Channel sounding for wireless communication

In channel sounding, channel measurements are performed by applying a known signal to the transmit antennas and observing the output signal of the receive antennas. Since the transmitted signal is known, information on the relation between the transmitted and received signals can be gathered. The output of channel sounding is the measurement data. It enables us to study and understand the radio channel characteristics. It is sometimes possible to observe a phenomenon directly from the measurement data. Radio channel sounding techniques, in general, can be categorized into narrowband and wideband sounding techniques, depending upon the transmit bandwidth. It can also be divided into time and frequency domain channel sounding, where the time domain sounding is in the interest of capturing the channel impulse response, and the frequency domain sounding aims to capture the frequency characteristics of the channel. Depending on the domain of interest, the channel sounder design of the sounding signal and sounder structure can be different. In this dissertation, two novel channel sounding system frameworks are introduced. The Swept Time Delay Cross Correlation (STDCC), defined by Parsons, was first employed by Cox in the measurement of 910 MHz band. A receiver in which the signal processing is based on correlation is designed. As an alternative to STDCC, channel transfer function can be estimated by using frequency domain sounder. It allows interpretation of the measurement result directly in the frequency domain since the power spectrum is approximately constant in the bandwidth of interest. The STDCC and frequency domain sounder techniques are simulated in MATLAB in order to investigate the performance of them. Pseudo noise is used to excite the channel. Although computational complexity are less in the frequency domain sounder than the STDCC technique due to the fast Fourier transform (FFT), similar channel impulse responses are obtained in same transmission scenario. Then, the STDCC and frequency domain sounder techniques are implemented with Universal Software Radio Peripheral (USRP) devices both in time-invariant and time-variant fading channels. It is seen that sampling clock of USRP devices are not synchronize. Then, synchronization is achieved by signal processing and measurements are repeated. It is shown that channel is constant in fixed transmission environment. Variations are observed in the amplitude, delay and frequency, when the channel is changed over the time. Channel impulse response, channel transfer function, delay-Doppler spread and frequency-Doppler spread functions are plotted. Therefore, relationship between time, delay, frequency and Doppler spread are seen clearly.