Cell Switch Off Technique Combined with Coordinated Multi-Point (CoMP) Transmission for Energy Efficiency in Beyond-LTE Cellular Networks Gencer Cili, Halim Yanikomeroglu, and F. Richard Yu Department of Systems and Computer Engineering, Carleton University, ON, Canada Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 1 ICC 2012 June 15, 2012
Introduction • Energy Efficiency of Cellular Systems became a major performance metric: Increased use of cellular devices -> 𝐷𝑃 2 emission rise in cellular networks - - Information and Communications Technology is responsible for 2-10% of global energy consumption - Access stratum is responsible for 60-80% the whole cellular network energy consumption - Energy Efficiency metric: Bits/Joule should be jointly considered with spectral efficiency metric • Methods for Energy Efficient Access Networks: - Energy efficiency in Base Stations - Energy efficiency using Cooperative Base Station Schemes - Energy Efficiency using renewable energy resources - Energy efficiency via heterogonous networks - Cognitive Radio & Cooperative relaying for Energy Efficiency Our contributions • - LTE-A Downlink CoMP used jointly with traditional Cell Switch Off Schemes - Model energy & spectral efficiency of CoMP + Cell Switch Off Schemes - Use DL CoMP to serve the users in switched off cell - Demonstrate CoMP challenges: Estimation Errors + System Delays Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 2 ICC 2012 June 15, 2012
Overview of Green Access Networks • Cell size adjustments according to traffic load fluctuations - Cells with the low traffic zoom into zero, and the neighbor cells zoom out by physical adjustments - Base stations with low Spectral Efficiency are turned off – Spectrally efficient BSs serve the users - 24- hour traffic routine is analyzed, optimum cell switch off/on periods are found - Ratio between the dynamic and the fixed power of a base station: Switch Off decision parameter 3GPP - Small Cell Switch Off Scheme [15]: Cell Switch Off Suggestion by Academia [6]: Proposal: Replace antenna tilt/Transmit power increase of active cells by DL CoMP to serve the users in the switched off cell. Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 3 ICC 2012 June 15, 2012
LTE Downlink Transmission and CoMP Procedures 𝑧 𝑂𝑂1 = 𝑦 𝑂𝑂𝑂 ℎ 𝑂𝑂1 + 𝑜 𝑂𝑂1 … 𝑧 1 ( 𝑙 ) 𝑦 1 ( 𝑙 ) 𝑦 𝑂 ( 𝑙 ) 𝑦 2 ( 𝑙 ) ℎ 1 ( 𝑙 ) 𝑜 1 ( 𝑙 ) ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ = + … 𝑧 𝑂 ( 𝑙 ) 𝑦 𝑂 ( 𝑙 ) 𝑦 𝑂−1 ( 𝑙 ) 𝑦 1 ( 𝑙 ) ℎ 𝑂 ( 𝑙 ) 𝑜 𝑂 ( 𝑙 ) 𝐼 𝑌 𝑂𝑂𝑂 𝐺 𝑧 𝑂𝑂1 = 𝐺 𝑂𝑂𝑂 𝑂𝑂𝑂 ℎ 𝑂𝑂1 + 𝑜 𝑂𝑂1 Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 4 ICC 2012 June 15, 2012
LTE Downlink Transmission and CoMP Procedures CoMP Definition: Dynamic coordination among multiple geographically separated points referred as CoMP cooperating set for downlink transmission and uplink reception Downlink CoMP Schemes: 1) Joint Processing: User Plane Data available at each Transmission Point 2) Coordinated Scheduling/Coordinated Beamforming: User Plane Data @ Serving Cell CoMP Deployment Scenarios: 1) eNB - eNB 2) RRH - RRH 3) eNB – High Power RRH 4) eNB – Low Power RRH Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 5 ICC 2012 June 15, 2012
CoMP + Cell Switch Off Model Cellular Layout + Parameters: 1) 19 eNBs with hexagonal layout 2) Center Cell Switched Off, 3) Remaining 18 eNBs are in CoMP Cooperating & Measurement Set 4) Uniform user distribution in the switched off cell 𝑗 ∈ [1, . . , 500] Cooperating Cell IDs: 𝑜 ∈ [1, . . , 18] 5) 6) Channel samples every TTI according to Winner SCME model: 𝑢 ∈ [1, . . , 1000] 7) Each UE-eNB link is modeled independently 8) Large scale path loss model according to ITU- R report M.2135 1500 1000 500 Distance (meters) 0 -500 -1000 -1500 -1500 -1000 -500 0 500 1000 1500 Distance (meters) Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 6 ICC 2012 June 15, 2012
CoMP + Cell Switch Off Model CoMP Transmission Set Forming: • Serving cell configures the UE for multi-point measurements for each eNB in CoMP measurement set CSI-RS enables Multi-Point Channel Estimation • • Actual measured received power from eNB n by user i at TTI t : 𝑄 𝑆𝑆 𝑜 , 𝑢 , 𝑗 = 𝑄 𝑈𝑆 𝑜 − 𝑄𝑄 𝑜 , 𝑗 − 𝑄 𝐺𝐺𝐺𝐺𝐺𝐺 𝑜 , 𝑗 , 𝑢 • • Implicit/Explicit multipoint channel feedback obtained at Serving Cell • Received feedback due to estimation error + delay: 𝑄 𝑆𝑆 _ 𝑓𝑓𝑓 𝑜 , 𝑢 , 𝑗 = 𝑄 𝑆𝑆 𝑜 , 𝑢 − ∆ , 𝑗 + 𝑄 𝑓𝑓𝑓 ( 𝜈 , 𝜏 ) • • Thresholded Decision to Form the CoMP Transmission Set: Serving Cell Power – Measured cell ≤ 3dB Time-varying CoMP Transmission Set: 𝐾𝐾 ( 𝑗 , 𝑢 ) • • Joint PDSCH transmission + Cross-point scheduling over certain time/frequency resources Note: Release-8 devices use CRS for channel estimation (8 REs over RB pair), but Rel -11 CoMP channel estimation uses CSI-RS (1 RE over RB pair per antenna port) = Multi-point channel estimation is more vulnerable to channel estimation errors due to scarce REs to track the channel using autocorrelation functions Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 7 ICC 2012 June 15, 2012
CoMP Performance Metrics - Capacity • Joint PDSCH transmission (TM-9) mitigates the Inter-cell Interference Single Point Transmission CoMP Downlink Transmission 𝑄 𝑡𝑓𝑓𝑡𝐺𝐺𝐺 𝑇𝑇𝑇𝑇 𝐷𝑂𝐷𝐷 = 𝑄 𝑡𝑓𝑓𝑡𝐺𝐺𝐺 + 𝑄 𝑘 + 𝑄 𝑛 𝑇𝑇𝑇𝑇 = 𝐿 ∑ 𝑄 𝐺 + 𝑄 𝑂𝑂𝐺𝑡𝑓 𝐿 ∑ 𝑄 𝐺 + 𝑄 𝑂𝑂𝐺𝑡𝑓 𝐺=1 𝑗=1 𝑗≠𝑘 , 𝑛 Total received Power from CoMP Transmission Set 𝑄 𝐾𝑈 ( 𝑗 , 𝑢 ) = � 𝑄 𝑆𝑆 𝑜 , 𝑢 , 𝑗 𝐺∈𝐾𝑈 ( 𝐺 , 𝑢 ) Perceived Downlink Capacity due to CoMP 𝑄 𝐾𝑈 ( 𝑗 , 𝑢 ) 𝐷 ( 𝑗 , 𝑢 ) = 𝐶𝐶 ( 𝑗 , 𝑢 ) ∗ log 2 (1 + ) 𝑄 𝑂𝑂𝐺𝑡𝑓 + ∑ 𝑄 𝑆𝑆 𝑜 , 𝑢 , 𝑗 𝐺∉𝐾𝑈 ( 𝐺 , 𝑢 ) Note: CoMP transmission set 𝐾𝐾 ( 𝑗 , 𝑢 ) is formed according to delayed and inaccurately estimated channel samples. 𝐶𝐶 ( 𝑗 , 𝑢 ) is dependent on the number of RBs assigned to UE Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 8 ICC 2012 June 15, 2012
CoMP Performance Metrics – Energy Efficiency CoMP Power Consumption Model 2 ) 𝑄 𝑇𝐷−𝐷𝑂𝐷𝐷 = 58 ∗ (0.87 + 0.1 𝑇 𝐷 + 0.03 𝑇 𝐷 Signal Processing Power 𝐷 𝐶𝐼 Backhauling Power 𝑄 𝐶𝐼 = 100𝑁𝑁𝑗𝑢𝑁 / 𝑁𝑡𝑡 ∗ 50𝐶 𝑂 𝑑 ∗ 2𝑂 𝐷 ∗𝑞∗𝑟 Additional Data capacity 𝐷 𝐶𝐼 = 𝑁𝑗𝑢𝑁 / 𝑁𝑡𝑡 𝑈 𝑇 for CoMP Backhauling 𝑄 𝑈𝑆 Total Power Consumption 𝑄 𝐷oMP = 𝑇 𝑡 ∗ 𝑇 ∗ + 𝑄 1 + 𝐷 𝐷 1 + 𝐷 𝐶𝐶 + 𝑄 𝐶𝐼 𝐷𝑄 𝑇𝐷 of an eNB using CoMP 𝑄𝑄 𝑓𝑓𝑓 𝑡𝑓𝑡𝑢𝑂𝑓 Power Consumption Parameters 𝑇 𝑡 = Number of Sectors 𝑇 = Power amplifiers per sector 𝑄 𝑈𝑆 = DL Transmit Power, 𝐷 𝐷 = Cooling Loss 𝑄𝑄 𝑡𝑡𝑑𝑡𝑡𝑡 𝐷 𝐶𝐶 = Battery Backup 𝑇 𝐷 = Number of points in Joint Transmission 𝑞 = pilot density 𝑟 = CSI signalling 𝐾 𝑇 = Symbol Period 𝑄𝑄 𝑓𝑓𝑓 = Power Amplifier Efficiency Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 9 ICC 2012 June 15, 2012
CoMP Performance Metrics – Energy Efficiency 𝐷𝐺𝑞𝐺𝑡𝐺𝑢𝐷 ( 𝑐𝐺𝑢𝑡 / 𝑡𝑓𝑡 ) 𝐷𝑂𝑄𝑓𝑓 𝐷𝑂𝐺𝑡𝐷𝑛𝑞𝑢𝐺𝑂𝐺 ( 𝐾𝑂𝐷𝐾𝑓𝑡 / 𝑡𝑓𝑡 ) = 𝑁𝑗𝑢𝑁 / 𝐾𝐾𝐾𝐾𝑡 Energy Efficiency = Time Varying Energy Efficiency Joint Transmission CoMP Operation ( 𝑇 𝐷 ≥ 2 ) 𝐹𝐹 ( 𝑗 , 𝑢 ) 𝐷 ( 𝑗 , 𝑢 ) = 𝑄 𝐷𝑂𝐷𝐷 + 𝑇 𝐾𝑈 ( 𝐺 , 𝑢 ) − 1 ∗ 𝑄 𝐷𝑂𝐷𝐷 − 𝑄 𝐶𝐺𝑡𝑓 𝐹𝐹 ( 𝑗 , 𝑢 ) = 𝐷 ( 𝑗 , 𝑢 ) Single Point Transmission ( 𝑇 𝐷 = 1 ) 𝑄 𝐶𝐺𝑡𝑓 Notes: 1) 𝑄 𝐶𝐺𝑡𝑓 has 𝑄 𝐶𝐼 = 0 since there is not need for multi-point CSI transfer to serving cell 2) 𝑄 𝑇𝐷−𝐷𝑂𝐷𝐷 = 58W since 𝑇 𝐷 = 1 Carleton University: G. Cili, H. Yanikomeroglu, F. R. Yu 10 ICC 2012 June 15, 2012
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