 code is fixed by specification and has SF = 256. The channel bit rate is 30 kbps but in order reduce the total interference it is sent alternatives with the SCH giving a 'net' bit rate of 27 kbps. The PCCPCH does not have any pilot bits in the frame because the channel estimation is done using the CPICH. Secondary Common Control Physical Channel (SCCPCH) SCCPCH carries two different common transport channels, the FACH (Forward Access Channel) and the PCH (Paging Channel). It is on air only when it has something to transmit. There can be up to three secondary CCPCHs configured. FACH and PCH can be mapped in two different physical chan- nels. In addition, if the Service Area Broadcast (SAB) service is implemented it requires an additional SCCPCH. Paging Indicator Channel (PICH) The Paging Indicator Channel (PICH) operates together with the Paging Channel (the transport channel is sent on the physical channel: SCCPCH). The paging indicator is sent on PICH, and the corresponding paging message is sent on the associated SCCPCH. Having one channel for indicators and one for messages provides terminals for an efficient sleep mode operation. The paging indicator (PI) uses a channelisation with SF = 256. Depending on the paging indicator ratio there can be 18, 36, 72 or 144 paging indicators per PICH frame. To each terminal registered to the network is allocated a paging group that corresponds to a PI. When the mobile detects the PI it decodes the next PCH frame transmitted on the secondary CCPCH. If the PICH is received with low reliability Radio Network Planning and Optimisation RADIO FRAME 10ms RADIO FRAME 10ms chips Access Slot 0 Access Slot 1 chips Access Slot 3 Each message part may be preceded by a number of preamble blocks Figure 2.41 PRACH radio frame then the PCH is decoded. The less the mobile needs to listen to the PICH, the longer the battery life. The drawback is a longer response time for a mobile terminated call. Physical Random Access Channel (PRACH) In a PRACH two radio frames are joined to form a '15 T