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

As one of the candidate wireless access techniques of 5G system, non-orthogonal multiple access (NOMA) is a power domain non-orthogonal multiple-access technique, which can greatly enhance spectral efficiency and system capacity. This paper mainly focus on user pairing and access theme of NOMA system, and respectively presents channel state sorting pairing algorithm (CSS-PA) as user pairing (UP) theme and user difference selecting access (UDSA) algorithm as new user access theme. The two new algorithms are proposed out of considerations on the features of NOMA system with a successive interference cancellation (SIC) receiver, and take the users' channel conditions into account, which is pairing the users with the most distinctive channel conditions. Analytical and simulation results demonstrate that the new algorithms can improve system capacity greatly compared to the existing algorithms while guarantee the user fairness. Furthermore, we discuss to apply SIC with interference rejection combining (IRC) receiver into the NOMA/MIMO system, which is a possible extension of NOMA system combined with multi-antennas, and simulation result shows that the performance gain of IRC-SIC over MRC-SIC can achieve about 2dB in high signal-to-noise ratio situation.

User pairing algorithm with SIC in non-orthogonal multiple access system

In this paper, new enhanced cognitive radio networks (E-CRNs) based on spectrum sharing (SS) and spectrum aggregation (SA) are proposed for fifth generation (5G) wireless networks. The E-CRNs jointly exploit the licensed spectrum shared with the primary user (PU) networks and the unlicensed spectrum aggregated from the industrial, scientific, and medical bands. The PU networks include TV systems in TV white space and different incumbent systems in the long term evolution time division duplexing bands. The harmful interference from the E-CRNs to the PU networks are delicately controlled. Furthermore, the coexistence between the E-CRNs and other unlicensed systems, such as WiFi, is studied. The E-CRNs framework including dynamic spectrum management (DSM) is designed for the key parameters of licensed SS and unlicensed SA. The essential tradeoff between sharing efficiency and aggregation efficiency for the E-CRNs is discussed. Based on this tradeoff, a spectrum lean-management scheme is proposed to fulfill the DSM. Moreover, a water-filling algorithm is designed to dynamically access the available spectrum. Numerical results demonstrate that the proposed E-CRNs can significantly improve the system performance in terms of data rate, outage probability, and spectrum efficiency. In particular, the E-CRNs framework provides a spectrum usage prototype for 5G wireless communication networks.

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Enhanced 5G Cognitive Radio Networks Based on Spectrum Sharing and Spectrum Aggregation

Herein, we present a detailed analysis of an eigenvalue-based sensing technique in the presence of correlated noise in the context of a cognitive radio (CR). We use standard-condition-number (SCN)-based decision statistics based on asymptotic random matrix theory (RMT) for the decision process. First, the effect of noise correlation on eigenvalue-based spectrum sensing (SS) is analytically studied under both the noise-only and signal-plus-noise hypotheses. Second, new bounds for the SCN are proposed to achieve improved sensing in correlated noise scenarios. Third, the performance of fractional-sampling (FS)-based SS is studied, and a method to determine the operating point for the FS rate in terms of sensing performance and complexity is suggested. Finally, a signal-to-noise ratio (SNR) estimation technique based on the maximum eigenvalue of the covariance matrix of the received signal is proposed. It is shown that the proposed SCN-based threshold improves sensing performance in correlated noise scenarios, and SNRs up to 0 dB can be reliably estimated with a normalized mean square error (MSE) of less than 1% in the presence of correlated noise without the knowledge of noise variance.

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Eigenvalue-Based Sensing and SNR Estimation for Cognitive Radio in Presence of Noise Correlation

In this paper,a new flux-weakening control method based on rotor flux orientation is presented to improve the current tracking capability and output characteristics of the motor torque,and the method is implemented in digital ac spindle driver system.Using Labview virtual oscilloscope to observe the real-time experimental data,the experimental results show that the method can effectively improve the dynamic response of motor as well as the output characteristics of the motor torque.

Maximum Torque Control of an Induction Machine in the Field Weakening Region

This paper presents a joint decoding scheme for an overloaded multiple input multiple output (MIMO) -orthogonal frequency division multiplexing (OFDM) system. In the overloaded MIMO system the number of receive antenna elements is less than that of transmit antenna elements. It has been shown that under the overloaded condition the performance of joint detection deteriorates while diversity reduces the amount of performance degradation caused by signal multiplexing. Thus, this paper proposes a maximum likelihood joint decoding scheme of block coded signals in the overloaded MIMO-OFDM system. The performance of joint decoding over Rayleigh fading channels is evaluated through the experiments. It is shown that the diversity through block coding realizes a limited amount of performance degradation in joint decoding of 2 Hamming coded signal streams.

Experimental investigation of joint decoding in overloaded MIMO-OFDM system

Wireless power transfer research has been receiving a great deal of attention in recent years. In resonant-type wireless power transfer, energy is transferred via LC resonant circuits. However, system performance is dependent on the circuit components. To transfer power efficiently and safely, information, such as frequency, required power and element values, need to be transmitted reliably in the system. This paper investigates data communication using orthogonal frequency division multiplexing (OFDM) modulation in resonant-type wireless power transfer systems. The equivalent circuit used in the transmitting and receiving antennas is a band pass filter (BPF) and its bandwidth is evaluated through circuit simulations and experimental measurements. Numerical results obtained through computer simulation show that the bit error rate (BER) performance is affected by the splitting resonant frequency. key words: OFDM, Wireless power transfer, BPF, communication, control

Reliable Data Transmission for Resonant-Type Wireless Power Transfer

This paper proposes a transformation matrix to generate Pulse Width Modulation (PWM) signals for Four Switch Three Phase Inverter (FSTPI) using vector control. The feasibility of the control strategy is verified by proving the power invariance before and after the transformation. Simulation and experimental results have verified the validity and effectiveness of the proposed method to obtain instantaneous response in different operating conditions and provide fast speed response.

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Instantaneous Vector Control of Four Switch Three Phase Inverter Fed Induction Motor Drive

Instantaneous vector control of four switch three phase inverter fed induction motor drive

In the IEEE 80211a WLAN standard, orthogonal frequency division multiplexing (OFDM) modulation is employed Diversity techniques are effective way to overcome multipath fading in the OFDM systems A fractional sampling (FS) scheme is one of the diversity techniques with a single antenna Through FS it is possible to separate multipath components and obtain diversity gain in OFDM Though FS has been analysed numerically, the experiment of FS on actual indoor channels with real filter characteristics has not been carried out In addition, though it has been suggested that in FS diversity a sharp filter limits the diversity gain, this limitation has not been confirmed especially with measurements Therefore we investigate the effect of filter bandwidth in FS through simulation and an experiment Numerical results through the simulation and the experiment indicate that the FS can achieve path diversity and improves the performance by about 2 dB if the bandwidth of the baseband filter is larger than the minimal bandwidth

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Effect of baseband filter bandwidth in fractional sampling orthogonal frequency division multiplexing on indoor channel model with measured impulse responses

Mamiko Inamori

Papers

Experimental investigation of joint decoding in overloaded MIMO-OFDM system

Reliable Data Transmission for Resonant-Type Wireless Power Transfer

Instantaneous Vector Control of Four Switch Three Phase Inverter Fed Induction Motor Drive

Instantaneous vector control of four switch three phase inverter fed induction motor drive

Effect of baseband filter bandwidth in fractional sampling orthogonal frequency division multiplexing on indoor channel model with measured impulse responses