Communication system design for white-fi (802.11af)

“Four and half billion people around the world still aren't connected to the Internet!” The gap between India's rural and urban areas, both economically and technologically, is enormous. It is quite obvious that the economic imbalance between India's metros and her villages is the most significant reason for miserable Internet adoption statistics currently found in the country's rural areas. People in the metropolitan cities enjoy the utilities offered by the Internet as a routine privilege while their rural counterparts are yet to come to terms with the convenience and efficiency of the Internet. Many government projects such as the NOFN (National Optical Fiber Network) and the APSFL (AP State Fiber Network Limited) meant to solve this divide are awfully slow and would undoubtedly encounter numerous cost overruns. A solution to this problem would be to tap into the potential of the unused TV spectrum and use it to provide Wi-Fi based broadband connectivity to geographically remote regions of the country. A key factor in deploying such a solution would be to design the related hardware effectively, as described in this paper. The hardware discussed consists of a UHF translator to up/down convert the 2.4 GHz Wi-Fi signals to the appropriate unused TV band in the UHF spectrum. We operate in the UHF Band-IV which extends from 470–582 MHz and comprises 14 channels of 8MHz each. The first section of this article provides a brief overview of the motivation behind our work and the potential applications of the proposed hardware prototype. In the second section, we present a brief description of the project and associated novelty when compared to existing state-of-the-art in the field of White Space communication. In the third section, the UHF translator design is outlined. The third section of this paper also talks about the Raised Cosine Filter and its roll-off factor, which is a primary constraint to ensure design compliance with the IEEE 802.11af standard. In the fourth section, the metrics of the FPGA-based UHF translator employing a Programmable Wideband Mixer with Integrated VCOs (Analog Devices ADRF6655), is described.