Multiple-input Multiple-output Receiver Research Articles

Arbitrary Analog/RF Spatial Filtering for Digital MIMO Receiver Arrays

Traditional digital multiple-input multiple-output (MIMO) receivers that feature element-level digitization face high instantaneous dynamic range challenges in the analog/RF domain due to the absence of analog/RF spatial filtering. Existing analog/RF spatial notch filtering techniques are limited in their noise, linearity, and spatial filtering bandwidth performance. More importantly, only single spatial notches have been demonstrated, providing insufficient filtering in practical scenarios. We propose a frequency-translational arbitrary spatial filtering technique that features not only arbitrary spatial filtering response generation at baseband for the protection of the following analog-to-digital converters, but modulated baseband input impedance that can be translated by passive mixers to achieve arbitrary spatial filtering at RF as well. This technique allows the synthesis and independent steering of an arbitrary number of spatial notches, and the independent adjustment of notch depths. Current-mode operation leads to superior linearity performance and ultra-wideband rejection. A four-element 65-nm CMOS 0.1-3.1 GHz prototype MIMO receiver array shows arbitrary spatial response formation, more than 50-dB spatial rejection across all measured directions, and an ultra-wide 320-MHz 20-dB rejection bandwidth for a single-notch setting at 500-MHz local oscillator (LO) frequency. Formation of a single spatial notch only moderately degrades the equivalent single-element double-sideband noise figure from 2.1-3.7 dB to 3.4-5.8 dB. In the notch direction, +34 dBV in-band output-referred IP3 is measured, an improvement of 33 dB compared with outside-notch directions. A wireless demonstration shows the receiver array demodulating a weak spatial signal in the presence of two strong in-band spatial signals, verifying the arbitrary spatial filtering functionality.

Multilevel Coding Scheme for Integer-Forcing MIMO Receivers With Binary Codes

An integer-forcing (IF) linear multiple-input multiple-output (MIMO) receiver has recently been proposed, which is theoretically shown to achieve near capacity with almost the same complexity as that of conventional linear receivers. The key idea is that the receiver attempts to directly decode integer-linear combinations of codewords. To ensure that this sum-decoding operation is feasible, in previous works, lattice codes over $\mathbb {Z}_{q}$ were employed. Although those codes can attain good theoretical performance, however, its implementation complexity can be considerably high in practice, especially when $q$ is large to support high-order modulations. In this paper, we propose a practical multilevel coding scheme for IF MIMO, in which multilevel encoding composed of binary linear codes $(q = 2)$ in conjunction with the natural mapping is employed on the transmitter side and multistage decoding adapted to the IF operation is employed on the receiver side. The performance of the proposed scheme is extensively evaluated both analytically and numerically, showing that the gain of IF over conventional receivers is indeed achievable in practical settings with almost the same complexity. Our results imply that the proposed IF MIMO can be an attractive solution for the 5G communications due to its ability of supporting high spectral efficiency with low complexity.

Link to system interfacing for multiple input and multiple output wireless system using maximum likelihood receiver

In this study an accurate method of link to system (L2S) interfacing for multiple input and multiple output system with a maximum likelihood (ML) receiver is proposed. L2S interfacing is used in system level simulation in order to predict the receiver link level performance using lookup tables. L2S interfacing normally uses signal to noise ratio (SNR) values at each received symbol for calculating the quality of the received code-words. While SNR values for linear and iterative receiver are easily calculated, its evaluation for ML receiver is not straight forward. In this study the SNR values at the output of a ML receiver are related to that of single input multiple output receiver and a linear multiple input multiple output receiver. Both of which are easy to calculate. Through different compression schemes a single scalar parameter is evaluated which is a very good measure of the quality of received signal. The results for different compression techniques show a marked improvement in the mean square error between the predicted and the actual frame error rates.

Carrier Multiplexing Generalized Space Shift Keying Modulation with Low Decoding Complexity

In this paper, carrier multiplexing generalized space shift keying (CM-GSSK) transmission scheme with low decoding complexity is proposed for multiple-input multiple-output (MIMO) systems, using quadrature carriers to increase the spectral efficiency. The CM-GSSK transmission scheme allows two antennas to be active during the same time slot, where the information is conveyed only by the transmit-antenna index. In CM-GSSK transmission scheme, each antenna transmits quadrature carriers, whereas conventional generalized space shift keying (GSSK) transmits the same radio frequency carrier pulse. Unlike a traditional linear decorrelator which is designed for MIMO receiver, a low complexity linear decorrelator based decoder for CM-GSSK scheme is presented and its performance is analyzed. At the receiver, the linear decorrelator decouples the received signal, which in turn, it significantly reduces the decoding complexity. The bit error rate (BER) performance results and the complexity of the proposed low complexity decoding scheme is compared with the baseline SSK schemes to demonstrate its efficiency.

Performance analysis of adaptive DFE using set-membership binormalized data-reusing LMS algorithm for frequency selective MIMO channels

This paper addresses the concern of complexity involved with adaptive equalization in wireless systems operating over time-varying and frequency selective multiple-input multiple-output (MIMO) channels. Here, we propose a decision feedback equalizer using binormalized data-reusing least mean square (BNLMS) algorithm with set-membership filtering for MIMO channels. The performance of the equalizer is investigated for a MIMO receiver in a multi-path fading environment as experienced in the indoor and pedestrian environment. The equalizer performance is also studied for channels having higher delay and Doppler spread. The convergence issues, BER performance and tracking capabilities are examined through computer simulations. Moreover, the computational complexity issue for this MIMO equalizer is compared with other existing data-selective algorithm based techniques.

A novel Segregated K-Best detection algorithm for low complexity near optimal MIMO receivers

This paper addresses the problem of computational and hardware complexity in higher order constellation Multiple Input Multiple Output (MIMO) detectors. A novel Segregated K-Best detection (SKD) algorithm is proposed to serve as low complexity near optimal detector for MIMO receivers. The algorithm reduces detection complexity by choosing an optimal value of K depending upon the layer of traversal. This allows lesser number of nodes to be traversed leading to reduced complexity with only slight degradation in error rate performance. Hardware Descriptive Language (HDL) implementation of SKD is performed using ‘one symbol detection per cycle architecture’ and a compatible ‘sequential linear sort’ algorithm is proposed for sorting in SKD. The proposed design achieves a throughput as high as 802Mbps with latency of 19.83ns.

Random Access Scheme for Sporadic Users in 5G

Machine-type communication (MTC) devices usually have low-data rate, and in some applications, latency is critical. In long-term evolution, establishing a connection requires a relatively complex handshaking procedure. Such an approach is suitable for a system serving only a few high-activity users, but it becomes cumbersome for MTC traffic, where large amounts of low-activity users intermittently transmit a small number of packets. We propose a random access channel (RACH)-based scheme for the future 5G system that allows MTC users to send small packets within the random access burst. Device activity detection, channel estimation, authentication, and data decoding are performed simultaneously from the same access burst. In addition to the inherent reduction in energy consumption, the scheme eliminates the signaling overhead and creates more resources for data transmission. We have constructed an analytical framework for the detection performance of a multiple-input–multiple-output receiver in a frequency-selective channel. This has been validated with simulations, and results show that a one-shot correlate-and-cancel algorithm is sufficient for activity detection and channel estimation when the base station either employs multiple receive antennas or schedules multiple resource blocks for MTC RACH.

Iterative Receiver Combining IB-DFE with MRC for Massive MIMO Schemes

Abstract: Once we are moving to the 5G system it is imperative to reduce the complexity of massive MIMO (Multiple-Input, Multiple Output) receivers. This paper considers the uplink transmission using massive MIMO combined with SC-FDE (Single-Carrier with Frequency-Domain Equalization). We propose an iterative frequency-domain receiver merging IB-DFE (Iterative Block Decision-Feedback Equalizer) with MRC (Maximal Ratio Combining). We propose a novel approach to reduce the complexity of the receiver by avoiding matrix inversions while maintaining a level of performance very close to the Matched Filter Bound (MFB), which makes it an excellent option for 5G systems.

Neutralizing interferences in two‐hop amplify‐and‐forward MIMO relay systems

In this paper, we present the interference neutralization technique for two‐hop multiple‐input multiple‐output (MIMO) relay systems. It enables multiple MIMO transmitters (sources) to simultaneously transmit independent data streams to their MIMO receivers (destinations) without mutual interferences, thereby improving spectral efficiency of the systems. To neutralize the mutual interferences using multiple amplify‐and‐forward (AF) MIMO relays, we establish the sufficient condition for the antenna configuration in the MIMO relay networks, and provide a filter design technique for the AF MIMO relays. The proposed method increases sum rates of the systems linearly with the number of transmitters participating in simultaneous transmission. To improve the sum rates further, this method is combined with transmit power allocation using the water‐filling algorithm. In addition, it is shown that by employing the minimum number of relays required to meet the sufficient condition, the system cost for the proposed method can be reduced without compromising the sum rate performance severely. Finally, simulation results successfully demonstrate that by exploiting radio resources such as frequency and time efficiently, the proposed method achieves a higher sum rate than the existing techniques based on interference avoidance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Hardware and Energy-Efficient Stochastic LU Decomposition Scheme for MIMO Receivers

In this paper, we design a hardware and energy-efficient stochastic lower–upper decomposition (LUD) scheme for multiple-input multiple-output receivers. By employing stochastic computation, the complex arithmetic operations in LUD can be performed with simple logic gates. With proposed dual partition computation method, the stochastic multiplier and divider exhibit high computation accuracy with relative short length stochastic stream. We have designed and synthesized the stochastic LUD with CMOS 130-nm technology. According to the postlayout report, the hardware efficiency of the stochastic LUD is as high as $1.5\times $ compared with the exiting LUD methods, and the energy efficiency is also higher than the state-of-the-art LUD when the matrix dimension is $8\times 8$ and larger.

Performance and Complexity Evaluation of Iterative Receiver for Coded MIMO-OFDM Systems

Multiple-input multiple-output (MIMO) technology in combination with channel coding technique is a promising solution for reliable high data rate transmission in future wireless communication systems. However, these technologies pose significant challenges for the design of an iterative receiver. In this paper, an efficient receiver combining soft-input soft-output (SISO) detection based on low-complexity K-Best (LC-K-Best) decoder with various forward error correction codes, namely, LTE turbo decoder and LDPC decoder, is investigated. We first investigate the convergence behaviors of the iterative MIMO receivers to determine the required inner and outer iterations. Consequently, the performance of LC-K-Best based receiver is evaluated in various LTE channel environments and compared with other MIMO detection schemes. Moreover, the computational complexity of the iterative receiver with different channel coding techniques is evaluated and compared with different modulation orders and coding rates. Simulation results show that LC-K-Best based receiver achieves satisfactory performance-complexity trade-offs.

BER Performance Analysis and Comparison for Large Scale MIMO Receiver

Objective: Multiple Input Multiple Output (MIMO) low complexity CHEMP (Channel Hardening Exploiting Message Passing) receiver which utilizes the channel hardening in the large scale MIMO channel to reduce the complexity. Methods: The Channel Hardening refers that the off diagonal elements of HTH matrix become progressively weaker than the diagonal elements because of the channel gain matrix H size increases. It is used for detection and estimation. The proposed receiver uses Message Passing Detection (MPD) algorithm and the estimation HTH matrix. Findings: Hence, the proposed receiver gives better performance than the Minimum Mean Square Error (MMSE) and Subspace Marginalization with Interference Suppression (SUMIS) detectors since the MPD detection algorithm uses only the matrix multiplication and it does not need the matrix inversion. Improvements: The optimized Low Density Parity Check (LDPC) codes are used to provide the considerable improvement than LDPC cods.

Mismatched filter optimization for radar applications using quadratically constrained quadratic programs

This paper deals with the problem of optimal filter computation for specific radar applications.We consider here a method for finding the mismatched filter that minimizes the peak-to-sidelobe ratio. This method is based on a reformulation of the optimization problem as a convex quadratically constrained quadratic program (QCQP) and ensures that any found solution is a global solution of the problem. This formulation also enables the insertion of additional constraints, e.g., a constraint on the loss in processing gain of the optimal filter. We study in this context the robustness of the proposed filter to phase errors. Then, we propose to adapt this QCQP to deal with Doppler shifts and provide results for specific applications. Next, we investigate the possibility to use mismatched filters to reduce the high sidelobe level observed along the range axis of multiple-input multiple-output (MIMO) ambiguity functions produced by phase codes. We propose two MIMO receiver architectures that enable the integration of mismatched filters. The first architecture tries to minimize all autocorrelations and cross-correlations of the transmitted phase codes, while the second architecture computes mismatched filters adapted to the signals transmitted in different angular direction. The latter approach enables us to obtain a MIMO ambiguity function close to the perfect thumbtack shape.

Effect of Different Modulation Techniques Comparison of Linear MIMO Receivers

In wireless communication, Multiple-Input Multiple-Output (MIMO) is the most propitious technology that enhances the system capacity and data rate by using multiple antennas at the receiver and at the transmitter. Efficient signal detection at the receiver is complex task in MIMO systems. The computational complexity of equalization based linear detection algorithms such as Minimum Mean Square Error (MMSE) and Zero Forcing (ZF) is less than that of algorithmic schemes. The simulated results presented in this paper are using various MIMO system configurations from 2x2 to 8x8. The results are compared and analyzed on the basis of Bit Error Rate (BER) for M-QAM modulation techniques using MMSE, ZF reduced complexity algorithms under Rayleigh fading channel. Simulations results reveal that the MMSE detection offers better performance over ZF detection however for 64-QAM modulation both linear detection shows same performance.

Expectation Propagation Detection for High-Order High-Dimensional MIMO Systems

Modern communications systems use multiple-input multiple-output (MIMO) and high-order QAM constellations for maximizing spectral efficiency. However, as the number of antennas and the order of the constellation grow, the design of efficient and low-complexity MIMO receivers possesses big technical challenges. For example, symbol detection can no longer rely on maximum likelihood detection or sphere-decoding methods, as their complexity increases exponentially with the number of transmitters/receivers. In this paper, we propose a low-complexity high-accuracy MIMO symbol detector based on the Expectation Propagation (EP) algorithm. EP allows approximating iteratively at polynomial-time the posterior distribution of the transmitted symbols. We also show that our EP MIMO detector outperforms classic and state-of-the-art solutions reducing the symbol error rate at a reduced computational complexity.

MIMO DWDM System Using Uncooled DFB Lasers With Adaptive Laser Bias Control and Postphotodetection Crosstalk Cancellation

A proof-of-principle demonstration of a multiple input-multiple output (MIMO) dense wavelength division multiplexing (DWDM) system is reported. It uses standard uncooled distributed feedback lasers with intensity modulation-direction detection (IM-DD), in which the temperature of each laser is allowed to drift independently within a 50 °C temperature range. A feedback-based laser bias control algorithm is introduced to guarantee acceptable wavelength spacing and a postphotodetection minimum mean square error decoder is applied to cancel the interchannel crosstalk. The relative sensitivity of the MIMO receiver in both a random laser temperature drift scenario and a worst-case scenario are investigated by simulations in MATLAB. Experimental results for a 40-channel × 12.5 Gb/s DWDM system transmitting over 28 km of single-mode fiber with worst possible wavelength distribution prove the feasibility of the technique.

Analog joint source-channel coding over MIMO channels

Analog joint source-channel coding (JSCC) is a communication strategy that does not follow the separation principle of conventional digital systems but has been shown to approach the optimal distortion-cost tradeoff over additive white Gaussian noise channels. In this work, we investigate the feasibility of analog JSCC over multiple-input multiple-output (MIMO) fading channels. Since, due to complexity constraints, directly recovering the analog source information from the MIMO channel output is not possible, we propose the utilization of low-complexity two-stage receivers that separately perform detection and analog JSCC maximum likelihood decoding. We study analog JSCC MIMO receivers that utilize either linear minimum mean square error or decision feedback MIMO detection. Computer experiments show the ability of the proposed analog JSCC receivers to approach the optimal distortion-cost tradeoff both in the low and high channel signal-to-noise ratio regimes. Performance is analyzed over both synthetically computer-generated Rayleigh fading channels and real indoor wireless measured channels.

Analysis of MIMO Receiver Using Generalized Least Squares Method in Colored Environments

The classical detection techniques for multiple-input multiple-output (MIMO) systems are usually designed with the assumption that the additive complex Gaussian noise is uncorrelated. However, for closely spaced antennas, the additive noise is correlated due to the mutual antenna coupling. This letter analyzes an improved zero-forcing (ZF) technique for MIMO channels in colored environments. The additive noise is assumed to be correlated and the Rayleigh MIMO channel is considered doubly correlated. The improved ZF detector, based on the generalized least squares estimator (GLS), takes into account the noise covariance matrix and provides an unbiased estimator of the transmitted symbol vectors. We introduce some novel bounds on the achievable sum rate, on the normalized mean square error at the receiver output, and on the outage probability. The derived expressions are compared to Monte Carlo simulations.

Decorrelation MIMO Receiver for Block Fading Channels

In this paper, we propose a novel decorrelation receiver for multiple-input multiple-output (MIMO) block fading channels. The proposed design breaks the correlation between soft-decision-directed channel estimation (SCE) and data detection, and thus improves the performance of existing receivers that do not take such correlation into account. Computer simulations confirm that the decorrelation receiver yields excellent performance when applied to the Markov Chain Monte Carlo (MCMC) MIMO detector and the soft minimum mean-square-error (MMSE) MIMO detector.

Analog nonlinear MIMO receiver for optical mode division multiplexing transmission

The complexity and the power consumption of digital signal processing are crucial issues in optical transmission systems based on mode division multiplexing and coherent multiple-input multiple-output (MIMO) processing at the receiver. In this paper the inherent characteristic of spatial separation between fiber modes is exploited, getting a MIMO system where joint demultiplexing and detection is based on spatially separated photodetectors. After photodetection, one has a MIMO system with nonlinear crosstalk between modes. The paper shows that the nonlinear crosstalk can be dealt with by a low-complexity and non-adaptive detection scheme, at least in the cases presented in the paper.