Traditional power grids are currently being transformed into smart grids (SGs). SGs feature multi-way communication among energy generation, transmission, distribution, and usage facilities. The reliable, efficient, and intelligent management of complex power systems requires integration of high-speed, reliable, and secure data information and communication technology into the SGs to monitor and regulate power generation and usage. Despite several challenges, such as trade-offs between wireless coverage and capacity as well as limited spectral resources in SGs, wireless communication is a promising SG communications technology. Cognitive radio networks (CRNs) in particular are highly promising for providing timely SG wireless communications by utilizing all available spectrum resources. We provide in this paper a comprehensive survey on the CRN communication paradigm in SGs, including the system architecture, communication network compositions, applications, and CR-based communication technologies. We highlight potential applications of CR-based SG systems. We survey CR-based spectrum sensing approaches with their major classifications. We also provide a survey on CR-based routing and MAC protocols, and describe interference mitigation schemes. We furthermore present open issues and research challenges faced by CR-based SG networks along with future directions.

Cognitive Radio for Smart Grids: Survey of Architectures, Spectrum Sensing Mechanisms, and Networking Protocols

With years of tremendous traffic and energy consumption growth, green radio has been valued not only for theoretical research interests but also for the operational expenditure reduction and the sustainable development of wireless communications. Fundamental green tradeoffs, served as an important framework for analysis, include four basic relationships: 1) spectrum efficiency versus energy efficiency; 2) deployment efficiency versus energy efficiency; 3) delay versus power; and 4) bandwidth versus power. In this paper, we first provide a comprehensive overview on the extensive on-going research efforts and categorize them based on the fundamental green tradeoffs. We will then focus on research progresses of 4G and 5G communications, such as orthogonal frequency division multiplexing and non-orthogonal aggregation, multiple input multiple output, and heterogeneous networks. We will also discuss potential challenges and impacts of fundamental green tradeoffs, to shed some light on the energy efficient research and design for future wireless networks.

Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks

The exponential traffic growth, demand for high speed wireless data communications, as well as incessant deployment of innovative wireless technologies, services, and applications, have put considerable pressure on the mobile network operators (MNOs). Consequently, cellular access network performance in terms of capacity, quality of service, and network coverage needs further considerations. In order to address the challenges, MNOs, as well as equipment vendors, have given significant attention to the small-cell schemes based on cloud radio access network (C-RAN). This is due to its beneficial features in terms of performance optimization, cost-effectiveness, easier infrastructure deployment, and network management. Nevertheless, the C-RAN architecture imposes stringent requirements on the fronthaul link for seamless connectivity. Digital radio over fiber-based common public radio interface (CPRI) is the fundamental means of distributing baseband samples in the C-RAN fronthaul. However, optical links which are based on CPRI have bandwidth and flexibility limitations. Therefore, these limitations might constrain or make them impractical for the next generation mobile systems which are envisaged not only to support carrier aggregation and multi-band but also envisioned to integrate technologies like millimeter-wave (mm-wave) and massive multiple-input multiple-output antennas into the base stations. In this paper, we present comprehensive tutorial on technologies, requirements, architectures, challenges, and proffer potential solutions on means of achieving an efficient C-RAN optical fronthaul for the next-generation network such as the fifth generation network and beyond. A number of viable fronthauling technologies such as mm-wave and wireless fidelity are considered and this paper mainly focuses on optical technologies such as optical fiber and free-space optical. We also present feasible means of reducing the system complexity, cost, bandwidth requirement, and latency in the fronthaul. Furthermore, means of achieving the goal of green communication networks through reduction in the power consumption by the system are considered.

Toward an Efficient C-RAN Optical Fronthaul for the Future Networks: A Tutorial on Technologies, Requirements, Challenges, and Solutions

Cognitive radio (CR) has been considered as a potential candidate for addressing the spectrum scarcity problem of future wireless networks. Since its conception, several researchers, academic institutions, industries, and regulatory and standardization bodies have put their significant efforts toward the realization of CR technology. However, as this technology adapts its transmission based on the surrounding radio environment, several practical issues may need to be considered. In practice, several imperfections, such as noise uncertainty, channel/interference uncertainty, transceiver hardware imperfections, signal uncertainty, and synchronization issues, may severely deteriorate the performance of a CR system. To this end, the investigation of realistic solutions toward combating various practical imperfections is very important for the successful implementation of cognitive technology. In this direction, first, this survey paper provides an overview of the enabling techniques for CR communications. Subsequently, it discusses the main imperfections that may occur in the most widely used CR paradigms and then reviews the existing approaches toward addressing these imperfections. Finally, it provides some interesting open research issues.

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Cognitive Radio Techniques Under Practical Imperfections: A Survey

Time-critical and delay-sensitive multimedia applications require more spectrum and transmission resources. With the provision of cognitive radios (CRs), the underutilized spectrum resources can be exploited to gain more bandwidth for the bandwidth hungry applications (multimedia applications). Cognitive radio networks (CRNs) also have the flexibility to adjust their transmission parameters according to the needs of multimedia services or applications. For this reason, wireless multimedia cognitive radio networks (WMCRNs) have gained much attentions in today’s research domain. In this paper, we present a comprehensive survey of WMCRNs. Various multimedia applications supported by CRNs, and various CR-based wireless networks are surveyed. We highlight the routing and link layer protocols used for WMCRNs. We cover the quality-of-experience design and security requirements for transmitting multimedia content over CRNs. We provide an in-depth study of white space, television white space, and cross-layer designs that have been used for WMCRNs. We also survey the major spectrum sensing approaches used for the communications of bandwidth hungry and time-critical data over CRNs.

Wireless Multimedia Cognitive Radio Networks: A Comprehensive Survey

In this paper, a novel segmental partial transmit sequence (S-PTS) scheme is proposed for the peak-to-average power ratio (PAPR) reduction in offset quadrature amplitude modulation based orthogonal frequency-division multiplexing (OQAM-OFDM) systems. The key idea of the S-PTS scheme is to divide the overlapped OQAM-OFDM signals into a number of segments, and then some disjoint subblocks are divided and multiplied with different phase rotation factors in each segment. Compared with the conventional PTS scheme directly employed in OQAM-OFDM sytems, the S-PTS scheme could offer better PAPR reduction with lower computational complexity.

PAPR Reduction of OQAM-OFDM Signals Using Segmental PTS Scheme With Low Complexity

In this paper, we mainly analyze the relations between peak-to-average power ratio (PAPR) reduction, spectrum efficiency (SE), and energy efficiency (EE) in orthogonal frequency division multiplexing (OFDM) systems, respectively. Through PAPR reduction, the efficiency of high power amplifier (HPA) could be substantially improved, and the nonlinear distortion noise caused by the HPA could also be significantly reduced. As a result, the SE and EE are increased with a total transmit power constraint over additive white Gaussian noise (AWGN) channel. Moreover, we derive the quantitative relations between PAPR reduction, SE, and EE, respectively. Simulation results show that the OFDM system with PAPR reduction could achieve higher SE and EE than the system without PAPR reduction.

Effect of PAPR Reduction on Spectrum and Energy Efficiencies in OFDM Systems With Class-A HPA Over AWGN Channel

In this letter, a novel phase offset selected mapping (SLM) scheme is proposed to reduce the peak-to-average power ratio (PAPR) in Alamouti coded multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, and its key idea is that different phase rotation sequences are multiplied by their corresponding phase offsets at the transmitter. Moreover, a minimum Euclidian distance (MED) decoder at the receiver is proposed to recover the phase rotation sequences. Therefore, the proposed SLM scheme does not need to reserve bits for the transmission of side information, resulting in the increase of the data rate. Theoretical analysis and simulation results show that the proposed SLM scheme could offer good performances of both the bit error rate and PAPR reduction.

A Novel Phase Offset SLM Scheme for PAPR Reduction in Alamouti MIMO-OFDM Systems Without Side Information

In this letter, a novel adaptive tone reservation (ATR) scheme is proposed for the orthogonal frequency division multiplexing-based large-scale multiuser multiple-input multiple-output systems to deal with the inherent peak-to-average power ratio (PAPR) problem. The key idea of the proposed ATR scheme is to iteratively perform the tone reservation (TR) scheme on the antenna with the maximum PAPR. Simulation results validate that the ATR scheme offers better PAPR reduction performance and lower computational complexity than the conventional TR scheme.

A Novel Adaptive Tone Reservation Scheme for PAPR Reduction in Large-Scale Multi-User MIMO-OFDM Systems

Due to the overlapping structure of the offset quadrature amplitude modulation-based orthogonal frequency-division multiplexing (OQAM-OFDM) signals, the peak-to-average power ratio (PAPR) in OQAM-OFDM systems cannot be efficiently reduced by existing PAPR reduction methods, which independently consider the PAPR reduction in each data block. In this paper, a novel multiblock tone reservation (MB-TR ) scheme is proposed for the PAPR reduction in OQAM-OFDM systems. The key idea of the MB-TR scheme is to exploit the overlapping structure of the OQAM-OFDM signals and jointly consider the adjacent data blocks to obtain the clipping noise. To effectively eliminate the peaks of the OQAM-OFDM signals, the MB-TR scheme generates the peak-canceling signal by employing the weighted least square algorithm to fit the waveform of the peak-canceling signal to the waveform of clipping noise. Simulation results and analysis show that the MB-TR scheme could offer better PAPR reduction with lower computational complexity than the clipping control tone reservation scheme directly employed in OQAM-OFDM systems.

Chunxing Ni

Papers

PAPR Reduction of OQAM-OFDM Signals Using Segmental PTS Scheme With Low Complexity

Effect of PAPR Reduction on Spectrum and Energy Efficiencies in OFDM Systems With Class-A HPA Over AWGN Channel

A Novel Phase Offset SLM Scheme for PAPR Reduction in Alamouti MIMO-OFDM Systems Without Side Information

A Novel Adaptive Tone Reservation Scheme for PAPR Reduction in Large-Scale Multi-User MIMO-OFDM Systems

A Novel Multi-Block Tone Reservation Scheme for PAPR Reduction in OQAM-OFDM Systems