Cellular and Wireless Networks Power Management and Consumption Fundamentals of Cellular and Wireless Networks Lecture ID: ET- IDA-113/114 20.06.2016 , v08 Prof. W. Adi Lecture-4 Power Management and Consumption in Mobile Systems

Mobile Systems and Power Management Long operation time is very essential for all mobile/Battery-powered equipment ! Factors affecting power consumption and operation time: Mobile equipment related factors Mobile System related factors

Factors Affecting System Power Consumption and Operation Time Mobile Equipment related factors: Battery capacity (proportional to weight). Light weight is required! Rechargeable cells technology VLSI technology used CMOS low power technology CPU power consumption ~ C Vcc2 f Where: C : VLSI sytem capacity, reduced by VLSI Technology size Vcc : supply voltage 5v, 3.6v, 1.2v, technology dependent f : clock frequency, can be reduced temporally Circuit design strategies (Design for low power mobile computing) Power-saving processing strategies in equipment Mobile system related factors: Base station distribution such that the mobile device does not need to send high RF power Intelligent power control and management such that base stations let mobile devices not transmit at unnecessary high RF power level Reduce handover operations and other similar operations and the corresponding related signaling traffic

Rechargeable Battery lifetime and Available Technologies NiCd Memory-Effect/Discharge Characteristics Typical standard Battery Discharge Characteristics Typical Rechargeable Battery Discharge Characteristics

Common Rechargeable Battery Technologies Nickel Cadmium (NiCd) Nickel Metal Hybrid (NiMH), 1.2 v have been in use for many years Long life Ni Cd (200-400 Charge/disch. cycles) for Ni M (700-900 Charge discharge cycles) Specific energy of around 55Wh/Kg “Memory Effect” ! If not completely discharged Modern technology: Lithium Ion (LI), 3.7 v High-power, high energy-density and high life cycle 2-3 times better Wh/kg than NiCd and NiMH. More safety and life cycle have been achieved Can be operated in a wide temperature range No “Memory Effect”

Example 4.1: Assume 1000 mA h battery is used for a cellular phone device which draws 35 mA in idle mode and 250 mA during a call. How long would the phone work (i.e., what is the battery life) if the user leaves the phone continually on and has one 3-minutes call every day? Every 6 hours? and every hour?. What is the maximum talk time available on this cellular phone? (Rappaport Prob. 1.9) Solution 4.1: For 3 minutes call every day 1000mAh x 60 min (mA minutes) = 1.17 days = 28 h [ (60 x 24min – 3 min) 35 mA + 3 min x 250 mA ] Battery life in days = Total consumed mA minutes per day Idle time per day Idle current Call time per day call current For 3 minutes call every 6 hours 1000mAh x 60 min (mA minutes) = 1.13 days = 27 h [ (60 x 24min – 4x3 min) 35 mA + 4x 3 min x 250 mA ] Battery life in days = For 3 minutes call every 1 hours 1000mAh x 60 min (mA minutes) = 0.91 days = 21 h [ (60 x 24min – 24x3 min) 35 mA + 24x 3 min x 250 mA ] attery life in days = 2. Maximum talk time = 1000 mAh x 60 / 250 mA = 240 minutes = 4 hours

Power saving techniques in mobile Equipment Idle Time and Wake-up Duty Cycle Consumed current Icall Tw Iwake-up Iidle time T TCall Idle/wake-up Cycle time Wake up Duty cycle = Tw / T If only the digital mobile controller is assumed to be active in idle mode then IIdle = k . C Vcc2 f This current can mostly be kept low in the range of several A

Example 4.2: Assume 1000 mAh LI battery is used for a cellular phone device which draws 1 mA in idle Mode. The current increases by 50 mA in wake-up mode and increases by 250 mA during a call. Assume that the wake-up time duration is 1 ms every 1 second. How long would the phone work (I.e., what is the battery life) if the user leaves the phone continually on and has one 3 minutes call every hour?. How long is the battery life if the user do not activate any calls Assume that the idle current is only dependent on the VLSI processor technology. What is the new battery life for case (2) if the supply voltage is changed from 3.6 volt to 1.2 volt and the processor clock frequency is doubled. (similar to Rappaport Prob. 1.10) Solution 4.2: 1. For 3 minutes call every 1 hours Battery life in days = 1000mAh x 60 (mA minutes) . (1) [ (60 x 24min ) 1 mA + TW /T (60 x24 min) 50 mA + 24x3 min x 250 mA ] Total consumed mA minutes per day Wake-up Time ratio Idle current per day call current per day Wake-up current Consumption per day 60 000 60 000 Battery life in days = = = 3.07 days = 73.8 h 1440 + (1/1000) (1440 ) 50 + 18 000 1440 + 72 + 18 000

Iidle(2) / Iidle(1) = 1.22 2 f / 3.62 f = (1/3)2 x 2 = 2/9 Maximum life time = 60 000 / 1440 + 72 + 0 = 39.7 days The current consumed for call time is set to zero in (1) For Vcc = 1.2v instead of 3.6 v and a processing speed of 2f instead of f Iidle(1) = k C 3.62 f Iidle(2) = k C 1.22 2f Iidle(2) / Iidle(1) = 1.22 2 f / 3.62 f = (1/3)2 x 2 = 2/9 Iidle(2) = Iidle(1) x 2/9 = 1 mA x 2 / 9 = 0.22 mA IIdle = k . C Vcc2 f Battery life in days = 1000mAh x 60 (mA minutes) = 154 days ! [ (60 x 24min ) 0.22 mA + (1/1000) (60 x24 min) 50 mA ]

Example 4.3: Assume 600 mAh battery is used for a cellular phone device which draws 1 mA in power saving mode. The current increases by 50 mA in wake-up (normal idle) mode and increases by 250 mA during a call. Assume that the power saving wake-up time duration is 1 ms every 1 second.   How long is the battery life if the user does not activate any calls and the power saving mode is not activated (mobile always in wake-up mode)? How long is the battery life if the user does not activate any calls but the power saving mode is activated? How long is the battery life with power saving operation and the user has one 3 minutes call every hour?   (F.E. 2003)

Solution 4.3: 1. Battery life= 600 mAh = 12 h = 0.5 days 50 mA   2 Battery life in days = 600 mAh x 60 (mA minutes) = [ (60 x 24min ) 1 mA + TW /T (60 x24 min) 50 mA ] Battery life in days = 600 mAh x 60 (mA minutes)  23.8 days [ (60 x 24min ) 1 mA + 1/1000 (60 x24 min) 50 mA ] 3. Battery life in days = 600 mAh x 60 (mA minutes) ___ _______ _  1.84 days [ (60 x 24min-24x3 ) 1 mA + 1/1000 (60 x24 min) 50 mA + 24 x 3 min x 250 mA ] - 1/1000 (60 x24 min) is neglected

Example 4.4: Assume that one 800 mAh battery is used for a mobile phone device, which draws 5 mA in idle mode and 200 mA during a call. How long would the phone work if the user leaves the phone continually on without making any calls? How long is the battery life if the user has 1 hour calls every day? How long would the battery life become in case 2 if the mobile applies a power saving wake up time of 2 ms every second with a sleep current of 0.1 mA and wake up current of 5 mA. (F.E. 2003)

Solution 4.4: 1. Battery life = 800 mAh = 160 h = 6.66 days 5 mA   1. Battery life = 800 mAh = 160 h = 6.66 days 5 mA 2 . Battery life in days = 800 mAh x 60 (mA minutes) = 2.54 days [ (60 x 24min – 60 ) 5 mA + (60 min) 200 mA ] 3. Battery life in days = 800 mAh x 60 (mA minutes) _____________  3.95 days [ (60 x 24min- 60 ) 0.1 mA + 2/1000 (60 x24 –60 min) 5 mA + 60 min x 200 mA ] - 2/1000 (60 x24 –60 min)= 2.76 minutes is neglected