A method for interference cancellation in automotive radar

The multiuser detection is a signal processing tech- nique which enhances the performance and capacity in DS- CDMA technology. Since its complexity issue was too expensive to handle, there was focus on the suboptimal detectors. In this paper we propose a hybrid method called adaptive differential interference cancellation method (ADIC) which is a hybrid of the differential interference cancellation method and which is then combined in a adaptive way to determine a weight matrix which will map the outcome of the differential interference cancellation method to come out with a better performance. This paper also looks into the computational cost of different methods using the floating point operation (flops) which is a good estimation of the comparative computational cost if not the exact one. I. INTRODUCTION The conventional DS-CDMA match filter detector fails to combat these issues due three prominent drawbacks: unrealis- tic ucorrelated code, near-far problem (even with strict power control (1)), and tough multiple access interference (MAI). Many advanced signal processing approaches have been made to improve the performances of these kinds of detectors. In this paper we will study the different approaches that were made in this field and implement these methods to reach a conclusion about the detection methods. As the name of the topic suggests the focus of our work will be study and propose cost effective better performing multiuser detection method. We will explore Multiuser Detection Techniques in Synchronous CDMA environment. Multi-user detection deals with the development and ap- plication of joint demodulation and interference cancellation cancellation techniques for improved detection of a desired set of digital signals in the presence of multiple access interfer- ence, intersymbol interference and noise. Since veterbi forward dynamic algorithm (2) is used in case of Optimum multiuser detection (3) the complexity grows in with the increase in the number of users. Hence the complexity is immense which increases exponentially with the increase in the number of users. Looking ahead for lower complexity hence lesser cost of implementation, the paper proposes the use of sub-optimal linear detectors (4). The sub-optimal detector the paper next focuses on is Decorrelator type of Detector (5) which is optimal in least squares. This detector out performs the optimal detector in many respects. Then the Minimum Mean Square Error (MMSE) linear detector is proposed which tries to minimize the squared error from the required transformation. It is one of the most popular detectors in use due to its easiness to implement and its lower complexity. But then in the above detection methods the decisions made were based on certain linear transformation criterion and there are missing efforts to check the performance in between the detection process to improvise the transformation method better detection. So then the paper proposes Adaptive multiuser detection. Then the paper focuses on Interference cancellation methods which utilize the feedback to reduce Multiple Access Interference (MAI) in the detected bits. Under the Interference Cancellation umbrella the Successive Interference Cancellation (SIC) (6), (7) method is explored and simulated to observe the results. Then the next method which performs better than SIC and more commonly used in real life, called Parallel Interference Cancellation (PIC) (6), (8) is also implemented. Before going ahead to implement the final proposed detection method, this paper implements Differential Interference Cancellation (DIC) (9) method. And then this paper finally proposes an Inter- ference Cancellation method called the Adaptive Differential Interference Cancellation Multiuser Detection method which is cost effective in comparison to other Interference Cancellation methods as we will require lesser hardware (multipliers as in the SIC or Parallel Interference Cancellation (PIC)) for that matter. More ever since we are using adaptive method the desired BER can be further reduced. This proposed method will be discussed in detail in the following section.

The wide application of digital radio communication systems in recent years has resulted in increasing demands for allocated frequencies and, due to the overcrowded spectrum, interference has become a crucial problem. In many cases, such interference appears in the upper sideband or in the lower sideband of the useful signal. In the present paper a binary PSK communication system with interference in either the upper or the lower sideband is considered and a method of interference cancellation is proposed for the Costas loop widely used in PSK receivers. Experiments are conducted to demonstrate the efficiency of this method. The results show that the maximum cancellation with a simple circuit added to the Costas loop is 23 dB if Af (the difference between the frequencies of the PSK carrier and the interfering signal) is above 0.3 fβ (fβ the data bit rate). At the same time, the bit error rate in the digital signal is greatly improved. Also, with respect to the impairment due to jitter caused by interference, the performance of the Costas loop is practically unchanged within the specification range of an ordinary Costas loop. The advantages of the present method are that the circuit is simple, it is stable because there is no feedback in the interference cancellation part and the cancellation is effective even for interfering signals of unknown δf.

Nonlinear interference cancellation multiuser detection algorithms have less BER and are less complex than linear multiuser detection methods. We present a hybrid switched mode detector that uses existing interference cancellation methods i.e. Parallel Interference Cancellation (PIC) and Successive Interference cancellation (SIC) based on channel conditions. This proposed detector takes decisions based on number of users on the channel and switches either to SIC method or PIC method. The switching mechanism is exploited by performance complexity tradeoff between matched filter detector and nonlinear interference cancellation methods.

Radar serves as an essential sensor for detecting distant targets. However, under multiple mainlobe and sidelobe interferences, conventional interference suppression techniques often introduce significant distortion to the radar antenna's mainlobe, severely degrading critical performance metrics such as ranging and direction finding. An algorithm reused based interference cancellation with mainlobe maintenance method is proposed to solve this problem. First, a low-complexity method for estimating the direction of arrival (DOA) of interference is proposed. This method directly reuses the interference cancellation (IC) algorithm to compute the optimal weights, which are then used to synthesize the array pattern. The DOA of the interference is then estimated by identifying the null steering in this pattern. This approach eliminates the need for the computationally intensive eigenvalue decomposition, thereby significantly reducing the computational complexity. Second, based on the estimated interference DOA, a method for interference cancellation with mainlobe maintenance is introduced. By directly exploiting the estimated interference DOA information to construct a projection matrix, this method significantly reduces the computational complexity of the mainlobe maintenance. Additionally, through the projection of mainlobe interference energy onto the subspace associated with sidelobe interferences, it not only preserves the mainlobe integrity but also achieves improved suppression of sidelobe interferences. Finally, simulation and experimental results demonstrate the effectiveness of the proposed method.

Non-orthogonal multiple access (NOMA) has become the key technology in 5G communication. NOMA can achieve multi-user multiplexing in transmit power domain by allocating different power, which can effectively improve the spectral efficiency, but also causes the multiple access interference of the receiver signal. The parallel interference cancellation (PIC) technology is applied to NOMA system in order to solve the problem of high-delay and error propagation in the successive interference cancellation (SIC) algorithm. PIC can effectively compensate for the deficiency of SIC algorithm but it has high complexity. Combined with the advantages of SIC and PIC, a joint interference cancellation (JIC) method is proposed. The performance and complexity of the three algorithms are simulated and analyzed. The results show that JIC can effectively reduce the delay and improve the error propagation problem in the case of low complexity.

One of the candidate methods for new generation communication systems is orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM). Because of its unique feature "intrinsic interference", new channel estimation methods have been developed for OFDM/OQAM. One of these is the interference cancellation method (ICM) which aims to eliminate the intrinsic interference. In the first studies related with ICM in the literature, "isotropic orthogonal transformation algorithm" (IOTA) was used as the waveform. However, these methods are valid only for isotropic waveforms. In this study, a new ICM preamble which suitable for both isotropic and anisotropic waveforms is proposed and the relation between isotropy of waveforms and ICM is discussed. The performance of the method against noise and peak to average power ratio (PAPR) of the method are examined via the simulations.

A method of interference cancellation using adaptive antenna arrays is investigated. A proposal for an adaptive antenna array is presented where the number of antenna sensors is minimized. The performance of both the proposed scheme and the ordinary one are compared through computer simulations. The effects of the number of array elements and interference to signal ratio (ISR) on the performance of the adaptive interference canceller is evaluated. It is found that the proposed scheme of the adaptive antenna array exhibits a better performance than the ordinary adaptive antenna array.

In mobile WiMAX, geo-location is possible at the PSS (personal subscriber station) by using the preamble signals broadcasted by all the RAS (Radio Access Station) simultaneously. Using relative arrival times of signals, user location can be obtained by TDoA (Time Difference of Arrival) positioning. However, sufficient number of RAS should be detected to obtain the location in this method. Since mobile WiMAX system employs cellular network structure, the number of RAS that PSS can detect is limited due to low SNR and CCI (co-channel interference) by neighboring RAS. To detect sufficient number of RAS at the PSS, hearability should be enhanced by increasing SNR (signal to noise ratio) and SIR (signal to interference ratio), which can be achieved using long integration and interference cancellation. In multipath environment, however, interference cancellation does not remove the CCI completely. Therefore, multipath mitigation and interference cancellation method should be merged and solved together. In this paper, detection performance after interference cancellation is analyzed using mobile WiMAX geo-location system. Simulation results show that trilateration is possible in most area of the cell coverage after interference cancellation in multipath environment, except at the vicinity of the RAS.

This paper analyzes large-scale networks that share the spectrum with interference cancellation (IC). The efficiency of spectrum sharing is determined primarily by interference, which in turn depends on the spatial densities, the interference cancellation method, and the spectrum sharing method, i.e., underlay or overlay. By assuming the Poisson distribution for transmitters, equal transmission power in the same system, and an interference-limited environment, this paper finds the performance gain from IC in terms of spectrum-sharing transmission capacity (S-TC), defined as the number of successful transmissions per unit area while guaranteeing the target outage probabilities of all coexisting systems. The effectiveness of IC is characterized by the coefficient of cancellation (CoC), and specific CoC values are derived for two simple IC scenarios, the strong interferer and the close interferer cancellation, with the assumption of having perfect information for channel states of interfering links and interferer locations. The sum S-TC optimal spatial densities of the two systems are given. Finally, CoC conditions to determine the superiority of an underlay or overlay method are presented. We verify that the underlay method could be preferred depending on the CoCs of coexisting systems; that is starkly different from the case without IC, in which the overlay method is always better.

Space-time coded orthogonal frequency division multiplexing (OFDM) is a promising scheme for future wideband multimedia wireless communication systems. The combination of space-time coding (STC) and OFDM modulation promises an enhanced performance in terms of power and spectral efficiency. Such combination benefits from the diversity gain within the multiple-input-multiple-output ST coded system and the matured OFDM modulation for wideband wireless transmission. However, STC transmit diversity impairs the system's interference suppression ability due to the use of multiple transmitters at each mobile. We propose an effective co-channel interference (CCI) cancellation method that employs angle diversity based on null-steering beamforming or minimum variance distortion response beamforming. It is shown that the proposed method can effectively mitigate CCI while preserving the space-time structure, thereby, significantly improving the system's interference suppression ability without significant bit-error rate performance degradation. Furthermore, it is demonstrated that the proposed method can significantly combat the delay spread detrimental effects over multipath fading channels without the use of interleaving.

In Single Frequency Networks, the effect of intersymbol interference (ISI) and inter-carrier interference (ICI) is great due to the delay spread of wireless channels is much longer than a cyclic prefix (CP). The performance of OFDM systems is degenerating seriously. This paper discusses a receiver design based on the implementation of a Decision Feed-back Equalizer (DFE). The proposed DFE receiver incorporates a Parallel Interference Canceller (PIC) as its feed-forward filter. The result shows that in long time delay or more serious fading multi-path, the proposed receiver has better performance for canceling ICI and ISI compared with the conventional OFDM receiver.

This paper proposes co-channel interference cancellation / equalization methods for downlink block transmission with cyclic prefix in multi-cell environments using multiple receiving antennas and iterative least-square (LS) interference cancellation. Due to circulant structure of channel matrices in block transmission schemes with cyclic prefix, pseudo inverse matrices, which is required in the iterative LS method, can be obtained with low computational complexity and is multiplied to the received signal in an efficient manner. Computer simulation results show that the proposed iterative LS interference cancellation and equalization method can achieve almost the same bit error rate (BER) performance as an minimum mean-square-error (MMSE) approach with lower computational complexity and without noise variance estimation.

In this tutorial paper, we systematically present the fundamental operating principles and analytical details of the discrete Fourier transform based signal processing techniques for the TDM MIMO FMCW millimeter-wave (mmWave) automotive radars. The mmWave radars provide a key sensing capability to support safety features of the conventional and autonomous vehicles. Automotive radar sensors are used to detect presence and location of the objects of interest to derive comprehensive and accurate knowledge of road conditions and surrounding environments. Automotive radars are subjected to an increasing demand to provide high-resolution measurements in the range-Doppler-azimuth-elevation domains. Therefore, the current state-of-the-art automotive radars commonly employ MIMO technologies, resulting in a large block of multidimensional data to process in real time through a long chain of signal processing algorithms. Detailed coverage on the fundamental radar signal processing techniques are scattered in a large body of literature for classical radar systems. Currently, there is no tutorial available that covers the technical details of the latest TDM MIMO FMCW radar technology, making it extremely hard for new researchers in the field of automotive mmWave radars. This paper contains sufficient technical details to serve as a tutorial. It can help lay a solid analytical foundation to facilitate exploration and development of advanced radar signal processing techniques for automotive applications. The algorithmic details and analytical results presented in this paper can be readily applied to both real-time implementation and post-processing. Simulation and experimental results are presented in this paper to validate analytical derivations and to demonstrate the capabilities of the TDM MIMO radar sensor in practical implementations.

该文分析了LFM干扰对伪码引信相关输出的影响,当干扰强度超出伪码引信自身的抗干扰容限时,相关输出严重恶化,因此必须采取相应的抗干扰措施。考虑到LFM干扰与伪码引信有用信号间存在着强的时频耦合,提出了基于FRFT的自适应干扰对消方法。该方法首先对观察信号进行FRFT,估计干扰的特征参数,利用估计出的干扰参数构造自适应干扰对消器,将干扰去除。仿真表明,该方法能够有效滤除LFM干扰,相关输出得到显著改善,该方法对单分量和多分量干扰均有效,不受交叉项影响。

Narrowband interference cancellation based on set-membership estimation in DCSK communication system