Essay by dcy4presCollege, UndergraduateB, May 2010

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IT331-02AU: Technology Infrastructure

Instructor Jason Litz

In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire. It originated in telegraphy, and is now widely applied in communications.

Multiplexing is provided by the physical layer of the OSI model, while multiple access also involves a media access control protocol, which is part of the data link layer. The frequency band from 88 MHz to 108 MHz is reserved over the public airwaves for commercial FM broadcasting. The 88-108 MHz frequency band is divided into 200 kHz sub-bands.

The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, can extract the original channels on the receiver side.

Interference is the biggest single problem with the AWS-3 band, as planned, permits the use of the entire 25 MHz of spectrum for both transmitting from the cell sites to the devices and for the devices to transmit back to the cell sites. Time Division Duplex or TDD, requires the cell site and device transmitters to share the same spectrum with the cell transmitter talking to the mobile device and then listening for a response. This gives customers the allusion that they are using a system that permits simultaneous two-way communications, which is called duplex and is common in all commercial wireless systems. Yes, Clearwire is using this type of system, but not adjacent to spectrum using the standard...