1. January 15, 20151 Mobile Computing COE 446 Network Operation Tarek Sheltami KFUPM CCSE COE http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

2. January 15, 20152  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 Outline

3. January 15, 20153 Radio Resources and Power Management  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 Mobile Management

4. January 15, 20154

5. 5

6. 6

7. 7 Open Loop Power Control  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 Mobile Management

8. January 15, 20158 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 Mobile Management

9. January 15, 20159 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

10. January 15, 201510

11. January 15, 201511

12. January 15, 201512 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 Mobile Management

13. January 15, 201513

14. January 15, 201514 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

15. January 15, 201515 Discontinuous Transmission and Repetition at Lower Transmit Powers  Voice Activity Detector (VAD)  A technique used in speech processing in which the presence or absence of human speech is detected  The main uses of VAD are in speech coding and speech recognition  It can facilitate speech processing, and can also be used to deactivate some processes during non-speech section of an audio session  It can avoid unnecessary coding/transmission of silence packets in Voice over Internet Protocol applications, saving on computation and on network bandwidth

16. January 15, 201516 Discontinuous Transmission and Repetition at Lower Transmit Powers..  Therefore various VAD algorithms have been developed that provide varying features and compromises between latency, sensitivity, accuracy and computational cost  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

17. VAD Behavior 17

18. January 15, 201518 Sleep Modes  MT enters into a sleep mode during periods of inactivity  Activate the MT when needed  Shutting off the MT when not needed

19. January 15, 201519

20. January 15, 201520