LTE and LTE-Advanced are complemented by an IP-based network core, the EPC. There is also strong IP-based internetworking in WiMAX. Such support will be crucial in creating heterogeneous network composites – not only for user access, but for generalized device access. As noted in Chapter 16, work within the 3GPP and 3GPP2, in addition to the efforts in IEEE 802.21 or Media Independent Handover, are all aimed at supporting inter-technology handovers at the access level. There are also efforts including those of the IEEE P1900 working group that are aimed at, among other things, enhancing operational coexistence between the different radio technologies.
A definite trend that is to grow over the coming years is the addition of satellite networks to the existing heterogeneity. Traditionally, and despite their great bandwidths, satellites have been avoided for user- and device level access due to both their cost and delay characteristics. However, there is currently great interest in near-space (17~22 km) satellites called High Altitude Platforms (HAP) . The delay characteristics for HAPs will be functional for terrestrial application. HAPs will also be characterized by wide coverage, offering reasonable coverage overlays for IMT-Advanced networks. Already, the ITU-R has issued the minimum performance requirements for HAPs providing 3G service in certain regions .