Energy-efficient femtocell: Practical implementation

Energy-efficient femtocell: PracticalimplementationIvaylo Haratcherev / ALU Bell Labs France03 October 2012

Problem statement (In a nutshell)• Densification -> large % of non-utilization• Flat P/load curve -> femto consumes fixed amount all the time -> no RF Power adaptation• Additional problems – periodic (regular) emissions -> lead to interference and RF pollution P P0 load

Approach• Switch off when not needed • What do we switch off? • How much power do we save? • What effort (HW/SW redesign) + price (important for industry)?• Switch on when needed • What triggers wake-up? • How wake-up signal gets to the femto? • What is the penalty in terms of wake-up delay

Evolution of the prototype1. With additional (external) wake-up channel – Wi-Fi• Pros • Independent and reliable solution v1 • Next-gen femtocells multi-standard (Wi-Fi + 3G + LTE) • Wi-Fi available in all recent smartphones • Wi-Fi and 3G have the same coverage• Cons • Not all phones have Wi-Fi (but fewer and fewer) • Still another radio active (but more efficient)2. RF probing• Pros • Universal • More energy-efficient v2 • No additional HW• Cons • Complexity

Current mode of operation• When all users leave femtocell coverage the femto goes on standby• An user comes into coverage and briefly switches on Wi-Fi• The Wi-Fi AP detects the user, authenticates it, and wakes-up the femto• The femto goes in fully operational mode, and the user’s 3G can connect UE 3G WiFi AP 3G WiFi Femto ))) 1 - 802.11 beacon Δdetect data connection 2 - 802.11 Probe Req 3 - Wake-up Req (3G) 5 - 802.11 Probe Rsp 4 - Wake-up Rsp Δwakeup 3G Femto Eth link ))) 6 - 3G connection establishment Δ3gconnect proximity & wake-up (Wi-Fi) WiFi AP 3G connection established

Results 140 120 100% 100 Wakup time, s 3G connection 80 Cell w ake-up 60 Proximity detection 40 50-90% XX% - potential 20-50% power saving 20 0 standby hibernate off Energy saving m ode• Simple femto electrical power estimation model PTOT = P0 + PRF + PTCXO_H + αB + nPLED , where: P0 – base power consumption (BB + ETH + MEM + TCXO + PowerSupply) PRF – RF power consumption (ADC/DAC + TRx + PA) PTCXO_H – TCXO heater power consumption B – Backhaul data rate PLED – indicator LED power consumption

Conclusions• Current state • V1 experience: • Total time for wakeup negligible longer than standard association time • UE de-association sometimes unreliable • 20% power saving • Simple model sufficient for power estimation• Next steps • Integration with TREND-Meter • Working on V2: • Without external wake-up channel • More options for power management (e.g. macro, house automation API, etc.) • 80-90% potential power savings

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Energy-efficient femtocell: Practical implementation

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