rd GSM and GPRS require only 16 kbps Abis channels since all radio link codings fit within this transmission channel structure. However, EGPRS radio transmission requires additional Abis channel capacity to support the higher coding schemes. This is a key factor when planning and optimising EGPRS networks since inadequate transmission planning will lead directly to lower radio and end user throughput in the specific cell served by the allocated transmission (Chapter 3 contains further discussion on this concept). While Packet Control Unit (PCU) architecture varies between different vendors, it must be dimensioned and balanced adequately to support the additional demand that EGPRS places on the processing load and logical Abis channel load. Inadequate PCU capacity leads to lower end user throughput due to less processing allocated to requested transmission, MCS, or EGPRS capable radio timeslots. In general, each PCU serves a large portion of the BSS coverage area SO it is very important to ensure that PCU capacity is dimensioned accordingly. Gb Link The transmission links between the BSS PCU and the Packet Core SGSN must be expanded to support the additional bandwidth demand that EGPRS places on the packet data network. Running out of Gb link capacity severely reduces the throughput of all cells connected to the Gb link. While adequate PCU, Abis and radio resources may be available in the BSS, users will experience degraded or no throughput for the times that Gb link congestion is present. Radio Network Planning and Optimisation 3.84 MHz 5 MHz Figure 2.5 WCDMA carrier 2.2.4 WCDMA in UMTS WCDMA - Air Interface in UMTS WCDMA is the air interface chosen for the UMTS. It is quite different from the air interface used in GSM networks. The quality (and delay) requirement is much higher in UMTS networks as compared to GSM networks. The bit rates are higher (up to 2 Mbps with Release 99 and up to 10 Mbps with HSDPA), which means that a larger bandwidth of 5 MHz is required to support these higher bit rates. The possibilit