Introduction 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 not limited to multimedia gaming, mobiTV, streaming media, P2P, etc. Data oriented network requires 20-fold fatter air link and backhaul as compared to typical voice communication. To meet this demand, the next generation networks considers OFDMA with MIMO support for air link and all-IP end-to-end system for backhaul at the behest of lower OPEX and CAPEX requirement 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 toward the same direction, of course with slight deviations. It is considered that all three technologies form basis for 4G along with next generation Wi-Fi. Key features desired from 4G wireless network 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 to cover more limited areas, but at much greater throughput. Thanks to IP technology and access gateway, remotely maintaining different size of base stations and efficiently backhauling the 4G traffic will be feasible.
WiMAX Architecture
WiMAX is the pioneering and most talked OFDMA based IP technology and is ready to deploy worldwide. WiMAX is based on IEEE 802.16e-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 network deals with end-to-end service such as IP connectivity and session management, security, QoS, and mobility.
The WiMAX NWG defines the end-to-end architecture in 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; and stage 3 details the architecture. Design principles that WiMAX considers include the following;
- The architecture shall be decomposed in to functions and well-defined reference points between functional entities for multivendor 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 path to full mobility.***
- The architecture shall support decomposition of access network and connectivity network; access network is radio -agnostic and connectivity network provides IP connectivity.
- The architecture shall support sharing of the network with variety of business models;
o Network Access Provider (NAP) owns the network and operates.
o Network Service Provider (NSP) owns the subscriber and provides service. NSPs shares the NAP or a NSP uses multiple NAPs.
o 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) which are owned by NSPs. Business relationship between WiMAX subscriber, NAP and CSN is depicted in Figure 2. The reference points as seen in Figure 1 are conceptual links that connects two functional entities. The reference points are;
- R1: Reference point between MS and BS: implements IEEE 802.16e-2005.
- R2: Reference point between MS and ASN-GW or CSN: logical interface used for authentication, authorization, IP host configuration and mobility management.
- R3: Reference point between ASN and CSN: supports AAA, policy enforcement, and mobility –management capabilities. Implements tunnel between ASN and CSN.
- R4: Reference point between ASN and ASN: used for MS mobility across ASNs.
