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We consider a cooperative X-channel with $\sf K$ transmitters (TXs) and $\sf K$ receivers (Rxs) where Txs and Rxs are gathered into groups of size $\sf r$ respectively. Txs belonging to the same group cooperate to jointly transmit a message to each of the $\sf K- \sf r$ Rxs in all other groups, and each Rx individually decodes all its intended messages. By introducing a new interference alignment (IA) scheme, we prove that when $\sf K/\sf r$ is an integer the sum Degrees of Freedom (SDoF) of this channel is lower bounded by $2\sf r$ if $\sf K/\sf r \in \{2,3\}$ and by $\frac{\sf K(\sf K-\sf r)-\sf r^2}{2\sf K-3\sf r}$ if $\sf K/\sf r \geq 4$. We also prove that the SDoF is upper bounded by $\frac{\sf K(\sf K-\sf r)}{2\sf K-3\sf r}$. The proposed IA scheme finds application in a wireless distributed MapReduce framework, where it improves the normalized data delivery time (NDT) compared to the state of the art.

The distributed nodes of a Wireless Sensor Network (WSN) cooperate among themselves to emulate a virtual multi-antenna system to get similar benefits as the conventional MIMO systems. In WSN, such a system is known as the Cooperative Multiple Input Multiple Output (CMIMO) system. A CMIMO system has an enormous capacity to improve the performance of a WSN. But the increasing demand in the data rate and the desired Quality of Services (QoS), necessitates a revival in the way CMIMO was originally perceived in the early 1990s. Therefore, this article identifies several emerging supportive technologies such as the Compressive Sensing (CS), Simultaneous Wireless Information and Power Transfer (SWIPT), over the air computation, etc. which can be integrated to the CMIMO framework for enhancing the network performance in terms of throughput, delay, Energy Efficiency (EE), etc. The inclusion of these novel ideas necessitates further exploration of CMIMO in WSN along with its associated challenges and their possible solutions. This article provides a comprehensive overview of a CMIMO WSN along with its challenges which have been classified based on the layers of the protocol stack. Since energy efficiency is a key concern in a WSN having scarce energy resources, the energy-saving techniques have been discussed in detail. Further, challenges and open issues have also been highlighted which opens up new research direction in the area.

Wireless sensor networks are typically operated on batteries. Therefore, in order to prolong network lifetime, an energy efficient routing algorithm is required. In this paper, an energy-aware routing protocol for the co-operative MIMO scheme in WSNs (EARPC) is presented. It is based on an improved cluster head selection method that considers the remaining energy level of a node and recent energy consumption of all nodes. This means that sensor nodes with lower energy levels are less likely to be chosen as cluster heads. Next, based on the cooperative node selection in each cluster, a virtual MIMO array is created, reducing uneven distribution of clusters. Simulation results show that the proposed routing protocol may reduce energy consumption and improve network lifetime compared with the LEACH protocol

The main objective of a Cooperative Multiple-Input Multiple-Output (CMIMO) system is to improve network throughput and network coverage and save energy. By grouping wireless devices as virtual multi-antenna nodes, it can thus simulate the functions of multi-antenna systems. A Space-Time Block Code (STBC) was proposed to utilize the spatial diversity of MIMO systems to improve the diversity gain and coding gain. In this paper, we proposed a cooperative strategy based on STBC and CMIMO, which is referred to as Space-Time Block Coded Cooperative Multiple-Input Multiple-Output (STBC-CMIMO) to inherit the advantages from both STBC and CMIMO. The theoretical performance analysis for the proposed STBC-CMIMO is presented. The performance advantages of the STBC-CMIMO are also shown by simulations. In the simulations, it is demonstrated that STBC-CMIMO can obtain significant performance compared with the existing CMIMO system.

Unmanned Aerial Vehicles (UAVs) are recently used for both civilian and military applications in worldwide. Energy Efficiency (EE) is an exceptional design approach for modern communication based systems. New advance technology is needed in order to support UAV applications with reduced energy usage. In this paper, an Energy Efficiency with Hybrid Fuzzy Firefly Algorithm (EE-HFFA) method is introduced for Multiple-Input–Multiple-Output (MIMO) Amplify-And-Forward (AF) systems in which Partial Channel State Information (PCSI) estimation is existing at the relays because of the high speed mobility. A new EE-HFFA algorithm is presented in this research, by means of merging the benefits of the Firefly Algorithm (FA) as well as Differential Evolution (DE). For increasing information sharing both the techniques are implemented in parallel and as a result improve searching efficiency. The outcomes of these two techniques are based upon the fuzzy membership function. For approximation of PCSI for the source node as well as relay nodes, Branch Convolutional Neural Network (B-CNN) classifier is presented to raise the capability of cooperative MIMO-AF systems. EE-optimal source and relay precoding matrices are cooperatively enhanced by means of EE-HFFA. Simulation out comes illustrate that the presented EE-HFFA as well as B-CNN classifier could enhance the EE of MIMO-AF systems with PSCI while matched up with direct/relay link merely precoding optimization.

In this work, we present a switched relaying framework for multiple-input multiple-output (MIMO) relay systems where a source node may transmit directly to a destination node or aided by relays. We also investigate relay selection techniques for the proposed switched relaying framework, whose relays are equipped with buffers. In particular, we develop a novel relay selection protocol based on switching and the selection of the best link, denoted as Switched Max-Link. We then propose the Maximum Minimum Distance (MMD) relay selection criterion for MIMO systems, which is based on the optimal Maximum Likelihood (ML) principle and can provide significant performance gains over other criteria, along with algorithms that are incorporated into the proposed Switched Max-Link protocol. An analysis of the proposed Switched Max-Link protocol and the MMD relay selection criterion in terms of computational cost, pairwise error probability, sum-rate and average delay is carried out. Simulations show that Switched Max-Link using the MMD criterion outperforms previous works in terms of sum-rate, pairwise error probability, average delay and bit error rate.

Duty cycle is a well-known approach for energy saving as well as life time enhancement of a wireless sensor network having scarce energy resources. In this paper, we have achieved energy savings by introducing duty cycle in an aggregation based cooperative-MIMO (CMIMO) framework. In the proposed CMIMO framework, instead of opting for the complete centralized or distributed approach, an optimum number of node performs aggregation and long haul transmissions which not only saves energy but also increases the reliability of the network. The aggregator and the long haul link nodes are selected based on the residual energy level. The role of a node to behave as an aggregator and/or long haul link node is rotated after certain number of rounds and duty cycle is implemented accordingly. This ensures load balancing which eventually leads to lifetime enhancement. The effect of varying the cluster size, the number of aggregator nodes and the long haul links on the average energy consumption have also been analysed. The result shows that by introducing duty cycle in an aggregation based framework contributes to a significant amount of energy savings. On an average 42.50% of energy is saved in the proposed framework when compared CMIMO without any data aggregation. And this energy saving is up to 99% when compared to the conventional single node transmission.

We consider a communication scheme in which two low earth orbit (LEO) satellites jointly transmit (at the same time and frequency) to a multi antenna land terminal (LT). This scheme can increase the achievable terminal throughput by up to a factor of 2, depending on the channel matrices. The implementation aspects of this scheme are well-known but the usefulness of this scheme for LEO satellites has yet to be studied. Because the satellite channel is dominated by its line-of-sight (LOS) component, the terminal's ability to separate the two streams depends critically on the system's instantaneous-configuration; i.e., the relative location of the satellites and the terminal antennas. Since the relative locations of LEO satellites vary rapidly, the throughput characterization is not straightforward. To characterize the network performance we consider two satellites having one antenna, transmitting to a single LT having multiple antennas. We introduce a novel stochastic framework that assumes the terminal orientation as random. Using the proposed framework, we show that if the terminal antennas are close, the network throughput is nearly independent of the terminal orientation. When the terminal antennas are sufficiently separated, the result is completely different. For this case, we define an outage event and calculate the outage probability. The definition of outage in our novel stochastic framework allows us to prove that dual satellite transmission can indeed increase the downlink throughput with high probability.

As compared with 2D wireless camera sensor networks (WCSNs), 3D WCSNs can capture more accurate and comprehensive information for exposure-path prevention in supervisory and military applications. However, 3D WCSNs impose many new challenges for energy-efficiency and interference-mitigation subject to required coverage rate constraint due to extensive power consumption over time-varying wireless channels. To overcome the above-mentioned problems, in this paper we propose the AQ-DBPSK/DS-CDMA (alternating quadratures differential binary phase shift keying/direct-sequence code division multiple access) based cooperative MIMO energy-efficient and interference-mitigating scheme under the constraint of optimal tradeoff between power consumption and coverage rate over multi-hop clustered WCSNs. In particular, we build sensing models to characterize the minimum coverage rate constraint and formulate the exposure-path prevention problem using the percolation theory. Then, we derive the critical density of camera sensors subject to minimum exposure-path prevention probability constraint. We develop the AQ-DBPSK/DS-CDMA scheme and also derive the optimal data rate to optimize transmit-power and data-rate trade-off. By deriving the critical density of camera sensors over 3D WCSNs, we apply the cooperative MIMO based NEW LEACH architecture for our multi-hop cooperative MIMO scheme. Also conducted is a set of simulations which show that our proposed scheme can outperform other existing schemes in terms of energy efficiency and interference-mitigation over multi-hop 3D clustered WCSNs.

In a multiple-input multiple-output (MIMO) cognitive radio network, the cognitive users (CUs) coexist with the primary users (PUs) in the same spectrum for boosting the spectrum efficiency. Based on the informed limit of the interference power from the PUs, the CUs' compete to minimise the total interference power generated. In this study, noncooperative and cooperative game theoretic approaches are derived for network interference management (NIM). In the first scenario, the NIM problem computes the sum of minimum individual CU's interference power produced on the PU to converge to equilibrium by using the best response iteration method. The second one, NIM estimates Nash product to converge to Nash bargaining solution by using the dual decomposition method. Numerical results prove the effectiveness of the cooperative scenario that minimises the network interference power. Two new metrics are proposed to evaluate the performance in these scenarios. The interference cooperative loss metric estimates the overall network interference power loss from CUs cooperation rather than non-cooperation in the game theoretic solution. Capacity cooperative gain metric estimates the overall network capacity gain from CUs cooperation rather than non-cooperation in the game theoretic solution for a fixed acceptable interference level.

This paper considers sparse device activity detection for cellular machine-type communications with non-orthogonal signatures using the approximate message passing algorithm. This paper compares two network architectures, massive multiple-input multiple-output (MIMO) and cooperative MIMO, in terms of their effectiveness in overcoming inter-cell interference. In the massive MIMO architecture, each base station (BS) detects only the users from its own cell while treating inter-cell interference as noise. In the cooperative MIMO architecture, each BS detects the users from neighboring cells as well; the detection results are then forwarded in the form of log-likelihood ratio (LLR) to a central unit where final decisions are made. This paper analytically characterizes the probabilities of false alarm and missed detection for both architectures. Numerical results validate the analytic characterization and show that as the number of antennas increases, a massive MIMO system effectively drives the detection error to zero, while as the cooperation size increases, the cooperative MIMO architecture mainly improves the cell-edge user performance. Moreover, this paper studies the effect of LLR quantization to account for the finite-capacity fronthaul. Numerical simulations of a practical scenario suggest that in that specific case cooperating three BSs in a cooperative MIMO system achieves about the same cell-edge detection reliability as a non-cooperative massive MIMO system with four times the number of antennas per BS., Comment: 14 pages, 9 figures, to appear in IEEE Transactions on Wireless Communications

In this paper, performance of a dual-hop cooperative multiple-input and multiple-output (MIMO) system for various futuristic QAM schemes is analyzed. A non-regenerative MIMO scheme with transmit antenna selection strategy is considered where a single transmit antenna maximizing the total received signal power is selected for transmission. In the considered system model, it is assumed that the source, relay and the destination are equipped with multiple antennas. As a performance measure, generalized expressions for average symbol error rate for hexagonal quadrature amplitude modulation, rectangular quadrature amplitude modulation, square quadrature amplitude modulation and 32-cross quadrature amplitude modulation are derived. The impact of pathloss is highlighted for the considered system model and finally, the derived analytical expressions are validated through Monte-Carlo simulations.

In this paper, we propose self-interference (SI) cancellation in cooperative multiple-input multiple-output (Co-MIMO) for full-duplex (FD) wireless communication systems. This proposal solves SI by applying the block diagonalization used in multi-user MIMO. Therefore, there is no need for a radio frequency (RF) canceller, which has a large hardware (HW) size and is difficult to extend to MIMO. Furthermore, we can achieve higher throughput by applying Co-MIMO, in which multiple access points (APs) work together to communicate. The proposed method's implementation uses field-programmable gate array (FPGA) and software-defined radio (SDR). In the experiment, a total of 33 [dB] SI can cancel with two cooperative APs and two antennas per AP in the IEEE 802.11 system.

We demonstrate a self-interference (SI) cancellation in cooperative multiple-input multiple-output (Co-MIMO) for full-duplex (FD) wireless communication systems by applying the block diagonalization used in multi-user MIMO. The proposed method's implementation uses a field-programmable gate array (FPGA) and software-defined radio (SDR). In the experiment, a total of 33 [dB] SI can cancel with two cooperative APs and two antennas per AP in the IEEE 802.11 system.

In recent years, relaying networks are promising for future wireless communication systems, which profoundly enhance link capacity and exploiting cooperative diversity. In this paper, we propose a prototype of a Decode-&-Forward (D&F) Relay Node system based on Software Defined Radio (SDR) using Universal Software Radio Peripheral (USRP) and Matlab™ software. The developed testbed platform allows implementing and test new algorithms and specifications for LTE/LTE-A and 5G. Both Single-Input Single-Output (SISO) and Multi-Input Multi-Output (MIMO) are supported in our testbed. The considered D&F MIMO cooperative system in this paper utilizes Orthogonal Space-Frequency Block Codes (OSFBCs) for the transmission of the data symbols of the source to the destination. The transmission data from eNB has been measured using commercial 4G/5G measurement equipment. It has been demonstrated that D&F cooperative system substantially improves the Bit Error Rate (BER) and throughput of the user, taking higher performance with the 2×2 MIMO technique.

This paper proposes a full-duplex wireless communication system applying cooperative multiple-input multiple-output (Co-MIMO). This proposal solves self-interference (SI) in full-duplex wireless communication systems by applying the block diagonalization used in multi-user MIMO (MU-MIMO). Therefore, there is no need for a radio frequency (RF) canceller, which has a large hardware size and is difficult to extend to MIMO. Furthermore, higher throughput can be achieved by applying Co-MIMO, in which multiple access points work together to communicate. We also introduce the implementation of the proposed method using a field-programmable gate array (FPGA) and software-defined radio (SDR) in this paper. It shows that SI cancellation can be realized by using them. The proposed method is implemented based on the IEEE 802.11n frame format as an example. In the experiment, a total of 30 [dB] SI cancellation is confirmed with a transmission power of -12 [dBm]. The SI cancellation amount can be further increased by increasing the transmission power.

In recent years, cooperative communication as well as relay selection problem have been known as a new research area that may provide many interesting applications in practical networking system. In this paper we consider a cooperative multiple input multiple output (Co-MIMO) system in which multiple antenna of mobile terminals are used. We examine the content of centralized cooperative relay selection and propose a new relay selection method based on channel priority matching algorithm. In the specific algorithm, we presented thresholds for Worst-Link-First Matching (WLF). Theoretical and simulated results indicated that our proposed algorithm can achieve higher performance and lower computational complexity .

In this paper, a combination system of multi-antenna multiple input multiple output (MIMO) and non-orthogonal multiple access (NOMA) technologies is investigated, in which the source communicates with users using a multiple amplify-and-forward (AF) relaying network. These relay nodes are equipped with a single antenna and employ a power-splitting protocol to harvest energy from received signals, whereas the source and users are multiple-antenna nodes. In addition, two antenna-relay selection methods are considered to enhance the harvested energy at the relay including the maximum ratio transmission (MRT) and transmit antenna selection (TAS) at the source, with maximal-ratio combining at the users, these methods are compared to the performance of the random selection (RS) scheme. To evaluate the performance of the proposed system, we derive analytical expressions of the outage probability and throughput for the MRT and TAS schemes over Rayleigh fading channels, and use a Monte Carlo simulation to verify the accuracy of the analytical results. The results demonstrate the benefit of using MRT and TAS schemes, which provide a better performance than RS schemes, in a MIMO/NOMA system. Moreover, these results characterize the effects of various system parameters, such as power allocation factors, the numbers of antenna and relay nodes, power-splitting ratio, successive interference cancellation and energy-harvesting efficiency, on the system performance of two users of MIMO/NOMA. This is further compared with multiple-antenna conventional orthogonal multiple access (MIMO/OMA) schemes.

The performance of wireless systems and transmission technologies is ultimately limited by radio channels. This paper characterizes multi-link multiple-input multiple-output (MIMO) channels for future high-speed train (HST) communication systems. The channel characterization is based on field measurements in a dedicated long-term evolution (LTE) network along a high-speed railway line of China. The raw channel data are collected by an LTE sounder with two antenna ports in the multi-link region between neighboring remote radio units of the network, which are further processed by a time-delay-window-based partitioning approach to acquire multi-link MIMO channel impulse responses. Before investigating the multi-link channel properties, MIMO channel characteristics for each single link in a plain viaduct scenario are analyzed and compared in terms of root mean square angular spread and spatial correlation. Then, the dual-link MIMO channel characteristics, such as correlation matrix collinearity and sum rate capacity, are newly presented and discussed. These results can provide the reference for realistic performance assessment of cooperative MIMO HST communication systems.

In this paper, we propose a closed-form (i.e., without the need of any iterative procedure) joint optimization framework of the source precoder, the amplify-and-forward relaying matrices, and the destination equalizer for a cooperative multiple-input multiple-output (MIMO) wireless network. We study in depth such a design and carry out its performance analysis in terms of average symbol error probability (ASEP), which allows one to calculate the diversity order of the cooperative system. The ASEP is also evaluated via Monte Carlo simulations and compared with recent competitive alternatives. Results show that the proposed design performs better than or comparably to recently proposed iterative approaches, with lower computational requirements.

In this letter, the coexistence of a multiple-input multiple-output (MIMO) radar and a distributed MIMO communication systems is studied. Target returns contributed from both the radar transmitters and communication transmitters are employed to complete the radar task, leading to a hybrid active-passive MIMO radar network. For the communication task, not only are the communication signals received directly from communication transmitters, but also those bounced off from the target are exploited to extract useful information. The target localization Cramer–Rao bound and mutual information are derived for the radar and communication systems, respectively. It is shown that there is a performance gain due to the cooperation between the radar and communication systems.

As a key technology to improve the coverage and throughput of distributed wireless network, cooperative multiple-input multiple-output (CO-MIMO) system jointly manipulates the precoders of multiple distributed base stations (BSs) to serve multiple mobile stations, simultaneously. However, in time division duplexing mode, independent ambiguity multiplicative factors induced by practical transceiver radio frequency circuits will break the reciprocity between the uplink–downlink channels, resulting in the failure of cooperative precoding in multiple BSs. In this paper, we develop an efficient decentralized reciprocity calibration approach with low overhead and complexity for CO-MIMO systems. Specifically, the calibration problem of CO-MIMO is first modeled as a least square (LS) problem. Based on the decomposition theory, the LS problem is decomposed into a master problem and several subproblems. In order to avoid gathering channel state information from distributed BSs, the master problem is solved jointly and iteratively at the BSs’ side, while the subproblems are solved independently at each BS. According to the decomposition results and the solving strategy, the calibration process is described as a decentralized algorithm. The simulation results demonstrate that better performance could be achieved compared with the centralized approach.

Most IoT devices are battery powered and have limited power supplies. To ensure communication between two nodes, multi-hop transmissions over relays could be used. However, this communication cannot be achieved if the Signal-to-Noise Ratio (SNR) at the destination does not reach a reasonable threshold. Different relay selection approaches have been proposed in the past. They assume that the battery discharge is linear, but the effectiveness of these schemes is not guaranteed when realistic non-linear battery models are considered. We propose a relay selection scheme by considering a realistic battery discharge model. We present an analytical study which demonstrates that, using cooperative relays nodes, offers a longer lifetime than using only one relay for each transmission round. Then, we derive an assignment scheme that attributes the transmission power for each relay in order to satisfy the SNR condition. The numerical results obtained demonstrate the effectiveness of our proposed solution.

Differential unitary space time modulation (USTM) is identified as one of the best non-coherent technique for future 5th generation mobile networks. Two or more nodes with single antennas cooperate with each other to form a cooperative multiple-input–multiple-output network. In, this paper we examine the use of differential cooperative USTM that avoids channel estimation and also prolong the lifetime of wireless sensor network. Aiming at minimizing the energy consumption per bit we form a differential cooperative energy minimization algorithm by optimally selecting the number of cooperative nodes and finding the route that consumes minimum energy.