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Presentation / Author
Module Objectives
Give an overview of the common BCCH and Multi BCF feature
Explain the concept of segments and associated Common BCCH parameters
Presentation / Author
Common BCCH Control
Tighter reuse of non BCCH carriers
Better quality (decreased number of HOs)
Non BCCH freq. BTS
Common BCCH
Allows integration of TRXs from different frequency bands into one cell (segment)
Provides service to MSs in all frequency bands which they support
Improved spectral efficiency: different bands of a cell share the same BCCH
BCCH is allowed in any of the supported frequency bands
Improved trunking gain
Presentation / Author
BCCH Allocation mainly similar to the single band network implementation
Adjacency information sent to the mobile station is based on the BCCH frequency of a common BCCH segment
Other frequency layers in a segment are invisible to the mobile stations
MS sees a segment as one BCCH frequency cell
MS sees many segments as a BCCH frequency network
Modified BA list to an MS on the non BCCH frequency layer of a segment
the BCCH frequency of the segment itself is added among the BCCH frequencies the MS measures
Presentation / Author
Initial SDCCH on the BCCH carrier band
the multiband capabilities of an accessing mobile station are not known at the time of the initial SDCCH allocation
no way to define the usability of the non-BCCH layer of the segment because the MS starts sending measurement reports only after it has moved to a dedicated channel
While the MS is on an SDCCH the BSC receives
in Classmark Change message Mobile Station Classmark 3 indicating the terminal's frequency capability of using other frequency bands than BCCH frequency band
Presentation / Author
2. IMMEDIATE ASSIGNMENT COMMAND (AGCH)
- MA list of BCCH frequency band (if FH)
Initial SDCCH allocation always from BCCH frequency band
Non BCCH freq. layer
The maximum number of BTSs in a segment is 32.
The maximum number of TRXs in a segment is 36.
BTS object in a segment must consist of TRXs of the same frequency band and base station type
This is an example only. It is also possible to have EGSM and PGSM resources in the same BTS object.
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Allows combination of several BTSs into one logical cell
BSC supports Multi BCF Control for Talk family, UltraSite, Flexi and MetroSite base stations (specific BTS combinations)
Allows the operator to increase the capacity of a cell to 24 TRX (Metro, Talk Family) or to 36 TRXs (Ultra, Flexi)while maintaining the maximum spectral efficiency (no extra BCCH)
Site expansion path from Talk Family to UltraSite/Metrosite (thus providing EDGE support to the site)
In the case of MetroSite the BSC allows only MetroSite base stations in a multi BCF segment
When Multi BCF Control and Common BCCH are combined you are allowed to configure both BTSs of different frequency bands and BTSs of different base station types to one segment.
Presentation / Author
UltraSite 8+8+8 configuration with separate BCCH (Dual BCCH)
altogether 6 BCCH carriers
improved spectral efficiency, 3 BCCH carriers
BTS-1,
BCCH-1
GSM 900 signal tends to be stronger than GSM 1800
-> wider coverage for GSM than for GSM 1800
-> useless if BCCH is taken from GSM 1800
Band specific maximum output power of BTS
bsTxPwrMax used for GSM 800/900
bsTxPwrMax1x00 used for GSM 1800/1900
bsTxPwrMax = peak power - 6 dB
bsTxPwrMax1x00 = peak power - 0 dB
Common BCCH
5...39 dBm, step 2 dBm
The maximum transmission power an MS may use when accessing a CCH in the cell for GSM 900/800 bands.
33 dBm
0...36 dBm, step 2 dBm
The maximum transmission power an MS may use when accessing a CCH in the cell for GSM 1800/1900 bands. Range: GSM 1800: 0..36 dBm (step size 2) GSM 1900: 0..32 dBm (step size 2) and 33 dBm
30 dBm
-40...40, step 1
Defines whether the predefined offset margin is used when evaluating the signal level of the non BCCH layer.
0
NBL
HOC
nonBcchLayerAccessThr
-110...-47 dBm, step 1 dBm
Threshold value for the estimated downlink signal level on non-BCCH layer for a moving MS from BCCH layer to non-BCCH layer.
-90 dBm
MS indicates its capabilities while on an SDCCH
=> BSC finds out if non BCCH frequency band resources could be included in channel allocation for the terminal
MS reports the downlink signal level on the SDCCH
=> BSC finds out if radio conditions are good enough for the MS to use non BCCH frequency resources of the segment with the criterion
RXLEV_DL – NonBcchLayerOffset >= NonBCCHLayerAccessThreshold
Where: RXLEV_DL is last received signal strength on the serving channel
With the decisions above the BSC determines the applicable frequency bands of a segment for an MS during call setup when the MS moves from an SDCCH to a TCH
Presentation / Author
Common BCCH
Intercell Handover
In BSC internal handovers between separate cells the usability of BCCH frequency hand resources in a target cell is defined using the BTS specific offset parameter and a neighbour parameter defined for the target cell:
AV_RXLEVNCELL (n) >= rxLevMinCell (n)
In BSC internal handovers between separate cells the usability of non BCCH frequency band resources in a target cell is defined using the BTS specific offset parameter and a new threshold parameter defined for the target cell:
AV_RXLEVNCELL (n) – NonBcchLayerOffset (n) >= NonBCCHLayerAccessThreshold (n)
Applies to both SDCCH and TCH allocation cases
Presentation / Author
Intra cell handover
When the call is going on on a non-BCCH frequency band the usability of different types of resources is defined based on the averaged BCCH measurement results. The following formulas are used:
AV_BCCH_RXLEV_DL – NonBcchLayerOffset >= rxLevAccessMin
AV_BCCH_RXLEV_DL – NonBcchLayerOffset >= NonBCCHLayerAccessThreshold
The first formula is used to evaluate the usability of BCCH frequency resources of the segment. The second formula is used to evaluate the usability of non-BCCH frequency resources of the segment.
Presentation / Author
Common BCCH
External handover
In case of handover to a segment of another BSC, the non-BCCH layer of the segment is usable if it is at least as strong as the BCCH layer.
The nonBCCHLayerOffset(n) on the target non-BCCH BTS must be equal to zero or less than zero for the BTS to be used for incoming handover
Applies to both TCH and SDCCH cases
Presentation / Author
SDCCH Handover based on duration of reservation
Since the allocation of the initial SDCCH takes place in the band where the BCCH is, a method is defined to trigger SDCCH handovers to other band(s)
Based on the SDCCH reservation duration on the initial band
Guided by a parameter IntraSegSdcchHoGuard (ISS)
SDCCH reservation duration exceeds IntraSegSdcchHoGuard
There are resources outside the initial band in a cell and satisfy the following:
RXLEV_DL - non BCCH layer offset >= non BCCH layer access threshold
MS has the required support for the other resource types
MO Class
Abbreviated Name
BSC
intraSegSdcchHoGuard
0...255 s, step 1 s 0: no time limit set for starting an SDCCH handover attempt from the BCCH BTS resource layer, attempt can be made as soon as possible 1..254: time after which an SDCCH handover from the BCCH BTS resource layer is attempted 255: no SDCCH handover from the BCCH BTS resource layer is attempted based on SDCCH reservation duration
guard time for attempting an SDCCH handover from the BCCH BTS resource layer to another resource layer in a segment.
255 s
Common BCCH & Multi BCF
Handover for balancing load
BSC initiates an intra cell handover when TCH load in a some BTS of the segment reaches a level defined with the BTS level parameter BTSLoadInSEG.
Triggering level = BTSLoadInSEG +((100 - BTSLoadInSEG )/2)
BSC checks the load of the BTSs every time it receives a TCH request for the segment
BSC accepts as target only the segment's BTSs
whose load is below the respective BTSLoadInSEG value
in which the radio conditions are good enough
which are not same resource type as the source BTS and the BCCH BTS
The handover is primarily used to move TCH load from the BCCH resource type but handovers can also be made between other resource types
Presentation / Author
0...100 %, step 1 %
Determines the load limit for a BTS. It is used in controlling the load distribution between BTSs in a segment.
70%
LSEG
Common BCCH
Intra cell handover from non BCCH layer based on signal level
BSC initiates an intra cell handover from non BCCH layer to BCCH layer when the averaged downlink signal level on serving channel decreases below the threshold defined by parameter NonBcchLayerExitThreshold (LER, Nx, Px)
This decreases the number of inter cell handovers from non BCCH layer
Handover is applicable in cells where BCCH layer has more coverage than non BCCH layer
BSC uses general Power Control and Handover Algorithm functions to trigger the handover
If intra cell handover fails then inter cell handover can be triggered
MO Class
Abbreviated Name
-110...-47 dBm, step 1 dBm
With this parameter you define a threshold value for the measured downlink signal level on non-BCCH layer for a moving MS from non-BCCH layer to BCCH layer
-95 dBm
1
LEN
HOC
nonBcchLayerExitThr_px
1
LEP