The mobile Nodes in wireless Ad hoc networks are fed by batteries,so the energy limitation has become a performance bottleneck for mobile ad hoc networks.IEEE 802.11 has been used as the current standard MAC protocol for ad hoc networks.However,it has not the ability of adjusting power level dynamically,which reduces the performance of network.Power control can enhance the power efficiency of nodes,reduce the interferer of neighbor nodes and improve the performance of network.A novel power controlled MAC protocol based on SNR in mobile Ad hoc networks is presented in this paper.Simulation results demonstrate that compared to the IEEE 802.11 MAC protocol,the proposed protocol can decrease the power consumption greatly,and improve the energy utilization of mobile terminals while maintaining the throughput performance.

A Power Control MAC Protocol for Ad hoc Networks

During the last decades, wireless communications have evolved from a scarce technology, used by professionals for niche applications to a rapidly advancing research field. Ever increasing proliferation of smart devices, the introduction of new emerging multimedia applications, together with an exponential rise in wireless data (multimedia) demand and usage are already creating a significant burden on existing wireless systems. Future wireless networks, with improved data rates, capacity, latency, and quality of service (QoS) requirements, are expected to be the panacea of most of the current wireless systems’ problems. Interference management is critical towards this goal, whereas transceiver design and implementation are expected to play an important role. This thesis investigates the influence of interference in wireless systems, revisits promising network- and user-side interference management solutions, as well as studies the impact of interference, caused by hardware imperfections, on the performance of the wireless link and propose countermeasures. The thesis is divided into two parts. In the first part of the thesis, different types of interference and modern interference management solutions, which are expected to be used in the future wireless networks, are reviewed. Moreover, the influence of fading and interference, due to the existence of multiple possible users operating simultaneously in the same carrier frequency, on the spectrum sensing capability of a low-complexity energy detector (ED) is investigated. Analytical tools for the performance evaluation of this problem, i.e., the false alarm and detection probabilities, are derived, while the problem of appropriately selecting the energy detection threshold and the spectrum sensing duration, in order to satisfy a specific requirement, is discussed. The results reveal the detrimental effect of interference and the importance of taking into consideration the wireless environment when evaluating the ED spectrum sensing performance and selecting the ED threshold. Finally, the offered analytical framework can be applied in cognitive radio systems, which are included in several wireless standards, and are expected to be employed in ultra-dense wireless environments. The second part of this thesis investigates the impact of transceivers radio frequency (RF) front-end imperfections on the performance of the wireless system. RF imperfections generally result to signal distortion in single-carrier communications, while, in multi-carrier communications, they additionally cause interference. In both cases, RF imperfections may cause significant degradation to the quality of the wireless link, which becomes more severe as the data rates increases. Motivated by this, after briefly illustrating the influence of different types of RF imperfections, namely in-phase and quadrature imbalance (IQI), phase noise, and amplifiers non-linearities, the analytical framework for the evaluation and quantification of the effect of IQI on wireless communications in the context of cascaded fading channels, is derived. To this end, closed-form expressions for the outage probability over N∗Nakagami-m channels for both the cases of single- and multi-carrier communications, when at least one communication node suffers from IQI, are provided. To justify the importance and practical usefulness of the analysis, the offered expressions along with several deduced corresponding special cases are employed in the context of vehicle-to-vehicle communications. This study gives critical insight for the performance degradation in wireless communications, due to RF imperfections, and indicates the need for designing proper RF imperfections compensation techniques. Next, the impact of IQI and partial successive interference suppression (SIS) in the spectrum sensing of full duplex CR systems, for both the cases of single- and multi-carrier ED, is studied. In this context, closed-form expressions are derived for the false alarm and detection probabilities, in the general case, where partial SIS and joint transmitter and receiver IQI are considered. The derived expressions can be used in order to properly select the energy detection threshold that maximizes the ED spectrum sensing capabilities. Additionally, the joint influence of fading and several RF impairments on energy detection based spectrum sensing for CR systems in multi-channel environments is investigated. After assuming flat-fading Rayleigh channels and complex Gaussian transmitted signals, as well as proving that, for a given channel realization, the joint effect of RF impairments can be modeled as a complex Gaussian process, closed-form expressions for the probabilities of false alarm and detection are derived. Based on these expressions, the impact of RF impairments and fading on the spectrum sensing capability of the ED is studied. The results illustrated the degrading influence of RF imperfections on the ED spectrum sensing performance, which bring significant losses in the utilization of the spectrum. Furthermore, the impact of uncompensated IQI on orthogonal frequency division multiple access (OFDMA) systems, in which a power allocation (PA) policy is employed in order to maximize each user’s capacity, is demonstrated. To overcome, the user’s capacity loss, due to IQI, a novel, low-complexity PA strategy is presented, which, by taking into account the levels of IQI of the served users, notably enhance each user’s achievable capacity. Finally, a novel low-complexity scheme, which improves the performance of single-antenna multi-carrier communication systems, suffering from IQI at the receiver, is proposed. The proposed scheme, which we refer to as I/Q imbalance self-interference coordination (IQSC), not only mitigate the detrimental effect of IQI, but, through appropriate signal processing, also coordinates the self-interference terms produced by IQI, in order to achieve second-order frequency diversity. In order to evaluate the performance of IQSC, closed-form expressions for the resulting outage probability and symbol error rate are derived. The findings reveal that IQSC is a promising low-complexity technique for significantly increasing the reliability of low-cost devices that suffer from high levels of IQI.

Interference mitigation techniques in modern wireless communication systems

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A fast, scalable acoustic resonator-based biosensor array system for simultaneous detection of multiple biomarkers

Diversity Combining (DC) and Multipacket Detection (MPD) are efficient techniques that cope with packet errors due to severe propagation conditions and/or collisions. To evaluate their network performance on a network simulator, an accurate characterization of the Bit Error Rate (BER) and Packet Error Rate (PER) can successfully replace the behavior of the PHY layer. This choice is better in terms of computational time than implementing a full PHY layer to be jointly simulated with the upper layers. In this paper, an analytical model is proposed to compute the BER and PER of DC, MPD and hybrid techniques, considering a Single-Carrier with Frequency-Domain Equalization (SC-FDE) scenario. The paper also considers two frequency-domain detection methods: a simple linear receiver and a powerful iterative receiver. The proposed model is simple and versatile, since it can support nonhomogeneous transmitting powers, and different channel conditions concerning retransmissions and channel randomization techniques. Several simulations show that the proposed model provides accurate BER and PER results for a wide range of scenarios.

/pdf/analytical-ber-and-per-performance-of-frequency-domain-4y6mpsjpyw.pdf

Analytical BER and PER Performance of Frequency-Domain Diversity Combining, Multipacket Detection and Hybrid Schemes

From typical metrology parameters for common wireless and microwave components to the implementation of measurement benches, this introduction to metrology contains all the key information on the subject. Using it, readers will be able to: Interpret and measure most of the parameters described in a microwave component's datasheet Understand the practical limitations and theoretical principles of instrument operation Combine several instruments into measurement benches for measuring microwave and wireless quantities. Several practical examples are included, demonstrating how to measure intermodulation distortion, error vector magnitude, S-parameters and large signal waveforms. Each chapter then ends with a set of exercises, allowing readers to test their understanding of the material covered and making the book equally suited for course use and for self-study.

Microwave and Wireless Measurement Techniques

This paper considers the use of SC-FDE techniques (single-carrier with frequency-domain equalization) with low-complexity soft combining ARQ schemes (automatic repeat request). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Moreover, the transmitter and receiver complexities are low and we can have excellent performances, especially when we have deep fading effects in slow-varying channels. By combining the advantages of SC-FDE schemes with soft combining ARQ, the proposed technique is particularly interesting for the uplink of wireless systems.

Soft Combining ARQ Techniques for Wireless Systems Employing SC-FDE Schemes

This paper proposes a solution for one of the major difficulties associated with arbitrary waveform generation at microwave frequencies: the nonideal RF circuits used for signal generation. It presents a practical implementation of a RF multisine signal generator that corrects for the linear and nonlinear impairments identified with its output RF circuitry. The integration of an adaptive predistortion algorithm with a previously presented methodology for multisine synthesis with prescribed higher-order statistics, proved the feasibility of a simple microwave arbitrary waveform generator that meets the aims of previously developed signal synthesis theory

A corrected microwave multisine waveform generator

This paper presents Hermes, a new modular platform that can be used in a variety of scenarios, including the role of body area network coordinator, enabling temperature, movement and heartbeat sensing, local and remote communication, and indoor and outdoor localization. Hermes is based on two main modules that can operate as a single system in a coordinated fashion or individually, depending on the application scenario. One of the modules uses a Telos-inspired architecture, with new processing, communication, sensing, storage and energy subsystems, and executing TinyOS. The other module is designed around a PIC 24F MCU, also supporting communication, sensing, storage, and executing a custom operating system. Both modules have expansion capabilities. The main innovative aspects of the implemented platform are its modularity and its capability to provide device abstraction, which considerably eases application development. The paper addresses the platform motivation, requirements, hardware architecture, implementation details, and performance evaluation.

Hermes: A versatile platform for wireless embedded systems

From a conceptual perspective, beyond-5G technologies promise to deliver very low latency, even higher data rates, and ultrareliable connections for future generations of communication systems. Modulation schemes based on orthogonal frequency-domain multiplexing (OFDM) can accommodate these requirements for wireless systems. Several hybrid OFDM-based systems, such as the time-interleaved block-windowed burst–OFDM (TIBWB–OFDM), are capable of achieving even better spectral confinement and power efficiency. This paper addresses the implementation of the TIBWB–OFDM system in more realistic and practical wireless link scenarios by addressing the challenges of proper and reliable channel estimation and frame synchronization. We propose to incorporate a preamble formed by optimal correlation training sequences such as the Zadoff–Chu (ZC) sequences. The added ZC preamble sequence is used to jointly estimate the frame beginning through signal-correlation strategies and a threshold decision device, and acquire channel-state information (CSI) by employing estimators on the basis of the preamble sequence and transmitted data. The employed receiver estimators show that it is possible to detect the TIBWB–OFDM frame beginning and highlight the robustness of the TIBWB–OFDM technique to imperfect channel estimations by showing that it can provide comparatively close BER performance to the one where the CSI is perfectly known.

Joint Channel Estimation and Synchronization Techniques for Time-Interleaved Block-Windowed Burst OFDM

This paper presents a new algorithm that allows the use of non-uniform multi-sines for CAD/CAE modeling and characterization procedures. The new measurement procedure explores the narrow bandwidth of the signals used to obtain a sparsely, possibly NON-uniformly sampled representation, from which the spectral coefficients can nevertheless be accurately estimated.

Joao Paulo Martins

Papers

Soft Combining ARQ Techniques for Wireless Systems Employing SC-FDE Schemes

A corrected microwave multisine waveform generator

Hermes: A versatile platform for wireless embedded systems

Joint Channel Estimation and Synchronization Techniques for Time-Interleaved Block-Windowed Burst OFDM

Complex signal measurement bench based on a special spectrum super-resolution algorithm