Mobile Computing COE 446 Network Operation

1. Mobile Computing COE 446Network 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. 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

3. Mobile Management 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

7. Mobile Management 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

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

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

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

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

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

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