This Small Business Technology Transfer (STTR) Phase I project will involve research on and development of a reconfigurable wireless platform enabling secondary access of wireless spectrum via simultaneous data transmission across several disjoint frequency channels. In particular, the proposed innovations will advance the current state-of-the-art in the area of non-contiguous orthogonal frequency division multiple access (NC-OFDMA) architectures. The anticipated reduction in NC-OFDMA out-of-band emissions and transmitted peak-to-average power ratio will greatly improve the co-existence of primary and secondary wireless transmissions. The resultant improved dynamic spectrum access (DSA) capability will then permit much more efficient use of limited spectrum resources. The proposed work will be targeted towards the development of a high throughput and robust hardware implementation for the 802.22 wireless regional area network, a recently ratified Institute of Electrical and Electronics Engineers (IEEE) standard that employs NC-OFDMA. The research will result in an NC-OFDMA optimization framework that will help shape the direction of this field and guide the design of viable 802.22 products.
The broader impact/commercial potential of this project stems from the opportunity to develop wireless products for the rural broadband and machine-to-machine markets. Data communication networks are needed by modern society for access to the Internet, providing both essential services and modern conveniences. Unfortunately, many communities, especially rural, currently lack the infrastructure to support such networks, with roughly three billion people in the world with little if any wireless service. Therefore, conducting research to optimize NC-OFDMA for high-speed communications systems including 802.22 in rural areas will benefit society while providing enormous commercialization potential. The optimization techniques and technology resulting from the proposed activities will also yield products for smart grids and sensor networks and support the public safety, emergency services, and first responder community efforts to provide better communications access to the network.
This Phase I STTR involved research on and development of a reconfigurable wireless platform enabling broadband communications in rural areas via secondary access of television white spaces (TVWS) spectrum. The recently ratified IEEE standard, 802.22, is the most promising technique proposed for TVWS operation. As with all TVWS solutions, 802.22 designs must satisfy FCC limits for out-of-band (OOB) emissions. 802.22 is based on Orthogonal Frequency Division Multiplexing (OFDM) and the TVWS FCC OOB limits are much more stringent than those required for other OFDM systems such as 802.11. In addition, spectrum sensing of microphones and TV signals is required for TVWS operation in areas (e.g., indoors, urban areas) where device geolocation may be impractical. Effective approaches for secondary user TVWS coexistence will also likely depend on spectrum sensing. Unfortunately, current 802.22 technology leads to unacceptable levels of OOB emissions, greatly degrading the performance of both primary and secondary TVWS users. Industry also has not yet produced a practical TVWS sensing solution – proposed approaches are either prohibitively complex or offer poor performance. Such limitations have contributed significantly to the delayed rollout of 802.22 solutions. The innovations developed in Phase I promise to overcome these limitations, leading to a low-cost, high throughput, and robust implementation for the 802.22 wireless regional area network (WRAN). In particular, reduced-complexity and adaptive digital filtering methods were developed that satisfy the FCC limits for OOB emissions while also allowing an 802.22 system to coexist with a narrowband wireless microphone on a TVWS channel. In addition, reduced-complexity sensing approaches were developed to sense potential TVWS systems including 802.11af, 802.22, and LTE at signal levels well below the noise floor. The performance and complexity of the Phase I innovations were validated using Field Programmable Gate Array (FPGA) testing. Prototype 802.22-standard compliant devices will be developed in Phase II. These devices will be tested in the laboratory and in the field to validate the viability of the Phase II design for rural broadband deployment. The resulting technology will offer a low-cost broadband solution to the 14.5 million Americans who live in rural areas currently beyond the reach of broadband access, while appealing to those in rural areas that have broadband access but are unable to afford the high equipment and service costs of current solutions.
