Multi-input Multi-output Orthogonal Frequency Division Research Articles

Multi-input multioutput orthogonal frequency division multiplexing radar waveform design for improving the detection performance of space-time adaptive processing

This paper addresses the waveform optimization problem for improving the detection performance of multi-input multioutput (MIMO) orthogonal frequency division multiplexing (OFDM) radar-based space-time adaptive processing (STAP) in the complex environment. By maximizing the output signal-to-interference-and-noise-ratio (SINR) criterion, the waveform optimization problem for improving the detection performance of STAP, which is subjected to the constant modulus constraint, is derived. To tackle the resultant nonlinear and complicated optimization issue, a diagonal loading-based method is proposed to reformulate the issue as a semidefinite programming one; thereby, this problem can be solved very efficiently. In what follows, the optimized waveform can be obtained to maximize the output SINR of MIMO-OFDM such that the detection performance of STAP can be improved. The simulation results show that the proposed method can improve the output SINR detection performance considerably as compared with that of uncorrelated waveforms and the existing MIMO-based STAP method.

Linear Receivers for Spectrally-Precoded MIMO-OFDM

A multi-input multi-output orthogonal frequency division multiplexing system using spectral precoding to reduce out-of-band power emission is considered. For single-antenna systems, existing spectral precoders that maintain the transmission rate cannot be linearly inverted, calling for iterative interference cancellation receivers. In this letter, it is shown that such spectral precoders when combined with a multiple-antenna transmission can allow a well-defined zero-forcing equalization. Numerical results show that the proposed receivers can achieve close-to-optimal performance as well as reduced complexity in the large antenna array regime.

Computationally Efficient Blind Estimation of Carrier Frequency Offset for MIMO-OFDM Systems

In this paper, we propose a new computationally efficient blind carrier frequency offset (CFO) estimator for multi-input multi-output orthogonal frequency division multiplexing systems. A cost function is carefully designed and can be exactly expressed as the superposition of very few harmonically related cosine waves even with the effect of the noise. Using this property, the minimization of the designed cost function can be solved in a quite computationally efficient manner without any exhaustive grid search procedure. It is seen that the proposed estimator can achieve comparable estimation performance as existing competitors with substantially reduced computational burden. Moreover, in order to improve the estimation performance, we further develop an enhanced CFO estimator by introducing an additional one-step adjustment. We find that the enhanced estimator can attain almost the same estimation performance as the existing maximum likelihood estimator but with a lower order of computational burden. We provide both numerical results and theoretical performance analysis to corroborate the proposed studies.

2 × 2 MIMO OFDM/OQAM radio signals over an elliptical core few-mode fiber.

We experimentally demonstrate a 4.46 Gb/s2×2 multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM)/OQAM radio signal over a 2 km elliptical core 3-mode fiber, together with 0.4 m wireless transmission. Meanwhile, to cope with differential channel delay (DCD) among involved MIMO channels, we propose a time-offset crosstalk cancellation algorithm to extend the DCD tolerance from 10 to 60 ns without using a circle prefix (CP), leading to an 18.7% improvement of spectral efficiency. For the purpose of comparison, we also examine the transmission performance of CP-OFDM signals with different lengths of CPs, under the same system configuration. The proposed algorithm is also effective for the DCD compensation of a radio signal over a 2 km 7-core fiber. These results not only demonstrate the feasibility of space division multiplexing for RoF application but also validate that the elliptical core few-mode fiber can provide the same independent channels as the multicore fiber.

Power Optimization in MIMO-OFDM Systems with Mixed Orthogonal Frequency Division and Space Division Multiple Access Scheme

In recent years, energy efficiency has become a critical metric for green system design and drawn universal attention. In this paper, we propose a new radio resource allocation algorithm to minimize the power consumption of the base station for the multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with different quality of service constraints of users. The discontinuous transmission (DTX) technique is applied in the systems with mixed orthogonal frequency division access and space division multiple access. Radio resources in time, frequency and space domain are optimally allocated to users in two steps: In the first step, the active time in the DTX mode is estimated under the assumption that every user experiences slow time-varying fading in an OFDM frame. In the second step, subcarriers, bits and power are allocated in the active time slots. Although the proposed algorithm is suboptimal due to high computation complexity, simulation results show that the proposed algorithm can reduce the power consumption of the base station and improve resource utilization.

Optimal Design for Energy-Efficient Per-Subcarrier Antenna Selection MIMO–OFDM Wireless Systems

In this paper, we consider a novel optimal design for per-subcarrier antenna selection multi-input multi-output orthogonal frequency division multiplexing systems from an energy-efficiency perspective. The optimal number of antennas, i.e., the number of radio frequency chains, that needs to be built-in on a transmitter to achieve the maximum energy-efficiency is determined. Specifically, an optimization problem for maximizing the average energy-efficiency with respect to the number of antennas is formulated. To solve this optimization problem, we first derive a closed-form formula expressing the cost function (i.e., the average energy-efficiency) as a function of the number of antennas. Search algorithms are then designed to obtain the optimal number of antennas. It is shown that the optimal number of equipped antennas depends on particular values of the circuit power consumption, the actual transmitted power, and the channel characteristics. Simulation results are provided to validate the analysis.

Blind Channel Estimation for MIMO-OFDM Systems With Low Order Signal Constellation

In this paper, we design a new blind channel estimation method for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems to cope with possible rank deficient signal covariance matrices when symbols are drawn from low order constellations, e.g., BPSK, QPSK, etc. By collecting the signal covariance matrices from a group of carefully selected subcarriers, the proposed method could identify the channel information from a small amount of received blocks. Moreover, the proposed method also outperforms the existing competitor in terms of both estimation performance and computational complexity. The numeral results are provided to corroborate the proposed studies.

Signal Detection in MIMO-OFDM Systems Based on SSDE Algorithm

Device-to-device communication enables to improve the application performance of multi-input multi-output (MIMO) technology. In a multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system, its performance is largely reflected by the signal detection algorithm used in receiver. As a sub-optimal maximum likelihood (ML) detection method, the Selective Spanning with Fast Enumeration algorithm can be successfully applied in MIMO-OFDM systems with high-order modulation. However, its Fast Enumeration scheme calculates constellation points based on fixed formula, which tends to yield pseudo constellation points outside of constellation maps, and consequently cannot work well in low-order modulation. To address this, a selective spanning with direct enumeration (SSDE) algorithm is proposed in this paper. Simulation results proved that the SSDE can achieve similar detection performance at a much lower computational cost in comparison with the ML method. The performance in terms of bit error rate (BER) obtained by SSDE method is also superior to those from the Minimum mean square error and Zero forcing detection algorithms with a huge savings in computational load. By adjusting the parameters used in the SSDE, the tradeoff between BER and computation complexity can be flexibly changed to satisfy specific design requirements in different applications.

Generation and transmission of 3 × 3 W-Band multi-input multi-output orthogonal frequency division multiplexing-radio-over-fiber signals using micro-ring resonators.

Using the micro-ring resonator (MRR) system, the single and multi-carriers at frequencies of f(1)=192.898, f(2)=192.990, f(3)=193.1, f(4)=193.315, and f(5)=193.537 THz with a free spectral range (FSR) of 92, 110, 215, and 222 GHz, respectively, are generated to be suitable for a radio-over-fiber (RoF) system based on multi-input multi-output (MIMO) with orthogonal frequency division multiplexing (OFDM). Demonstrated are the concepts of all-optical MIMO signal generation and its transmission over a 50 km single mode fiber (SMF) optical link and an up to 3 m wireless link. Sixty-four multi-carriers are used in the all-optical generation of three MIMO W-Band RF signals, where the single carriers (f(3)-f(5)) transport the signals over the RoF link. The bit error rate (BER) of the overall system performance is discussed; thus, the transmission of MIMO signals is feasible for up to an SMF path 50 km long and a wireless distance of 3 m.

Statistical modelling of a non‐linear high‐power amplifier with memory in multi‐input–multi‐output orthogonal frequency division multiplexing systems

A simple and accurate statistical model (SASM) for a high-power amplifier (HPA) with memory in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems is proposed. This model is statistically equivalent to the more complex generalised memory polynomial (GMP) model, which is one of the most accurate models. The HPA distortion is modelled using stationary white Gaussian noise sources that pass through finite impulse response (FIR) filters. The filter coefficients and the variance of noise sources are derived analytically from the GMP model parameters by spectral decomposition of the GMP noise power spectrum. The number of FIR filters is equal to the memory length of the GMP model. The HPA effect on the OFDM signal, considered as frequency-dependent attenuation coefficients, is modelled using another FIR filter. These FIR filters with small lengths make the model computationally inexpensive and mathematically tractable. The main characteristics of this model are identical bit error rate (BER) and error vector magnitude of subcarriers with those in the GMP model. The proposed model is the simplest representation of a HPA with memory effects. An excellent agreement between the simulation results of the SASM and GMP model is observed. This verifies the accuracy and efficiency of the proposed method.

A joint swarm intelligence algorithm for multi-user detection in MIMO-OFDM system

In the multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system, traditional multi-user detection (MUD) algorithms that usually used to suppress multiple access interference are difficult to balance system detection performance and the complexity of the algorithm. To solve this problem, this paper proposes a joint swarm intelligence algorithm called Ant Colony and Particle Swarm Optimisation (AC-PSO) by integrating particle swarm optimisation (PSO) and ant colony optimisation (ACO) algorithms. According to simulation results, it has been shown that, with low computational complexity, the MUD for the MIMO-OFDM system based on AC-PSO algorithm gains comparable MUD performance with maximum likelihood algorithm. Thus, the proposed AC-PSO algorithm provides a satisfactory trade-off between computational complexity and detection performance.

Optimal control with monotonicity constraints for a parallel-server loss channel serving multi-class jobs

We study a parallel-server loss channel serving multi-class jobs, which appears in many real-world systems, e.g., cloud computing, multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM), and call centre. An -discounted optimal control with monotonicity constraints (OCMC) model over infinite time horizon is established by using the physical queueing model with linear revenue function. Existence of a solution to the OCMC model is proved, whose optimal value provides an upper bound of the corresponding values of the physical queueing model under Markovian decision rules. Algorithms with lower complexity in solving the OCMC model are proposed, which are further used to design an admission control policy for the loss channel. Furthermore, a simulation algorithm is proposed to implement the designed policy. Performance comparisons through numerical examples are conducted among our newly designed policy, the first-in first-out (FIFO) policy, an arbitrarily selected (AS) policy, and the Markov decision process (MDP) based threshold policy. Advantages and disadvantages of these policies are identified under different channel parameters and channel (e.g., Markovian and non-Markovian) conditions. Particularly, we find out that our designed policy outperforms the other three policies when the traffic intensity is relatively large, and the differences of the revenues per unit of time and the penalty costs among different classes of jobs are large.

A Novel Phase Offset SLM Scheme for PAPR Reduction in Alamouti MIMO-OFDM Systems Without Side Information

In this letter, a novel phase offset selected mapping (SLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) in Alamouti coded multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, and its key idea is that different phase rotation sequences are multiplied by their corresponding phase offsets at the transmitter. Moreover, a minimum Euclidian distance (MED) decoder at the receiver is proposed to recover the phase rotation sequences. Therefore, the proposed SLM scheme does not need to reserve bits for the transmission of side information, resulting in the increase of the data rate. Theoretical analysis and simulation results show that the proposed SLM scheme could offer good performances of both the bit error rate and PAPR reduction.

MIMO-OFDM Transceivers With Dual-Polarized Division Multiplexing and Diversity for Multimedia Broadcasting Services

This brief paper presents multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with dual-polarized division multiplexing (PDM) and diversity for multimedia broadcasting services. In particular, the polarized diversity is realized by transmitting two independent and distributed space-frequency coded signals through two sets of dual-polarized transmit antennas. In the corresponding polarized receptions, MIMO zero-forcing (ZF) detection and ZF detection combined with a group-wise or a symbol-wise successive cancelation (SIC) are used to minimize a depolarization effect caused by a cross-polarization discrimination (XPD). Furthermore, we analyze the output signal-to-interference-plus-noise ratio (SINR) of such MIMO detections in terms of the XPD effect. It is shown that the output SINR of MIMO ZF detection increases as the absolute XPD value increases. It is also shown that the output SINR of ZF-SIC detection converges to that of ZF detection as the absolute XPD value increases. Finally, we compare the performances of uni-polarized and dual-polarized MIMO-OFDM systems over a multipath Rician channel with XPD. From simulation results, we conclude that as the absolute XPD value increases, the polarized MIMO-OFDM systems provide a lower symbol error rate than uni-polarized MIMO-OFDM systems.

Analytical Modeling of MIMO-OFDM System in the Presence of Nonlinear Power Amplifier with Memory

In this paper, the effects of nonlinear High Power Amplifier (HPA) with memory on Multi-Input Multi-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system are analyzed and a theoretical framework is proposed. The memory effects are represented by Generalized Memory Polynomial (GMP) model. Moreover, we derive an analytical formulation with infinite nonlinearity order and infinite memory length. The channel is assumed MIMO frequency selective and it is modeled as a linear dispersive channel with uniform power profile. We show that the decision variables of the nonlinearity distortion can be modeled by the complex attenuation and zero mean additive noise model. The analytical expressions for complex attenuation, mean and variance of nonlinear noise are derived and SER of MIMO-OFDM system using HPA with memory is presented. Excellent agreement between the analytical results and numerical simulations is observed that verifies the accuracy and efficiency of the proposed method.

Efficient Pilot Patterns and Channel Estimations for MIMO-OFDM Systems

In this paper, we present the efficient pilot patterns and channel estimations for a high-rate multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system. In particular, we propose the scattered pilot (SP), edge pilot (EP), and continuous pilot (CP) by exploiting a basic orthogonal property of a unitary matrix. From the orthogonal property, we then propose the efficient channel frequency response (CFR) and channel impulse response (CIR) estimations. Finally, we evaluate the efficiency of the proposed schemes by comparing with a multi-input single-output OFDM (MISO-OFDM) system.

Underwater Acoustic Multimedia Communication Based on MIMO–OFDM

A transmission scheme is proposed based on multi-input multi-output orthogonal frequency-division multiplexing (OFDM) for underwater acoustic multimedia (UWAM) communication. The proposed scheme integrates direct mapping and space-time block code strategies, a power assignment mechanism, OFDM, adaptive modulation, and unequal error protection in a UWAM system. The proposed UWAM system employs high power, low speed modulation, with schemes providing significant error protection for transmission of sensor data messages requiring a stringent bit-error rate (BER). In contrast, low power, high speed modulation schemes with reduced error protection are provided for messages that can tolerate a high BER, such as image and audio signals. Simulation results show that the proposed scheme not only fulfils the quality of services requirements of a UWAM system, but also maximizes transmission bit rates or minimizes transmission power requirements.

Spectral efficient hybrid wireless optical broadband access network (WOBAN) based on transmission of wireless MIMO OFDM signals over WDM PON

In this paper, a spectral efficient hybrid wireless optical broadband access network (WOBAN) is proposed and demonstrated based on the transmission of wireless multi-input multi-output orthogonal frequency division multiplexing (MIMO OFDM) signals over wavelength division multiplexing passive optical network (WDM PON). By using radio over fiber (ROF) techniques, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. It is a known fact that multiple wireless signals having the same carrier frequency cannot propagate over a single optical fiber at the same time, such as MIMO signals feeding multiple antennas in fiber wireless (FiWi) system. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. This technique allows four pairs of wireless MIMO OFDM signals with the same carrier frequency for each pair to be transmitted over a single optical fiber by using one optical source per wavelength. The crosstalk between the different MIMO channels with the same frequency is eliminated, since each channel is upconverted on specified wavelength with enough channel spacing between them. Also the maximum crosstalk level between the different MIMO channels with different frequencies is very low around −76dB. The physical layer performance of the proposed WOBAN is analyzed in terms of the bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR). The proposed WOBAN achieves 7.68Gb/s data rate for 20km for the optical back-end and 240Mb/s for the outdoor wireless front-end.

Applying Bargaining Solutions to Resource Allocation in Multiuser MIMO-OFDMA Broadcast Systems

Multiuser multi-input multi-output orthogonal frequency division multiple access (MIMO-OFDMA) is regarded as an important technology for increasing the flexibility and efficiency of wireless communication systems. A well-behaved resource allocation strategy is crucial for the performance of such systems. In this paper, we systematically study the allocation problem from a game theory perspective for the multiuser downlink broadcast channel. First, we investigate the application of the Nash and Kalai-Smorodinsky bargaining games to a general resource allocation problem and propose algorithms to find the corresponding solutions. Then we apply the general solutions to the special case where spatial block diagonalization is combined with time-sharing to multiplex a subset of the users on every subcarrier. To reduce the computational complexity, a framework for simplifying the resulting algorithms is also given. Numerical results and analysis are provided to compare the performance of the different resource allocation methods.

Novel High Performance MIMO-OFDM Based Measures for NLOS Identification in Time-Varying Frequency and Space Selective Channels

This paper proposes new measures for non-line-of-sight (NLOS) identification in wireless localization systems. The measures are defined based on the space-time-frequency channel correlation features of multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Here, space-time channel correlation refers to the correlation across antenna elements and time, and frequency channel correlation refers to the correlation across subcarriers. The probability-of-detection performance of these NLOS identification methods is investigated. The results represent a high identification performance when the LOS and NLOS powers are in the same order of magnitude.