le 5.1) are mapped into the physical packet data channel (PDCH). Different logical channels can find their place on one single physical channel. Table 5.1 GPRS Logical Channels Channel Abbreviation Function/Application Packet Broadcast Control PBCCH Broadcast system information Channel (DL) specific to packet data Packet Common Control Channel PCCCH Contain logical channels for common control signalling Packet Data Traffic Channel PDTCH Channel temprorily used for data transfer. Packet Associated Control PACCH Used for signalling information Channel transfer for a given mobile Packet Access Grant Channel PAGCH Notifies that mobile about resource assignment before actual packet transfer Packet Notification Channel (DL) Used for sending information to multiple mobile statios. Packet Paging Channel (DL) Pages a mobile station before packet transfer process begins Packet Random Access Channel PRACH Used by the mobile station for initialisation of the uplink packet transfer. Coding Schemes The radio block consists of header, data and control information, which are basically the MAC header, the RLC data block and MAC/RLC control information. RLC data are encoded for security. In GPRS systems, there are four coding schemes that are used for the packet data: CS-1, CS-2, CS-3 and CS-4. Table 5.2 shows the coding schemes and related parameters. GPRS: NETWORK PLANNING AND OPTIMISATION Table 5.2 Coding Scheme in GPRS Data Rates Data Rates (kbps) Coding Schemes Code Rate (kbps) (excl. headers: RLC/MAC) ~ 2/3 ~ 3/4 In coding scheme CS-1, half-rate convolution code is used for forward error correction (FEC). It has a data rate of 9.05 kbps. Coding schemes CS-2 and CS-3 are the same as CS-1 but in punctured format. Puncturing is done SO as to increase the data rate but it comes at the cost of reduction in redundancy. Coding scheme CS-4 has 'no coding' (i.e. no FEC), so further increasing the data rate to 21.4 kbps. Radio Resource and Mobility Management In the GSM system, IDLE and DEDICATED are the two states of a mobile station