Vertical Bell Laboratories Layered Space-time Research Articles

Spatial Multiplexing Aided OTFS With Index Modulation

In this paper, spatial multiplexing aided orthogonal time-frequency space with index modulation (OTFS-IM) is conceived, which combines the benefits of both OTFS-IM and vertical-bell laboratories layered space-time (VBLAST) techniques. Specifically, in the proposed VBLAST-OTFS-IM, information bits are divided into groups, each of which is modulated by OTFS-IM before being transmitted via different antennas. This allows the proposed system to fully exploit the spatial multiplexing gain. To further analyze its theoretical performance gain over the original OTFS-IM, we summarize the mathematical input-output relations of OTFS-IM and VBLAST-OTFS-IM in the form of equivalent channel matrices. Based on that, the ABEP upper bounds are derived for both original OTFS-IM and VBLAST-OTFS-IM systems by exploiting the moment-generating function (MGF) to bypass the dismantling of the sparse structure of OTFS-IM. Finally, the superiority of VBLAST-OTFS-IM and the validity of the derived ABEP upper bounds are verified by our simulation results.

Integrated Spatial Modulation and STBC-VBLAST Design toward Efficient MIMO Transmission.

In this contribution, the concept of spatial modulation (SM) is firstly integrated into the structure of space-time block codes (STBC)-aided vertical Bell-labs layered space-time (VBLAST) systems, in order to strike a balanced tradeoff among bit error ratio (BER), spectral efficiency and computational complexity. First of all, in order to enhance the BER performance of STBC-VBLAST, we advocate an effective transmit power allocation (TPA) scheme with negligible implementation costs, while dividing the STBC and VBLAST layers with alleviated interference, so as to facilitate combination with SM. Then, we further utilize the unique structure of SM for enhancing the spectral efficiency of original STBC-VBLAST, wherein the information is conveyed by not only the amplitude/phase modulation (APM) symbols but also the antenna indices. In addition, constellation sets of STBC symbols are specifically designed to be rotated to make full use of the degrees of freedom. Finally, the performance advantages of the above-mentioned structures over traditional STBC-VBLAST are demonstrated by the theoretical derivation of a closed-form expression for the union bound on the bit error probability for various spectral efficiencies, and they are supported by simulation results.

The Achievable Rate Analysis of Generalized Quadrature Spatial Modulation and a Pair of Low-Complexity Detectors

Generalized quadrature spatial modulation (GQSM) seamlessly amalgamates the generalized spatial modulation (GSM), quadrature spatial modulation (QSM) and vertical Bell Laboratories layered space-time (V-BLAST) techniques. In contrast to traditional multiple-input multiple-output (MIMO) schemes transmitting information bits only through the constellation defined on the complex plane, GQSM transmits additional information bits implicitly by selecting the transmit antenna (TA) activation pattern. The philosophy of QSM is that of separating the indices of the real and the imaginary parts of the transmit symbols, which increases the attainable throughput. In this paper, we analyze the inherent benefits of GQSM in terms of throughput. More specifically, we first derive the achievable rate expression of the recent GQSM scheme and unveil the condition for GQSM to approach the maximum rate. Furthermore, we compare the rate of the GQSM scheme to that of other transmission schemes and reveal the conditions for the GQSM’s maximum throughput to exceed that of the benchmark schemes. Simulation results show that when the number of TAs is 40 and quadrature phase shift keying (QPSK) is adopted, the rate of the GQSM scheme may reach 150% of that of V-BLAST. Additionally, a pair of low-complexity detectors are conceived-one based on ordered successive interference cancellation (OSIC) and another one on the orthogonal matching pursuit (OMP) algorithm.

Performance Evaluation of VBLAST and Linear Receivers for mmWave MIMO Systems with Ray-Tracing Channel Models

In this paper, the performance of a millimeter wave (mmWave) Multi-Input Multi-Output (MIMO) system is investigated using low complexity receivers. The receivers include linear Maximum Ratio Combiner (MRC), linear Zero Forcing (ZF) receiver, or linear Minimum Mean-Square Error (MMSE) receiver, in addition to ZF Vertical Bell Laboratories Layered Space-Time (ZF-VBLAST). A MIMO channel model based on a ray-tracing approach and the uniform theory of diffraction has been used. The effect of increasing the number of rays used in the channel model is investigated on the performance of all receivers. For all the scenarios, it has been found out that the ZF-VBLAST structure provides the best symbol-error-rate performance followed by the linear MMSE, then the ZF receiver, and finally the MRC receiver. The trade-off paid for achieving better performance is the increased receiver complexity. The system’s performance is compared under a conventional statistical channel model and a ray-based channel model for a fifth-generation (5G) mobile radio system. It is noted that these models do not accurately characterize the specific environment, hence resulting in an optimistic estimate of the system performance. Finally, the ray-tracing channel model is modified to account for the impact of the presence of trees within the environment. The results show that the performance degradation due to the presence of trees is between 2 to 5 dB for ZF and MMSE receivers, respectively.

BLAST PERFORMANCE IN MIMO WIRELESS COMMUNICATION SYSTEMS

Recently, a new detection algorithm for the Vertical Bell Laboratories Layered Space Time (V-BLAST) system, which we call Enhanced-V-BLAST, or simply E-V-BLAST, was proposed. V-BLAST has demonstrated very high spectral efficiency, there is a wide gap between the original V-BLAST algorithm and the Maximum Likelihood (ML) algorithm. Recently, some algorithms have been presented to make narrower this gap. In a new detection algorithm (Enhanced (E) V BLAST) for V-BLAST system was presented which showed significantly better performance and flexibility than the original V-BLAST detection. The E-V-BLAST algorithm gets closer to the optimum detection Maximum Likelihood (ML) algorithm by making decisions based on multiple symbols. The Enhanced (E)-V-BLAST has two parameters which can be adjusted to achieve a desired performance and complexity trade-off. In the present paper, we analyze the performance of EV-BLAST as a function of the two inherent adjustable parameters of E-V-BLAST. On the basis of this analysis, we obtain some useful characteristics of the E-V-BLAST algorithm which allow one to achieve the desired performance and complexity trade-off.

MIMO Detectors: A Comprehensive Performance Analysis

Multiple-input multiple-output (MIMO) systems are increasingly becoming popular due to their ability to multiply data rates without any expansion in the bandwidth. This is critical in this era of high-data rate applications but limited bandwidth. MIMO detectors play an important role in ensuring effective communication in such systems and as such the performance of the following are compared in this paper with respect to symbol error rate (SER) versus signal-to-noise ratio (SNR): maximum likelihood (ML), zero forcing (ZF), minimum mean square error (MMSE) and vertical Bell laboratories layered space time (VBLAST). Results showed that the ML has the best performance as it has the least Symbol Error Rate (SER) for all values of Signal to Noise Ratio (SNR) as it was 91.9% better than MMSE, 99.6% better than VBLAST and 99.8% better than ZF at 20db for a 2x2 antenna configuration., it can also be deduced that the performance increased with increase in number of antenna for all detectors except the V-BLAST detector.

Comparison and Analysis of Sub-optimal performance of OFDM/SDMA uplink System that use Conventional Multiuser Detection Techniques

The major challenge in the practical accomplishment of OFDM/SDMA system depends on the efficient implemen- tation of a multiuser detection (MUD) technique that separates the spatially multiplexed signal streams. Several algorithms for MIMO detection for spatially-multiplexed signals have been developed till today. The MIMO MUDs that are mostly used in previous research works and practically used are minimum mean squared error (MMSE), decorrelator (ZF), Vertical-Bell laboratories layered space-time (V-BLAST), successive inter- ference cancellation (SIC) and maximum likelihood detection (MLD). MMSE and ZF are linear MIMO detection techniques, while the remaining procedures are non linear techniques. All MUD techniques in general can be explained as a solution to a quadratic optimization problem in most cases. In this work, basic principles of ZF, MMSE, ZF-OSIC, MMSE-OSIC and ML have been explained briefly and a comparison of their performances have been done. Although the detection techniques evolved so far are matured in theory, their implementation in a real-time scenario is still challenging. It is analyzed in this paper that the poor BER results of sub-optimal detection method in comparison to MLD is due to bad channel effects.

Optimality of Linear MIMO Detection for 5G Systems via 1-Opt Local Search

Multiple input multiple output (MIMO) symbol detection problem belongs to non-deterministic polynomial acceptable hard combinatorial optimization (CO) class. One of the key trials in design of MIMO scheme is to develop a low complexity detection algorithm without much compromise in performance. Detection approaches proposed in the literature can be split into non-linear and linear algorithms. Vertical Bell-Labs Layered Space Time (V-BLAST) and Sphere Decoder (SD) are non-linear methods used for extracting transmitted data; whereas, Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) detections are comparatively in complex and effectual linear techniques. In this work, the heuristic 1-Opt local search method used for solving computationally hard combinatorial optimization problems is applied to the ZF and MMSE detection algorithms. First, simple MIMO decoding using ZF and MMSE is accomplished to find the estimated symbol then the transmitted symbol is calculated using the heuristic 1-opt approach by means of the estimated symbol. Simulation results demonstrate that 1-opt search when applied to the ZF and MMSE displays better bit error rate (BER) performance than the simple ZF and MMSE detectors. It is also verified through simulations that the proposed 1-Opt based detectors display better BER performance as compared to the complex nonlinear VBLAST and SD at considerably reduced complexity. Hence, the proposed detectors are appropriate for effective hardware implementations.

ENHANCED V-BLAST PERFORMANCE IN MIMO WIRELESS COMMUNICATION SYSTEMS

We have presented performance analysis of E-V-BLAST and according to this analysis, we found some useful characteristics of the E-V-BLAST algorithm for performance and complexity trade-off. Increasing S is applying ML detection with depth T for some most error likely signals. Increasing T is improving the ML detection with depth T. Increasing T will not affect so much to the performance of E-V-BLAST at high SNR. The importance of increasing T depends on S. Recently, a new detection algorithm for the Vertical Bell Laboratories Layered Space Time (V-BLAST) system, which we call Enhanced-V-BLAST, or simply E-V-BLAST, was proposed. In the present paper, we analyze the performance of E-V-BLAST as a function of the two inherent adjustable parameters of E-V-BLAST. On the basis of this analysis, we obtain some useful characteristics of the E-V-BLAST algorithm which allow one to achieve the desired performance and complexity trade-off.

A novel signal detection algorithm of multiple-input multiple-output Vertical-Bell Laboratories Layered Space-Time for underwater acoustic networks based on the improved minimum mean square error

Multiple-input multiple-output is a commonly used technology supporting for high-rate transmission over frequency-selective fading channels with multiple antennas. Vertical-Bell Laboratories Layered Space-Time is a detection method of a multiple-input multiple-output system, which establishes a direct correspondence between antennas and layers. Studies demonstrate that multiple-input multiple-output Vertical-Bell Laboratories Layered Space-Time is a meaningful way for underwater acoustic networks of high performance. However, considering the hardware constraints and energy consumption, achieving a trade-off between the bit error ratio and complexity is a crucial issue for underwater acoustic networks of multiple-input multiple-output Vertical-Bell Laboratories Layered Space-Time systems. This article proposes a novel signal detection algorithm of multiple-input multiple-output Vertical-Bell Laboratories Layered Space-Time. First, we address the unitary matrix of the underwater acoustic channel by LDLHdecomposition. Second, we order the detection sequence based on the permutation matrix. Third, we detail the implementation of interference cancelation and slice processing. Finally, we perform experiments for comparing the bit error ratio, energy consumption, processing delay, and complexity of the proposed algorithm with zero-forcing Vertical-Bell Laboratories Layered Space-Time, minimum mean square error Vertical-Bell Laboratories Layered Space-Time, and maximum likelihood Vertical-Bell Laboratories Layered Space-Time. Results indicate that our algorithm maintains bit error ratio and the processing delay to that of maximum likelihood Vertical-Bell Laboratories Layered Space-Time algorithm. However, it reduces the energy consumption, which achieves a good trade-off between performance and complexity. This work supports on constructing underwater acoustic networks of multiple-input multiple-output Vertical-Bell Laboratories Layered Space-Time system.

Partial Tree Search Assisted Symbol Detection for Massive MIMO Systems

In the era of the fifth generation (5G) communication networks, massive multiple-input multiple-output (MIMO) systems demand even lower computation complexity and power consumption while catching up with good detection performance. In this paper, a low-complexity nonlinear detection algorithm is proposed for massive MIMO systems, which is based on partial tree search and successive interference cancellation (SIC). The proposed scheme allows us to expedite the detection process by coping with the transmit symbols group by group. As compared to vertical-Bell laboratories layered space time (V-BLAST), the major breakthrough of computation reduction lies in the fact that the partial tree search can assist the detection process to avoid the inversion of the detection matrix required in each recursion of the SIC process. Both computational complexity analysis and simulation results show that our proposed algorithm not only significantly reduces computational complexity, but also has better bit error rate (BER) performance.

NOMA With Zero-Forcing V-BLAST

In this study, power-domain non-orthogonal multiple access (NOMA) is combined with zero-forcing (ZF) vertical Bell Labs layered space-time (V-BLAST) technique. Motivated by the fact that the successive interference cancellation (SIC) is a pivotal element in either technique, we thoroughly investigate the impact of SIC on inter-user and inter-layer interference. A two-user downlink scenario is investigated where a multi-antenna base station with no instantaneous channel state information simultaneously communicates with two users each with multiple antennas. The average sum rate of the considered system is analytically derived in an exact form. Correspondingly, the power allocation value on each substream is optimized such that the average sum rate is maximized. We show that when the classical power-domain NOMA idea is incorporated into the ZF V-BLAST algorithm, the far user cannot completely cancel inter-layer interference. Nonetheless, the proposed approach turns out to yield an average sum rate performance near to that of a higher-complexity method based on maximum likelihood detection.

Reconfigurable Intelligent Surface-Empowered MIMO Systems

Reconfigurable intelligent surface (RIS)-assisted communications appear as a promising candidate for future wireless systems due to its attractive advantages in terms of implementation cost and end-to-end system performance. In this article, two new multiple-input multiple-output (MIMO) system designs using RISs are presented to enhance the performance and boost the spectral efficiency of state-of-the-art MIMO communication systems. Vertical Bell Labs layered space-time (VBLAST) and Alamouti's schemes have been considered in this article and RIS-based simple transceiver architectures are proposed. For the VBLAST-based new system, an RIS is used to enhance the performance of the nulling and canceling-based suboptimal detection procedure as well as to noticeably boost the spectral efficiency by conveying extra bits through the adjustment of the phases of the RIS elements. In addition, RIS elements have been utilized in order to redesign Alamouti's scheme with a single radio frequency signal generator at the transmitter side and to enhance its bit error rate (BER) performance. Monte Carlo simulations are provided to show the effectiveness of our system designs and it has been shown that they outperform the reference schemes in terms of BER performance and spectral efficiency.

Two-Source Asymmetric Turbo-Coded Cooperative Spatial Modulation Scheme with Code Matched Interleaver

This paper proposes, for the first time, a two-source asymmetric turbo-coded-cooperative spatial modulation (SM) scheme over the slow Rayleigh fading channel. As in any coded cooperative communication, the interleaver plays a vital role in mitigating the harsh effect of the wireless channel. Therefore, the code matched interleaver (CMI) is effectively used in the proposed design. The simulated results reveal that the bit error rate (BER) performance of the proposed coded cooperative communication system outperforms the asymmetric turbo-coded non-cooperative scheme under identical conditions. This prominent performance improvement has been made possible due to the joint asymmetric turbo decoding at the destination node. Furthermore, to check the effectiveness of the proposed scheme, we have also developed a two-source asymmetric turbo-coded cooperative scheme based on the vertical bell labs layered space-time (VBLAST), incorporating the CMI as the suitable benchmark. It is observed that the proposed scheme employing SM has a better BER performance than the VBLAST scheme under identical conditions.

BER Performance of Spatial Modulation Systems Under a Non-Stationary Massive MIMO Channel Model

In this paper, the bit error rate (BER) performance of spatial modulation (SM) systems is investigated both theoretically and by simulation in a non-stationary Kronecker-based massive multiple-input-multiple-output (MIMO) channel model in multi-user (MU) scenarios. Massive MIMO SM systems are considered in this paper using both a time-division multiple access (TDMA) scheme and a block diagonalization (BD) based precoding scheme, for different system settings. Their performance is compared with a vertical Bell labs layered space-time (V-BLAST) architecture based system and a conventional channel inversion system. It is observed that a higher cluster evolution factor can result in better BER performance of SM systems due to the low correlation among sub-channels. Compared with the BD-SM system, the SM system using the TDMA scheme obtains a better BER performance but with a much lower total system data rate. The BD-MU-SM system achieves the best trade-off between the data rate and the BER performance among all of the systems considered. When compared with the V-BLAST system and the channel inversion system, SM approaches offer advantages in performance for MU massive MIMO systems.

Improvement of Symbol Error Rate Performance in Spatial Multiplexing Systems Using Transmit Antenna Selection

In this paper, we consider Mt×M system (Mt > M), where Mt and M are the numbers of antennas at the transmitter and receiver, respectively. We select M out of Mt transmit antennas using two different antenna selection schemes. In scheme 1, we select the subset of M antennas out of total $$(\begin{array}{l}{M_{t}} \\{M}\end{array})$$ subsets. In the selected subset, the minimum SNR is maximum compared to minimum SNR of all the remaining subsets. In scheme 2, Mt available transmit antennas are divided into Mtg disjoint groups of successive antennas, where Mtg = Mt/N. It means that there are N antennas in each group, where N ≤ M. Further both Mt and M are divisible by N and the total possible combinations of available groups are given $$(\begin{array}{l}{M_{tg}} \\{C}\end{array})$$ Then we select the subset of M antennas out of total $$(\begin{array}{l}{M_{tg}} \\{C}\end{array})$$ subsets. In the selected subset, the minimum SNR is maximum compared to minimum SNR of all the remaining subsets. In this scheme, N and C are chosen to meet the requirements of M selected antennas for transmission. After antenna selection, the resulting system will be M×M. We use Minimum Mean Square Error (MMSE) Vertical Bell Laboratories Layered Space Time (VBLAST) detection at the receiver for both the antenna selection schemes. We present MIMO Symbol Error Rate (SER) versus MIMO Symbol SNR using simulations for M-QAM constellations with Rayleigh fading channels. We have compared the performance of the considered systems with prevailing high complexity schemes ML and MMSE Improved VBLAST. The considered scheme 1 with MMSE VBLAST outperforms the prevailing schemes while scheme 2 with MMSE VBLAST provides similar performance in a wide range of SNR compared to prevailing schemes. However, the number of feedback bits used in scheme 2 is less as compared to scheme 1. There is a tradeoff between the SER performance and the number of required feedback bits. As N decreases, scheme 2 performance starts moving towards the performance of scheme 1. Both the systems provide the diversity gain in the fading channel.

Investigation of error performance in network coded MIMO-VBLAST wireless communication systems

Abstract Paper aims to enhance the performance of bit error rate (BER) in wireless communication based on the multiple-input multiple-output (MIMO) system of vertical Bell laboratories layered space-time (VBLAST) algorithm. The VBLAST algorithm uses zero-forcing (ZF) and the minimum mean square error (MMSE) to evaluate the BER of wireless communication. MIMO VBLAST techniques function as an adaptive filter and can minimize the interference and multipath fading in the received signal of the channel. Physical layer network coding (PNC) is a new technique used to exploit the spatial diversity of the MIMO VBLAST system to improve the throughput and performance of wireless communication. The bit-error-rate (BER) of proposed VBLAST MIMO with PNC with binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation over the additive white Gaussian noise and Rayleigh fading channel are analyzed. The performance of both BPSK and QPSK modulation in two and four antennas are compared. From the simulation results, it was found that the proposed scheme MIMO VBLAST PNC has a 45.2 % higher BER performance compared to the traditional MIMO scheme with an increase in the BER using MMSE and ZF respectively in both two and four antennas.

Optimal Massive MIMO Detection for 5G Communication Systems via Hybrid n-Bit Heuristic Assisted-VBLAST

Being increasingly spectral and energy efficient, massive multiple-input multiple-output (MIMO) is envisaged as a potential technology for fifth generation (5G) wireless communication networks. Radio spectrum has become a scarce resource in wireless communications and consequently imposes excessive cost on the high data rate transmission. Several linear and non linear detection techniques such as Zero-Forcing (ZF), Minimum Mean Square Error (MMSE), and Vertical Bell-Labs Layered Space Time (VBLAST) have been introduced. The purpose of such schemes is to mitigate the signal detection problems which are based on trade-offs between the bit error rate (BER) performance and computational complexities. The challenge in the design of massive-MIMO systems is developing less complex and efficient detection algorithms. The problem in building a receiver for massive-MIMO is to de-correlate the spatial signatures on the receiver antenna array. In this paper, we propose a novel algorithm viz: Hybrid n-Bit Heuristic Assisted-VBLAST (HHAV) to perform an optimum decoding. We have simulated this structure in dynamic Rayleigh fading channel. We have also evaluated the AMP algorithm with two threshold functions which include AMP with ternary distribution (AMPT) and AMP with Gaussian distribution (AMPG). Numerical results confirm that HHAV algorithm performs significantly better than the in vogue aforementioned detection systems as introduced in recent years.

Fast group detection for massive MIMOs

In this study, the authors consider symbol detection at the receiver of the base station for uplink massive multiple-input multiple-output (MIMO) systems over a fading channel, in which the base station uses a large number of antennas to serve many users. First, the authors review the existing detection methods such as the minimum mean square error and Vertical-Bell Laboratories Layered Space Time (V-BLAST). In addition, because the bit error rate (BER) performance of V-BLAST is close to that of the optimal method, the authors describe the procedures of the V-BLAST in detail. Then, to achieve a satisfactory trade-off between the BER performance and the computational complexity for practical implementation in massive MIMO systems, the authors propose a fast group-based symbol detection scheme. They also derive the expressions needed to select the symbol indices of a group for detection. Our simulation results and complexity analysis show that the performance of the proposed scheme is close to that of the V-BLAST algorithm with a significant saving in computational complexity.

Improved VBLAST MAP: A Novel Point-to-Point Symbol Detection Algorithm for MIMO Wireless Communication Systems

A novel point-to-point symbol detection algorithm in multiple input multiple output (MIMO) system is proposed. This algorithm is an augmentation of two popular algorithms, namely, vertical Bell laboratories layered space-time (VBLAST) and maximum a posteriori probability (MAP). Here, layers are distinguished or ordered based on the a posteriori probabilities of output symbols and not on signal-to-noise ratio (SNR). For each layer, a set of a posteriori probabilities is computed for all output symbols using all possible signal constellations. The layer corresponding to the output symbol having minimum a posteriori probability is selected first from the set of a posteriori probabilities for detection by doing the comprehensive search over all the possible signal constellations. Then, the remaining layers are detected by the conventional VBLAST MAP technique. The relationship of MIMO symbol error rate (MIMO SER) versus MIMO symbol SNR is presented using simulations for 16x16 MIMO systems and 16-QAM constellation. The results show that the proposed algorithm outperforms conventional VBLAST MAP and improved VBLAST algorithms.