On Tuesday, July 17, the FCC held an all-day forum on Future of Wireless Band Plans. While there has been a lot of news about the need for more spectrum for wireless broadband, little attention has been paid to the challenges engineers will face in adding these new bands.
The forum served to illustrate the problems that base station and consumer device designers and manufacturers face in connection with spectrum allocations in many discrete bands ranging from UHF up to 5 GHz or higher. Such a wide spectrum range causes problems for antennas, filters and power amplifiers and even simple devices such as RF switches. In addition to two-way bands, coverage of broadcast bands worldwide, including 88-108 MHz for FM radio and 54-870 MHz for television was also discussed.
The Forum on Future of Wireless Band Plans web page has links to the presentations. I recommend viewing Ethertronics' presentation as it focuses on antenna development. Active antennas are presented as one solution. These antennae use open and closed loop impedance matching, band switching (dynamically tuned radiators) and beam steering.
William Mueller from Avago Technologies provided a Filter Design Tutorial on RF Front End Components and Limitations. He listed three filter design categories--easy, hard and extremely difficult. The extremely difficult cases include TV51 and E block, with no guard band, and GPS interference with band B24.
WiSpry's Art Morris proposed a compact agile front-end as a solution. WiSpry makes electronically tuned RF networks, so it isn't surprising that their solution included gain/power/frequency tunable amplification, tunable filters and distributed ultra-small tunable antennas integrated with a tunable duplexer and impedance matching.
Gene Tkachenko from Skyworks said the answer is integration and multi-mode/band. He showed how this would improve performance per band by optimizing the power amplifier-filter, switch-filter, and power amplifier-switch interfaces, noting this might not have to be done in a 50-ohm environment. In connection with power amplifiers, solutions included envelope tracking, digital pre-distortion, and Doherty amplifiers.
The FCC opened the Forum with Thoughts on Future Band Plans. The presentation includes some interesting options for wireless band plans, including asymmetric FDD to match current broadband traffic, which is dominated by downlink. The last side was a spectrum chart showing “band proliferation,” which ranges from the incentive auction spectrum in the UHF TV band, to a possible “clearing or sharing” by the government in the radar, amateur radio, and fixed satellite band that ranges from 3550 to 3650 MHz.
The Webcast of the Forum had not been posted as of Wednesday midnight, but I suspect there were some interesting discussions captured. Based on the quality of the posted presentations alone, I have to give the FCC staff credit for organizing another enlightening forum highlighting practical engineering issues associated with current, proposed and future spectrum changes.
