Evolution Evolution/LTE Dual mode Handsets Figure 4.2-3 One HSPA and LTE deployment strategy: upgrade to HSPA Evolution, then deploy LTE as islands in the WCDMA/HSPA the physical layer fundamentals need to be the same as Core. This work was done under the umbrella System for WCDMA release 99. In particular, the bandwidth Architecture Evolution study item lead by TSG SA AWG2. needs to be the same (that is 5 MHz) which limits the The System Architecture Evolution study focused on deployment possibilities and puts a lower bound on the how the 3GPP core network will evolve into the core peak rate than LTE have the potential to deliver. On network of the next decades. The existing core network the other hand, HSPA Evolution is built on the existing was designed in the 1980s for GSM, extended during the specifications and only those parts of the specifications 1990s' for GPRS and WCDMA. The philosophy of the that need to be upgraded are touched. Thus there is less SAE is to focus on the packet-switched domain, and standardization, implementation and testing work for migrate away from the circuit-switched domain. This is HSPA Evolution than LTE since the HSPA Evolution done through the coming 3GPP releases ending up with philosophy is to apply new more advanced technology on the Evolved Packet Core. the existing HSPA standard. This will bring HSPA to Knowing that HSPA Evolution is backward compati- a performance level comparable to LTE when compared ble and knowing that the Evolved Packet Core will sup- on a 5 MHz spectrum allocation. port both HSPA Evolution and LTE assures that LTE can be deployed in smaller islands and thus only where it is needed. A gradual deployment approach can be selected 4.2.2.2 An evolved core network: System (see Figure 4.2-3). First the operator can upgrade its architecture evolution HSPA network to HSPA-Evolution-capable network, and then add LTE cells where capacity is lacking or where Roughly at the same time as LTE and HSPA Evolution the operator wants to try out new services that cannot