Abstract
Challenges involved in space communications across wireless channels call for new approaches to radio systems. Due to the growing need for frequency change in modern wireless systems, an adaptive radio system has the highest demand. Software-defined radios (SDR) offer this type of adaptivity as well as compatibility with other standard platforms such as USRP/GNU radio. Despite limitations of this approach due to hardware components, viable modeling and simulation as well as deployable systems are possible using this platform. This chapter presents a detailed implementation procedure for a USRP/GNU radio-based SDR communication system that can be used for practical experiments as well as an academic lab in this field. In this experiment the USRP has been configured to receive signal from a local radio station using the BasicRX model daughterboard. The programmable USRP executes Python block code implemented in the GNU Radio Companion (GRC) on Ubuntu OS.
TopBackground
In most of the communication systems, having a priori information about direction and source of transmitted signal is of great importance. One of the practical ways to compute such information is through calculation of in-phase and quadrature phase of the received signal. In-phase components (I) are the components of a waveform that have the same frequency and travel through time together. Quadrature phase (Q) are the components of a waveform that are 90° out of phase with the main, or in-phase, carrier (Proakis, 2008). The BasicRX Daughterboard (Figure 1) that is a low-cost daughterboard has been used to receive frequencies between 1-250 MHz. The 93.9 WKYS radio station located in Silver Spring, MD was used as a source of transmission to be received by the proposed receiver. The radio station is approximately 15 miles away from NASA Goddard Space Flight Center (Anon, 2014; Mathworks, 2014; Ettus, 2014, 2015). USRP can also be programmed to be a FM receiver if the right blocks in GRC are used.
Key Terms in this Chapter
SDR: It is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.
USRP: It is a range of software-defined radios designed and sold by Ettus Research and its parent company, National Instruments. Developed by a team led by Matt Ettus, the USRP product family is intended to be a comparatively inexpensive hardware platform for software radio, and is commonly used by research labs, universities, and hobbyists.