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Jenhui Chen, Chih-Chieh Wang and Jiann-Der Lee
International Conference on Wireless Broadband and Ultra Wideband
Communications, 2007
AusWireless, 2007 1
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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.
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Architecture of IEEE 802.16e (AE) standard.9
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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
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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
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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
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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
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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
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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
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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
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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 ))((
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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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