gy of GSM that the requirement on spectrum flexibility, since the global have added new features constantly since the in- spectrum situation becomes more and more complex. troduction in the early 1990s. The success stems from Operators get more and more scattered spectrum, spread the fact that there are millions of existing terminals at the over different bands with different contiguous band- launch time of the new features that can take the cost of widths. LTE needs to be able to operate in all these bands the upgrade of the network for the initially few new and with the bandwidths that is available to the operator. terminals before the terminal fleet is upgraded. The time However, in practice only a limited set of bandwidths can it takes to upgrade the terminal fleet is different from be used since otherwise the RF and filter design would be country to country, but a rule of thumb is that a terminal too costly. LTE is therefore targeted to operate in 1.25, is used for 2 years before it is replaced. For HSPA Evo- 1.6, 2.5, 5, 10, 15, and 20 MHz spectrum allocations. lution that means that millions of HSPA-capable termi- The spectrum flexibility support with the possibility to nals need to be supported at launch. In other words, operate in other bandwidths than 5 MHz makes LTE very HSPA Evolution needs to be backward compatible with attractive for operators. The low-bandwidth operations the previous releases in the sense that it is possible to are suitable for refarming of spectrum (for example, serve terminals of earlier releases of WCDMA on the GSM spectrum and CDMA2000 spectrum). The higher- same carrier as HSPA-Evolution-capable terminals. bandwidth options are suitable for new deployments in The backward compatibility requirement on the unused spectrum, where it is more common to have larger HSPA Evolution puts certain constraints on the tech- chunks of contiguous spectrum. nology that LTE does not need to consider, for example CHAPTER 4.2 The motives behind the 3G evolution WCDMA/HSPA WCDMA/HSPA WCDMA/HSPA 