y of offering subscriber variable bit rates and bandwidth - on demand - is an attractive feature in UMTS networks. For this, ATM technology (described in detail in Chapter 3) becomes handy. Asymmetric traffic is supported. Transmit diversity can be used to improve downlink capacity in WCDMA networks. Also, as only one frequency is used, frequency planning is therefore not such a tedious task as it is in the GSM networks. Packet data scheduling is load based as compared to timeslot based as in the GSM network, thus making the system more efficient. The algorithms that are used for Radio Resource Management (RRM) functionality are more advanced as compared to GSM networks. WCDMA Carrier WCDMA is a DS-CDMA, or Direct Sequence CDMA, system. This technology enables multiple accesses that are based on a spread spectrum. This means that user information bits are spread over a wide bandwidth by multiplying user information with the quasi-random bits called chips, derived from CDMA spreading codes. The rate at which the data spreads is called the chip rate. The ratio of the chip rate to the symbol rate is called the spreading Factor (SF). The destination mobile phone uses the same spreading code as the one used at the transmission point and performs correlation detection. Each user is identified by a unique spreading code assigned to it. The chip rate of 3.84 Mcps (megachips per second) is used, which leads to a carrier bandwidth of 5 MHz, as shown in Figure 2.5. The narrowband signal R has different bit rates according to the amount of information to be transmitted. The SF tells how many baseband chips are used to transmit one narrowband information bit: R SF = constant = W = 3.84 Mcps (2.1) All the users in DS-CDMA can be allocated the same frequency band and timeframe for communication. As a result, the signal-to-interference ratio at the receiver can easily be less than unity as the power of the signal of a user is typically lower than the aggregate power of signals of other users. Preplanning in a GSM Radio Network S