Wireless Communications and Mobile Technology

An AP attached directly to a wired network provides a centralized point for wireless end users to remain attached to a wired Internet. If more than one AP is connected to the wired network, users can roam from one area (or wireless cell) of a facility to another cell without losing their connection to the network in a large facility (Figure 3). As users move out of range of one AP, they automatically connect to the network through another AP; consequently, the roaming process is seamless and transparent to the user. 1c- WLAN Repeater Roaming

Another Wi-Fi™ Mesh comprise of a Root-AP and a collection of adjacent Repeater-APs. Another wireless roaming configuration is attaching a principal AP to a wired network and arranging other access points as a repeater or central router for mobile end users. The WLAN repeater-roaming configuration is a chain of repeaters overlapping be neighboring wireless cells and maintain an indirection association to the wired AP. Similar to a teacher leading a group of children, by the hand, across a street intersection. The AP wired to the backbone network is designated as a Root Access Point (Root-AP) and the wireless APs not attached to the wired network are called Repeater Access Points (Repeater-APs).

The IEEE 802.16 standard, WIMAX is a broadband wireless access to link homes and business to core telecommunications networks worldwide. The wireless MAN technology bringing the  network  toa building, users  inside  the  building  will  connect  to it with conventional in-building networks. This technology allows for the efficient extension  of the individual users laptop computer in a home.

The working group’s initial interest was the 10to 66 GHZ range which is developed for a point-to-multipoint broadband wireless access over 30 miles.The standards covers both the media access control (MAC) and the physical (PHY) layers. Task groups a and b are jointly producing an amendment to extend  the specification to cover both the licensed and unlicensed bands in the 2 to 11GHZ range [2]. The data rate is of70 mbps  over30miles (50Kms).WIMAX is speed broadband network.

The WIMAX network is as shown in figure 2. A WIMAX system consists of two parts.

(1)    A WIMAX TOWER:
A single WIMAX tower can provide coverage to Avery large area [5].

(2)    A WIMAX RECEIVER:
The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop.
A WIMAX tower station  can  connect directly  to  the  internet  using a high-bandwidth, wired connection (for example, a T3 line). It can also
connect to another WIMAX tower using a line-of-sight, microwave link. This connection to a second tower(often referred to as a back haul).A long with the ability of a single tower to cover up to 3,000 square miles is what allows WIMAX to provide coverage to remote  rural  areas.WIMAX is capable of delivering flexible and affordable last-mile broadband access  for  millions of subscribers in homes and business throughout the world.

2.2 Wimax Radio Channels

This figure shows the key components of a basic WiMax radio system. This diagram shows that the major component of a WiMax system include subscriber station (SS), a base station (BS) and interconnection gateways to data com (e.g. Internet) and telecom (e.g. PSTN). An antenna and receiver (subscriber station) in the home or business converts the microwave radio signals into broadband data signals for distribution in the home. In this example, a WiMax system is being used to provide telephone and broadband data communication services. When used for telephone services, the WiMax system converts broadcast signals to an audio format (such as VoIP) for distribution to IP telephones or analog telephone adapter (ATA) boxes. When WiMax is used for broadband data, the WiMax system also connects the Internet through a gateway to the Internet. This example also shows that the WiMax system can reach distances of up to 50 km when operating at lower frequencies (2-11 GHz).

2.3  WIMAX BROADBAND CONNECTIVITY

RESIDENTIAL BROADBAND

For residential broadband WIMAX can be used to fill the gaps in cable and DSL coverage. Practical limitations prevent cable and DSL technologies from reaching many potential broadband customers. Due to the absence a line of sight requirement, high bandwidth and the inherent flexibility and low cost, IMAX helps to overcome the limitations of traditional wired and proprietary wireless technologies.
3- Practical Application of Mesh Networks

A Wireless Mesh Network has two practical applications in the Wi-Fi community: Static Wireless Mesh and Dynamic Wireless Mesh. With a Static Wireless Mesh, the permanent IP address is assigned to a centralized or specific wireless device, like a wireless router, as it rarely change in physical location. Adjacent wireless routers can overlap in RF coverage to produce a roaming effect or extend the range via a repeater configuration as well as several pockets of mobile wireless end users.

Users or wireless devices wishing to communicate without any infrastructure or vital administration primarily form the Dynamic Wireless Mesh. Each node is free to enter or leave the network area at any time; however, a very complex IP layer is required to assign or de-assign IP addresses because of an every changing mobile environment.

Static Wireless Mesh: Wireless Bridge delivers Internet access to Homes and roaming can occur between neighboring home.