资 源 简 介
The telecommunicaTIon industry has advanced rapidly over the past century. TheinvenTIon of telephone has sparked the beginning of the telecommunicaTIons era.Today, an immense Public Switching Telephone Network (PSTN) exists to provideservices to millions of users worldwide. Though for many years our communicaTIonneeds have been satisfied by the telephone networks, in the past few decadescomputer and integrated circuits (IC) technology have reshaped our communicationneeds to include not only voice but data and video as well. Conveying datainformation worldwide, computer networks, such as the Internet, have becomeprevalent. This growth has been fueled by advances in IC technology that haveenabled affordable consumer products, such as high speed modems which have madecomputer accesses as easy as making a phone call. Sophisticated image and speechprocessing are also becoming available in integrated circuits to enable embeddedmultimedia capabilities in portable laptops.Currently, high quality affordable multimedia content is becoming available through emerging technologies, such as digital cable and digital subscriber lines (DSL).Communication speed on twisted pair using sophisticated echo cancellation andequalization is enabling data rates up to several megabits per second on twisted pairs and hundreds of megabits per sec on coaxial cable. In this new millennium, abundant bandwidth will be supplied through optical fiber backbones, enabling the delivery of high quality multimedia services to homes via cable, twisted pair, or even directly through fibers.Concurrent with rapid advances in wireline-based technology, there is a surgingdemand for wireless communications. Although most of our communication needs arebeing met by the current wireline systems, our communications are limited to areaswith pre-installed wireline access to information services. We are, in a sense, tetheredto the wire or fiber that carries our communications. When we are on the move, it is desirable to have untethered communications such that we may have ubiquitousaccess to the available information services. The key to this ubiquitouscommunication lies in the ability to communicate via wireless links.
