Also , the digital signalling rate per Hertz should be high . Digital wireless communication has to address both these problems , again under the shadow of multipath propagation . A very important advantages that can also arise by switching to digital operation is that of the 'universality' . The network can be extended across national borders , allowing international roaming of the subscribers . The multipath problem in mobile radio is casued by reflection and scattering from buildings, trees and other obstacles along the radio path.
Radio waves arrives at a mobile receiver from many different directions, with different time delays.
Together with a possible direct ray, a ground reflected ray and other possible scattered rays, these combine vertorially at the receiver antenna to give a resultant signal which depends on the differences in path length that exist in this multipath field. With these relative motion exists ther is a Doppler shift of the frequency components within the received signal. Conclusion Wireless Communication is in the process of revolutionising telecommunications services and the way in which people use them. Overall growth in the cordless and cellular markets during recent years has exceeded exceptations. There is widespread anticipation that customer demand for wireless telecommunication will continue to expand for the foreseeable future.