Cat-NB, also known as NB-IoT, NB1, or Narrow Band IoT, is another LPWAN protocol governed by the 3GPP in release 13. Like Cat-M1, Cat-NB operates in the licensed spectrum. Like Cat-M1, the goal is to reduce power (10-year battery life), extend coverage (+20 dB), and reduce cost ($5 per module). Cat-NB is based on the Evolved Packet System (EPS) and optimizations to the Cellular Internet of Things (CIoT). Since the channels are much narrower than even the 1.4 MHz Cat-M1, cost and power can be reduced even further with the simpler designs of the analog-to-digital and digital-to-analog converters.

Significant differences between Cat-NB and Cat-M1 include:

• Very narrow channel bandwidth: As with Cat-M1, which reduced the channel width to 1.4 MHz, Cat-NB reduces it further to 180 kHz for the same reasons (reducing cost and power).
• No VoLTE: As the channel width is so low, it does not have the capacity for voice or video traffic.
• No mobility: Cat-NB will not support handover and must remain associated with a single cell or remain stationary. This is fine for the majority of secured and fastened IoT sensor instruments. This includes handover to other cells and other networks.

Regardless of these significant differences, Cat-NB is based on OFDMA (downlink) and SC-FDMA (uplink) multiplexing and uses the same subcarrier spacing and symbol duration. The E-UTRAN protocol stack is also the same with the typical RLC, RRC, and MAC layers, and remains IP-based but is considered a new air interface for LTE. 

Since the channel width is so small (180 kHz), it allows for the opportunity to bury the Cat-NB signal inside a larger LTE channel, replace a GSM channel, or even exist in the guard channel of regular LTE signals. This allows for flexibility in LTE, WCDMA, and GSM deployments. The GSM option is simplest and fastest to market. Some portions of the existing GSM traffic can be placed on the WCDMA or LTE network. That frees up a GSM carrier for IoT traffic. In-band provides a massive amount of spectrum to use as the LTE bands are much larger than the 180 kHz band. This allows for deployments of up to 200,000 devices in theory per cell. In this configuration, the base cell station will multiplex LTE data with Cat-NB traffic. This is entirely possible since the Cat-NB architecture is a self-contained network and interfaces cleanly with existing LTE infrastructure. Finally, using Cat-NB as the LTE guard band is a unique and novel concept. Since the architecture re-uses the same 15 kHz subcarriers and design, it can be accomplished with existing infrastructure.

The following figure illustrates where the signal is allowed to reside:

Since the Maximum Coupling Loss (MCL) is 164 dB, it allows for deep coverage in basements, tunnels, rural areas, and open environments. The 20 dB improvement over standard LTE is a 7x increase in the coverage area. The data rate obtainable is a function of the SNR and the channel bandwidth, as we have seen in Shannon-Hartley's theorem. For the uplink communication, Cat-NB will assign each UE one or more 15 kHz subcarriers in a 180 kHz resource block. Cat-NB has the option to reduce the subcarrier width to as low as 3.75 kHz, which allows more devices to share the space. However, one must carefully inspect the interference potential between edge 3.75 kHz subcarriers and the next 15 kHz subcarrier. 

Power management is very similar to Cat-M1. All the power management techniques in release 12 and 13 apply to Cat-NB as well (PSM, eDRX, and all the other features are included).