Broadband access: the last mile

Driven by deregulation, a multitude of new transmission technologies have been deployed and standardized in recent years. The classical plain old telephony service (POTS) network is reused for DSL applications. Optical fiber is increasingly deployed in new networks, though its cost is still high. Air interface is used in sparsely-populated areas when deployment speed is needed. Although all these media intend to bring broadband to the home, they do it differently, using transmission principles which affect parameters such as line coding and equalization. They offer different bandwidths (less for twisted pair, highest for optical fiber) and differ in network topology (point-to-point or point-to-multi-point). Because of complex evolving standards, proposed architectures are at least partly based on programmable platforms consisting of DSPs, standard processors, and control memories. This approach is complemented by downloadable software. Design is dominated by analog aspects. Achieving transmitter performance with reasonable power consumption needs to be tackled by new structures for analog drivers, power amplifiers, ADCs, and DACs. Three families of access technology are discussed: DSL, best-known of the broadband technologies, outpacing the others in deployment speed; wireless in the local loop (WLL) and local multipoint distribution system (LMDS); and point-to-multipoint optical (PON) offering large bandwidth.