Iterative OFDM receiver with combined interference suppression and cancellation

In this paper, the interference suppression method for GPS, GLONASS, GALILEO, and BEIDOU signals using the adaptive antenna array is considered. The model of the adaptive antenna array is demonstrated. The model includes 3D radiation pattern, elements that control the signal amplitude and signal phase, linear signal adder. The adaptation equation that allows solving the task by suppression of interference from the given direction is presented. The process of interference suppression using the real data received by 33 satellites is analyzed. It is shown that when interference suppression, the signals from some satellites are below the acceptable threshold. These signals are not used for solving a navigation task. The presented study is illustrated with diagrams and spatial adaptive antenna array patterns.

The performance of adaptive antenna arrays in the presence of weak interfering signals (below noise level) is studied. It is shown that conventional adaptive arrays are unable to suppress such interfering signals. To overcome this problem, the feedback loops controlling the array weights are modified. In the modified feedback loops, the noise level in the feedback loops is reduced by reducing the correlation between the noise components of the two inputs to the loop correlator. Two techniques to decorrelate these noise components are discussed. It is shown that adaptive arrays with the modified feedback loops provide the desired interference suppression. An expression is given for the amount of noise decorrelation required to achieve a specified interference suppression.

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 this paper, LMS (Least Mean Square) adaptive array antenna is applied to IVC(Inter-Vehicle Communication) in order to reduce interference which is caused by surrounding vehicles. The LMS adaptive array antenna has a characteristic that the control of directivity is possible according to surrounding radio wave condition, if the receiving vehicle knows the information of the target vehicle. Under the case where the adaptive array antenna is used in IVC systems, packet error rate characteristic, throughput performance and improvement in near-far problem are evaluated by comparing with the performance of the IVC system using omni-directional antenna.

In this paper, the authors propose a widely-linear (WL) receiver structure for multiple access interference (MAI) and jamming signal (JS) suppression in direct-sequence code-division multiple-access systems. A vector space projection (VSP) scheme is also considered to cancel the JS before detecting the desired signals. They develop a novel multiple-candidate successive interference cancellation (MC-SIC) scheme which processes two consecutive user symbols at one time to process the unreliable estimates and a number of selected points serve as the feedback candidates for interference cancellation, which is effective for alleviating the effect of error propagation in the successive interference cancellation (SIC) algorithm. WL signal processing is then used to enhance the performance of the receiver in non-circular modulation scheme. By bringing together the techniques mentioned above, a novel interference suppression scheme is proposed which combines the WL MC-SIC minimum-mean-squared error (MMSE) algorithm with the VSP scheme to suppress MAI and JS simultaneously. Simulations for binary phase shift keying modulation scenarios show that the proposed structure achieves a better MAI suppression performance compared with previously reported SIC MMSE receivers at lower complexity and a superior JS suppression performance.

This paper considers a successive light interference cancellation and allocation algorithm (SLICA) practicing interference cancellation for an indoor visible light communication (VLC) system based on successive interference cancellation (SIC) technique. The interference among users is cancelled with the help of the proposed approach to reduce computational complexity. VLC has become the cornerstone of intelligence in the current scenario. The data services allocated to the users are demand based and rely on their channel conditions. The data is allocated to user by modulating light waves via illuminated LEDs. The receiving end has photodiode installed in it to recover back the data. Better performance rate is achieved with lesser interference with the proposed approach. To guarantee good (quality-of service) QoS, considerable simulations are carried out considering real- time scenario which further demonstrates the high level performance of the proposed approach over conventional approach. Based on the analysis, the SINR and interference level is demonstrated for the conventional and the proposed approach and there is a hike in the performance rate of SINR and interference level of about 20 – 30 % with the applied proposed approach. The prior motto of this study is to enhance the system throughput and improve per user average performance rate and reducing the complexity of the system. This contributes to the total efficiency of the optical indoor VLC network. Our proposed algorithm will provide a strong backbone for the 6G deployment.

The article describes the computer model of an adaptive digital antenna array. We considered in detail its features and specifications. The results of experimental research methods beamforming digital adaptive antenna array using a computer model. We studied four methods of providing independent beams forming the directivity pattern, calibration of the receiving channels, interference suppression and measurement navigation parameters.

In DS/CDMA systems, overcoming near/far effects and fading is imperative for satisfactory performance. One way to combat the near/far effect is to use stringent power control, as is done in most of the commercial systems. Another approach is Multi-User Detection (MUD). In addition to mitigating the near/far effect, MUD has the more fundamental potential of raising capacity by canceling Multiple Access Interference (MAI). This paper analyses the convergence behavior and performance of successive interference cancellation (SIC) for CDMA systems. This analysis will be generalized for Parallel Interference Cancellation (PIC) also. In this paper a Hybrid Interference Cancellation (HIC) receiver is designed by combining the successive and Parallel Interference Cancellation algorithms, so that the advantages of both the schemes are utilized effectively. The Hybrid Interference Cancellation scheme results in a simple, faster and reliable receiver. With the help of simulations, it is shown that this hybrid approach outperforms the other Multi-User Detection schemes.

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.

Linear precoded OFDM systems with channel coding have already been demonstrated to efficiently exploit frequency and time diversities of the transmission channel. Iterative receivers which iteratively perform channel decoding and deprecoding provide very good performance. In the literature, these iterative receivers are based on maximum likelihood based functions for both linear deprecoding and channel decoding leading to a high complexity for large size of preceding matrices or high modulation order. In this paper, a simple linear operation instead of a maximum likelihood based one is carried out for deprecoding allowing the use of large preceding matrices and thus an optimal exploitation of the signal diversity.

The performance of an adaptive antenna array is strongly affected by the electromagnetic characteristics of the array. The mutual coupling effect degrades the performance significantly, especially when the inter element spacing is decreased. A method to eliminate the effect of mutual coupling was proposed by R.S. Adve and T.K. Sarkar (see AP-S Int. Symp. Digest, p.1164-67, 1996). The method of moments (MOM) is used to model the mutual coupling effect on the weights and on the final directivity pattern of the adaptive array. Using an example of a two-element half wavelength adaptive dipole array, it is shown that the mutual coupling between the elements of an adaptive array causes significant degradation in the performance of the array and thus should not be neglected. It is demonstrated that, using the algorithm proposed by Adve and Sarkar, the effects of mutual coupling in adaptive arrays can be eliminated successfully.

In a mobile broadband wireless communication system, an adaptive antenna array can be used to equalize and demodulate multiple users' signals while suppressing interference. In a broadband mobile system operating at 2 GHz or higher, there is a strong potential for severe levels of time and frequency selectivity, which must be accurately tracked for proper multi-user demodulation and interference suppression. We present new frequency-domain techniques that allow for multi-user demodulation even in the presence of high levels of frequency selectivity, and severe time variations across a data block (where a data block is defined to be a group of samples that are FFTd into the frequency domain). These techniques include a time-varying multi-user channel estimation process and a frequency-domain adaptive antenna combining algorithm. The efficacy of the channel estimator and adaptive antenna combining algorithm is demonstrated through simulation results.

We develop iterative turbo receivers for time-variant fading channels which jointly perform channel and frequency offset estimation together with data detection and decoding. Three versions of the joint estimator, the Bayesian, the maximum likelihood and the regularised-maximum likelihood are presented depending on how much knowledge of channel statistics is available. The estimation and detection are based on the basis expansion model of the fading time variations and use the di-chotomous search frequency estimation technique. Soft information generated in the turbo decoder is used to improve the quality of detection in the subsequent iterations. Simulation results show that the proposed receivers provide as good performance as the corresponding ones operating with perfect knowledge of the frequency offset.

Spatial processing with adaptive antenna array has shown real promise for substantial capacity enhancement in wireless communications. We propose in this paper a simple method to evaluate the probability of error in DS-CDMA receivers using a beamformer. We used a beamformer with adaptive antenna arrays followed by a RAKE receiver. Adaptive array can reduce the interference only when the directions of arrivals (DOAs) of the interferers are misaligned with the DOAs of the user of interest. The evaluation of bit error rate is counted differently according to the beam pattern and can provide good agreements with simulation results

It is well-known that the capacity of a direct sequence CDMA system is multiple access interference limited. Adaptive antenna arrays and interference cancellation can significantly reduce the multiple access interference and can greatly enhance the system performance. This paper investigates the performance improvement that can be achieved by integrating adaptive antenna array processing and interference cancellation, where the receiver steers the beams of the adaptive antenna towards not only the desired user but the interferers as well to facilitate the interference cancellation process. We analyze how the use of an FFT beamformer preceding the 2-D RAKE receiver reduces the complexity of the receiver without severe degradation in the overall system performance.