Description
Narrowband Reference Signal Received Power (NRSRP) is a key radio measurement specific to Narrowband Internet of Things (NB-IoT) and LTE-M (Cat-M1) technologies within the 3GPP LTE and 5G NR frameworks. It represents the linear average power received by a User Equipment (UE) over the resource elements that carry narrowband reference signals (NRS) within a specified measurement bandwidth, typically 180 kHz for NB-IoT. NRSRP is derived from the downlink reference signals transmitted by the base station (eNodeB in LTE, gNB in NR), which are designed for channel estimation and synchronization. The measurement process involves the UE demodulating these reference signals, which are spaced in time and frequency across the narrowband carrier, and calculating the received power in units of dBm. This value is crucial for evaluating signal strength in low-power, wide-area scenarios where IoT devices often operate in challenging radio conditions, such as deep indoors or rural areas. NRSRP is used by the UE for cell selection and reselection procedures, determining the best cell to camp on based on signal quality. It also informs handover decisions and power control mechanisms, ensuring reliable connectivity while minimizing battery consumption. The measurement is reported to the network via Radio Resource Control (RRC) signaling, enabling the network to optimize resource allocation and coverage. Compared to wider-band measurements like RSRP in legacy LTE, NRSRP is tailored for narrowband operations, providing accurate assessments in bandwidth-constrained environments essential for IoT deployments.
Purpose & Motivation
The purpose of Narrowband Reference Signal Received Power (NRSRP) is to address the unique requirements of IoT devices in cellular networks, particularly for NB-IoT and LTE-M technologies introduced in 3GPP Release 13 and beyond. Traditional LTE measurements like RSRP were designed for wider bandwidths (e.g., 1.4 MHz to 20 MHz) and higher data rates, which are inefficient for IoT devices that prioritize low power consumption, extended coverage, and operation in narrow bandwidths (e.g., 180 kHz). NRSRP was created to provide a precise signal strength measurement optimized for these narrowband carriers, enabling accurate cell evaluation in environments with limited spectrum and challenging propagation conditions. It solves problems like reliable cell selection in coverage-enhanced modes (e.g., up to 20 dB additional gain for NB-IoT), where devices need to detect very weak signals. The motivation stems from the proliferation of massive IoT applications, such as smart meters, sensors, and trackers, which require long battery life and robust connectivity in areas with poor signal strength. By introducing NRSRP, 3GPP enabled efficient radio resource management for IoT, supporting features like extended discontinuous reception (eDRX) and power saving mode (PSM), ultimately facilitating scalable and energy-efficient IoT deployments.
Key Features
- Measures received power of narrowband reference signals in 180 kHz bandwidth
- Used for cell selection, reselection, and handover in NB-IoT and LTE-M
- Supports coverage enhancement modes up to 20 dB gain
- Enables accurate signal assessment in low-power, wide-area scenarios
- Integrated with RRC signaling for network reporting and optimization
- Tailored for IoT devices with limited bandwidth and battery constraints
Evolution Across Releases
Defining Specifications
| Specification | Title |
|---|---|
| TS 32.857 | 3GPP TR 32.857 |
| TS 36.355 | 3GPP TR 36.355 |
| TS 37.355 | 3GPP TR 37.355 |