Compensation of Physical Impairments in Multi-Carrier Communications

Among various multi-carrier transmission techniques, orthogonal frequency-division multiplexing (OFDM) is currently a popular choice in many wireless communication systems. This is mainly due to its numerous advantages, including resistance to multi-path distortions by using the cyclic prefix (CP) and a simple one-tap channel equalization, and efficient implementations based on the fast Fourier and inverse Fourier transforms. However, OFDM also has disadvantages which limit its use in some applications. First, the high out-of-band (OOB) emission in OFDM due to the inherent rectangular shaping filters poses a challenge for opportunistic and dynamic spectrum access where multiple users are sharing a limited transmission bandwidth. Second, a strict orthogonal synchronization between sub-carriers makes OFDM less attractive in low-power communication systems. Furthermore, the use of the CP in OFDM reduces the spectral efficiency and thus it may not be suitable for short-packet and low-latency transmission applications. Generalized frequency division multiplexing (GFDM) and circular filter-bank multi-carrier offset quadrature amplitude modulation (CFBMC-OQAM) have recently been considered as alternatives to OFDM for the air interface of wireless communication systems because they can overcome certain disadvantages in OFDM. Specifically, these two systems offer a flexibility in choosing the shaping filters so that the high OOB emission in OFDM can be avoided. Moreover, the strict orthogonality requirement in OFDM is relaxed in GFDM and CFBMC-OQAM which are, respectively, non-orthogonal and real-field orthogonal systems. Although a CP is also used in these two systems, the CP is added for a block of many symbols instead of only one symbol as in OFDM, which, therefore, improves the spectral efficiency. Given that the performance of a wireless communication system is affected by various physical impairments such as phase noise (PN), in-phase and quadrature (IQ) imbalance and imperfect channel estimation, this thesis proposes a number of novel signal processing algorithms to compensate for physical impairments in multi-carrier communication systems, including OFDM, GFDM and CFBMC-OQAM. The first part of the thesis examines the use of OFDM in full-duplex (FD) communication under the presence of PN, IQ imbalance and nonlinearities. FD communication is a promising technique since it can potentially double the spectral efficiency of the conventional half-duplex (HD) technique. However, the main challenge in implementing an FD wireless device is to cope with the self-interference (SI) imposed by the device's own transmission. The implementation of SI cancellation (SIC) faces many technical issues due to the physical impairments. In this part of research, an iterative algorithm is proposed in which the SI cancellation and detection of the desired signal benefit from each other. Specifically, in each iteration, the SI cancellation performs a widely linear estimation of the SI channel and compensates for the physical impairments to improve the detection performance of the desired signal. The detected desired signal is in turn removed from the received signal to improve SI channel estimation and SI cancellation in the next iteration. Results obtained show that the proposed algorithm significantly outperforms existing algorithms in SI cancellation and detection of the desired signal. In the next part of the thesis, the impact of PN and its compensation for CFBMC-OQAM systems are considered. The sources of performance degradation are first quantified. Then, a two-stage PN compensation algorithm is proposed. In the first stage, the channel frequency response and PN are estimated based on the transmission of a preamble, which is designed to minimize the channel mean squared error (MSE). In the second stage the PN compensation is performed using the estimate obtained from the first stage together with the transmitted pilot symbols. Simulation results obtained under practical scenarios show that the proposed algorithm effectively estimates the channel frequency response and compensates for the PN. The proposed algorithm is also shown to outperform an existing algorithm that implements iterative PN compensation when the PN impact is high. As a further development from the second part, the third part of the thesis considers the impacts of both PN and IQ imbalance and proposes a unified two-stage compensation algorithm for a general multi-carrier system, which can include OFDM, GFDM and CFBMC-OQAM. Specifically, in the first stage, the channel impulse response and IQ imbalance parameters are first estimated based on the transmission of a preamble. Given the estimates obtained from the first stage, in the second stage the IQ imbalance and PN are compensated in that order based on the pilot symbols for the rest of data transmission blocks. The preamble is designed such that the estimation of IQ imbalance does not depend on the channel and PN estimation errors. The proposed algorithm is then further extended to a multiple-input multiple-output (MIMO) system. For such a MIMO system, the preamble design is generalized so that the multiple IQ imbalances as well as channel impulse responses can be effectively estimated based on a single preamble block. Simulation results are presented and discussed in a variety of scenarios to show the effectiveness of the proposed algorithm

マルチホップ無線ネットワークの特性解析に関する研究

九州工業大学博士学位論文 学位記番号:情工博甲第309号 学位授与年月日:平成28年3月25日1 Introduction||2 Impact of Transceiver Hardware Impairments on Cognitive Network||3 Case study: Two-Way Cognitive Relay in RF Energy HarvestingWireless Sensor Network||4 Soft Information Relaying Protocol||5 Overall Conclusion and FutureWorkWireless communication has been considered as the most efficient mean of data transmission. We have been witnessed the breakthrough of wireless communication era in many manifolds, such as speech, coverage area, and stability. However, frequency bands, the resource to convey information wirelessly, are limited and expensive to be granted usage licenses. Attaining the goals of ubiquitous wireless devices will require the future wireless networks stepping forward to overcome the scarcity and expensiveness of wireless frequency bands. Thus, the future wireless networks should evolve to utilize wireless frequencies more efficiently, such as cognitive relay network where non-license users are able to transmit data in the same frequency band that officially allocated to primary users. Subsequently, the transmit power of users in a cognitive network is limited and the performance is vulnerable to impairments of transceiver hardware. This dissertation aims to analyze the performance of the cognitive relay network under the impact of transceiver hardware impairments. A case study of two-way cognitive relay network is given for further investigate the impact of transceiver hardware impairments on end-to-end outage performance and throughput. Furthermore, we provide a new relaying scheme in order to lessen the impact of transceiver hardware impairment and further boost the system performance. For the purposes, this dissertation is organized into five (5) chapters. Chapter 1: Introduction. In this chapter, multihop wireless networks and the performance metrics are overviewed. In particular, the relay networks and cognitive relay networks are presented. Moreover, the general model of the practical transceiver hardware impairment is detailed for further analysis. Chapter 2: The impact of transceiver hardware impairments on cognitive relay networks. By using the general hardware impairment model for the received signal, the closed forms of outage probability of the relay network with decode-and-forward (DF) and amplify-and-forward (AF) under the impact of transceiver hardware imperfection are derived. Based on these results, we provide further discussion on transceiver hardware selection guideline. Chapter 3: Case study: two-way cognitive relaying in energy harvesting wireless sensor networks. A two-way relay wireless sensor network equipped with RF energy harvesting node is introduced. This network is aimed to be implemented in hazardous or remote areas where power supply for the relay node is difficult to maintain. In this chapter, we consider four configurations of the network with formed by combining two bidirectional relaying protocols and two wireless power transfer policies. The detailed performance analysis of outage probability and throughput of the case-study network with four configurations are presented. Based on the analysis, we provide performance comparison between the four and suggest the network configuration with the best performance. Chapter 4: Soft information relaying protocol. The soft information relaying protocol is proposed and analyzed. The analysis shows that this relaying protocol can gradually reduce the impact of transceiver hardware impairment on cognitive relay networks. Hence, soft relaying protocol is considered as a solution for cognitive relay network with cost-effective wireless transceiver devices. Chapter 5: Overall conclusion. An overall summary of the works presented in the above is provided in this chapter. Moreover, the future related work is also discussed. The results in this dissertation acknowledge the impact of transceiver hardware impairment by presenting the reduction of outage probability and throughput of the cognitive relay network. It puts forward the consideration of including the impact of transceiver hardware impairments on wireless network performance analysis, especially for the cognitive networks of which the transmit power is limited. Furthermore, a new relaying protocol, namely soft information relaying protocol, is proposed as a solution to lessen the impact of transceiver hardware impairment. The analysis shows that the impact of transceiver hardware impairment in cognitive relay network is reduced in compared to conventional relaying schemes. As a final point, we have provided a full picture of performance analysis for the cognitive relay network under the impact of transceiver hardware imperfection and the solution to reduce the performance loss by applying soft information relaying scheme. This research would contribute to boost the development of cognitive relay networks where frequency bands are used more efficiently

On the performance of digital adaptive spur cancellation for multi-standard radio frequency transceivers

15 pagesInternational audienceThis study deals with the asymptotic performance of a multiple-spur cancellation scheme. Radio frequency transceivers are now multi-standard and specific impairment can occur. The clock harmonics, called spurs, can leak into the signal band of the reception stage, and thus degrade the performance. The performance of a fully digital approach is presented here. A one-spur cancellation scheme is first described, for which we exploit the a priori knowledge of the spur frequency to create a reference of the polluting tone with the same frequency. A least-mean-square (LMS) algorithm block that uses this reference to mitigate the polluter is designed. However, due to imperfections in the physical components, there is a shift between the a priori frequency and the actual frequency of the spur, and the spur is affected by Brownian phase noise. Under these circumstances, we study the asymptotic and transient performance of the algorithm. We next improve the transient performance by adding a previously proposed adaptive-step-size process. In a second part of this paper, we present a multiple-spur parallel approach that is based on the one-spur cancellation scheme, for which we provide a closed-form expression of the asymptotic signal-plus-noise interference ratio in the presence of frequency shifts and phase noise

Radio-Communications Architectures

Wireless communications, i.e. radio-communications, are widely used for our different daily needs. Examples are numerous and standard names like BLUETOOTH, WiFI, WiMAX, UMTS, GSM and, more recently, LTE are well-known [Baudoin et al. 2007]. General applications in the RFID or UWB contexts are the subject of many papers. This chapter presents radio-frequency (RF) communication systems architecture for mobile, wireless local area networks (WLAN) and connectivity terminals. An important aspect of today's applications is the data rate increase, especially in connectivity standards like WiFI and WiMAX, because the user demands high Quality of Service (QoS). To increase the data rate we tend to use wideband or multi-standard architecture. The concept of software radio includes a self-reconfigurable radio link and is described here on its RF aspects. The term multi-radio is preferred. This chapter focuses on the transmitter, yet some considerations about the receiver are given. An important aspect of the architecture is that a transceiver is built with respect to the radio-communications signals. We classify them in section 2 by differentiating Continuous Wave (CW) and Impulse Radio (IR) systems. Section 3 is the technical background one has to consider for actual applications. Section 4 summarizes state-of-the-art high data rate architectures and the latest research in multi-radio systems. In section 5, IR architectures for Ultra Wide Band (UWB) systems complete this overview; we will also underline the coexistence and compatibility challenges between CW and IR systems

Millimeter wave link configuration in practical scenarios

Acquiring channel state information (CSI) for link configuration in wideband millimeter wave (mmWave) massive multiple-input-multiple-output (MIMO) systems with hybrid architectures is challenging, due to the high dimensions of the channel matrices, the low signal-to-noise ratio (SNR) before beamforming, the various hardware constraints and the high mobility in the vehicular context. Previous work in this area exploits channel sparsity, statistical priors or side information to reduce the overhead associated to initial channel estimation or channel tracking. These works consider, however, a system model that neglects hardware imperfections. In addition, many of the proposed solutions are unable to operate in some realistic scenarios, such as vehicle-to-everything (V2X) communications. In this dissertation, we develop new signal processing solutions that can enable low-overhead mmWave link configuration under various disturbances and practical limitations, e.g., hardware impairments, calibration errors, beam squint effect, channel blockage, high mobility, to name a few. In the first part of this dissertation, we focus on the problem of wideband channel estimation for mmWave MIMO systems with different hardware imperfections. We first design a dictionary learning aided channel estimation strategy for wideband mmWave MIMO systems by explicitly considering the hardware uncertainties and calibration errors, and then derive algorithms that learn the optimal sparsifying dictionaries for channel representation and estimation. In a second contribution of this part, we further develop a dictionary learning aided compressive channel estimation scheme for mmWave MIMO systems by incorporating beam squint into the model of array responses. Numerical results show the proposed solutions can adapt to the practical scenarios and help reduce the overhead associated with channel estimation significantly. In the second part of this dissertation, we deal with the problem of wideband channel tracking for mmWave MIMO systems with or without the impact of blockage. We first introduce statistical channel models that include the evolution models for channel gains and angles of arrival/departure, as well as the statistics of blockage events. Then, we design novel blockage detection schemes and efficient Bayesian channel tracking algorithms to facilitate the low-overhead tracking with or without blockage. Numerical results corroborate that the proposed solutions achieve better channel tracking performance even in mobile scenarios that suffer from highly dynamic blockage events.Electrical and Computer Engineerin

Learning-Driven Decision Mechanisms in Physical Layer: Facts, Challenges, and Remedies

Future communication systems must include extensive capabilities as they will embrace a vast diversity of devices and applications. Conventional physical layer decision mechanisms may not meet these requirements due to the frequent use of impracticable and oversimplifying assumptions that lead to a trade-off between complexity and efficiency. By utilizing past experiences, learning-driven designs are promising solutions to present a resilient decision mechanism and provide a quick response even under exceptional circumstances. The corresponding design solutions should evolve following the learning-driven paradigms that offer increased autonomy and robustness. This evolution must take place by considering the facts of real-world systems without restraining assumptions. This paper introduces the common assumptions in the physical layer to highlight their discrepancies with practical systems. As a solution, learning algorithms are examined by considering implementation steps and challenges. Additionally, these issues are discussed through a real-time case study that uses software-defined radio nodes, demonstrating the potential performance improvement. A remedial perspective is presented to guide future studies

Multitones’ Performance for Ultra Wideband Software Defined Radar

This chapter proposes and tests an approach for an unbiased study of radar waveforms’ performances. Through an empirical performance analysis, the performances of Chirp and Multitones are compared with both simulations and measurements. An ultra wideband software defined radar prototype was designed and the prototype has performances comparable to the state of the art in software defined radar. The study looks at peak-to-mean-envelope power ratio, spectrum efficiency, and pulse compression as independent waveform criteria. The experimental results are consistent with the simulations. The study shows that a minimum of 10 bits resolution for the AD/DA converters is required to obtain near-optimum performances