the device is not reachable from the network. Meanwhile, it could wake up at any time to transmit data when necessary. The eDRX is a temporary idle state that does not listen to the radio channel but periodically becomes active to receive paging messages from the network for possible incoming data before switching to PSM. This periodic activeness is guided by a specified timer, and the paging system is the process of monitoring the control channel for downlink or uplink data indication. Without any activity on the control channel and the expiration of the specified timer, the device switches from the idle state to the PSM state. These two basic features allow for the energy saving of NB-IoT, which surpasses the legacy LTE. Figure 11 shows the idle and paging states [13]. Timer T3324 is the time required to enter into deep sleep mode. Figure 9: Participating companies in NB-IoT standardization. Figure 11: The PSM and eDRX modes. Figure 10: Block diagram of transmission tone mechanism. _NB-IoT Deployment modes_: NB-IoT is stipulated by RP-151621 to be deployed in FDD transmission [15] and has three types of deployment modes. These include the stand-alone, in-band, and guard-band modes. Figure 12 presents these modes. The stand-alone is an independent type of deployment that utilizes a bandwidth of 200 kHz and does not overlap with the LTE frequency band. The guard-band is a deployment type that utilizes the guard frequency of the LTE or the edge band. It has a 180 kHz bandwidth allocation.