Multiuser Interference Suppression Research Articles

Intelligent Hierarchical Network Slicing Based on Dynamic Multi-Connectivity in Cell-Free Distributed Massive MIMO Systems

In order to provide customized services for the future sixth-generation (6 G) mass business, we propose a two-timescale intelligent radio access network (RAN) slicing scheme under the architecture of cell-free distributed massive multiple-input multiple-output (MIMO) systems. Cell-free distributed massive MIMO systems have powerful macro diversity gain and multi-user interference suppression capabilities to improve the performance of different slices, and are more flexible in terms of service types based on network slicing. In the proposed scheme, we utilize the long-term and short-term trends of network to achieve adaptive resource allocation at different timescales, so as to utilize resources more effectively and meet performance requirements in parallel. Moreover, multi-connectivity is utilized to improve link reliability and further improve system performance, and user clustering reduces the impact of pilot contamination on system performance. In order to implement the RAN control strategy effectively, an efficient two-level deep reinforcement learning framework is proposed and the multi-agent reinforcement learning algorithm is used to realize efficient network resource interaction in multi-device scenarios. Simulation results further verify the effectiveness of the proposed intelligent RAN slicing scheme.

Low Spatial Peak-to-Average Power Ratio Transmission for Improved Energy Efficiency in Massive MIMO Systems.

A significant portion of the operating power of a base station is consumed by power amplifiers (PAs). Much of this power is dissipated in the form of heat, as the overall efficiency of currently deployed PAs is typically very low. This is because the structure of conventional precoding techniques typically results in a relatively high variation in output power at different antennas in the array, and many PAs are operated well below saturation to avoid distortion of the transmitted signals. In this work, we use a realistic model for power consumption in PAs and study the impact of power variation across antennas in the array on the energy efficiency of a massive MIMO downlink system. We introduce a family of linear precoding matrices that allow us to control the spatial peak-to-average power ratio by projecting a fraction of the transmitted power onto the null space of the channel. These precoding matrices preserve the structure of conventional precoders; e.g., they suppress multiuser interference when used together with zeroforcing precoding and bring advantages over these precoders by operating PAs in a more power-efficient region and reducing the total radiated distortion. Our numerical results show that by controlling the power variations between antennas in the array and incorporating the nonlinearity properties of PA into the precoder optimization, significant gains in energy efficiency can be achieved over conventional precoding techniques.

Constrained Tensor Decomposition-Based Hybrid Beamforming for Mmwave Massive MIMO-OFDM Communication Systems

Hybrid beamforming design for OFDM systems is hugely challenging since their analog precoders and combiners are shared among all subcarriers. This paper proposes a novel two-stage joint hybrid precoder and combiner design for maximizing the average achievable sum-rate of frequency-selective millimeter-wave massive MIMO-OFDM systems. In the proposed approach, the analog precoder and combiner design is formulated as a constrained Tucker2 tensor decomposition problem, which allows maximizing the sum of the effective baseband gains over every subcarrier while suppressing inter-user and intra-user interferences. The solution is obtained by a projected alternate least-square-based algorithm, which is suitable for both single-user (SU) and multiuser (MU) systems. The digital precoder and combiner for SU systems is obtained from the effective baseband channel' SVD. In contrast, for MU systems, it is obtained from the regularized channel diagonalization method, which balances multiuser interference and noise suppression. Numerical simulation results validate the effectiveness of the proposed method.

Model-Driven Deep Learning for Massive Multiuser MIMO Constant Envelope Precoding

Constant envelope (CE) precoding design is of great interest for massive multiuser multi-input multi-output systems because it can significantly reduce hardware cost and power consumption. However, existing CE precoding algorithms are hindered by excessive computational overhead. In this letter, a novel model-driven deep learning (DL)-based network that combines DL with conjugate gradient algorithm is proposed for CE precoding. Specifically, the original iterative algorithm is unfolded and parameterized by trainable variables. With the proposed architecture, the variables can be learned efficiently from training data through unsupervised learning approach. Thus, the proposed network learns to obtain the search step size and adjust the search direction. Simulation results demonstrate the superiority of the proposed network in terms of multiuser interference suppression capability and computational overhead.

Constrained Channel Decomposition-Based Hybrid Beamforming for mmWave Massive MIMO Systems

In this article, we propose a hybrid beamforming design for multiuser mmWave massive MIMO systems. We adopt a two-stage approach for designing the analog and digital beamforming separately. The analog beamforming design is based on a constrained low-rank channel decomposition and aims to simultaneously harvest the array gain and reduce the intra- and inter-user interference. The digital beamforming design is conducted by using the regularized channel diagonalization method, which provides a better trade-off between multiuser interference suppression and transmit diversity, thus attaining a better performance in low-SNR scenarios or when communicating to many users or through many data streams. We validate the effectiveness of the proposed design through numerical simulations, which have shown that our design outperforms several other hybrid beamforming designs in the literature.

Multiuser Transmit Precoding Design for Dimming Compatible Visible Light Communications

In multiuser visible light communication (VLC) systems, many transmit precoding (TPC) techniques have been investigated to suppress multiuser interference. However, these conventional works restrict their modulation to the special case of zero mean, which inherently limits their application to some popular modulations associated with the non-zero mean in VLC, such as pulse position modulation (PPM). Since the modulation with non-zero mean leads to more intricate optical power constraints and design objective functions than the case of zero mean, the TPC design that can support a general modulation is still an open problem. In the paper, we conceive of a general solution of the TPC scheme combined with dimming control for multiuser VLC systems, which is capable of mitigating multiuser interference, while at the same time, achieving the desired dimming level. The proposed scheme is applicable to a wide range of modulations in VLC, such as pulse amplitude modulation (PAM), PPM, and so on. Simulation results demonstrate that the proposed scheme outperforms the traditional pseudo-inverse-based zero-forcing TPC in terms of bit error rate (BER).

Frequency Synchronization for Uplink Massive MIMO With Adaptive MUI Suppression in Angle Domain

In this paper, we develop a novel angle-domain adaptive filtering (ADAF)-based frequency synchronization method for the uplink of a massive multiple-input multiple-output (MIMO) multiuser network, which is applicable for users with either separate or overlapped angle-of-arrival (AoA) regions. For each user, we first introduce the angle-constraining matrix (ACM), which consists of a set of selected match-filter (MF) beamformers pointing to the AoAs of the interested user. Then, the adaptive beamformer can be acquired by appropriately designing the ADAF vectors. Such beamformer can achieve two-stage adaptive multiuser interference (MUI) suppression, i.e., inherently suppressing the MUI from non-overlapping users by ACM in the first stage and substantially mitigating the MUI from adjacent overlapping users by ADAF vector in the second stage. For both separate and mutually overlapping users, the carrier frequency offset (CFO) estimation and subsequent data detection can be performed independently for each user, which significantly reduces computational complexity. Moreover, ADAF is rather robust to imperfect AoA knowledge and side cluster of scatterers, making itself promising for multiuser uplink transmission. We also analyze the performance of CFO estimation and obtain an approximated closed-form expression of mean-squared error (MSE). The effectiveness of the proposed method and its superiority over the existing methods are demonstrated by numerical results.

Adaptive Reduced-Rank Receive Processing Based on Minimum Symbol-Error-Rate Criterion for Large-Scale Multiple-Antenna Systems

In this work, we propose a novel adaptive reduced-rank receive processing strategy based on joint preprocessing, decimation and filtering (JPDF) for large-scale multiple-antenna systems. In this scheme, a reduced-rank framework is employed for linear receive processing and multiuser interference suppression based on the minimization of the symbol-error-rate (SER) cost function. We present a structure with multiple processing branches that performs a dimensionality reduction, where each branch contains a group of jointly optimized preprocessing and decimation units, followed by a linear receive filter. We then develop stochastic gradient (SG) algorithms to compute the parameters of the preprocessing and receive filters, along with a low-complexity decimation technique for both binary phase shift keying (BPSK) and $M$-ary quadrature amplitude modulation (QAM) symbols. In addition, an automatic parameter selection scheme is proposed to further improve the convergence performance of the proposed reduced-rank algorithms. Simulation results are presented for time-varying wireless environments and show that the proposed JPDF minimum-SER receive processing strategy and algorithms achieve a superior performance than existing methods with a reduced computational complexity.

Dual-Hop N-Relay Assisted Transmission for IDMA Systems over Weibull Fading Channels

This paper proposes and investigates dual-hop N-relay assisted transmission scheme for interleave-division multiple access with decode-and-forward relaying. In the considered system, chip-by-chip detection method is employed to suppress multiuser interference at relay and destination nodes. We assumed binary phase shift keying modulation and analyse the system under study in terms of bit error rate when the source-relay and relay-destination links experience Weibull fading. Our simulation results show that the dual-hop N-relay assisted decode-and-forward relaying can be a promising alternative for the performance improvement of interleave-division multiple access by efficiently mitigating the multiuser interference at the relay nodes as well as destination node. DOI: http://dx.doi.org/10.5755/j01.eee.21.4.12787

Performance analysis of optical CDMA communication systems with M‐ary PWM signalling

ABSTRACTIn this paper, a novel M‐ary pulse‐width modulation (PWM) coded optical code division multiple access (O‐CDMA) system is proposed. At the transmitter end, in order to increase the number of transmitted bits per pulse, each chip of signature sequence is further divided into M time slots to realise the M‐ary PWM signal format. Two types of detection schemes are developed, and the performance in terms of symbol error rate is analysed. In the first scheme, the correlation receiver is employed followed by an M‐level threshold detection. To enhance the multiuser interference suppression capability, we apply the chip‐level‐based diversity detection in the second scheme. Adding optical hard‐limiters at the front end of the receiver, both schemes are free from the near–far problem that is suffered severely in O‐CDMA system employing pulse‐amplitude modulation (PAM). Numerical results demonstrate that the proposed M‐ary PWM O‐CDMA system with the chip‐level receiver achieves better symbol error rate and multiuser interference mitigation capability than the correlation receiver. Moreover, the performance of the proposed M‐ary PWM O‐CDMA system is much better than the M‐ary pulse‐amplitude modulation scheme. And the complexity is substantially reduced as we compare to the existing M‐ary pulse‐position modulation O‐CDMA system. Copyright © 2014 John Wiley & Sons, Ltd.

Multiuser Receiver Scheme with SIC for PUCCH in High Speed Train Environment

A multiuser receiver scheme with successive interference cancellation (SIC) is proposed to suppress multiuser interference for physical uplink control channel (PUCCH) in high speed train (HST) environment. In the proposed algorithm, each user’s signal is detected iteratively in a descending order according to the signal strength at eNB. During each iteration, the strongest signal of all users’ is detected and regenerated, and then is subtracted from the composite signal before decoding the next user. Simulation results show that the proposed scheme obtains remarkable gains, e.g. 2 dB for PUCCH format 2 with 3 users in HST scenario 1. The improvement is more pronounced in the case of increasing number of users, e.g. 3.3 dB with 6 users.

Joint Interference Suppression for Multi-User TDD MIMO Downlink with Other-Cell Interference

In multiuser TDD MIMO downlink communications, system performance suffers from multiuser interference(MUI) and other-cell interference(OCI). This paper proposes designing a precoder to jointly suppress MUI and OCI. Firstly, a precoding matrix is designed for multiuser interference suppression, with the help of the QR decomposition of generalized MMSE channel inversion. And then, using a signal leakage criterion, the second precoding matrix is designed to suppress OCI and residual MUI. The proposed algorithm can avoid user feedback in multiuser TDD MIMO systems. Simulation results demonstrate the effectiveness of the proposed scheme.

Performance of multi-relay coded cooperative diversity in asynchronous code-division multiple-access over fading channels

In this study, multi-relay decode-and forward (DAF) cooperative networks employing convolutional coding are studied for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems over frequency-selective slow fading channels. The authors show that the full benefits of coded cooperative diversity cannot be achieved if no multi-user interference suppression is employed at the cooperative end. The authors consider two scenarios; perfect and imperfect inter-user channels. In that, the bit-error-rate performance of the cooperative system is investigated for an uplink transmission where a decorrelator detector is used at both the relay and base station receivers. Both simulation and analytical results are presented to demonstrate the diversity gains of the convolutionally coded cooperative network.

Generalized Channel Inversion Methods for Multiuser MIMO Systems

Block diagonalization (BD) is a well-known precoding method in multiuser multi-input multi-output (MIMO) broadcast channels. This scheme can be considered as a extension of the zero-forcing (ZF) channel inversion to the case where each receiver is equipped with multiple antennas. One of the limitation of the BD is that the sum rate does not grow linearly with the number of users and transmit antennas at low and medium signal-to-noise ratio regime, since the complete suppression of multi-user interference is achieved at the expense of noise enhancement. Also it performs poorly under imperfect channel state information. In this paper, we propose a generalized minimum mean-squared error (MMSE) channel inversion algorithm for users with multiple antennas to overcome the drawbacks of the BD for multiuser MIMO systems. We first introduce a generalized ZF channel inversion algorithm as a new approach of the conventional BD. Applying this idea to the MMSE channel inversion for identifying orthonormal basis vectors of the precoder, and employing the MMSE criterion for finding its combining matrix, the proposed scheme increases the signal-to-interference-plus-noise ratio at each user's receiver. Simulation results confirm that the proposed scheme exhibits a linear growth of the sum rate, as opposed to the BD scheme. For block fading channels with four transmit antennas, the proposed scheme provides a 3 dB gain over the conventional BD scheme at 1% frame error rate. Also, we present a modified precoding method for systems with channel estimation errors and show that the proposed algorithm is robust to channel estimation errors.

A new class of pseudo-random sequences from Mersenne numbers

A new class of pseudo random sequences is proposed that can be constructed from modulo-2 (mod 2) operations of two different maximal length sequences (m-sequences) where the period of the input sequences are Mersenne numbers. It is shown that the output sequences have certain properties to make these sequences effective in multi-user interference suppression and communication security.

MULTIUSER INTERFERENCE SUPPRESSION TECHNIQUES FOR DIRECT-SEQUENCE CDMA COMMUNICATION SYSTEMS

In this paper, several techniques for multi-user interference suppression from power-controlled direct-sequence CDMA systems are proposed and the emphasis is on the one-shot structure. The proposed schemes arise from the optimum detector that takes into account the existence of power-controlled chip-synchronous multi-user interference and white Gaussian noise. Restricting the multi-user interference to the power-controlled chip-synchronous case strongly reduces the complexity of the optimum detector. For more reduction in the complexity, some approximations of the obtained techniques are also considered. It is shown that in asynchronous CDMA systems and in the presence of white Gaussian noise, the proposed detectors outperform the correlator with comparable complexity

Simple MMSE Interference Suppression for Real and Rate-1/2 Complex Orthogonal Space-time Block Codes

Orthogonal space-time block codes (OSTBCs) are known to provide transmit diversity gain with negligible decoding complexity. In this paper, we present a single-stage MMSE multi-user interference suppression technique that exploits the temporal and spatial structure of OSTBCs, leading to simple linear processing. In particular, we show that MMSE-based detection can be implemented for real OSTBCs as well as the derived rate-1/2 complex OSTBCs, using simple linear processing that avoids computationally intensive matrix inversions.

Performance of multiantenna multicarrier direct-sequence code division multiple access using orthogonal variable spreading factor codes-assisted space–time spreading in time-selective fading channels

A downlink (base-to-mobile) multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) system employing multiple antennas at both the base station and each of the mobile terminals is investigated, when communicating over fast time-varying fading channels resulting in time-selective fading. In the considered multiantenna MC DS-CDMA, space–time spreading (STS) based on the family of orthogonal variable spreading factor (OVSF) codes is proposed in order to achieve the time diversity because of the time-selective fading, in addition to the transmit/receive diversity. In this contribution, the closed-form expressions for the single-user bit-error rate (BER) are derived, in order to gain insight into the achievable BER performance of the multiantenna MC DS-CDMA. The BER performance of the multiantenna MC DS-CDMA system is investigated, when communicating over correlated time-selective Rayleigh fading channels. The study and performance results show that the multiantenna MC DS-CDMA using OVSF codes-assisted STS constitutes a high-efficiency downlink space–time transmission scheme. It is capable of achieving the full diversity provided by the time-selective fading and multiple transmit/receive antennas. Furthermore, the proposed multiantenna MC DS-CDMA is capable of achieving a self-balance between the time diversity achieved and the multiuser interference suppression capability, when using low-complexity correlation detection.

Multistage Channel Estimation and Data Detection for Multi-Antenna CDMA Systems with Single Spreading Code Per User

A training-based vector channel estimation method has been proposed for single-user code-division multiple access (CDMA) systems in fast-varying correlated multipath fading channels. In this paper, we extend it in an iterative way to multiuser multiple-input multiple-output (MIMO) CDMA systems where both the transmitter and receiver have multiple antennas. In the training period, we propose to add the minimum mean square error (MMSE) front end before channel estimation to suppress multiuser interference (MUI) from substreams with difference spreading codes, so then we can get good initial vector channel estimation for each user. In the data transmission period, we proposed to add MMSE/parallel interference cancellation (PIC) front end to suppress MUI, interference suppression, and vector channel estimation in an iterative way. The perfect channel estimation is assumed in Liu et al., and the inter-play between channel estimation and multiuser detection is not discussed either. On the contrary, the novelty of the proposed method is that we add MMSE/PIC front end (in addition to matched filter) before channel estimation and we repeatedly switch between MMSE/PIC front end and channel estimation.

The Pathwise Semi-Blind Algorithm for Downlink DS-CDMA Systems Using Antenna Arrays

This paper presents a semi-blind algorithm for multiuser interference cancellation and fading amplitude estimation for downlink MIMO DS-CDMA systems with multipath fading channels. Taking advantage of the space-time information of the parametric multipath channel, the proposed algorithm first uses a space-time channel decoupler to suppress multiuser interference and then decomposes the channel into a set of parallel subchannels each containing the signal of the desired user on an individual multipath. Two criteria, the complementary orthogonal projection (COP) and the minimum variance distortionless response (MVDR), are employed by the space-time decoupler to achieve interference suppression and signal separation. The fading amplitudes can then be estimated from the eigen space of the output of the space-time channel decoupler. It follows that the signal of interest can be maximally combined in a pathwise manner and then differentially decoded.