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Multiplexing
When some "multiple things" are carried by the same physical resources, we call the multiple things being "multiplexed".
When you multiplex something, you always have to think about how to "de-multiplex" them. It means that you have to multiplex somethings in such a way that they can be easily separated into individual things. If you multiplex things and those things cannot be demultiplexed, it is called a garbage -:).
There are many different types of multiplexing that has been used in communication and you'd better know of at least some name of these techniquest. (Details of each of these technique is a huge topics on their own). There are some communication system that is using only one of these technique and there are some other communication systems that are using multiples of these techniques in combination.
- TDM (Time Division Multiplexing) : This would be the most straightfoward method. We split the data exchange time into multiple small slots and transmit/receive different data onto different slot. GSM is one of example of communication system that is extensively using this technology)
- FDM (Frequency Division Multiplexing) : In this technique, we split a communication channel(physical resource) into different frequency blocks and transmit/receive different stream of data through different frequency blocks. OFDM (Orthogonal Frequency Division Multiplexing) is one typical example.
- CDM (Code Division Multiplexing) : In this technique, we split a communication channel(physical resource) into different code (orthogonal code) and allocate each stream of data onto different code. CDMA and WCDMA is the most widely used example.
- SDM (Space Division Multiplexing) or Spatial Multiplexing : In this technique, we split a communication channel(physical resource) into multiple different physical locations and allocate each stream of data onto each of the location. In real implementation, 'differet physical location' mean 'different transmission or reciever antenna'. MIMO (Multiple Input Multiple Output) is the
most common example of SDM.
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