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

2. 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

3. 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

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

5. 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 ( Charge/disch. cycles)
for Ni M ( 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”

6. 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) = 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) = 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

7. 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

8. 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 = mAh x (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
(1/1000) (1440 )

9. Iidle(2) / Iidle(1) = 1.22 2 f / 3.62 f = (1/3)2 x 2 = 2/9
Maximum life time = / = 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 f
Iidle(2) = k C f
Iidle(2) / Iidle(1) = f / 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 = mAh x (mA minutes) = 154 days !
[ (60 x 24min ) 0.22 mA + (1/1000) (60 x24 min) 50 mA ]

10. 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)

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

12. 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)

13. Solution 4.4: 1. Battery life = 800 mAh = 160 h = 6.66 days 5 mA
Battery life = mAh = 160 h = 6.66 days
5 mA
Battery life in days = mAh x (mA minutes) = days
[ (60 x 24min – 60 ) 5 mA + (60 min) 200 mA ]
Battery life in days = mAh x (mA minutes) _____________  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