Introduction to WiMAX (IEEE 802.16)

In this article an overview will be given, enough depth on the IEEE 802.16 WiMAX. Most interesting topics will be covered in the standard protocol stack structure, description of the various layers, as is sliced ​​to authenticate a client and much more.

Let's start by saying that WiMAX stands for Worldwide Interoperability for Microwave Access and is a standard part of the family of IEEE 802.
The term was coined by the WiMAX WiMAX Forum, an association formed by a group of companies in the sector, which sets standards and cooperate in marketing devices compatible and interoperable. The WiMAX Forum has an important task, namely to certify devices by releasing a proposed form of WiMAX Forum Certified mark for approved devices. Only devices that have this certification are compatible, in their totality, the 802.16 standard.

WiMAX is a wireless transmission technology (wireless) access to broadband and has the ability, like other wireless technologies, to be used on many types of land (WiMAX systems can be used in environments dall''urbano rural). Mainly created to try to increase the access rate (the nominal data rate) allowed by the Wi-Fi and wants to extend the coverage area of service. It 'also created to improve some critical aspects of Wi-Fi and in particular to:

• Help manage the quality of service (QoS).
• Increasing network security is to increase the confidentiality of information exchanged.

The band of the WiMAX is at frequencies higher than those of the Wi-Fi and this leads to a better use of the network, but the disadvantage is the fact that they decrease the mobility of users. Essentially created to serve metropolitan areas and is often referred to as a wireless residential.

Structure of a WiMAX network

To better understand the operation of a WiMAX network now do a quick overview of the main devices that make it up. The devices, which we'll bervemente are basically two: the Base Station (BS) and Subscriber Station (SS).
If we wanted to make a parallel computer with a LAN, as regards the role played by devices, we can certainly associate the role of the base station router the role of the various terminals connected to the subscriber station.

The main role played by the Base Station is to allocate the necessary bandwidth to the various subscriber station, receiving signals sent from the subscriber station connected, regenerate the received signal and retransmit it to the destination. A Base Station then will have a variable number of subscriber station will be connected and in turn connected to other base stations that handle different areas.
So how is intuitive thinking, connecting multiple base stations can be obtained even large networks and, as a Base Station will handle only part of the network, in case of failure will remain isolated malfuzionamenti or only part of the network and not the network in its entirety.

WiMAX protocol stack

Let us now analyze the protocol stack implemented by the WiMAX viewable in the diagram below:

One of the technical prescriptions of WiMAX is to have different signal modulation techniques in the physical layer. These three different modulations differ from each other for different amounts of bits transmitted at the same time:

• QPSK transmits 2 bits
• The 16-QAM transmits 4 bits
• The 64-QAM transmits 8-bit

Because there are three types of signal modulation layer convergence is of obvious necessity, as each type of modulation will require the construction of a packet of information that differs from the other. In the protective layer contains the functions that make it secret, who is not authorized, the information provided. In practice this level of encryption plays a role in the message, using mainly the 'RSA encryption algorithm.
In the discussion of this article, intentionally, will not be described in the "upper levels" because of little scholarly interest. We are now going to analyze the physical layer, the MAC layer and the degree of convergence in the service in more depth.

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