Multi-input Multi-output Schemes Research Articles

Multivariable short-term electricity price forecasting using artificial intelligence and multi-input multi-output scheme

In deregulated power markets, electricity price forecasting is the most valuable tool. However, with inherent electricity price characteristics, such as high frequency and volatility, constructing an electricity price forecasting model remains a difficult task for decision-makers and scholars. Accurate electricity price point forecasting (PF) can guide market participants in maximizing benefits. Moreover, appropriate interval forecasting (IF) can provide further information based on PF. Accordingly, a novel electricity price multi-bi-forecasting system using multivariable and multi-input multi-output structures is formulated. The system has three stages: data preprocessing, combination forecasting, and performance evaluation. The data preprocessing stage removes and smooths the high-frequency electricity price and load data. Because the load series has a more regular cycle and smoother fluctuation than the electricity price series, two variables, electricity price and load, are employed for forecasting using a multivariable data arrangement rolling forecast mechanism. In addition, a multi-input multi-output structure is utilized by three member models (back propagation, bidirectional long short-term memory, and gated recurrent unit) to derive PF and IF results concurrently. The final results are obtained using a combined strategy based on the multi-objective salp swarm algorithm. Finally, three experiments are conducted in the Australian electricity market to evaluate the proposed system quantitatively. Results show that the designed system has superior ability in forecasting electricity price and practical application in real situations.

Novel Multiplexing Scheme for Resolving the Velocity Ambiguity Problem in MIMO FMCW Radar Using MPSK Code

For the high-resolution DoA (Direction of Arrival) estimation, various multiplexing schemes are considered for the multi-input multi-output (MIMO) fast chirp frequency-modulated continuous-wave (FMCW) radar. However, current schemes such as time-division multiplexing (TDM) and binary-phase modulation (BPM) may reduce the maximum detectable velocity, which causes the velocity ambiguity problem. As an extension of the BPM scheme to mitigate this issue, we propose a novel multiplexing scheme using M phase-shift keying (MPSK) code which duplicates shifted target peaks at unequal intervals over the velocity domain. The proposed scheme finds the true peaks to resolve the velocity ambiguity problem by the inversion of the circulant matrix with low additional computation. In addition, the successful implementation of the proposed scheme is conducted with 4 by 8 MIMO uniform linear array (ULA) antennas through the state-of-the-art FMCW radar. Finally, the proposed scheme is compared to the conventional TDM based MIMO scheme regarding signal to noise ratio (SNR) and phase calibration issues for moving targets. The proposed scheme is to estimate the accurate 4D information of targets while resolving the velocity ambiguity problem in the MIMO FMCW radar systems.

Complex-Valued Phase Transmittance RBF Neural Networks for Massive MIMO-OFDM Receivers.

Multi-input multi-output (MIMO) transmission schemes have become the techniques of choice for increasing spectral efficiency in bandwidth-congested areas. However, the design of cost-effective receivers for MIMO channels remains a challenging task. The maximum likelihood detector can achieve excellent performance—usually, the best performance—but its computational complexity is a limiting factor in practical implementation. In the present work, a novel MIMO scheme using a practically feasible decoding algorithm based on the phase transmittance radial basis function (PTRBF) neural network is proposed. For some practical scenarios, the proposed scheme achieves improved receiver performance with lower computational complexity relative to the maximum likelihood decoding, thus substantially increasing the applicability of the algorithm. Simulation results are presented for MIMO-OFDM under 5G wireless Rayleigh channels so that a fair performance comparison with other reference techniques can be established.

A novel gas sensing scheme using near-infrared multi-input multi-output off-axis integrated cavity output spectroscopy (MIMO-OA-ICOS)

We demonstrated a novel multi-input multi-output (MIMO) laser-to-cavity coupling scheme in off-axis integrated cavity output spectroscopy (OA-ICOS) for cavity mode noise suppression. Theoretical investigation was performed to explore the relation between the number of splitting beams and the MIMO parameters. Mode distribution and propagation inside the cavity was simulated. The noise suppression factor of the MIMO scheme and the noise level and dominated noise in the cavity were studied based on cavity mode simulation. Methane measurements were carried out using a dual-input dual-output (DIDO, N = 2) sensor system to validate the presented scheme, and good agreement was found between simulation and experiment.

Robust Single-Carrier Frequency-Domain Equalization for Broadband MIMO Systems With Imperfect Channel Estimation

Single-carrier frequency-domain equalization (SC-FDE) with multi-input multi-output (MIMO) has been recognized as an alternative technology to orthogonal frequency-division multiplexing with MIMO for broadband wireless communication systems because of its single carrier transmission advantages. Conventional SC-FDE MIMO schemes are designed under the assumption of perfect channel estimation. In this paper, we investigate the robust SC-FDE MIMO design for systems with imperfect channel estimation. Based on a statistical model for channel estimation, the optimal equalization coefficients for the robust SC-FDE MIMO schemes with both parallel interference cancellation and successive interference cancellation (SIC) are derived with the objective of minimizing the sum of the multiple data streams’ mean square errors (sum-MSE). We propose an optimal ordering algorithm in the sense of minimum sum-MSE for the SC-FDE MIMO scheme with SIC, and further propose a low complexity sub-optimal ordering algorithm. The bit-error-rate (BER) performance in the uncoded case is analyzed and a tight BER approximation is derived. Numerical results show that the proposed robust SC-FDE MIMO schemes achieve 1.5dB~4dB gains in $ E_{b}/N_{0}$ over the conventional non-robust schemes.

Quality of Service Aware Inter Carrier Interference Mitigation and Antenna Selection Schemes for Beyond 4G Systems

Future broadband wireless communication systems demand high quality of service (QoS) for anytime anywhere multimedia applications. The standards which use orthogonal frequency division multiplexing (OFDM) coupled with multi input multi output (MIMO) are expected to rule the future wireless world. Time selective nature of the channel introduces inter carrier interference (ICI), which is the major performance limiting parameter in OFDM based systems. ICI causes loss in spectral efficiency and results in poor bit error rate (BER) performance, affecting the QoS of MIMO-OFDM systems. The conventional single input single output (SISO)-OFDM-flexible subcarrier spacing (FSS) system offers better performance than the fixed subcarrier spacing systems in terms of ICI mitigation. But BER and spectral efficiency performance of SISO-OFDM-FSS is not good enough to satisfy the requirements of future wireless broadband services. To improve the BER performance, SISO-OFDM system is replaced by space frequency block coded (SFBC)-OFDM system, which adds spatial and frequency diversity benefits to the conventional system. More number of antennas in the MIMO scheme increases the hardware cost, computational complexity and percentage of overhead. In the present study, to improve the spectral efficiency and to reduce the complexity and cost, optimal transmit antenna selection (OTAS) is combined with the SFBC-OFDM-FSS scheme. The simulation results prove that the proposed SFBC-OFDM-FSS-OTAS scheme offers better QoS than the conventional SISO-OFDM-FSS scheme.

A Novel Low-Complex Antenna Selection Scheme for Beyond 4G (B4G) Systems

Multi input multi output (MIMO) based transmission modes are very popular in 4G and beyond wireless standards. It offers high quality services at the cost of increased hardware and signal processing complexity. Antenna selection is one of the suitable solutions to overcome the limitations of MIMO scheme. Antenna selection schemes are becoming very popular in the recent wireless techniques like massive MIMO, cognitive radio, multi-hop relay networks (MHR) and wireless local area networks. Instead of using all the available antennas for transmission and reception, antenna selection schemes select good antennas based on the channel state information (CSI). To attain the full benefits of transmitter and joint antenna selection schemes, accurate CSI is required at the transmitter side. The non-zero feedback delay and time varying channel conditions, make the CSI available at the transmitter outdated, which also affects the antenna selection process. In this work, we have derived the closed form average symbol error rate (SER) expression of M-ary phase shift keying (PSK) modulation, for three different antenna selection schemes, by considering the effect of delayed CSI. All these derived expressions are the function of correlation between CSI at the receiver and delayed CSI at the transmitter. The simulation results show that the antenna selection gain decreases with the decrease in correlation. It is also observed that scheme 1 based antenna selection is optimal under delayed CSI conditions, for different constellations and more suited for future wireless standards.

Quality of service aware antenna selection scheme for multi-hop relay networks

Multi input multi output (MIMO) based multi-hop relay (MHR) networks has become one of the promising technologies in improving the quality of wireless links. The optimal antenna selection is one of the suitable solutions to overcome the limitations of MIMO scheme. To attain the full benefits of transmitter antenna selection schemes, perfect channel quality information (CQI) is required at the transmitter. The time varying channel and the feedback delay make CQI at the transmitter outdated and also affect the antenna selection process. In this work, we have derived the symbol error probability (SEP) of M-ary quadrature amplitude modulation (QAM) for three different antenna selection schemes by considering the effect of delayed CQI. All these derived expressions are the function of correlation between CQI at the receiver and delayed CQI at the transmitter. The simulation results show that the antenna selection gain decreases with the decrease in correlation. It is also observed that scheme 1 based antenna selection is optimal for different constellations and more suited for MHR network.

MIMO transmit scheme based on morphological perceptron with competitive learning

This paper proposes a new multi-input multi-output (MIMO) transmit scheme aided by artificial neural network (ANN). The morphological perceptron with competitive learning (MP/CL) concept is deployed as a decision rule in the MIMO detection stage. The proposed MIMO transmission scheme is able to achieve double spectral efficiency; hence, in each time-slot the receiver decodes two symbols at a time instead one as Alamouti scheme. Other advantage of the proposed transmit scheme with MP/CL-aided detector is its polynomial complexity according to modulation order, while it becomes linear when the data stream length is greater than modulation order. The performance of the proposed scheme is compared to the traditional MIMO schemes, namely Alamouti scheme and maximum-likelihood MIMO (ML-MIMO) detector. Also, the proposed scheme is evaluated in a scenario with variable channel information along the frame. Numerical results have shown that the diversity gain under space-time coding Alamouti scheme is partially lost, which slightly reduces the bit-error rate (BER) performance of the proposed MP/CL-NN MIMO scheme.

Performance analysis of free space optical links using multi‐input multi‐output and aperture averaging in presence of turbulence and various weather conditions

The authors study the effect of multi-input multi-output (MIMO) spatial diversity schemes when used in a free space optical (FSO) communication link in the presence of turbulence and varied weather conditions such as very clear air, drizzle, haze, fog etc. The performance is evaluated in terms of the bit error rate (BER) and outage probability P out. We show that MIMO schemes cause a decrease in the BER and P out which, at low signal-to-noise ratios, is more significant in presence of very clear air and clear air as compared with haze and fog weather conditions. The diversity gain at a BER of 10−6 is evaluated and observed to increase as the number of transmit/receive apertures increase. However, it remains almost constant over all the weather conditions for a given MIMO scheme and turbulence strength. The performance of FSO link with MIMO schemes is compared with a FSO link using aperture averaging. Owing to constraint on the receiver aperture diameter, the aperture averaging technique fails to give the same kind of performance as provided by the higher order MIMO schemes.

An Estimation of Achievable Rate for Digital Transmissions over MIMO Channels

Achievable rate (AR) is significant to communications. As to multi-input multi-output (MIMO) digital transmissions with finite alphabets inputs, which greatly improve the performance of communications, it seems rather difficult to calculate accurate AR. Here we propose an estimation of con-siderable accuracy and low complexity, based on Euclidean measure matrix for given channel states and constellations. The main contribution is explicit expression, non-constraints to MIMO schemes and channel states and constellations, and controllable estimating gap. Numerical results show that the proposition is able to achieve enough accurate AR computation. In addition the estimating gap given by theoretical deduction is well agreed.

Bit Error Probability of Spatial Modulation over Measured Indoor Channels

The Spatial Modulation (SM) transmission scheme boosts the spectral efficiency and achieves the multiplexing gain by activating a single transmit antenna in each time slot. Radio wave propagation characteristics determined by the environment is a decisive factor for the SM system. In this paper, we investigate the performance of the SM scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios. Firstly, a MIMO channel sounder is established. Based on the sounder, 15150 complex 4×4 MIMO channel matrices are measured inside a typical teaching building under both Line of Sight (LOS) and None Line of Sight (NLOS) scenarios. Secondly, by comparing the SM system over the measured channel and commonly-used channel models, we prove that both the Independently and Identically Distribute (i.i.d.) Rayleigh and the Spatial Correlation (SC) channel model are oversimplified, and that only practical experiences can yield definitive answers to the achievable real-world system performance. Thirdly, the Average Bit Error Probability (ABEP) performance of the SM system is studied based on the measured data under a variety of system configurations. The study of different receive antenna array settings (4×4, 4×2 and 4×1 MIMO setups) approves the significance of combining scheme at the receiver. SM systems employing different signal constellations (Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM)) are also investigated and some interesting results are revealed. Lastly, performance assessment of SM against State-Of-The-Art (SOTA) MIMO schemes (Space-Time Block Code (STBC) and Vertical Bell Labs Layered Space-Time (V-BLAST) code) is conducted. Results show that for a 4×4 MIMO, the low-complexity SM scheme outperforms both STBC and V-BLAST.

Enhanced channel estimation and symbol detection for high speed multi-input multi-output underwater acoustic communications

The need for achieving higher data rates in underwater acoustic communications leverages the use of multi-input multi-output (MIMO) schemes. In this paper two key issues regarding the design of a MIMO communications system, namely, channel estimation and symbol detection, are addressed. To enhance channel estimation performance, a cyclic approach for designing training sequences and a channel estimation algorithm called the iterative adaptive approach (IAA) are presented. Sparse channel estimates can be obtained by combining IAA with the Bayesian information criterion (BIC). Moreover, the RELAX algorithm can be used to improve the IAA with BIC estimates further. Regarding symbol detection, a minimum mean-squared error based detection scheme, called RELAX-BLAST, which is a combination of vertical Bell Labs layered space-time (V-BLAST) algorithm and the cyclic principle of the RELAX algorithm, is presented and it is shown that RELAX-BLAST outperforms V-BLAST. Both simulated and experimental results are provided to validate the proposed MIMO scheme. RACE'08 experimental results employing a 4 x 24 MIMO system show that the proposed scheme enjoys an average uncoded bit error rate of 0.38% at a payload data rate of 31.25 kbps and an average coded bit error rate of 0% at a payload data rate of 15.63 kbps.

Cooperative diversity over log-normal fading channels: performance analysis and optimization

Although there has been a growing interest on cooperative diversity, the current literature is mainly limited to the results obtained for Rayleigh, Rician, or Nakagami fading channels. In this paper, we investigate the performance of cooperative diversity schemes over log-normal fading channels which provide an accurate channel model for indoor wireless environments. We focus on single-relay cooperative networks with amplify-and-forward relaying and consider three TDMA-based cooperation protocols: which correspond to distributed implementations of MIMO (multi-input multi-output), SIMO (single-input multi-output), and MISO (multi-input single-output) schemes. For each protocol under consideration, we derive upper bounds on pairwise error probability over log-normal channels and quantify the diversify advantages. Based on the minimization of a union bound on the bit error rate performance, we further formulate optimal power allocation schemes which demonstrate significant performance gains over their counterparts with equal power allocation.

Energy efficiency of a per-hop relay selection scheme for sensor networks using cooperative MIMO

The energy efficiencies of cooperative Multi-Input Multi-Output (MIMO) schemes are analysed in the context of dense multi-hop wireless sensor networks. The framework of per-hop relay selection is employed, which decides on the next-hop relay based on a metric that captures the trade-off between the performance and the energy cost. Such a framework makes the analysis tractable and suggests a practical way to implement opportunistic cross-layer routing with physical layer adaptation. A few representative cooperative MIMO transmission schemes such as spatial multiplexing, Alamouti coding and selection diversity are analysed as well as an adaptive scheme that switches the transmission strategy based on channel conditions. Simulation results reveal that the cooperative MIMO schemes achieve significant performance enhancement over the Single-Input Single-Output (SISO) scheme when the circuit power consumption is small compared to the transmit power. However, when the circuit power consumption is not negligible compared to the transmit power, the cooperative MIMO may not be energy efficient in the cross-layer setting compared to the SISO scheme.

2310 High Yield Batch Fabrication of Micro Spiral Beam for Multi-input Multi-output Optical Switch

We present the result of application of an etch-stop technique in the chip level fabrication process in order to improve the button flatness and depth variation of bulk micromachined cavities. The chips will be used in micro mirror manipulator device as an optical switch in a multi-input multi-output scheme. In order to increase the process yield, we tried to use a 1μm Silicon Nitride membrane as an etch-stop layer and pattern carrying membrane to increase the process yield in the batch fabrication stage.

Frequency domain pre-equalization with transmit precoding for MIMO broadcast wireless channels

Recent research has shown that frequency domain pre-equalization (FDPE) can provide broadcast transmissions over multi-input multi-output (MIMO) frequency selective channels, where the multiple receivers need limited processing. In this paper, we consider the combination of FDPE with parallel and successive Tomlinson-Harashima Precoding (THP) and propose two novel FDPE MIMO schemes, which are referred to as FDPE-P-THP and FDPE-S-THP, respectively, based on the minimum mean square error (MMSE) criterion. The ordering algorithm in the FDPE-S-THP scheme is considered and it is shown that the system with even a randomly selected order can perform almost as well as that with the optimal one. This paper further develops an accurate theoretical performance analysis methodology for the proposed FDPE-THP schemes. Numerical results along with analytical results demonstrate the significant performance improvement of our proposed schemes compared to the conventional FDPE MIMO schemes. The channel estimation errors and channel variation effects on the proposed system are also investigated. It is shown that the performance degradation due to channel variation can be efficiently reduced by applying channel prediction.

Frequency domain equalization with tomlinson-harashima precoding for single carrier broadband MIMO systems

In this paper, we combine the transmit Tomlinson-Harashima precoding (THP) technique with single carrier frequency domain equalization (SC-FDE) and propose two new FDE multi-input multi-output (MIMO) schemes, which we refer to as parallel THP-FDE and successive THP-FDE, based on the minimum mean square error (MMSE) criterion. For the successive THP-FDE scheme, where all transmit streams are subsequently preceded, we propose an optimal MMSE ordering algorithm. Since the feedback processing is performed at the transmitter, no error propagation problem exists in the proposed THP-FDE MEMO schemes. Numerical results will demonstrate the significant performance improvement of our proposed schemes compared to the conventional FDE MIMO schemes. We will also analyze the error probability, and investigate the channel estimation errors and channel variation effects on the proposed THP-FDE MIMO systems. It will be shown that by applying channel prediction and THP compensation techniques such detrimental effects can be greatly reduced.

Single-Carrier Frequency-Domain Equalization With Noise Prediction for MIMO Systems

Single-carrier frequency-domain equalization (SC-FDE) has recently been receiving much attention as an attractive method for broadband wireless communications for its advantages such as lower peak-to-average ratio and reduced sensitivity to carrier frequency offsets, when compared with orthogonal frequency-division multiplexing (OFDM) systems. In this paper, we investigate its combination with multi-input multi-output (MIMO) technology and propose two novel FDE-MIMO structures, which we refer to as FDE with noise prediction (FDE-NP) and FDE-NP with successive interference cancellation (FDE-NP-SIC). It is shown that the proposed schemes have lower complexity and achieve better performance and complexity tradeoff than the conventional FDE scheme with decision feedback processing. To evaluate the system performance, we will propose an accurate theoretical analysis based on the modified Chernoff bound (MCB) and show that it is not only applicable to the proposed FDE-NP and FDE-NP-SIC schemes, but also to general MIMO systems with equalization. By using the developed MCB along with simulation results, we will show that the proposed FDE-NP and FDE-NP-SIC schemes can achieve significant performance improvement over the conventional FDE MIMO schemes