2G Optimization 2012

8/12/2019 2G Optimization 2012

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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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PLMN Selection

Cell Selection.

Cell Reselection.



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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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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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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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PLMN Selection.

Cell Selection

Cell Reselection.



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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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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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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 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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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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PLMN Selection.

Cell Selection.

Cell Reselection



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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 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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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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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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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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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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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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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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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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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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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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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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Non Default Mapping on TS0/C0 (BCH+CCCH)

2*51 TDMA Frames = 2 Control Multi-frame


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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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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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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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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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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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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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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


BCCHTYPE COMB COMBC NCOMB NCOMB

SDCCH0 to 16 (0: No SDCCH/8

configured-combined mode)1

IMSI Attach/Detach Parameters


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


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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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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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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Initiation

Filtering

Basic Ranking

Urgency Conditions Handling. Auxiliary Radio Network Features Evaluation.




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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


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


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




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



(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


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



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



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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Initiation

Filtering

Basic Ranking

Urgency Conditions Handling Auxiliary Radio Network Features Evaluation.




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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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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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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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Initiation

Filtering

Basic Ranking


Auxiliary Radio Network Features Evaluation Organizing the List.



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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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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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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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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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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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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.



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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.



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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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Initiation

Filtering

Basic Ranking



Organizing the List



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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


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


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


EVALTYPE 1 or 3 3

Flow Control Parameters

Parameter


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


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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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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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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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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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



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Mechanism of the HCS Algorithm



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(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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(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



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(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.



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(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.



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(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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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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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



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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



E -72 Band 8 Layer 6 Strongest in Layer 6 - 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



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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.



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g


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.






C -75 Band 8 Layer 7 Out of the HCS EvaluationBack to the Basic Ranking list

F -75 Band 4 Layer 4




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g


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.






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




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g

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



HCS prioritized list

(Layer Ranking)

B(Serving) -73 Band 4 Layer 4



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 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.



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Mechanism of the HCS Algorithm when HCS Traffic Distribution is in use



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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




(Layer Ranking)




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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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




(Layer Ranking)





C -75 Band 8 Layer 7Basic Ranking list (SS Ranking)




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Solution:

The final list will be as below:

FinalList




(Layer Ranking)





Basic Ranking list (SS Ranking)C -75 Band 8 Layer 7




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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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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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Solution:

The final list will be as below:

Final List


B(Serving) -73 Band 4 Layer 4Priotirized Basic Ranking List



Basic Ranking list (SS Ranking)



C -75 Band 8 Layer 7




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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)



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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.



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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.


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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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.



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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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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.



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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.



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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.



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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.



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Algorithm


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.



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Algorithm


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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Algorithm


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.


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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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.


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.


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


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.


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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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




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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




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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




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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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2G Optimization 2012