Suppress Inter-user Interference Research Articles

Near-Field Modeling and Performance Analysis for Multi-User Extremely Large-Scale MIMO Communication

This letter studies the near-field modeling and performance analysis for multi-user extremely large-scale multiple-input multiple-output (XL-MIMO) communication. With the spherical wavefront phase modeling, and by taking into account the variations of signal amplitude and projected aperture across array elements, the performance of the three typical beamforming schemes are investigated, namely the maximal-ratio combining (MRC), zero-forcing (ZF), and minimum mean-square error (MMSE) beamforming. Compared to existing uniform plane wave (UPW) model where inter-user interference (IUI) can only be suppressed in angular domain, XL-MIMO enables a new degree-of-freedom (DoF) for IUI suppression by distance separation, even for users along the same direction. Simulation results are provided to validate the modeling and performance analysis of multi-user XL-MIMO communications.

Dimensionality reduction of interference subspace for multiuser massive MIMO null-space expansion

This paper proposes a dimensionality reduction of interference subspace to improve the interference suppression capability of null-space expansion (NSE) for multiuser massive multiple-input-multiple-output (MIMO) systems. The fundamental concept of the NSE is to nullify the interference subspace generated by the combined multiple past channel state information (CSI) vectors. It can suppress inter-user interference (IUI) leaked due to outdated CSI in a mobility environment. It is enabled by plentiful degrees of freedom (DoF) brought by massive antenna elements the base station has, and hence NSE can outperform existing channel prediction based precoding approaches. However, additive noise-induced CSI estimation error limits its effectiveness; expanded dimension of null-space cannot be appropriately spanned to interference subspace. The key idea of our new proposal is to extract principal interference subspace channel. Null-space can be appropriately expanded with reduced its dimension, and remaining DoF can be assigned to beamforming. It results in improving overall signal-to-interference-plus-noise power ratio (SINR) performance which is verified via numerical simulation.

Regularized Block Diagonalization Precoding Transmission Scheme Using Relay in NOMA

In Multiuser Multiple Input Multiple Output (MU-MIMO) system, Block Diagonalization (BD) and Regularized Block Diagonalization (RBD) are schemes which completely suppress Inter-User Interference (IUI). BD and RBD use the same number of RF chains and transmit antennas as the number of data streams in general. This paper proposes a RBD precoding transmission scheme using relay in Non-orthogonal Multiple Access (NOMA) system to reduce complexity of transmitter structure. The proposed scheme uses only half the number of RF chains and transmit antennas compared to the conventional RBD scheme. The number of Singular Value Decomposition (SVD) of the proposed scheme is also reduced compared to the conventional RBD, while Successive Interference Cancellation (SIC) is needed additionally. However, the proposed algorithm can achieve low computational complexity since SIC is simpler than SVD. However, the proposed scheme has poor BER performance compared to the conventional RBD. Therefore, further study is needed to increase the BER performance while the complexity is reduced.

Uplink Null-Space Expansion for Multiuser Massive MIMO in Time-Varying Channels Under Unknown Interference

This article proposes a novel postcoding design scheme for suppressing inter-user interference (IUI) and inter-cell interference (ICI) in uplink multiuser massive multiple-input multiple-output (MIMO) system in time-varying channel environments. In the uplink system, the base station (BS) designs postcoding weight based on estimated channel state information (CSI) to suppress IUI. When user terminals move, the estimated CSI is outdated because actual channels vary with time. This causes IUI and leads to degrading the system capacity. Besides, ICI extensively arises in multiuser massive MIMO systems since many users are simultaneously supported in each cell. The accuracy of CSI estimates is degraded since ICI contaminates the uplink pilot sequences from desired users. Adopting a weight design based on minimum mean square error (MMSE) criteria, we can suppress ICI adequately, and exploiting plentiful degrees of freedom (DoFs) of massive array, we can also suppress IUI even in time-varying channels by steering many nulls for one user based on null-space expansion (NSE) scheme. The computer simulations clarify that the proposed scheme has superior SINR performance in Rayleigh fading channel at low speed, low SIR, and high SNR regions while it is effective at almost all conditions in Rician fading channel.

Uplink Transmit Power Control for Single-Carrier Grouped FDMA with Iterative Multiuser Detection

We consider an uplink power allocation scheme for single-carrier frequency-division multiple access (FDMA) with iterative multiuser detection, called single-carrier grouped FDMA (SC-GFDMA). SC-GFDMA is a non-orthogonal scheme in which several users share a single time-frequency resource. Hence, the uplink signal of a user can be regarded as both a signal and a source of interference. The signal power of each user should be sufficiently high to ensure reliable signal detection and sufficiently low to suppress inter-user interference. That is, the transmit power of each user should be adjusted appropriately to achieve high spectral efficiency. In this context, a power control method for an uplink SC-GFDMA system is proposed by analyzing the signal-to-interference-plus-noise ratios of users sharing each time-frequency resource. In particular, the uplink spectral efficiency is improved by limiting the transmit power of each user according to a criterion derived using a semi-analytic method called signal-to-noise ratio-variance density evolution. Simulation results demonstrate that the proposed method can significantly increase the spectral efficiency of the system, even with a considerably reduced total transmit power.

An Auxiliary Antenna Based Inter-User Interference Mitigation Approach in Full-Duplex Wireless Networks

When a full-duplex (FD) base station (BS) serves an uplink and a downlink half-duplex (HD) users, the uplink user would produce the inter-user interference (IUI) on the downlink user. In this letter, an IUI suppression scheme is proposed based on the auxiliary antenna at the downlink user. A problem of maximizing the sum achievable rate of the uplink and downlink is formulated by adjusting the weighted vector at the downlink user with limited uplink and downlink transmit power. This problem is solved by two steps. First, the optimal weighted vector at the downlink user is derived. Second, the optimal downlink power is given for a fixed uplink power and the optimal uplink power is obtained by a search method. The single-cell simulation results show that the average achievable rate of the proposed IUI suppression scheme significantly outperforms the existing schemes especially when the cell radius is small and can nearly approach the performance of the ideal FD case with IUI perfectly suppressed.

An interuser interference suppression approach in full‐duplex wireless communications

AbstractConsidering that a full‐duplex network is composed of a full‐duplex base station (BS) and 2 half‐duplex users, one user transmits on the uplink channel and the other receives through the downlink channel on the same frequency. The uplink user will generate interuser interference (IUI) on the downlink user through the interference channel. In this paper, we propose a novel IUI suppression scheme when the BS knows the full channel state information. The main idea of this scheme is to retransmit the weighted uplink signal as soon as it has been received by the BS. For the narrowband case, we first assess the performance of the proposed scheme through simulation with residual self‐interference at the BS. Specially, we derive the closed‐form expression of the optimum weighted coefficient when self‐interference is perfectly canceled at the BS and then discuss the performance of the proposed IUI suppression scheme in practical considerations. Furthermore, the proposed IUI suppression scheme can be extended to the broadband case using a time‐domain weighted filter. Simulation results show the advantage over existing IUI suppression schemes.

Spectral Efficiency of Massive MIMO Systems With Multiple Sub-Arrays Antenna

In this paper, we study the achievable spectral efficiency (SE) for multi-user massive multiple-input multiple-output (MIMO) systems in a single cell, where the base station (BS) has the perfect channel state information and utilizes the maximum ratio transmission precoding. The channel model is built based on a finite dimensional mmWave channel by taking the azimuth angle into account and all users are assumed to have a random distribution in a circular-shaped cell. When the BS is deployed with a full uniform linear array (ULA) configuration, an analytical expression is derived by taking into account the expectation of the squared inner product between every two channel vectors that is viewed as inter-user interference. To effective suppress inter-user interference, we focus on studying the BS installing a multiple sub-arrays antenna configuration, in which all antennas are divided into three sub-ULA configurations to cover three regions of the cell, respectively. A closed-form expression on the inter-user interference is derived. Furthermore, we evaluate the performance of full ULA and three sub-ULA configurations and derive approximated expressions on the achievable SE. Numerical results reveal that the achievable SE of system increases with the number of antennas, while it approaches saturation in the high-SNR regime. Interestingly, it is also found that three sub-ULA configurations are able to suppressive user interference and their achievable SE is superior to full ULA configuration, which has a great potential of mmWave massive MIMO systems.

Massive MIMO for Full-Duplex Cellular Two-Way Relay Network: A Spectral Efficiency Study

This paper presents the new analysis of the applications of massive multiple-input-multiple-output (MIMO) in full-duplex (FD) cellular two-way relay networks, and sheds valuable insights on the interactions between massive MIMO, and relay and duplex modes. Practical scenarios are considered, where massive MIMO is deployed at the base station and the relay station. Based on generic relay modes, namely, antenna-selection-based decode-and-forward (DF) relay and signal-space alignment based amplify-and-forward (AF) relay, closed-form expressions for the asymptotic signal-to-interference-plus-noise ratios (SINRs) are derived. The difference between AF and DF in the FD mode is quantified, and so is that between FD and half-duplex (HD) under the two relay modes. With massive MIMO, the superiority of DF in the FD mode is confirmed in terms of spectral efficiency. The sufficient conditions for the FD mode to outperform the HD mode are identified. The effectiveness of massive MIMO in terms of self-loop interference cancellation and inter-user interference suppression is proved. All these insightful findings are corroborated by simulations.

Null-Space Expansion for Multiuser Massive MIMO Inter-User Interference Suppression in Time Varying Channels

Null-Space Expansion for Multiuser Massive MIMO Inter-User Interference Suppression in Time Varying Channels

Position-Based Limited Feedback Scheme for Railway MU-MIMO Systems

In future railway communications, the system architecture is highly likely to be based on the mobile relay structure. However, during the transition period, onboard passenger equipment can only directly connect to wayside public mobile networks to get wireless services. As an efficient technology to increase the capacity widely used in Long-Term Evolution (LTE) public mobile networks, multiuser multiple input–multiple output (MU-MIMO) requires channel state information (CSI) of users at base stations to suppress interuser interference, which poses a bandwidth burden on feedback links. Thus, how to reduce the MU-MIMO feedback load becomes an urgent problem. In railway scenarios, onboard passenger equipment of a user set almost has the same signal-to-noise ratio (SNR), which provides a new way to reduce the MU-MIMO feedback overheads. Accordingly, we propose a position-based limited feedback scheme for railway MU-MIMO systems, in which dedicated feedback resource positions are preassigned to codebook vectors. A resource position where users feed back channel quality indicators (CQIs) indicates a special codebook vector. Then, overheads due to precoding matrix index (PMIs) are saved. Even if bandwidth resources assigned to feedback positions may be insufficient to supply every user with a feedback chance, it still has little impact on the total capacity for whether the user with the largest CQI in an active user set is selected in highly populated railway scenarios. Moreover, a novel performance criterion called feedback efficiency is proposed. Simulation results demonstrate that the proposed scheme can achieve higher feedback efficiency compared with the conventional scheme.

A New Multi-User Beamforming Algorithm

In R9 version of LTE system, the double multi-user beamforming is proposed. To suppress inter-user interference of multi-user multiple input multiple output (MU-MIMO) system, a new algorithm is presented in this paper: on condition that current user eliminates the interference to other users, it designs its own transmit beamforming vector; if all users take such measures, the interference that each user suffers from others will be reduced to a minimum, which improves the performance of the system. Simulation shows that, as the number of user increases, the algorithm used in this paper can reduce the bit error rate (BER) of the system more obviously than the traditional signal-to-leakage-and-noise ratio (SLNR) algorithm.

Joint Space-Frequency Iterative Interference Suppression in Multiuser MIMO-OFDM Systems

In uplink multiuser multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems, inter-user interference includes co-channel interference (CCI) due to spatial multiplexing and inter-carrier interference (ICI) due to carrier-frequency offset (CFO). In this letter, a space-frequency joint processing scheme is proposed to suppress the two-dimensional interference alternatively and iteratively. Moreover, by the studies of convergence behavior of iterations, a sufficient condition for convergence is presented. The theoretical analysis and simulation results both show that this iterative scheme can effectively suppress inter-user interference with low complexity.

Blind equalization of MIMO systems based on orthogonal Constant Modulus Algorithm

This paper investigates adaptive blind source separation and equalization for Multiple Input Multiple Output (MIMO) systems. To effectively recover input signals, remove Inter-Symbol Interference (ISI) and suppress Inter-User Interference (IUI), the array input is first transformed into the signal subspace, then with the derived orthogonality between weight vectors of different input signals, a new orthogonal Constant Modulus Algorithm (CMA) is proposed. Computer simulation results illustrate the promising performance of the proposed method. Without channel identification, the proposed method can recover all the system inputs simultaneously and can be adaptive to channel changes without prior knowledge about signals.