Vertical Bell Laboratories Layered Space-time Research Articles

New Trellis Code Design for Spatial Modulation

Spatial modulation (SM), in which multiple antennas are used to convey information besides the conventional M-ary signal constellations, is a new multiple-input multiple-output (MIMO) transmission technique, which has recently been proposed as an alternative to V-BLAST (vertical Bell Labs layered space-time). In this paper, a novel MIMO transmission scheme, called spatial modulation with trellis coding (SM-TC), is proposed. Similar to the conventional trellis coded modulation (TCM), in this scheme, a trellis encoder and an SM mapper are jointly designed to take advantage of the benefits of both. A soft decision Viterbi decoder, which is fed with the soft information supplied by the optimal SM decoder, is used at the receiver. A pairwise error probability (PEP) upper bound is derived for the SM-TC scheme in uncorrelated quasi-static Rayleigh fading channels. From the PEP upper bound, code design criteria are given and then used to obtain new 4-, 8- and 16-state SM-TC schemes using quadrature phase-shift keying (QPSK) and 8-ary phase-shift keying (8-PSK) modulations for 2,3 and 4 bits/s/Hz spectral efficiencies. It is shown via computer simulations and also supported by a theoretical error performance analysis that the proposed SM-TC schemes achieve significantly better error performance than the classical space-time trellis codes and coded V-BLAST systems at the same spectral efficiency, yet with reduced decoding complexity.

Energy efficiency of virtual MIMO transmission schemes for cluster-based wireless sensor networks

In this paper, a cluster-based virtual multiple-input multiple-output (MIMO) transmission architecture is proposed for energy-constrained wireless sensor networks. In the proposed architecture, instead of using cluster members as cooperative nodes, multiple cluster heads cooperate to form virtual antenna array so that MIMO transmission can be implemented. According to the MIMO techniques used in this architecture, two different schemes, vertical Bell Laboratories layered space-time (V-BLAST) based cluster heads cooperative transmission (VCHCT) and space time block code (STBC) based cluster heads cooperative transmission (SCHCT), are developed. Based on the communication energy consumption model, the overall energy consumption model for both VCHCT and SCHCT are derived. Detailed comparison between these two schemes and the original low-energy adaptive clustering hierarchy (LEACH) is performed to investigate the performance of these two schemes. Simulation results not only verify the theoretical analysis but also show that the two schemes have their specific application scenarios. When the sink is far from the sensor area, SCHCT scheme is much more energy efficient than LEACH and VCHCT scheme even if it consumes additional inter-cluster communication energy. When the distance to sink is near the sensor area, VCHCT is preferable.

Low complexity antenna selection for V-BLAST systems with OSIC detection

Multiple-input multiple-output (MIMO) systems have an advantage of spectral efficiency compared to single-input single-output systems, which means that the MIMO systems have significantly higher data throughput. The V-BLAST (Vertical Bell Laboratories Layered Space Time) scheme is a popular transceiver structure which has relatively good performance. In the V-BLAST scheme, ordered successive interference cancellation (OSIC) technique was proposed as a possible efficient detection method in terms of performance and complexity. However, MIMO systems suffer from high complexity and implementation cost. As a practical solution, a technique called antenna selection has been introduced. Since the existing literature considered only the capacity-based selection, we develop an optimal selection method for V-BLAST scheme using OSIC detection with respect to error rate performance in this article. Its complexity is shown to be proportional to the fourth power of the number of transmit antennas. To reduce the complexity without significant performance degradation compared to the optimal selection method, a near-optimal selection method is also proposed. Simulation results show that the proposed selection method is very close to the performance of optimal selection.

Improved ICI Mitigation Scheme over Time-varying Channels for High-Mobility OFDM Systems

Based on the space alternating generalized expectation maximization (SAGE) technique, and the ordered serial interference cancellation (OSIC) algorithm, an improved low-complexity inter-carrier interference (ICI) mitigation scheme, named SAGE-OSIC, is proposed for high mobile orthogonal frequency division multiplexing (OFDM) systems, where the subcarriers are updated in series, according to the order of the decreasing signal to interference plus noise ratio (SINR) or signal to noise ratio (SNR). The computational complexity is investigated, and simulation studies are concluded over multipath fading and rapidly time-varying channels. It is indicated that the proposed SAGE-OSIC scheme significantly outperforms the existing low-complexity ICI mitigation methods based on SAGE, without any increase in the computational complexity, especially for the large Doppler shifts in highly mobile environments. Furthermore, it can also be concluded that the performance of the proposed SAGE-OSIC approaches that of the vertical Bell laboratory layered space-time (VBLAST) scheme, which demands very high computation.

Performance Analysis of ZF and MMSE Equalizers for MIMO Systems: An In-Depth Study of the High SNR Regime

This paper presents an in-depth analysis of the zero forcing (ZF) and minimum mean squared error (MMSE) equalizers applied to wireless multiinput multioutput (MIMO) systems with no fewer receive than transmit antennas. In spite of much prior work on this subject, we reveal several new and surprising analytical results in terms of output signal-to-noise ratio (SNR), uncoded error and outage probabilities, diversity-multiplexing (D-M) gain tradeoff and coding gain. Contrary to the common perception that ZF and MMSE are asymptotically equivalent at high SNR, we show that the output SNR of the MMSE equalizer (conditioned on the channel realization) is ρmmse = ρzf+η\ssrsnr, where ρzf is the output SNR of the ZF equalizer and that the gap η\ssrsnr is statistically independent of ρzf and is a nondecreasing function of input SNR. Furthermore, as \ssr snr\ura ∞, η\ssrsnr converges with probability one to a scaled F random variable. It is also shown that at the output of the MMSE equalizer, the interference-to-noise ratio (INR) is tightly upper bounded by [(η\ssrsnr)/(ρzf)]. Using the decomposition of the output SNR of MMSE, we can approximate its uncoded error, as well as outage probabilities through a numerical integral which accurately reflects the respective SNR gains of the MMSE equalizer relative to its ZF counterpart. The e-outage capacities of the two equalizers, however, coincide in the asymptotically high SNR regime. We also provide the solution to a long-standing open problem: applying optimal detection ordering does not improve the D-M tradeoff of the vertical Bell Labs layered Space-Time (V-BLAST) architecture. It is shown that optimal ordering yields a SNR gain of 10log10N dB in the ZF-V-BLAST architecture (where N is the number of transmit antennas) whereas for the MMSE-V-BLAST architecture, the SNR gain due to ordered detection is even better and significantly so.

Soft‐output MMSE V‐BLAST receiver with MMSE channel estimation under correlated Rician fading MIMO channels

ABSTRACTFor wireless multiple‐input multiple‐output (MIMO) communications systems, both channel estimation error and spatial channel correlation should be considered when designing an effective signal detection system. In this paper, we propose a new soft‐output MMSE based Vertical Bell Laboratories Layered Space‐Time (V‐BLAST) receiver for spatially‐correlated Rician fading MIMO channels. In this novel receiver, not only the channel estimation errors and channel correlation but also the residual interference cancellation errors are taken into consideration in the computation of the MMSE filter and the log‐likelihood ratio (LLR) of each coded bit. More importantly, our proposed receiver generalizes all existing soft‐output MMSE V‐BLAST receivers, in the sense that, previously proposed soft‐output MMSE V‐BLAST receivers can be derived as the reduced forms of our receiver when the above three considered factors are partially or fully simplified. Simulation results show that the proposed soft‐output MMSE V‐BLAST receiver outperforms the existing receivers with a considerable gain in terms of bit‐error‐rate (BER) performance. Copyright © 2011 John Wiley & Sons, Ltd.

MVDR‐combining‐aided diversity and spatial multiplexing for MIMO multi‐cellular networks with cochannel interference

ABSTRACTTwo multiple‐input multiple‐output (MIMO) schemes (a diversity scheme and a spatial multiplexing scheme) that employ the minimum variance distortionless response (MVDR) combining are proposed for multi‐cellular networks with cochannel interference. With the receive diversity provided by the MVDR combining, the proposed diversity scheme can be benefited by both the transmit diversity and the receive diversity, also, the proposed spatial multiplexing scheme can be benefited by both the receive diversity and the spatial multiplexing. The proposed MIMO schemes do not require the space‐time coding or the successive interference cancellation, thus they can result in less computational complexity than space‐time block code (STBC) and vertical‐Bell Labs layered space‐time (V‐BLAST). We show that the capacity of the proposed diversity scheme is close to or larger than that of STBC for the noise‐corrupted case and is much larger than that of STBC for the interference‐corrupted case. We also show that the capacity of the proposed spatial multiplexing scheme can be much larger than that of V‐BLAST for the interference‐corrupted case and the noise‐corrupted case, and the proposed spatial multiplexing scheme can achieve good compromise between diversity and spatial multiplexing. Copyright © 2011 John Wiley & Sons, Ltd.

The Behaviour of Vertical Bell Laboratories Layered Space-Time Algorithm Combined with Multiuser Detection Schemes in Wireless Communication System

This paper provides the performance analysis of multiuser Vertical Bell Laboratories Layered Space-Time (V-BLAST) system receiver structures for Multiple-input Multiple-Output (MIMO) channel at a base station with assumption of perfect channel estimation and perfect timing delay estimation. In MIMO channels the receivers such as decorrelator, Minimum Mean Square Error (MMSE) and Multistage Parallel Interference Cancellation (MPIC) receiver outperform the conventional receiver. Withal, since the multiple antenna interference led to a strong impact on the performance degradation of a multistage interference cancellation receiver, the performance of MPIC receiver was highly degraded based on system loading.

A Novel Recursive Algorithm for Efficient ZF-OSIC Detection in a V-BLAST System

To reduce the implementation complexity of the Vertical Bell Labs layered space-time (V-BLAST) systems with respect to the zero-forcing (ZF) criterion, a computationally efficient recursive algorithm is proposed. A fast implementation of the proposed algorithm is developed and its complexity is analyzed in detail. The proposed algorithm matches the ZF-OSIC detection well, and its three significant advantages can be demonstrated by analyses and simulations. Firstly, its speedups over the conventional ZF-OSIC with norm-based ordering, the original fast recursive algorithm (FRA) and the fastest known algorithm (FKA) in the number of flops are 1.58, 2.33 and 1.22, respectively. Secondly, a much simpler implementation than FRA and FKA can be expected. Finally, the storage requirements are lower than those of FRA and FKA. These advantages make the proposed algorithm more efficient and practical.

An Improved Square-Root Algorithm for V-BLAST Based on Efficient Inverse Cholesky Factorization

A fast algorithm for inverse Cholesky factorization is proposed, to compute a triangular square-root of the estimation error covariance matrix for Vertical Bell Laboratories Layered Space-Time arch...

MIMO Systems Based on Modulation Diversity

This letter proposes a new approach to achieve the maximum diversity gain in the vertical Bell Laboratories Layered Space-Time (V-BLAST) system over multiple-input multiple-output (MIMO) Rayleigh channels. First, we will briefly review the modulation diversity scheme based on real-valued multidimensional rotated constellations that has been proposed to obtain high diversity orders for single-input single-output (SISO) systems. Then, this letter extends the modulation diversity scheme to V-BLAST MIMO systems in order to achieve the maximum diversity gain without additional power or bandwidth consumption. The proposed method is particularly suitable for MIMO applications which employ channel codes with high rate in order to support high spectral efficiency.

Joint BLAST-STTC for MIMO-OFDM System

This study focuses on improving MIMO-OFDM systems by combining a wireless communication architecture known as vertical BLAST(bell laboratories layered space-time) or V-BLAST and STTC(space time trellis coding). In this paper, the combination is done by introducing STTC in each V-BLAST layer. Moreover, this architecture uses multiple antennas that are grouped into small number of antennas which makes it less complex to decode by decoding every group. Whereas, in traditional V-BLAST, all the antennas form one group and they are decoded together at the receiver, therefore, this increases the complexity as the number of antennas is getting high. We compare the bit error rate performance of this system with MIMO-OFDM that uses convolutional coding instead of STTC. Under the same spectral efficiency, the simulation results prove that joining V-BLAST with STTC improves MIMO-OFDM systems performance.

Rectangle blocking matrices based unitary multistage Wiener reduced-rank joint detection algorithm for multiple input multiple output systems

Traditional equalization algorithms for multiple input multiple output (MIMO) systems suffer from high complexity and low convergence rate. So an improved adaptive reduced-rank joint detection algorithm of multistage Wiener filter (MSWF) based on rectangle blocking matrices is proposed. The MSWF is implemented by the correlation subtraction algorithm (CSA) structure and is called unitary multistage Wiener filter (UMSWF). The new scheme adopts rectangle submatrix as blocking matrix, which is chosen from the square blocking matrix for UMSWF. The proposed algorithm can reduce the size of the observation data vectors step by step in the forward recursion decomposition of UMSWF. Thus, the computational complexity is reduced and the convergence rate is increased. Theoretical analysis and simulation results show that this improved adaptive reduced-rank joint detection algorithm of UMSWF based on rectangle blocking matrix has better performance such as lower complexity and faster convergence rate. In particular, simulations are conducted in the vertical-Bell Labs layered space-time (V-BLAST) system which adopts BPSK modulation, where 4 and 8 antennas are equipped at the transmitter and receiver, respectively. Compared with traditional equalization algorithm based on UMSWF, our new method can achieve the same BER performance at high SNR with only 0.5 times that of computational complexity.

An efficient VLSI architecture for 4 × 4 16-QAM sorted QR-factorisation based V-BLAST decoder

This paper presents a practically realisable VLSI architecture for a 4 × 4 16-QAM MIMO wireless communication system using the Vertical Bell Labs Layered Space-Time (V-BLAST) detection scheme. The proposed implementation employs the QR-factorisation technique. The design and optimisation of the pre-decoder block are carried out using the COordinate Rotation DIgital Computer (CORDIC) processors. In order to avoid the numerical problems associated with Back Substitution (BS) based Symbol Interference Cancellation (SIC), a modified BS-SIC architecture that eliminates the need for division and multiplication is proposed. Not only does this substantially reduce the hardware cost, but also enjoys improved numerical stability. As the decoder hardware design can also be simplified by rendering it oblivious to the power normalisation in the transmitter side of the MIMO wireless system, we have designed a matching compensation unit at the receiver. The resulting VLSI architecture was implemented on an Altera Stratix Field Programmable Gate Array (FPGA) platform and on a 0.18 μm Application Specific Integrated Circuits (ASIC) platform. Detection throughput ratings of 149 Mbps and 212 Mbps were achieved. However, the lower hardware complexity of the BS-SIC based decoder architecture comes at the cost of a degradation in the Bit Error Rate (BER) performance with respect to the original higher complexity V-BLAST. Therefore, we also propose a novel parallel decoding scheme that is aimed at improving the system BER. This novel scheme allows for a compromise between the hardware overhead and the BER performance. As the hardware complexity is increased, the performance approaches the original V-BLAST limit.

A Power Efficient Baseband Engine for Multiuser Mobile MIMO-OFDMA Communications

In this paper, the authors present a configurable and power efficient multiuser MIMO-OFDMA baseband processor for uplink mobile communications. To solve the carrier frequency offset (CFO) problem in multiuser transmission, an inter-carrier interference-based (ICI-cancellation-based) CFO estimator is implemented based on an iterative search criterion of minimum signal-to-interference-noise (SINR) ratio. Compared to the state-of-the-art methods, the proposed CFO estimator is more robust to transmission configurations (MIMO and multiuser) and CFO variations. Moreover, the authors propose an efficient architecture that saves 78% of the hardware complexity compared to the direct implemented architecture by employing Taylor series expansion for ICI/multiple-access interference (MAI) cancellation. Meanwhile, a 2-D linear channel estimator is also proposed to assist the CFO estimator and track the time-variant multipath channel. Two kinds of MIMO detector, vertical Bell Laboratory layered space-time (V-BLAST) and V-BLAST with maximum likelihood (V-ML), are adopted to minimize output latency and achieve the best ML bit-error-rate (BER) performance. An ASIC fabricated by 0.13 μm 1P8M CMOS technology is measured with 2.31 Mbps/mW power efficiency and less than 1.5 dB implementation loss. In addition, the whole transceiver is integrated and verified by a system-on-chip (SoC) platform to demonstrate its efficacy.

Trellis Coded Spatial Modulation

Trellis coded modulation (TCM) is a well known scheme that reduces power requirements without any bandwidth expansion. In TCM, only certain sequences of successive constellation points are allowed (mapping by set partitioning). The novel idea in this paper is to apply the TCM concept to the antenna constellation points of spatial modulation (SM). The aim is to enhance SM performance in correlated channel conditions. SM considers the multiple transmit antennas as additional constellation points and maps a first part of a block of information bits to the transmit antenna indices. Therefore, spatial multiplexing gains are retained and spectral efficiency is boosted. The second part of the block of information bits is mapped to a complex symbol using conventional digital modulation schemes. At any particular time instant, only one antenna is active. The receiver estimates the transmitted symbol and the active antenna index and uses the two estimates to retrieve the original block of data bits. In this paper, TCM partitions the entire set of transmit antennas into sub-sets such that the spacing between antennas within a particular sub-set is maximized. The scheme is called trellis coded spatial modulation (TCSM). Tight analytical performance bounds over correlated fading channels are proposed in this paper. In addition, the performance and complexity of TCSM is compared to the performance of SM, coded V-BLAST (vertical Bell Labs layered space-time) applying near optimum sphere decoder algorithm, and Alamouti scheme combined with TCM. Also, the performance of all schemes with turbo coded modulation is presented. It is shown that under the same spectral efficiency, TCSM exhibits significant performance enhancements in the presence of realistic channel conditions such as Rician fading and spatial correlation (SC). In addition, the complexity of the proposed scheme is shown to be 80% less than the V-BLAST complexity.

Improved linear soft-input soft-output detection via soft feedback successive interference cancellation

We propose an improved minimum mean square error (MMSE) vertical Bell Labs layered space-time (V-BLAST) detection technique, called a soft input, soft output, and soft feedback (SIOF) V-BLAST detector, for turbo multi-input multioutput (turbo-MIMO) systems. We derive a symbol estimator by minimizing the power of the interference plus noise, given a priori probabilities of undetected layer symbols and a posteriori probabilities for past detected layer symbols. For a low-complexity implementation, an approximate SIOF algorithm is presented, which allows for a time-invariant realization of the symbol ordering and an MMSE filtering process. Another implementation, referred to as the iterative SIOF algorithm is introduced, which decides on symbol detection order based on a posteriori symbol probabilities to improve the detection performance. Simulations performed on a space-time bit-interleaved coded modulation (STBICM) architecture over quasi-static MIMO fading channels demonstrate that the SIOF V-BLAST detector provides performance gains over previous turbo-BLAST detectors, most notably when more transmit antennas are used.

Layered Steered Space–Time-Spreading-Aided Generalized MC DS-CDMA

We present a novel trifunctional multiple-input-multiple-output (MIMO) scheme that intrinsically amalgamates space-time spreading (STS) to achieve a diversity gain and a Vertical Bell Labs layered space-time (V-BLAST) scheme to attain a multiplexing gain in the context of generalized multicarrier direct-sequence code-division multiple access (MC DS-CDMA), as well as beamforming. Furthermore, the proposed system employs both time- and frequency-domain spreading to increase the number of users, which is also combined with a user-grouping technique to reduce the effects of multiuser interference. Further system performance improvements can be attained by serially concatenating our proposed scheme with an outer code that is amalgamated with a unity-rate code for the sake of improving the achievable decoding convergence behavior of the proposed system, which is evaluated with the aid of extrinsic information transfer charts. We also propose a novel logarithmic likelihood ratio (LLR) postprocessing technique to improve the iteratively detected system's performance. Explicitly, the proposed system can attain a second-order spatial diversity gain and a frequency diversity gain of order V, where V is the number of subcarriers. Additionally, the proposed system attains a beamforming gain and a multiplexing gain that is twice that of a single-input-single-output system. Furthermore, after I = 10 decoding iterations and employing an interleaver depth of Dint = 160 000 bits, a time-domain spreading factor of Ne = 4, and V = 4 subcarriers, the overloaded system supporting K = 8 users requires an Eb/N0 that is only about 0.45 dB higher than the single-user system.

Reduced-complexity near-capacity downlink iteratively decoded generalized multi-layer space-time coding using irregular convolutional codes

This paper presents a low complexity iteratively detected space-time transmission architecture based on Generalized Multi-Layer Space-Time (GMLST) codes and Irregular Convolutional Codes (IRCCs). The GMLST combines the benefits of the Vertical Bell-Labs LAyered Space-Time (VBLAST) scheme and Space-Time Coding (STC). The GMLST is serially concatenated with a Unity-Rate Code (URC) and an IRCC which are used to facilitate near-capacity operation with the aid of an EXtrinsic Information Transfer (EXIT) chart based design. Reduced-complexity iterative multistage Successive Interference Cancellation (SIC) is employed in the GMLST decoder, instead of the significantly more complex Maximum Likelihood (ML) detection. For the sake of approaching the maximum attainable rate, iterative decoding is invoked to achieve decoding convergence by exchanging extrinsic information across the three serial component decoders. Finally, it is shown that the SIC-based iteratively detected IRCC-URC-GMLST system is capable of providing a feasible trade-off between the affordable computational complexity and the achievable system throughput.

Optimal power allocation and power control for VBLAST systems with M-ary modulations

In this study, the authors propose the optimal power allocation scheme that minimises the symbol error probability (SER) of vertical Bell Laboratories layered space-time (VBLAST) systems using M-ary modulations. The essence of the power allocation is to intentionally cause different received power from each layer at the receiver. By judiciously allocating the transmitting power to the layers, the performance of the successive interference cancelation at the receiver can be significantly improved. The exact SER of the VBLAST systems with non-uniform power allocation is analysed for the Rayleigh fading case. The SER is minimised to determine the optimal power allocation pattern for the VBLAST systems with M-ary modulations. Simulations show that our SER analysis is accurate and the proposed power allocation scheme significantly improves the performance of the VBLAST systems in fast fading environments by 3.5-4 dB. The work is applied to the power control of VBLAST systems in slow fading environments. Significant SNR gains of 8.5-10 dB are observed in the numerical experiments. It is also observed that the proposed optimal power allocation scheme can effectively reduce the SER variation among the layers.