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Rising demand for multimedia applications and mobile usage requires new paradigm to shift voice-oriented cellular architecture into data-oriented networks in order to serve bandwidth hungry packet based applications which include but are not limited to multimedia gaming, mobilTV, streaming media, P2P, etc. Data oriented networks require a 20-fold fatter air link and backhaul compared with typical voice communication. To meet this demand, next generation networks consider OFDMA with MIMO support for air link and all IP end-to-end systems for backhaul at the behest of lower OPEX and CAPEX requirements of operators.
These two coalesce in WiMAX. Long Term Evolution (LTE) out of Third Generation Partnership Project, and Ultra Mobile Broadband (UMB) out of 3GPP2 also clearly project towards the same direction, of course with slight deviations. All three technologies form a basis for 4G along with next generation Wi-Fi.
Key features from a 4G wireless network point of view include open architecture for productivity, increased end-user throughput, reduced latency, support for full mobility and end-to-end QoS.
The 4G networks will also make extensive use of femtocell, picocell and microcell technologies to deliver very high data rates in high-usage areas along with macro cells. These will facilitate covering more limited areas, but at a much greater throughput. Thanks to IP technology and access gateway, remotely maintaining differed sized base stations and efficiently backhauling, the 4G traffic will be feasible.
WiMAX Architecture
WiMAX is the pioneering and most talked about OFDMA-based IP technology and is ready to deploy worldwide. WiMAX is based on the IEEE 801.16e-2005 standard and WiMAX Forum Network Working Group (NWG) specification. IEEE 802.16e-2005 standard specifies the PHY and MAC of the radio link. This alone is not adequate to build an interoperable broadband wireless network. Interoperable networks involve end-to-end service such as IP connectivity and session management, security, QoS, and mobility.
The WiMAX NWG defines the end-too-end architecture in a three-stage standard: Stage 1 is for use case scenarios and service requirements and defined along with Service Provider Working Group; Stage 2 describes the architecture; Stage 3 details the architecture.
WiMAX design principles include the following:
- The architecture shall be decomposed into functions and well-defined reference points between functional entities for multi-vendor interoperability.
- The architecture shall provide modularity and flexibility in deployment. Multiple types of decomposition topologies may coexist such as distributed, centralized, and hybrid.
- The architecture shall support fixed, nomadic, portable, and mobile operation and evolution paths to full mobility.
- The architecture shall support decomposition of access networks and connectivity networks. The access network is radio-agnostic and connectivity networks provide IP connectivity.
- The architecture shall support sharing of the network with a variety of business models:
- Network Access Provider (NAP) owns the network and operations
- Network Service Provider (NSP) owns the subscriber and provides service. NSPs share the NAP or a NSP uses multiple NAPs
- Application Service Provider (ASP) provides application services.
- The architecture shall support internetworking with 3GPP, 3GPP2, WiFi, and wireline networks using IETF protocols.
Figure 1 shows the WiMAX network reference model (NRM). The figure illustrates the reference points and functional entities. The NRM is composed of three logical parts: mobile stations, Access Service Network (ASN) which is owned by NAP, and the Connectivity Service Network (CSN) owned by NSPs. Business relationships between WiMAX subscriber, NAP and CSN are depicted in Figure 2.
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