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There have been a number of researches on block transmission systems via MIMO channels due to really high data transmission rate. However, because of the existence of inter-symbol interference (ISI) in the systems, guard intervals are added to eliminate the ISI, leading to a reduction in channel energy and bandwidth efficiency. In order to optimize these systems, there are many solutions in which a combining design of precoder and equalizer appears as a potential candidate. In this paper, a jointly optimal design for precoder and equalizer for ISI multiple input multiple output (MIMO) channels based on sharing redundancy is proposed. Theory analysis and simulation results demonstrate that the proposed design produces a significant improvement in the system performance such as a reduction in bit error rate, a decrease in channel energy loss and an increase in system throughput. [ABSTRACT FROM AUTHOR]

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For massive multiple-input multiple-output (MIMO) circumstances with time division duplex (TDD) protocol, pilot contamination becomes one of main system performance bottlenecks. This paper proposes an uplink pilot sequence assignment to alleviate this problem for spatially correlated massive MIMO circumstances. Firstly, a single-cell TDD massive MIMO model with multiple terminals in the cell is established. Then a spatial correlation between two channel response vectors is established by the large-scale fading variables and the angle of arrival (AOA) span with an infinite number of base station (BS) antennas. With this spatially correlated channel model, the expression for the achievable system capacity is derived. To optimize the achievable system capacity, a problem regarding uplink pilot assignment is proposed. In view of the exponential complexity of the exhaustive search approach, a pilot assignment algorithm corresponding to the distinct channel AOA intervals is proposed to approach the optimization solution. In addition, simulation results prove that the main pilot assignment algorithm in this paper can obtain a noticeable performance gain with limited BS antennas. [ABSTRACT FROM AUTHOR]

This study describes the design of a very compact dual-band-notched ultrawide band (UWB) multiple-input multiple- output (MIMO) antenna. The main features of the proposed antenna are its compact dimensions and high isolation between the two antenna elements. The UWB performance of the antenna is attained by designing two identical triangular-shaped patch elements, which are designed opposite to each other and connected to a tapered microstrip feedline. The ground plane of the proposed antenna consists of a funnel-shaped patch connected with two triangles at the lower end. In addition, two J-shaped slits are etched in the radiator to get the band rejection characteristics at wireless local area network band from 5.1 to 5.8 GHz and IEEE INSAT/Super-Extended C-band from 6.7 to 7.1 GHz. The designed antenna has the smallest dimension of 26 X 15 X 1.6mm3. Results show that the MIMO antenna has a large impedance bandwidth of 31.9 GHz from 3.1 to 35 GHz. The diversity performance of the proposed antenna is also analysed using different parameters such as envelope correlation coefficient (ECC), diversity gain, total active reflection coefficient and so on. Due to the low mutual coupling of <-24 dB and ECC of <0.2 across the frequency band this antenna is a good candidate for portable UWB applications. [ABSTRACT FROM AUTHOR]

This paper derives a stability criterion for switching Lur’e MIMO systems with time-varying nonlinearities, where switching is subject to given restrictions. These restrictions are encoded via the notion of a switching path, interpolating the criterion between the single-system case and arbitrary switching. The criterion for switching Lur’e systems is shown to boil down to a familiar LMI criterion for linear switching systems for the case the Lur’e systems have a linear feedback. The model of a switching Lur’e system is used to describe an MPC control scheme subject to loss of output readings. This example illustrates the practical and theoretical usefulness of the introduced switching path restrictions. [ABSTRACT FROM AUTHOR]

In this paper, a two-element UWB MIMO antenna with bi-directional radiation pattern is designed for superior UWB MIMO performance. The designed antenna adopts asymmetric coplanar waveguide ground feeding. The proposed antenna ECC is lower than the ECC of its omni-directional peer antenna. Simulated and measured ECC is lower than 0.016 over the entire ultra-wide bandwidth (3.1-10.6 GHz). The isolation between elements of the designed antenna is 20-25 dB exceeding the average in recently published works. The designed antenna has a diversity gain of almost 10 dB and average multiplexing efficiency of 85% over the entire ultra-wide bandwidth. The antenna preserves radiation efficiency higher than 0.96 and gain 3 dB. The diversity performance of the proposed UWB MIMO antenna is proven through real rich-multipath indoor environment measurements. Stationarity of the elected channel is evaluated through 100 successive measurements separated by a 3-min period for 5 h long. The measured spatial correlation coefficients are much lower than 0.5 in different scenarios. [ABSTRACT FROM AUTHOR]

We investigate the benefits of incorporating relays in future multi-user wireless networks that seek to exploit unexplored bands of very high frequency spectrum, where transmitted signals are known to be highly susceptible to outages. To this end, we examine a two-user bursty MIMO Gaussian interference channel with an in-band relay, where Bernoulli random states conceptually capture signal outages. As our main result, we show that an in-band relay can provide a degrees of freedom (DoF) gain in this bursty channel. This beneficial role of in-band relays in the bursty channel is in direct contrast to their role in the non-bursty channel which is not as significant to provide a DoF gain. More importantly, we demonstrate that in certain antenna configurations, an in-band relay can help achieve interference-free performances with increased DoF. We find the benefits particularly substantial in high-outage circumstances, as the DoF gain can grow linearly with the number of antennas at the relay. In this paper, first we derive an outer bound from which we obtain a necessary condition for interference-free DoF performances. Then we develop a novel scheme that exploits information of the bursty channel states to achieve them. [ABSTRACT FROM AUTHOR]

For a very high frequency radar, multiple reflection paths, i.e., multipaths, of target echoes may cause severe errors in elevation estimation of low-angle targets, especially in the case of complex terrain where exact information of reflection paths is unknown. To deal with this problem, a practical multipath signal model for multiple-input multiple-out (MIMO) radar in complex terrain is first presented, where both transmitted multipaths and received multipaths are considered. A novel altitude estimation technique based on rank-1 constraint and sparse representation is then proposed. Simulation results show that the target localization accuracy can be efficiently improved by using our proposed technique under both simple and complex multipath scenarios. [ABSTRACT FROM AUTHOR]

In this paper, a new two-phase-feedback-based user-scheduling-and-beamforming method is proposed for multi-user multiple-input multiple-output downlink in the context of two-stage beamforming. The key ideas of the proposed method are: 1) to use a set of orthogonal reference beams and construct a cone around each reference beam to select “nearly-optimal” semi-orthogonal users based only on channel quality indicator feedback; and 2) to apply post-user-selection beam design with zero-forcing beamforming (ZFBF) based on channel state information (CSI) feedback only from the selected users. It is proven that the proposed scheduling-and-beamforming method is asymptotically optimal as the number of users increase. Furthermore, the proposed scheduling-and-beamforming method almost achieves the performance of the existing semi-orthogonal user selection with ZFBF that requires full CSI for all users, with a significantly reduced amount of required channel information which is even less than that required by random beamforming. [ABSTRACT FROM PUBLISHER]

This paper studies the impact of the multiple interferers with different power on performance of a scheduled space–time block coding (STBC) using the statistical channel state information (CSI) in cognitive radio-multiple input multiple output (CR-MIMO) systems. This paper derives the exact closed-form cumulative density function (CDF) expression of the instantaneous post-processing signal to noise plus interference ratio (SINR) random variable at the user terminal of the proposed system. Using the derived CDF, the exact closed-form symbol error rate (SER) expression of the proposed system is derived for M -ary quadrature amplitude modulations (QAM). Further, this paper derives the exact closed-form expressions of outage probability and capacity for the proposed system. From the results, we know that the performance of the proposed system is saturated at different peak power constraint depending on the peak interference constraint. Also, the performance floor gets better by multi-user diversity and receive spatial diversity below the peak interference constraint in the presence of multiple interferers. [ABSTRACT FROM AUTHOR]

A new concept named the self-curing decoupling technique is proposed for the first time to reduce the mutual coupling between two closely located inverted-F antennas (IFAs). The decoupling technique only requires a capacitive load on the shorting arm of each coupled IFA without connecting a circuitry or inserting a physical structure between the two coupled antennas. The capacitive load occupies very little space and is frequency-insensitive; therefore, the decoupling technique is a very favorable choice for low-frequency applications. Network analysis is presented to mathematically justify the working mechanism and to provide a design guideline. Several practical cases of two IFAs situated at different positions on the periphery of a PCB board are studied. The experimental results show that with the decoupling technique, significant improvements in the port isolation (from 10 to 20 dB), antenna correlation coefficient (from 0.25 to 0.05), multiplexing efficiency (from 46% to 60%), and above all the system throughput (1.2 and 0.8 dB power saving in Urban Microcell and Urban Macrocell channels, respectively) can be obtained. [ABSTRACT FROM PUBLISHER]

This paper includes a design of a four-port stacked patch antenna with band enhancement for multi-in multi-out application. The proposed stacked patch antenna consists of two collocated microstrip patches printed on the upper and lower substrates. Through the analysis of characteristic modes, we find that eight desired modes forced to resonant at the operating band. By exciting the resonant modes on the lower patch, four different radiation patterns are achieved. For each radiation pattern, there are three resonance frequencies at interested frequency band—two parallel resonances and one series resonance—which have been combined to form a wider operating band. The proposed antenna is operating at 2.6 GHz frequency band with at least 7.3% in simulated and 6.5% in measurement impedance bandwidth for each port with low profile. A high port isolation (>24.5 dB) and low correlation (<1e−3) have been achieved. Numerical and experimental results illustrate the validity of the design. [ABSTRACT FROM PUBLISHER]

A multiplexing antenna system is proposed for high data rate wireless transmission applications in the non-far region. The system is composed of two identical flat rectangular antennas directed toward each other and separated by a distance. Each antenna radiates four beam modes with 2-D orthogonality in the rectangular coordinate system by means of a passive and low-loss beam forming network. Thanks to the orthogonality relation among the modes up to four independent channels in the same direction with the same frequency and polarization can be carried and the signal demultiplexing is facilitated in the reception side. To validate the proposed concepts, the antennas have been designed and fabricated in the E-band around 78.5 GHz. Based on that, the multiplexing system has been experimentally tested. Good agreement between simulations and measurements has been obtained. [ABSTRACT FROM PUBLISHER]

Multiobjective optimization design of compact multiple-input and multiple-output (MIMO) antennas with canonical structures (viz., transformation or combination by regular shapes) for wideband radiation and fragment structures (viz., combination by discrete fragment patches) for high isolation is proposed and demonstrated. In the design, multiobjective evolutionary algorithm based on decomposition combined with differential evolution (MOEA/D-DE) for optimization of canonical structures and MOEA/D combined with genetic operator (MOEA/D-GO) for optimization of fragment structures are combined and iterated. The design is demonstrated with compact bow-tie MIMO antennas sharing a small common ground plane. The four orthogonally deployed bow-tie antennas are optimized by using MOEA/D-DE to acquire dual polarization and wideband radiation. Fragment-type structures on the common ground plane are optimized by using MOEA/D-GO to acquire very high isolation. Both simulation and measurement show that the optimized MIMO bow-tie antennas provide isolation higher than 30 dB in a relative bandwidth of 40% (from 2.6 to 3.9 GHz). With the proposed design technique, dual-band high-isolation MIMO antennas may also be designed. [ABSTRACT FROM PUBLISHER]

This article provides an overview of key features pertaining to CSI reporting and beam management for the 5G New Radio (NR) currently being standardized in 3GPP. For CSI reporting, the modular design framework and high-resolution spatial information feedback offer not only flexibility in a host of use cases and deployment scenarios, but also improved average user throughput over state-of-the-art 4G LTE. To accommodate cellular communications in the milimeter-wave regime where a combination of analog and digital beamforming is typically used at both a base station and user equipment, beam management procedures such as measurement, reporting, and recovery are introduced. The utility and joint usage of these two features are demonstrated along with some potential upgrades for the next phase of 5G NR. Introduction [ABSTRACT FROM AUTHOR]

This letter considers joint design of transmit waveform and receive filter in colocated multiple-input multiple-output (MIMO) radars in order to enhance target detection performance in the presence of signal-dependent interference. Here, signal-to-interference-plus-noise ratio (SINR) is maximized under the practical constraints of integrated sidelobe level (ISL) and peak sidelobe level (PSL) at the pulse compression output. We have also shown that the joint transmit signal and receive filter design can be formulated as a convex optimization problem, which can be efficiently solved using optimization toolbox (CVX). Simulation results show that our proposed algorithm is able to suppress interference efficiently under ISL and PSL constraints and get close to the SINR efficiency of unconstrained methods. [ABSTRACT FROM AUTHOR]

The goal of this study was to investigate the performance of a realistic wireless sensor nodes deployment in order to support modern building management systems (BMSs). A three-floor building orientation is taken into account, where each node is equipped with a multi-antenna system while a central base station (BS) collects and processes all received information. The BS is also equipped with multiple antennas; hence, a multiple input-multiple output (MIMO) system is formulated. Due to the multiple reflections during transmission in the inner of the building, a wideband code division multiple access (WCDMA) physical layer protocol has been considered, which has already been adopted for third-generation (3G) mobile networks. Results are presented for various MIMO orientations, where the mean transmission power per node is considered as an output metric for a specific signal-to-noise ratio (SNR) requirement and number of resolvable multipath components. In the first set of presented results, the effects of multiple access interference on overall transmission power are highlighted. As the number of mobile nodes per floor or the requested transmission rate increases, MIMO systems of a higher order should be deployed in order to maintain transmission power at adequate levels. In the second set of results, a comparison is performed among transmission in diversity combining and spatial multiplexing mode, which clearly indicate that the first case is the most appropriate solution for indoor communications. [ABSTRACT FROM AUTHOR]

In this paper, we consider a point-to-point multi-input multi-output wireless-powered communication system, where the source S is powered by a dedicated power beacon (PB) with multiple antennas. Employing the time splitting protocol, the energy constrained source S first harvests energy through the radio-frequency signals sent by the PB and then uses this energy to transmit information to the destination D. Unlike several prior works, we assume that the energy transfer link is subjected to Rician fading, which is a real fading environment, due to relatively short range power transfer distance and the existence of a strong line of sight path. We present a comprehensive analysis of the achievable ergodic capacity in two scenarios, depending on the availability of channel state information (CSI) at PB, namely, the absence of CSI and partial CSI. For the former case, equal power allocation is used, while for the later one, energy beamforming is used to enhance the energy transfer efficiency. For both the cases, closed-form expressions for the upper and lower bounds of the ergodic capacity are derived. Furthermore, the optimal time split is discussed, and the capacity in the low and high signal-to-noise ratio regimes is studied through simple closed-form expressions. Numerical results and simulations are provided to validate the theoretical analysis. The results show that the Rician factor $K$ has a significant impact on the ergodic capacity performance, and this impact strongly depends on the availability of the CSI at the PB. [ABSTRACT FROM AUTHOR]

In this paper, we study the capacity and symbol error probability (SEP) of generalized spatial modulation (GSM) multiple-input multiple-output (MIMO) using measured channels that are obtained by channel sounding in an indoor office environment at 60GHz. Spatial modulation (SM) and GSM are emerging low-complexity MIMO schemes that have been extensively researched for low-GHz (below 6GHz) communications. Recently, they have been considered and shown to be promising also for (mmWave) communications. In the simplest possible case, they require only one RF chain both at the transmitter (TX) and receiver (RX), and thus, are especially attractive for mmWave communications, in which the number of RF chains needs to be as low as possible. Despite of some early works on the theoretical analysis of SM/GSM for mmWave communications, there have been no investigations using real-world channel data. We focus on the office line-of-sight (LOS) scenario and investigate three problems: 1) the performance of GSM using the extracted LOS component of measured channels; 2) the impact of non-LOS NLOS components on the performance of GSM; and 3) possible simple modulation and reception algorithms for GSM that rely only on the LOS component of the channel. The results being reported in this paper not only validate the main claims of previous studies based on ideal pure LOS channels, but also lead to novel findings. One major conclusion is that NLOS components are harmful to the SEP of GSM and should be avoided. As another important outcome, our results strongly motivate the use of precoding in GSM systems to simultaneously improve the channel capacity and reduce the physical size of MIMO arrays (thus eliminating one major issue of LOS GSM). [ABSTRACT FROM AUTHOR]

Channel estimation is employed to get the current knowledge of channel states for an optimum detection in fading environments. In this paper, a new recursive multiple input multiple output (MIMO) channel estimation is proposed which is based on the recursive least square solution. The proposed recursive algorithm utilizes short training sequence on one hand and requires low computational complexity on the other hand. The algorithm is evaluated on a MIMO communication system through simulations. It is realized that the proposed algorithm provides fast convergence as compared to recursive least square (RLS) and robust variable forgetting factor RLS (RVFF-RLS) adaptive algorithms while utilizing lesser computational cost and provides independency on forgetting factor. [ABSTRACT FROM AUTHOR]

This paper proposes a novel efficient precoding algorithm to maximize the rate of the cognitive link, where a pair of multiple-input multiple-output cognitive radio users shares the spectrum allocated to multiple primary users as long as the interference power is acceptable. In our method, the precoding vectors are firstly obtained by solving an unconstrained convex problem which is formulated by using the penalty function idea and has a closed-form solution. Then, power is allocated to different precoding vectors to satisfy both the transmit-power constraint and interference-power constraints through interior method. Moreover, an effective set of the penalty weights is presented. Our method has much lower complexity than the optimal solution and similar complexity to other low-complexity methods. Simulation results show that our method significantly outperforms the existing low-complexity methods and has almost the same performance as the optimal solution. [ABSTRACT FROM AUTHOR]

In this paper, a new variant of Spatial Modulation (SM) Multiple-Input Multiple-Output (MIMO) transmission technique, designated as Redesigned Spatial Modulation (ReSM) has been proposed. In ReSM scheme, a dynamic mapping for antenna selection is adopted. This scheme employs both single antenna as well as double antenna combinations depending upon channel conditions to combat the effect of spatial correlation. When evaluated over spatially correlated channel conditions, for a fixed spectral efficiency and number of transmit antennas, ReSM exhibits performance improvement of at least 3 dB over all the conventional SM schemes including Trellis Coded Spatial Modulation (TCSM) scheme. Furthermore, a closed form expression for the upper bound on Pairwise Error Probability (PEP) for ReSM has been derived. This has been used to calculate the upper bound for the Average Bit Error Probability (ABEP) for spatially correlated channels. The results of Monte Carlo simulations are in good agreement with the predictions made by analytical results. The relative gains of all the comparison plots in the paper are specified at an ABER of 10. [ABSTRACT FROM AUTHOR]

Slow fading channel is one of the most important channels, which appears widely in a cellular mobile system. It has several problems such as bad effects of fading, which causes an attenuation to the signal. This paper presents a new scheme in cooperative communication system under slow fading channel to enhance and increase the quality of communication systems performance. This new scheme is called a cooperative multiple input-multiple output Antenna. The main idea of this scheme depends on transmitting multi copy of message via two paths. It's performance has been compared with MIMO technique in term of outage probability. The results show that the negative effects of fading are mitigated and the outage probability and diversity gain are enhanced. Furthermore, the reliability in communication system under slow fading channel is improved. [ABSTRACT FROM AUTHOR]

As for the massive MIMO (multiple-input and multiple-output) enabled HCNs, we design a QoS-aware association scheme to maximize the sum of achievable rates under long-term rate constraints. Since the various BSs have different transmit power and antennas, this scheme (unbalanced association) may result in an extremely imbalanced load distribution. To fully exploit the network resources, we design another scheme (balanced association) to maximize the network-wide utility that is a logarithmic function of long-term rates. In fact, these schemes can be well implemented in the practical scene since the users can introduce long-term rate constraints to guarantee their QoS requirements. Significantly, it is not the case for the most existing schemes. Considering that these formulated problems are in a nonlinear and mixed-integer form and hard to tackle, we try to develop centralized algorithms using Lagrange multiplier method and distributed algorithms using dual decomposition. Numerical results show that the balanced association significantly outperforms the unbalanced association on the load balancing gain, rate fairness, but the QoS guarantee. In addition, we also show the impacts of the number of massive antennas on the association performance. [ABSTRACT FROM AUTHOR]

In this paper, spatial modulation (SM)-orthogonal frequency division multiplexing is introduced to massive multi-input multi-output high speed train systems to reduce the complexity of the receiver. First, the mathematic model of signal detection in frequency domain is formed as a compressive sensing (CS) problem. Based on this model, a novel detector, which exploits the unique group sparsity of the signal, is proposed to improve the accuracy of the nonzero elements localization. On the basis of the channel matrix decomposition, the detector combines the CS algorithms and the iteration process together to overcome the performance deterioration brought by inter-carrier interference. Moreover, theoretical analysis about the performance gain guarantee of our proposed detector is conducted and the complexity of the proposed detector is compared with the related works. Furthermore, we also extend our proposed detector into the special scenario that the train passes the overlapped area of the adjacent two cells and receives the superimposed signal. In order to deal with the inter-cell interference, a generalized SM framework is adopted to model the signal detection. Simulation results verify that the proposed detectors have an apparent performance gain compared to the conventional CS schemes with the same complexity order. [ABSTRACT FROM PUBLISHER]

In order to decode an enhanced layer (EL) signal for a layered-division multiplexing (LDM) system at fixed receivers in ATSC 3.0, low-density parity-check (LDPC)/BCH decoding and successive interference cancellation should be performed to eliminate the core layer (CL) signal. For a high signal-to-noise ratio environment and sufficient low injection level of the EL signal, the CL bit-interleaved coded modulation decoder can easily achieve quasi error free for the whole LDPC codeword. However, for high injection levels, there may be still many erroneous bits in the parity part even after LDPC/BCH decoding since the ATSC 3.0 LDPC codes have the characteristic of unequal error protection due to the unequal weight distributions in their parity-check matrices. Therefore, ATSC 3.0 receivers should include re-encoding module for CL LDPC codes to completely recover the CL signal for LDM system. In this paper, we propose an efficient method to reconstruct CL signal in ATSC 3.0 LDM systems, which can be realized by a modified re-encoding after LDPC decoding of the CL signal. It significantly reduces the computational complexity and worst case latency without any loss of coding performance. [ABSTRACT FROM PUBLISHER]

We tackle the problem of minimizing the maximum expected delivery time of all transmission pairs in 60 GHz mmWave networks. The network is dual-hop with multiple transmitter-receiver pairs, relays, and a centralized controller (termed PicoNet coordinator). We jointly optimize relay and link selection for the transmitter–receiver pairs to minimize delivery time, while the reflected non-line-of-sight transmission links are exploited to get around obstacles. To reduce computational complexity, we develop a decomposition principle to transform the joint-optimization problem into a link selection subproblem and a relay assignment subproblem when there are a sufficient amount of relays. A tight performance bound for the proposed algorithm is proved. We also develop a heuristic scheme to handle the case when there are no enough relays. The superior performance of our proposed algorithms is validated with extensive simulations and comparisons with benchmark schemes. [ABSTRACT FROM AUTHOR]

This paper considers multicell scheduling for coordinated multiple-input multiple-output cellular networks. In a multicell scenario, intercell interference, which is the major challenge degrading system performance, can be suppressed via multicell coordination. However, when the number of users is larger than that can be served, user/multimode selection is necessary, and can significantly enhance the performance in such interference-limited environment. Nevertheless, user selection in a multicell scenario incurs high computational complexity and overhead signalling. To this end, in this paper, low complexity greedy algorithms are proposed for user selection. The algorithms are based on the concept of angle between subspaces and intersection of null spaces, and work in partially distributed fashion with limited information exchange. By these algorithms, channel feedback can be greatly reduced with reasonable computational complexity. In addition, multimode scheduling schemes are proposed for this multicell set up, where the spatial streams are adaptively selected. The proposed algorithms are analysed and compared with the optimal solution obtained by exhaustive search. Simulation results show that the algorithms achieve most of the throughput achievable by the optimal solution. [ABSTRACT FROM AUTHOR]

At the time of writing, vehicle-to-vehicle (V2V) communication is enjoying substantial research attention as a benefit of its compelling applications. However, the ever-increasing tele-traffic is expected to result in overcrowding of the available band. As a first resort, multiple input multiple output (MIMO) can be utilized to enhance the attainable bandwidth efficiency or link reliability. However, in hostile V2V wireless propagation environments, the achievable multiple-antenna gain is eroded by the channel correlation. As a promising MIMO technique, spatial modulation (SM) only activates a single transmit antenna (TA) in any symbol interval and, hence, completely avoids the inter-antenna interference, hence showing robustness against channel correlation. As a further powerful solution, non-orthogonal multiple access (NOMA) has been proposed for improving the bandwidth efficiency. Inspired by the robustness of SM against channel correlation and the benefits of NOMA, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless V2V environments as well as to support improved bandwidth efficiency. Moreover, the bandwidth efficiency of NOMA-SM is further boosted with the aid of a massive TA configuration. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We investigate the bit error ratio performance of NOMA-SM via Monte Carlo simulations, where the impact of the Rician $K$ -factor, spatial correlation of the antenna array, time-varying effect of the V2V channel, and the power allocation factor is discussed. Furthermore, we also analyze the capacity of NOMA-SM. By analyzing the capacity and deriving closed-form upper bounds on the capacity, a pair of power allocation optimization schemes are formulated. The optimal solutions are demonstrated to be achievable with the aid of our proposed algorithm. Again, instead of simply invoking a pair of popular techniques, we intrinsically amalgamate SM and NOMA to conceive a new system component exhibiting distinct benefits in the V2V scenarios considered. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the effects of pilot assignment (PA) in multicell massive multiple-input-multiple-output systems. When deploying linear detection/precoding algorithms and a large number of antennas at base station (BS), it is well-known that system performance in both uplink (UL) and downlink (DL) is mainly restricted by pilot contamination. Such interference is proper of each pilot sequence, and thus, system performance can be improved by suitably assigning the pilots to the users within a given cell, according to a certain desired metric. We show in this paper that UL and DL performances constitute conflicting metrics, since it is not possible to achieve the best performance in UL and DL concomitantly. Thus, we propose an alternative metric, namely, total capacity, aiming to simultaneously achieve a suitable performance in both directions, ie, UL and DL. Since the PA problem is combinatorial, and the search space grows with the number of pilots in a factorial fashion, we also propose a low-complexity suboptimal algorithm that achieves promising capacity performance avoiding the exhaustive search. In addition, to fully benefit from the large excess of BS antennas, we combine our proposed PA schemes with an efficient power control algorithm, unveiling the great potential of the proposed schemes to provide improved performance for more users, even with a not-so-large number of BS antennas. In a limit condition, for example, our numerical results demonstrate that with 64 BS antennas serving 10 users, our proposed method can assure a 95% likely rate of 4.2 Mbps for both DL and UL, and a symmetric 95% likely rate of 1.4 Mbps when serving 32 users. If a higher number of antennas is allowed at BS, the guaranteed rates can be significantly higher. [ABSTRACT FROM AUTHOR]

Both caching and interference alignment (IA) are promising techniques for next-generation wireless networks. Nevertheless, most of the existing works on cache-enabled IA wireless networks assume that the channel is invariant, which is unrealistic considering the time-varying nature of practical wireless environments. In this paper, we consider realistic time-varying channels. Specifically, the channel is formulated as a finite-state Markov channel (FSMC). The complexity of the system is very high when we consider realistic FSMC models. Therefore, in this paper, we propose a novel deep reinforcement learning approach, which is an advanced reinforcement learning algorithm that uses a deep $Q$ network to approximate the $Q$ value-action function. We use Google TensorFlow to implement deep reinforcement learning in this paper to obtain the optimal IA user selection policy in cache-enabled opportunistic IA wireless networks. Simulation results are presented to show that the performance of cache-enabled opportunistic IA networks in terms of the network's sum rate and energy efficiency can be significantly improved by using the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper provides a comprehensive scaling law-based performance analysis for multicell multiuser massive multiple-input-multiple-output (MIMO) downlink systems. Imperfect channel state information (CSI), pilot contamination, and channel spatial correlation are all considered. First, a sum-rate lower bound is derived by exploiting the asymptotically deterministic property of the received signal power, while keeping the random nature of other components in the signal-to-interference-plus-noise-ratio (SINR) intact. Via a general scaling model on important network parameters, including the number of users, the channel training energy and the data transmission power, with respect to the number of base station antennas, the asymptotic scaling law of the effective SINR is obtained, which reveals quantitatively the tradeoff of the network parameters. More importantly, pilot contamination and pilot contamination elimination (PCE) are considered in the analytical framework. In addition, the applicability of the derived asymptotic scaling law in practical systems with large but finite antenna numbers are discussed. Finally, sufficient conditions on the parameter scalings for the SINR to be asymptotically deterministic in the sense of mean square convergence are provided, which covers existing results on such analysis as special cases and shows the effect of PCE explicitly. [ABSTRACT FROM PUBLISHER]

Multiple input and multiple output (MIMO) relay could provide broader wireless coverage, better diversity, and higher throughput. Most existing precoder designs for either source or relay node are based on the assumption of Gaussian input signals. However, recent works have revealed possible performance loss of MIMO systems originally optimized for Gaussian source signals when applied to practical finite-alphabet source signals. In this work, we investigate the design problem of joint MIMO precoding for wireless two-hop nonregenerative cooperative relay networks under finite-alphabet source signals. We identify several structural properties of optimal precoders. Specifically, we provided the optimal left singular vectors of the relay precoder, and proved the convexity of mutual information with respect to the square of relay precoder singular value. These results generalize the two-hop relay networks in Gaussian input assumption to the cooperative relay networks in arbitrary finite-alphabet input signals. Furthermore, we propose gradient-based numerical iterative optimization algorithms not only for arbitrary finite-alphabet source signal precoding but also for cooperative relay networks which may or may not have a direct source to destination link. Our results demonstrate substantial performance improvement over existing precoder designed traditionally under Gaussian input assumption, which indicates that the waterfilling based precoding strategy is not suitable for finite-alphabet constellation source inputs. [ABSTRACT FROM PUBLISHER]

5G New Radio (NR) operating in the unlicensed spectrum is accelerating the Fourth Industrial Revolution by supporting Internet of Things (IoT) networks or Industrial IoT deployments. Specifically, LTE-Advanced (LTE-A) is looking to achieve spectrum integration through coexistence with multi-radio access technology (RAT) systems in the same unlicensed bands with both licensed-assisted and stand-alone access. The listen-before-talk (LBT) mechanism is mainly considered to enable an LTE operator to protect other incumbent unlicensed systems. In this article, we investigate the behaviors of multiple LTE operators along with the deployment of WiFi networks in the unlicensed spectrum from both short- and long-term points of view. In countries without mandatory LBT requirements, we show that an LTE operator is susceptible to collusion with another LTE operator, thus exploiting scarce spectrum resources by deceiving other wireless networks into thinking that channels are always busy; hence, mandatory usage of LTE with LBT is highly recommended at national level to achieve harmonious coexistence in the unlicensed spectrum. We discuss several possible coexistence scenarios to resolve the operator's dilemmaas well as to improve unlicensed spectrum efficiency among multi-RAT systems, which is viable in the near future. [ABSTRACT FROM AUTHOR]

Linear precoding has been widely studied in the context of massive multiple-input multiple-output (MIMO) together with two common power normalization techniques, namely, matrix normalization (MN) and vector normalization (VN). Despite this, their effect on the performance of massive MIMO systems has not been thoroughly studied yet. The aim of this paper is to fulfill this gap by using large system analysis. Considering a system model that accounts for channel estimation, pilot contamination, arbitrary pathloss, and per-user channel correlation, we compute tight approximations for the signal-to-interference-plus-noise ratio and the rate of each user equipment in the system while employing maximum ratio transmission (MRT), zero forcing (ZF), and regularized ZF precoding under both MN and VN techniques. Such approximations are used to analytically reveal how the choice of power normalization affects the performance of MRT and ZF under uncorrelated fading channels. It turns out that ZF with VN resembles a sum rate maximizer while it provides a notion of fairness under MN. Numerical results are used to validate the accuracy of the asymptotic analysis and to show that in massive MIMO, noncoherent interference and noise, rather than pilot contamination, are often the major limiting factors of the considered precoding schemes. [ABSTRACT FROM PUBLISHER]

In ambient rescatter communications, devices convey information by modulating and rescattering the radio frequency signals impinging on their antennas. In this correspondence, we consider a system consisting of a legacy modulated continuous carrier multiple-input-multiple-output link and a multiantenna modulated rescatter (MRS) node, where the MRS node modulates and rescatters the signal generated by the legacy transmitter. The receiver seeks to decode both the original message and the information added by the MRS. We show that the achievable sum rate of this system exceeds that which the legacy system could achieve alone. We further consider the impact of channel estimation errors under the least squares channel estimation and study the achievable rate of the legacy and MRS systems, where a linear minimum mean square error receiver with successive interference cancellation is utilized for joint decoding. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a massive multiple-input multiple-output (MIMO) system for urban macro cellular networks. A new technique named vertical spatial filtering (VSF) is proposed to achieve low radio frequency (RF) complexity by exploiting the spatial beam redundancy in elevation domain. Specifically, VSF consists of two parts: beam mapping and beam selection. We first adopt beam mapping to transform the received signals from antenna space into beam space. Then, we use beam selection to pick out part of the RF chains so as to realize the reduction of RF complexity. A three-dimensional channel model is adopted to evaluate the system performance. Two strategies for beam selection are proposed and numerical results are presented. The results show that the reduced system with VSF has the performance comparable to the complete system, while only a small amount of RF chains is required in vertical dimension of the two-dimensional base station array. [ABSTRACT FROM PUBLISHER]

In this paper, a novel multiple-input multiple-output (MIMO) transmission scheme termed space-time block coded differential spatial modulation (STBC-DSM) is proposed. It employs the hybrid concept of differential spatial modulation (DSM) and space-time block coding (STBC) to exploit the diversity benefits of STBC without the channel state information (CSI). In the STBC-DSM scheme, information bits are conveyed via the antenna matrix (AM) indices, as well as STBC blocks. Specifically, a novel AM set is first designed such that the transmitter requires only sparse (one or two) frequency radio (RF) chains. Then, the proposed STBC-DSM scheme is extended to the large-scale MIMO scenarios, and a low-complexity near-optimal detection algorithm is developed. Finally, an upper bound for the average bit error probability of the proposed scheme is derived. Both analytical and simulation results have shown that the proposed scheme is capable of achieving considerable performance gains over the existing DSM and differential Alamouti schemes. [ABSTRACT FROM PUBLISHER]

Massive MIMO promises large spectral and power efficiency gains. However, pilot contamination limits these aspired gains. In this paper, we propose a structured, i.e., non-random, pilot hopping and a weighted moving average channel estimation for time-varying massive MIMO systems. The proposed algorithm diversifies the contaminating (interfering) sources, such that all the users enjoy the hopping advantages. We analyze the performance of multi-cell network, where the base stations perform matched filtering or zero-forcing for data detection. Using polynomial expansion approximations, we obtain achievable rates that are tight even at finite (not very large) number of antennas. It is shown that the spectral efficiency gain achieved by pilot hopping is not a monotonic function of the pilot reuse factor $\beta $ in some cases and, therefore, brings to attention that careful cell planning is required when applying pilot hopping. Moreover, the proposed algorithm involves a weighted moving average that uses the previously obtained channel estimates (of the preceding blocks) if they are correlated with the current one. Due to the massive MIMO properties, the algorithm is robust to channel time-variations and can be used with any previously proposed channel estimation method. [ABSTRACT FROM AUTHOR]

This paper studies the optimal frequency reuse for the transmission of multimedia scalable sources, such as embedded images or scalable video, which need unequal error protection or unequal transmission rates in the bitstream. First, we analyze the crossover of the outage probabilities for full and partial frequency reuse cases in terms of the data rate. We prove that we can find a crossover of the outage probability curves for a data rate lower than a given threshold, which is a function of the parameters such as the partial frequency reuse factor and the user location in the cell. Moreover, the crossover point in the signal-to-noise ratio (SNR) is a strictly increasing function of the data rate. On the other hand, for a data rate higher than or equal to the threshold, there is no crossover; for all SNRs, the outage probability of full-frequency reuse is lower than that of partial-frequency reuse. The results are proven for the arbitrary location of a user in a cell, and for an arbitrary partial frequency reuse factor. Furthermore, the results hold, regardless of the numbers of transmit and receive antennas in the multiple-input multiple-output systems of orthogonal space-time block codes, and of the vertical Bell Labs space-time architecture with a zero-forcing linear receiver. Based on the analysis, we propose unequal-frequency reuse for the optimal transmission of scalable sources. The numerical results show that the peak-SNR performance improves when a sequence of scalable packets is transmitted at the subbands governed by unequal-frequency reuse in cellular networks. [ABSTRACT FROM AUTHOR]

We propose a max–min multicell-aware regularized zero-forcing (MCA-RZF) precoding and power allocation scheme for downlink multicell massive multiple-input multiple-output systems. A general correlated channel model is considered, and the adopted channel state information (CSI) acquisition model includes the effects of estimation errors and pilot contamination. We use results from random matrix theory to derive deterministic equivalents for the proposed max–min power allocation in the large system limit, which solely depend on statistical CSI, but not on individual channel realizations. Our numerical results show that the proposed max–min MCA-RZF precoder achieves a substantially higher network-wide minimum rate than the MCA-RZF and the conventional RZF precoders with uniform power allocation, respectively, as well as the conventional RZF precoder with max–min power allocation. [ABSTRACT FROM AUTHOR]

In this paper, a multiple model adaptive control (MMAC) method is proposed for a gas turbine engine. The model of a twin spool turbo-shaft engine driving a variable pitch propeller includes various operating points. Variations in fuel flow and propeller pitch inputs produce different operating conditions which force the controller to be adopted rapidly. Important operating points are three idle, cruise and full thrust cases for the entire flight envelope. A multi-input multi-output (MIMO) version of second level adaptation using multiple models is developed. Also, stability analysis using Lyapunov method is presented. The proposed method is compared with two conventional first level adaptation and model reference adaptive control techniques. Simulation results for JetCat SPT5 turbo-shaft engine demonstrate the performance and fidelity of the proposed method. [ABSTRACT FROM AUTHOR]

As real-time applications typically require short length code words, this paper analyzes the minimum achievable code word error rate of the given finite-length code words, namely, maximum likelihood (ML) decoding error probability. For coding schemes ML decoding is too complex, the key contribution of this paper is to analytically assess the performance gap between ML decoding and a practical decoding scheme. We analyze the combination of turbo codes and bit-interleaved coded-modulation that is a spectrally efficient coding scheme adopted in 3GPP long term evolution (LTE). In single-input single-output (SISO) systems, it was shown in the literature that turbo decoding delivers near-ML decoding performance. In this paper, we extend the analysis to a multi-input multi-output (MIMO) system. In contrast to the SISO case, the turbo principle-based iterative decoding scheme is subject to appreciable performance loss compared with the ML decoding, even in good MIMO channel conditions. For this reason, we further analyze potential reasons and examine possible improvements. By means of simulation, it is shown that convergence to a non-ML code word rather than non-convergence is the key reason for the observed performance loss in good channel conditions. [ABSTRACT FROM PUBLISHER]

This contribution analyses the performance of efficient multiple-input-multiple-output (MIMO) detectors under correlated channels and imperfect coefficients channel estimation. A number of signal detection principles and techniques, including the minimum mean squared error detector with and without ordered successive interference cancellation; the sphere decoding MIMO detection, as well as promising near-orthogonal transformation techniques combined with these detectors, namely the lattice reduction and the QR decomposition are analysed under the perspective of complexity-performance tradeoff. While in most of available works perfect channel state information and uncorrelated channels have been considered, herein the complexity-performance tradeoff has been analysed and compared with the maximum likelihood (ML) limit under specific but practical scenarios of interest, namely: high spectral efficiency scenario; channel error estimates; channel/antenna correlation; combined channel errors and correlated channels. Under performance-complexity perspective, the optimum ML-MIMO detector is deployed as reference aiming to evaluate the efficiency and performance degradation of those sub-optimal MIMO detectors operating under hostile channel conditions. [ABSTRACT FROM AUTHOR]

This paper presents results from a wide band single-input–single-output (SISO) and 16 × 16 virtual multiple-input–multiple-output (MIMO) measurement campaign at a center frequency of 1.4725 GHz in a 100-meter long tunnel laboratory which is terminated by a vertical wall with a metallic door. The path loss, root-mean-square delay spread (RMS-DS) characteristics, and power delay profiles (PDPs) are described. In addition, we provide results for the MIMO channel amplitude matrix, which offers a new perspective in understanding MIMO characteristics in tunnel scenarios. Our measurement results are analyzed and compared to ray tracing simulations. The relationships among the angle spread, channel matrix singular values, and MIMO capacity at various link distances are illustrated, and these provide insights into MIMO system deployment. [ABSTRACT FROM AUTHOR]

In magnetic resonant coupling (MRC) enabled multiple-input multiple-output (MIMO) wireless power transfer (WPT) systems, multiple transmitters (TXs) are used to enhance the efficiency of simultaneous power transfer to multiple receivers (RXs) by constructively combining their induced magnetic fields, a technique termed “magnetic beamforming”. In this paper, we study the optimal magnetic beamforming design in a multiuser MIMO MRC-WPT system. We introduce and characterize the multiuser power region, which constitutes all the achievable power tuples for all RXs, subject to the given total power constraint over all TXs as well as their individual peak voltage and current constraints. For the special case without TX peak voltage and current constraints, we derive the optimal TX current allocation for the single-RX setup in closed-form and that for the multi-RX setup by applying the techniques of semidefinite relaxation (SDR) and time-sharing. In general, the problem is a nonconvex quadratically constrained quadratic programming (QCQP), which is difficult to solve. For the case of one single RX, we show that the SDR of the problem is tight and thus solve the problem efficiently. For the general case with multiple RXs, based on SDR we obtain two approximate solutions by applying the techniques of time-sharing and randomization, respectively. Moreover, we propose a new method to estimate the magnetic MIMO channel between TXs and RXs for practical implementation of magnetic beamforming. Numerical results show that our proposed magnetic channel estimation and adaptive beamforming schemes are practically effective and can significantly improve the power transfer efficiency and multiuser performance tradeoff in MIMO MRC-WPT systems compared with the benchmark scheme of uncoordinated WPT with fixed identical TXs' current. [ABSTRACT FROM PUBLISHER]

The characterization of the global maximum of energy efficiency (EE) problems in wireless networks is a challenging problem due to their nonconvex nature in interference channels. The aim of this paper is to develop a new and general framework to achieve globally optimal solutions. First, the hidden monotonic structure of the most common EE maximization problems is exploited jointly with fractional programming theory to obtain globally optimal solutions with exponential complexity in the number of network links. To overcome the high complexity, we also propose a framework to compute suboptimal power control strategies with affordable complexity. This is achieved by merging fractional programming and sequential optimization. The proposed monotonic framework is used to shed light on the ultimate performance of wireless networks in terms of EE and also to benchmark the performance of the lower-complexity framework based on sequential programming. Numerical evidence is provided to show that the sequential fractional programming framework achieves global optimality in several practical communication scenarios. [ABSTRACT FROM PUBLISHER]

A massive MIMO system entails a large number (tens or hundreds) of base station antennas serving a much smaller number of terminals. These systems demonstrate large gains in spectral and energy efficiency compared with the conventional MIMO technology. As the number of antennas grows, the performance of a massive MIMO system gets limited by the interference caused by pilot contamination. Ashikhmin and Marzetta proposed (under the name of Pilot Contamination Precoding) large scale fading precoding (LSFP) and large scale fading decoding (LSFD) based on limited cooperation between base stations. They showed that zero-forcing LSFP and LSFD eliminate pilot contamination entirely and lead to an infinite throughput as the number of antennas grows. In this paper, we focus on the uplink and show that even in the case of a finite number of base station antennas, LSFD yields a very large performance gain. In particular, one of our algorithms gives a more than 140 fold increase in the 5% outage data transmission rate! We show that the performance can be improved further by optimizing the transmission powers of the users. Finally, we present decentralized LSFD that requires limited cooperation only between neighboring cells. [ABSTRACT FROM PUBLISHER]

In this paper, the performance analysis of Receive Space Modulation (RSM) in the shadowing Multiple-Input Multiple-Output (MIMO) broadcast channel is presented. This is undertaken by considering Zero Forcing (ZF) precoding and both small and large scale fading. In particular, a closed form and accurate framework for the evaluation of the Symbol Error Rate (SER) is derived. In addition, the diversity order and the coding gain of the new architecture are also obtained. The derived framework can be directly extended to the conventional spatially multiplexed shadowing MIMO broadcast channel. It is shown that RSM achieves the same diversity order and, in certain scenarios which are well defined, higher coding gain than spatially multiplexing (SMX). Also, the performance difference between RSM and SMX in the shadowing broadcast channel is mathematically quantified. Finally, numerical results that verify the new framework and conclusions are provided. [ABSTRACT FROM PUBLISHER]

In multiple-input multiple-output (MIMO) radar, for desired transmit beampatterns, appropriate correlated waveforms are designed. To design such waveforms, conventional MIMO radar methods use two steps. In the first step, the waveforms covariance matrix \mathbf R is synthesized to achieve the desired beampattern. Whereas in the second step, to realize the synthesized covariance matrix, actual waveforms are designed. Most of the existing methods use iterative algorithms to solve these constrained optimization problems. The computational complexity of these algorithms is very high, which makes them difficult to use in practice. In this paper, to achieve the desired beampattern, a low complexity discrete-Fourier-transform based closed-form covariance matrix design technique is introduced for an MIMO radar. The designed covariance matrix is then exploited to derive a novel closed-form algorithm to directly design the finite-alphabet constant-envelope waveforms for the desired beampattern. The proposed technique can be used to design waveforms for large antenna array to change the beampattern in real time. It is also shown that the number of transmitted symbols from each antenna depends on the beampattern and is less than the total number of transmit antenna elements. [ABSTRACT FROM PUBLISHER]