Bell Laboratories Layered Space-Time Research Articles

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.

Adaptive Switching Hybrid Blast-STBC MIMO System

Fading in a wireless channel has negative effects on the performance of communication systems. Bell Laboratories layered space-time (BLAST) has been used to get a high data rate while space-time block codes (STBC) have been used to get a low bit error rate (BER) performance. Under deep faded channels, hybrid BLAST-STBC systems are considered as a trade-off between BLAST and STBC systems. By exploiting the benefits of both systems, a new method to represent a 4 × 4 multiple-input and multiple-output (MIMO) system is proposed and studied, in which the transmission process is carried out adaptively between both 4 × 4 VBLAST, Quasi-Orthogonal STBC (QOSTBC) and Hybrid systems according to the transmit links state. The proposed adaptive switching hybrid system (ASHS) reduces the total transmitted power, achieves the maximum throughput by obtaining the best BER. An adaptive switching transmission scheme using the strategy of measuring the transmit links fading is investigated as well. The simulated results are obtained in an environment of a 4 × 4 MIMO system using MATLAB platform where the total transmitting power is normalized to unity. The detections are done using the maximum likelihood (ML) receiver. The proposed ASHS system shows a lot of advantages such as maximum throughput is obtained in bad channel states, no additional transmit power is needed and no additional bandwidth is needed. Finally, under deep fading condition, the proposed ASHS transmission scheme obtains the best BER, reduces wasting the total transmitted power, achieves the maximum throughput and obtains the best BER.

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.

Improving Performance of Bell Labs Layered Space-Time Systems by Multiframe Space-Time Interleavers

Turbo-BLAST (T-BLAST) is a multiple-input multiple-output (MIMO) wireless communication system. It is based on three main concepts: Bell laboratories layered space-time (BLAST) architecture, random space-time interleaving, and the turbo principle. T-BLAST system has many advantages including high data rate, excellent performance, and low complexity. These advantages make T-BLAST one the most important choices for future wireless communication systems. In this article, the authors study the effect of the space-time interleaver on the performance of T-BLAST system. This interleaver is split into two separated stages, time interleaving followed by space interleaving. They show that, in a quasi-static channel, the enhancement in performance provided by the time interleavers is very small compared to the gain provided by space interleavers. They also propose a new technique to improve the system performance, called multiframe space-time interleaving (MUSTI). Simulation results show an improvement in performance up to 6 dB at BER=10-4 for a (2,2) configuration.

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.

A Novel Linear Antenna Synthesis for Linear Dispersion Codes Based on an Innovative HYBRID Genetic Algorithm

As far as taking-away of the symmetry constraints is concerned, as a scientifically symmetry problem, the global synthesis for antenna arrays that produce the desired radiation pattern is also a highly nonlinear optimization issue in fact. Besides this, the built criteria offer the reasonable power patterns. The consequent synthesis could be implemented by looking for a nominal pattern. When the criteria are already sufficient, it can simply do the whole synthesis process. To utilize multiple antennae, a method to choose a transmit antenna for the linear dispersion codes (LDC-TAS) is implemented in this paper. The authors used the max–min-post- signal to noise ratio (SNR) criteria to select these optimal transmitting antennae while this dependent, linear receiver is applied to the varying and slow channel. The simulated results illustrate that this max–min-post-SNR criterion outperforms the Bell Labs layered space time transmitting antenna selection (BLAST-TAS) applying the same spectral efficiency than space–time block codes (STBC)-TAS in the environment with low SNR. Furthermore, once the M antennae are selected under the selection criteria, a max–min-post-SNR rule, a novel linear antenna synthesis to linear dispersion codes on the basis of an innovative HYBRID (of mixed characters or solutions) genetic algorithm has been presented and evaluated to formulate and address the optimal problem to non-uniformly spaced and linear arrays. The restricted side-lobes level, the main-lobe width, and the shaped beam pattern are contemporarily concerned via maximizing a pretty suitable cost function through the innovational advanced genetic-algorithm-based algorithm. The method proposed in this paper can provide flexibility and a simple insertion of the a priori knowledge under a small computing pressure. At last, a computing simulation is completed well and the results are shown. It should be noticed that some extensions of the presented method could also be easily utilized without an obvious increase in the algorithm complexity.

Turbo-Space Time Block Coded and Turbo-Vertical Bell Laboratories Layered Space Time coded Wireless Communication: Which One is better to Use and under What Circumstances?

In this research, performance of Turbo-Space Time Block Coded and Turbo-Vertical Bell Laboratories Layered Space Time coded Multiple Input Multiple Output Wireless Communication System is compared and investigated to find which one is better under which circumstances. The Turbo Encoder accepts binary bits as input and generates turbo encoded bits as output which is sent to 64 QAM modulator. These 64 QAM Modulated symbols are further mapped using Space Time Block Code and Vertical Bell Laboratories Layered Space Time code for Turbo-Space Time Block Coded system and Turbo-Vertical Bell Laboratories Layered Space Time coded system respectively and then divided into several streams based on number of transmit antennas before transmission. It is found that there is 3 to 22 dB coding gain at 10-5 for using Turbo-STBC instead of using Turbo-VBLAST for 2 or 3 or 4 transmit antennas and 2 or 3 or 4 or 5 or 6 receive antennas. On the other hand, at low SNR STBC shows 1-2 b/s/Hz improvement in capacity compare to VBLAST but capacity declines significantly at high SNR for using STBC. It is also observed that VBLAST improves the capacity around 5 to 15 b/s/Hz at high SNR.

A C-V-BLAST spread spectrum massive MIMO NOMA scheme for 5G systems with channel imperfections

In this paper, a spread spectrum non orthogonal multiple access (NOMA) scheme with massive multiple input multiple output (MIMO) deployment is investigated. The proposed scheme utilizes a low complexity Vertical Bell Laboratories Layered Space Time (C-V-BLAST) receiver in an uplink setting with distributed single-antenna users and a co-located base-station with massive antenna array system. We study the performance of the proposed scheme under a variety of channel imperfections including imperfect channel estimation, channel correlation, and mutual coupling among antenna elements. Analytical evaluation of the system performance under these conditions is presented in terms of the group error probability and validated through extensive simulations. It is shown that the proposed spread spectrum NOMA scheme provides significant improvements in performance compared to conventional V-BLAST system in case of a large MIMO deployment under channel imperfections.

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.

Efficient Signal Detection Methods for High Mobility OFDM System with Transmit Diversity

In this paper, we propose two efficient signal detection methods for high mobility space–time block code based orthogonal frequency division multiplexing (OFDM). The first proposed method is based on order block decision feedback equalizer (OBDFE) which is the column norm ordering version of the conventional BDFE method. To improve the system performance further, we have proposed a hybrid OBDFE–MPD method by cascading the OBDFE method with a multistage parallel decoder (MPD). The advantage of the OBDFE–MPD method is that it does not need additional complexity as most of the computations are performed in the initial stage by the OBDFE method. These two proposed methods are compared with minimum mean square error (MMSE), block linear minimum mean square error (BLMMSE), block decision feedback equalizer (BDFE), vertical Bell laboratories layered space–time (VBLAST) and space alternating generalized expectation maximization (SAGE) in terms of performance and computational complexity. From the simulation results and computational complexity, it is shown that both the proposed OBDFE and OBDFE–MPD methods provide a great trade-off between performance and computational complexity for high mobility OFDM system with transmit diversity.

Performance Analysis of a Multi-layered SVD Based STBC System

Multiple-Input Multiple-Output transmission systems using orthogonal frequency-division multiplexing is a key solution in wireless communications. The performance of MIMO-OFDM systems can be improved using coding schemes such as Space–Time Block Coding (STBC), Singular Value Decomposition (SVD) and Vertical Bell Labs Layered Space–Time Architecture (VBLAST). In this paper we present a (4 × 4) cascaded STBC–SVD multi-layered encoder structured in a VBLAST architecture. The STBC output streams are SVD encoded to improve symbol error rate (SER) performance. The introduced system achieves both spatial multiplexing and diversity gains simultaneously and maintains reliable SER performance. We study the effect of ordering the output streams of the STBC before applying the SVD encoding. We show that there is an optimum ordering that guarantees a minimum overall SER. MATLAB® simulations show that the proposed system performs better over other conventional VBLAST systems. Moreover, we show that better performance is not associated with an increase in the computational complexity.

Cycled efficient V-BLAST GNSS ambiguity decorrelation and search complexity estimation

Decorrelation reduction and search techniques play important roles in solving integer ambiguities of global navigation satellite system (GNSS) positioning. This contribution focuses on these two issues and can mainly be divided into two parts. (1) An efficient strategy to realize the popular vertical Bell Labs layered space–time (V-BLAST) algorithm is studied. Then, a cycled efficient V-BLAST (ceV-BLAST) reduction algorithm is constructed. The decorrelation outcome of ceV-BLAST reduction is demonstrated by analysis to be stronger than LAMBDA and LLL. (2) A search complexity estimator which can give a priori estimation of the search complexity is proposed. This estimator evaluates the search nod number directly and turns out to follow the real search complexity better than other estimators of the same type. At the same time, it is very time efficient. Utilizing two sets of GNSS observation data, we compare ceV-BLAST and the new search complexity estimator with existing decorrelation algorithms and estimators, respectively. The results have confirmed our arguments.

Particle Filtering for Joint Symbol Detection, Frequency Offset and Channel Estimation in Time-Varying MIMO Channels with Multiple Frequency Offsets

We develop three methods for the joint symbol detection, frequency offset and channel estimation in time-varying multiple-input multiple-output channels with multiple frequency offsets between transmit and receive antennas. These methods are based on particle filtering. The first method utilizes the posterior proposal distribution (PD) to generate particles, which is optimal PD because it minimizes the variance of the importance weights, conditionally on the observations and past particles. Second, we develop an improved sampling strategy, which exploits the discrete nature of the symbol variable. The improved sampling strategy has same computational complexity as the posterior PD, while its performance is significantly improved. Finally, we derive a suboptimal complexity-reduced method, which utilizes the artificial sequential structure of the Bell-Labs layered space–time detection scheme to compress the sample space of symbol variable. Compared to the posterior PD, the computational complexity of the suboptimal method is largely reduced, while it still significantly outperforms the posterior PD. Simulation results are provided to illustrate the performance of these methods.

Performance Analysis of Massive Spatial Modulation MIMO in High-Speed Railway

For high-speed railway (HSR), an essential characteristic of the propagation channels is the specific spatial–temporal correlation caused by a dominant strong line-of-sight (LOS) component. Multiple-antenna gain is therefore far from being achieved due to this strong channel correlation. However, it is interesting to note that if the resulted intercarrier interference (ICI) is elaborately controlled, high mobility may decrease the channel correlation. Spatial modulation (SM) is one of the promising multiple-antenna technologies for wireless communication systems, which needs only the activation of one transmit antenna to convey information bits implicitly through the index of the active transmit antenna, in addition to conveying information bits through modulation symbols during transmission. In SM, ICI is avoided, which therefore helps in the implementation of the idea of decreasing channel correlation by increasing the velocity in an HSR scenario. In this paper, the performance of massive SM multiple-input multiple-output (MIMO) over a spatial–temporal correlated Rician fading channel is investigated under an HSR scenario. The impacts of velocity, Rician factor K, and signal-to-noise ratio (SNR) are discussed. In addition, the correlation factor and the correlation comparison function are defined as metrics of channel correlation. We theoretically find out that higher velocity makes the impact of temporal correlation more dominant, which weakens the influence of spatial correlation. In other words, spatial correlation can be weakened by high mobility. Our theoretical analysis and simulations further demonstrate that, with an appropriate scheme, massive SM MIMO outperforms Vertical Bell Laboratories Layered Space–Time (VBLAST), except at a lower SNR region with high velocity (usually more than 360 km/h). Consequently, massive SM MIMO is a promising solution within an appropriate range of velocity for HSR wireless communication systems.

A Brief Survey on V-Blast Detection in MIMO OFDM System

Multiple input multiple outputs-orthogonal frequency division multiplexing (MIMO-OFDM) is the key procedure for era correspondences frameworks. In this paper, a few identification calculations dependent upon MIMO-OFDM frameworks are quickly presented. Different input–multipleyield frameworks give an extremely swearing up and down to means to build the ghastly proficiency for remote frameworks. By utilizing orthogonal recurrence division multiplexing (OFDM), wideband transmission might be attained over recurrence particular blurring radio channels. Initially, in this paper, we present an improved vertical Bell Labs layered space–time (V-BLAST) recipient which considers the choice mistakes and second, give short evaluation of diverse calculation.

An improved scheme based on log-likelihood-ratio for lattice reduction-aided MIMO detection

Lattice reduction (LR)-aided detectors have been shown great potentials in wireless communications for their low complexity and low bit-error-rate (BER) performance. The LR algorithms use the unimodular transformation to improve the orthogonality of the channel matrix. However, the LR algorithms only utilize the channel state information (CSI) and do not take account for the received signal, which is also important information in enhancing the performance of the detectors. In this paper, we make a readjustment of the received signal in the LR domain and propose a new scheme which is based on the log-likelihood-ratio (LLR) criterion to improve the LR-aided detectors. The motivation of using the LLR criterion is that it utilizes both the received signal and the CSI, so that it can provide exact pairwise error probabilities (PEPs) of the symbols. Then, in the proposed scheme, we design the LLR-based transformation algorithm (TA) which uses the unimodular transformation to minimize the PEPs of the symbols by the LLR criterion. Note that the PEPs of the symbols affect the error propagation in the vertical Bell Laboratories Layered Space-Time (VBLAST) detector, and decreasing the PEPs can reduce the error propagation in the VBLAST detectors; thus, our LLR-based TA-aided VBLAST detectors will exhibit better BER performance than the previous LR-aided VBLAST detectors. Both the BER performance and the computational complexity are demonstrated through the simulation results.

MGF Based Approximate SER Calculation of SM MIMO Systems Over Generalized η − μ and κ − μ Fading Channels

Spatial modulation (SM) is a multiple input multiple output (MIMO) wireless communication system that gives better spectral efficiency without costing extra bandwith for the same signal constellation size. In an SM MIMO system with $$N_t$$Nt transmitting antennas, spectral efficiency increases by $$log_2(N_t)$$log2(Nt). The superior performance of SM systems over other MIMO systems like Alamouti Space-Time Block Codes and Vertical Bell Laboratories Layered Space-Time is already reported in the literature. In this paper, we analyzed the symbol error rate (SER) performance of an SM system in generalized $$\eta-\mu $$?-μ and $$\kappa - \mu $$?-μ fading channels for several modulation schemes. A closed form expression for approximate SER is derived using moment generating function (MGF) approach and the results are validated using Monte Carlo simulations. The approximate SER expression obtained in this communication is applicable for any fading channels whose MGF is known. The SER analysis over generalized fading channels can be easily deduced to various classical fading channels like Rayleigh, Rician, Nakagami-m and Nakagami-q fading channels by choosing appropriate values of $$\kappa $$?, $$\mu $$μ and $$\eta $$?.