 also refer to slices of spec- trum (as is does for the topic at hand: HSPA+). The next version, HSPA+2, uses spectrum from two different bands. It has peak speeds of 42Mbps. In 3G protocols, advertised speeds refer to peak speeds reached in a laboratory environment, under ideal conditions. In actual usage, attainable speeds are lower. 4G advertised speeds are those attainable under many network conditions. For HSPA- to reach even higher speeds in the future, spectrum from four carriers will need to be knit together. However, these techniques are complex. In addition, they decrease the top speeds and amount of spectrum available to other subscribers in the cell to accommodate more subscribers. Combining carriers results in less spectrum and fewer carriers available to other subscribers. Therefore, during peak hours, when there is more traffic, users might not reach these advertised speeds. Carriers (network service providers, this time) choose HSPA+ when they don't have spectrum compatible with LTE or WiMAX. Not every country has made these spectrum bands available to carriers. They might also not choose HSPA+ if they have relatively new WCDMA infrastructure that is not fully depreciated. Carriers that do upgrade can often upgrade to HSPA+ at a relatively low cost by adding new software. However, if they use HSPA+ in new spectrum bands, they are likely to need to add new antennas, as well. Definitions of 4G The ITU-R specifies that IMT Advanced, true 4G services must support data rates of 100Mbps and an all-IP infrastructure. Although HSPA+ and current implementations of LTE and WiMAX do not meet these criteria, carriers advertise them as 4G services in marketing campaigns. Equipment with true 4G capabilities is expected to be avail- able by approximately 2014. But, current LTE, HSPA+, and WiMAX deployments are pre-4G services that deliver major improvements over earlier 3G technologies. A major goal of true 4G technology developers is the capability of mobile devices to keep up with the expected volume of mobile