Calibration of Nonlinear Crosstalk in MIMO Transmitter

This paper investigates the issue of high complexity of digital predistortion for the nonlinear distortion introduced due to crosstalk in addition to the nonlinear distortion generated by a power amplifier (PA) in 2 × 2 MIMO transmitters. This paper proposes a less complex, novel model for digital predistortion (DPD) for linearizing multiple-input multiple-output (MIMO) transmitters. This model is constructed by taking account of both linear and nonlinear crosstalks, along with the fact that the nonlinearity generated due to crosstalk would be lesser than the nonlinearity already available due to PA. For proof-of-concept, it is shown for two different scenarios that proposed model provides similar linearization performance as compared to 2 × 2 PH model with less number of coefficients.

The demand for ubiquitous telecommunications services forces operators to have a special concern about signal quality and the coverage area they offer to their customers. This was usually checked by using suitable propagation models for Single Input Single Output (SISO) systems, which are no longer the case for new and future mobile generations, such as 5G and beyond. To guarantee good signal quality coverage, operators started to replace these models with Multiple Input Multiple Output (MIMO) ones. To achieve the best results, these models are usually calibrated with Drive Test (DT) measures; however, the DTs available for MIMO propagation models are sparse, in contrast to SISO ones. The main contribution presented in this paper is a methodology to extend the propagation models of SISO systems so they can be applied in MIMO sytems with Single-Carrier and Frequency-Domain Equalization (SC-FDE), while still using DTs acquired for SISO systems. This paper presents the impact on Bit Error Rate (BER) performance and its coverage area resulting from the application of our proposed method. We consider a MIMO SC-FDE system with an Iterative Block Decision Feedback Equalization (IB-DFE) receiver and we present the improvement expressions for the BER that we illustrate with some simulations.

High-capacity video, control and situation awareness data should be transmitted efficiently to control robots properly in the ground unmanned system, which requires the technology maximizing the communication range and the data transmission throughput. This technology is connected to the OFDMA(Orthogonal Frequency Division Multiple Access)-MIMO(Multiple Input Multiple Output) transmission technology under the limited bandwidth and transmission power. In this paper, we design MIMO communication system for ground unmanned systems, and investigate the data reception performance experimentally, comparing with SISO(Single Input Single Output) system. Experiment results show that the data reception performance of MIMO is significantly improved compared to that of SISO, e.g. 4dB gain of sensitivity and 5dB of SNR at the value MPR = 1, for the mobile stations with <TEX>$2{\times}2$</TEX> STBC diversity.

In recent years, several approaches have been proposed aiming the optimal joint design of finite impulse response (FIR) multiple-input multiple-output (MIMO) transmitter and receiver. Assuming that the channel input is power constrained and that the channel model is a known FIR MIMO system, it is possible to design high performance transceivers in the presence of additive noise. Unfortunately, most optimal transceivers available so far, do not have fast implementation and simple design approaches. This work proposes a minimum mean square error (MMSE) design approach where constraints are incorporated into the structure of the FIR MIMO transmitter, in such a way that the resulting optimal MIMO transmitter, in the MMSE sense, has inherent fast algorithm implementation. In comparison with the general jointly optimized transceivers recently proposed, the new approach allows substantial reduction in the computational complexity at expense of mild performance degradation.

The soon to be deployed 5G systems are expected to cater an agglomerate of services at profuse data rates wirelessly. Radio over fiber (RoF) networks are the most suitable to implement such systems. In situations where the practical implementation of RoF systems are non-viable, radio over free space optical (RoFSO) links can be employed. The traditional wavelength division multiplexing (WDM) technology can be incorporated to multiply the data rates. However, the link performance may be degraded due to various atmospheric factors. This can be compensated using multiple input multiple output (MIMO) techniques. In this paper, the performance analysis of such a WDM RoFSO link for 5G frequencies is carried out. The work also presents quantitative performance comparison between single input single output (SISO) and MIMO RoFSO links for 5G systems which will be useful for researchers in this area. It is observed that, while WDM provides additional data capacity, it degrades the link performance under adverse weather conditions which can be counterbalanced using MIMO techniques.

Visible Light Communication (VLC) has emerged as a powerful technique for wireless communication systems. Providing high data rate and increasing capacity are the major problems in VLC. Recent evidence suggests that Multiple Input Multiple Output (MIMO) technique can offers improved data rates and increased link range. This paper describes the design and implementation of visible light communication system in indoor environment exploring the benefits of MIMO. The specific objective of this research was to implement a 4×4 Multiple Input (LEDs) Multiple Output (photodetectors)-VLC communication system, where a 16 white power LEDs in four arrays are setting up at transmitter and four RX modules are setting up at receiver side without the need for additional power or bandwidth as well as analyze a mathematical model for a VLC- 4×4 MIMO with different modes such as the suitable angles to cover the entire room. The research designs practically an electronic circuit for the transmitter and receiver with inexpensive components. The power distribution of different propagation modes is calculated for Single Input Single Output (SISO) and MIMO channels in typical room dimensions. The results in this paper indicate that the power is distributed uniformly for entire room when implemented VLC-MIMO as compared to VLC-SISO. Furthermore, a 4×4 MIMO implementing VLC is compared in term of BER vs. SINR with SISO communication system for both Line of Sight (LOS) and Non Line of Sight (NLOS) propagation modes. Comparing the two results of LOS and NLOS, it can be seen that a 4×4 MIMO implementing VLC for LOS perform better than the same system with NLOS due to decreasing in the received power resulted from the multipath effect.

A channel state information (CSI) feedback algorithm based on scalar quantization is proposed for a multiple-input multiple-output (MIMO) transmission. The performance of the proposed algorithm is evaluated using the effective transmission rate, which incorporates the effect of the CSI feedback overhead on transmission time. Besides that, the power consumed due to the computational complexity of the CSI feedback algorithm is taken into account together with the transmit power when evaluating the energy efficiency. We compare our proposed algorithm to other typical CSI feedback algorithms under correlated channel conditions. Simulation results show that the proposed algorithm enables practical MIMO transmission to achieve an relative transmission rate at 95% of the ideal rate.

The channel capacity of multiple-input multiple-output (MIMO) wideband CDMA system with coherent RAKE receiver is considered. General multi-path intensity Nakagami fading and multiple-access near/far interference channel are assumed. The analysis for system performance shows that the error of channel estimation significantly degrades BER performance and can be effectively suppressed by RAKE receiver and MIMO schemes. Also, an attempt for comparing the channel capacity on different performance improvement schemes has been made. In particular, the channel capacity of MIMO system is compared with single-input single-output (SISO) system. The MIMO complex spreading CDMA system with path correlation yields better performance with respect to channel capacity than a SISO system with i.i.d. input and output. And a discussion on the multiple-access near/far interference is also included, which illustrates that it can be effectively limited by power control and channel estimation schemes.KeywordsChannel EstimationChannel CapacityPilot SymbolInterference ModelCDMA SystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The design of a multi-level fuzzy-logic control system for the control of turbine engines using type-1 fuzzy-logic is presented in this paper. A Matlab-Simulink model of an advanced turbine engine was used to test and validate the performance of the developed fuzzy control system. The model provided comprehensive and complex model of a turbine engine. As with most modeling of turbine engines, it was assumed that the fundamental dynamic characteristics of a turbine engine can be achieved by control of the engine fuel flow. In this model a single input single output (SISO) system is used to control the engine fuel flow, where the input to the SISO system is the low spool speed error signal and the output is the fuel flow actuator control signal. A fuzzy controller was developed for the SISO system and its performance is compared with that of the existing proportional integral (PI) controller. Both controllers were tested under normal operating conditions and with introduction of engine faults embedded in the model.

In order to decrease system implementation cost of fiber-optic relaying systems for multiple-input multiple output (MIMO) mobile transmissions, we have proposed a novel relaying scheme using spatial modulation (SM) technology. The proposed scheme uses much fewer radio over fiber (RoF) links than the conventional fiber-optic relaying schemes. We studied the performance of the proposed scheme through computer simulations and confirmed that the proposed scheme can achieve much better transmission performance than the conventional ones. Computer simulations show that the optimum number of RoF links of the proposed scheme is around 2 or 3 for 4×4 MIMO transmissions, and around 3 or 4 for 8×8 MIMO transmissions.

An adaptive digital predistortion (PD) technique is proposed for linearization of power amplifiers (PAs) in multiple-input multiple-output (MIMO) transmitters. Instead of constructing a separate feedback path at each PA, we propose a PD technique based on a combined feedback, which adds all the PAs' outputs to form a single feedback. We develop an algorithm for finding the multiple PA characteristics jointly from the combined feedback. The PD parameters are calculated from the identified PA characteristics. Although the proposed method requires more computations for PA identification than the conventional method, its hardware implementation is much simpler and can overcome the crosstalk problem of a radio frequency (RF) selector, which is necessary for multiple feedback selection. The simulation results show that, despite its simple structure, the linearization performance of the proposed method is almost the same as the separate multiple feedback method.

For higher order modulation, the reliabilities of the bits Gray-mapped onto the modulated symbol vary from the most significant bits (MSBs) to the least significant bits (LSBs). This paper introduces one constellation rearrangement method for SISO (Single-Input Single Output) system. For MIMO (Multiple-Input Multiple Output) system, the constellation rearrangement works also for lower order modulation by the construction of spatial signal. One constellation remapping method for MIMO system is also introduced in the paper. The simulation results show the performance gain for the SISO constellation remapping method.

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.

MIMO (Multiple Input Multiple Output) enabled systems are characterized by higher reliability and transmission rates, as compared to conventional SISO (Single Input Single Output) systems. However, unless administered properly, the MIMO technology may not facilitate very high throughputs on point-to-point wireless links. Therefore, it becomes imperative for the network architect to design such networks in ways that fully exploit the inherent properties of MIMO. In this paper, we first conduct an extensive experimental study, using a powerful hardware platform, in order to understand the behavior of MIMO links in different topological scenarios. Our experiments involve scenarios with MIMO links in isolation, as well as in competition with other MIMO and SISO links. Second, we perform measurements with different commercial platforms towards assessing the ability of each platform to efficiently support the MIMO technology. Based on our experimental observations we deduce that the CPU processing speed of the underlying hardware platform is an important factor that can hide the performance benefits of a MIMO enabled tranceiver. We comment on the applicability of the different hardware choices that we test; furthermore, we suggest the most appropriate choice for building a MIMO testbed, taking into account the cost, the extend-ability and the re-usability of the selected platform. Finally, having adopted this choice in our testbed design, we provide a description of our testbed architecture.

Orbital Angular Momentum (OAM) has been considered as a new dimension in wireless transmission. In Multiple Input Multiple Output (MIMO) system, OAM can also be utilized as the new Degrees of Freedom (DoF) to manipulate the beamforming instead of the traditional Channel State Information (CSI) feedback, so that the computation complexity of the beamforming dramatically decreases, as well as the capacity of the transmission is maintained approaching the upper bound of the MIMO system. For example, this beamforming manipulation with OAM is extremely efficient in the Line of Sight (LoS) MIMO system. In this paper, the mathematical model of the DoF in beamforming manipulation in MIMO with OAM is established. The computation complexity is evaluated, and compared in LoS environment within MIMO, MIMO-OAM, and OAM. The quantitatively simulation confirms the fact that MIMO-OAM has the best trade-off between the capacity and the computation complexity, which gives a consolidated evidence that the MIMOOAM scheme can be adopted as an efficient beamforming scheme in LoS backhaul links between the base station and the self backhaul small cell station, or Near Field Communications (NFC) directly between mobile terminals. Due to these promising applications, MIMO-OAM may become one of the candidate technologies in Beyond 5G (B5G) mobile communications.