Radio Resource Management and Logical Channels

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.