Cat-NB1
Understanding Cat-NB1
Narrowband Cellular IoT Standard
While Cat-M1 simplifies LTE to a 1.4 MHz bandwidth, some Internet of Things (IoT) applications require even simpler hardware and deeper signal penetration. Static devices like water meters, smart agriculture sensors, and parking monitors transmit small packets of data infrequently and do not require mobility handovers or voice support. To meet this demand, 3GPP defined the Cat-NB1 (Narrowband IoT, or NB-IoT) standard in Release 13. Cat-NB1 reduces the device complexity and power consumption to absolute minimums, allowing modules to operate on single-cell batteries for over a decade.
Cat-NB1 operates with an extremely narrow channel bandwidth of 180 kHz, which corresponds exactly to a single LTE Physical Resource Block (PRB). This allows cellular network operators to deploy NB-IoT flexibly within their existing LTE bands. Cat-NB1 supports three deployment modes: In-band (allocating one LTE PRB for NB-IoT), Guard-band (using the unused frequency blocks between adjacent LTE channels), and Standalone (using separate carrier frequencies, such as re-farmed GSM channels).
Subcarrier Spacing and Uplink Configurations
To optimize transmission efficiency, Cat-NB1 supports two subcarrier spacings (SCS) on the uplink: a standard 15 kHz spacing (matching LTE) and a narrow 3.75 kHz spacing. The 3.75 kHz spacing divides the 180 kHz channel into 48 subcarriers, which increases the power spectral density of the transmission. This high density improves the link budget by up to 20 dB compared to standard LTE, allowing signals to penetrate deep walls and reach underground equipment. Additionally, the uplink supports single-tone transmissions (using BPSK or QPSK), which minimizes peak-to-average power ratio (PAPR) and saves battery power.
Key Mathematical Relations
Technical Specifications Comparison
| Deployment Mode | Spectrum Requirements | Interference Risk | Power Overhead | Operator Strategy |
|---|---|---|---|---|
| In-Band | 1 PRB inside active LTE band | Moderate (competes with LTE traffic) | Low (uses LTE infrastructure) | Ideal for high-capacity urban LTE areas |
| Guard-Band | 1 PRB in LTE guard channel | Low (uses unused spectrum edge) | Low | Commonly used to preserve active LTE capacity |
| Standalone | Dedicated 200 kHz channel | Very Low (isolated spectrum) | Moderate (requires dedicated carrier) | Ideal for re-farming GSM/2G spectrum |
Frequently Asked Questions
What is the channel bandwidth of a Cat-NB1 transmission?
The channel bandwidth of Cat-NB1 is exactly 180 kHz. This is equivalent to one LTE Physical Resource Block (PRB), enabling highly flexible deployment within existing cellular spectrum.
Does Cat-NB1 support cell handover while connected?
No, Cat-NB1 does not support active-mode handover, meaning connected mode mobility. If a device moves between cell towers, it must disconnect, re-select the new cell in idle mode, and establish a new connection, which is optimized for static devices.
What are the three deployment modes of Cat-NB1?
The three modes are In-Band (uses a resource block within an active LTE carrier), Guard-Band (uses the guard band between active carriers), and Standalone (uses a dedicated 200 kHz channel, typically from re-farmed GSM spectrum).