# A Comprehensive Experimental Emulation For OTFS Waveform RF-Impairments
### Motivation and Contribution  
The waveform's behavior is directly impacted by RF-impairments effects. Furthermore, RF-impairments including non-linearity, CFO, I/Q imbalances, DC-offset, and phase noise have been shown to significantly degrade the performance of the waveform. Since OTFS is the promising waveform for communication under high mobility conditions and exhibits resilience to narrow-band interference, the degradation due to the design of the OTFS system should be known to provide the optimal system design. Furthermore, taking into consideration one RF-impairment when designing an OTFS communication system may increase the effect of another impairment. Therefore, the OTFS system should be investigated under different RF-impairments. Thus, understanding the effects of RF impairments on system performance is one of the most significant and critical issues. Moreover, to obtain a clear view of the OTFS waveform's performance, it is necessary to carry out an experimental study of the system.  
Each work in the literature models, mathematically analyzes and/or compensates for one or two RF-impairments, which meant the result was only valid within the range of the authors' assumptions without considering the effect of the rest of the RF impairments. Our study satisfies the need for a comprehensive experimental investigation that provides specifics on the impact that RF impairments have on the performance of the OTFS waveform. It is required to perform an experimental investigation in order to provide sufficient knowledge of the RF-impairments degradation. Furthermore, investigating each RF impairment independently helps researchers obtain a deeper comprehension of the essential compensation method to make up for these RF impairments. Therefore, the purpose of this paper is to acquire specific information on the impact that each RF impairment has on the OTFS system separately. In this study, we concentrate on uncoded OTFS for different purposes. As shown in [19], there is a trade-off between the coding gain and the diversity gain. This trade-off will affect the number of resolvable paths and could affect the evaluation results of the effect of RF impairments, especially CFO, as we will illustrate in Section 3.1. Secondly, most of the papers that discuss the related work modeled the uncoded OTFS. Thus, we follow these papers to validate our model and results.  
Testing and evaluation of the RF impairments of the OTFS and OFDM waveforms are conducted in a real-time experiment using the Keysight Agilent Technologies EXA signal analyzer N9010A. The contributions of this paper are summarized as follows:  
* Experimental research of the nonlinearity effect on the performance of the OTFS system has been investigated, taking into account a variety of delay bins \(N\) and Doppler bins \(M\) and comparing it with an OFDM waveform.
* The CFO influence was studied and emulated using a reverberation chamber and stirrer. The impact of CFO from LO mismatching and CFO from Doppler shift on the OTFS waveform's performance is shown experimentally over a variety of normalized frequency offset values.
* We visualize and present the effect of the DC-offset on both the in-phase(\(\gamma_{I}\)) and quadrature (\(\gamma_{Q}\)) components, and then we show the effect of the DC-offset on the OTFS system performance and compare it with OFDM.  
Furthermore, the phase noise of a practical 2.4 GHz CMOS voltage control oscillator (VCO) is modeled to examine its impact on the OTFS performance.
* Finally, we study the influence of the I/Q-imbalance on the performance of the OTFS while taking into account imperfections in the local oscillator. We did this by comparing the OTFS and OFDM waveforms with different values of gain imbalance (\(\epsilon\)) and phase offset (\(\Delta\phi\)).