RSSI (Received Signal Strength Indicator) in LTE

Wireless communication today depends on more than just raw power—it depends on smart, precise understanding of signal behaviour. While LTE has brought incredible speed and reliability to the world of mobile communication, its success hinges on measurements like RSRP, RSRQ, SINR, and—foundationally—RSSI.

RSSI has been around since the early days of mobile networks. And although newer metrics have taken centre stage, RSSI still plays a vital role in assessing signal strength, troubleshooting coverage issues, and verifying network health. This article aims to uncover everything there is to know about RSSI in LTE, from basics to advanced deployment use cases.

What is RSSI?

RSSI (Received Signal Strength Indicator) is a measurement of the total power received by a device’s antenna across a given frequency bandwidth. It includes everything:

• Useful signal (your actual LTE data/control)
• Noise
• Interference
• Neighbouring signals

This makes RSSI a wide net—it doesn’t filter what’s good or bad—it just sums everything. It is measured in dBm (decibel-milliwatts) and is available at Layer 1 (PHY layer) of the LTE protocol stack.

Imagine standing in a crowded room trying to hear one person speak. RSSI tells you how loud the room is, not how clearly you can hear the person.

Why RSSI Still Matters in LTE

Although RSRP and SINR are more sophisticated and informative, RSSI remains crucial for:

• Cell search and selection in idle mode
• Initial signal acquisition
• Troubleshooting signal holes
• Calculating RSRQ, which uses RSSI as an input

Additionally, many low-level hardware and modem diagnostics still rely on RSSI due to its simplicity.

RSSI and LTE Signal Structure

In LTE, the downlink channel is structured into Resource Elements (REs). These REs carry:

• Reference Signals (CRS)
• Control Channels (PDCCH)
• Data Channels (PDSCH)
• Broadcast Channels (PBCH)
• Synchronization Signals (PSS/SSS)

RSSI aggregates power from all these elements. Specifically, it includes all OFDM symbols within the measured bandwidth that carry any signal (not just CRS).

How RSSI is Measured in LTE

At What Layer?

RSSI is measured at the Physical Layer (L1) of the UE or test equipment.

What is Included?

RSSI = wideband power = noise + serving cell power + interference power

RSSI includes:

• Power from reference signals
• Power from data/control channels
• Thermal noise
• Interference from other eNodeBs and non-LTE sources

Is RSSI Bandwidth Dependent?

Yes. LTE supports various channel bandwidths.

Since RSSI is a summation, the wider the bandwidth, the higher the RSSI value.

Bandwidth	Number of RBs	Impact on RSSI
1.4 MHz	6 RBs	Lower RSSI
3 MHz	15 RBs	Higher RSSI
5 MHz	25 RBs	Even higher
10 MHz	50 RBs	Increases
20 MHz	100 RBs	Max RSSI

RSSI vs RSRP vs RSRQ vs SINR

These four KPIs form the core of LTE radio measurement. Let’s compare them:

Metric	What It Measures	Includes	Purpose
RSSI	Total signal power	Data + control + noise + interference	Raw signal strength
RSRP	Reference signal power only	CRS	Coverage estimation
RSRQ	Signal quality vs. total power	RSRP and RSSI	Handover and quality
SINR	Signal vs. noise+interference	Precise quality	Throughput & decoding

RSSI, throughput, and modulation schemes

As RSSI improves (moves from -110 dBm to -50 dBm), the throughput increases.

The modulation scheme also shifts upward—from QPSK to 256QAM, indicating higher data-carrying efficiency at better signal strength.

RSSI Calculation and 3GPP Specifications

Defined in 3GPP TS 36.214, RSSI is: “The linear average over the total received power (in [W]) observed only in OFDM symbols containing reference signals, over the measurement bandwidth.”

RSSI=12*N*RSRP

RSRP is the average received power of one reference signal RE.
RSSI is the total received power over the entire bandwidth.
N is the number of RBs used in the RSSI measurement and varies with bandwidth.

Typical RSSI Ranges and What They Mean

RSSI doesn’t guarantee good service. High RSSI with low SINR = likely interference issues.

RSSI (dBm)	Quality
-44 to -65	Excellent
-66 to -75	Good
-76 to -90	Fair
-91 to -105	Weak
< -105	Poor coverage / likely unusable

Impact of RSSI on User Experience

High RSSI but low throughput? That’s common in interference-heavy environments.

Poor RSSI leads to:

• Poor MCS selection
• More retransmissions (HARQ)
• Lower throughput
• Voice quality degradation

Common Misconceptions About RSSI

• “High RSSI = good network” – Not always. Could be full of interference.
• “Low RSSI = bad quality” – Possibly, but clean channels can still work.
• “RSSI and RSRP are interchangeable” – False. RSRP is filtered, RSSI is raw.

Interference and RSSI Relationship

When interference is high:

• RSSI increases
• SINR drops
• RSRQ worsens

Engineers use this pattern to identify co-channel interference or overshooting cells.

RSSI in 5G vs LTE

5G still uses the concept of RSSI, but:

• It’s now SS-RSSI (from Synchronization Signal Block)
• Used in beam management for initial access
• 5G RSSI also combines multiple beams and frequencies

While RSRP, RSRQ, and SINR are the stars of LTE measurement, RSSI remains the original signal story-teller. It gives us the base layer of what the UE is receiving—useful or not.

If you’re building, optimizing, or troubleshooting LTE networks, ignoring RSSI is like ignoring the foundation of a building.

RSSI may not be refined, but it’s raw, honest, and always tells you something. It’s up to you to interpret it wisely.

References

1. CableFree. (n.d.). RSRP, RSRQ and RSSI Measurement in LTE.
2. TechTrained. (n.d.). LTE RSRP, RSRQ, RSSI Measurements – Explained.
3. 3GPP TS 36.214 V16.0.0. (2019). Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements. 3rd Generation Partnership Project (3GPP). Available at: https://www.3gpp.org/ftp/Specs/archive/36_series/36.214/
4. Dahlman, E., Parkvall, S., & Skold, J. (2016). 4G: LTE/LTE-Advanced for Mobile Broadband. Academic Press.
5. Rohde & Schwarz. (n.d.). Understanding LTE Signal Strength Parameters. Technical Whitepaper.
6. Keysight Technologies. (n.d.). Field Testing of LTE Networks: Signal Quality and RF Performance Metrics. Application Note.
7. Qualcomm. (n.d.). QXDM and LTE Signal Metrics Overview. Internal Training Material.