Throughout this study and visits to selected sites in Europe and Japan and interactions with selected U.S. industries, the WTEC panel recognized that hardware technologies for future wireless applications provide substantial research opportunities on a worldwide scale. The following technological areas are either emerging or evolving and are considered important for the future health of wireless technologies:
Some specific additional features are as follows:
Amplifier efficiency and linearity are contradictory requirements. The typical approach is to design an amplifier operated in a nonlinear mode and then provide schemes to improve linearity. The latter can be a simple output power back-off or a more sophisticated feed-forward or predistortion technique. In any case, not only good devices but also synergistic approaches are essential. It is important to optimize the amplifier block or transmitter containing an amplifier and output circuits including antenna, or to make use of digital technology for "signal processing" for the amplifier. Modulation format often dictates the choice of control. For instance, a spectrally inefficient constant-envelope modulation is very resistive to nonlinear effects. Combining digital techniques with an amplifier may lead to a form of "software" oriented radio.
A mixed signal IC may be a good ingredient for a futuristic one-chip radio or system-on-a-chip. But both good devices and also low loss and high isolation interconnects are needed.
Software oriented radio has drawn much attention. However, often software issues and digital circuits issues are emphasized while the RF front end is sometimes neglected. Therefore, front-end architecture should be included in the studies for software radio.
Smart antennas are another example where the software and hardware collaborate well. Integrated antennas alleviate some of the hardware difficulties associated with smart antennas. Also, reconfigurable circuits and antennas should play important roles in developing the smart antenna.
Three-dimensional integration schemes are required to provide communication systems that are very small, very low in weight and very low in cost without compromising performance. The use of heterogeneous materials for the circuits and devices incorporated in the system may lead to unique solutions in integration and packaging.
High-Q, low-loss passive devices are also needed for high performance. The development of RF MEMS also provides new directions with the possibility of new functions and system architectures.
The above are some of the possible future directions of research. What should be emphasized is that future research must require interdisciplinary approaches not only in terms of different hardware components but also hardware and software.