The WiMAX family of standards (802.16) concentrate on two types of usage models a fixed WiMAX usage model and a mobile WiMAX usage model. The basic element that differentiates these systems is the ground speed at which the systems are designed to manage. Based on mobility, wireless access systems are designed to operate on the move without any disruption of service; wireless access can be divided into three classes; stationary, pedestrian and vehicular.
A mobile WiMAX network access system is one that can address the vehicular class, whereas the fixed WiMAX serves the stationary and pedestrian classes. This raises a question about the nomadic wireless access system, which is referred to as a system that works as a fixed WiMAX network access system but can change its location.
Broadband service and consumer usage of fixed WiMAX access is expected to reflect that of fixed wire-line service, with many of the standards-based requirements being confined to the air interface. Because communications takes place via wireless links from WiMAX Customer Premise Equipment (WiMAX CPE) to a remote Non Line-of-sight (NLOS) WiMAX base station, requirements for link security are greater than those needed for a wireless service. The security mechanisms within the IEEE 802.16 standards are sufficient for fixed WiMAX access service.
Another challenge for the fixed WiMAX access air interface is the need to set up high performance radio links capable of data rates comparable to wired broadband service, using equipment that can be self installed indoors by users, as is the case for Digital Subscriber Line (DSL) and cable modems. IEEE 802.16 standards provide advanced physical (PHY) layer techniques to achieve link margins capable of supporting high throughput in NLOS environments. (Tom Carpenter, 2006)
The 802.16a extension, refined in January 2003, uses a lower frequency of 2 to 11 GHz, enabling NLOS connections. The latest 802.16e task group is capitalizing on the new capabilities this provides by working on developing a specification to enable mobile WiMAX clients. These clients will be able to hand off between WiMAX base stations, enabling users to roam between service areas.
WiMAX backhaul is actually a connection system from the Access Point (AP) back to the provider and to the connection from the provider to the network. A wimax backhaul can set out any technology and media provided; it connects the system to the backbone. In most of the WiMAX deployments circumstances, it is also possible to connect several wimax base stations with one another by use of high speed WiMAX backhaul microware links. This would also allow for roaming by a WiMAX subscriber from one WiMAX base station coverage area to another, similar to roaming enabled by cellular phone companies. (Xiaole Song, 2007)
There can be two cases of portability; full mobility or limited mobility. The effortless case of portable service involves a user transporting a WiMAX modem to a different location. Provided this visited location is serve by wireless broadband service, in this scenario the user re-authenticates and manually re-establishes new IP connections and is afforded broadband service at the visited location. (Tom Carpenter, 2006)
In the fully mobile scenario, user expectations for connectivity are comparable to facilities available in third generation (3G) voice/data systems. Users may move around while engaged in a broadband data access or multimedia streaming session. Mobile wireless systems need to be robust against rapid channel variation to support vehicular speeds.
There are significant implications of mobility on the IP layer owing to the need to maintain rout-ability of the host IP address to preserve in-flight packets during IP handoff. This may require authentication and handoffs for uplink and downlink IP packets and Medium Access Control (MAC) frames. The need to support low latency and low packet loss handovers of data streams as users transition from one base station to another is clearly a challenging task. For mobile data services, users will not easily adapt their service expectations because of environmental limitations that are technically but not directly relevant to the mode of user. For these reasons, the network and air interface must be designed to anticipate these user expectations and deliver accordingly. (Deepak Pareek, 2006)