Enabling High-Fidelity Ultra-Wideband Radio Channel Emulation: Band-Stitching and Digital Predistortion Concepts

Channel emulators are the key instrument in radio performance testing. The fidelity of the emulated channel with respect to the target channel models directly affects the credibility of the testing result. In practice, due to some non-idealities of the radio-frequency (RF) components of the emulator, its intrinsic frequency response, i.e., the response of the bypass mode, may not be flat over the frequency band of interest, which leads to an excessive distortion over the target channel models, and hence a less accurate emulated channel. This problem could be even more profound when the emulator engages the band-stitching process for a wider-bandwidth emulation, especially in the transition frequency band between adjacent sub-bands. To enable high-fidelity band-stitched or even ultra-wideband channel emulation, we propose a novel digital pre-distortion concept in this work, where we pre-distort the target channel models according to the measured intrinsic response of the emulator to compensate for its effect on the emulated channel. The proposed method is numerically assessed with measured intrinsic responses of a commercial emulator, and the magnitude and phase variations of the stitched channel reduce by one order of magnitude in comparison to that of the conventional method.