SC-FDMA Radar: Waveform Design and Signal Processing
In a pulsed radar, the range resolution and the target detectability are usually coupled in an inverse relationship. Pulse compression is considered as a viable solution for this perplexity. However, the existing single-carrier and multicarrier pulse compression waveforms suffer from several setbacks that lead to undesirable trade-offs. Pushing the boundaries of wireless communication and radar technologies, this thesis proposes Single-carrier Frequency Division Multiple Access (SC-FDMA) waveform for radar applications, which has it origin in Cellular Communications such as LTE. The proposed SC-FDMA radar system is not only a solution to the perplexity of range resolution and target detectability but also exploits all the benefits of single and multicarrier waveforms and offers null PAPR and improved Ambiguity Function and autocorrelation properties. The thesis begins with the proposed interleaved SC-FDMA radar signal design while presenting a complete radar architecture and signal processing mechanism. The proposed radar system is analyzed for its ambiguity function and autocorrelation properties. The autocorrelation properties include autocorrelation function (ACF), and autocorrelation peak-to-sidelobe ratio (PLSR) of the radar waveform. The performance of the proposed radar waveform is compared with those of the notable existing radar waveforms including a standard OFDM radar, Cyclic Algorithms – New (CAN), Hadamard, and Periodic correlation Weighted Cyclic Iteration Algorithm (PWCIA). It is observed from the comparative analysis that the proposed scheme exhibits a higher PLSR and better autocorrelation properties as compared to OFDM and other notable radar waveforms.
Since the proposed interleaved SC-FDMA waveform aims at reducing the timedomain fluctuations of the signal, which is a major issue in multicarrier radar systems such as OFDM, therefore, a comparative analysis of the PAPR values of the proposed and OFDM radar waveforms is carried out using the same number of subcarriers for different fixed and random phase-coded initiating sequences. In each case, the proposed interleaved SC-FDMA signal exhibits a constant envelope resulting in a PAPR value of almost 0 dB as compared to the chaotic fluctuating envelope exhibited by OFDM signal resulting in a high PAPR value. It is, therefore, concluded from the PAPR analysis results, that the proposed Interleaved SC-FDMA waveform is the most suitable waveform for multicarrier radar systems in term of achieving minimum possible PAPR. This enables the power amplifier of the radar transmitter to utilize its maximum capability without compromising its power efficiency and hence consequently extends the detection range of the radar many folds. In order the evaluate the performance of the proposed interleaved SC-FDMA radar in terms of target detection and parameter estimation, a complete end-to-end radar is simulated with monostatic configuration for single and multiple moving target scenarios. The target parameters include pulse delay and Doppler shift, referring to range and radial speed of the target respectively. The comparative analysis of the simulation results for each scenario show that the proposed radar outperforms the Linear Frequency Modulated (LFM) and OFDM radars while offering extremely high range and velocity resolutions. This shows that the proposed radar exhibits the ability to pinpoint and discriminate a target, even with a very small radar crosssection (RCS), in single as well as multiple target scenarios, at any unambiguous range and speed.
The proposed radar design opens portals to multiple research realms for the development of futuristic high performance radars. The wideband characteristics of the proposed SC-FDMA waveform makes it resistant against active and passive interference. As a future work, the performance of the proposed SC-FDMA radar can be analyzed in terms of this feature against jammers and electronic deception devices. Moreover, the proposed work can be extended to develop multiple tasking radars, as the different source signals can correspond to independent tasks to be performed simultaneously. The proposed extension can not only find its applications in Radar-Communications (Rad-Comm) hybrid systems but also in multiple target tracking radars. In addition to this, as a future work, the SCFDMA waveform can be implemented in MIMO radars. Exploiting the spatial diversity provided by MIMO systems, the SC-FDMA-MIMO duo would be able to achieve not only a higher angle estimation accuracy and better sensitivity for moving target detection but also higher range and Doppler resolutions as compared to the conventional single as well as multicarrier radars.