Andrew Reid Title: Circuit and System Design for Future Microwave Systems Due to the rapid growth of ideas for the future uses of adaptive microwave system, such as active phased array radars, wireless local area networks, and the cellular phone, this paper aims to summarize the requirements for signal processing and the types of future devices that will realize this technology and also this paper expands on the research areas that will advance the development of this field. It serves as a good starting point to learn about the hardware hurdles that need to be leaped in order to realize wide spread deployment of cognitive radio devices. Trends in radio and the spectrum use show that allocated spectrum is currently inefficient, both technically and economically. From studies cited in this paper, as much as 20% of a given commercially allocated spectrum would not be regularly utilized in urban areas. This is an opportunity for the wireless industry to provide the services craved by the ever increasing market of wireless users, but the technology that will take advantage of this opportunity is not currently available. For example, this papers highlights one of the well known problems, from what I have read, that current radio frequency devices operate over a wide range of standards, such as GSM, UMTS, 802.11, Bluetooth, Wimax, GPS, etc. Each operates at a different baseband frequency and would require a baseband processor for each standard. These problems are not only at the consumer level but also at the military level as well. A cited paper stated that in a shared spectrum on a 3150 km2 battlefield could experience 10,000 different emitters capable of transmitting. Another problem with cognitive radio is realizing the ability to collect information about its surround environment, change its operation parameters, and learn from previous actions and conclusions; all while distributing that information to fellow cognitive radios. The radios of the future would become highly adaptive in order to provide the level of performance need to take full advantage of present day opportunities stated in the previous paragraph. Among the greatest requirements for broadband frequency monitoring and processing in receivers for cognitive radio is the need for Analog to Digital Converters to operate over multiple modes, GPRS/WCDMA/802.11A, etc. Cited from a previous paper, a 14-bit 150 MSPS analog to digital converter with less than 50mW power consumption is needed to perform this task. Currently this is unrealizable and years away. The requirements present by cognitive radio create too large a gap, a gap which would require several breakthroughs in research to shorten. Another technical area that needs to advance would be that of tunable front-end filters and impedance matching elements. These provide the dynamic reconfiguration found in any description of the cognitive radio. This paper provide a good example, the receiver filter in a cellular application would have to tune its center frequency over several frequency bands and so not to experience intermodulation with an undesired signal notch filters would have to implemented. This paper cited other work where alternative approaches were being developed with MEMS, voltage variable dielectrics, and varactors. Each have their trade-offs, for example, although a MEMS approach would deliver great performance with loss and linearity, the manufacturability is still an issue. Other cited work has been experience similar performances out of varactor-diode based approaches. But, this paper still sees the need to note that with all the advances more work is needed to provide the best from all the current approaches. Some sort of hybrid approach is need for wide spread deployment of this technology.
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