01-02-2013, 12:28 PM
Communication Systems
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Wireless LAN
In addition to cell phones, there are many more wireless systems and applications in common use today.
These are primarily short-range systems that have a range of a few inches up to several miles depending upon the application.
Each of these popular systems is defined by a specific industry standard and is identified with one or a few well-known applications.
Local-area networks (LANs) within a company or an organization are still interconnected mainly by CAT5 or CAT6 twisted pair.
Wireless extensions and even complete wireless LANs have become more common now that reliable, low-cost wireless modems are available.
Wireless is a great way to expand an existing network.
What makes the wireless LAN so appealing is that it offers flexibility, convenience, and lower costs.
Hardware of Wireless LANs
The hardware devices in a wireless LAN are the access point or the gateway/router and the radio modems in the PCs.
The access point is a box containing a transceiver that interfaces to an existing LAN by way of CAT5/6 wiring.
It gets its dc operating power via the twisted-pair cabling.
The IEEE 802.3af standard related to furnishing dc power over the network cable is referred to as Power over Ethernet (PoE).
Wireless LAN Standards
One standard for wireless LANs has emerged as the most flexible, affordable, and reliable.
Known as the IEEE 802.11 standard, it is available in multiple forms for different needs.
The earliest useful and most widely adopted version of the 802.11 standard is 802.11b.
It operates in 11 channels in the 2.4-GHz unlicensed ISM band.
This band extends from 2.4 to 2.4835 MHz for a total bandwidth of 83.5 MHz.
PANs and Bluetooth
A personal-area network (PAN) is a very small network that is created informally or on an ad hoc basis.
A PAN typically involves two or three nodes, but some systems permit many nodes to be connected in a small area.
PANs can be wired, but today all are wireless.
The most popular wireless PAN system is Bluetooth, a standard developed by the cell phone company Ericsson for use as a cable replacement.
ZigBee and Mesh Wireless Networks
ZigBee is the commercial name for another PAN network technology based on the IEEE 802.15.4 wireless standard.
Like Bluetooth, it is a short-range technology with networking capability.
It was designed primarily for commercial, industrial, and home monitoring and control applications.
ZigBee is designed to operate in the license-free spectrum.
WiMAX and Metropolitan-Area Networks
Its primary applications will fit into two basic categories: point-to-point (P2P) or point-to-multipoint (PMP).
The P2P mode is for applications requiring the transfer of data between two points.
The PMP mode is a broadcast mode from a central base station to multiple surrounding nodes. In this mode WiMAX serves as a WISP for homes or businesses.