Vertical Bell Labs Space Time Research Articles

A Unified Implementation Framework for Index Modulation Assisted MIMO Backscatter Communication

In this letter, a unified hardware implementation framework is designed for index modulation (IM) assisted multi-input multi-output (MIMO) backscatter communication, including space shift keying (SSK), spatial modulation (SM), SM assisted vertical bell labs space-time (SM-VBLAST), as well as SM assisted space-time block code (SM-STBC) schemes. Specifically, the concepts of SM-VBLAST and SM-STBC architectures are successfully applied into backscatter communication to balance an elegant tradeoff between spatial multiplexing and diversity gain. Then the coupled channel estimation and interference-cancellation-based signal detection algorithms are designed for hardware implementation. Furthermore, a unified IM-MIMO-based backscatter hardware prototype and experimental platform are designed. Experimental results verify that the proposed IM-MIMO implementation framework works efficiently and we can choose one proper IM-MIMO backscatter communication based on the required throughput, diversity gain as well as implementation complexity.

A Compressive Sensing Assisted Massive SM-VBLAST System: Error Probability and Capacity Analysis

The concept of massive spatial modulation (SM) assisted vertical bell labs space-time (V-BLAST) (SM-VBLAST) system [1] is proposed, where SM symbols (instead of conventional constellation symbols) are mapped onto the VBLAST structure. We show that the proposed SM-VBLAST is a promising massive multiple input multiple output (MIMO) candidate owing to its high throughput and low number of radio frequency (RF) chains used at the transmitter. For the generalized massive SM-VBLAST systems, we first derive both the upper bounds of the average bit error probability (ABEP) and the lower bounds of the ergodic capacity. Then, we develop an efficient error correction mechanism (ECM) assisted compressive sensing (CS) detector whose performance tends to achieve that of the maximum likelihood (ML) detector. Our simulations indicate that the proposed ECM-CS detector is suitable both for massive SM-MIMO based point-to-point and for uplink communications at the cost of a slightly higher complexity than that of the compressive sampling matching pursuit (CoSaMP) based detector in the high SNR region.

MIMO channels: optimizing throughput and reducing outage by increasing multiplexing gain

The two main aims of deploying multiple input multiple out (MIMO) are to achieve spatial diversity (improves channel reliability) and spatial multiplexing (increase data throughput). Achieving both in a given system is impossible for now, and a trade-off has to be reached as they may be conflicting objectives. The basic concept of multiplexing: divide (multiplex) transmit a data stream several branches and transmit via several (independent) channels. In this paper, we focused mainly on achieving spatial multiplexing by modeling the channel using the diagonal Bell Labs space time scheme (D-BLAST) and the vertical Bell Labs space time architecture (V-BLAST) Matlab simulations results were a lso given to further compare the advantages of spatial multiplexing.

Computation of System Performance of MIMO Technique in Communication Channel using V-BLAST Method.

In order to improvement both system performances and data rate Multiple Input Multiple Output techniques play an important role in transmission system. A number of techniques are used to do the needful work for performance improvement in MIMO systems belongs to different block codes, apart from that BLAST architecture are used Such as Diagonal Bell laboratories layered space-time (D-BLAST), Vertical Bell Labs Space-Time Architecture (V-BLAST) method. This work defines the performance improvement using V-BLAST technique in Multiple Input Multiple Output detector. Here we discuss the concept of Multiple Input Multiple Output with BLAST architecture. Depends upon the Bit Error Rate and Frame Error Rate, the comparison is made with the existing methods.

Compressed-Sensing Assisted Spatial Multiplexing Aided Spatial Modulation

Spatial-multiplexing aided spatial modulation (SMx-SM) is proposed, which intrinsically amalgamates the concept of vertical bell labs space-time (V-BLAST) and SM to attain a high transmission rate, despite its low number of radio frequency (RF) chains at the transmitter. Specifically, in the SMx-SM scheme, the transmit antennas are partitioned into groups and the SM technique is applied individually to each group. Furthermore, low-complexity threshold-aided compressive sensing-based and message passing-based detectors are derived for our SMx-SM system. Our simulation results show that the proposed SMx-SM system exhibits a better performance despite its lower complexity than the conventional generalized spatial modulation system. More importantly, the proposed SMx-SM system is capable of providing considerable performance gains over the V-BLAST system at the same number of RF chains and throughput. Finally, an upper bound is derived for the average bit error probability, which is confirmed by our simulation results.

Optimization of Scalable Broadcast for a Large Number of Antennas

In this paper, for a system incorporating a large number of antennas, we address the optimal space–time coding of multimedia scalable sources, which require unequal target error rates in their bitstream. First, in terms of the number of antennas, we analyze the behavior of the crossover point of the outage probability curves for the vertical Bell Laboratories space–time (V-BLAST) architecture with a linear or a maximum-likelihood receiver, and orthogonal space–time block codes (OSTBCs). We prove that, as the number of antennas increases with the transmission data rate fixed, the crossover point in outage probability monotonically decreases. This holds for any data rate employed by the system and is valid over propagation channels such as spatially correlated Rayleigh or Rician fading channels, as well as independent and identically distributed Rayleigh channels. We next show that, over such propagation channels with a large number of antennas, those analytical results can be used to simplify the computational complexity involved with the optimal space–time coding of a sequence of scalable packets, with no performance degradation.

Performance and efficiency analysis of THP algorithms: A practical perspective

As an attractive interference cancellation (IC) technique, Tomlinson–Harashima precoding (THP) has been investigated thoroughly in theory. Several high performance THP variants have been proposed, e.g., sorted QR decomposition (SQRD), Cholesky decomposition, vertical Bell Laboratories space time (V-BLAST) and lattice reduction aided THPs. From a practical perspective, however, limited hardware implementations have been reported in the literature so far. To bridge the progress gap between the theory and the practice, we present a comprehensive analysis of these THP variants in terms of performance and implementation efficiency in this paper. We first evaluate their bit-error rate (BER) performance under perfect and imperfect channel state information (CSI) scenarios. Subsequently, the emphasis is put on their implementation efficiency, including the computational complexity, the numerical precision requirement and the parallelism potential. Our analysis shows a wide trade-off space exists between the performance and the implementation efficiency in different THP variants, which is especially valuable for hardware designers to implement cost-efficient architectures biased towards practical systems.

Performance analysis of spatial multiplexing MIMO-OFDM system with different equalisers and guard intervals

Multiple-input multiple-output MIMO system is a very popular solution in the field of wireless communications, in order to improve the capacity and reliability of radio link. Nevertheless, during any transmission over fading channel, the performance of MIMO system is degraded due to the inter symbol interference ISI. The combination of orthogonal frequency division multiplexing MIMO-OFDM and the use of equalisation at the reception have become very effective to eliminate the ISI and reduce the imperfection of the channel. The optimal maximum likelihood ML equaliser suffers from high computational complexity. In this context, we propose the combination of vertical bell labs space time VBLAST multiplexing and ordered successive interference cancellation OSIC equaliser in MIMO-OFDM system, whose performance is compared with different equalisers, in particular zero forcing ZF, minimum mean square error MMSE, and ML using cyclic prefix CP and zero padding ZP intervals in Rayleigh time-selective fading channel. The simulation results show that the performance of ZF/MMSE-OSIC equaliser with ZP-ODFM is close to the ML with a low complexity and it works better as compared to other algorithms.

Extensive Survey on MIMO Technology using V-BLAST Detection Technique

Wireless communication using Multiple Input Multiple Output (MIMO) systems increases efficiency for a given total transmits power. Here investigate a novel approach to perform decodingorder optimization in the vertical Bell Labs layered space-time (V-BLAST) planning. Allowing for instantaneous transmission of multiple, independently encoded data streams, the V-BLAST transmit-receive method applies to the uplink of a multi-user communication system. A multi-antenna receiver decodes data streams consecutively, trade with inter-stream interference by means of cancelling and nulling; interference from before decoded streams is cancelled by subtraction, and residual interference is nulled by linear equalization. The order in which the streams are decoded can have a visible impact on system presentation. Multiple Input Multiple Output (MIMO) channels can offer high capability to wireless systems and the capacity increases linearly with the number of antennas. There are many schemes that can be applied to MIMO systems such as space time block codes, space time trellis codes, and the Vertical Bell Labs Space-Time structural design (V-BLAST). We study the broad-spectrum MIMO system, the general VBLAST structure, and the Successive Interference Cancellation (SIC) Zero-Forcing (ZF) detectors in this paper.

Low-Complexity Signal Detection for Generalized Spatial Modulation

Generalized spatial modulation (GSM), in which only part of the transmit antennas are activated in each time slot, was recently proposed as a trade-off between spatial modulation (SM) and vertical Bell laboratories space-time (V-BLAST). Although the maximum likelihood (ML) detector is able to achieve the optimal performance, its exhaustive search leads to intractable computational complexity. In this letter, an efficient signal detection algorithm, termed ordered block minimum mean-squared error (OB-MMSE), is proposed for achieving near-ML performance with low complexity. On one hand, an ordering algorithm is proposed to sort the possible transmit antenna combinations (TACs). On the other hand, the possible signal vector for each ordered TAC is detected by block-MMSE equalization. Simulation results show that the proposed OB-MMSE detector provides similar performance to ML with near 80% reduction in complexity.

Performance of Layered Steered Space–Time Codes in Wireless Systems

Layered Steered Space–Time Codes (LSSTC) is a recently proposed multiple-input multiple-output (MIMO) system that combines the benefits of vertical Bell Labs space–time (VBLAST) scheme, space–time block codes (STBC) and beamforming. In this paper, we derive the error performance and capacity of a single-user LSSTC system. The analysis is general enough to any layer ordering and modulation schemes used. In addition, the derived analysis is general for any LSSTC structure in which layers may have different number of antenna arrays and may be assigned power according to any power allocation. Furthermore, we analytically investigate the tradeoff between the main parameters of the LSSTC system, i.e., diversity, multiplexing and beamforming. Our results give recursive expressions for the probability of error for LSSTC which showed nearly perfect match to the simulation results. Results have also revealed the possibility of designing an adaptive system in which it was shown that combining beamforming, STBC, and VBLAST has better performance than VBLAST at high SNR range.

Effects of applying realistic channel conditions on performance prediction of UCA-VBLAST-MIMO systems

Recently, many realistic spatially and temporally clustered channel models were developed to be applied in the simulations of multiple input multiple output (MIMO) systems. IEEE 802.11n standard channel model includes spatio-temporal fading correlation effects and accounts for six various real propagation profiles. These profiles represent variety of propagation scenarios for indoor environments. This paper presents the impact of applying various channel model conditions on the link performance of Vertical Bell Laboratories Space-Time detection (VBLAST-MIMO) systems that employ Uniform Circular array (UCA). Also, capacity and channel estimation accuracy for this system are investigated under different channel conditions. The effect of varying the SNR on the Channel State Information (CSI) error and capacity for UCA-MIMO systems are included. Training based techniques such as Least Square (LS), scaled least square (SLS) and minimum mean square error (MMSE) methods and relaxed MMSE (RMMSE) are considered for estimating channel properties. It is found that the presence of spatial correlation can help to improve the Channel estimation accuracy at low SNR for UCA-VBLAST-MIMO system under different spatial correlation conditions.

Optimized Power Allocation for Layered-Steered Space-Time Codes

Layered Steered Space-Time Codes (LSSTC) is a recently proposed multiple-input multiple-output system that combines the benefits of vertical Bell Labs space-time (VBLAST) scheme, space-time block codes and beamforming. We suggest a new downlink scheme employing LSSTC with asymmetric power allocation, by assuming that the user feeds the BS with the average signal-to-noise ratio per VBLAST layer through the uplink feedback channel. The motivation behind proposing such a system is to enhance the error performance by assigning power to the layers in an optimal manner. We refer to the system proposed as the optimal power allocation LSSTC (OPA-LSSTC). Our analysis is general such that it includes asymmetric layered systems in which each layer may have different number of antennas and also the power can be assigned to layers asymmetrically.

Hybrid-ARQ for layered space time MIMO systems with channel state information only at the receiver

The authors investigate hybrid automatic repeat request (H-ARQ) schemes for spatially multiplexed multiple-input multiple-output (MIMO) systems with channel state information available only at the receiver. In particular, the authors compare the multiple H-ARQ scheme and the single H-ARQ scheme with repetition. The authors first propose a system model for symbol detection for the multiple H-ARQ processes, and then discuss joint and separate detection algorithms for both multiple H-ARQ and single H-ARQ. Simulation results show that with linear detection the single H-ARQ outperforms multiple H-ARQ in the high signal-to-noise ratio region. With the vertical Bell Labs space-time (V-BLAST) architecture, multiple H-ARQ always outperforms single H-ARQ. Additionally, joint detection always outperforms separate detection.

Effects of inaccurate training-based minimum mean square error channel estimation on the performance of multiple input–multiple output Vertical Bell Laboratories Space-Time zero-forcing receivers

The authors investigate the effects of an imperfect channel estimate, rendered through the employment of a practical, online training-based minimum mean square error estimator, on uncoded multiple input-multiple output Vertical Bell Laboratories Space-Time architecture with a zero-forcing receiver in the presence of uncorrelated frequency-non-selective Rayleigh block fading. The post-processing signal to interference plus noise ratio and its probability distribution function will be derived using no approximation. Exact closed-form expressions will be provided for the average symbol probability of error for M-ary PAM modulation. For quadrature phase shift keying (QPSK) modulation, the symbol error probability is derived in the form of an integral, which has an analytical solution only when the number of receive antennas equals or exceeds that of the transmit antennas by one and may otherwise be numerically calculated. The average outage probability will be exactly calculated. All this is accomplished by an approximation-free mathematical approach and by taking into account the fundamental limitations between the accuracy of the channel estimate and the channel capacity. Perfect agreement is seen to exist between our analysis and Monte Carlo simulations.

On error analysis and distributed phase steering for wireless network coding over fading channels

Network coding notions promise significant gains in wireless networks' throughput and quality of service. Future systems employing such paradigms are known to be also highly scalable and resilient to node failure and churn rates. We propose a simple framework where a single relay listens to two nodes transmitting simultaneously over the same band in the presence of Nakagami-m fading. For this multiple-access channel (MAC), we derive in closed-form the exact bit error rate of antipodal signaling with maximum-likelihood detection. As the MAC is the bottleneck in error of the overall system, this provides a good performance measure of the aggregate architecture. Using the new error expressions derived, we then propose a simple closed-loop cooperation strategy where via a ternary feedback from the relay node, significant gains in signal to noise ratio at the relay can be achieved. Our novel error analysis method is applicable to a number of other systems such as the vertical Bell labs spacetime (V-BLAST) scheme and synchronous multi-user systems.

Re-scalable V-BLAST MIMO system for FPGA

The development of a re-scalable hardware implementation of a V-BLAST (Vertical Bell Labs Space–Time) multiple input multiple output system for future wireless communications systems is described. Re-scalability will support rapid prototyping of such systems. A floating-point model of the re-scalable system is constructed to guide the development of a fixed-point model, and subsequently a re-scalable hardware implementation. The system uses the Gauss–Jordan elimination method to perform channel matrix inversion and altering the division-by-zero threshold in this matrix inversion process is shown to have a significant effect on bit error rate performance results. The re-scalable hardware implementation is described in a hardware description language in the form of an intellectual property block and several V-BLAST systems are synthesised onto field programmable gate arrays.