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IDLE MODE BEHAVIOR
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MS in Idle Mode
Doesnt have a dedicated channel, but able to access the Network and able to be
reached by the Network.
MS will always try to camp on the best cell based on the signal strength criterion.
MS will continuously monitor the serving and neighbor BCCH carriers to decide which
cell to camp on.
The purpose behind studying the Idle Mode Behavior is to always ensure that the MSis camped on the cell where it has the highest probability of successful
communication.
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MS Tasks during Idle Mode
PLMN Selection.
Cell Selection.
Cell Reselection.
Location Updating. Monitor the Incoming Paging.
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MS Tasks during Idle Mode
PLMN Selection
Cell Selection.
Cell Reselection.
Location Updating. Monitor the Incoming Paging.
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PLMN Selection Criterion
PLMN identity is defined as MCC+MNC which is part of the LAI, whereLAI=MCC+MNC+LAC.
MCC: Mobile Country Code - MNC: Mobile Network Code -LAC: Location Area Code
When the MS is powered ON, it will check if it needs to perform a Location Update
by comparing the new LAI with the old stored one.
An MS will need to make a PLMN selection only incase:
1. MS is powered ON for the 1st time i.e. No PLMN was registered on before
(No Information on MCC&MNC is stored on SIM)2. Old PLMN is not available any more (Out of coverage/Roaming)
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PLMN Selection Criterion
When the MS has to do a PLMN selection due to one of the previous cases, theselection mode will depend on the MS settings either Automatic or Manual.
Automatic PLMN Selection Mode steps:
1. Home PLMN.
2. Each PLMN stored on the SIM card in priority order.
3. Other PLMNs have Signal Strength > -85 dBm.
4. All other PLMNs in order of decreasing Signal Strength.
Manual PLMN Selection Mode:
1. Home PLMN.
2. All other available PLMNs and give the user the choice to select.
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PLMN Selection Criterion
National Roaming
If National Roaming is permitted then a MS can register on a PLMN in its home
country other than its home PLMN.
National Roaming may be allowed on a certain location areas (LAs) of the visitorPLMN.
MS should periodically try to access back his home PLMN, but this periodic attempts
will occur only on automatic selection mode.
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MS Tasks during Idle Mode
PLMN Selection.
Cell Selection
Cell Reselection.
Location Updating. Monitor the Incoming Paging.
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Cell Selection Criterion
The Cell Selection algorithm tries to find the most suitable cell in the selected PLMN
and make the MS camp on.
Cell Selection is done by the MS itself.
During Idle Mode the Network doesnt know the cell which the MS is camping on, it
only knows the Location Area where the mobile registed himself in.
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Cell Selection Criterion
MS will synchronize to the BCCH
frequency and read system information
(LAI,BA List,etc)
Scan RF Frequencies one by one and
calculates the Average received signalstrength over 3 5 seconds
Tune to the RF Frequency with the
highest average received signal strength
Camp on the Cell
Check if the chosen frequency is a
BCCH carrier frequency or not
Check if C1 > 0 or not
Check if Cell is barred or not
Check if PLMN is desired or not
Tune to the next higher frequency that
wasnt tried before
Yes
Yes
No
Yes
No
Yes
No
No
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Cell Selection Criterion
Scanning RF Frequencies may occur in 2 ways:
1. Normal Scanning: Scan all Frequencies in the band ex:124 freq. in GSM900 Band.
2. Stored List Scanning: Scan the Frequencies in the Idle BA list (BCCH Allocation)
stored on the MS SIM before being switched off.
(BA list can have maximum 32 frequencies)
If MS found cell belongs to the desired PLMN but not suitable, the MS will start to
scan the Idle BA list of this cell.
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Cell Selection Criterion
Cell is said to be suitable if:
1. Cell belongs to the desired PLMN
If at least 30 strongest frequencies from GSM900 band were tried and no suitable
cell was found, then the MS will try another PLMN based on PLMN criterion.
2. Cell is not Barred ( CB = NO)
Some cells can be barred for access at selection and reselection or given lower
priority based on settings of parameters: CB
3. C1 > 0
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Cell Selection Criterion
C1 is called Cell Selection Quantity
It is calculated at the MS based on the below equation:
C1 = (Received SSACCMIN) max (CCHPWR-P,0)
ACCMIN Minimum allowed DL received SS at the MS in order to access the system
CCHPWR
Maximum allowed transmitting power by the MS in the UL.P Maximum out put power of the MS according to its class.
N.B:
1. ACCMIN and CCHPWR are cell parameters sent to the MS at the BCCH channel.
2. If CCHPWR > P then C1 will decrease and so the Received SS should be large
enough to keep C1 > 0 (May be this cell is not designed for this MS class)
3. ACCMIN, CCHPWR, P are all measured in dBm, where C1&C2 are measured in dBs
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MS Tasks during Idle Mode
PLMN Selection.
Cell Selection.
Cell Reselection
Location Updating. Monitor the Incoming Paging.
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Cell Reselection Criterion
After a cell has been selected, the MS will start the cell reselection measurements toknow if it is better to stay on the current cell or to camp on another cell.
Cell reselection measurements:
1. Monitors the SS (Signal Strength) of the BCCH carrier of the serving cell.
2. Monitors the SS of the BCCH carrier of all defined neighbors in the Idle BA list.
3. Continuously read system information sent on the serving BCCH carrier at least
every 30 seconds.
4. Continuously read system information sent on the BCCH carrier for the six strongest
neighbors at least every 5 minutes.
5. Try to decode BSIC of the six strongest neighbors every 30 seconds to assure thatit is still monitoring the same cells.
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Cell Reselection Criterion
Cell reselection measurements summary
BSIC BCCH Data (System Information)
Serving Cell - Every 30 Seconds
Six Strongest Neighbors Every 30 Seconds Every 5 Minutes
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Cell Reselection Criterion
When Cell Reselection will occur ?
1. Serving Cell became barred ( CB = YES )
2. C1 serving cell falls below zero for more than 5 seconds.
3. MS tried to access the network through this cell unsuccessfully for the allowed no.
of times defined by the parameter MAXRET
4. C2 neighbor cell
( one of the six strongest neighbors) became greater than C2 serving cellfor more than 5 seconds.
5. MS detects Downlink Signaling Failure.
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Cell Reselection Criterion
What will happen when the MS needs to make cell reselection?
The MS will camp on the cell that has the highest C2 value.
C2 is called Cell Reselection Quantity
C2 = C1 + CROTO * H( PT T ) where PT 31
C2 = C1CRO where PT = 31
0 , X < 0
Where H(x)
1 , X 0
CRO Cell Reselection Offset, unit = 2 dB, value range = 0 to 63TO Temporary Offset, unit = 10 dB, value range = 0 to 7
PT Penalty Time during which TO is valid
T Initiated from zero when the MS places the neighbor in the list of the Six Strongest
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Cell Reselection Criterion
CRO : defines a signal strength offset to encourage or discourage MSs to reselectthat cell.
TO : defines a negative temporary offset for certain time according to settings of PT
(Practically this is useful to prevent fast moving MS from camping on microcells)
PT: If PT is set to 31, this means that a (ve) SS offset CRO will be applied to this
cell and it appears less favorite for cell reselection.
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Cell Reselection Criterion
Down Link Signaling Failure Algorithm The Algorithm of type Leaky Bucket and used a counter D, where D = 90/MFRMS
MFRMS is a cell parameter defines the no. of multiframes between the transmission
of each paging group i.e. if MFRMS=4 then a MS attached to a certain paging group
will wait in sleeping mode for 4 multiframes (4*235msec) until it is up again to listen to
paging.
When the MS is up to listen to its paging group, if the message is not decoded
successfully then D is decremented by 4 and if the message is decoded correctly
then D is incremented by 1.
If D reaches zero, then a Down Link Signaling Failure is detected and cell reselection
took place.
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Cell Reselection Criterion
Down Link Signaling Failure Algorithm Ex: Assume that MFRMS = 4
Downlink signaling failure counter is initialized: D = round(90/MFRMS)=22.
If the MS unsuccessfully decodes a paging message, then: D = D - 4 = 18.
If the MS successfully decodes a paging message, then: D = D + 1 = 19.
If D reaches zero, then a Down Link Signaling Failure is detected and
cell reselection took place.
N.B: D cant exceed the bucket size given by round(90/MFRMS)
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Cell Reselection Criterion
CRH ( Cell Reselection Hysteresis ) Cell Reselection between two cells lie in two different Location Areas, will be
accompanied by Location Update.
At the border between cells the Signal level may be comparable, cell reselection may
occur many times accompanied by many location updating leading to huge signalingload.
To avoid this, a parameter CRH is introduced such that a cell in another location area
LA2 should have C2LA2 should greater than C2LA1 of serving cell lie in LA1 by at least
CRH in order to be selected.
If C2LA1 = 5 dB, CRH = 4 dB, then C2LA2 9 dB in order to be selected.
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MS Tasks during Idle Mode
PLMN Selection.
Cell Selection.
Cell Reselection.
Location Updating Monitor the Incoming Paging.
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Location Updating
To make it possible for the mobile subscriber to receive a call and initiate a callwhenever needed, the network must know where the MS is located whenever it
moves thats why Location Updating is needed.
In the Idle Mode, the Network knows the location of the MS on a Location area
resolution not on a cell resolution.
There are three different types of location updating defined:
1. Normal Location Updating.
2. Periodic registration.
3. IMSI attach & IMSI detach (when the MS informs the network when it enters aninactive state)
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Location Updating
1. Normal Location Updating
Initiated by the MS when it enters a cell belongs to a new Location Area (LA).
The MS will compare the LAIold stored on the SIM with the LAInew broadcasted from
the new cell and it will found them different so itll perform Location Update type
normal.
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Location Updating
2. Periodic Registration
Regularly the MS should update the Network with its current location Area.
The Network will inform the MS how often it should report the location Area he is
registering himself in.
Based on the value of the Parameter T3212 the MS will know how frequent it should
make periodic registration.
T3212 take values from 1 (6min) to 255 (25.5 Hours), default = 40 (4 Hours)
MSC has a supervision time = BTDM+GTDM if it doesnt hear from the MS during
this period, the MSC will consider the MS implicitly detached. BTDM+GTDM should >T3212 , to not consider the MS detach before periodic
location update is performed.
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Location Updating
3. IMSI Attach/Detach
IMSI attach/detach operation is an action taken by the MS to inform the Network
either it will go to inactive state (Power off) or it returned back to idle mode.
ATT is a cell parameter that will inform the MS whether IMSI attach/detach is
operational or not.
If ATT=Yes, then before the MS will be switched off, it will send an IMSI detach
request to the Network, so no paging messages will be sent to this MS while it is in
this state.
When the MS is switched on again it will send an IMSI attach request to the
Network so now paging messages can be sent normally to this MS.
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MS Tasks during Idle Mode
PLMN Selection.
Cell Selection.
Cell Reselection.
Location Updating. Monitor the Incoming Paging
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Monitor the Incoming Paging
Let us revise the DL logical channels and their mapping:
I) BCH(Broadcast Channels): includingFCCH(Frequency Correction Channel)
SCH(Synchronization Channel) Always Mapped on TS0/C0
BCCH(Broadcast Control Channel)
II) CCCH(Common Control Channels): includingPCH(Paging Channel) Always Mapped on TS0/C0
AGCH(Access Grant Channel)
III) DCCH(Dedicated Control Channels): including
SDCCH(Stand Alone Dedicated Control Channel) May be Mapped on either
SACCH(Slow Associated Control Channel) TS1/C0 or TS0/C0
CBCH(Cell Broadcast Channel)
FACH(Fast Associated Control Channel) Work in Stealing mode by
replacing the TCH time slot
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CBBBBSF
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
F S F S F S F S F S I
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7
Default Mapping on TS0/C0 (BCH+CCCH) Non Combined Mode
51 TDMA Frames = 1 Control Multi-frame
B C C C C C C C C C
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Default Mapping on TS1/C0
(SDCCH+SACCH+CBCH(optional))
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Monitor the Incoming Paging
Combination of Control channels (Different Mapping Criteria)
Mapping on TS0/C0 is controlled by Parameter called BCCHTYPE
BCCHTYPE = NCOMB (Non Combined, BCH&CCCH)
TS1/C0 will carry SDCCH+SACCH
= COMB (Combined, BCH&CCCH&SDCCH/4)TS1/C0 will be free for TCH
= COMBC (Combined with cell broadcast channel CBCH is in use,
BCH&CCCH&SDCCH/4&CBCH) TS1/C0 will be free for TCH
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Monitor the Incoming Paging
Combination of Control channels (Different Mapping Criteria)
SDCCH may have on of the following 4 configurations based on parameter SDCCH
SDCCH = (i) SDCCH/8 (8 SDCCH Sub-channels i.e. make call setup for 8 users)
= (ii) SDCCH/8 including CBCH (7 SDCCH Sub-channels + 1 CBCH)
For these two cases, the BCCHTYPE=NCOMB and the mapping of the SDCCH channel
is done on TS1/C0
= (iii) SDCCH/4 (4 SDCCH Sub-channels)
= (iv) SDCCH/4 including CBCH(3 SDCCH Sub-channels + 1 CBCH) For these two cases, the BCCHTYPE=COMB or COMBC and the mapping of the SDCCH
channel is done on TS0/C0
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Monitor the Incoming Paging
Combination of Control channels (Different Mapping Criteria)
Non Default Mapping on TS0/C0 (BCH+CCCH)
2*51 TDMA Frames = 2 Control Multi-frame
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Monitor the Incoming Paging
Combination of Control channels (Different Mapping Criteria)
The Table below summarizes all the previous details
Default Mapping (Non Combined) Non Default Mapping (Combined)
BCH+CCCH on TS0/C0 and
SDCCH+SACCH+CBCH on TS1/C0BCH+CCCH+SDCCH+SACCH+CBCH on TS0/C0
CBCH doesn't exist CBCH exist CBCH doesn't exist CBCH exist
1 block for BCCH 1 block for BCCH 1 block for BCCH 1 block for BCCH
9 blocks for CCCH 9 blocks for CCCH 3 blocks for CCCH 3 blocks for CCCH
8 blocks for SDDCH 7 blocks for SDDCH 4 blocks for SDDCH 3 blocks for SDDCH
1 block for CBCH 1 block for CBCH
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Monitor the Incoming Paging
Paging Groups
The MS will monitor the incoming paging in only specific times, and the rest of the time it
will remain in sleeping mode.
In this way we save the MS battery and we decrease the UL interference on the system.
The MS will monitor the incoming paging when the Paging Group assigned for this MS is
transmitted only.
The CCCH block can be used by either PCH or AGCH.
When the CCCH block is used for paging it will be called Paging Block
The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive frames.
The Paging Block can be used to page 4/3/2 users according to IMSI or TMSI is used
when paging the MS ( Length IMSI = 2 TS, Length TMSI = 1 TS) The group of users belong to the same paging block will be called Paging Group
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CBBBBSF
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
F S F S F S F S F S I
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7
Default Mapping on TS0/C0 (BCH+CCCH) Non Combined Mode
51 TDMA Frames = 1 Control Multi-frame
B C C C C C C C C C
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Monitor the Incoming Paging
Paging Groups
As appeared the MS will listen to paging in only specific times.
The MS will utilize the time between the 4 TS that lie in 4 consecutive frames to make the
required measurements on the neighbor cells.
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Monitor the Incoming Paging
Paging Groups
How many Paging Groups we have? This will depend on a parameter MFRMS
MFRMS is a parameter defined per cell and it defines how frequent the paging group
assigned for certain MS will be transmitted.
MFRMS takes values from 1 to 9,
if MFRMS=1 then the paging group assigned for certain MS will be transmitted every 1control Multiframes=235 msec
if MFRMS=9 then the paging group assigned for certain MS will be transmitted every 9
control Multiframes = 9*235msec=2.3 seconds.
If MFRMS is large:
Positive Side: The MS battery life time will increase coz the MS remains in sleeping mode forlonger time + paging capacity will increase.
Negative Side: Call setup time will increase coz the paging wont be sent to the MS except
when the time of its paging group came.
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Monitor the Incoming Paging
Paging Strategies
Paging Strategies are controlled by parameters in the MSC.
Setting of parameters will decide whether the paging will be local paging (within the LA) or
global paging (within the MSC service area).
Setting of parameters will decide also whether paging will be done via IMSI or TMSI.
Using the parameters we can decide also how the second paging will be incase the first
paging failed, ex: If 1st paging was local with TMSI then we can set the 2nd paging to be
global with IMSI.
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Related Feature to the Idle Mode Behavior
Adaptive Configuration of Logical Channels (ACLC)
As we know the SDCCH channel is used for signaling i.e. call setup, while the TCH
channel is used to carry real user traffic (speech/data).
As per the GSM standards, the GOS for TCH=2% i.e. within 100 calls if 2 of them areblocked then this will be acceptable, for the SDCCH/8 the GOS=0.5% and for the
SDCCH/4 the GOS=1%
As we know in the default settings for frequency C0, TS0 is used to carry BCH+CCCH
and TS1 used to carry SDCCH+SACCH, and TS2TS7 used to carry speech/data
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Related Feature to the Idle Mode Behavior
Adaptive Configuration of Logical Channels (ACLC)
Now if the signaling load is high, ex: many users need to make call setup, then high
blocking will occur exceeding the acceptable value = 0.5%
To solve the blocking we have 2 ways:
i) Static configuration of a TCH TS to be used as SDCCH forever
( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data)
But in this case we lost 1 TCH channel i.e. 5 users can talk simultaneously instead of 6
ii) Adaptive configuration of a TCH TS to be used as SDCCH/8 when there is high SDCCH
utilization only
( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data, but
When the utilization is back to its normal trend, TS2 will be configured back automatically as a
TCH and used to carry speech/data)
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Related Feature to the Idle Mode Behavior
Adaptive Configuration of Logical Channels (ACLC)
Main Controlling Parameters:
ACSTATE:Activates/Deactivates the feature on cell basis, values: ON/OFF
SLEVEL: No. of Idle SDCCH sub-channels below which the feature will work.
The conditions that should be fulfilled for the ACLC feature to work:
1) ACSTATE=ON
2) No. of Idle SDCCH sub-channels SLEVEL (Indication for high utilization)
3) No. of already defined SDCCH channels/8 < Max. allowed configuration of SDCCHs in
the cell.4) No. of Idle TCHs > 4
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Parameters Summary
SCH Parameters
Parameter Name Value Range Recommended Value UnitBSIC NCC: 0 to 7 BCC: 0 to 7
RACH Control Parameters
Parameter Name Value Range Recommended Value Unit
MAXRET 1,2,4,7 4
Control Channel Parameters
Parameter Name Value Range Recommended Value Unit
BCCHTYPE COMB COMBC NCOMB NCOMB
SDCCH0 to 16 (0: No SDCCH/8
configured-combined mode)1
IMSI Attach/Detach Parameters
Parameter Name Value Range Recommended Value Unit
ATT Yes, No Yes
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Parameters Summary
Paging Parameters and Periodic Update
Parameter
NameValue Range Recommended Value Unit
MFRMS 2 to 9 6Control Channel Multi
frame
AGBLK 0 or 1 0
T32120 to 255 (0: infinite-No periodic
registeration)40 6 minutes
Cell Selection and Reselection Parameters
Parameter
NameValue Range Recommended Value Unit
ACCMIN 47 dBm to 110 dBm 110 dBm dBm
CCHPWRGSM900: 13 to 43 in steps of 2
GSM1800: 4 to 30 in steps of 2
GSM900: 33 dBm
GSM1800: 30 dBmdBm
CRO 0 to 63 0 2 dBTO 0 to 7 (7:infinite) 0 10 dB
PT 0 to 31 0
CRH 0 to 14 in steps of 2 dB
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Thank You
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Handover (Locating)
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Handover (Locating) Algorithm
The Handover (Locating) Algorithm is the basic feature to provide mobility in the Radio
Network.
Aims At? i) Keep the continuity of a current call with acceptable quality.
ii) Cell size control in-order to decrease total interference in the system.
Implemented where? In the BSC.
Location process initiated when? After Hand Over (HO), Assignment or Immediate
Assignment.
Inputs to the Algorithm? Signal Strength, Quality measurements &TA for serving cell and
Signal Strength measurements for neighbor cells.
Output from the Algorithm? List of candidates which the algorithm judges to be possible
candidates for HO (List of HO candidates are ranked and sorted in descending order)
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Handover (Locating) Algorithm
The main Flow of the Handover (locating) Algorithm goes as follow:
Filtering Basic Ranking Urgency Conditions HandlingInitiations
Auxiliary Radio Network
Features Evaluation
Organizing the List
Sending the List &
Allocation Reply
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Handover (Locating) Algorithm
Initiation Filtering.
Basic Ranking.
Urgency Conditions Handling. Auxiliary Radio Network Features Evaluation.
Organizing the List.
Sending the List & Allocation Reply
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Filtering
Simply it is the process of collecting the required data on Signal Strength (SS),Quality and Time Advance (TA) for serving and neighbor cells and average these
consecutive measurements over a specified period to rank these cells.
This is accomplished in two steps:
1. Measurements preparation
2. SS, Quality and TA filtering
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Filtering
1. Measurements preparation
Data that is measured:
The MS can measure the SS of up to 32 neighbor frequencies but only the six strongestneighbors (which it succeeded to decode its BSIC over the last 10 seconds) are reported
and considered candidates for HO.
Cell on which measurements
are reportedMeasured Quantity
Who makes the
measurements?
Serving Cell
SS DL MS
Quality DL (rxqual_DL) MSQuality UL (rxqual_UL) BTS
TA BTS
6 Strongest neighbor cells SS DL MS
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Filtering
1. Measurements Preparation
SS measurements are delivered as integer values 0 63 corresponds to real SS from
-110 dBm - 47 dBm
Quality is measured based on the BER and it may be represented in two forms:i) Integers 0 (Best) 7 (Worst)
ii) Decitransformed Quality units (dtqu) from 0 (Best) 70 (Worst)
Time Advance (TA) is reported as values between 0 63 bit period.
N.B: If TA=1 then the MS is at nearly 0.5 km from the cell
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Filtering
2. SS, Quality and TA filtering:
The consecutive measurements for SS, Quality and TA are averaged in some way
based on the equation of the filter used.
Weve 5 Types of Filters that may be used, each one has its own equation or its way toproduce output results from the collected consecutive measurements:
A. General FIR filters (Finite Impulse response)
B. Recursive Straight Average filter
C. Recursive exponential filter
D. Recursive 1st order Butterworth filter
E. Median filter
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Filtering
2. SS, Quality and TA filtering:
In addition to the way each filter use to produce output results from the consecutive
measurements, each filter has what we call filter length which is the period over which
measurements are considered.
We have controlling parameters on cell basis to select the type of filter used and the
length of the filter.
Also the type of the filter used in signaling (call setup) and dedicated phases may be
configured separately as well see.
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Handover (Locating) Algorithm
Initiation
Filtering
Basic Ranking
Urgency Conditions Handling. Auxiliary Radio Network Features Evaluation.
Organizing the List.
Sending the List & Allocation Reply
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Basic Ranking
It is called Basic coz in this stage ranking is done before handling the urgencyconditions and evaluation of the auxiliary radio network features.
As mentioned earlier, two algorithms are available for basic ranking (SS&Path loss
based Algorithm and SS based Algorithm) and theyre selected according to the
parameter EVALTYPE
EVALTYPE=1, SS & Path loss based Algorithm is used for basic ranking taking into
consideration both Signal Strength measurements and the path loss.
EVALTYPE=3, SS based Algorithm is used for basic ranking taking into consideration
Signal Strength measurements only.
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm will be done on four steps:
A. Correction of Base Station output power. Common for
B. Evaluation of the minimum signal strength condition for neighbors. both Algorithms
C. Subtraction of signal strength penalties.
D. Rank the Candidates after applying Offsets and Hysteresis.
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Basic Ranking
Basic Ranking Algorithm following the SS based AlgorithmA. Correction of Base Station output power
(A-i) Correction for Neighbor Cells
The MS is informed by the BCCH frequencies of the neighbors cells on which he has to
perform his measurements via the Active BA list.
SS_corrected_DLneighbor = SS_measured_DLneighbor - ( BSPWR -BSTXPWR )
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Basic Ranking
Basic Ranking Algorithm following the SS based AlgorithmA. Correction of Base Station output power
(A-ii) Correction for Serving Cell
1) TCH Time Slot (TS) is on the BCCH frequency
SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR -BSTXPWR )
2) TCH TS is hopping between a BCCH frequency and a TCH frequency:
SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR -BSTXPWR )/N ,
Where N is the no. of the hopping frequencies
3) TCH TS is on the OL (Over Laid sub cell)
SS_corrected_DLUnderLaid = SS_measured_DLOverLaid+ ( BSTXPWR Under LaidBSTXPWROverLaid )
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
B. Evaluation of the minimum Signal Strength condition for Neighbors
Not all the neighbors are allowed to be ranked!!
The neighbor should pass the minimum signal strength condition in order to be ranked.
SS_corrected_DLneighbor will be compared with respect to parameter called MSRXMIN,If SS_corrected_DLneighbor MSRXMIN this neighbor will be included in ranking
If SS_corrected_DLneighbor < MSRXMIN this neighbor will be excluded from ranking
If UL measurements are included then SS_corrected_ULneighbor will be compared with
respect to parameter called BSRXMIN,If SS_corrected_ULneighbor BSRXMIN this neighbor will be included in ranking
If SS_corrected_ULneighbor < BSRXMIN this neighbor will be excluded from ranking
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
C. Subtraction of signal strength penalties
Penalties or Punishments will be applied on cells that are for some reasons temporarily
undesirable.
A Penalty value will decrease the rank of some cells for certain penalty time.
SS_punished_DL = SS_corrected_DL Locating Penalties HCS Penalties
In the coming slides well talk about the two types of penalties:
(C-i) Locating Penalties
(C-ii) HCS Penalties
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Basic Ranking
Basic Ranking Algorithm following the SS based AlgorithmC. Subtraction of signal strength penalties
(C-i) Locating Penalties
1) Due to HO failure: If HO to a neighbor cell failed then weve to apply a penalty value forsome time on this neighbor so when basic ranking is done again we dont
go back to this cell.
Penalty value will be configured using parameter PSSHF (default 63 dB)
Penalty time will be configured using parameter PTIMHF (default 5 sec)
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
C. Subtraction of signal strength penalties
(C-i) Locating Penalties
2) Due to Bad Quality (BQ) Urgency HO:
If a cell was abandon due to BQ, then it should have been the best cell from SS point ofview so without penalties using the basic ranking well be back to this cell.
Penalty value will be configured using parameter PSSBQ (default 7 dB)Penalty time will be configured using parameter PTIMBQ (default 5 seconds)
3) Due to Excessive TA Urgency HO:Handled in the same manner like the BQ case.
Penalty value will be configured using parameter PSSTA (default 63 dB)
Penalty time will be configured using parameter PTIMTA (default 30 seconds)
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
C. Subtraction of signal strength penalties
(C-ii) HCS Penalties
It is related to the HCS (Hierarchical Cell Structure) feature when a MS is detected as a fastmoving mobile (If fast moving mobile feature is activated)
A penalty will be applied on lower layer cells so in ranking we will prioritize cells in the same
layer of the serving cell and cells in higher layers and in this way unnecessary HOs are
prevented ( ex: layer2 cells will be prioritized than layer1 cells)
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
D. Rank the Candidates after applying Offsets and Hysteresis
Ranking for neighbor cells will be done after
applying Offsets and Hysteresis.
Offset:Displace the cell border as compared to
The border strictly given by SS.
Controlling parameter: OFFSET (default: zero dB)
Hysteresis: To reduce the risk of ping pong HO
a region for Hysteresis is applied
around the cell border.
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
D. Rank the Candidates after applying Offsets and Hysteresis
If the Hysteresis value is too high there will be a risk that the MS will be connected to the cell
of low SS for long time and if the Hysteresis is too low then there will be a risk that ping
pong HOs occur.
So the applied value of Hysteresis will be variable based on the received SS of the serving
cell.
SS_corrected_DLservingcell will be compared to value HYSTSEP (default -90 dBm),
If SS_corrected_DLservingcell
> HYSTSEP, then the serving cell is strong enough and high
value of Hysteresis will be applied such that Hysteresis value=HIHYST (default 5 dB)
If SS_corrected_DLservingcell < HYSTSEP, then the serving cell is not strong enough and lowvalue of Hysteresis will be applied such that Hysteresis value=LOHYST (default 3 dB)
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Basic Ranking
Basic Ranking Algorithm following the SS based Algorithm
D. Rank the Candidates after applying Offsets and Hysteresis
SS_corrected_DLservingcell > HYSTSEP
Yes
HYST=HIHYST
Now,
Rankservingcell
= SS_corrected_DLservingcell
Rankneighbor= SS_punished_DLneighborOFFSETneighbor HYSTneighbor
HYST=LOHYST
Output from Basic
Ranking
No
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Handover (Locating) Algorithm
Initiation
Filtering
Basic Ranking
Urgency Conditions Handling Auxiliary Radio Network Features Evaluation.
Organizing the List.
Sending the List & Allocation Reply
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Urgency Conditions Handling
1. Bad Quality (BQ) Urgency HO
The Quality measured at the DL and UL for the serving cell will be compared with two
parameters QLIMDL & QLIMUL (default 50 dtqu) and if:
rxqual_DL > QLIMDL
rxqual_UL > QLIMUL
The Quality may drop like that as a result of Co-Channel Interference or when the SS
became very low.
When Urgency condition is detected the MS has to leave the cell and make HO to other cell,
but in this case the serving cell is the one that has the highest SS so the MS has to HO to acell of worse SS, but is the MS allowed to HO to any worse cell?
Or Urgency HO due to BQ should be performed
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Urgency Conditions Handling
1. Bad Quality (BQ) Urgency HO
Is the MS allowed to HO to any worse cell? No, this will be based on a parameter called
BQOFFSET which will ensure that far neighbors wont be selected.
If Rankservingcell Rankneighbor BQOFFSET+HYST, then this neighbor is near to the serving
cell and it is not much worse than the serving cell and it can be candidate for HO.
If Rankservingcell Rankneighbor > BQOFFSET+HYST, then this neighbor is far from the serving
cell and it will be removed from the candidate list.
Ex: If Urgency condition is detected where Rankservingcell = -75 dBm and the neighbors:
RankB = -79 dBm ,RankC = -90 dBm ,RankD = -87 dBm and BQOFFSET=5dB,HYST=0 dB
Rankservingcell RankB = 4dB < BQOFFSET= 5dB Cell B is kept in the candidate list
Rankservingcell RankC = 15dB > BQOFFSET= 5dB Cell C is removed from the candidate list
Rankservingcell RankD = 8dB > BQOFFSET=5dB Cell D is removed from the candidate list
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Urgency Conditions Handling
2. Excessive Time Advance (TA) Urgency HO
TA can be used as a measure for the distance between the BTS and the MS.
If TA > TALIM (63 bit period) Urgency HO due to TA is initiated.
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After Basic Ranking and Evaluation of the Urgency Conditions, the Serving
cell and Neighbor cells will be divided into 3 Groups
Categorization #1
Better Cell
Serving Cell
Worse Cell
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Handover (Locating) Algorithm
Initiation
Filtering
Basic Ranking
Urgency Conditions Handling
Auxiliary Radio Network Features Evaluation Organizing the List.
Sending the List & Allocation Reply
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Auxiliary Radio Network Features Evaluation
1. Assignment to Another Cell Evaluation
2. Cell Load Sharing Evaluation
3. Over Laid/Under Laid sub-cell Evaluation
4. IHO Evaluation
5. HCS Evaluation
After these Evaluations, some candidates will be removed from the HO candidate list and
Categorization#2 will be performed.
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Auxiliary Radio Network Features Evaluation
1. Assignment to Another Cell Evaluation
The Locating Algorithm may be initiated after immediate assignment to know whether it is
better for the MS to take a TCH time slot on the current cell or not.
If during the signaling phase a better cell was found after ranking, then
Assignment to Better Cell will be initiated.
If during the signaling phase no better cell was found, then the MS will normally be assigned
a TCH time slot on the current cell.
If the Better/Serving cells were congested then Assignment to Worse Cell will be initiated
if possible.
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Auxiliary Radio Network Features Evaluation
1. Assignment to Another Cell Evaluation
Is the MS allowed to take TCH time slot on any worse cell? No, this will be based on a
parameter called AWOFFSET which will ensure that far neighbors wont be selected.
Only if Rankservingcell Rankneighbor AWOFFSET+HYST, then this neighbor is near to theserving cell and it is not much worse than the serving cell and assignment to it can be done.
If Rankservingcell Rankneighbor > AWOFFSET+HYST, then this neighbor is far from the serving
cell and it will be removed from the candidate list.
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Auxiliary Radio Network Features Evaluation
2. Cell Load Sharing (CLS) Evaluation
This feature is used to reduce congestion on the serving cell.
When CLS is activated and the load on the serving cell becomes higher than certain
threshold then:
i) Valid CLS HO candidates are definedii) Re-calculation of their ranking values will be performed.
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Auxiliary Radio Network Features Evaluation
3. OL/UL Sub-Cell Evaluation
The OL/UL feature provides a way of increasing the traffic capacity in a cellular network
without building new sites.
Since OL subcell serves smaller area than the corresponding UL subcell a smaller reuse
distance can be used in in the OL subcell than in the under laid.
The OL/UL evaluation may result in a recommendation to change the subcell from the one
currently in use, this evaluation is based on:
DL SS, TA serving Cell, Distance to cell border, Traffic Load in the cell
This feature will be discussed in details afterwards.
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Auxiliary Radio Network Features Evaluation
4. Intra Cell HO (IHO) Evaluation
The IHO feature provides a way to improve the speech quality during the conservation when
bad quality is detected while the SS is high.
This is can be accomplished by changing the channel the connection is currently usingwithin the same cell.
This feature will be discussed in details afterwards.
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Auxiliary Radio Network Features Evaluation
5. Hierarchical Cell Structure (HCS) Evaluation
The HCS feature provides the possibility to give priority to cells that are not strongest but
provide sufficient SS.
The priority of a cell is given by associating a layer to the cell.
We have 8 layers from layer 1 (Highly prioritized) to layer 8 (least prioritized).
Micro cells are prioritized than Macro cells for capacity purposes.
Cells of lower layers will be ranked higher than cells of higher layers in the HO candidate
list.
This feature will be discussed in details afterwards.
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Organizing the List
A. Removal of Candidates Some Candidates may be removed coz:
Some Controlling timers are active and preventing HO to certain cell:
TALLOC: This timer prevents HO on a target cell for some time after assignment/HO failure due
to congestion on target cell. (N.B: No penalties are applied on this cell)
TURGEN: This timer prevents HO on a target cell for some time after urgency HO failure due
to congestion on target cell. (N.B: No penalties are applied on this cell)
N.B: TALLOC and TURGEN are BSC parameters (Default Values= 2 SACCH periods)
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Organizing the List
B. Ordering the Candidate list based on the Current Conditions
Means what? Means in what order the 3 categories (Above S, S, Below S) will be arranged
before sending the candidate list. This will be based on some condition flags.
Condition flags: 1Assignment Request Arrived
2
Assignment to Worst Cell is in use3 Excessive TA detected
4 BQ Urgency HO
5 OL/UL Subcell load change or IHO
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Handover (Locating) Algorithm
Initiation
Filtering
Basic Ranking
Urgency Conditions Handling
Auxiliary Radio Network Features Evaluation
Organizing the List
Sending the List & Allocation Reply
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Sending the List & Allocation Reply
The resulting candidate list will form the basis on which HO will be performed.
Empty list means that no options are better than remaining on the current cell and no HO
will occur.
The channel allocation reply may be success or failure.
Failure may be due to congestion or signaling failure on the target cell.
Based on the result of allocation either success/failure, some actions will be taken likeapplying some penalties or enabling of certain timers as we saw previously.
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Example1:
Assume that the o/p from the Filtering stage for the SS measurements is as below and we
want to prepare the Basic Ranking Candidate list for HO:
Where,
BSPWR = BSTXPWR, MSRXMIN = -90 dBm,
Cell A was abandon due to BQ urgency HO (PSSBQ=7dB)
SS based Algorithm is in use where OFFSET=0, HYSTSEP= -90 dBm,
HIHYST= 5 dB, LOHYST= 3 dB
Cell SS(dBm)
A -70
B (Serving Cell) -74
C -78
D -68
E -80
F -92
G -95
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Solution:
A) Correction of Base Station output power:
Since BSPWR = BSTXPWR then the current measurements will be kept as it is.
SS_corrected_DLneighbor = SS_measured_DLneighbor
SS_corrected_DLserving = SS_measured_DLserving
B) Evaluation of the minimum Signal Strength condition for Neighbors The SS for neighbors will be compared against MSRXMIN = -90 dBm
Cell F and Cell G have SS < MSRXMIN then they will be removed
from the list and cant be candidates for HO.
Cell SS(dBm)
A -70
B (Serving Cell) -74
C -78
D -68
E -80
F -92
G -95
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Solution:
C) Subtraction of signal strength penalties
Since Cell A was abandon due to BQ urgency HO (PSSBQ=7dB) then it will be punished,
SS_punished_DL Cell A = SS_corrected_DLPSSBQ = -70 7 = -77 dBm
The candidate list will now be in the following form:
Cell SS(dBm)
A -77
B (Serving Cell) -74
C -78
D -68
E -80
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Solution:
Now the final list according to Categorization#1 will be arranged as follows:
Categorization#1
Cell RANK(dBm) Category
D -73 Better Cell
B -74 Serving Cell
A -82 Worse Cell
C -83 Worse Cell
E -85 Worse Cell
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Disconnection Criteria
The Disconnection algorithm is not part of the locating algorithm but for completeness, the
topic is treated here.
The Disconnection algorithm manages when the connection between the MS and the
Network shall be dropped when signaling failure is detected.
The Disconnection criterion can be made in both the DL and the UL such that:
In the DL: managed by the MS and in the UL: managed by the BSC.
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Disconnection Criteria
In DL: Controlled by a parameter RLINKT (max. bucket size) , when the MS couldnt decode a
SACCH message (0.48 sec), the bucket will be decreased by 1 unit, when the MS
successfully decodes a SACCH message, the bucket will be increased by 2 units, if the
bucket reached value = Zero then disconnection will occur, recommended value
RLINKT=16
In UL:
The disconnection algorithm will run in the same way, the BSC will make the evaluation,
and the controlling parameter is called RLINKUP, , recommended value RLINKUP=16
N.B: The bucket cant have values larger than the max. value given by RLINKT/ RLINKUP
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Parameters Summary
Algorithm SelectionParameter
NameValue Range Recommended Value Unit
EVALTYPE 1 or 3 3
Flow Control Parameters
Parameter
NameValue Range Recommended Value Unit
TALLOC 0 to 120 2 SACCH period=480 msec
TURGEN 0 to 120 2 SACCH period=480 msec
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Parameters Summary
Urgency Conditions ParametersParameter Name Value Range Recommended Value Unit
QLIMUL 0 to 100 55 dtqu
QLIMDL 0 to 100 55 dtqu
BQOFFSET 0 to 63 3 dB
PSSBQ 0 to 63 7 dB
PTIMBQ 0 to 600 15 Seconds
TALIM 0 to 63 62 Bit Period (0.577msec)
PSSTA 0 to 63 63 dB
PTIMTA 0 to 600 30 Seconds
Disconnection Algorithm Parameters
Parameter Name Value Range Recommended Value Unit
RLINKT 4 to 64 in steps of 4 16 SACCH period=480 msec
RLINKUP 1 to 63 16 SACCH period=480 msec
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Thank You
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Hierarchical Cell Structure (HCS)
HCS E l ti Al ith
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HCS Evaluation Algorithm
HCS feature provides the ability and flexibility to give priority to cells that are not
strongest but provide sufficient Signal Strength.
The priority of a cell is given by associating an HCS layer to the cell where each cell will
be belonging to an HCS band.
The lower the layer ( and the HCS band), the priority is higher,
i.e. layer 1 has higher priority than layer 2, layer 3, layer 4, ..
layer 2 has higher priority than layer 3, layer 4, layer 5, ..
Up to 8 layers (in up to 8 bands) may be defined, where one or several layers can beassigned to the same HCS band.
HCS E l ti Al ith
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HCS Evaluation Algorithm
The lower HCS bands will only include lower layers compared to a higher HCS bands.
A mixture of small micro cells (lower layers) and large macro (higher layers) cells will
achieve both high capacity and good coverage.
Micro cells will be used for capacity issues while macro cells will be used to provide
coverage, fill coverage holes and handle the fast moving mobiles.
HCS E l ti Al ith
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HCS Evaluation Algorithm
With Basic Ranking only, micro cells will be ranked as the strongest server in very small
area, so to let micro cells serve in an area where acceptable SS is guaranteed then HCSshould be used.
HCS E l ti Al ith
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HCS Evaluation Algorithm
The idea with a layered cell structure is to let lower layer cells serve MSs that receive
sufficient SS even if there is other cells with strongest received SS in the area. But how to decide if the lower layer cell has sufficient SS to be prioritized over strongest
cells?
This will be according to two thresholds LAYERTHR (Layer Threshold) and HCSBANDTHR
(HCS Band Threshold)
LAYERTHR: Decides if the cell should be prioritized over stronger cells lie in the same HCS
band or not.
HCSBANDTHR: Decides if the cell should be prioritized over stronger cells from differentHCS bands or not.
HCS E l ti Al ith
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HCS Evaluation Algorithm
The input to the HCS Evaluation Algorithm is the Basic Ranking list we prepared from the
locating process.
The output will be in the form of two lists: HCS prioritized list (on Top) then Basic Ranking list.
HCS prioritized list: will include cells that fulfilled the HCS conditions & rules and will be
ranked according to HCS evaluation (layered ranking)
Basic Ranking list: will include cells that didnt fulfill the HCS conditions and will be ranked
according to basic ranking rules (SS ranking)
HCS EvaluationAlgorithm
HCS Prioritized Cell
List
Basic Ranking List
Basic Ranking List Input Output
HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
(A) Band Evaluation: In order to be a candidate in the HCS evaluation process, then the SS of
serving and neighbor cells should be greater than their band threshold ( HCSBANDTHR )
SSservingcell > HCSBANDTHRservingcellHCSBANDHYSTservingcell
SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell
Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in
priority order according to SS.
Cells that will fulfill the criterion will pass to the next step in the HCS evaluation.
N.B: HCSBANDTHR and HCSBANDHYST are BSC parameters.
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HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
(C) Layer Threshold Evaluation
Cells that passed the band evaluation in step (A) and they are not strongest within their own
band, their SS will be checked against the Layer threshold (LAYERTHR)
SSservingcell LAYERTHRservingcellLAYERHYSTservingcell
SSneigbhorcell LAYERTHRneighborcell + LAYERHYSTneighborcell
Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in
priority order according to SS.
Cells that will fulfill the criterion will pass to the next step in the HCS evaluation
HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
(D) Identify the Strongest Cells within each layer
Now we will deal with cells that passed the band evaluation (in Step A) and they were not
strongest within their own band (in Step B) and they passed the layer threshold condition
(in Step C)
Cells that are strongest within their own layer will be identified and theyll pass direct to be
HCS ranked.
Cells that are not strongest within their own layer will be moved to the next step.
HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
(E) Check how many cells from each layer are allowed to pass to be HCS ranked
Now we will deal with cells that passed the band evaluation (in Step A) and they were not
strongest within their own band (in Step B) and they passed the layer threshold condition
(in Step C) and they are not strongest within their own layer (in step D)
MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCSranked, ex: if MAXCELLSINLAYER = 2 then two cells only are allowed to pass to be HCS
ranked.
MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the
strongest cell in the layer.i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x MAXDBDEVINLAYER
then the next strongest cell is not weak and it will pass to be HCS ranked.
HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Mechanism of the HCS Algorithm
(F) Form the Final list
Now all cells that succeeded to pass to be HCS ranked, will be sorted in ascending order
according to their layer not SS (as in Basic Ranking) i.e. layer1 cells, then layer2 cells,
and these cells will form an HCS prioritized list that will lie on Top.
All cells that failed to pass to be HCS ranking, will go to be sorted in a Basic Ranking list
and this list will lie after the HCS prioritized list
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HCS Evaluation Algorithm
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HCS Evaluation Algorithm
Solution: (A) Band Evaluation: In order to be a candidate in the HCS evaluation process, then theSS of serving and neighbor cells should be greater than their band threshold (HCSBANDTHR )
SSservingcell > HCSBANDTHRservingcellHCSBANDHYSTservingcell
SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell
HCSBANDTHRservingcell =HCSBANDTHRneighborcell = -90 dBm
HCSBANDHYSTservingcell =HCSBANDHYSTneighborcell = 0 dBm
Cell SS(dBm) Band Layer
G -68 Band 8 Layer 7
E -72 Band 8 Layer 6
B (Serving) -73 Band 4 Layer 4
A -74 Band 4 Layer 3
C -75 Band 8 Layer 7F -75 Band 4 Layer 4
D -95 Band 4 Layer 4
Cell D didnt fulfill the condition (SS_CellD = -95 dBm < -90 dBm) so it will be out of the HCS evaluation
and it will go to be sorted in the Basic Ranking list.
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HCS Evaluation Algorithm
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g
Solution: (C) Layer Threshold Evaluation
Cells E,A,C&F that are not strongest within their own band, their SS will be checked against the Layerthreshold (LAYERTHR) if
SSservingcell LAYERTHRservingcellLAYERHYSTservingcell
SSneigbhorcell LAYERTHRneighborcell + LAYERHYSTneighborcell
LAYERTHRservingcell =LAYERTHRneighborcell = - 80 dBm
LAYERHYSTservingcell
=LAYERHYSTneighborcell
= 0 dBm
Cell SS(dBm) Band Layer Comment
G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list
E -72 Band 8 Layer 6 SS > LAYERTHR = -80 dBm, Will go to the next step
B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list
A -74 Band 4 Layer 3 SS > LAYERTHR = -80 dBm, Will go to the next stepC -75 Band 8 Layer 7 SS > LAYERTHR = -80 dBm, Will go to the next step
F -75 Band 4 Layer 4 SS > LAYERTHR = -80 dBm, Will go to the next step
D -95 Band 4 Layer 4 Out of the HCS Evaluation Back to the Basic Ranking list
HCS Evaluation Algorithm
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g
Solution: (D) Identify the Strongest Cells within each layer
After Cells E,A,C&F all of them passed the layer threshold condition (LAYERTHR), Cells
that are strongest within their own layer will be identified and theyll pass direct to be HCS
ranked.
Cells E&A are strongest within their own layer so they will go direct to be HCS ranked.
Cells C&F are not the strongest within their own layer, so they will be examined in the next
step to know if they can pass to be HCS ranked or not
Cell SS(dBm) Band Layer Comment
G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list
E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list
B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list
A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list
C -75 Band 8 Layer 7 Not Strongest in Layer-Will be examined in the next step
F -75 Band 4 Layer 4 Not Strongest in Layer-Will be examined in the next step
D -95 Band 4 Layer 4 Out of the HCS EvaluationBack to the Basic Ranking list
HCS Evaluation Algorithm
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g
Solution: (E) Check how many cells from each layer are allowed to pass to be HCS ranked
MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCS In
our example MAXCELLSINLAYER = 3 then three cells only are allowed to pass to be HCS
ranked.
MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the
strongest cell in the layer.i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x MAXDBDEVINLAYER = 3 dB
then the next strongest cell is not weak and it will pass to be HCS ranked.
HCS Evaluation Algorithm
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g
Solution: (E) Check how many cells from each layer are allowed to pass to be HCS ranked
Cell C:
Check1: Lies in layer 7 and ranked as the 2nd strongest cell in the layer and since 3 cells are
allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed.
Check2: Is SS_Strongest Celllayer 7 - SS_next strongest celllayer 7 < MAXDBDEVINLAYER=3dB
SSCell G - SSCell C = -68-(-75) = 7 dB > MAXDBDEVINLAYER=3dB then Check2 failed.
Cell SS(dBm) Band Layer Comment
G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list
E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list
B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list
A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list
C -75 Band 8 Layer 7 Out of the HCS EvaluationBack to the Basic Ranking list
F -75 Band 4 Layer 4
D -95 Band 4 Layer 4 Out of the HCS EvaluationBack to the Basic Ranking list
HCS Evaluation Algorithm
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g
Solution: (E) Check how many cells from each layer are allowed to pass to be HCS ranked
Cell F:
Check1: Lies in layer 4 and ranked as the 2nd strongest cell in the layer and since 3 cells are
allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed.
Check2: Is SS_Strongest Celllayer 4 - SS_next strongest celllayer 4 < MAXDBDEVINLAYER=3dB
SSCell G - SSCell C = -73-(-75) = 2 dB < MAXDBDEVINLAYER=3dB then Check2 is passed.
Cell SS(dBm) Band Layer Comment
G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list
E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list
B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list
A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list
C -75 Band 8 Layer 7 Out of the HCS EvaluationBack to the Basic Ranking list
F -75 Band 4 Layer 4 2nd Strongest in Layer4-Go to HCS Evaluation list
D -95 Band 4 Layer 4 Out of the HCS EvaluationBack to the Basic Ranking list
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Solution: (F) Form the Final list
Now all cells that succeeded to pass to be HCS ranked, will be sorted in ascending order according
to their layer not SS (as in Basic Ranking) i.e. layer1 cells, then layer2 cells, and these cells willform an HCS prioritized list that will lie on Top.
All cells that failed to pass to be HCS ranking, will go to be sorted in a Basic Ranking list and this list
will lie after the HCS prioritized list
Final
List
Cell SS(dBm) Band Layer Comment
A -74 Band 4 Layer 3
HCS prioritized list
(Layer Ranking)
B(Serving) -73 Band 4 Layer 4
F -75 Band 4 Layer 4
E -72 Band 8 Layer 6
G -68 Band 8 Layer 7C -75 Band 8 Layer 7
Basic Ranking list (SS Ranking)D -95 Band 4 Layer 4
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HCS Evaluation Algorithm
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Mechanism of the HCS Algorithm
HCS Traffic Distribution Concept
(i) Check on the serving cells availability:
If AvailabilityServingCell > HCSOUT, then this cells has too many free Time slots and it is not
preferred to leave this cell.
(ii) Check on the neighbor cells availability:
If AvailabilityneighborCell < HCSIN, then this cells has few free Time slots and it cant accept
HOs due to HCS prioritization.
HCS Evaluation Algorithm
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Mechanism of the HCS Algorithm when HCS Traffic Distribution is in use
HCS Evaluation Algorithm
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I) Example when HCS Traffic Distribution is enabled (AvailabilityServingCell < HSCOUT)
After ordinary HCS evaluation we formed the below list from the previous example.
Assume HCSOUT=50%, HCSIN=30%, Availability of Cell B (serving) = 40%
and availability of Cell F (neighbor cell) = 10% only, while all other cells have availability = 45 %
What will be the final list form ?
Final
List
Cell SS(dBm) Band Layer Comment
A -74 Band 4 Layer 3
HCS prioritized list
(Layer Ranking)
B(Serving) -73 Band 4 Layer 4
F -75 Band 4 Layer 4
E -72 Band 8 Layer 6
G -68 Band 8 Layer 7C -75 Band 8 Layer 7
Basic Ranking list (SS Ranking)D -95 Band 4 Layer 4
HCS Evaluation Algorithm
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Solution:
Availability of Serving Cell (B) = 40% < HCSOUT (50%), then the serving cell has few free Time Slots
and we can leave this cell i.e. outgoing HO from this cell is enabled.
Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell cant accept HOs due to HCS
prioritization coz it has few free TS i.e. this cell is congested.
This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.
Final
List
Cell SS(dBm) Band Layer Comment
A -74 Band 4 Layer 3
HCS prioritized list
(Layer Ranking)
B(Serving) -73 Band 4 Layer 4
F -75 Band 4 Layer 4
E -72 Band 8 Layer 6
G -68 Band 8 Layer 7
C -75 Band 8 Layer 7Basic Ranking list (SS Ranking)
D -95 Band 4 Layer 4
HCS Evaluation Algorithm
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Solution:
The final list will be as below:
FinalList
Cell SS(dBm) Band Layer Comment
A -74 Band 4 Layer 3
HCS prioritized list
(Layer Ranking)
B(Serving) -73 Band 4 Layer 4
E -72 Band 8 Layer 6
G -68 Band 8 Layer 7
F -75 Band 4 Layer 4
Basic Ranking list (SS Ranking)C -75 Band 8 Layer 7
D -95 Band 4 Layer 4
HCS Evaluation Algorithm
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g
II) Example when HCS Traffic Distribution is enabled (AvailabilityServingCell > HSCOUT)
If the serving cell has a channel availability above HCSOUT it is considered to be taking too
little traffic so it is decided to not allow handovers out due to HCS from the cell.
Instead, all the remaining HCS prioritized candidate cells, fulfilling the HCSIN criterion and
that are in a lower layer or in the same layer as the serving cell, will be basic ranked amongthemselves and added to a Prioritized basic ranked cells list that will be put above the other
basic ranked cells in the final candidate list.
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HCS Evaluation Algorithm
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Solution:
Availability of Serving Cell (B) = 60% > HCSOUT (50%), then the serving cell has Too many Time slots
and HO out from this cell due to HCS is not allowed.
Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell cant accept HOs due to HCS
prioritization coz it has few free TS i.e. this cell is congested.
This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.
Cells E&G are layers 6&7 respectively i.e. they are of higher layers than the serving cells.
These cells will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.
Now cells A&B will be ranked according to SS Prioritized Basic Ranking list
cells C,D,E,F&G will be ranked according to SS Basic Ranking list
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HCS Evaluation Algorithm
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Solution:
The final list will be as below:
Final List
Cell SS(dBm) Band Layer Comment
B(Serving) -73 Band 4 Layer 4Priotirized Basic Ranking List
A -74 Band 4 Layer 3
G -68 Band 8 Layer 7
Basic Ranking list (SS Ranking)
E -72 Band 8 Layer 6
F -75 Band 4 Layer 4
C -75 Band 8 Layer 7
D -95 Band 4 Layer 4
HCS Evaluation Algorithm
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Optimizing a problematic Traffic Case:
Assume we have the below case with 3 Macro cells (layer 4) and 1 Micro cell (layer2) and all of them
belong to the same HCS band, HCSBAND 1
One of the Macro cells carries very high traffic and it is about to congest, how could we solve this case?
Macro Cell (L4) Macro Cell (L4)
Micro
Cell (L2)
Macro Cell (L4)
HCS Evaluation Algorithm
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Solution 1: Direct more Traffic to the Micro Cell
We can decrease the LAYERTHR of the Micro cell (Layer 2) from -75dBm to -80dBm for example, sothe micro cell will capture more traffic from the congested macro cell.
HCS Evaluation Algorithm
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Solution 2: Direct more Traffic to the adjacent Macro Cells
We can increase the Layer of the congested Macro cell (Layer 4 Layer 5) so it will appear less
prioritized with respect to the adjacent neighbor cells and it will offload its traffic to them.
HCS Evaluation Algorithm
S l i 3 Di T ffi f h dj M C ll
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Solution 3: Direct more Traffic to one of the adjacent Macro Cells
We can decrease the Layer of one of the adjacent Macro cell (Layer 4 Layer 3) so it will appear
more prioritized with respect to the congested cell and it will capture some of its traffic.
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Concentric Cells (Overlaid Underlaid Subcells)
& Multi Band Cells (MBC)
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Concentric Cells (Overlaid Underlaid Subcells)
Concentric Cells (Overlaid Underlaid Subcells)
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Traffic Capacity of a cellular network can be increased by either adding more frequencies or
reducing the frequency reuse distance.
One approach is to apply a second frequency re-use pattern with a tighter frequency reuse
(Overlay) on the existing pattern.
These cells should be restricted in size, so shorter reuse distance can be accomplished
without causing Co-channel/Adjacent channel interference.
They are termed Overlaid (OL) Subcells, whereas the original cells will be called
Underlaid(UL) Subcells.
Now by having more frequencies per cell, then Network capacity is increased.
Concentric Cells (Overlaid Underlaid Subcells)
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The fundamental idea behind the OL/UL subcells is to let the traffic close to the site to bemoved to the OL subcell, while traffic close to the cell border to be moved to the UL subcell.
In that way of treading the traffic, the frequencies in the OL subcell can have tighter frequencyreuse.
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Concentric Cells (Overlaid Underlaid Subcells)
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Using the OL/UL concept we can solve the case as follows:
f4 will be used in the OL subcell and it will be restricted to serve in a small area only near tothe site so interference from the neighbor cell will be minimized and a good C/I can beenjoyed.
Concentric Cells (Overlaid Underlaid Subcells)
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To maintain the service area of the OL subcell restricted to a certain region we have three
thresholds we can play with:
A. Path Loss Threshold
B. Timing Advance Threshold
C. Distance to Cell Border Threshold
With the ordinary OL/UL subcells, the MS near the cell will camp on the overlaid subcell but even if the
OL subcell got high utilized there is no way to push traffic to the UL subcell.
Using Subcell Load Distribution (SCLD) Concept, we can configure the cell to use the OL as the
preferred subcell initially and when traffic on the OL increased beyond certain load, any extra traffic will
be offloaded to the UL subcell.
Concentric Cells (Overlaid Underlaid Subcells)
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Algorithm
(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated As we stated before, the service area of the OL subcell can be defined based on one of three
criteria: Path Loss, Time Advance and Distance to cell border.
1. Path Loss Criterion:
Controlling parameters are the path loss threshold LOL and the path loss hysteresis
LOLHYST
DL path loss L= (BSTXPWR - BTS power reduction) Received_SS_DLfiltered
BSTXPWR: BTS output power for the TCH frequencies.
DL path loss L will be checked vs. LOL (path loss threshold) and LOLHYST to knowwhether a subcell change from OLUL or ULOL is needed.
Concentric Cells (Overlaid Underlaid Subcells)
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Algorithm
(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated
2. Time Advance Criterion:
Time Advance can be used as a measure for the distance between the BTS and MS.
Controlling parameters are the time advance threshold TAOL and the time advance
hysteresis TAOLHYST
The TA of the MS will be measured via BTS and checked vs. TAOL and TAOLHYSTto know whether subcell change is needed or not.
Concentric Cells (Overlaid Underlaid Subcells)
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Algorithm
(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated
3. Distance to Cell Border Criterion:
DTCBSC: Is a BSC parameter that enables/disables the distance to cell border
evaluation criterion on whole cells on the BSC.
Controlling parameters are the distance to cell border threshold DTCB and the distance
to cell border hysteresis DTCBHYST
The cell border is defined as the difference between the Received_SSServingCell and theReceived_SSStrongest Neighbor ,where this strongest neighbor should meet the following:
Non-Cosited, Same System type (900/1800), Same HCS Layer.
Concentric Cells (Overlaid Underlaid Subcells)
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Algorithm
(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated
3. Distance to Cell Border Criterion:
Received_SSServingCell - Received_SSStrongest Neighbor will be checked vs. DTCB and
DTCBHYST to see whether subcell change is needed or not.
But for the evaluation to be triggered (initiated), the serving cell should have number of
neighbor cells > NNCELLS (if NNCELLS=2, at least 2 neighbor cells) that are
measured by the MS having enough SS such that:
Received_SSServingCell - Received_SSNeighbor< DTCB+DTCBHYST+NDIST where,NDIST is a threshold measured in dBs.
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Concentric Cells (Overlaid Underlaid Subcells)
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Algorithm
(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated
N.B:
If parameter TAOL is set to its maximum value = 61 bit periods and DTCB is set to its
minimum value = - 63 dB then the OL/UL subcell change will only be controlled by the
path loss using LOL coz:
OLUL: Time Advance & Distance to cell border conditions will never be met and so the
path loss only using LOL will control the evaluation.
ULOL: Time Advance & Distance to cell border conditions will always be met and so the
path loss only LOL will control the evaluation.
Concentric Cells (Overlaid Underlaid Subcells)
Algorithm
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Algorithm
(II) OL/UL Subcell Change with Subcell Load Distribution Activated
A subcell load distribution is used to control the traffic between the OL/UL subcells, so if
the initially preferred cell got congested we will try to allocate resources in the other
subcell. (Activated by setting cell parameter SCLD = ON)
SCLDSC: Is a cell parameter used to define the preferred cell in allocation whether UL
or OL i.e. the subcell which will carry traffic first. N.B: if the OL subcell is the preferred one, i.e. if SCLDSC=OL, then the below
conditions should be met otherwise a TCH on the UL subcell will be allocated.
L < LOLLOLHYST and ta < TAOLTAOLHYST and
SSServing - SSNeighbor DTCB + DTCBHYST
Strongest, Non Cosited, Same type, Same HCS Layer
No. of neighbor cells NNCELLS should be reported meeting the following equation:
SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST
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Concentric Cells (Overlaid Underlaid Subcells)
Al ith
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Algorithm
(II) OL/UL Subcell Change with Subcell Load Distribution Activated
If some traffic will be moved from the OL UL subcell due to load distribution, then the
MSs with the high path loss will be chosen first i.e. MSs that are near to cell border.
If some traffic will be moved from the UL OL subcell due to load distribution, then the
MSs with the low path loss will be chosen first i.e. MSs that are near to the site.
Apart from the subcell change due to SCLD, as we mentioned before the MS can also
request to move from OL UL because of path loss, TA or distance to cell border
criterion and in this case the load is not checked coz the thresholds :SCLDLUL&SCLDLOL are only controlling the load incase of subcell change due to
load distribution.
Concentric Cells (Overlaid Underlaid Subcells)
Parameters Summary
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Parameters Summary
Overlaid/Underlaid Control ParametersParameter Name Value Range Default Value Recommended Value Unit
SCTYPE UL,OL
LOL 0 to 200 dB
LOLHYST 0 to 63 3 3 dB
TAOL 0 to 61 Bit Periods (3.69 sec)
TAOLHYST 0 to 61 Bit Periods (3.69 sec)DTCBSC 0,1 0
DTCB 63 to 63 -63 dB
DTCBHYST 0 to 63 2 2 dB
NDIST 0 to 63 10 dB
NNCELLS 1 to 5 3 1
SCLD ON,OFF OFF
SCLDLOL 0 to 99 20 %
SCLDLUL 0 to 99 20 %
SCLDSC UL,OL UL OL
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Multi Band Cells (MBC)
U i MBC i h l 1 BCCH hi ill d h f d fi d i hb
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Using MBC concept with only 1 BCCH, this will reduce the no. of defined neighbors to
50% leading to better accuracy for the measurement reports coz there will be more timeavailable for measurements for each neighbor.
Multi Band Cells (MBC)
Th D i OL/UL b ll (C t i ll ) i i it f t f th M lti
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The Dynamic OL/UL subcells (Concentric cells) is a prerequisite feature for the Multi
Band Cells.
Mostly the frequency band with Better coverage (i.e. lower frequency band) is
configured as the Underlaid subcell while the other frequency band with Worse
coverage (i.e. higher frequency band) is configured as the Overlaid Subcell.
Ex: 900MHz frequency band
UL, while 1800MHz frequency band
OL
It is recommended to select the BCCH frequency to lie in the Better Coverage
i.e. UL subcell.
for the previous example then BCCH frequency will belong to the 900MHz band
Multi Band Cells (MBC)
A t CSYSTYPE d fi th b d f th d BCCH f i lti
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A parameter CSYSTYPE defines the band of the used BCCH frequency in a multi
band cell. A parameter BAND defines the band of the Channel Group, where the channel
group consists of no. of frequencies as will be seen later.
As mentioned before, the path loss/Distance to cell border/time advance criteria will
define the coverage limit of the frequency band used in the OL subcell vs. UL subcell,(In this case the OL&UL will belong to two different bands)
Also the traffic load can be maintained between the two subcells (that belong to two
different bands) using the subcell load distribution feature where the SCLDSC
parameter will define which subcell is preferred first.
Multi Band Cells (MBC)
Th ti f th di d d th d f b d i th
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The propagation of the radio waves depend on the used frequency band, i.e. the
reported signal strength from one MS will differ depending on the frequency band used.
MS
MS
MS is in the same location but
the reported SS differs depend
on the used frequency band
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Multi Band Cells (MBC)
Applying a frequency Band Offset:
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pp y g q y
FBOFFS (Frequency Band Offset): is the parameter that determines the differencebetween the path loss between bands (BCCH Frequency Band Group and the
Non-BCCH Frequency Band Group), it is measured in dBs and take values
between -40 40 dBs
If the MS is served by 1800 band frequency and reporting SS 1800 band = -85 dbmand FBOFFS=7dB then the compensated SS if the MS was served by the 900
band frequency will be SS 900 band = -85 dbm + 7 = -78 dBm
FBOFFS has to be adjusted in a correct way coz:
a. It will be used to locate the MS correctly with respect to neighbors
b. It will be used to locate the MS correctly in the Subcell change Evaluation
Multi Band Cells (MBC)
Applying a frequency Band Offset:
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pp y g q y
a. FBOFFS will be used to locate the MS correctly with respect to neighbors
Ex: MS is on the OL subcell (1800 band) and reporting SS_Serving_cellA1800 band = -85 dBm
FBOFFS =7dB, and after applying the offset and Hysteresis
SS_neighbor_cellB900 band = -83dBm
Without applying FBOFFS
SS_Serving_cellA 1800 band < SS_neighbor_cellB900 band
HO from Cell A Cell B will occur
Wrong Decision
With applying FBOFFS
SS_Serving_cellA 900band = SS_Serving_cellA1800 band+ 7 dB
SS_Serving_cellA 900band = -78 dBm
SS_Serving_cellA 900 band > SS_neighbor_cellB900 band
Cell A will remain the serving cell but subcell change
may occur if needed.
Right Decision
Multi Band Cells (MBC)
Applying a frequency Band Offset:
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b) FBOFFS will be used to locate the MS correctly during the Subcell change Evaluation
When the MS is served by the OL 1800 band subcell (non-BCCH Band), the path lossin this case will be checked vs. LOLLOLHYST + FBOFFSET
Ex: Assume a MS is served by the OL 1800 subcell and reporting SS1800 band = -90 dBm,
BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero
-85 dBm
-92 dBm
Subcell change OLUL
-90 dBm
-83 dBm
Multi Band Cells (MBC)
Applying a frequency Band Offset:
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b) FBOFFS will be used to locate the MS correctly during the Subcell change Evaluation
Ex: Assume a MS is served by the OL 1800 subcell and reporting SS1800 band = -90 dBm,BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero
Without applying FBOFFS
Path loss= BSTXPWR - SS1800 band = 46-(-90)=136 dB
Path loss=136 dB > LOLLOLHYST=131 dB
Subcell change from OL UL will occur
Wrong Decision
With applying FBOFFS
Path loss= BSTXPWR - SS1800 band = 46-(-90)=136 dB
Path loss=136 < LOLLOLHYST+FBOFFSET=138dB
The MS w
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