EMLMR (Enhanced Multi-Link Multi Radio)

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EMLMR (Enhanced Multi-Link Multi-Radio) is a key feature introduced in Wi-Fi 7 (IEEE 802.11be). Basically EMLMR is a multi-link operations (MLO) to enable devices with multiple radios to simultaneously transmit and receive data across different frequency bands (2.4/5/6GHz).

EMLMR Frame Exchange Sequence:

1. Multi-Link Association (Initial Setup)

Before data transmission, the AP and client negotiate MLO capabilities:

Outcome: Client is now associated on both 5GHz and 6GHz links.

2. Simultaneous Data Transmission (EMLMR Mode)

Once associated, the AP and client can exchange data on multiple links at the same time:

Scenario: Client downloads a 4K video stream (6GHz) while uploading sensor data (5GHz).

6GHz: Used for high-priority downlink (video).

5GHz: Used for best-effort uplink (sensor data).

No switching delays (true simultaneous Tx/Rx).

3. Multi-Link Block Ack (BA) Mechanism

Instead of per-frame ACKs, EMLMR uses Multi-Link Block Acknowledgments for efficiency:

Advantage: Reduces overhead compared to per-link ACKs.

Traditional Wi-Fi vs. EMLSR vs. EMLMR:

Feature	Traditional Wi-Fi	EMLSR (Single Radio)	EMLMR (Multi-Radio)
Radios	1	1	2+
Simultaneous MLO	❌ No	❌ (Switching)	✅ Yes
Throughput	Low	Medium	Highest
Latency	High	Medium	Lowest
Power Consumption	Low	Medium	High
Cost	Low	Medium	High

Scenario possible in EMLMR:

• AP transmits on 5GHz while receiving on 6GHz from client.
• Dynamic Load Balancing : AP intelligently distributes traffic across links based on:
  • Congestion (e.g., 5GHz crowded? Use 6GHz).
  • Latency requirements (e.g., gaming on 6GHz, backups on 5GHz).
• A device has separate radios for each band:
  • Radio 1: 2.4GHz
  • Radio 2: 5GHz
  • Radio 3: 6GHz

Benefits of EMLSR:

1. Zero Switching Overhead:
   • No delay between links (unlike EMLSR’s ~16–32 μs switching time).
2. Higher Capacity:
   • Example: 5GHz (1Gbps) + 6GHz (2Gbps) = 3Gbps total.
3. Better QoS (Quality of Service):
   • Critical traffic (e.g., Zoom calls) can be prioritized on one link while downloads run on another.

Use Cases:

High-end routers, laptops, AR/VR headsets, and enterprise APs.

• Wi-Fi 7 Routers (e.g., Qualcomm Networking Pro Series).
• Premium Laptops (e.g., Dell XPS with Intel Wi-Fi 7).
• Metaverse/VR Devices (low latency is critical).

Real-World Example:

1. 8K Video Streaming:
   • 6GHz for video + 5GHz for background downloads.
2. Cloud Gaming:
   • Ultra-low latency on 6GHz while 5GHz handles updates.
3. Enterprise Networks:
   • Multiple users split across bands for congestion-free performance.

Latency Values:

Scenario	Wi-Fi 6 (Single-Link)	EMLSR (Single-Radio)	EMLMR (Multi-Radio)
Cloud Gaming	25 ms	15 ms	3 ms
4K Video Call	20 ms	12 ms	2 ms
VR Motion-to-Photon	30 ms	18 ms	5 ms

Limitations:

1. Higher Power Consumption:
   • Multiple radios drain battery faster (not ideal for smartphones).
2. Cost:
   • Extra hardware (radios, antennas) increases device prices.
3. Interference Risk:
   • Requires advanced algorithms to avoid cross-link interference.

Conclusion:

EMLMR enables Wi-Fi 7’s multi radio with limited simultaneous multi-link to achieve low latency with higher cost and power than EMLSR.