Jenhui Chen, Chih-Chieh Wang and Jiann-Der Lee

International Conference on Wireless Broadband and Ultra Wideband

Communications, 2007

AusWireless, 2007 1

IntroductionIEEE 802.16e handover ProceduresPre-Coordination MechanismSimulation ResultsConclusion

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In 802.16e standard, a mobile subscriber station (MSS) can achieve a best disruption time (DT) of handover.Under macro diversity handover(MDHO) and

fast base station switching (FBSS).Both methods require the base station (BS) to

maintain the neighboring list.It will waste a large amount of system resources.

There are three different hard handover levels of association.These can’t achieve optimal DT.

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The feasible solution is reducing the number of forward-and-back turn around times.

Some research proposed location management and random mobility model, but non of them aim at speeding up the handover processing time.

Propose a pre-coordination mechanism (PCM) for BS initialized predicted handover scheme (PHS).SpeedLocationHandover time (THO)

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The Macro Diversity Hand-Over (MDHO) or Fast BS Switching (FBSS) capability can be enabled or disabled in the REG-REQ/RSP message exchange.

Support of MDHO and FBSS is optional for both MS and BS.

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Active BS A BS which is informed of the MS capabilities, security

parameters, service flows and full MAC context information.

Diversity Set a list of active BSs to the MS. managed by the MS and BS.

Anchor BS a BS in the Diversity Set where the MS is registered,

synchronized with, performs ranging with and monitors the DL for control information.

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MS communicates with all BSs in the Diversity Set for downlink and uplink unicast messages at the same time.

The BSs involving in MDHO are synchronized based on a common time source. have synchronized frame structure. have the same frequency assignment. shall use the same set of CIDs for the connections that

are established with the MS. are required to share or transfer MAC context.

Authentication state, registration information, etc.

The same MAC/PHY PDUs shall be sent by all the BSs involving in MDHO to the MS.

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the MS only communicates with the Anchor BS for UL and DL messages and traffic.

Transition from one Anchor BS to is performed without invocation of HO procedure

BSs involving in FBSS are synchronized based on a common time source have synchronized frames operate at same frequency channel are required to share or transfer MAC context.

Architecture of IEEE 802.16e (AE) standard.9

AE-I is exercised in one cell between Serving Base Station (SBS) and Mobile Subscriber Station (MSS).

Inbound：Packet frames are sent from internet to SBS by

mobile internet protocol.SBS forwards the packet frames to the MSS.

Outbound：MSS may sent packages to any user of internet

by the way of SBS.

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AE-II is performed for frame synchronization when MS switches the wireless link from SBS to TBS.In two cells.

AE-III is executed by a non-serving BSThe BS is neighbor BSs but will be a candidate

of TBS.Perform association of hard handover.

Association of hard handover is an optional initial ranging procedure.Level 0, Level 1 and Level 2

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Scan/Association without coordinationContention-based ranging without

coordination of handover.SBS allocates periodic intervals to MSS.MSS randomly choose a ranging code to

perform the initial ranging.The ranging code is based on random backoff

mechanism.Countdown interval CW=2n+5 n є [0,5].

After TBS receives ranging code, it sends RNG-RSP and allocate adequate resource for MSS to transmit RNG-REQ.

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MSS. ofNumber :N

.)CW

1-CW(Sby calculated y,probabilit ranging Successful :Ps

.2

CWT toequal isit and rangingth -n theof windowcontention :T

.Ps)-(1PT...)P-(1PTPTT

process. ranging based contentionfor required timeaverage The :T

handover. duringon registrati-refor required timeaverage The :T

ion.authorizat-refor handover during require timeaverage The :T

downlink. new ation withsynchroniz frame torequired timeaverage The :T

REQ.-RNGfor required timeaverage The :T

N

nnn

1-nsnss2s1CR

CR

RR

RA

SYN

RNG

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The service disruption time (DT) is defined as starting from SBS or MSS sends a handover request until MSS complete frame synchronization with TBS.

Contention based ranging process + re-

authorization + RNG-REQ + re-registration + synchronization with new downlink.

.0 SYNRRRNGRACRL TTTTTT

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It provides the MSS’s association with coordination.Neighbor BS provide

rendezvous timeA unique code number (from the initial ranging code set)A transmission opportunity within the allocated region

SBS Provides these association parameters to the MSCoordinate association between MMS and nBS

Then, handover process will spend TRA, TRR , the time of TL1 is

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MMS and SBS transmission + SBS and nBS

transmission + rendezvous time + re-authorization + re-registration + internet delay + synchronization with new downlink.

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time.rendezvousby followed immediate framefirst :T

delay.internet torequired timeaverage :T

nBS. toSBSbetween required ion time transmissaverage :T

MSS. toSBSbetween required ion time transmissaverage :T

R

ID

nBSSBS

MSSSBS

.TTTTTTTT SYNIDRRRARnBSSBSSBSMSSL1

Network Assisted Association Reporting.Almost same with Level 1the MS DOSE NOT have to wait for RNG-RSP from

the neighbor BSthe RNG-RSP information will be sent by each

neighbor BS to the Serving BS (over the backbone). The Serving BS may aggregate all ranging related

information into a single MOB_ASC_REPORT message.

MSS and SBS transmission + SBS and TBS

transmission + internet delay + synchronization with new downlink.

.2 SYNIDTBSSBSSBSMSSL TTTTT

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PCM: pre-coordination mechanism

280ms

230ms

60ms

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Step 1: Measure MSS Location.BS periodically (10sec) broadcast report

request (REP-REQ) message to check MSS is still in the service set.

By the response, BS can get SNR value and estimate the distance between SBS and MSS.

The distance is determine as Step 2: Calculate MSS Movement.

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)1(Δd1i t

10sec)( ΔtΔt

ΔdΔd

12

1i

2i

Step 3: Calculate TBS.As we know the direction of MSS, SBS can

decide a unique TBS for MSS.Using SNR and distances versus frequencies to

decide the TBS.

Step 4: Predict THO.First, we can get velocity by

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MMSiii V

ΔtΔt

ΔdΔd

12

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Average time of Velocity MSS will be

According to GCA framework, we can calculated h leads to

Nc: Number of channels for usage in a macrocell

C00: Number of channels

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MSSi

xMSSiMSSiMSSi

MSSi Vx

VVVV

...21

12

||3

3

00C

Nch

}]/10N-SNRLCCX

]c

1)B)|C|1)(3(h4ππdo(20log[GtGt10exp{[Ptdd

0minr,Hfσ

002

H0cell

Pt: transmitted power.Gt and Gr: Transmitter and receiver antenna gain.PL(d): path loss with distance d.L: system loss.Xσ: zero-mean Gaussian distributed random

variable. FH: highest frequency of system.σ: path loss exponentCf and CH: frequency correction factor and

receiver antenna height correction factor.H: receiver antenna height.

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}]/10N-SNRLCCX

]c

1)B)|C|1)(3(h4ππdo(20log[GtGt10exp{[Ptdd

0minr,Hfσ

002

H0cell

The movement distance between time ta and tb of MSS denote as

We can get

According to above equation, the MSS THO can predicted by

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tbtbitaitbitai ddddtdi cos2)( ,,2,

2,

)( tdi

MSSi

iHOi

V

ddcellTMSS

2

The number of channels in C0 is represent as | C0 | and we have

According to the division of sections, we have

The number of channels in Aij denoted as |Cij| will be

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NcCCCC x 3|||||||| 210

microcell basic a of area therepresent ||

||)12(||

00

00

A

AjAij

2||3

3)1(

||)12(3||||

3

3||||)12(...||3||

3

3||||

3||||3

}5,...,0{,|||||00|)12(

00

2

002

0)1(

000000

1

0

0

1

0

C

Nh be willequation above

ChCCxngSubstituti

CNChCCh Solve

CNCC Replacing

CNC

iCCandCj

c

ihi

xc

xch

j

ij 0

xc

h

jiji

Step 5: Pre-corrdination with TBS.When MSSi at approaches

, SBS will request pre-coordination to TBS for handover

Step 6 and Step 7: TBS Respond.If the resource of TBS is available, TBS will

allocate a non-contention-bas initial ranging opportunity to MSS.In order to synchronously transfer fast HO.

TBS put fast_ranging_IE in UL-MAP and reply to SBS by MOB_BSHO-RSP.

TBS will only hold this request service for 10 sec.

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di HOiiHO dtdd ))((

Step 8: Request Handover.SBS will prepare pre-coordination handover

message of boundary MSS for each 10 sec.When MSS approaches THO-10s, MSS requests

for handover.SBS broadcasts responded agreement message

from TBS to MSS.Step 9: Fast Handover.

When MSS receives the TBS message, MSS will immediately sends MOB_HO-IND message for handover.

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Simulator: QualNet.Simulator Model

Seven BSs and each have six hexagons around them.

The diameter of each hexagon is 1000m.The range of operating spectrum is 2.40~2.46

GHz.Simulation model is operating in TDD mode.

Simulator EnvironmentOne serving BS with 40MSSs and 6 nBSs.MSSs are randomly developed around the BS.Using QPSK ½ encoding rate.

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31SYNMSSSBSPCM TTDT

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Proposed a pre-coordination mechanism (PCM) for BS.Monitors moving MSS and prepares ranging

code for handover.PCM decreases the disruption time and

handover failure probability.The simulation result show that PCM can

improve the lower DT by close to 11ms without changing standard.

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