Data Communication

A limited amount of bandwidth is allocated in wireless services. A wireless system is required to accommodate as many user as possible by effectively sharing the limited bandwidth. Therefore in the field of communications, multiple access could be defined as means of allowing multiple user. To share the finite bandwidth simultaneously.There are 4 basis schemes for this 1] Frequency Division Multiple Access (FDMA) 2] Time Division Multiple Access (TDMA) 3] Code Division Multiple Access (CDMA) 4] Space Division Multiple Access (SDMA)

- WDM is analog multiplexing technique. - It's working is same as  FM. - In WDM different signals are from optical fibers. - Various light waves from different source combined to form a composite light signal that is transmitted across the channel to receive. - At the receive side the composite signal light signed is broken into different light waves by demultiplexing. - This combining and splitting of light wave is done by using prism.

- It is an analog technique. - Signals of different frequencies are combined into a composite signal and is transmitted on the signal link. - Bandwidth of link should be greater than the combined bandwidth of various channels. - Each signals have different frequencies. - Channels are separated by strip of unused bandwidth called Guard bands to prevent from overlapping.Application: - FDM is used for FM and AM radio broadcasting. - FDM is used for television broadcasting. - First generation telephone also use FDM.

    - It is digital multiplexing technique. - Channel is not divided on the basis of frequency but on the basis of time. - Total time available in channel is divided between several users. - Each users is allocated to particular time interval called time slot. Types of  TDM 1] Synchronous TDM 2] Asynchronous TDM 1] Synchronous TDM Number of Input = 5 Number of Slot in frame = 5 - Each device is given some time slot to transmit the data over the link whether the device has any data to transmit or not. - Each device place its…

Multiplexing: Multiplexing is a method by which multiple analog signal or digital data streams are combined into one signal over a shared medium. The aim is to share expensive resource. For eg. in telecommunication, several telephone calls may be carried using one wire. A device that performs the multiplexing is called multiplexer (MUX) and the device that performs the reverse process is called de-multiplexer. Fig. Multiplexer and De-multiplexer