January 15, 20151 Mobile Computing COE 446 Network Operation Tarek Sheltami KFUPM CCSE COE Principles.

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Mobile Computing COE 446

Network OperationTarek Sheltami

KFUPMCCSECOE

http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm

Principles of Wireless Networks

K. Pahlavan and P. Krishnamurth

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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

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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

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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

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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

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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

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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

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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

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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

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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

VAD Behavior

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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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