ABSTRACT
In today’s connected and automated world, data communication plays the most pivotal role for information transmission from one place to another. For reliable communication to take place between source and destination, the important parameters are: synchronization, error detection and correction, flow control, proper addressing, formatting, routing, data recovery, data security, network management, etc. Data transmission can be serial or parallel in nature and can be of synchronous, asynchronous, and isochronous types.
Modems are used at transmitting and receiving ends for proper data transmission. During transmission, data may be impaired due to attenuation, distortion, limited bandwidth, and noise. Multiplexing is used to transmit a number of signals over a single link. Various schemes employed are: time division multiplexing (TDM), frequency division multiplexing (FDM), wavelength division multiplexing (WDM), etc.
Spread spectrum technique is used to spread the spectrum of the original signal in order to avoid being detected by possible eavesdroppers. Secrecy requirements far outweigh the greater bandwidth required in this technique. Spread spectrum can be frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) types and in many cases their spectral density lies below the noise floor.
Data is coded before being sent due to simplified transmitter and receiver designs, to decrease errors, achieve higher transmission efficiency, and provide secrecy in transmission. Some of the codes used are: Manchester, cyclic redundancy code (CRC), Huffman, parity, Hamming, etc.
