1. Mobile Computing COE 446 Network Operation
Tarek Sheltami
KFUPM
CCSE
COE
Principles of Wireless Networks
K. Pahlavan and P. Krishnamurth
April 20, 2017

2. Outline Radio Resources and Power Management Power Control
Open Loop Power Control
Closed Loop Power Control
Centralized and Distributed Power Control
Power Saving Mechanism in Wireless Networks `
April 20, 2017

3. Mobile Management Radio Resources and Power Management Power control
Signals from MTs operating in the coverage area of a BS cause interference to MTs operating in the coverage area of another BS
Power control enhances battery life of the MTs
In order to reduce interference and maximize the battery life, there is a need for the wireless network to keep track of the radio resources, signal strength, and other associated information related to communication between an MT and neighboring BSs
Power control
It means the algorithms, protocols, and techniques that are employed to dynamically adjust the transmit power of both MTs and BSs `
April 20, 2017

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7. Mobile Management Open Loop Power Control Disadvantages:
Usually implemented on the uplink
An MT measures the quality of a reference channel from the BS; RSS or BER frames may be used
If the RSS or BER above certain thresholds, the mobile will reduce its transmit power and vise versa
Disadvantages:
The decision is based on the measurement of the downlink
These channels are not usually correlated, which means a good signal reception on the uplink channel does not necessarily mean the same at the downlink channel
There may be a significant delay before implementing the power control
In TDMA, the MT reception and transmission times are different, and there will be a lag time in implementing time open loop control `
April 20, 2017

8. Mobile Management Closed Loop Power Control
Eliminates the disadvantage of open loop power control by implementing a feedback mechanism between the BS and the MT
The BS measures the quality of the signal received from the MT and indicates what actions the MT should take via control signaling on the downlink channel
Closed loop power control can be used to control the transmit signal of the BS `
April 20, 2017

9. Types of Power Control Open-loop power control
Depends solely on mobile unit
No feedback from BS
Not as accurate as closed-loop, but can react quicker to fluctuations in signal strength
Closed-loop power control
Adjusts signal strength in reverse channel based on metric of performance
BS makes power adjustment decision and communicates to mobile on control channel
April 20, 2017

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12. Mobile Management Centralized and Distributed Power Control
In centralized power control (CPC), a central controller in the BSC or MSC has full info of the radio links in the system
The scheme is extremely hard to implement because the centralized controller has to dynamically keep track of all the links in the system and compute the transmit power for each MT
In distributed power control (DPC), the mobile adjust their transmit power in discrete step
Power adjustment made by MTs result in the transmit powers iteratively converging to the optimum power control solution `
April 20, 2017

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14. Power Saving Mechanism in Wireless Networks
The most consumed power in the transmission process
The second most consumed power in the reception process
The least consumed power in the standby process
April 20, 2017

15. Discontinuous Transmission and Repetition at Lower Transmit Powers
Voice Activity Detector (VAD)
While a VAD’s performance does not affect clarity directly
Problems:
If it is not operating correctly, it can certainly decrease the intelligibility of voice signals and overall conversation quality
April 20, 2017

16. VAD Behavior

17. Sleep Modes MT enters into a sleep mode during periods of inactivity
Activate the MT when needed
Shutting off the MT when not needed
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