Energy Efficient Wireless Communications

1. Energy Eﬃcient Wireless Communications Jingon Joung ACT: Advanced Commun. Tech. Dept. I2 R: Institute for Infocomm Research A⋆ STAR: Agency for Science, Technology, And Research, Singapore Tutorial 2: The 14th International Conference on Electronics, Information and Communication (ICEIC’2015), Singapore 29 January 2015 Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 1 / 112

2. Index 1 Introduction and Background (35 min, 24 pages) Green Wireless Communications Efficiency in Communications Theoretical Spectral Efficiency (SE) Energy Efficiency (EE) Tradeoff Practical SE-EE Tradeoff 2 Technologies for Energy Efficiency (20 min, 11 pages) Device-Level Approach System-Level Approach Network-Level Approach 3 Review (30 min, 60 pages) PA Switching/Selection (PAS) Method Large-scale Distributed-Antenna Systems (L-DAS) 4 Conclusion and QnA (5 min, 3 page) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 2 / 112

5. Green Wireless Communications • Green – to reduce energy consumption – to reduce CO2 emission Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 5 / 112

6. Green Wireless Communications • Green Information & Communications Tech. (ICT) [1] – the 5th largest industry in power consumption – energy consumption: 3% (2007’) – CO2 emission: 2% (2007’) will increase X35, 4% (2020’) – e.g., cellular networks: ƒ energy: 77.5 TWh (2/60/3.5/10 TWh for 3b/4MM/20,000/etc. subscribers/radio stations/radio controllers/others) ƒ CO2: 35 Mt (1/20/2/5 Mt for “ ) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 5 / 112

7. Green Wireless Communications • Wireless access communication networks consume significant amount of energy to overcome [2] – fading, distortion, degradation (path loss) – obstacles, interferences TX wirelesschannel RX Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 5 / 112

8. Green Wireless Communications • The energy is mostly consumed at the transmitter • e.g., 80-85% power at base station (BS) in cellular networks [2] Base Band Module D A C Informationbinarybits Filter Filter LO LFTPA Attn. control DC control Mixer VGA Synthethesizer Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 5 / 112

9. Green Wireless Communications • 50–80% of transmitter’s power is consumed at power amplifier (PA) [3] PA input signal output signal DC Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 5 / 112

10. References [1]: [McK, 2007] [Fettweis and Zimmermann, 2008] [Mancuso and Sara Alouf, 2011] [Chatzipapas et al., 2011] [2]: [Richter et al., 2009] [Baliga et al., 2011] [Vereecken et al., 2011] [Chatzipapas et al., 2011] [Joung and Sun, 2012] [3]: [Gruber et al., 2009] [Bogucka and Conti, 2011] [Joung et al., 2012a] [Joung et al., 2014c] [Joung et al., 2013] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 6 / 112

11. Green ICT Projects & Consortiums C2Power: Project, EU, Jan. 2010–Dec. 2012 - cognitive radio and cooperative strategies - power saving in multi-standard wireless devices eWIN, Project, KTH, Sweden ECOnet: low Energy COnsumption NETworks, EU, Oct. 2010–Sept. 2013 - dynamic adaptive technologies G-MC2: Project, Green Multiuser-MIMO Cooperative Communications, I2 R, Singapore, Jan. 2012–Dec. 2014 GREENET: Consortium, green wireless networks, EU GREENT: Consortium, green terminals for next generation wireless systems, EU CO2GREEN Project: Spain - cooperative and cognitive techniques - green wireless communications GreenTouch: Consortium, architecture, speciﬁcations and roadmap, since 2010 earth: Project, Energy Aware Radio and neTwork tecHnologies Green Radio: mobile virtual center of excellence (VCE) and personal communications, UK Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 7 / 112

13. What’s Efficiency? Efficiency: has widely varying meanings in different disciplines “refers to the use of resources so as to maximize the production of goods and services” – economics “is an important factor in determination of productivity” – business “describes the extent to which time, effort or cost is well used for the intended task or purpose” – wikipedia “is the ratio of the energy developed by a machine, engine, etc., to the energy supplied to it” – dictionary Efficiency in general η valuable resource produced valuable resource consumed Efficiency in communications? Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 9 / 112

16. Efficiency in Communications valuable resource produced in comm: information, coverage, subscribers, ... valuable resource consumed in comm: frequency, space, time, power, ... Spectral Efficiency (SE) and Energy Efficiency (EE) SE, b/s/Hz: number of reliably decoded bits per channel use [Cover and Thomas, 2006, Verdú, 2002, Chen et al., 2011] - Shannon (channel) capacity, data rate (throughput), goodput EE, b/J: number of reliably decoded bits per energy - various EEs in communications Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 10 / 112

19. Various EEs in Comms. Table 1: Various EEs [Richter et al., 2009, Tombaz et al., 2011, Hasan et al., 2011, Zhou et al., 2013, Joung et al., ]. Metric Type Units power usage efficiency facility-level ratio (≥ 1) data center efficiency facility-level % telecommun. energy effi. ratio equipment-level Gbps/W telecommun. equipment energy effi. rating equipment-level − log(Gbps/W) energy consumption rating equipment-level W/Gbps area power consumption network-level Km2 /W user power consumption network-level users/W network energy effi. with delay effect network-level dB/J pecuniary efficiency network-level bits/$ Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 11 / 112

21. Theoretical SE-EE Tradeoff SE, b/s/Hz EE,b/J Figure 1: Theoretical SE-EE tradeoff. Figure 2: Ideal power consumption. SE = log2(1 + Pout/σ2 ): Gaussian signalling, perfectly linear PA [Cover and Thomas, 2006] EE = Ω SE Pc : ideal power consumption model in Fig. 2 [Verdú, 2002, Chen et al., 2011] [Pout: transmit power; σ2: noise power; Ω: total bandwidth] Convex and wide (good) tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 13 / 112

22. Theoretical SE-EE Tradeoff SE, b/s/Hz EE,b/J Figure 1: Theoretical SE-EE tradeoff. Pc PPA Pout== Figure 2: Ideal power consumption. SE = log2(1 + Pout/σ2 ): Gaussian signalling, perfectly linear PA [Cover and Thomas, 2006] EE = Ω SE Pc : ideal power consumption model in Fig. 2 [Verdú, 2002, Chen et al., 2011] [Pout: transmit power; σ2: noise power; Ω: total bandwidth] Convex and wide (good) tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 13 / 112

23. Theoretical SE-EE Tradeoff SE, b/s/Hz EE,b/J 1 σ2 ln 2 Figure 1: Theoretical SE-EE tradeoff. Pc PPA Pout== Figure 2: Ideal power consumption. SE = log2(1 + Pout/σ2 ): Gaussian signalling, perfectly linear PA [Cover and Thomas, 2006] EE = Ω SE Pc : ideal power consumption model in Fig. 2 [Verdú, 2002, Chen et al., 2011] [Pout: transmit power; σ2: noise power; Ω: total bandwidth] Convex and wide (good) tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 13 / 112

25. Practical PA Package (a) SM2122-44L (b) SM0822-39 Figure 3: (a) High power PA with Pmax out = 25 W(44 dBm) and g = 55 dB. Frequency band 2.1 GHz −2.2 GHz. (b) Low power PA with Pmax out = 8 W and g = 45 dB. PA: a type of electronic amplifier - converts a low-power RF signal into a larger signal of significant power - typically, for driving the antenna of a transmitter Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 15 / 112

26. Basic Circuit Model of PA ACRF-drive,Pin DC input, PDC PAoutput,Pout Power Amplifier (PA) Figure 4: Power amplifier model with field-effect transistor (FET) [Cripps, 2006, Kazimierczuk, 2008]. Transistor is a core semiconductor device: amplifies and switches electronic signals and electrical power changes a voltage or current: terminals (G,D) to terminals (S,D) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 16 / 112

27. Basic Circuit Model of PA ACRF-drive,Pin DC input, PDC PAoutput,Pout gate drainsource transistor RFC DC blocking capacitor inputnetwork outputnetwork resistor Figure 4: Power amplifier model with field-effect transistor (FET) [Cripps, 2006, Kazimierczuk, 2008]. Transistor is a core semiconductor device: amplifies and switches electronic signals and electrical power changes a voltage or current: terminals (G,D) to terminals (S,D) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 16 / 112

28. Ideal PA Linearity 0 0.5 1 1.5 2 0 0.2 0.4 0.6 0.8 1.0 1.2 normalized input signal amplitude, |vin| normalizedoutputsignalamplitude,|vout| (a) −30 −20 −10 0 10 −1 0 1 input power, dBm normalizedgain,dB (b) −30 −20 −10 0 10 −1 0 1 input power, dBm phaseshift,degree (c) Figure 5: (a) and (b): Dynamic amplitude-to-amplitude modulation (AM/AM) distortion characteristics. (c) amplitude-to-phase modulation (AM/PM) characteristic. between RF input and output signals, i.e., Pin and Pout Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 17 / 112

29. Ideal PA Eﬃciency 5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 PDC dBm Pout(Pmax)dBm Figure 6: Maximum output power at linear region versus PA power consumption. between input and output signals, i.e., Pout/PDC. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 18 / 112

30. Linearity Models [Teikari, 2008] Transistor-level System-level accurate yet difficult to obtain, generalize or analyze a few parameters obtained from measurements, tractable, and reasonably accurate PA Linearity Models [23][Vuolevi et al., 2000], [24][Boumaiza and Ghannouchi, 2003], [25][Gadringer et al., 2005], [26][Morgan et al., 2006], [27][Kim and Konstantinou, 2001], [28][Jeruchim et al., 2000] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 19 / 112

31. Linearity Models [Teikari, 2008] Transistor-level System-level Memory Memoryless accurate yet difficult to obtain, generalize or analyze a few parameters obtained from measurements, tractable, and reasonably accurate a frequency-domain fluctuation due to the capacitance and Inductance in the circuits and the thermal fluctuation of the PAs, i.e., an electrical and thermal memory effects, respectively [23,24] Volterra series model [25] Wiener, Hammerstein models [26] Memory polynomial [27] previous PA output signal does not affect the current PA output signal PA Linearity Models [23][Vuolevi et al., 2000], [24][Boumaiza and Ghannouchi, 2003], [25][Gadringer et al., 2005], [26][Morgan et al., 2006], [27][Kim and Konstantinou, 2001], [28][Jeruchim et al., 2000] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 19 / 112

32. Linearity Models [Teikari, 2008] Transistor-level System-level Memory Memoryless Passband Baseband accurate yet difficult to obtain, generalize or analyze a few parameters obtained from measurements, tractable, and reasonably accurate a frequency-domain fluctuation due to the capacitance and Inductance in the circuits and the thermal fluctuation of the PAs, i.e., an electrical and thermal memory effects, respectively [23,24] Volterra series model [25] Wiener, Hammerstein models [26] Memory polynomial [27] previous PA output signal does not affect the current PA output signal difficult to do simulation and computation Nonlinearity of complex baseband frequency approximation is captured simply [28] PA Linearity Models [23][Vuolevi et al., 2000], [24][Boumaiza and Ghannouchi, 2003], [25][Gadringer et al., 2005], [26][Morgan et al., 2006], [27][Kim and Konstantinou, 2001], [28][Jeruchim et al., 2000] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 19 / 112

33. Memoryless Baseband PA Models Generic model: simplified baseband model for tractable analysis Ideal model for analysis: y = gx, where x and y are PA input and output signals; and g > 0 is a linear gain. Linear model for analysis [Minkoff, 1985]: y = gx + n, where n is the nonlinear distortion that is independent of x and modeled as Gaussian noise based on Bussgang’s theorem [Bussgang, 1952]. Soft limiter model for analysis [Tellado et al., 2003]: y = γ (|x|) e2πjΦ(|x|) - γ(·): amplitude-dependent gain function - Φ(·): phase shift function γ (|x|) |x|, if |x| < vsat, vsat, otherwise, Φ(|x|) 0 where vsat is a saturation output amplitude. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 20 / 112

37. Memoryless Baseband PA Models PA-specific model: accurate baseband model specified to PA type Saleh model for traveling wave tube amplifier [Saleh, 1981]: γ (|x|) a1|x| 1 + a2|x|2 ; Φ(|x|) b1|x|2 1 + b2|x|2 where ai and bi are the distortion coefficients Ghorbani model for FET PA and for low amplitude nonlinearity [Ghorbani and Sheikhan, 1991]: γ (|x|) a1|xa2 | 1 + a3|xa2 | + a4|x|; Φ(|x|) b1|xb2 | 1 + b3|xb2 | + b4|x| Rapp model for envelope characteristic of solid state PA (especially, class-AB) [Rapp, 1991, Falconer et al., 2000]: γ (|x|) |x| 1 + |x| vsat 2p − 1 2p ; Φ(|x|) 0 where p is a smoothness factor. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 21 / 112

41. PA Linearity = Nonlinear 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 1.0 1.2 Ideal model Linearized model (35dB) Soft limiter model Rapp model (p=10) Rapp model (p=2) Saleh model Ghorbani model p=10 p=2 normalized input signal amplitude, |vin| normalizedoutputsignalamplitude,|vout| Figure 7: AM/AM distortion characteristics for various baseband PA models. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 22 / 112

42. Efficiency Models Efficiencies of PA [Kazimierczuk, 2008, Raab et al., 2002] 1 Drain efficiency: ηD Pout PDC 2 Power-added efficiency (PAE): ηPAE Pout−Pin PDC = ηD 1 − 1 g 3 Overall efficiency: ηO Pout PDC+Pin Typically η ηD ≃ ηPAE ≃ ηO, ∵ Pin ≪ PDC, Pin ≪ Pout Two important factors Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 23 / 112

45. PA Eﬃciency < 100% 5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 30 35 40 45 50 55 20% drain efficiency line 30% drain efficiency line 100% drain efficiency line PAs: 0−1 GHz PAs: 1−2 GHz PAs: 2−3 GHz PAs: 3−4 GHz PAs: 4−5 GHz PDC dBm Pout(Pmax)dBm Figure 8: Maximum output power (at the linear region) versus PDC. η < 100% [Raab et al., 2003a] Typically between 20% and 30% [Joung et al., 2012a] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 24 / 112

46. PA Efficiency Drop 0 5 10 15 20 25 28 30 34 40 45 50 0 10 20 30 40 50 60 70 Power-addedefficiency(PAE),ǫ% Pout dBm SKY65162-70LF optimal matching Doherty class-AB MAX2840 RF2132 RF2146 SST13LP01 AN10923 Doherty 21180 Figure 9: PAE versus Pout. η usually drops rapidly as the output power decreases [Shirvani et al., 2002] a peak η is achieved at the peak envelope power (PEP) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 25 / 112

47. PA Classes Table 2: Examples of PA Classes [Raab et al., 2002, Raab et al., 2003a, Raab et al., 2003b]. Class Linearity Efficiency Utilization Factor Main Applications A high ≤ 50% 0.125 millimeter wave (30-100GHz) 4W/30%/Ka-band 250mW/25%/Q-band 200mW/10%/W-band B high ≤ 78.5% 0.125 broadband at HF and VHF C ≤ 85% - high-power vacuum-tube Tx D low ≤ 100% 0.159 100W to 1kW HF E low ≤ 100% 0.098 high-efficiency at K-band 16W with 80% efficiency at UHF 100mW with 60% efficiency at 10GHz F low very high ≥ 50% from 0.125 to 0.159 UHF and microwave (operation) class: amplification method power-output capability (transistor utilization factor): output power (# of transistor)×(peak drain voltage)×(peak drain current) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 26 / 112

48. Applications of PAs HF VHF UHF L S C X Ku K Ka V W G THF 3M 30M 300M 1G 2G 12G 18G4G 8G 26.5G 40G 110G 300G 3T3G 75G (1-300M) Comm. Submarines (3-30K) AM broadcasts (153K-26M) Navigation FM (87.5-108M) TV (54M-890M, VHF, UHF) Weather radio (162M) Aircraft comm. Land/maritime mobile comm. RFID (ISM band) Shortwave Broadcasts Citizens' band radio Over-the-horizon radar/comm. Amateur radio (3G-30G) WLAN 802.11a/ac/ad/n (5G) DBS (10.7G-12.75G) Satellite comm./TV (C,Ku,Ka) Microwave devices/communications Modern radars Radio astronomy Amateur radio (30G-300G) LMDS (26G-29G, 31G-31.3G) WLAN 802.11ad (60G) HIgh-frequency microwave radio relay MIcrowave remote sensing DIrected-energy weapon MIllimeter wave scanner Radio astronomy Amateur radio (1T~) Terahertz imaging Ultrafast molecular dynamics Condensed-matter physics Terahertz time-domain spectroscopy Terahertz computing/communications Sub-mm remote sensing Amateur radio (300M-3G) FRS/GMRS (462M-467M) ZigBee (ISM: 868M,915M,2.4G) Z-Wave (900M) DECT/Cordless telephone (900M) GPS (1.2,1.5G) GSM (900M,1.8G) UMTS (2.1G) LTE (698M-3.8G) WLAN (802.11b/g/n/ad 2.4G) Bluetooth (2.4-2.483.5MHz) BAN/WBAN/BSN (2.36G-2.4G) UWB (1.6G-10.5G) Modern Cordless telephone (1.9G,2.4G,5.8G) Si LDMOS GaN-HEMT Si RF CMOS SiGe-HBT, SiGe-BiCMOS GaAs-HBT, GaAs-pHEMT InP-HBT InP-HEMT, GaAs-mEHMT SiC-MESFET 0 Figure 10: Power amplifier applications over IEEE bands [Joung et al., 2014b]. FET: field effect transistor MOSFET: metal oxide semiconductor FET MESFET: metal epitaxial semiconductor FET DMOS: diffued metal oxide semiconductor LDMOS: laterally DMOS CMOS: complementary metal oxide semicond. BiCMOS: bipolar CMOS HBT: heterojunction bipolar transistor HEMT: high electron mobility transistor mHEMT: metamorphic HEMT pHEMT: pseudomorphic HEMT SiGe: silicon Germanium GaAs: Gallium Arsenide GaN: Gallium Nitride InP: Indium Phosphide ISM: industrial, scientific and medical WPAN: wireless personal area network WLAN: wireless local area network LTE: long term evolution GSM: Global system for mobile communications UMTS: universal mobile telecommun. system UWB: ultra-wide band GPS: global positioning system FRS: family radio service GMRS: general mobile radio service BSN: body sensor network BAN: body area network WBAN: wireless body area network DBS: direct-broadcast satellite LMDS: local multipoint distribution service DECT: digital enhanced cordless telecommun. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 27 / 112

49. PA in Wireless Communications The LDMOS PA are employed for many communication equipments. The international technology roadmap for semiconductors (ITRS) reports that 48 volt LDMOS transistor is widely used in cellular infrastructure market in 2011 [ITRS, 2011]. ∵ The LDMOS can support high output power required for a base station (BS) in cellular networks. Table 3: Transmit Power of BSs [Auer et al., 2011, earth, 2015] Type Pmax out back-off average max output power ISD [m] Macro 54 dBm (250 W) 8 dB 43 dBm (20 W) 1 Km −5 Km Micro 46 dBm (40 W) 8 dB 38 dBm (6.3 W) 100 m −500 m Pico 33 dBm (2 W) 12 dB 21 dBm (125 mW) 10 m −80 m Femto 29 dBm (800 mW) 12 dB 17 dBm (50 mW) indoor To compensate poor efficiency of LDMOS devices in the low power regime, envelope tracking architecture or Doherty technique is used for 3G and 4G networks that employs high PAPR waveform signals. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 28 / 112

50. Previous Studies on the Practical SE-EE Tradeoff Practical SE analysis with PA nonlinearity for multicarrier systems [Tellado et al., 2003, Zillmann and Fettweis, 2005, Gutman and Wulich, 2012] Practical SE-EE tradeoff conjecture [Chen et al., 2011] Practical SE-EE tradeoff analysis with practical power consumption model [Héliot et al., 2012, Onireti et al., 2012] Analytical and numerical quantification of SE-EE tradeoff with BOTH nonlinearity and imperfect efficiency of PA [Joung et al., 2012a, Joung et al., 2014c] Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 29 / 112

53. Practical SE-EE Tradeoff SE, b/s/Hz EE,b/J ? Figure 11: Practical SE-EE tradeoff. Pc PPA Pout≫≫ Figure 12: Practical Power Consumption. Practical system’s power consumption model in Fig. 12 efficiency < 100% and PA nonlinearity SE is not a log function anymore [Joung et al., 2012a, Joung et al., 2014c] Concave, narrow (bad), and biased tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 30 / 112

54. Practical SE-EE Tradeoff SE, b/s/Hz EE,b/J ? Figure 11: Practical SE-EE tradeoff. Pc PPA Pout≫≫ Figure 12: Practical Power Consumption. Practical system’s power consumption model in Fig. 12 efficiency < 100% and PA nonlinearity SE is not a log function anymore [Joung et al., 2012a, Joung et al., 2014c] Concave, narrow (bad), and biased tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 30 / 112

55. Practical SE-EE Tradeoff SE, b/s/Hz EE,b/J Theoretical tradeoff in Fig. 1 Figure 11: Practical SE-EE tradeoff. Pc PPA Pout≫≫ Figure 12: Practical Power Consumption. Practical system’s power consumption model in Fig. 12 efficiency < 100% and PA nonlinearity SE is not a log function anymore [Joung et al., 2012a, Joung et al., 2014c] Concave, narrow (bad), and biased tradeoff Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 30 / 112

56. Practical SE-EE Tradeoff 1 σ2 ln 2 SE, b/s/Hz EE,b/J PA inefficiency and SE degradation resulting in drop of EE PA nonlinearity resulting in drop of SE Theoretical SE-EE tradeoff Practical SE-EE tradeoff Figure 13: Illustration of SE-EE tradeoff. SE maximization or EE maximization? EE for a single antenna (PA) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 31 / 112

57. Practical SE-EE Tradeoff 1 σ2 ln 2 SE, b/s/Hz EE,b/J PA inefficiency and SE degradation resulting in drop of EE PA nonlinearity resulting in drop of SE Theoretical SE-EE tradeoff Practical SE-EE tradeoff Figure 13: Illustration of SE-EE tradeoff. SE maximization or EE maximization? EE for a single antenna (PA) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 31 / 112

59. Energy Eﬃcient Technologies • 50–80% of transmitter’s power is consumed at power amplifier (PA) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 33 / 112

60. Energy Eﬃcient Technologies Device-Level Approach Transmitter architecture PA package structures Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 33 / 112

61. Energy Eﬃcient Technologies Device-Level Approach Transmitter architecture PA package structures System-Level Approach Transceiver signal processing IBO/PAPR/DPD/… Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 33 / 112

62. Energy Eﬃcient Technologies Device-Level Approach Transmitter architecture PA package structures System-Level Approach Transceiver signal processing IBO/PAPR/DPD/… Network-Level Approach Network processing SC/HetNet/CZ/CoMP/CoNap/DTX/… Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 33 / 112

63. EE Tech. [Joung et al., 2014b] Approaches Methods Improvement Challenges 1. PA Design linear architecture Linearity (L) high cost, parallel architecture Efficiency (E) large form factor switching architecture (PAS) E envelope tracking (ET) architecture E PA circuit architecture envelope elimination & restoration (EER/Kahn) L, E outphasing technique (LINK) L, E Doherty technique E 2. Signal Design PAPR reduction clipping L, E out-of-band emission coding additional resource,partial transmit sequence (PTS) latency, PA input/output selective mapping (SLM) complexity signal processing tone reservation (TR) tone insertion (TI) Linearlization feed forward sensitive to PA, feedback additional circuit, digital predistortion (DPD) complexity 3. Network Design Network densification E infrastructure, in/out band small cells overhead signalling, distributed antenna system (DAS) scalability, Efficient network cooperative communications (relay) handover, topology & protocol Network protocol interference design by cell zooming deploying low power PA coordinated multipoint (CoMP) or using PA on/off cell discontinuous TX/RX (DTX/DRX) coordinated sleep and napping (CoNap) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 34 / 112

65. 1. PA Design Architecture: a building block of various circuits (e.g., multiple PAs, oscillators, mixers, filters, matching networks, combiners, and circulators) Transmitter Architecture: direct approach, PA package structures 1 Linear architecture [Raab et al., 2003c] 2 Corporate architecture [Cripps, 2006] 3 Parallel architecture [Shirvani et al., 2002, Alc, 2008] 4 Stage bypassing and gate switching [Raab et al., 2003c, Staudinger, 2000] 5 Envelope elimination and restoration (EER) technique (or Kahn) [Raab et al., 2003c, Kahn, 1952] 6 Envelope tracking architecture [Raab et al., 2003c] F 7 Outphasing using linear amplification using nonlinear components (LINK) [Raab et al., 2003c, Cox, 1974] 8 Doherty technique [Cha et al., 2004, Doherty, 1936, Correia et al., 2010, Auer et al., 2011, Arnold et al., 2010] F 9 Combined complex architecture, etc. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 36 / 112

66. 1. PA Design Architecture: a building block of various circuits (e.g., multiple PAs, oscillators, mixers, filters, matching networks, combiners, and circulators) Transmitter Architecture: direct approach, PA package structures 1 Linear architecture [Raab et al., 2003c] 2 Corporate architecture [Cripps, 2006] 3 Parallel architecture [Shirvani et al., 2002, Alc, 2008] 4 Stage bypassing and gate switching [Raab et al., 2003c, Staudinger, 2000] 5 Envelope elimination and restoration (EER) technique (or Kahn) [Raab et al., 2003c, Kahn, 1952] 6 Envelope tracking architecture [Raab et al., 2003c] F 7 Outphasing using linear amplification using nonlinear components (LINK) [Raab et al., 2003c, Cox, 1974] 8 Doherty technique [Cha et al., 2004, Doherty, 1936, Correia et al., 2010, Auer et al., 2011, Arnold et al., 2010] F 9 Combined complex architecture, etc. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 36 / 112

67. Transmit Architectures DC A,P gA,P DC A,P gA,P DC + A,P gA,P DC A,P gA,P A,P gA,P E-Det. A A,P A,P gA,P E-Det. A P DC + A,P gA,P P1 P2 DC + A,P gA,P DC : DC power supply : PA A: amplitude information P: phase information g: gain: RF-drive input : RF output : delay+ : combiner (a) (b1) (d) (e) (b2) (c) (f) (g) SCS limitter DC DC/DC Figure 14: Various transmit architectures: a) Linear architecture. b) Parallel architecture. c) Switching architecture. d) Envelope tracking (ET) architecture. e) EER technique (or Kahn). f) Outphasing technique. g) Doherty technique (DT). ET: DC power is controlled by the envelope of the RF input signal DT: Class-B (carrier or main PA) + Class-C (peaking or auxiliary PA) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 37 / 112

68. Key Points Table 4: Efficiency, costs and environmental impact of a 20,000-base-station network with different power amplifier technologies [Mancuso and Sara Alouf, 2011]. Traditional technology Doherty technology Envelope tracking PA efficiency 15 % 25 % 45 % Power consumption 51.7 MW 27.2 MW 16.1 MW CO2 emission 194,600 tons 102,400 tons 60,800 tons Power cost 54.3 MM$ 28.6 MM$ 17.0 MM$ Challenges: Nonlinearity and inefficiency are fundamental and inevitable. mathematical model: modeling and empirical evaluation, i.e., simulated-annealing-based custom computer-aided design high manufacturing cost large form factor wide dynamic range with high efficiency advanced materials and metamaterials Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 38 / 112

69. Key Points Table 4: Efficiency, costs and environmental impact of a 20,000-base-station network with different power amplifier technologies [Mancuso and Sara Alouf, 2011]. Traditional technology Doherty technology Envelope tracking PA efficiency 15 % 25 % 45 % Power consumption 51.7 MW 27.2 MW 16.1 MW CO2 emission 194,600 tons 102,400 tons 60,800 tons Power cost 54.3 MM$ 28.6 MM$ 17.0 MM$ Challenges: Nonlinearity and inefficiency are fundamental and inevitable. mathematical model: modeling and empirical evaluation, i.e., simulated-annealing-based custom computer-aided design high manufacturing cost large form factor wide dynamic range with high efficiency advanced materials and metamaterials Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 38 / 112

71. 2. Signal Design Transceiver Signal Processing: knowledge of the signal properties 1 Input backoff (IBO) [Kowlgi and Berland, 2011] - Reducing the transmit power to sufficiently below its peak output power - Broadband signal having a high peak-to-average power ratio (PAPR), e.g., 8 to 13 dB PAPR for ODFM signals [Kowlgi and Berland, 2011], requires high IBO - High IBO reduces the PA efficiency 2 PAPR reduction methods [Jiang and Wu, 2008] Clipping/ coding/ partial transmission sequence and selective mapping/ nonlinear companding transform/ tone reservation and tone injection 3 Linearization [Pothecary, 1999, Kenington, 2000] To mitigate the nonlinearity of PAs in the low power regime, various linearization methods such as feedforward/ feedback/ predistortion 4 Active antenna systems (reducing feeder loss) 5 SE improving system design: large (massive) MIMO, 3D MIMO, etc. 6 Combined complex architecture Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 40 / 112

75. Key Points Impact: avoidance/compensation of the adverse impact of PA nonlinearity Cost: - PA efficiency reduction (high power consumption) for input back off - out-of-band radiation increase for signal clipping - SE reduction for side information - additional computational complexity (see e.g., parameter optimization and multiple candidate sequence generation [Rahmatallah and Mohan, 2013]) - additional analog circuits Challenges: hardware capability limitation high sensitivity to PA status additional resource requirement additional circuits tradeoff between: linearity and efficiency; SE and EE Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 41 / 112

76. Key Points Impact: avoidance/compensation of the adverse impact of PA nonlinearity Cost: - PA efficiency reduction (high power consumption) for input back off - out-of-band radiation increase for signal clipping - SE reduction for side information - additional computational complexity (see e.g., parameter optimization and multiple candidate sequence generation [Rahmatallah and Mohan, 2013]) - additional analog circuits Challenges: hardware capability limitation high sensitivity to PA status additional resource requirement additional circuits tradeoff between: linearity and efficiency; SE and EE Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 41 / 112

78. 3. Network Design Network Processing: using small power PA/reducing PA activation time 1 Network densification - in/out band small cell, inter-cell interference coordination (ICIC), heterogeneous network (HetNet) [Chen et al., 2011, Richter et al., 2009] - DAS [Choi and Andrews, 2007, Joung and Sun, 2013, Joung et al., 2014a] - relay [Joung and Sun, 2012, Yang et al., 2009] Figure 15: Example of network densification. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 43 / 112

79. 3. Network Design Network Processing: using small power PA/reducing PA activation time 1 Network densification - in/out band small cell, inter-cell interference coordination (ICIC), heterogeneous network (HetNet) [Chen et al., 2011, Richter et al., 2009] - DAS [Choi and Andrews, 2007, Joung and Sun, 2013, Joung et al., 2014a] - relay [Joung and Sun, 2012, Yang et al., 2009] carrier frequency 1 carrier frequency 2 joint processing cross-tier interference intra-tier interference in-band small cell coverage out-band small cell coverage cooperative communication region Macro BS coverage usermacro BS small BS relay AP/RRH Figure 15: Example of network densification. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 43 / 112

80. Network Design 1 Network densiﬁcation 2 Network protocol design - Cell zooming [Niu et al., 2010] - CoMP [Han et al., 2011] - DTX/CoNap [Frenger et al., 2011, 3GPP, TR 25.927 V11.0.0, 2012, Adachi et al., 2012, Adachi et al., 2013, Shirvani et al., 2002] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 44 / 112

81. Network Design 1 Network densiﬁcation 2 Network protocol design - Cell zooming [Niu et al., 2010] deactivated BS deactivated BSactive BS - CoMP [Han et al., 2011] - DTX/CoNap [Frenger et al., 2011, 3GPP, TR 25.927 V11.0.0, 2012, Adachi et al., 2012, Adachi et al., 2013, Shirvani et al., 2002] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 44 / 112

82. Network Design 1 Network densiﬁcation 2 Network protocol design - Cell zooming [Niu et al., 2010] deactivated BS deactivated BSactive BS - CoMP [Han et al., 2011] deactivated BS active BSactive BS - DTX/CoNap [Frenger et al., 2011, 3GPP, TR 25.927 V11.0.0, 2012, Adachi et al., 2012, Adachi et al., 2013, Shirvani et al., 2002] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 44 / 112

83. Network Design 1 Network densiﬁcation 2 Network protocol design - Cell zooming [Niu et al., 2010] deactivated BS deactivated BSactive BS - CoMP [Han et al., 2011] deactivated BS active BSactive BS - DTX/CoNap [Frenger et al., 2011, 3GPP, TR 25.927 V11.0.0, 2012, Adachi et al., 2012, Adachi et al., 2013, Shirvani et al., 2002] fre q u e n c y P A c a n b e tu rn e d o ff P A is o p e ra tin g in h ig h e ffic ie n c y T ra n s m it p o w e r Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 44 / 112

84. Key Points Requirements for cell densification: cross-tier interference management - cell range expansion [Damnjanovic et al., 2011] and eICIC [Kosta et al., 2013] in 3GPP - optimization of beamforming and radio resource management [Joung et al., 2012b, Joung et al., 2012c] Requirements for network protocol design: cooperation or coordination among different nodes - decide how often the cooperation/coordination performs PA on and off to balance the system performance and the power saving - optimization of the radio resource allocation Challenges: high infrastructure cost overhead signalling and frequent handover network (backbone) overhead scalability to already-deployed networks Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 45 / 112

85. Key Points Requirements for cell densification: cross-tier interference management - cell range expansion [Damnjanovic et al., 2011] and eICIC [Kosta et al., 2013] in 3GPP - optimization of beamforming and radio resource management [Joung et al., 2012b, Joung et al., 2012c] Requirements for network protocol design: cooperation or coordination among different nodes - decide how often the cooperation/coordination performs PA on and off to balance the system performance and the power saving - optimization of the radio resource allocation Challenges: high infrastructure cost overhead signalling and frequent handover network (backbone) overhead scalability to already-deployed networks Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 45 / 112

88. System Model x y IDFTF addCP→P/S→DAC ADC→S/P→removeCP DFTFH x PA LPA(·) {h0, · · · , hL−1} w z y Figure 16: An OFDM system with a nonlinear memoryless PA [Joung et al., 2014c]. x = [x0, · · · , xN−1] T ∼ CN(0, Pin): OFDM symbol consisting of N complex-valued data symbols x = [x0, · · · , xN−1]T = F x: time domain signal vector Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 48 / 112

89. Signal Model F : N-by-N unitary IDFT matrix wt = LPA(xt): PA output signal, w = [w0, · · · , wN+NCP−1]T xt = atejθt : at |xt|, θt is the phase of xt (0 ≤ θt < 2π) wt = btejθt : bt |wt| {h0, h1, · · · , hL−1}: L-tap multipath channel Yt = ht ⊗ wt + zt: received signal - perfect timing synchronization - the CP is removed - indices are shifted to start from 0 - zt ∼ CN(0, σ2 z ): AWGN - yt rtejφ : rt and φt represent the amplitude and phase of Yt - y = [Y0, · · · , YN−1]T : vector representation y = [y0, · · · , yN−1]T = F H y: frequency domain signal vector after DFT of y Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 49 / 112

90. Assumptions A1: {xn} are i.i.d. with distribution x ∼ CN(0, Pin) A2: Soft limiter model for PA input/ouput power: LPA(at) = √ gat, if at < amax bmax, if at ≥ amax - amax Pmax in and bmax Pmax out - Linearity in low power regime can be obtained with linearization techniques (e.g., feedforward, feedback, and predistortion) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 50 / 112

91. Assumptions A1: {xn} are i.i.d. with distribution x ∼ CN(0, Pin) A2: Soft limiter model for PA input/ouput power: LPA(at) = √ gat, if at < amax bmax, if at ≥ amax - amax Pmax in and bmax Pmax out - Linearity in low power regime can be obtained with linearization techniques (e.g., feedforward, feedback, and predistortion) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 50 / 112

92. Mutual Information (MI) in Flat Fading Channels (L = 1) Achievable rate averaged over N transmissions is given by I(X; Y )/N (a) = I(X; Y )/N (a) Unitary transform (IDFT) (b) = N−1 t=0 I(Xt; Yt)/N (b) independency in time domain (c) = I(X; Y ) = H(Y ) − H(Y |X) (c) identical MI over t (d) = H(Y ) − log2 πeσ2 z [b/s] (d) H(Y |X) = H(N) = log2 πeσ2 z The entropy of Y is given by [Cover and Thomas, 2006] H(Y ) = − y fY (y) log2 fY (y)dy Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 51 / 112

97. Entropy H(y) in Flat Fading Ch. Define S as a binary random variable denoting the clipping at the PA: S = 0, if A ≤ amax 1, otherwise The pdf of y can be rewritten as fY (y) = fY (y, S = 0) + fY (y, S = 1) A closed-form expression of fY (y, S = 0) and fY (y, S = 1) (see [Joung et al., 2014c] for the proof): fY (y, S = 0) = N0(y) 1 − Q1 µ(y), √ ρmax fY (y, S = 1) = N1(y) exp − a2 max Pin − 2bmaxyRe σ2 z I0 2bmax|y| σ2 z - N0(y): pdf of CN 0, gPin + σ2 z , N1(y): pdf of CN bmax, σ2 z - Q1(·, ·): Marcum-Q-function [Papoulis and Pillai, 2002] with parameters ρmax 2(gPin+σ2 z) gPin √ bmax and µ(y) 8gPin(gPin+σ2 z) σ4 z |y|2 - yRe: real part of y - I0(·): modified Bessel function of first kind Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 52 / 112

100. Analytical Results on SE SE(ξ) = H(Y ) − log2 πeσ2 z = − y s=0,1 fY (y, S = s) log2 s=0,1 fY (y, S = s) dy − log2 πeσ2 z If the PA is perfectly linear, i.e., bmax → ∞ and thus amax → ∞ fY (y, S = 0) = N0(y) 1 − Q1 µ(y), √ ρmax = N0(y) fY (y, S = 1) = N1(y) exp − a2 max Pin − 2bmaxyRe σ2 z I0 2bmax|y| σ2 z = 0 SEideal (ξ) = log2 (1 + γξ) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 53 / 112

103. Analytical Results on SE If PA input power is low, i.e., ξ ≪ 1 fY (y, S = 0) = N0(y) 1 − Q1 µ(y), √ ρmax ≈ N0(y) fY (y, S = 1) = N1(y) exp − a2 max Pin − 2bmaxyRe σ2 z I0 2bmax|y| σ2 z ≈ N1(y) SEIBO (ξ) ≈ log2 (1 + γξ) + e− 1 ξ log2 πσ2 z e1− 1 ξ − log2 σ2 z Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 54 / 112

106. Analytical Results on SE Theorem 1. The approximated SE, SEIBO (ξ), is a concave function over max 0, − 1 ln πσ2 z < ξ ≤ 1 2 . Theorem 2. The SE-aware optimal power loading factor ξ⋆ SE which maximizes SEIBO (ξ) is obtained by the solution of the following equality: γ 1 + γξ = e−ξ−1 ξ−2 −ξ−1 + 1 − ln πeσ2 z Proposition 3. A closed form approximation of ξ⋆ SE is given by ξ⋆ SE ≈ ξ⋆ SE −1 W 1 ln(πeσ2 z ) where W(·) denotes the Lambert W function [Chapeau-Blondeau and Monir, 2002] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 55 / 112

107. Analytical Results on SE Theorem 1. The approximated SE, SEIBO (ξ), is a concave function over max 0, − 1 ln πσ2 z < ξ ≤ 1 2 . Theorem 2. The SE-aware optimal power loading factor ξ⋆ SE which maximizes SEIBO (ξ) is obtained by the solution of the following equality: γ 1 + γξ = e−ξ−1 ξ−2 −ξ−1 + 1 − ln πeσ2 z Proposition 3. A closed form approximation of ξ⋆ SE is given by ξ⋆ SE ≈ ξ⋆ SE −1 W 1 ln(πeσ2 z ) where W(·) denotes the Lambert W function [Chapeau-Blondeau and Monir, 2002] Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 55 / 112

108. Numerical Results on SE Bandwidth: Ω = 10 MHz Channel attenuation: G − 128 + 10 log10 (d−α ) [LTE, 2011] - G = 5 dB: TRx feeder loss + antenna gains - d = 200 m: distance between Tx and Rx - α = 3.76: path loss exponent AWGN: σ2 z = −174 dBm / Hz PA: SM2122-44L Pmax out = 25 W g = 55 dB 0 0.2 0.4 0.6 0.8 1 0 2 4 6 8 10 12 14 16 18 Power loading factor, ξ SE(ξ),b/s/Hz SEideal (ξ) SE(ξ) SEIBO (ξ) SE(ξ⋆ SE) : ideal SE with an ideal PA : practical SE with a practical PA : approximated SE : optimal SE Figure 17: SE evaluation results. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 56 / 112

109. Power Consumption And Losses Power Amplifier (PA) Module DC Power Supply (PS) Module Base Band (BB) Module Radio Frequency (RF) Module (except PA) Active Cooler and Battery Back up (CB) Module (if present) PBB PRF PPA PCB Pin Pout loss loss loss loss Figure 18: Block diagram for system power consumption [Auer et al., 2011, Arnold et al., 2010, Deruyck et al., 2010, Deruyck et al., 2011, Kumar and Gurugubelli, 2011]. Pfix (1 + CPS)(1 + CCB)(PBB + PRF) CPS: power supply coefficient between 0.1 and 0.15 CCB: active cooler and battery coefficient less than 0.4 Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 57 / 112

110. PA-Dependent Nonlinear Power Consumption Model PA-dependent nonlinear power consumption model (0 < ξ ≤ 1): Pc(ξ) = Pfix + c c1 + c2 ξ Pmax out - c: power loading-dependent scaling coefficient - ℓ-way Doherty PA [Raab, 1987] (for class-A and B, ℓ = 1) (c1, c2) = 4 ℓπ ×    (2, 0) , 0 < ξ ≤ 1, (0, 1) , 0 < ξ ≤ 1 ℓ2 , (−1, ℓ + 1) , 1 ℓ2 < ξ ≤ 1. Ideal power consumption model with ideal PA (100% efficiency): Pideal c (ξ) = Pfix + c 1 − g−1 ξPmax out Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 58 / 112

111. PA-Dependent Nonlinear Power Consumption Model PA-dependent nonlinear power consumption model (0 < ξ ≤ 1): Pc(ξ) = Pfix + c c1 + c2 ξ Pmax out - c: power loading-dependent scaling coefficient - ℓ-way Doherty PA [Raab, 1987] (for class-A and B, ℓ = 1) (c1, c2) = 4 ℓπ ×    (2, 0) , 0 < ξ ≤ 1, (0, 1) , 0 < ξ ≤ 1 ℓ2 , (−1, ℓ + 1) , 1 ℓ2 < ξ ≤ 1. Ideal power consumption model with ideal PA (100% efficiency): Pideal c (ξ) = Pfix + c 1 − g−1 ξPmax out Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 58 / 112

112. Power Consumption 0 0.2 0.4 0.6 0.8 1 60 90 120 150 180 210 240 Power loading factor, ξ Powerconsumption,Pc(ξ),W idle mode linear model nonlinear model with class B PA nonlinear model with 2-way Doherty PA model with ideal PA Figure 19: Power consumption of microcell base station with Pﬁx = 130 W and c = 4.7π 4 . Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 59 / 112

113. Analytical Results on EE Practical EE EE(ξ) = ΩSE(ξ) Pc(ξ) Ideal EE with a perfectly linear and eﬃcient PA EEideal (ξ) ΩSEideal (ξ) Pideal c (ξ) PA-dependent EE with a perfectly linear PA EElinear (ξ) ΩSEideal (ξ) Pc(ξ) Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 60 / 112

116. Analytical Results on EE Theorem 4. EElinear (ξ) is a piecewise quasi-concave function over ξ ≥ ζ v + √ 1 + v2 2 /γ2 , where v = Pmax out c0c2/(P0 + Pmax out c0c1). Speciﬁcally, EElinear (ξ) is quasi-concave over ζ ≤ ξ ≤ 1/ℓ2 and also over 1/ℓ2 < ξ ≤ 1. Theorem 5. Assuming ξ⋆ EE ≥ ζ, ξ⋆ EE equals either [ξ⋆ 1 ] 1/ℓ2 ζ or [ξ⋆ 2 ]1 1/ℓ2,, where ξ⋆ 1 and ξ⋆ 2 are the solutions of ∂EElinear (ξ) ∂ξ = 0 with given (c1, c2). Proposition 6. A closed form approximation of ξ⋆ EE, denoted by ξ⋆ EE, equals either [ξ⋆ 1 ] 1/ℓ2 ζ or [ξ⋆ 2 ]1 1/ℓ2,, where ξ⋆ i (i ∈ {1, 2}) approximates ξ⋆ i and is given by ξ⋆ EE = ξ⋆ i ≈ ξ⋆ i = 1 γ exp 2 + 2W √ γ ev , i = 1 or 2. where W(·) > 0 as √ γ ev > 0, so that W(·) is unique. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 61 / 112

117. Analytical Results on EE Theorem 4. EElinear (ξ) is a piecewise quasi-concave function over ξ ≥ ζ v + √ 1 + v2 2 /γ2 , where v = Pmax out c0c2/(P0 + Pmax out c0c1). Speciﬁcally, EElinear (ξ) is quasi-concave over ζ ≤ ξ ≤ 1/ℓ2 and also over 1/ℓ2 < ξ ≤ 1. Theorem 5. Assuming ξ⋆ EE ≥ ζ, ξ⋆ EE equals either [ξ⋆ 1 ] 1/ℓ2 ζ or [ξ⋆ 2 ]1 1/ℓ2,, where ξ⋆ 1 and ξ⋆ 2 are the solutions of ∂EElinear (ξ) ∂ξ = 0 with given (c1, c2). Proposition 6. A closed form approximation of ξ⋆ EE, denoted by ξ⋆ EE, equals either [ξ⋆ 1 ] 1/ℓ2 ζ or [ξ⋆ 2 ]1 1/ℓ2,, where ξ⋆ i (i ∈ {1, 2}) approximates ξ⋆ i and is given by ξ⋆ EE = ξ⋆ i ≈ ξ⋆ i = 1 γ exp 2 + 2W √ γ ev , i = 1 or 2. where W(·) > 0 as √ γ ev > 0, so that W(·) is unique. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 61 / 112

118. Numerical Results on EE 0 0.2 0.4 0.6 0.8 1 0 0.5 1.0 1.5 2.0 2.5 Power loading factor, ξ EE(ξ),Mb/J EElinear (ξ⋆ EE);× EE(ξ⋆ EE); ξ⋆ EE in Prop. 6 EElinear (ξ) EEideal (ξ) EE(ξ): 2-way Doherty PA EE(ξ): class-B PA EE(ξ): class-A PA Figure 20: EE evaluation with Pﬁx = 130 W and c = 4.7. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 62 / 112

119. Practical SE-EE Tradeoff 0 2 4 6 8 10 12 14 16 18 0 0.5 1.0 1.5 2.0 2.5 SE(ξ), b/s/Hz EE(ξ),Mb/J SE-EE tradeoff with PAlow SE-EE tradeoff with PAhigh ◦ × : (SE(ξ⋆ SE), EE(ξ⋆ SE)) : (SE(ξ⋆ EE), EE(ξ⋆ EE)) Fig. 24 Figure 21: SE-EE tradeoff with 2-way Doherty PAs. PAlow with Pmax out = 25 W and g = 55 dB, and PAhigh with Pmax out = 100 W and g = 50 dB. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 63 / 112

120. PA Switching (PAS) Method SE EE Low power PA, PA-1 SE EE High power PA, PA-2 Figure 22: Illustration of PAS Concept. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 64 / 112

121. PA Switching (PAS) Method SE EE Low power PA, PA-1 SE EE High power PA, PA-2 SE EE PA switching Figure 22: Illustration of PAS Concept. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 64 / 112

122. PAS for FDD/TDD Frame switching time ǫ frame k − 1, PA-1 frame k, PA-1 frame k + 1, PA-2 time · · ·· · · (a) FDD Systems switching time ǫ DL frame, PA-1 UL frame DL frame, PA-2 UL frame length + TTG + RTG > ǫ time · · ·· · · TTG RTG (b) TDD Systems Figure 23: Illustration of PA switching between PA-1 and PA-2. K: frame number; T: frame length; ǫ: switching time Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 65 / 112

123. SE and EE of PAS SEs(ξ, κ) = kT SE′ 1(ξ) + (K − k)T SE′ 2(ξ) KT + ǫ EEs(ξ, κ) = KT ΩSEs(ξ, κ) kT P1 c (ξ) + (K − k)T P2 c (ξ) κ = k K is PA time sharing factor. Switch power consumption is ignored as it is relatively negligible compared to Pi c (ξ). FDD: ǫ > 0 unless there is switching. TDD: ǫ < 1 ms and UL frame length (10 ms) [LTE, 2011]; PAs can be switched between consecutive DL frames while receiving UL frame, without consuming any switching time overhead, i.e., ǫ = 0. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 66 / 112

124. SE-EE Tradeoff of PAS ǫ = 10 µs, LS = 1 dB, T = 10 ms, and K = 20 A → B(D) : EE ↑ 210%(41%) SE ↓ 12% A → C(E) : EE ↑ 323%(69%) SE ↓ 15% 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 SE(ξ), b/s/Hz EE(ξ),Mb/J GS = 0 dB, ǫ = 0 µs, ideal GS = 1 dB, ǫ = 0 µs, TDD GS = 1 dB, ǫ = 10 µs, FDD GS = 1 dB, ǫ = 1 ms, FDD A DE B C SE-EE tradeoff with PAhigh Figure 24: SE-EE tradeoff. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 67 / 112

125. TAS-MRC Syst. with Partial CSIT x z1 z2 y1 MRC ˆx y2 √ Ah2 √ Ah1S1 M +1 feedback for S1 and PC PC power contorl 1 2 : high-power main power ampliﬁers Figure 25: A transmit antenna selection with maximum ratio combining system. Switch S1 selects a transmit antenna Switch S2 selects a PA [Joung et al., 2013] Pmax out : maximum output power of TX subject to regulatory constraints µmPmax out : Maximum output power of PA m 0 < µ1 < µ2 < · · · < µM+1 = 1 Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 68 / 112

126. TAS-MRC Syst. with Partial CSIT x z1 z2 y1 MRC ˆx y2 √ Ah2 √ Ah1S1S2 off − mode M +1 M 1 ... feedback for S1 and S2 0 M + 1 M 1 1 2 : high-power main power amplifiers : low-power auxiliary power amplifiers Figure 25: A transmit antenna selection with maximum ratio combining system. Switch S1 selects a transmit antenna Switch S2 selects a PA [Joung et al., 2013] Pmax out : maximum output power of TX subject to regulatory constraints µmPmax out : Maximum output power of PA m 0 < µ1 < µ2 < · · · < µM+1 = 1 Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 68 / 112

127. PA Switching Probability A switching probability for given target rate R b/s/Hz fm = Pr(Rm−1 < R ≤ Rm) = (Υm−1 − Υm) (Υm−1 + Υm − 2) by using order statistics [David, 1970, Proakis and Salehi, 2007] - Υm 2R − 1 σ2 m + 1 e−(2R −1)σ2 m - σ2 m σ2 z AµmP max out , where σ2 z is variance of AWGN - Υ0 = 0 and ΥM+2 = 1 EE of the proposed TAS-MRC systems for the given R EETAS MRC = ΩR(1 − fM+2) M+2 m=1 PTx,mfm - PTx,m 100cµmP max out ǫ(µm) + Pfix, if m = 1, . . . , M + 1, Pfix, if m = M + 2 (off-mode) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 69 / 112

128. PA Switching Probability A switching probability for given target rate R b/s/Hz fm = Pr(Rm−1 < R ≤ Rm) = (Υm−1 − Υm) (Υm−1 + Υm − 2) by using order statistics [David, 1970, Proakis and Salehi, 2007] - Υm 2R − 1 σ2 m + 1 e−(2R −1)σ2 m - σ2 m σ2 z AµmP max out , where σ2 z is variance of AWGN - Υ0 = 0 and ΥM+2 = 1 EE of the proposed TAS-MRC systems for the given R EETAS MRC = ΩR(1 − fM+2) M+2 m=1 PTx,mfm - PTx,m 100cµmP max out ǫ(µm) + Pfix, if m = 1, . . . , M + 1, Pfix, if m = M + 2 (off-mode) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 69 / 112

129. PA Output Power (Pout W) and Efficiency (ǫ%) Table 5: Proposed PAS TAS-MRC with M = 2. PAS m PA Pout W ǫ% FB s1 s2 fm Auxiliary PA 1 PA1 0.63 W 55% 110/1 1/2 1 f1 2 PA2 2.5 W 43% 010/1 1/2 2 f2 Main PA 3 PA3 10 W 60% 100/1 1/2 3 f3 off-mode 4 off-mode 0 0 000 – 0 f4 Table 6: Conventional TAS-MRC System with Power Control. Level l PA Pout W ǫ% feedback s1 fpow l P1 1 PA3 0.63 W 9% 110/1 1/2 fpow 1 P2 2 PA3 2.5 W 32% 010/1 1/2 fpow 2 P3 3 PA3 10 W 60% 100/1 1/2 fpow 3 P4 4 off-mode 0 0 000 – fpow 4 Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 70 / 112

130. Mode Switching Probability 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 R b/s/Hz Probability,fm f1:PA1 Figure 26: Switching probabilities. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 71 / 112

133. Mode Switching Probability 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 R b/s/Hz Probability,fm f4:PA4, oﬀ-mode Figure 26: Switching probabilities. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 71 / 112

134. Mode Switching Probability 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 R b/s/Hz Probability,fm f1:PA1 f2:PA2 f3:PA3 f4:PA4, oﬀ-mode Figure 26: Switching probabilities. Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 71 / 112

135. EE Comparison Simulation Environments PA1(0.63 W, 55%), PA2(2.5 W, 43%), PA3(10 W, 60%) 8 dB IBO Switch insertion loss: GS = 0 dB for S1, GS = 1 dB for S2 Channel attenuation: A dB = G − 128 + 10 log10(d−α) [LTE, 2011] G = 5 dB, d = 0.6 km, α = 3.76 σ2 = −174 dBm / Hz, Ω = 10 MHz, Pfix = 40 W and c = 4.7 [Joung et al., 2014c] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 1.2 R b/s/Hz Energyefficiency(EE)Mb/J no power control Figure 27: EE comparison. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 72 / 112

136. EE Comparison Simulation Environments PA1(0.63 W, 55%), PA2(2.5 W, 43%), PA3(10 W, 60%) 8 dB IBO Switch insertion loss: GS = 0 dB for S1, GS = 1 dB for S2 Channel attenuation: A dB = G − 128 + 10 log10(d−α) [LTE, 2011] G = 5 dB, d = 0.6 km, α = 3.76 σ2 = −174 dBm / Hz, Ω = 10 MHz, Pfix = 40 W and c = 4.7 [Joung et al., 2014c] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 1.2 R b/s/Hz Energyefficiency(EE)Mb/J 1-bit FB for off-mode off-mode gain Figure 27: EE comparison. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 72 / 112

137. EE Comparison Simulation Environments PA1(0.63 W, 55%), PA2(2.5 W, 43%), PA3(10 W, 60%) 8 dB IBO Switch insertion loss: GS = 0 dB for S1, GS = 1 dB for S2 Channel attenuation: A dB = G − 128 + 10 log10(d−α) [LTE, 2011] G = 5 dB, d = 0.6 km, α = 3.76 σ2 = −174 dBm / Hz, Ω = 10 MHz, Pfix = 40 W and c = 4.7 [Joung et al., 2014c] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 1.2 R b/s/Hz Energyefficiency(EE)Mb/J 2-bit FB for Pow Ctrl off-mode power control gain gain Figure 27: EE comparison. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 72 / 112

138. EE Comparison Simulation Environments PA1(0.63 W, 55%), PA2(2.5 W, 43%), PA3(10 W, 60%) 8 dB IBO Switch insertion loss: GS = 0 dB for S1, GS = 1 dB for S2 Channel attenuation: A dB = G − 128 + 10 log10(d−α) [LTE, 2011] G = 5 dB, d = 0.6 km, α = 3.76 σ2 = −174 dBm / Hz, Ω = 10 MHz, Pfix = 40 W and c = 4.7 [Joung et al., 2014c] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0.2 0.4 0.6 0.8 1.0 1.2 R b/s/Hz Energyefficiency(EE)Mb/J 2-bit FB for Pow Ctrl 2-bit FB for PAS Figure 27: EE comparison. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 72 / 112

139. MIMO Syst. with Partial CSIT x2 x1 z2 z1 y2 y1 MRC/MIMO ˆx2 ˆx1 √ Ah2 √ Ah1 M +1 M +1 Ant.2 Ant.1 : high-power main power ampliﬁers PC PC power contorl feedback for PC Figure 28: PAS MIMO system model with two main PA and M auxiliary PAs. Switch S0 selects a communication mode Switch S1 selects a PA [Joung et al., 2014d] µmPmax out : Maximum output power of PA m ∈ {1, · · · , M + 1} 0 < µ1 < · · · < µM < µM+1 = 1 2Pmax out : maximum output power of TX subject to regulatory constraints Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 73 / 112

140. MIMO Syst. with Partial CSIT x2 x1 z2 z1 y2 y1 MRC/MIMO ˆx2 ˆx1 √ Ah2 √ Ah1S0 S1 M +1 M +1 M 1 Ant.2 Ant.1 0 0 M + 1 M 1 1 : high-power main power amplifiers : low-power auxiliary power amplifiers feedback for S1 and S2 ... off-mode Figure 28: PAS MIMO system model with two main PA and M auxiliary PAs. Switch S0 selects a communication mode Switch S1 selects a PA [Joung et al., 2014d] µmPmax out : Maximum output power of PA m ∈ {1, · · · , M + 1} 0 < µ1 < · · · < µM < µM+1 = 1 2Pmax out : maximum output power of TX subject to regulatory constraints Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 73 / 112

141. Commun. Mode Selection Prob. A switching probability for given target rate R b/s/Hz - PAS-MRC mode: fm = fU (2R − 1)σ2 m ≤ u < (2R − 1)σ2 m−1 , m = {1, · · · , M} = Υm − Υm−1 where Υm 1 + 2R − 1 σ2 m e−(2R −1)σ2 m . - Oﬀ-mode: fM+3 fC(x < R|σ2 M+1) = FC(R|σ2 M+1) FC(x|σ2 M+1)= ∞ −∞ ∞ 0 e−x 1+ x 2σ2 M+1 j2πu ln 2 dx ∞ 0 x2 e−x 1+ x 2σ2 M+1 j2πu ln 2 dx − ∞ 0 xe−x 1+ x 2σ2 M+1 j2πu ln 2 dx 2 1 − ej2πux j2πu du. - MIMO mode: fM+2 = 1 − M+1 m=1 fm − fM+3 Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 74 / 112

142. EE Analysis EE can be derived as EEPAS MIMO = ΩR(1−fM+3) M+3 m=1 PTx,mfm . - Numerator represents system throughput over bandwidth Ω Hz and given target rate R - Denominator is total power consumption with model defined as [Joung et al., 2013, Héliot et al., 2012]: PTx,m =    Pant,m + Psp1Ω + Pfix, if m = 1, · · · , M + 1, 2Pant,m + Psp1Ω + Pfix, if m = M + 2, Pfix, if m = M + 3 + Pant,m: power consumption that is proportional to the number of transmit antennas NT [Xu et al., 2011], as Pant,m = cµmP max out ǫ(µm) + Pcc + Psp2Ω + c: a system dependent power loss coefficient which can be empirically measured and obtained + ǫ(µm): a PA efficiency that depends on the input power (or equivalently PA output power) + Pcc and Psp2 are the RF circuit and signal processing related power consumptions per bandwidth, respectively, which are proportional to NT + µ4 = µ3 + Psp1: a sig. proc.g related power consumption which is independent of NT + Pfix: a fixed power consumption, for power supply and cooling system, which is independent of P max out , NT , and Ω Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 75 / 112

143. PA Output Power (Pout W) and Efficiency (ǫ%) Table 7: Proposed PAS MIMO with M = 2. Comm. Mode m PA Pout W ǫ% FB s0 s1 fm PAS-MRC 1 PA1 0.63 W 55% 00 0 1 f1 2 PA2 2.5 W 43% 01 0 2 f2 3 PA3 10 W 60% 10 0 3 f3 MIMO 4 two PA3’s 2 × 10 W 60% 11 1 3 f4 off-mode 5 PA4 0 0 null 0 0 f5 Table 8: Conventional MIMO System with Power Control. Level l PA Ptotal out W ǫ% feedback fpow l P1 1 PAa 3, PAb 3 2 × 0.315 W 5% 00 fpow 1 P2 2 PAa 3, PAb 3 2 × 1.25 W 15.5% 01 fpow 2 P3 3 PAa 3, PAb 3 2 × 5 W 32% 10 fpow 3 P4 4 PAa 3, PAb 3 2 × 10 W 60% 11 fpow 4 P5 5 off 0 0 null fpow 5 Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 76 / 112

144. Mode Switching Probability 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.2 0.4 0.6 0.8 1.0 Target rate, R b/s/Hz Probability,fm m = 1, PA1: 0.63 W m = 2 m = 3 m = 4 PA2 2.5 W PA3 10 W PA3+PA3 2 × 10 W m = 5, PA4: off-mode (a) 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.2 0.4 0.6 0.8 1.0 Target rate, R b/s/HzProbability,fpow l l = 5, P5: off-model = 1, P1: 2 × 0.315 W l = 2, P2 2 × 1.25 W l = 3, P3 2 × 5 W l = 4, P4 2 × 10 W (b) Figure 29: Probabilities. (a) fm of PAS. (b) fpow l of power control. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 77 / 112

145. EE Comparison Simulation Environments Switch insertion loss: GS = 0 dB for S0, GS = 0 dB for S1 σ2 = −174 dBm/ Hz, Ω = 5 MHz, with 512 FFT size (300 subcarriers) Pfix = 36.4 W, c = 2.63, Pcc = 66.4 W, Pfix = 36.4 W, Psp1 = 1.28 µW / Hz, Psp2 = 3.32 µW / Hz 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.05 0.10 0.15 0.20 0.25 Target rate, R b/s/Hz Energyefficiency(EE)Mb/J Conventional MIMO w/o Pow Ctrl. Figure 30: EE comparison of the proposed MIMO-MRC with PAS and the conventional MIMO w/ or w/o Pow Ctrl. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 78 / 112

146. EE Comparison Simulation Environments Switch insertion loss: GS = 0 dB for S0, GS = 0 dB for S1 σ2 = −174 dBm/ Hz, Ω = 5 MHz, with 512 FFT size (300 subcarriers) Pfix = 36.4 W, c = 2.63, Pcc = 66.4 W, Pfix = 36.4 W, Psp1 = 1.28 µW / Hz, Psp2 = 3.32 µW / Hz 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.05 0.10 0.15 0.20 0.25 Target rate, R b/s/Hz Energyefficiency(EE)Mb/J Conventional MIMO w/ Pow Ctrl. Figure 30: EE comparison of the proposed MIMO-MRC with PAS and the conventional MIMO w/ or w/o Pow Ctrl. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 78 / 112

147. EE Comparison Simulation Environments Switch insertion loss: GS = 0 dB for S0, GS = 0 dB for S1 σ2 = −174 dBm/ Hz, Ω = 5 MHz, with 512 FFT size (300 subcarriers) Pfix = 36.4 W, c = 2.63, Pcc = 66.4 W, Pfix = 36.4 W, Psp1 = 1.28 µW / Hz, Psp2 = 3.32 µW / Hz 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.05 0.10 0.15 0.20 0.25 Target rate, R b/s/Hz Energyefficiency(EE)Mb/J Conventional MIMO w/ Pow Ctrl. Proposed MIMO w/ PAS Figure 30: EE comparison of the proposed MIMO-MRC with PAS and the conventional MIMO w/ or w/o Pow Ctrl. Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 78 / 112

149. System Model [Joung et al., 2014a] BBU deactivated DA user equipment SISO MISO MU-MIMO activated DA optical fibre large-scale distributed antennas (DAs) cellular communication networks Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 80 / 112

150. EE Model of L-DAS EE (S, W, P ) System throughput per unit time Total power consumption System throughput: R(S, W, P ) = u∈U Ω log2 (1 + SINRu(S, W, P )) SINRu(S, W, P ) = |hr u(sc u◦wc u)|2 puu U u′=1,u′=u hr u sc u′ ◦wc u′ 2 pu′u′ +σ2 Total power consumption: C(S, W, P ) = f(S, W, P ) + g(S, W ) f(·): TPD (transmit power dependent) term g(·): TPI (transmit power independent) term Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 81 / 112

153. Power Consumption Model: TPD ASIC, FPGA, DSP Examples: -digital up converter -digital predistorter -scrambling -CRC check -conv. encoder -interleaver -modulation -IFFT -CP insertion -parallel-to-serial eRF module oRF module oRF module eRF module Examples: -O/E converter Examples: -E/O converter -laser -driver -modulator Examples: -D/A converter -filters -synthesizer Examples: -VGA -driver -PA Examples: -AC/DC -DC/DC -active cooler ... ... ... ... ... ... baseband module mth RF module at BBU baseband unit (BBU) mth distributed antenna (DA) port 1st Ant. mth Ant. Mth Ant. 1 m M fiber Psp1, Psp2, Psig (TPI) Pcc1,m (TPI) Pcc2,m (TPI)Pcc2,m (TPI) Pfix (TPI) Ptx,m (TPD) TPD term f(S, W, P ) = m∈M c ηm (S ◦ W )P (S ◦ W )H mm eRF (electric RF) oRF (optical RF) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 82 / 112

154. Power Consumption Model: TPI TPI term g(S, W ) = grf(S) + gbb(W ) + gnet(M) + Pfix grf(S) = m∈M Pcc1,m + Pcc2,m u∈U Ru maxu smu gbb(W ) = ΩPsp1 [dim(W )]β+1 + ΩPsp2 gnet(M) = MΩPsig Pcc1: eRF Pcc2: per unit-bit-and-second of oRF Ru: target rate of user u β ≥ 0: implies overhead power consumption of MU processing compared to SU-MIMO Pfix: fixed power consumption (e.g., pow supply, AC/DC, DC/DC, and cooling system) Jingon Joung Tutorial 2: Energy Efficient Wireless Communications 83 / 112

155. EE of L-DAS EE (S, W, P ) = u∈U Ω log2 1 + |hr u (sc u ◦ wc u)| 2 puu U u′=1,u′=u |hr u (sc u′ ◦ wc u′ )|2 pu′u′ + σ2 m∈M c ηm (S ◦ W )P (S ◦ W )H mm + m∈M Pcc1,m + Pcc2,m u∈U Ru max u smu + ΩPsp1 [dim(W )] β+1 + ΩPsp2 + MΩPsig Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 84 / 112

156. Original Problem Formulation Po: original problem max {S,W,P } EE (S, W, P ) s.t. (S ◦ W )P (S ◦ W )H mm ≤ Pm, ∀m ∈ M, Ru(S, W, P ) ≥ Ru, ∀u ∈ U, pu1u2 = 0, ∀u1 = u2 ∈ U, smu ∈ {0, 1}, ∀m ∈ M, ∀u ∈ U objective function: EE per-ant pow constraints with max-output pow Pm per-user rate constraints with a target rate Ru diagonal structure of P DA selection Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 85 / 112

161. Problem Decomposition Issues to solve the original problem Po: Non-convex objective function Integer variables {smu} in the constraints Signaling overhead Computational complexity Suboptimal decomposition approach Step 1: DA selection: S Step 2: DA clustering Step 3: Cluster-based optimization (cluster index ℓ) Step 3-1: Precoding, Wℓ Step 3-2: Power allocation, Pℓ Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 86 / 112

172. Step 1: DA Selection 20 UEs activated DA: Mu = 1 non-activated DA: M = 400 IAD BBU Channel-gain-based greedy AS: received signal strength indicator (RSSI) Min-dis-based greedy AS: localization information Jingon Joung Tutorial 2: Energy Eﬃcient Wireless Communications 87 / 112

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