What is SINR (Signal-to-Interference-plus-Noise Ratio) in LTE and 5G

In modern cellular systems (LTE, 5G NR), one of the key performance indicators for the downlink (and uplink) is SINR, the Signal-to-Interference-plus-Noise Ratio. While metrics like RSRP (Reference Signal Received Power) describe how strong the signal is, SINR goes a step further and tells us how clean that signal is relative to unwanted interference and noise.

SINR is central to decisions for modulation & coding, scheduling, throughput capacity, and ultimately user experience.

SINR is defined as the ratio of the power of the desired useful signal to the sum of the power of interfering signals plus the noise power. In symbols:

Where:

• S= Received useful signal power
• I= Interference power (from other cells, UEs, sources)
• N= Noise power (thermal noise, receiver noise)

In decibels:

This aligns with standard definitions used in wireless communications.

In LTE, unlike RSRP or RSSI, SINR is typically a UE‐internal or chipset measurement (not always standardized in 3GPP in the same way) and its exact measurement procedure can vary by vendor.

Why SINR matters

• Signal Quality vs Strength – You can have a strong signal (good RSRP) yet very low SINR if interference is high. Low SINR limits achievable throughput and usability.
• Modulation & Coding – Higher SINR allows higher order modulation (64QAM, 256QAM) and higher code rates. Lower SINR forces conservative modulation & coding (QPSK, lower rates).
• Throughput & Capacity – SINR directly influences spectral efficiency (bits/s/Hz). In practical terms, a UE with say 20 dB SINR will get much higher throughput than one with 2 dB.
• Coverage & Mobility – At the cell edge or interference heavy zones, SINR drops , more retransmissions (HARQ), higher error rate, mobility/handover failures, link outages.
• Beamforming / MIMO (5G) – In 5G Systems, beamforming and advanced antennas are used to raise SINR by reducing interference and focusing signal power, thus enhancing capacity and reliability.

How SINR is Measured & Reported

• In LTE, UE hardware may compute SINR over Resource Blocks or Reference Signal symbols. Some sources note that SINR is not strictly defined by 3GPP for UE measurement and reporting in some builds.
• In 5G NR, SINR becomes more formalized: for example, SS-SINR (Synchronization Signal blocks) or CSI-SINR (CSI-RS reference) can be defined.
• Reporting: Many UEs report a coded value which maps via table to dB value. For example, in 5G, value 0 might map to SINR < -23 dB, value 127 to > 40 dB.

Thus, while RSRP/RSRQ are standardized broadly, SINR measurement details may vary between devices and vendors.

Typical SINR Ranges and Interpretation

Here is a guideline for SINR interpretation (downlink):

SINR (dB)	Approximate Quality	Typical implications
> 20 dB	Excellent	High order modulation, high throughput possible
~13 – 20 dB	Good	64QAM likely stable
~5 – 13 dB	Moderate	Possibly 16QAM, modest throughput
~0 – 5 dB	Poor	Likely QPSK, lower throughput, higher error rate
< 0 dB	Very poor	Link likely unusable, high failure rate

Relationship with RSRP / RSRQ / RSSI

• RSRP measures the average received power of the reference signals (strength only).
• RSRQ (Reference Signal Received Quality) gives relative quality via the ratio of RSRP to RSSI (which includes interference + noise + total received power).
• SINR complements these by focusing on the useful signal versus interference+noise.

1. You may see good RSRP but low SINR if interference is high (i.e., many neighbouring cells or uplink noise).
2. Conversely, moderate RSRP but high SINR may mean clean band and good throughput.

Engineers often use all these together:

• RSRP – tells about coverage (signal strength)
• RSRQ – signals quality of that strength under load/interference
• SINR – more predictive of throughput and link performance.

• RSRP (Signal Strength) is necessary but not sufficient for High Throughput. Observing the entire range of RSRP values (x-axis), you can see that for any given signal strength (e.g., around -90 dBm), throughput ranges from near zero up to 100 Mbps. This wide variance demonstrates that simply having a strong signal does not guarantee good performance.
• RSRQ/SINR (Signal Quality) determines the achievable Throughput. High throughput (points clustered near 100 Mbps on the y-axis) is almost exclusively achieved by data points with High RSRQ (yellow/light green) and Large SINR (large circles). This illustrates the key engineering principle that high interference (low RSRQ/SINR) limits performance even when the signal strength (RSRP) is excellent.

Enhancing SINR (Both Network & UE Measures)

Network side

• Use interference coordination (ICIC, eICIC, FeICIC)
• Employ beamforming and massive MIMO to boost signal and reduce interference
• Optimize antenna tilt/patterns so that overlapping cells don’t cause strong inter-cell interference
• Manage cell load and scheduling to limit interference in dense deployments

UE side

• Better shielding from interference: avoid moving device near metal surfaces, deep indoors etc.
• Use external antenna (if applicable) or move closer to the window/outdoors
• Ensure UE firmware/RF is updated (some interference mitigation algorithms help)
• In 5G devices, pick cells/beams with higher SINR (where UE reports beam quality)

SINR and Modulation/CQI/MCS Mapping

SINR is the primary driver of modulation selection.
Below is a practical mapping table (varies by vendor):

SINR Range (dB)	Likely MCS	Modulation
> 20 dB	High MCS	256QAM
13–20 dB	Mid-high MCS	64QAM
5–13 dB	Mid MCS	16QAM
0–5 dB	Low MCS	QPSK
< 0 dB	Very low MCS	Robust QPSK or no data

SINR in LTE vs 5G NR Differences

• In LTE: SINR concept exists, but measurement/reporting architecture is less formalised compared to RSRP/RSRQ.
• In 5G NR: SINR is more emphasised, e.g., SS-SINR or CSI-SINR. UE measurement capabilities include SINR reporting in some bands.
• Beamforming and wide bandwidths in 5G make SINR improvement an essential part of achieving very high throughput (e.g., mmWave, large carrier aggregation).
• Interference patterns in 5G may differ (with small cells, heterogeneous deployments), so managing SINR becomes even more critical.

SINR is a quality metric — it tells how cleanly a UE is receiving the signal in the presence of interference and noise. While strength (RSRP) and simple quality (RSRQ) tell useful parts of the story, SINR gives a more direct insight into throughput capability and link reliability. Good SINR leads to higher modulation, higher throughput, better user experience; poor SINR leads to limited performance, more errors, lower capacity.

For anyone working on LTE, 5G, O-RAN or similar telecom systems: monitoring SINR (alongside RSRP/RSRQ) is essential for coverage mapping, performance optimization, mobility design, and capacity planning.

References

• 3GPP TS 36.101 — E-UTRA; User Equipment (UE) Radio Transmission and Reception.
• 3GPP TS 36.104 — E-UTRA; Base Station (BS) Radio Transmission and Reception.
• 3GPP TS 36.213 — Physical Layer Procedures.
• 3GPP TS 36.331 — Radio Resource Control (RRC).
• 3GPP TS 38.101 — NR; User Equipment Radio Transmission and Reception.
• 3GPP TS 38.104 — NR; Base Station Radio Transmission and Reception.
• 3GPP TS 38.211 — NR; Physical Channels and Modulation.
• 3GPP TS 38.214 — NR; Physical Layer Procedures for Data.
• 3GPP TS 38.215 — NR; NR Physical Layer Measurements.
• Dahlman, Parkvall, Sköld — 4G: LTE/LTE-Advanced for Mobile Broadband.