Optimization Thresholds Between Beamforming and MIMO in LTE/5G

TechRadar · July 9, 2025, 10:32am

In LTE and 5G, choosing the right Transmission Mode (TM) based on SINR levels and UE capabilities is key to improving spectral efficiency, coverage, and throughput.

This graph beautifully illustrates how each TM performs and when to switch between them during optimization.

Transmission Modes Explained:

TM7 – Single-Stream Beamforming
- Pure beamforming with a single layer
- Ideal for cell-edge users and low SINR areas
  Use when SINR < 5 dB
TM2 & TM3 – Traditional MIMO
- TM2 (open-loop) and TM3 (closed-loop with feedback)
- Both Support Rank 1 and Rank 2, but do not involve beamforming
- Suitable for moderate SINR environments
  Use when SINR is between 5–12 dB
TM8 – Dual-Stream Beamforming
- Closed-loop beamforming with 2 spatial streams
- Delivers both directional gain and spatial multiplexing
  Use when SINR > 12–15 dB
TM9 – 8-Stream Beamforming (Massive MIMO)
- Uses CSI-RS feedback and supports up to 8 layers
- Delivers best performance in excellent radio conditions with capable UEs
- Commonly used in TDD Massive MIMO deployments, especially in 5G NR and LTE-Advanced Pro
  Use when SINR > 18 dB

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Rajesh_kulhar · July 28, 2025, 12:22am

In the world of LTE & 5G, improving coverage and speed isn’t just about throwing more hardware — it’s about making smart decisions every millisecond.

One of the most powerful decisions the network makes is:
“Which Transmission Mode should I use for this user, right now?”

Behind this decision lies a lot of complexity — SINR reports, UE capabilities, and a whole set of predefined thresholds that help the network adapt automatically.

Transmission Modes – Real Field Logic:

TM7 – Single Beam, Single Hope
• Used for users struggling at the edge
• No fancy tricks — just one focused beam trying to hold on
When SINR < 5 dB

TM2 & TM3 – Old School MIMO
• Think of it as teamwork without direction
• Two antennas trying to help, but no beam steering
Best between 5–12 dB

TM8 – When Beamforming meets MIMO
• A powerful duo — spatial multiplexing + beam focus
Use when SINR > 12–15 dB

TM9 – The Powerhouse (Massive MIMO)
• 8-layer beamforming, precision-controlled via CSI feedback
• You need a strong UE and crystal-clear RF
Use when SINR > 18 dB

But how does the network decide all this?

That’s the real magic.

It’s not manual.
Not fixed.
The eNodeB/gNodeB is continuously analyzing:
• Who is the user?
• What’s their SINR now?
• What modes can their phone support?
• What happened in the last 10ms?

All this is fed into an automated logic engine that uses predefined SINR thresholds, sometimes even prediction algorithms, to choose the best TM in real time.

The network adapts like a smart chess player — picking the best move for every single UE, every moment.

The SINR thresholds and Transmission Mode (TM) mapping are aligned with 3GPP specifications — particularly TS 36.213 and TS 36.211 — which define the physical layer procedures and CSI-based feedback mechanisms.

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