Multi-antenna Systems Research Articles

Multidimensional Index Modulation in Wireless Communications

In index modulation schemes, information bits are conveyed through indexing of transmission entities, such as antennas, subcarriers, times slots, precoders, subarrays, and radio frequency (RF) mirrors. Index modulation schemes are attractive for their advantages, such as good performance, high rates, and hardware simplicity. This paper focuses on index modulation schemes in which multiple transmission entities, namely, antennas, time slots, and RF mirrors, are indexed simultaneously. Recognizing that such multidimensional index modulation schemes encourage sparsity in their transmit signal vectors, we propose efficient signal detection schemes that use compressive sensing based reconstruction algorithms. Results show that, for a given rate, improved performance is achieved when the number of indexed transmission entities is increased. We also explore indexing opportunities in load modulation (LM), which is a modulation scheme that offers power efficiency and reduced RF hardware complexity advantages in multiantenna systems. Results show that indexing time and RF mirrors in load modulated multiantenna systems can achieve improved performance. A stagewise algorithm based on message passing suited for the detection of indexed LM signals is also proposed.

Performance Trades for Multiantenna GNSS Multisensor Attitude Determination Systems

We present various performance trades for multiantenna global navigation satellite system (GNSS) multisensor attitude estimation systems. In particular, attitude estimation performance sensitivity to various error sources and system configurations is assessed. This study is motivated by the need for system designers, scientists, and engineers of airborne astronomical and remote sensing platforms to better determine which system configuration is most suitable for their specific application. In order to assess performance trade-offs, the attitude estimation performance of various approaches is tested using a simulation that is based on a stratospheric balloon platform. For GNSS errors, attention is focused on multipath, receiver measurement noise, and carrier-phase breaks. For the remaining attitude sensors, different performance grades of sensors are assessed. Through a Monte Carlo simulation, it is shown that, under typical conditions, sub-0.1-degree attitude accuracy is available when using multiple antenna GNSS data only, but that this accuracy can degrade to degree level in some environments warranting the inclusion of additional attitude sensors to maintain the desired level of accuracy. Further, we show that integrating inertial sensors is more valuable whenever accurate pitch and roll estimates are critical.

DESIGN AND ANALYSIS OF ENERGY EFFICIENT WIRELESS SENSOR NETWORKS FOR DIFFERENT APPLICATIONS AND VARIABLE DATA RATE

In the wireless sensor networks, where nodes are working on batteries, energy expenditure smear is most important for similar throughput and BER requirements. Using various (BPSK, MQAM) modulation schemes to lower the total energy consumption including transmission and circuit energy both. For these rechargeable batteries end to end delay maintenance is also important. It will be started with the comparison between SISO and MIMO (MISO, SIMO and MIMO) for BPSK. Then by using contrasting modulation technique (MQAM) in which constellation size will vary and can optimize for huge energy saving. Then our work will widen to multi-node system in which both long-haul and local transmissions are bob up. We will show the comparison of MIMO, MISO and SIMO with traditional approach (SISO) for used energy and will see that how multi-antenna systems acquire energy savings.

Unified Performance Analysis of Transmit Antenna Selection With OSTBC and Imperfect CSI Over Nakagami- m Fading Channels

A unified error analysis of multi-antenna systems with orthogonal space-time block coding (OSTBC) using transmit antenna selection (TAS) over Nakagami- $m$ channels in the presence of feedback delay and channel estimation error is presented, where the number of transmit antennas is arbitrarily selected. For imperfect channel state information (CSI), the Nakagami- $m$ channel is modeled as the sum of Nakagami- $\hat{m}$ channel and independent Gaussian channel error. By this model, accurate and closed-form approximate bit error rate (BER) expressions of TAS-OSTBC for M-ary quadrature amplitude modulation and M-ary phase-shift keying are derived by using the moment generating function of received SNR. With the approximate BER formula, the number of antennas to be selected for transmission can be adapted by minimizing the BER of the system with imperfect CSI. The diversity and coding gains of TAS-OSTBC with $K$ receive antennas and $M$ antennas selected from $N$ transmit antennas for transmission are analyzed at high SNR. For noninteger $mK$ , the upper and lower bounds of the diversity gain for different CSI and estimation error scenarios are derived. But for integer $mK$ , the results indicate that the upper and lower bounds are equal achieving the full diversity order of $mKN$ for perfect CSI, zero diversity order and partial diversity order of $mMK$ for estimation error variance being fixed and being a decreasing function of average SNR, respectively. The coding gain is affected by $M$ , $N$ , $K$ , Nakagami parameter $m$ , code rate, modulation, and channel correlation coefficients. Simulation results verify the validity of the theoretical analysis and effectiveness of the adaptive antenna selection scheme.

Parameter estimation in multi-antenna system based on iterative adaptive approach

As one of the main means for remote sensing and detecting, synthetic aperture radar is playing more important role in many fields such as country reconnaissance, ocean observation, environment disaster monitoring and military reconnaissance. The synthetic aperture radar system based on multi-antenna technology can achieve high resolution of still image and estimate the motion parameter. The echo model of target is set up for motion parameter estimation and the performance of system parameter estimation is given according to the moving target velocity estimation method based on iterative adaptive approach.

Power Allocation and Performance Analysis of Cooperative Spatial Modulation in Wireless Relay Networks

In this paper, the error performance analysis of an amplify-and-forward (AF) relay-aided cooperative multi-antenna system using spatial modulation (SM) over Rayleigh channels is presented. The SM is a simple and spectral efficient modulation technique that can increase the data rate by using input data bits to select a transmit antenna to send a constellation point. The relay transmission deploying SM not only can enhance the coverage and but also can improve the spectral efficiency. In the performance analysis, the overall average bit error rate (BER), which is related to the error probability of an antenna index detection ( $P_{a}$ ) and the error probability of symbol detection ( $P_{d}$ ) given transmit antenna index, is analyzed. With the derivation of the probability density function and the moment generating function of output signal-to-noise ratio (SNR), closed-form expressions of $P_{a}$ and $P_{d}$ are obtained to compute the overall BER. With the obtained BER expression, asymptotical BER expressions are derived to reveal the BER performance of the system at high SNR. By minimizing the asymptotical BER, a suboptimal power allocation (PA) scheme is developed. The diversity gain is analyzed at high SNR. The results indicate that the cooperative AF-SM can achieve full diversity order. Simulation results verify the effectiveness of the theoretical BER analysis, and the cooperative AF-SM with PA scheme outperforms upon the equal PA scheme.

Hardware-Efficient QR-Decomposition Using Bivariate Numeric Function Approximation

Bivariate function approximation has proven its feasibility in terms of hardware-efficient arithmetic signal processing. However, its impact on high performance QR decomposition (QRD) has only been roughly studied so far. In this paper, a novel hardware architecture for Givens-Rotation-based QRD is proposed targeting hardware efficient signal processing. To this end, an ingenious triangular systolic array structure is considered. Complex-valued matrices are efficiently processed by means of a sophisticated bivariate numeric function approximation methodology. In order to get a comprehensive insight in the performance, exhaustive evaluation is carried out with a modern multi-antenna wireless communication system. In detail, the proposed QRD hardware architecture is used in a suitable channel pre-coding setup. For a meaningful proof-of-concept, our work is evaluated on several levels of the computing stack. In addition, our design is implemented and physically synthesized in a state-of-the-art 65-nm Taiwan Semiconductor Manufacturing Company technology and compared with other publications. The results indicate our approach to be a powerful solution for hardware-based QRD, especially in terms of energy and area requirements.

Secure beamforming for two-way multiantenna relay systems

In two-way multiantenna relay systems, confidential information can be easily intercepted by eavesdroppers. To overcome this problem, two secure beamforming schemes are proposed: secrecy sum rate maximization beamforming (SSRMB) and null space beamforming (NSB). For the SSRMB scheme, the nonconvex secrecy sum rate maximization problem is solved using a successive convex approximation strategy, which is convergent. The obtained beamforming solution is locally optimal to the original problem. For the special scenario where the number of antennas at the relay is more than the number of eavesdroppers, the NSB scheme with a low complexity is proposed. The beamforming solution is obtained by solving a generalized Rayleigh quotient problem. Simulation results demonstrate that the proposed schemes can effectively improve the security performance, and the SSRMB scheme has a fast convergence rate.

Enhancing Energy Efficiency via Cooperative MIMO in Wireless Sensor Networks: State of the Art and Future Research Directions

CMIMO is an effective approach to increase throughput and energy efficiency through the collaboration of individual antennas working together as a virtual multi-antenna system. Several CMIMO strategies have been propounded as major candidates for achieving green communications in wireless sensor networks. Compared to conventional MIMO, CMIMO provides significant gains in terms of flexibility. Recently, more advanced cooperation strategies have been proposed to improve the performance of CMIMO by using emerging techniques such as spatial modulation and coding. Although some breakthroughs have been made in this area, the problem of how to accurately adopt these emerging techniques to model CMIMO is far from being fully understood. This article surveys several state-of-the-art CMIMO models for different scenarios, including data aggregated, multihop-based, and clustered schemes. Moreover, it discusses the implementation of CMIMO techniques, which are expected to be candidate techniques for green communications in modern applications. In the implementation, the trade-offs between energy efficiency and spectral efficiency, quality of service, fairness, and security are discussed. Several simulation results are given to show how emerging techniques in CMIMO design can lead to energy efficiency enhancement. Finally, some challenges and open issues that present future research directions are discussed.

Multiple‐input–multiple‐output cooperative spatial modulation systems

In this study, the authors propose novel cooperative spatial modulation (SM) systems with two main relaying techniques [amplify-and-forward (AF) and decode-and-forward (DF)], where all nodes have multiple transmit and/or receive antennas. Most of the studies in the literature of cooperative SM systems, which combine the advantages of cooperative communications and SM systems, consider only the space shift keying (SK) scheme with single receive/transmit antenna at relay and destination. Since the error performance of SM highly depends on the number of receive antennas and more flexible cooperative communications systems can be obtained by using SM with multiple antennas, it is essential to investigate multi-antenna cooperative SM systems. They derive analytical expressions of the average bit error probability for both the newly proposed cooperative SM-DF and cooperative SM-AF systems and validate with the computer simulation results. Furthermore, they present the bit error rate comparison of considered systems with classical M-ary phase SK/quadrature amplitude modulation cooperative systems. Computer simulation results indicate that multiple antennas cooperative SM systems provide better error performance than classical cooperative systems for both relaying techniques.

Position-Based Interference Elimination for High-Mobility OFDM Channel Estimation in Multicell Systems

Orthogonal frequency-division multiplexing (OFDM) and multicell architecture are widely adopted in current high-speed train (HST) systems for providing high-data-rate wireless communications. In this paper, a typical multiantenna OFDM HST communication system with multicell architecture is considered, where the intercarrier interference (ICI) caused by high mobility and the multicell interference (MCI) are both taken into consideration. By exploiting the train position information, a new position-based interference elimination method is proposed to eliminate both the MCI and the ICI for a general basis expansion model. We show that the MCI and the ICI can be completely eliminated by the proposed method to get the ICI-free pilots at each receive antenna. In addition, for the considered multicell HST system, we develop a low-complexity compressed channel estimation method and consider the optimal pilot pattern design. Both the proposed interference elimination method and the optimal pilot pattern are robust to the train speed and position, as well as the multicell multiantenna system. Simulation results demonstrate the benefits and robustness of the proposed method in the multicell HST system.

Optimization of Mixed-ADC Multi-Antenna Systems for Cloud-RAN Deployments

We propose a mixed analog-to-digital converter ADC (mixed-ADC) structure for a cloud-RAN system, where a single-antenna user terminal communicates with a multi-antenna remote radio head (RRH). In the proposed structure, the RRH is equipped with a mixed-ADC pool that includes multiple ADC units with various resolutions. In this pool, the RRH selects the appropriate ADCs and connects the selected ADCs to each antenna to quantize the received signals; thereby each antenna can have a different resolution ADC. The fronthaul capacity is limited, so that the sum of the bits produced in the selected ADCs is also limited. To maximize the spectral efficiency or the energy efficiency of such a system, we propose algorithms for ADC resolution selection based on an approximation of the generalized mutual information in the low signal-to-noise regime. In the proposed algorithms, we show that for spectral efficiency, using high-resolution ADC on the strong channels is beneficial. The results for energy efficiency maximization are similar, though the largest resolutions are reduced to save power. The simulations show that the proposed method provides significant performance improvement.

Two-Stage Interference Management for Multicell Multiantenna Cellular Downlink Systems

The sum degrees of freedom (DoFs) of $L$ -cell multiantenna cellular downlink systems are studied. Each base station (BS) equipped with $M_{t}$ transmit antennas sends independent messages to its $K$ serving users equipped with $M_{r}$ reconfigurable antennas, each of which can choose its receiving mode from $N$ preset modes at each time. It is assumed that each BS and user only knows channel state information (CSI) of its own cell. A novel two-stage interference management scheme is proposed in which intra-cell interference is first nulled out by zero-forcing outer beamforming based on intra-cell CSI and inter-cell interference is then aligned by inner beamforming in a blind manner without inter-cell CSI. It is proved that, for $M_{t}>KM_{r}$ and $N>1$ , the proposed scheme achieves an improved sum DoF compared with the conventional time division multiple access among cells. We further demonstrate that such DoF improvement yields an improved sum rate at the finite signal-to-noise ratio regime.

Asymptotic Approximation of the Standard Condition Number Detector for Large Multi-Antenna Cognitive Radio Systems

Standard condition number (SCN) detector is a promising detector that can work efficiently in uncertain environments. In this paper, we consider a Cognitive Radio (CR) system with large number of antennas (eg. Massive MIMO) and we provide an accurate and simple closed form approximation for the SCN distribution using the generalized extreme value (GEV) distribution. The approximation framework is based on the moment-matching method where the expressions of the moments are approximated using bi-variate Taylor expansion and results from random matrix theory. In addition, the performance probabilities and the decision threshold are considered. Since the number of antennas and/or the number of samples used in the sensing process may frequently change, this paper provides simple form decision threshold and performance probabilities offering dynamic and real-time computations. Simulation results show that the provided approximations are tightly matched to relative empirical ones.

Parameter estimation of air maneuvering target for multi-antenna system via reconstructing time samples and signal

A novel algorithm for estimating the motion parameters of air maneuvering target by means of reconstructing time samples and signal is proposed in this paper. Firstly, the received data of multiple antennas are spliced together to reconstruct time samples of a single antenna by compensating a proper phase. This reconstruction is equivalent to increasing time samples within a single coherent processing interval for a single antenna. After that, an ideal signal whose time sample number is equal to the length of the reconstructed time samples is constructed. At last, the estimation results of initial velocity and acceleration of the air maneuvering target are obtained by applying the nonlinear least squares method to compare the similarity between the reconstructed time samples and signal. The proposed algorithm can achieve accurate parameter estimation with limited pulses. The effectiveness of this algorithm is verified and its performance is very close to the Cramer–Rao bound as shown by our simulation results.

Rate-Splitting to Mitigate Residual Transceiver Hardware Impairments in Massive MIMO Systems

Rate-splitting (RS) has recently been shown to provide significant performance benefits in various multiuser transmission scenarios. In parallel, the huge degrees-of-freedom provided by the appealing massive multiple-input multiple-output (MIMO) necessitate the employment of inexpensive hardware, being more prone to hardware imperfections, in order to be a cost-efficient technology. Hence, in this paper, we focus on a realistic massive multiple-input single-output broadcast channel hampered by the inevitable hardware impairments. We consider a general experimentally validated model of hardware impairments, accounting for the presence of multiplicative distortion due to phase noise, additive distortion noise and thermal noise amplification. Under both scenarios with perfect and imperfect channel state information at the transmitter (CSIT), we analyze the potential robustness of RS to each separate hardware imperfection. We analytically assess the sum-rate degradation due to hardware imperfections. Interestingly, in the case of imperfect CSIT, we demonstrate that RS is a robust strategy for multiuser MIMO in the presence of phase and amplified thermal noise, since its sum-rate does not saturate at high signal-to-noise ratio (SNR), contrary to conventional techniques. On the other hand, the additive impairments always lead to a sum-rate saturation at high SNR, even after the application of RS. However, RS still enhances the performance. Furthermore, as the number of users increases, the gains provided by RS decrease not only in ideal conditions, but in practical conditions with residual transceiver hardware impairments as well. Notably, although a deterministic equivalent analysis is employed, the analytical and simulation results coincide even for finite system dimensions. As a consequence, the applicability of these results also holds for current “small scale” multiantenna systems.

Current Misuses and Future Prospects for Printed Multiple-Input, Multiple-Output Antenna Systems [Wireless Corner

In the past six years or so, the number of scientific articles and conference papers providing possible multiple-input, multiple-output (MIMO) antenna system solutions has noticeably increased. Flagship conferences on antennas and propagation have recently had multiple sessions addressing MIMO antenna systems and their applications. The importance of such antenna systems lies in the magnitude of their application in current wireless devices and gadgets, and this thrust will continue because fourth-generation (4G) and the upcoming fifth-generation (5G) wireless standards rely heavily on MIMO technology. But throughout the years, and up until now, a wide range of publications still suffer from some major misconceptions and unclear understanding of the fundamental aspects while designing, characterizing, and evaluating such multiantenna systems.

Coverage Analysis of Multi-User Multi-Antenna System with Spatial Combining

Objective: To provide coverage analysis of Multi-user Multi-antenna systems with spatial combining. Specifically, our objective is to analyze the coverage probability of uplink communication where a base station equipped with multiple antennas is communicating with many single antenna mobile stations via independent Rayleigh fading channels. Methods: We formulate the outage probability by utilizing the expression for the Signal-to-Interference-Noise-Ratio (SINR). The SINR expression is a function of channel vector, spatial combining vector, number of users and the noise power. Findings: The coverage probability is then obtained as the complementary of outage probability. Monte-Carlo simulations are presented by varying number of base station antenna size, the number of users and the noise power. This analysis provides a framework for system designers to set the system parameters in order to achieve the desired coverage performance. Results: The results show that the coverage probability decreases by increasing the number of users and the noise power. On the other hand, the coverage probability increases as the size of base station antenna increases.

An Analysis of the Effect of Carrier Platforms on Electromagnetic Characteristics of Multi-antenna

The effect of the locomotive roof environment on multi-antenna electromagnetic compatibility is an important issue in wireless communication. This paper is intended to build different platform models of multi-antenna and then analyze mutual interference roundly between antennas in different carrier platforms in order to focus on the effect of working performance of interference antennas to the target antenna, and the variation trend of antenna coupling and gain direction maps of the system with times of distance changing between antennas. The analysis and results can be used as a means or basis for multi-antenna system designing and the analysis tool of electromagnetic compatibility.

Time allocation optimisation for multi‐antenna wireless information and power transfer with training and feedback

Time allocation optimisation for a multi-antenna wireless energy and information transfer system is studied in this study. The terminal first harvests the wireless energy from the base station (BS) during phase I, and then uses the harvested energy to power its information transmission during phase II. Realistic channel state information (CSI) assumptions are made where the CSI at the BS is obtained via training and feedback and is subject to channel estimation error and quantisation error. Therefore, in addition to the tradeoff between information and power transfer, there is also a tradeoff in determining the overheads of training and feedback. To gain insight into this problem, the authors characterise the asymptotic behaviour of the parameters in the large system limit where the number of transmit antennas N t and transmission block length L tot tend to infinity with fixed ratio L tot / N t . The optimal overheads of training and feedback within each phase are first derived to maximise the harvested power and the information transmission rate, respectively. The optimised time allocation between phase I and phase II is then obtained by maximising the bounds of the effective average information transmission rate. Finally, numerical results are presented to verify the proposed theorems.