Advances in smart antennas - Cooperative wireless communications: a cross-layer approach

Topicality. Intermunicipal cooperation is a relevant tool for community development in any country with a decentralized territorial administrative system. The study is motivated by the need to reorganize and improve relations between the communities of the Tyligul subregion in order to solve the problems of financing large-scale projects of intermunicipal and interregional importance and ensure the sustainable development of the subregion.Aim and tasks. The purpose of this study is to develop a methodological toolkit for choosing the best form of organization of cooperation of communities belonging to an objectively formed integral subregion using the signs of sustainable development, that is, in terms of economic, social, and environmental components. Separate tasks of the research are the analysis of institutional support and the essence of various forms of cooperation of territorial communities, the identification of relevant features, which determine the common characteristics and prerequisites for the organization of cooperation of communities; determination of the best form of economic cooperation of communities and joint use of spatial and resource potential, on the example of the Tyligul subregion.Materials and Methods. Evaluation of various forms of intermunicipal cooperation with the aim of finding the best options for organizing economic cooperation of subregions was carried out using methods of systematic, logical analysis. Taking into account the experience of the best practices of the organization of economic cooperation of territorial economic systems in the EU countries was carried out using the means of benchmarking analysis. Generalization and comparison of data on the prospects of cooperation between communities of the Tyligul subregion, determination of the expected activity and effectiveness of such cooperation was carried out using methods of statistical analysis.Research results. The article examines the current state of inter-municipal cooperation in Ukraine and the Black Sea region. The main factors that create prerequisites for successful inter-municipal cooperation of territorial communities of the Tyligul subregion are also defined. Since the most important issues that will be faced by territorial communities during the implementation of inter-municipal partnership are the determination of the essence, the subject and the most successful form of cooperation, each of the five forms of inter-municipal cooperation was considered and their positive and negative sides were determined. On the basis of the conducted research, prospects for the further development of cooperation between territorial communities of the Tyligul subregion are proposed.Conclusion. The result of this study is the determination of the most promising option for the cooperation of territorial communities of the Tyligul subregion, based on the formation of a joint management body, namely the Department of Strategic Project Activities and Investments of Territorial Communities of the Tyligul Subregion. The implementation of the proposed scenario will solve the problem of financing large-scale projects of inter-municipal and inter-regional importance, and the possibilities of the proposed format of cooperation discussed in the article will, as a result, allow to ensure the sustainable development of the subregion.

Cross-layer optimization for wireless mesh networks with smart antennas

In wireless communications, the cooperative communication (CC) technology\npromises performance gains compared to traditional Single-Input Single Output\n(SISO) techniques. Therefore, the CC technique is one of the nominees for 5G\nnetworks. In the Decode-and-Forward (DF) relaying scheme which is one of the CC\ntechniques, determination of the threshold value at the relay has a key role\nfor the system performance and power usage. In this paper, we propose\nprediction of the optimal threshold values for the best relay selection scheme\nin cooperative communications, based on Artificial Neural Networks (ANNs) for\nthe first time in literature. The average link qualities and number of relays\nhave been used as inputs in the prediction of optimal threshold values using\nArtificial Neural Networks (ANNs): Multi-Layer Perceptron (MLP) and Radial\nBasis Function (RBF) networks. The MLP network has better performance from the\nRBF network on the prediction of optimal threshold value when the same number\nof neurons is used at the hidden layer for both networks. Besides, the optimal\nthreshold values obtained using ANNs are verified by the optimal threshold\nvalues obtained numerically using the closed form expression derived for the\nsystem. The results show that the optimal threshold values obtained by ANNs on\nthe best relay selection scheme provide a minimum Bit-Error-Rate (BER) because\nof the reduction of the probability that error propagation may occur. Also, for\nthe same BER performance goal, prediction of optimal threshold values provides\n2dB less power usage, which is great gain in terms of green communicationBER\nperformance goal, prediction of optimal threshold values provides 2dB less\npower usage, which is great gain in terms of green communication.\n

In order to cope with the degradation of communication quality due to fading of wireless signals when transmitted over long distances, cooperative communication techniques are often applied to long-distance wireless communications due to their relay cooperative forwarding characteristics. A reasonable relay assignment scheme can significantly improve the network throughput. In order to solve the problem of irrational relay resource assignment in the existing relay assignment under the multi-node cooperative communication network, this paper proposes a relay assignment method that balances the communication quality (BQRA). Firstly, a multi-node cooperative communication system model is established, and a node pre-assignment set is established based on node distance. Then, with the goal of maximizing the overall network capacity, the proposed relay assignment method is used to allocate relay nodes for each source node. The effective performance of the proposed method is evaluated through simulation experiments. Simulation results show that the system channel capacity index is slightly better than several other methods. 15% increase in system channel capacity compared to the classical relay assignment method, LIRA.

The fundamental idea of cooperative communications in wireless networks originates from the design of multiple-antenna systems. In multiple-antenna systems, communicating terminals are equipped with multiple antennas to mitigate the effects of multipath fading and optimise the communication rate in the network. Wireless communication nodes like cellular phones and sensor nodes have size restrictions, power supply limitations and are only able to accommodate a limited level of complexity. It is thus unfeasible to equip them with multiple antennas. The effects of multipath fading are critical in cellular, ad hoc and sensor networks because the physical deployment of communicating nodes makes them susceptible to interference. It is imperative to adopt a mechanism to combat fading in such networks. The broadcast nature of the wireless medium makes it easy for the communicating nodes to hear each other. They can share their physical resources specifically their single antennas, thereby creating a virtual multiple-antenna array. Cooperative communications is a concept where several single-antenna nodes cooperate and form a distributed multiple-antenna system which combats multipath fading. In recent years, cooperative communications have received extensive world-wide attention and significant advances in both research and applications have been achieved.

Cooperative communication has emerged as a promising technique to improve transmission reliability and spectral efficiency by utilizing virtual antenna arrays formed by multiple nodes in wireless networks. In this paper, we study distributed interference-aware random access strategies based on cooperative link selection scheduling for multi-hop wireless networks. In order to fully exploit the broadcast feature of wireless channels, improve spatial reuse, and achieve diversity gains, the cooperative random access is formulated as a network utility optimization problem with probabilistic model and interference avoidance. In the multi-hop wireless networks, the nodes near the destination node in the current hop that can decode the data packets from the source node are able to serve as candidate relays to take part in the cooperative transmission in the next hop. Simulation results show that our proposed spectrum access strategy significantly improves the system average throughput and spectrum efficiency compared with the existing solutions.

The significant concepts in the area of wireless communication are cooperative communication and physical layer security. Since current related research does not involve detailed performance analysis in different scenarios, the performance in different scenarios between amplify-and-forward scheme and cooperative-jamming scheme is compared. In combination with the characteristics of the both concepts, the physical layer security model based on cooperative communication, and the optimal secrecy capacity on amplify-and-forward scheme and cooperative-jamming scheme is analyzed. The number increase of antennas for relays can improve the secrecy performance, just like the number increase of relays. Simulation results show that amplify-and-forward scheme is more difficult to be effected by the scenarios and is more stable than cooperative-jamming scheme.

A new cooperative communication algorithm for improving connectivity in the event of network failure in VANETs

Wireless multi-hop networks are candidate communication infrastructures in developing regions because their installation cost is quite low comparing to that for conventional wired networks. Reliable and scalable dissemination mechanism is required in practical multi-hop networks. Cooperative communication is a new scheme to improve communication performance to realize a reliable dissemination mechanism. However, high mobility networks have a big issue for autonomous control for cooperative communication. Additionally, conventional cooperative schemes cannot reduce packet collisions even if packet collisions are a big degradation factor of performance in dense multi-hop networks. We have discussed a new cooperative communication scheme that employs Orthogonal Frequency-Division Multiplexing (OFDM). Our scheme can improve communication performance and reduce packet collisions based on distributed control matter. Our advance evaluation has shown a good potential of the proposed scheme to improve communication performance in multi-hop network simulations. On the contrary, the feasibility of the proposed scheme with a real hardware device was not shown. This paper evaluates the feasibility of our original cooperative communication scheme on IEEE 802.11a standard devices. Almost all conventional cooperative communication schemes require a special physical layer and a media access control mechanism. We have focused on a characteristic of OFDM, where a receiver can demodulate multiple signals within a guard interval period. The experimental evaluation has been performed with software defined radio devices (USRP B200). We have implemented multiple transmitters, a receiver and a fading simulator for each transmitter with two USRP B200 devices. The results can show that the proposed scheme works well on IEEE 802.11a standard devices and improves communication performance in practical situations. Hence, the proposed scheme will be a new candidate of cooperative communication mechanisms that can employ general consumer devices and can realize effective dissemination mechanism for multi-hop networks.

In order to increase the bandwidth efficiency and further improve the performance of orthogonal frequency division multiplex (OFDM) systems, adaptive resource allocation and smart antennas techniques are widely applied. However, the employment of fully adaptive beamforming in physical layer for OFDM systems significantly raises the issues in medium access control (MAC) layer, hence affects the implementation of adaptive resource allocation. From a cross-layer approach, we propose a new adaptive resource allocation strategy with hybrid smart antennas for OFDM systems. By applying different smart antennas schemes according to the different quality of service (QoS) requirement of different users, the new strategy reaches a good trade-off between the complexity and the performance of OFDM systems

Smart antennas have gained significant importance in multi-hop wireless networks in recent years, because of their sophisticated signal processing capabilities that hold the potential for increased data rates and reliability. In this work, we consider the problem of communication in multi-hop wireless networks with smart antennas (specifically digital adaptive arrays). These smart antennas provide degrees of freedom (DOFs) that can be used to suppress co-existing communication links, thereby increasing spatial reuse in the network. Thus, the communication problem comprises of not just determining a channel access mechanism to be used by the communication links, but also involves the determination of the communication pattern (usage of DOFs) to be used by each node during channel access. To the best of our knowledge, our work is the first step towards addressing this problem.We first consider the problem of determining the communication pattern to be used by the nodes and formulate it combinatorially with the goal of optimizing network performance through interference minimization. We present efficient centralized and distributed algorithms that are within a factor of ¾ and ½ of the optimum solution respectively. We then extend the distributed algorithm to incorporate TDMA-based scheduling in a purely localized manner. The distributed algorithms are then evaluated through simulations in ns2 and insights are drawn into the potential performance benefits of smart antennas in multi-hop wireless networks.

Cooperative communication (CC) has been proposed to increase the wireless channel capacity and reliability by employing multiple single-antenna nodes to form a virtual antenna array. Many efforts focus on exploiting the benefits of CC among multiple source-destination pairs with an unrealistic assumption that each of them communicates over a dedicated channel without interference. In this paper, we investigate the transmission scheduling problem for multiple source-destination pairs under the assistance of a set of dedicated relay nodes on a single channel. By applying the protocol interference model, we propose a concept of cooperative link to characterize the interference regions of CC. Due to the NP-completeness of optimal scheduling, LP (linear programming) based heuristic algorithms are proposed to maximize the minimum transmission rate under a given relay assignment. Then, without specifying a relay node for each source-destination pair, we study the max-min rate problem by jointly considering transmission scheduling and relay assignment. Heuristic algorithms are proposed to solve this more challenging problem. Finally, extensive simulations are conducted to show that the proposed algorithm outperforms direct transmission substantially.

High power time-varying interference or jamming can severely disrupt wireless communication. Therefore, the technique of relevant interference mitigation is needed. Cooperative communication technique can organize a group of single-antenna systems in the same area at different locations as a distributed antenna array. Thus it can approximately achieve the diversity gain of regular multiple-antenna system. This paper is focused on cooperative communication for time-varying interference mitigation. Since some of traditional collaborative reception techniques have the constraint of requiring accurate estimation of SNR, an improvement of time-varying interference mitigation technique based on log-likelihood ratio (LLR) and jammer cancellation is proposed. The simulation results demonstrate that this new improved method enables communication in much more severe interference conditions.

In this letter, a relay-assisted transmission scenario over frequency-selective fading channels perturbed by different random carrier frequency offsets is considered. OFDM and block-double differential (BDD) design are implemented to overcome the problem of intersymbol interference (ISI) and carrier frequency offsets (CFOs). We analyze the symbol error rate (SER) performance of decode-and-forward relaying with BDD design in wireless cooperative communications over frequency-selective fading channels and derive a theoretical upper bound for average SER when the relay (R) is error free. It can be seen from our analysis that the system performance is influenced by the ability of R to decode, and when R decodes without error, both spatial and multipath diversity can be obtained without requiring any knowledge of channel state information and CFO information at the receivers. Numerical examples are provided to corroborate our theoretical analysis.

In this research, the combination of the relay selection and network coding is used to measure the performance in LOS and NLOS condition over cooperative communication. The research aims are to select the best relay as assisted relay as well as to improve performance system. The research method used four nodes, two nodes as source and destination and two nodes as relays. The single relay selection is used to select best relay of several relays. Measurements are conducted by altering the positions of the relays to achieve optimal outcomes. The findings indicate that the relay with the lowest Bit Error Rate (BER) and the shortest distance is chosen. The study's outcomes, when measuring throughput, reveal that network coding throughput is 21.8% higher than that without network coding in Non-Line of Sight (NLOS) conditions. In Line of Sight (LOS) conditions, the throughput is increased by 23%.