dth. To understand this, it's important to realize that in the context of CDMA, "bandwidth" refers to the capability of any phone to get data from one end to the other. It doesn't refer to the amount of spectrum used by the phone, because in CDMA every phone uses the entire spectrum of its carrier whenever it is transmitting or receiving, as shown in Figure 1-30. One of the terms you'll hear in conjunction with CDMA is "soft handoff." A handoff occurs in any cellular system when your call switches from one cell site to another as you travel. In all other tech- nologies, this handoff occurs when the network informs your phone of the new channel to which it must switch. The phone then stops receiving and Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright© 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Introduction to GSM Figure 1-30 User 4 CDMA. User 3 User 2 User 1 transmitting on the old channel, and commences transmitting and receiv- ing on the new channel. It goes without saying that this is known as a hard handoff. In CDMA, however, every phone and every site are on the same fre- quency. In order to begin listening to a new site, the phone only needs to change the pseudo-random sequence it uses to decode the desired data from the jumble of bits sent for everyone else. While a call is in progress, the net- work chooses two or more alternate sites that it feels are handoff candi- dates. It simultaneously broadcasts a copy of your call on each of these sites. Your phone can then pick and choose between the different sources for your call, and move between them whenever it feels like it. It can even combine the data received from two different sites to ease the transition from one to the other. CDMA is more efficient about that kind of thing. In both TDMA and CDMA, the outgoing voice traffic is digitized and compressed. However, the CDMA codec can realize when the particula