Nulling-cancelling algorithm with selective maximum-likelihood detection for MIMO communication

Multiple transmit and receive antennas can increase the system capacity, as well as increase reliability in wireless communication. Vertical Bell Laboratories layered spaces-time (V-BLAST) scheme is widely used to achieve high spectral efficiencies in scattering environments. In V-BLAST systems, receiver design is usually based on the nulling-canceling algorithm which offers a good tradeoff between the computational complexity and system performance.;In this thesis, we propose a nulling-canceling based detection algorithm that performs selective maximum-likelihood decoding. We first compare the symbol estimates from two nulling-canceling implementations with different orders. If the symbol estimates do not agree, then maximum-likelihood detection is performed on the discrepant symbols and the rest of the symbols are detected via nulling and canceling. If there is no discrepancy in the comparison, then only nulling and canceling are performed. In our numerical results, 4-QAM (Quadrature Amplitude Modulation) and 16-QAM constellations are considered, and both Minimum Mean Squared Error (MMSE) and Zero-Forcing (ZF) based detections are implemented. We show that our proposed algorithm can achieve a better performance than the nulling-canceling algorithm and requires a relatively small increase in computational complexity, especially at high SNR.;Based on the Bit Error Rate (BER) performance result, we show that our proposed algorithm can achieve a better performance than the nulling-canceling algorithm and requires a relatively small computational complexity increase, especially at high Signal-to-Noise Ratio (SNR) scenario. The BER performances of an unordered system with BPSK (Binary Phase Shift Keying) or 4-QAM modulation and hybrid detection algorithms are given, under the joint consideration of nulling-canceling of several subchannels and block maximum-likelihood detection of several subchannels

High-rate codes that are linear in space and time

Multiple-antenna systems that operate at high rates require simple yet effective space-time transmission schemes to handle the large traffic volume in real time. At rates of tens of bits per second per hertz, Vertical Bell Labs Layered Space-Time (V-BLAST), where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet V-BLAST suffers from its inability to work with fewer receive antennas than transmit antennas-this deficiency is especially important for modern cellular systems, where a base station typically has more antennas than the mobile handsets. Furthermore, because V-BLAST transmits independent data streams on its antennas there is no built-in spatial coding to guard against deep fades from any given transmit antenna. On the other hand, there are many previously proposed space-time codes that have good fading resistance and simple decoding, but these codes generally have poor performance at high data rates or with many antennas. We propose a high-rate coding scheme that can handle any configuration of transmit and receive antennas and that subsumes both V-BLAST and many proposed space-time block codes as special cases. The scheme transmits substreams of data in linear combinations over space and time. The codes are designed to optimize the mutual information between the transmitted and received signals. Because of their linear structure, the codes retain the decoding simplicity of V-BLAST, and because of their information-theoretic optimality, they possess many coding advantages. We give examples of the codes and show that their performance is generally superior to earlier proposed methods over a wide range of rates and signal-to-noise ratios (SNRs)

Space-time coding for UMTS. Performance evaluation in combination with convolutional and turbo coding

Space-time codes provide both diversity and coding gain when using multiple transmit antennas to increase spectral efficiency over wireless communications systems. Space-time block codes have already been included in the standardization process of UMTS in conjunction with conventional channel codes (convolutional and turbo codes). We discuss different encoding and decoding strategies when transmit diversity is combined with conventional channel codes, and present simulations results for the TDD and FDD modes of UTRA.Peer ReviewedPostprint (published version

MIMO communication systems: receiver design and diversity-multiplexing tradeoff analysis

After a few decades\u27 evolution of wireless communication systems, to ensure reliable high-speed communication over unreliable wireless channels is still one of the major challenges facing researchers and engineers. The use of multiple antennas at transmitter and receiver, known as multiple-input multiple-output (MIMO) communications, is one promising technology delivering desired wireless services. The main goal of this thesis is to study two important issues in wireless MIMO communication systems: receiver design for coded MIMO systems, and diversity-multiplexing tradeoff analysis in general fading channels;In the first part of this thesis, we decompose the receiver design problem into two sub-problems: MIMO channel estimation and MIMO detection. For the MIMO channel estimation, we develop an expectation-maximization (EM) based semi-blind channel and noise covariance matrix estimation algorithm for space-time coding systems under spatially correlated noise. By incorporating the proposed channel estimator into the iterative receiver structure, both the channel estimation and the error-control decoding are improved significantly. We also derive the modified Cramer-Rao bounds (MCRB) for the unknown parameters as the channel estimation performance metric, and demonstrate that the proposed channel estimation algorithm can achieve the MCRB after several iterations. For the MIMO detection, we propose a novel low-complexity MIMO detection algorithm, which has only cubic order computational complexity, but with near-optimal performance. For a 4x4 turbo-coded system, we show that the proposed detector had the same performance as the maximum a posteriori (MAP) detector for BPSK modulation, and 0.1 dB advantage over the approximated MAP detector (list sphere decoding algorithm) for 16-QAM modulation at BER = 10-4;In the second part of this thesis, we derive the optimal diversity-multiplexing tradeoff for general MIMO fading channels, which include different fading types as special cases. We show that for a MIMO system with long coherence time, the optimal diversity-multiplexing tradeoff is also a piecewise linear function, and only the first segment is affected by different fading types. We proved that under certain full-rank assumptions spatial correlation has no effect on the optimal tradeoff. We also argued that non-zero channel means in general are not beneficial for multiplexing-diversity tradeoff

Towards closing the capacity gap on multiple antenna channels

In recent years, soft iterative decoding techniques have been shown to greatly improve the bit error rate performance of various communication systems. For multiple antenna systems, however, it is not clear what is the best way to obtain the soft-information required of the iterative scheme with low complexity. In this paper, we propose a modification of the Fincke-Pohst (sphere decoder) algorithm to estimate the MAP probability of the received symbol sequence. The new algorithm solves a nonlinear integer least-squares problem and, over a wide range of rates and SNRs, has polynomial-time (often cubic) complexity. The performance of the algorithm, combined with convolutional, turbo, and LDPC codes is demonstrated on several multiple antenna channels

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 paper, 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 study 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 sub-optimal 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 (RF) 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.Comment: To appear in IEEE SYSTEMS JOURNAL, 9 pages, 6 figures, and 1 tabl

Cooperative spatial multiplexing with mixed modulation for high-rate wireless communications

Multiple-antenna systems, denoted as multiple-input multiple-output (MIMO), promise huge performance gains over conventional single-antenna systems. However, it is not possible to employ multiple antennas in size limited scenarios. Recently new schemes called cooperative diversity and cooperative spatial multiplexing have been proposed. In these schemes, various users cooperate among themselves to form virtual antenna array and thus emulate multiple transmit antenna scenario. An extension of cooperative spatial multiplexing in which source and relays use different modulation techniques, called as cooperative spatial multiplexing with mixed modulations is investigated in this thesis. Detection algorithms at relays and destination are outlined. It is shown that this scheme performs better than the cooperative spatial multiplexing scheme which uses same modulation techniques at source and relays. Also, this scheme outperforms cooperative diversity scheme for high spectral efficiency regimes. Some of the significant findings of this thesis are as follows. In a cooperative spatial multiplexing scheme using mixed modulations, it is advantageous to place relays close to source and the system performs best if more relays are used and each relay employs modulations with smaller constellation size, thereby reducing the complexity and power requirements at relays. Extensive simulations are performed to compare this scheme in several scenarios

Improved QR Decomposition-Based SIC Detection Algorithm for MIMO System

Abstract: Multiple-Input Multiple-Output (MIMO) systems can increase wireless communication system capacity enormously. Maximum Likelihood (ML) detection algorithm is the optimum detection algorithm which computational complexity growing exponentially with the number of transmit-antennas, which makes it difficult to use it in practice system. Ordered Successive Interference Cancellation (SIC) algorithm with lower computing complexity will suffer from error propagation when an incorrect symbol is selected in the early layers. An MIMO signal detection algorithm based on Improved Sorted-QR decomposition (ISQR) is presented in this study. According to the rule of SNR, ISQR can obtain the optimum detection order with less calculation. Based on ISQR an improved detection algorithm is proposed which providing 2 adjustable parameters. Trade-off between performance and complexity can be selected properly by setting the 2 parameters at different values. Simulation experiments are given under the multiple scattering wireless communication environments and the simulation experiment results show the validity of proposed algorithm