Can anybody tell me plz : what is the need of clock recovery in digital communication?? how randomization process is helpful in clock recovery and spectral shaping ???
Clock recovery is necessary to synchronize the a receiver with the transceiver. It consist in regenerating the clock from the incoming data. Generaly it is used in serial data reception.
randomization process is not generally carried perfectly random... they have their own algorithm such that they avoid continuous occurence of 0 or 1 which may lead to loss of synchronisation...
In fact it is not 100 % a randon process. All the data rise/fall transition represent a good information for synchronization. The Manchester encoding for exemple enable a very easy recovery. It become a problem when the data sent is for exemple a set of zeros (000000) or one (1111111) in this case the data doesn't change and there is no transition. For this reson we use that we call the technique of bit stuffing. There is anoter techniques such as the 8/10 bit encoding.
In addition don't forget that the receiver uses a PLL to generate it's local clock using as reference the data transistions.
For additional informations google it using the highligthed bold technical terms.