A “Wiimote”-based Spatio-Temporal Wireless Channel Sounder (Non-Refereed)

Guaranteeing reliable and ubiquitous signal reception is one of the current challenges faced by wireless communications systems. Ideally, wireless transmissions suffer only from propagation losses. In reality, the landscape through which wireless information travels often contains structures that contribute to significant losses in signal reception. While increasing broadcast power will boost signal integrity, it will invariably contribute to increased co-channel interference. The high demand for ubiquitous signal reception, coupled with the aforementioned challenges, has motivated research into the development of propagation prediction models based upon extensive spatio-temporal wireless channel measurements. In response to the shortcomings of conventional spatiotemporal measurement systems, a team of undergraduate researchers at Georgia Tech are currently developing a compact, portable, and cost-effective inertial navigation system (INS) that will be integrated with a broadband spread spectrum channel sounder. With careful processing, the INS will provide accurate relative position data for tracking the position of the channel sounder’s receiver antenna in a local area. When synchronized with coherent, wideband channel measurements, this enables synthetic aperture-style spatio-temporal channel measurements without necessitating expensive and bulky track-and-motorbased positioning systems. The spatio-temporal channel sounder’s INS is currently implemented by way of the Nintendo’s Wii RemoteTM (referred to as "Wiimote"). A generic Bluetooth dongle running on the integrated Microsoft Bluetooth stack allows the PC to read the accelerometer data from Wiimote’s integrated ADXL330 3-axis iMEMS® accelerometers. Following data acquisition, the acceleration and time values are processed in order to deliver accurate position data. Current research is aimed at evaluating and improving the accuracy of the Wiimote-based INS using a calibration signal to adjust for accelerometer biases and a Kalman filter to attenuate random noise and improve the signal-to-noise ratio. The planned integration of a 3-axis gyroscope (Nintendo’s MotionPlus adapter) is expected to significantly improve the system’s position accuracy. Successful implementation of the described channel sounding system will provide wireless channel measurements at different positions. For non-coherent path loss measurements, the INS’s position data provides critical feedback on the quality of the spatially-averaged path loss measurement obtained within a local area by indicating the path traversed by the receiver antenna. For coherent wireless channel measurements, this spatio-temporal data may be used directly as a synthetic aperture array or with recent quasi 2-D field reconstruction techniques. Fourier analysis will be used to obtain a conjoint cylindrical wave expansion (CWE) of the channel. This conjoint CWE allows interpolation of the wireless channel without taking readings throughout an entire region and thereby significantly reduces the time required for channel acquisition. The interpolation of the wireless channel will provide comprehensive channel fading statistics and a complete spatio-temporal wireless channel, which will aid investigations into the propagation mechanisms (i.e. refraction, diffraction, scattering) underlying the wireless channel. The 700 MHz band, also known as the D block spectrum, is of particular interest to this investigation because a portion of the band has been allocated for public safety communications interoperability. Consequently, reliability and low latency requirements set by the Federal Communications Commission (FCC) motivate a better understanding of the propagation properties of 700 MHz signals. The reconstruction of a wireless channel based upon data provided by the channel sounder system will enable a better understanding of the penetration losses, propagation mechanisms, and other properties of the 700 MHz band. Execution of an extensive measurement campaign will provide the data necessary for investigating 700 MHz radio propagation as well a demonstrate the utility and versatility of an INS-based spatio-temporal wireless channel sounder.