Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

242 ApplicationsWiMAX(2 - 11 GHz)Central office/Local ExchangeCORENETWORKTSBSLocalExchangeContentProviderTSBSRouterIP RouterHead End GWLegacy Acc GWCore NW I/FFibre Dist’nCopper Dist’n.IP-NetworkPSTNTSBSFigure 5-20WiMAX core architecture5.3.3 System ArchitectureAs stated earlier, WiMAX will cover different kinds of wireless applications. Packet IPtransport is considered to be the main service to be transported. Both cellular point tomulti-point and mesh point to point topologies are supported (see Figure 5-20). Furthermore,the transport of the classical switched TDM traffic (e.g. POTS, E1/T1) is alsosupported. The physical connection of the WiMAX base station (BS) to the core networkequipments can be done by using optical fiber or a high speed point to point wirelessconnection at high carrier frequencies (above 11 GHz). Self-backhauling is also offered,but due to the limited bandwidth availability at frequencies between 2 and 11 GHz, thisoption may not be practicable.As licensed bandwidths, the primary targets are the 2.3–2.7 GHz and 3.3–3.6 GHz.Here the main application would be both data and voice at the first stage fixed/indoor andoutdoor (802.16d) and later mobile broadband (802.16e), offered by large data and voiceoperators. Supported main carrier frequencies for unlicensed applications is 4.9–5.85 GHz,where it encourages the Wi-Fi type of isolated spots with primarily fixed outdoor installationoffered by small and medium data operators.The WiMAX core components and network structure are illustrated in Figure 5-21.The air interface interoperability, i.e. compatibility between different terminals (TS) andbase stations (BS) from different vendors, and the roaming interoperability, i.e. enablingportable and mobile applications, are considered to be the main challenges for the WiMAXnetworks.