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What follows is a research report detailing the steps taken to apply signal-processing algorithms to USRP. One should be able to follow these steps with the specified set of hardware and software to get the same configuration on the proper USRP device. These projects were implemented under the supervision of NASA scientists and faculty advisors in dedicated NASA labs. Following lessons learned here and authors’ previous experiences in data visualization and signal processing research and training, (Javidi & Sheybani, 2008; Sheybani & Javidi, 2006; Sheybani, Ehsan; Garcia-Otero, Adnani, Javidi & Deshpande, 2012; Ouyang et al., 2010; Sheybani, Javidi & Garcia-Otero, 2008; Javidi & Sheybani, 2010; Varde et al., 2007; Sheybani, Javidi, Hardy, Denton & Campbell, 2007; Sheybani & Javidi, 2007; Badombena-Wanta & Sheybani, 2010; Sheybani & Sankar, 2002; Sheybani & Arora, 1992, Sheybani, 2011; Garcia-Otero & Sheybani, 2011) relevant labs were designed to enhance the Computer Engineering program at the Virginia State University (VSU).
To accomplish our overall goal of retrieving the carrier signal of the L1 band from a GPS satellite using USRP we had to be familiarized with the hardware. The USRP needs a daughterboard, which is used to hold the radio frequency receiver interface or the transmitter interface. Daughter boards are selected based on the project that one is set on doing. In many cases, the selection of an RF daughterboard is made solely on the application requirements for frequency coverage. Figure 1 shows the ranges of different daughter boards (Anon, 2014).
Figure 1. Daughterboard frequency coverage
The next step was to determine what software can be used to program the USRP. GNU Radio is easy to use software that consists of mostly GUI blocks programmed by Python. The user has to fill in the parameters for each block depending on the application parameters. To become familiar with GNU Radio we constructed a simple dial tone. A dial tone is generally just two Sine waves, one with a frequency of 350 Hz and another with a frequency of 440 HZ. Combining the two waves into an audio sink will produce a dial tone. Figure 2 shows the simple flow graph used to make the dial tone.
Figure 2. Flow graph of the dial tone in GNU