Multi-BCF and Common BCCH

*Module Objectives:

• Give an overview of the common BCCH and Multi BCF feature.

• Explain the concept of segments and associated Common BCCH parameters

*Common BCCH:

*Dual Band Operation

• Every BTS has its BCCH and SDCCH channels

*Common BCCH Control

• Improved spectral efficiency (one BCCH)

• Optimised use of signaling channels

• Tighter reuse of non BCCH carriers

• Better quality (decreased number of HOs)

*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.

• Base stations: Talk Family, Ultra, Flexi and Metrosite.

• 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.

• 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 Class mark Change message Mobile Station Class mark 3 indicating the terminal's frequency capability of using other frequency bands than BCCH frequency band.

*Initial SDCCH allocation:

*Segment and BTS objects:

Segment:

• Segment = Telecom cell

• A segment may consist of several BTS objects.

• BTSs of a segment are co-located and synchronised.

• 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

*Multi BCF:

• 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.

*Multi BCF, example:

1-UltraSite 8+8+8 configuration with separate BCCH (Dual BCCH):

Altogether 6 BCCH carriers.

2- UltraSite 8+8+8 configuration with Multi BCF:

improved spectral efficiency, 3 BCCH carriers

*Band Specific Power Control:

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:

Bs Tx Pwr Max used for GSM 800/900

Bs Tx Pwr Max 1x00 used for GSM 1800/1900

MO Class

Abbreviated Name Range And Step

Description Default value

BSC - MML Name

BTS msTxPwrMaxCCH 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

TXP1

BTS msTxPwrMaxCCH1x00 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

TXP2

* Access to non-BCCH layer:

MO Class

Abbreviated Name Range And Step

Description Default value

BSC - MML Name

BTSnonBCCHLayerOffse

-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

LAR

*Call Setup:

• 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 – NonBcch Layer Offset >= NonBCCH Layer Access Threshold

NOTE: 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.

*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) – NonBcch Layer Offset (n) >= NonBCCH Layer Access Threshold (n)

• Applies to both SDCCH and TCH allocation cases

*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.

*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 nonBCCH Layer Offset(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.

*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 Intra Seg SDCCH Ho Guard (ISS)

• SDCCH reservation duration exceeds Intra Seg SDCCH Ho Guard

• 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

Range And Step Description Default value

BSC - MML Name

BSC Intra Seg SDCCH Ho Guard

0...255 s, step 1 s0: no time limit set for starting an SDCCH handover attempt from the BCCH BTS resource layer, attempt can be made as soon as possible1..254: time after which an SDCCH handover from the BCCH BTS resource layer is attempted255: 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 ISS

*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 BTS Load In SEG.

• Triggering level = BTS Load In SEG +((100 – BTS Load In SEG )/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 BTS Load In SEG 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.

*BTS Load in SEG:

MO Class

Abbreviated Name

Range And Step

Description Default value

BSC - MML Name

BTS btsLoadInSeg

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 NonBcch Layer Exit Threshold (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

Range And Step

Description Default value

BSC - MML Name

HOC Rx Level -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 LER

HOC NonBcch Layer Exit Thr_n

1.32, step 1 Nx value for the above threshold

1LEN

HOC NonBcch Layer Exit Thr_px

1.32, step 1 Px value for the above threshold

1 LEP