Multi-access Interference Research Articles

Analysis of Multiuser Detectors and Performance improvement in DS-CDMA system using Multistage Multiuser Detection Techniques

The Direct Sequence Code Division Multiple Access (DS-CDMA) system faces several disruptions, this is most crucial of which is the Multi Access Interference (MAI) caused by its users. The efficiency of the system gradually declines as every quantity rises, and the MAI rises, especially in faded environments. This work proposes a multiple-phase multiuser identification approach called Differencing Partial Parallel Interference Cancellation (DPPIC), which improves the overall efficiency. The methods known as Differencing Parallel Interference Cancellation (DPIC) and Partial Parallel Interference Cancellation (PPIC) are combined in this methodology. Current solutions for Parallel Interference Cancellation (PIC) and PPIC have enhanced overall effectiveness; however, this has come at the expense of increasing the complexity of computation. As the variety of consecutive stages grows, the MAI falls. Using the DPIC approach may reduce the computational burden without improving system functionality. The use of the Partial Differencing Parallel Interference Cancellation (PDPIC) technique can enhance system performance while lowering the level of complexity. According to the simulation findings, Bit Error Rate (BER) vs normalized signal strength (i.e., Eb / N0) performs more effectively for the suggested DPPIC approach than for PIC, the PPIC, and PDPIC.

Two constructions for optimal Z-complementary sequence sets

Z-complementary sequence sets (ZCSSs) can be applied to multi-carrier code division multiple access (MC-CDMA) systems as user address codes to eliminate multi-path interference and multi-access interference. In this paper, two constructions of ZCSSs are investigated. First of all, flexible and diverse seed sequence sets are employed to generate a large number of optimal ZCSSs, which is a generalization of an existing construction. Next, note that most ZCSSs obtained by orthogonal-matrix-based constructions have lengths that are multiples of the ZCZ widths. Toward the challenge of designing ZCSSs of various lengths, we proposed a noval construction that can yield ZCSSs with arbitrary lengths based on orthogonal matrices. In this way, different transmission rates can be facility provided to cater for different application scenarios. In addition, the flock sizes and ZCZ widths can be chosen flexibly. It means that, in theory, the obtained ZCSSs can be applied to MC-CDMA systems of various sub-carriers. To the best of our knowledge, the construction of ZCSSs have not been reported in the literature.

Bit Error Rate Performance in CDMA Free Space Optical Links with SIK Receiver under Fog Conditions

This article presents a novel analytical method for evaluating fog's impact on Bit Error Rate (BER) in an Optical Code Division Multiple Access (OCDMA) Free Space Optical (FSO) connection. The investigation employs an optical encoder and direct detection receiver employing a balanced photo detector with Sequence Inverse Keying (SIK) to explore fog effects. By scrutinizing multi-access interference (MAI) current and signal current values at the SIK receiver's output under varied fog conditions, we deduce BER expressions for diverse scenarios. These encompass different fog thickness levels, code lengths, simultaneous users, and system parameters. The results reveal substantial OCDMA degradation due to fog thickness and users. Also, the system incurs a marked power penalty at a specific BER, especially with higher fog and user density. However, we identify a potential solution: increasing code length, effectively mitigating fog-induced performance decline.

Accumulation and Elimination: A Hard Decision-Based Multi-User Interference Cancellation Method in Satellite Communication System

With the increasing number of users in the Medium-Orbit (MEO) satellite communication system, multi-access interference (MAI) has become an important factor that restricts the reliability and capacity of the system. Additionally, the low carrier-power-to-noise-density ratio (C/N0) resulting from long-distance transmission poses a significant concern. The parallel interference cancellation (PIC) algorithm, utilized within the paradigm of multi-user detection (MUD), exhibits the capability to effectively mitigate the impact of MAI within the same system. Simultaneously, coherent accumulation serves as a means to substantially enhance the correct detection probability (Pcd) at low C/N0. In this study, a signal acquisition method for multi-user spread spectrum satellite receivers is proposed, which employs interference cancellation and coherent accumulation as its core mechanisms. Furthermore, we introduce a power estimation method based on the outcomes of signal acquisition, which can be integrated into the signal reconstruction module of PIC. Finally, we implement the aforementioned algorithms in both simulation and hardware platforms. Remarkably, we observe that when the interference-to-signal ratio (ISR) caused by MAI equals 20 dB, the improved algorithm attains a maximum Pcd of 0.95 within the high signal-to-noise ratio (SNR) region, closely approaching the theoretical limit for the bit error rate (BER). The experimental results prove the effectiveness and feasibility of the acquisition algorithm. In summary, the enhanced algorithm holds vast potential for widespread implementation in multi-user spread spectrum communication systems.

Distributed Unsupervised Learning for Interference Management in Integrated Sensing and Communication Systems

Nowadays, the multi-access interference problem in the ISAC systems can not be ignored. The study on interference management in ISAC has been envisioned as one of key technologies to support ubiquitous sensing functions. Different from the current work, a communications-sensing-intelligence converged network architecture is proposed to coordinate interference in this paper. Each base station equips with the individual deep neural networks to allocate power and beamforming. On this basis, the interference management is transformed into a functional optimization with stochastic constraints. An unsupervised learning algorithm is proposed to allocate power for interference management. Furthermore, a transfer learning method is presented to obtain the interference management in terms of transmit beamforming. Finally, the distributed management is obtained from the local channel state information in the multi-cell scenario. Simulation results verify the effectiveness of the proposed unsupervised learning interference management method in the ISAC systems.

A METHOD FOR SYNTHESIS OF FAMILIES OF SETS OF PHASE MANIPULATED SIGNALS WITH OPTIMAL CORRELATION PROPERTIES

In the paper a method for synthesis of families of sets of phase manipulated signals with optimal correlation properties is substantiated. The method could be used in the development of new radar sensor networks, which exploit effectively the electromagnetic spectrum and can operate practically without self-interferences and multiaccess interferences

Research on IMU-Assisted UWB-Based Positioning Algorithm in Underground Coal Mines.

The application of an ultra-wideband (UWB) positioning system in a Global Positioning System (GPS) denial environment such as an underground coal mine, mainly focuses on position information and rarely involves information such as direction attitude. Position accuracy is often affected by multipath, non-visible ranges, base station layout, and more. We proposed an IMU-assisted UWB-based positioning system for the provision of positioning and orientation services to coal miners in underground mines. The Error-State Kalman Filter (ESKF) is used to filter the errors in the measured data from the IMU-assisted UWB positioning system to obtain the best estimate of the error for the current situation and correct for inaccuracies due to approximations. The base station layout of the IMU-assisted UWB positioning system was also simulated. The reasonable setting of the reference base station location can suppress multi-access interference and improve positioning accuracy to a certain extent. Numerous simulation experiments have been conducted in GPS denial environments, such as underground coal mines. The experimental results show the effectiveness of the method for determining the position, direction, and attitude of the coal miner under the mine, which provides a better reference value for positioning and orientation in a GPS rejection environment such as under the mine.

Time Synchronization and Signal Detection in Non-Orthogonal Unicast and Broadcast Networks

The next generation digital TV (DTV) broadcast, namely Advanced Television System Committee (ATSC) 3.0, relies on substantial single frequency networks (SFN), each of which requires a studio to transmitter link (STL) to transmit data from the broadcast gateway (BG), leading to significant construction costs. Therefore, the wireless in-band distribution link (IDL) technology is proposed, which uses layered-division multiplexing (LDM) to transmit the STL data via wireless links from the BG to the SFN transmitters within the same spectrum as the broadcast services. In this paper, we propose the time synchronization and signal detection algorithm for wireless IDL systems with both unicast and broadcast signals. We introduce two multiplexing schemes, N-LDM and 3-LDM, and demonstrate their superiority over traditional frequency division multiplexing (FDM). To overcome the challenge of multi-access interference and synchronization errors caused by multipath, we develop a unique word (UW) design algorithm for transmitted signals and a double threshold correlation detection algorithm (DTCDA) that outperforms traditional ones. We employ a second threshold to enhance detection performance at low signal-to-noise ratios, and utilizes successive interference cancellation (SIC) to mitigate multiple-access interference. More importantly, our approach requires no knowledge of the unicast user number or channel state information. Simulation results validate the effectiveness of the proposed scheme.

New Zero Cross-Correlation Codes Based on Zech Method’s for OCDMA Systems

A new structure code for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC–OCDMA) system with zero cross-correlation (ZCC) is presented in this paper. The principle idea of this method is based on the use of Zech logarithms in the construction of the code sequences to ensure orthogonality and compare their performances with previously reported codes. The maximum cross-correlation of this code is zero signifying that Multi-Access Interference (MAI) and Phase-Induced intensity noise (PIIN) effects are eliminated thus the system performances are improved. The BER simulation results against the total number of active users show a significant improvement in the performance of the proposed code over preceding reported codes. The system can accommodate more than 90 simultaneous users compared to other codes at a bit error rate of 10^(-9). Furthermore, the construction method offers good flexibility in the choice of the number of users, the weight, and the code length.

A Joint Denoising Learning Model for Weight Update Space–Time Diversity Method

Space–time diversity (STD) has been widely applied in underwater acoustic (UWA) communication due to its exceptional anti-multipath performance. However, underwater noise can seriously affect the processing results of STD. The conventional filtering algorithms cannot deal with the nonlinear components of underwater noise and may not work well for complex-type signals. This study proposes an improved STD method with a joint noise-reduction learning model for the above issues. We construct a noise-reduction learning model dedicated to complex-type UWA signals in the first stage. Complex-type features based on UWA data are extracted for pre-processing data, and a conditional generative adversarial network (CGAN) is used as the backbone network for noise-reduction. Residual learning is used to accomplish noise cancellation and yield noise-reduction estimates. In the second stage, an STD structure based on a weight update strategy is constructed. The STD structure can further constrain the weights of the signals from the main path, enhance the reception of the main path, and suppress the multi-access interference (MAI) caused by the spread spectrum communication. Finally, combining the signals on each path can improve the communication quality of the system based on the principle of the maximum signal-to-interference plus noise ratio (SINR). The simulation and experiments on a lake showed that the proposed method is more robust over the changing signal-to-noise ratio (SNR) and has a lower bit error rate (BER) than conventional methods.

Optimal Low-Hit-Zone Frequency-Hopping Sequence Sets With Wide-Gap for FHMA Systems Under Follower Jamming

This letter is concerned with tackling both of the multi-access interference (MAI) and the follower jamming (FJ) in frequency-hopping multiple-access (FHMA) systems via novel FH sequence (FHS) design. We consider low-hit-zone (LHZ) FHS which provides lower MAIs in quasi-synchronous FHMA systems but suffers from FJ attack. We introduce an improved LHZ-FHS with wide-gap (i.e., WG-LHZ-FHS) for the neighboring carrier frequencies so as to combat the MAI and the FJ. We first present a general method to generate new WG-FHS sets and then construct the first known WG-LHZ-FHS sets with optimal periodic Hamming correlation (PHC) properties. Besides, the error-rate performance of the constructed WG-LHZ-FHS set imposed in an FHMA system under FJ is investigated. The numerical analysis and the system simulation results indicate that the proposed WG-LHZ-FHS set provides the better error-rate performance to combat the FJ as well as satisfactory capability of MAI suppression due to its combined merits of WG and LHZ.

INTERFERENCE MITIGATION BASED ON CARRIER INTERFEROMETRY CODES IN THE DOWNLINK LOW EARTH ORBIT SATELLITE CHANNEL

The multi-carrier code division multiple access (MC-CDMA) system employs the Hadamard-Walsh (HW) code in the low earth orbit (LEO) satellite systems. It has been used as spreading code to maintain the multi-access interference (MAI) in the downlink LEO satellite channel. However, due to the non-orthogonality of the HW codes, these interferences are observed at the MC-CDMA satellite receiver. As a result, the LEO satellite system performance is degraded. In this paper, we propose to employ the orthogonal Carrier Interferometry (CI) code with MC-CDMA in the downlink LEO satellite channel. A new system is called CI/MC-CDMA which is used to mitigate the MAI. Moreover, the performance of the CI/MC-CDMA satellite system in terms of bit error rate (BER) is analyzed and simulated. To confirm the analysis, the system is compared to the HW/MC-CDMA system. It has been shown that CI/MC-CDMA satellite system outperforms HW/MC-CDMA

Novel channel-hopping pattern-based wireless IoT networks in smart cities for reducing multi-access interference and jamming attacks

In smart cities, the Internet-of-Thing (IoT) provides an enabling communication infrastructure to support tremendous amount of data exchange. Most IoT applications, e.g., wireless local area network, Bluetooth and so forth, utilize the channel-hopping scheme to suppress the transmission security threats. In this paper, to reduce the mutual interference and external jamming attacks, multiple novel channel-hopping patterns, i.e., traditional no-hit-zone (NHZ) hopping pattern and generalized NHZ hopping pattern, are introduced to suit to IoT networks. Particularly the design of probabilistic hopping pattern is first proposed, which has the various usage probabilities with regard to various channels. The properties of these hopping patterns are investigated by the step-to-step examples. Then, the error-rate performance of the multi-node IoT systems adopting these hopping patterns in the presence of jamming attacks is comprehensively analyzed. The extensive simulations show that the traditional/generalized NHZ hopping patterns are in favor of combating the mutual interference but with the limited capability of reducing jamming attacks, while the probabilistic hopping pattern possesses the opposite feature, that is, it has the predominant merit in suppressing jamming attacks. Thus, the novel channel-hopping pattern-based IoT could provide the secure transmission for communication applications in smart cities. Note that, as the physical-layer security technique, the channel-hopping patterns investigated in this paper are convenient to integrate with the security policies implemented in upper layers (e.g., encryption, authentication and so forth).

A criterion based adaptive RSIC scheme in underwater communication

Multi-access interference (MAI) is the main source limiting the capacity and quality of the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system which fulfills the demand of high-speed transmission rate and high quality of service for future underwater acoustic (UWA) communication. Therefore, multi-user detection (MUD) is needed at the receiver of the MIMO-OFDM system to suppress the effect of MAI. In this research, MUD is achieved by using a criterion based adaptive recursive successive interference cancellation (RSIC) scheme at the receiver of a MIMO-OFDM system whose transceiver model in underwater communication is implemented by using the Bellhop simulation system. The proposed scheme estimates and eliminates the MAI through user signal detection and subtraction from received signals at the receiver of the MIMO-OFDM system in underwater environment. The bit error rate (BER) performance of the proposed scheme is analyzed by using weight filtering and weight selection criteria. By Matlab simulation, it is shown that the BER performance of the proposed scheme outperforms the conventional matched filter(MF) detector, the adaptive successive interference cancellation(SIC) scheme, and the adaptive RSIC scheme in the UWA network.

Multiuser Detection for MIMO-OFDM system in Underwater Communication Using a Hybrid Bionic Binary Spotted Hyena Optimizer

Multi Access Interference (MAI) is the main source limiting the capacity and quality of the Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system which fulfills the demand of high-speed transmission rate and high quality of service for future underwater acoustic (UWA) communication. Multi User Detection (MUD) is needed to overcome the performance degradation caused by MAI. In this research, both local and global optimal solutions are obtained in Bionic Binary Spotted Hyena Optimizer (BBSHO) algorithm using the Position Coordinate Vectors (PCVs) of the social behavior of spotted hyenas to achieve MUD. Further, Extremal Optimization (EO) is introduced in BBSHO algorithm to improve the local search ability within the search space. Hence, a hybrid BBSHO algorithm is proposed for achieving MUD at the receiver of the MIMO-OFDM system whose transceiver model in underwater is implemented using BELLHOP simulation system. By MATLAB simulation, it is shown that the Bit Error Rate (BER) performance of the proposed hybrid algorithm outperforms with best optimal solution within the search space towards MUD for Interference to Noise Ratio (INR) at 10 dB, 20 dB, and 40 dB over conventional detectors and metaheuristic approaches such as Binary Spotted Hyena Optimizer (BSHO), Binary Particle Swarm Optimization (BPSO) in the UWA network.

Investigation of Blind Multi-User Detection Technology

Blind multi-user detection algorithm is an effective method to overcome multi-access interference and influence of near-far effect. This paper briefly describes commonly used algorithms of blind multi-user detection technology, introduces the application of the least mean square algorithm (LMS) and compares the performance with other algorithms. Aiming at the shortcomings of the LMS algorithm, the variable step size LMS algorithm and the relatively low complexity LMK algorithm based on the change of the input signal vector are studied.

Cyclic interleaving scheme for an IFDMA system

In this paper, a new interleaving scheme for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme combines the advantages of code division multiple access (CDMA) with maximal length sequence (m-sequence) and orthogonal frequency division multiple access (OFDMA). Multiaccess interference (MAI) among users is eliminated by employing orthogonal carriers, and the intersymbol interference (ISI) due to multipath channels is minimized by using cyclic interleaving. Diversity gain is achieved in the proposed method with maximal ratio combining (MRC) in the case of a Rayleigh environment. Compared to complex multiuser (MU) detection, the detection process in the proposed method is relatively simple. Multipath orthogonality is achieved in the proposed method, avoiding the need for channel equalization. The proposed method is compared with the conventional interleaving employing well-known minimum mean square error frequency domain equalization (MMSE-FDE). The Monte Carlo simulation results prove the superiority of the proposed interleaving over conventional interleaving with MMSE-FDE, showing that the present scheme is suitable for both uplink and downlink mobile radio transmissions.

A novel multiuser detection based on honey bees mating optimisation and tabu search algorithm for SDMA-OFDM systems

In the wireless communication systems, the classic Multi-User Detection (MUD) techniques such as the Minimum Mean Square Error (MMSE) detector have some limitations and imperfections due to Multi-Access Interference (MAI) especially in overloaded scenarios when the number of users is more than the number of receiving antennas. The optimal Maximum Likelihood (ML) detector gives an excellent result to estimate the transmitted data but suffers from a computational complexity that grows exponentially with the number of users. In this paper, we propose a new metaheuristic approach for multiuser detection based on Honey Bees Mating Optimisation (HBMO) hybridised with Tabu Search (TS) for an uplink Space Division Multiple Access-Orthogonal Frequency Division Multiplexing (SDMA-OFDM) system in a flat Rayleigh fading channel. Indeed, the HBMO algorithm provides a good estimation for TS while exploring the largest regions, while the TS algorithm uses this estimation to find the best solution of the problem. The simulation results show that the proposed algorithm HBMO-TS-MUD provides the best trade-off between performance and computational complexity comparing to the conventional detector and the other MUD detectors proposed as Genetic Algorithm hybridised with the Tabu Search (GA-TS).

A Spatial–Temporal Subspace-Based Compressive Channel Estimation Technique in Unknown Interference MIMO Channels

Spatial–temporal (ST) subspace-based channel estimation techniques formulated with $\ell 2$ minimum mean square error (MMSE) criterion alleviate the multi-access interference (MAI) problem when the interested signals exhibit low-rank property. However, the conventional $\ell 2$ ST subspace-based methods suffer from mean squared error (MSE) deterioration in unknown interference channels, due to the difficulty to separate the interested signals from the channel covariance matrices (CCMs) contaminated with unknown interference. As a solution to the problem, we propose a new $\ell 1$ regularized ST channel estimation algorithm by applying the expectation-maximization (EM) algorithm to iteratively examine the signal subspace and the corresponding sparse-supports. The new algorithm updates the CCM independently of the slot-dependent $\ell 1$ regularization, which enables it to correctly perform the sparse-independent component analysis (ICA) with a reasonable complexity order. Simulation results shown in this paper verify that the proposed technique significantly improves MSE performance in unknown interference MIMO channels, and hence, solves the BER floor problems from which the conventional receivers suffer.

On the performance of wireless sensor network time difference of arrival localization under realistic interference and timing estimation errors

The article addresses the modeling and performance analysis of wireless sensor network localization with direct-sequence spread-spectrum signals and network-based, time difference of arrival measurements. Realistic radio channel propagation and interference conditions are taken into account. Synchronization by means of a delay-locked loop is adopted for sensor signal tracking at the wireless sensor network anchor nodes. A comprehensive timing estimation analysis is presented with channel impairments, including pathloss attenuation, shadowing, multipath fading, and multi-access interference. The full statistics of the delay-locked loop tracking jitter are derived, which serves to assess the practically achievable synchronization accuracy and its variability with radio channel conditions and specific sensor location. The time difference of arrival measurements are then used for sensor localization based on an efficient iterative maximum likelihood estimation approach shown to outperform weighted least squar...