OFDM waveform design compromising spectral nulling, side-lobe suppression and range resolution

Simple pulsed radar is limited in range sensitivity by the average radiation power and, in range resolution by the pulse length. The design of any radar always involves a compromise between the two constraints. Waveform design aims to seek an appropriate harmony that best suits the relevant application. The pulse compression theory has been introduced in order to get a high range resolution as well as a good detection probability. One of the basic types of pulse compression is binary phase coding which encodes the transmitted pulse with information that is compressed (decoded) in the receiver of the radar. The study of the peak sidelobe level (PSL) binary sequences occurs as a classical problem of signal design for digital communication and, in equivalent guise, in analytic number theory. It has also become a notorious problem of combinatorial optimization. For years mathematicians, engineers, physicists and chemists have sought a systematic way to construct long binary sequences with low PSL. In this Chapter, we describe pulse compression technique in radar waveform design. In order to make the presentation self-contained, we start by providing a short summary of waveform design and an introduction to principle behind pulse compression by compiling the basic tools required for analyzing and comparing different radar signals. After that, we talk about binary sequence, its desired properties and general types of methods for finding and generating such waveforms. We keep on by an overview and introducing the existing methods and search routine done. We conclude the chapter with a brief survey of the results exhibited yet for low autocorrelation binary sequences. We mention a table of complete results presented and also introduce a histogram to unscramble them visually and predict the future.

A hybrid technique for joint PAPR reduction and sidelobe suppression in NC-OFDM based cognitive radio systems

This paper describes a brief description of Orthogonal Frequency Division Multiplexing (OFDM) waveform design and parameter for submarine radars. The radar works when the submarine is floating on the sea surface and it uses a radio frequency signal to detect multiple moving objects in the surrounding area. The OFDM parameters discussed here are including the carrier frequency, number of sub-carriers, number of OFDM symbols and the frequency spacing between subcarriers. By varying those parameters value to see how significant are their impact on radar performance, includes its maximum unambiguous range, maximum speed of the target and also its range and speed resolution. The simulation results show that there is a trade-off for frequency spacing parameter to have a good radar performance. Set the space too wide would destroy radar's speed resolution and too narrow would ruin its range resolution.

The sidelobe suppression plays an important role in modern radar and sonar system. Traditional sidelobe suppression methods based on weighted processing will bring about a series of problem such as the loss of signal-to-noise ratio (SNR) and resolution reduction. In order to solve these problems, this paper mainly studies the waveform design and performance analysis of nonlinear frequency modulation (NLFM) signal, and proposes a new waveform design method which analyzes the influence of the main lobe width and peak sidelobe ratio of the new NLFM signal. Finally, a computer simulation experiment was used to verify the designed signal. Based on the simulation results, the new proposed waveform design method does not require any weighting processing to achieve a lower sidelobe ratio. It has very important practical significance for the detection and resolution of weak targets in the radar and sonar environment.

The use of pulse compression to obtain simultaneous long-range detection and good range resolution is described. The types of modulation that can be used to obtain pulse compression are outlined with particular emphasis on their performance under Doppler shift. It is shown that nonlinear frequency-modulated (FM) signals are capable of providing low range-sidelobes while being compressed using a matched filter. A design method for nonlinear FM signals based on window functions is outlined. Simulation results for pulse compression of nonliner FM signals based on four different window functions with Doppler shift are presented. The results are used to define the effects of Doppler shift on the pulse compression. An analysis is presented, and interpreted pictorially, that explains the effects of Doppler shift on the pulse compression. The analysis is also extended to explain the better Doppler performance of hybrid FM pulse compression systems.

Multi-Carrier Waveform (MCW) modeling and design are envisioned as one of the most important and challenging for the 6th generation (6G) communication networks. In oppose to Orthogonal Frequency Division Multiplexing (OFDM) waveforms, new and innovative design techniques for MCWs have been designed and proposed in recent literature because of their performance superiority. The typical OFDM waveforms have dominated the previous generation of communication systems and proven their potential in many real-time communication environments, but it may not be sufficient to meet the ambitious target of 6G communication systems. Hence, need for new solutions like flexible MCWs and relevant technological advancements in waveform design are needed. This paper proposes designing and evaluating a new MCW design to meet the 6G requirements for spectral efficiency, throughput, and overall system capacity. On the transmitter side, the MCW design proposed in this article employs power domain multiplexing, such as Non-Orthogonal Multiple Access (NOMA), and phase-rotations of the input signal to the Universal Filtered Multi-Carriers (UFMC) modulations, where the Base-Station (BS) assigns different power levels to each user while using the same frequency resources. MATLAB® simulations were performed to assess the proposed MCW performance. Detailed simulation data are employed for comparative performance analysis of the proposed MCW. The results have shown the superior performance of the proposed MCW approach compared to the conventional 5th generation (5G) NOMA-UFMC waveform.

Designing radar waveforms with notched spectral regions can mitigate mutual interference with other proximate RF users. However, this capability comes at the cost of degraded range-Doppler sidelobe performance. To evaluate the limitations of correlation-based processing, the null-constrained power spectral density that minimizes correlation sidelobe levels is determined for comparison with waveform and pulse compression filter design methods. Existence of the least-squares (LS) global optimum indicates a fundamental dynamic range limitation for notched power spectra (notwithstanding further receive compensation or range resolution spoiling). Recent work investigated spectrally notched random FM (RFM) waveform design where ad-hoc tapering was incorporated into the null shape as a heuristic means of reducing range sidelobes. Here, waveforms designed according to the optimal null-constrained spectral template are demonstrated to have improved sidelobe performance after pulse compression and slow-time processing. Further, because these waveforms are designed according to the LS optimal spectral template, application of the LS mismatched filter provides additional sidelobe reduction (toward the global limit) with minimal mismatch loss.

To improve the anti-interference capability of high range resolution radar, the random hopping frequency signal is required. A waveform design method of random hopping frequency signal based on S curve is presented. Firstly, the random hopping frequency signal with low peak side lobe is obtained by optimization. Then the frequency distribution is analyzed and fitted by S curve. The ambiguity function of RHF signal based on different window functions is evaluated. The results show that the random hopping frequency signal has low peak sidelobe level, small mainlobe broadening, strong anti-interference capability and low implementation cost, which indicates its high practical value in real applications.

Pulse compression refers to the design of a radar waveform, i.e. a “pulse compressed waveform”, so that its matched Alter response or, equivalently, its autocorrelation function (ACF), has a narrow main lobe. The narrow ACF lobe enhances the ability to resolve between closely spaced targets, i.e. good range resolution, without relying entirely on narrow pulse widths, which, at a fixed pulse amplitude, lowers the pulse energy and degrades the detection range. The appearance of sidelobes in the ACF that mask targets with low return signal power presents a challenge in the design of pulse compression waveforms. Additionally, the Doppler tolerance of pulse compression waveforms need to be examined. That is, the behavior of the sidelobe level (SLL) should be kept low to preserve good range resolution even as the velocity of the target increases. In this paper, a new pulse compression waveform called Doppler Tolerant Modified P4 Code (DTMP4 Code) is presented and analyzed. The waveform can be generated by modulating a pulse using linear frequency modulation (LFM) then applying phase coding (P4 Code) to the resulting waveform. Simulation results shows that the proposed waveform has lower average SLL than the LFM and P4 code. In addition, it is less affected by Doppler shift compared to the P4 Code.

The choice of a suitable transmit waveform is an important problem in radar design. This is so because the waveform controls resolution and clutter performance and also bears heavily on the system cost. Theoretical studies which provide the basis for technical advances have not, so far, solved the general signal design problem. The knowledge of the properties of the pulse trains, a class of signals particularly well suited to digital processing is therefore, of increasing practical importance. This paper presents a method for generating finite length sequences that have high energy ratio and low side lobe energy in their autocorrelation function. The multilevel sequences with spike like autocorrelation function are generated iteratively, starting with a sequence that has relatively low side lobes in its autocorrelation function. The method can be used to generate sequences of any desired length. It is shown that energy ratio of polyphase sequences that have low side lobe energy, is improved through the process of clipping. Such sequences then can be effectively used to improve the range and Doppler resolution of radars.

In this paper, the problem of adaptive waveform design for cognitive radar (CR) in signal-dependent interference, as well as additive channel noise is investigated. With constraints on waveform energy and bandwidth, a flexible waveform optimization method taking both detection and range resolution into account is proposed. Unlike existing optimal waveforms designed by a single design criterion, waveform designed by the proposed method can be updated according to the environment information fed back by receiver and radar performance demands simultaneously at each cycle of CR. Simulations are conducted to illustrate that CR with the proposed waveform performs better than traditional radar system with fixed waveform, and offers more practical and flexible.

The typical approach to radar target classification is to image the target with waveforms that provide high resolution and low sidelobes, and then to compare the target images to a template library. In this chapter, we reconsider whether imaging-based metrics for waveform design are best for target classification, and develop alternative design strategies that result in waveforms with improved classification ability, but not necessarily a good ambiguity function by traditional notions. After presenting waveform design strategies based on optimizing signal-to-noise ratio or mutual information from a wide-sense stationary (WSS) ensemble of target impulse responses, we apply the design methods to the problem of radar target classification through a two-step process. The first step is to modify the design methodology that was based on WSS targets to account for the finite duration of practical target responses. The second step is to use the target class probabilities and impulse response library to calculate a weighted power spectral variance over target classes, which is then substituted into the design equations. The use of target class probabilities enables the waveform to be adapted in response to previous transmissions. Waveform behaviour and performance are studied over several different clutter and noise scenarios. The target impulse response library for these studies is based on finite-difference time-domain (FDTD) simulation of a publically available CAD model of an F-16 aircraft.

Airborne radar system performance primarily depends on the target characteristics and the type of waveform used. Based on the type of waveform used, target detection, range resolution, doppler resolution and peak to side lobe level ratio (PSLR) can be improved in a radar system. Hence for a radar engineer choosing a proper waveform is critical in order to meet the system performance in different target environment conditions. This paper focuses on designing a suitable radar waveform for sea environment considering Sea clutter, Sea states, doppler and Swerling target models in X Band. In order to design a waveform under different Sea environments, an end to end radar system will be modelled, simulated and verified the system performance in Matlab. PSLR, Integrated Side Lobe ratio (ISLR), range resolution and target detection will be considered as performance metrics for the design of the waveform.

High-resolution acoustical imaging requires the use of short-duration (wideband) pulses for good resolution in range, and two-dimensional (2-D) transducer arrays for good resolution and scanning in both lateral directions. However, 2-D arrays often contain an impractically large number of elements, so it is important to find sparse 2-D arrays which can perform as well as densely populated 2-D arrays. Boundary arrays are a particular class of sparse arrays which have elements located only on the boundary of some planar region. Signal processing techniques have been developed that effectively fill in the missing elements in the interior of the boundary array. These techniques were originally proposed in the context of narrowband imaging of far-field scenes. The techniques are applied to near-field imaging with wideband pulses. Simulations indicate that the methods are effective in this context also, and thus 2-D boundary arrays can produce high-quality images in acoustical imaging applications. >

The article discusses the problem of synthesis of complex broadband signals in the spectral area. It is shown that the formation of complex broadband signals in the spectral area allows to determine the classes of signals that have good resolution in range and speed. Mathematical models of uncertainty functions for polyharmonic and strip signals are presented.