CBCCH

Common BCCH

• Benefits– Improved trucking gain,

(improve blocking probability)

– Reduced frequency used– Reduced number of cell,

reduced LAC, reduced paging

– Reduced neighboring cells, improve performance due to decreased handover

Restrictions• BCCH on Comon BCCH system must be the same band throughout the whole network

• There can be only 31 frequency in adjacent cell and BA list

• Only 5 strongest neighbours are included in the adjacent cell measurement

• Initial SDCCH channel for call setup is always allocated in the BCCH segment, since FACCH setup take place as a response to an SDCCH allocation request, FACCH has the same restriction as SDCCH

• Dynamic SDCCH can be utilised only in the BCCH frequency band.

DCS

GSM

Problem on CBCCH

Difference cell coverage difference radio attenuation between DCS & GSM

DCS

GSM

Problem on CBCCH

CCCH problem

DCSGSM

Parameter_1 (NBL)

NBL = NonBCCH Layer offsetSuggested value = 10

DCS GSM

Parameter_2 (LAR)

LAR = non BCCH layer access threshold

Average_Rxlev_DL – NBL >= LAR

DCS GSM

Parameter_3 (LER)

LER = non BCCH layer Exit threshold

Parameter_4(LSEG)

BTSloadInseg + ( (100 – BTSloadInseg ) / 2 ) = HO triggered

Example :

BTSloadInseg GSM = 20

BTSloadInseg DCS = 80

20 % 60 %

80 %

TCH allocation priority to DCS

Handover triggered

Parameter_5 (extend SD)

ISS = guard time for attempting an SDCCH handover from the BCCH BTS resource layer to another resource layer in a segment. (BSC level)

ESD = enable SDCCH handove (BTS level)

Thank you

by dimas