|
We all want the same kinds of things from our personal communication appliances. We want them to be 100% reliable, convenient, simple to use, cheap to buy and cheap to operate. In the last few years the list has been expanded to include the desires to be totally tetherless and totally mobile. Figure 1 illustrates this wireless dream, wherein one device maps to one person and to one address in the public network. How close are we coming to these objectives? What are the current trends in technology, business, and regulatory affairs that underlie attainment of the model? What are the technical challenges in device development that must be overcome? Successful implementations and large-scale rollouts of cellular (high-tier, fullymobile) and cordless (low-tier, limited-mobility) systems have been achieved in several markets and with a handful of different communication system approaches. We will examine one or two examples of design practices at the systems and circuit level to appreciate the current state of the art now in high-volume deployment. Strong moves to deregulate communication services and willingness to open large segments of the RF spectrum for novel new uses mark the trends in both the US domestic and many international administrations. These events are guaranteed to cause rapid acceleration of the acceptance of wireless services by the general public while also moving the choice of RF carrier frequencies upward. To fundamentally improve on appliance cost and performance (see Figure 2 for block diagram of wireless handset), a number of semiconductor and circuit-level breakthroughs will be required. For example, theorists are finding new and better ways to compress information sources and encode, modulate, and interleave the resulting information stream. Much has also been contributed on the increasingly complex techniques for selectively accessing the physical medium of the channel. Some of these techniques put special stress on RF componentry, some on the digital processors, memories, and/or fixed-logic functions that must deliver more performance at lower cost and lower power. Figure 3 shows the march of progress in one area, voice compression, and the resultant increase in digital signal processing required RF components (microwave monolithic ICs), on the other hand, must have high dynamic range, excellent linearity, low noise, low bias current, high isolation, and high passive component accuracy. We find that price/performance progress in RF componentry does not usually obey any trend close to "Moore's Law. " In addition, few fabs in the world have tackled the problems of understanding and controlling the parameters necessary to produce these high-performance RF devices. Now that the mass markets are developing, more companies are finding it worthwhile to examine which technologies have the best price/performance balance to solve the overall wireless engineering problems. For system designers there is a constant struggle to move the digital/analog boundary higher in the frequency domain, or alternatively to reduce the RF side of the problem to simpler architectures. This has the benefit of increasing the fraction of the wireless appliances' device production relegated to digital component fabrication. In this talk we will review and summarize some of the key challenges that system designers face as they sort through the myriad of tradeoffs and applications.
Keywords: radio, telecommunications, wireless, digital, DSP, MMIC, PCS, cellular, cordless, pagin
|
