SDR to fit the application
Many designers at the Radio and Wireless Symposium addressed the design of configurable RF and baseband blocks for cognitive radio systems. But Hiroshi Harada of Japan's National Institute of Information and Communications Technology took configurable-device speculation a step further by relating chip design to government plans for the allocation of spectrum. In an invited speech, Harada explained how ending analog TV broadcast in July 2011 poses the same problems and opportunities for opening up spectrum in Japan that now confront the United States, which is scheduled to halt analog telecasts in February 2009.
When designers in industry and academia consider cognitive radio, Harada said, they should look at aspects of the anticipated frequency bands available and how that could influence the dynamic range of the devices under design. This related directly to a multiband SiGe-BiCMOS mixer being developed at the institute, with a range of 0.4 to 5.3 GHz.
This mixer was combined with a two-board baseband DSP system using a 430-Mips micro-iTron processor and a multiband antenna designed to shift among multiple available frequency bands.
A cognitive radio can do more than choose frequency bands, Harada said. He showed how a change in volume of the RF signal started a process in which a basestation self-loads wireless local-area network (LAN) software and shifts from cellular to Wi-Fi operation. "Ideally, a single appliance could serve mobile communications, digital terrestrial TV, wireless LAN and UWB, and configure its software for the different types of links," he said.
This year's Radio and Wireless Symposium was unique in broadening analysis of wireless networks beyond the physical-layer characteristics of RF and baseband devices. Several papers looked at using the characteristics of Layer 2 and Layer 3 bridging and routing for directly influencing the topology of wireless networks. In an invited paper, Ozgur Oyman, research scientist at Intel Corp.'s communications technology lab, described multihop routing as a way to increase the diversity of antennas for picocellular broadband orthogonal frequency-division multiplexing services like WiMax or meshed Wi-Fi. Just as spatial or frequency diversity can optimize broadband networks, multihop routing patterns can themselves influence the topology of broadband OFDM cellular, he said.
Intel's work showed that throughput maximization for wireless wide-area networks is equivalent to familiar minimum-cost routing problems encountered in IP routing networks. Oyman's study also maps into the multihop relay work of the IEEE 802.16j relay study group.