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GPRS uses the same frequency spectrum as GSM i.e. 890-960MHz for up-link
and 935-960MHz for down-link. There are 124 channels of 200kHz each and one
channel is left as guard band. Some of these channels are allocated to GPRS
arbitrarily. The channel allocation in GPRS is much more flexible than GSM.
The channel is allocated to MS only when it needs to send data. More than
one slot can be given to a single MS leading to maximum data rate of 172kbit/s.
GPRS uses similar logical channel structure as the GSM. The channel can be
divided in two categories: traffic channels and signaling channels. The
different channels are:
- PDTCH (Packet Data Traffic Channel) is used for user data transfer.
- PBCCH (Packet Broadcast Control Channel) is unidirectional
point-to-multipoint signaling channel from BSS to MS. It is used by BSS
to broadcast control information to all MS in cell.
- PCCCH (Packet Common Control Channel) is bidirectional
point-to-multipoint signaling channel which transports the signaling
information for network access management.
- PRACH (Packet Random Access Channel) is used by MS to request one
or more PDCH.
- PAACH (Packet Access Grant Control Channel) is used to allocate one
or more PDTCH to MS.
- PPCH (Packet Paging Channel) is used by BSS to find out the location
of a MS (paging) prior to down-link packet transfer.
- PNCH (Packet Notification Control Channel) is used to inform the MS
of incoming PTM message (multicast or group call).
- PACCH (Packet Associated Control Channel) is used for sending
signaling information related to one particular MS (e.g. power control
information).
- PTCCH (Packet Timing advance control Channel) is used for adaptive
frame synchronization.
Next: Channel Coding
Up: GPRS: General Packet Radio
Previous: Session, Mobility and Location
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2002-10-12