Battery Based Handover2

7/30/2019 Battery Based Handover2

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Terminal Battery based handover.

The Idea aims to save the battery power of the mobile terminal during Network Discovery

by reducing the frequency of Network Discovery and the number of Scanned Networks.

The frequency of scanning is reduced by exploiting clustering in which mobile terminals in

the same geographical location are grouped into clusters. The number of scanned numbersis reduced basing on the battery status level of the mobile terminal.

How it works.

The mobile terminals in the same geographical location are grouped into clusters. When a

mobile terminal wants to perform vertical handover, it sends a handover request to the

central server. The handover request is accompanied with information regarding the

current battery level of the mobile terminal and the geographical location. The server first

checks if it has the information requested by the mobile terminal. In case the required

information is available at the server end, the server forwards the information to the

requesting terminal instructing it to perform handover mechanism.

In case there is no information on the server end, the server first estimates the energy

consumption rates of the previously reported access networks. It then checks the battery

level of the mobile terminal. If the battery level is below a given threshold, the server will

instruct the requesting terminals to scan only networks whose estimated power

consumption rate is below a given threshold value that will not drain the battery of the

terminal before end of data transmission. One way in which the server is able to know the

wireless networks under its control is through the reports from the previous

scans/discoveries performed by the mobile terminals. For every discovery conducted, the

server updates the list of available Networks in a given cluster to include the new wirelessnetworks discovered if any otherwise it maintains the hold table and assumes those are the

only available networks.

The mobile terminal will not attempt to discover wireless networks whose power

consumption cannot be met by the battery level of the mobile terminal. As the mobile

terminal power decreases further, it means the number of networks that the terminal can

hand over to decreases hence the scanned networks also decrease hence enabling a low

power mobile terminal to spend less energy in network discovery. This power based

selective scanning decreases the number of scanned Networks hence increasing terminal

battery life time. The discovery attempts are further reduced by clustering approach in

which nodes of the same cluster can share the handover information.

Note: We can permit a mobile terminal whose battery level can sustain the network with

the highest energy consumption among the previously discovered networks to activate all

its interfaces to discover more available networks. This will ensure that we do not only

stick to networks discovered previously.


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Energy consumption Estimation

The energy consumed by a given wireless network can be estimated by considering the

energy spent during transitions between different states and the energy consumed in the

states. We consider the different transitions to different states as events. The energy

consumption of cellular networks differs from that of WLAN due to the dialup

requirements of the cellular networks.

The transition diagram of the energy consumption between different states is shown

below.

SOFF SNCI SPISTRA

SOFF

SI SAI STRA

SPSI STRPS

A

B

(EF,TF ) (EPD , TPD)(ED, TD)

(EA, TA)(EPC, TPC)(EO, TO)

(EA, TA)

(ED, TD)

(EPA, TPA)

(EAP,TAP)

(EF,TF ) (EDS,TDS) (ED,TD)

(EA, TA)(EAS,TAS)(E0 ,TO)

B- Transition diagram for WLAN device.

A- Transition diagram for dial up device.Where

States:

-SOFF- Power off. - SNCI- Not (PPP) connected, idle. - SPI- PPP connected, idle- STRA- Tx,Rx, active. - SI- Idle (not associated). - SAI - Active (mode),idle.

- SPSI- Power save (mode) idle. - STRPS- Tx-Rx power save (mode)

Events

-ED- Power-on -EF- Power-off -EPC- Dialup/ppp connect -EPD- Dialup/PPP

disconnect -EA- Data comm..start -ED- Data comm.end -EAS(AP) Association


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-EDS- (AP) Disassociation - EAP- Active mode to PS mode -EPA- PS mode to

Active mode

States such as Power off (EF) , End of active data communication (ED), AP disassociation

(EDS) that take less power can be ignored in the analysis. Also, events such as association

(EAS) and switching between active mode and power save mode (EAS and EPA ) can beignored.

The main energy consumption for a given network interface occurs during the active data

communication. This involves transmission and reception of data.

The energy consumed during active data communication varies depending on the type of

application such as browsing, downloading, streaming as well as network condition, radio

situation etc. The power consumption pattern can be modeled considering two main

independent variables namely time (duration) of data communication and amount of data

being received (or sent) by a particular type of application or protocol. Therefore the

general equation of energy consumption can be framed as;E=rd d + rtt + c

Where

rd = energy consumption rate for data (Joules/ KByte).

d =amount of data (Kbyte)

rt =Energy consumption per unit time(w)

t= transaction time (sec),

C= constant

E= total energy consumed to receive d amount of data which took t amount of time (J)

The energy consumption estimation is made considering the highest energy consumingdata communications which occur for real time applications (such as video streaming) and

non-real time applications( such as file download).

The amount of data that would be received can be determined if we predict the duration of

the communication. In general this requires the user to know how long he wants to talk or

how long the video clip is. If the data rate, Rreq , required by the particular session is known

to the terminal, the energy Estimation can be rewritten as;

E=t [ rt+ Rreq rd]+ C where tRreq =d

From the above equation, it is possible to estimate the energy required for a session if we

can predict how long the session will last.

File download

In this case, the terminal can predict the time required to download d amount of data if the

current available data rate, Rcur is known. Substituting d/Rcur .The energy estimation is

given as;

E=d[rt/Rcur + rd] + c.


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Hence from this equation, once the size of the file to be downloaded is known, the terminal

can predict as to how much energy will be consumed to download the file.

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Battery Based Handover2