Hybrid Interference Cancellation Research Articles

Low-complexity hybrid interference cancellation for sparse code multiple access

Sparse Code Multiple Access (SCMA) is one of Non Orthogonal Multiple Access (NOMA) candidates for 5G, the fifth generation mobile network. Multiple overlapped blocks of SCMA code are transmitted per frequency layer which compels the receiver to cancel unwanted SCMA code blocks. Thanks to the sparsity of SCMA, Message Passing Algorithm (MPA) achieves near-optimal performance. Nevertheless, this process is time-consuming and has a high degree of complexity even if Max-Log Algorithm is used. The major contribution of this paper is to propose a new decoding scheme called Hybrid Interference Cancellation (HIC) to reduce time processing without degrading a target Bit Error Rate (BER). The HIC decodes and removes the strongest user, reducing the complexity of Log Domain MPA decoding of remaining users, followed by a Low Density Parity Code (LDPC) decoder. The interference cancellation decoder is either a hard interference cancellation or a soft interference cancellation. The originality of the paper is to calculate a threshold value based on power measurements to decide whether hard decoder or soft decoder should be used to reach the BER target with a lower complexity. Results show a significant reduction in terms of complexity as compared to the traditional MPA process for the same values of BER.

Intelligent Reflecting Surface Assisted Interference Mitigation for Cellular-Connected UAV

Air-ground interference mitigation is a challenging issue for integrating unmanned aerial vehicles (UAVs) into cellular networks, since UAVs can cause/suffer severe interference to/from a large number of co-channel base stations (BSs) in their uplink/downlink communications due to line-of-sight (LoS) UAV-ground channels. In this letter, we propose a new and efficient interference mitigation scheme to tackle this challenge by exploiting the intelligent reflecting surfaces (IRSs) deployed near the BSs. Specifically, in the downlink, the IRS near each co-channel BS tunes its passive beamforming to suppress the BS’s interference to the UAV. While in the uplink, its passive beamforming is tuned to suppress/enhance the interference from the UAV for facilitating the linear/nonlinear interference cancellation (IC) at each co-channel BS. To achieve the optimal UAV-ground performance trade-off, we further propose a hybrid IC scheme to maximize the weighted sum rate of the UAV and ground users in the uplink, by jointly optimizing the set of BSs applying the linear/nonlinear IC and the UAV’s transmit power. Simulation results demonstrate the performance gain of the proposed schemes over benchmark schemes and draw important design insights for IRS-aided UAV communication in cellular networks.

Transmission capacity analysis of relay-assisted D2D cellular networks with interference cancellation

D2D communication has been identified as one of the technologies for meeting the unique traffic demands of the fifth-generation wireless network communication. However, the effectiveness of D2D highly depends on the proximity of devices. In other words, whenever such devices are very far apart, communication may become ineffective. Thus, relay assisted D2D positions itself as an approach by which some of the limitations of traditional D2D communication can be addressed. This makes the applications of D2D communication more versatile. However, the introduction of relays also poses interference within the D2D communication network especially when the density of relay is high. Such scenarios call for techniques by which interference posed by relays can be averted while taking the benefits of relay-assisted communication. This motivates the consideration of interference cancellation (IC) in this paper where two IC models are adapted into the transmission capacity analysis of relay-assisted D2D communication. We show the performance gains attainable by interference cancellation and how the interplay between its parameters affect the network performance. Furthermore, two hybrid IC models are investigated and the impact of interference cancellation in these scenarios and the inherent trade-offs are revealed.

Convergence and BER Approximation of HIC Detector for DS-CDMA System in Rayleigh Fading Multipath Environment

In this paper we present mathematic analysis and implementation of hybrid interference canceller (HIC) for direct sequence-code division multiple access (DS-CDMA) system in multipath environment over Rayleigh channel. The HIC detector is examined for convergence. The bit error rate (BER) for the system is obtained using Simplified Improved Gaussian Approximation (SIGA). Using this expression, BER is plotted for the Rayleigh channel having exponentially decaying power delay profile (PDP) as well as flat PDP. The theoretical results are compared with the simulated system results.

Optimal rate profile for multi‐user multi‐rate transmission systems by bivariate fixed‐point analysis

A K-user multi-rate code is proposed for a Gaussian multiple access channel with binary inputs, equal-power, and symbol synchronisation. In this multi-rate transmission, K users are equally divided into M groups. For each user in the mth group, a rate- 1 / q m regular repeat-accumulate code serially concatenated with a length- L m spreading is employed. The transmitted rate of each user in the mth group is 1 / ( q m L m ) . At the receiver, iterative joint decoding (IJD) and hybrid interference cancellation (HIC) schemes are considered. For each decoding scheme, a bivariate fixed-point analysis is applied to explicitly represent ( q m , L m ) as a function of mutual information outputs. On the basis of these basic explicit representations, a united unreliable region is given, where users in at least one group are undecodable. The complementary set of the united unreliable region gives an optimal rate profile that achieves the maximum sum rate. Numerical results show that, for the IJD scheme with M increments, the maximum sum rate increases, approaches the Shannon limit, and exceeds that in conventional equal rate transmission. The maximum sum rate of the HIC scheme, which provides much lower decoding complexity than the IJD scheme, is superior to the conventional successive interference cancellation scheme.

Modified hybrid interference cancellation algorithm for uplink cognitive radio transmission based on overloaded DS-CDMA

In this paper, cognitive radio network architecture based on overloaded direct sequence code division multiple access (O-DS-CDMA) is proposed. In this method, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. Orthogonality between the spreading codes is lost due to non-zero cross correlation between the codes and timing synchronisation error in the uplink transmission, which causes interference among primary and secondary users. In this paper, a modified hybrid parallel/successive interference cancellation algorithm is proposed for the primary and secondary user base station receivers with multiple antennas, to suppress the interference among the users. Interferences among same group users are cancelled using parallel interference cancellation and the interferences between groups are cancelled using successive interference cancellation. The simulation results show that, the proposed modified interference cancellation algorithm improves the BER performance of the system significantly.

Performance analysis of overloaded CDMA system under imperfect synchronization using Parallel/Successive Interference Cancellation

A hybrid Interference cancellation (HIC) technique employing both Parallel and Successive Interference Cancellation (PIC/SIC) is proposed for Overloaded Direct Sequence Code Division Multiple Access (OCDMA) system under imperfect synchronization. Two types of receivers are proposed to efficiently mitigate the multiuser interference (MUI). In type I receiver, the MUI within group-1 users are first cancelled using Parallel Interference Cancellation (PIC). Then the multistage Successive Interference Cancellation (m-SIC) is performed on the resultant output of PIC to efficiently cancel the interference of group-2 users on group-1 users. The type II receiver is designed by performing PIC immediately followed by SIC and this combined process is repeated till a major chunk of multi user interference is cancelled. The BER performance of type II receiver is proved to be better than other cancellation techniques such as PIC, SIC and the proposed type I receiver.

A Hybrid Interference Cancellation technique for overloaded CDMA with timing offset error

A novel method of Hybrid Parallel/Successive Interference Cancellation (HIC) for Overloaded Direct Sequence Code Division Multiple Access (OCDMA) system involving two groups of users is proposed in this paper. The impact of timing synchronization error on acceptable channel load in a synchronous binary spread CDMA system is studied by mitigating the effect of multi-access interference (MAI). A small timing synchronization error is introduced in the DS-CDMA system under study to disturb the orthogonality of group-1 users and group-2 users. This orthogonality loss leads to Multi User Interference (MUI) in group-1 users and it is cancelled using Parallel Interference Cancellation (PIC). The interference of group-2 users on group-1 users is cancelled using Successive Interference Cancellation (SIC). The analytical expressions of the Bit Error Rate (BER) are derived. The simulation results prove that the BER performance of the proposed HIC method is better than the conventional PIC and SIC.

그룹화 CMA 알고리즘을 이용한 RF 중계기의 적응 간섭 제거 시스템(Adaptive Interference Cancellation System)에 관한 연구

본 논문에서는 RF(Radio Frequency) 중계기에서 그룹화 CMA(Constant Modulus Algorithm)와 LMS(Least Mean Square) 알고리즘을 이용하여 적응 필터를 적용시킨 새로운 혼합 간섭 제거기를 제안한다. 송신 안테나에서 수신안테나로 궤환되는 신호는 수신 시스템의 성능을 저하시킨다. 제안한 간섭 제거기는 그룹화 CMA 알고리즘 간섭 제거 기법을 적용시키기 때문에 기존 구조보다 나은 채널 적응 성능과 낮은 MSE(Mean Square Error)을 가진다. 이 구조는 기존 비선형 간섭 제거기에 비해 같은 MSE(Mean Square Error)에 대한 반복수와 하드웨어 복잡도를 줄여준다. 즉, 제안한 알고리즘은 LMS 알고리즘에 비해 평균 자승 에러가 적응 상수에 따라 2.5 dB 또는 4 dB 정도 낮은 값을 보였다. 또한, VSS(Variable Step Size)-LMS 알고리즘에 비해 수렴 속도가 빠르고, 비슷한 평균 자승 에러를 가진다. In this paper, we proposed a new hybrid interference canceller using the adaptive filter with Grouped CMA(Constant Modulus Algorithm)-LMS(Least Mean Square) algorithm in the RF(Radio Frequency) repeater. The feedback signal generated from transmitter antenna to receiver antenna reduces the performance of the receiver system. The proposed interference canceller has better channel adaptive performance and a lower MSE(Mean Square Error) than conventional structure because it uses the cancellation method of Grouped CMA algorithm. This structure reduces the number of iterations fur the same MSE performance and hardware complexity compared to conventional nonlinear interference canceller. Namely, MSE values of the proposed algorithm were lower than those of LMS algorithm by 2.5 dB and 4 dB according to step sizes. And the proposed algorithm showed fast speed of convergence and similar MSE performance compared to VSS(Variable Step Size)-LMS algorithm.

Joint Doppler-Frequency Diversity for OFDM Systems Using Hybrid Interference Cancellation in Time-Varying Multipath Fading Channels

In time-varying fading channels, orthogonal frequency division multiplexing systems suffer severe performance degradation caused by interchannel interference (ICI). We utilize this ICI as a source of diversity by using a new ICI-cancellation algorithm and Wiener filter. The proposed algorithm can support joint Doppler-frequency diversity gain. In addition, both the computational complexity and total detection time are reduced.

A New Ordering and Grouping Algorithm for the Linear Weighted Group Matched Filter Successive Interference Cancellation Detector

A linear group-wise successive interference canceller in a synchronous code-division multiple-access system (CDMA) is considered in this paper. The proposed hybrid detector that combines successive and parallel cancellation techniques makes use of advantages offered by the two techniques. The convergence of the hybrid interference cancellation (HIC) detector is guaranteed by an adjustable parameter that depends upon the largest eigenvalue of the system's transition matrix. Since the largest eigenvalue is difficult to estimate, an upper bound is necessary for successful convergence. For this reason, a new upper bound for the maximum eigenvalue of the system's transition matrix was developed. Moreover, a new ordering and grouping algorithm that results in a higher convergence speed is proposed. Simulation results show that a significant improvement in performance is obtained using this technique.

Space-Time Interference Cancellation in MIMO-OFDM Systems

In this paper, a two stage hybrid interference cancellation and equalization framework is proposed for interference cancellation in the uplink of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The first stage uses time domain equalization to suppress cochannel interference, mitigate asynchronism, and shorten the postequalization channel response to be no longer than the length of the cyclic prefix. The second stage performs low-complexity single tap equalization and detection in the frequency domain. The framework is developed specifically for spatial multiplexing and is applied to multiuser MIMO-OFDM systems with asynchronism between users as well as to single-user MIMO-OFDM systems. Various equalizer design methods are proposed that determine the coefficients directly from the training data and are compared with methods based on channel estimates. The equalizer coefficients and postequalization channel response are found by solving a joint optimization that maximizes the signal to interference-plus-noise ratio (SINR) in the frequency domain. Simulations compare various training-based methods and show the proposed methods provide good bit error rate (BER) and SINR performance in a variety of interference scenarios.

A hybrid interference cancellation scheme for blind multiuser detection in multipath fading channels

This paper introduces and analyzes a detection scheme for adaptive suppression of Multiuser Access Interference (MAI) and MultiPath Distortion (MPD) for mobile station of DS/CDMA system. The proposed detection scheme may amount to a RAKE receiver structure, wherein each branch is considered as a linear multiuser filter designed under a Linear Constrained Minimum Variance (LCMV) optimization strategy to suppress MAI, followed by a proper combining rule to suppress MPD. The adaptive blind multiuser detecting and optimum combining of the proposed receiver are realized, based on the Least-Mean-Square (LMS) algorithm and an adaptive vector tracking algorithm respectively. Finally, the feasibility of the above two algorithms is proved by the numerical results provided by computer simulation.

A Hybrid Interference Cancellation Scheme for Multiuser Systems in Multipath Fading Channels

AbstractA new hybrid interference cancellation (IC) scheme is proposed for the uplink of multirate direct‐sequence code division multiple access (DS‐CDMA) systems communicating over mobile radio channels. The hybrid IC scheme includes both non‐decision directed and decision directed IC, together with a modified RAKE combiner to utilize the diversity in a frequency‐selective channel. The performance is evaluated via computer simulations for the two multiple data rate schemes, mixed modulation and multicode, in a multipath environment. Both known channel parameters and channel estimation using pilot symbols are considered. The results show that rnulticode or a combination of multicode and mixed modulation are preferable when handling multirate system and the loss in performance compared to the single‐user bound is small.