the W-CDMA standard was to have a wider bandwidth (compared with IS-95) to facilitate the required transmission rate of 2 Mbps. This resulted in allocation of 5 MHz bandwidth for W-CDMA frequency carrier, compared with the approximately 1.66 MHz bandwidth of IS-95. Another feature of W-CDMA was usage of different length codes, which facilitated multi-rate data transmis- sions. This meant that higher transmission rates could be supported by W-CDMA as com- pared with IS-95. The first release of W-CDMA standard specified transmission rates for uplink and downlink as listed in Table 10.4. Two initial releases of the W-CDMA standard (Release 99 in 2000 and Release 4 in 2001) were based fully on circuit switching technology. While data communications were supported in the standard, its implementation was inefficient as the data traffic behaviour best fits with packet switching. Subsequent releases of the W-CDMA standard in 2002 and later specified a Broadband Telecommunications Technologies and Management Table 10.4 W-CDMA transmission rates for uplink and downlink Uplink Downlink Spreading factor Transmission rate (kbps) Spreading factor Transmission rate (kbps) packet-switched air interface which heralded the age of broadband wireless communications based on the IP. The W-CDMA standard has been updated regularly through the issue of successive 'releases'. The system of ongoing releases allows for the addition of new features. It also enables mobile communications equipment manufacturers to develop devices that are interop- erable with devices made by other manufacturers for previous releases of the standard. Furthermore, each release is amended with consecutive new 'versions' containing relatively minor enhancements and changes to that release of the WCDMA standard. While the 4G stan- dards have been released and rolled out, the 3G standards still form a major part of operators' networks worldwide. Case Study 10.2: Time Division Synchronous CDMA (TD-SCDMA) The original CDMA IS-95 standard used the FDD mode for its up