MIMO Power Save / Downgrade MIMO
MIMO Power Save / Downgrade MIMO
If power is not enough for full MIMO capability access points operate in MIMO Power Save / Downgrade MIMO mode. In this mode MIMO capability is reduced to match the max power available from POE injector or POE switch for access points.
For clients, dynamic MIMO Power Save technique allows MIMO-based (802.11n) radios to downshift to less-aggressive radio configurations when traffic loads are light.
MIMO and Power-over-Ethernet
One of the technologies in 802.11n that allows for higher data rates is multiple-input multiple-output (MIMO). In 802.11n MIMO capability is typically described as NxM:S meaning N transmitters, M receivers, and S streams. By using additional transmit and receive radio chains a device can reach the max data rate possible per stream (150 Mbps).
2×3:2, 3×3:2 and 3×3:3 systems are very common and allow data rates to reach 300 – 450 Mbps. The additional radio chains require additional electronics and therefore power. 802.3af POE is usually OK for an access point with one hardware radio but if a second or third is added additional power may be needed above the maximum 15.4 watts of DC power in 803.3af POE. The IEEE amendment for higher power POE is 802.3at and is commonly known as POE+ or POE Plus and provides up to 25.5 watts of DC power.
Always check vendor specifications for power requirements per device and radio. Some vendors may call MIMO Downgrade, MIMO Power Save Mode.
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Filed under: WLAN Deployment
