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| ■Software Defined Radio and Cognitive Radio Technologies |
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●What Kind of Technology? Software defined radio (SDR) terminals incorporate programmable signal processing devices along with multiband RF circuits and multiband antennas for use at different frequencies, allowing flexible support of various services and systems simply by changing the software, similar to a PC. At the NTT Network Innovation Laboratories, we developed the world's first prototype SDR terminal able to switch freely between PHS and wireless LAN by software control. With the aim of developing an SDR mobile terminal, we further studied a reconfigurable processor featuring both high signal processing capability and low power dissipation, for the first time anywhere achieving a commercially feasible design. We are now working on further developing these technologies through research and development on autonomous adaptive network system configuration technology for future mobile communications and ubiquitous networks, and on cognitive radio technologies for realizing the ultimate in effective use of communication resources and frequencies, robust communications, and advanced seamless communications.  ●The Substance of Our Work Important keys to realizing an SDR mobile terminal include achieving fast signal processing in a compact package with low power needs, and also designing a compact, low-power, wideband and highly linear multiband RF module (see Figure 1). For the signal processing module, we studied the applicability of a programmable processor as a new architecture, and using an evaluation prototype, conducted the world's first demonstration showing sufficient processing capacity for a 54 Mbit/s wireless LAN system (see Figure 2). For the multiband RF module, we designed and test-produced a wideband monolithic microwave integrated circuit (MMIC), creating a multiband MMIC with the world's top level of wideband performance. For the low-noise amplifier (LNA), a key device in this module, we devised a new bias circuit consisting of transistors and passive components, achieving both wideband performance and high linearity in a low-noise amplifier, something never before attainable with conventional technology. In addition, we are pursuing research on ultra-wideband voltage controlled oscillators (VCO) incorporating RF-MEMS technology (see Figure 3). 
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 ●What Does the Future Hold? The technologies described here will make possible flexible wireless services and wireless access in future mobile communications and ubiquitous networks, featuring a variety of coexisting wireless systems. Wireless terminals and base stations will be able to recognize the status of their communication environment and autonomously reconfigure their equipment makeup, communication mode, and frequencies accordingly, providing optimal services that meet user needs and assure the most effective use of communication resources and frequencies. Wireless terminals will be able to adapt to 2G, 3G, 3.5G, 4G or other cellular systems, or support technologies such as WiMAX and wireless LAN, simply by software changes. Wireless terminals will also be able to switch effortlessly for use with ITS or RFID. Service addition and removal will be easily accomplished by software changes alone, doing away with the need to buy a new terminal to take advantage of service changes. Users will be able to download the necessary software by wireless links without leaving home. When going overseas, users will be able to make use of the wireless systems in other countries simply by loading the necessary software (see Figure 4). 
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