Spectrum handoff in cognitive radio networks

The cognitive femtocell has emerged as an exciting technology to solve the indoor coverage problem in future cellular networks. Recently, several technical issues for the cognitive femtocell have been studied, e.g., spectrum sharing and interference mitigation. However, the incentive method that is very important for practical hybrid access cognitive femtocell deployment has not been well investigated. In this paper, we propose a new dynamic spectrum allocation method for the hybrid access cognitive femtocell. In the proposed method, the macro base station (BS) allocates a portion of subchannels to the femto access point (FAP) to spur the FAP to serve the macro users (MUs). Then, the FAP allocates the subchannels and power to maximize the femtocell network utility, whereas the throughput of the served MUs is guaranteed. Moreover, we formulate the corresponding resource allocation problem as a sum-utility maximization problem and propose an optimization method to solve it via the dual decomposition method. Simulation results show that both the wireless service provider and the femtocell could benefit from the proposed method.

Dynamic Spectrum Allocation for the Downlink of OFDMA-Based Hybrid-Access Cognitive Femtocell Networks

Despite the promising role of orthogonal frequency-division multiplexing (OFDM) in communication systems, the spectrum sensing of OFDM signals and its practical considerations for cognitive radios (CRs) remain vital and challenging topics. This paper presents a new scheme for detecting OFDM signals based on the Neyman–Pearson (NP) principle. In contrast to conventional approaches in which additive white Gaussian noise (AWGN) channels are considered or empirical second-order statistics based on correlation coefficients are employed, to improve the detection performance, the proposed approach involves considering multipath fading channels and the classical NP detector. The log-likelihood ratio (LLR) test is formulated without requiring additional pilot symbols by using the redundancy of the cyclic prefix. Analytical results indicate that the LLR of received samples is the sum of the log-likelihood function (LLF) of the samples, which is typically used for estimating unknown parameters, and the LLR of an energy detector (ED). These results provide insight into the NP detector and the relationship between the NP detector, a detector based on the LLF, and the ED. 1 Because many unknown parameters must be estimated in the NP detector, two practical generalized log-likelihood ratio test (GLRT) detectors are designed. To develop a channel-independent GLRT, which is crucial for achieving favorable performance over multipath fading channels, the complementary property of the correlation coefficient is employed to derive an estimate independent of multipath channel profiles. Simulation results confirm the advantages of the proposed detector compared with the state-of-the-art detectors. 1 EDs are optimal only for independent and identically distributed random samples.

Spectrum Sensing of OFDM Signals Over Multipath Fading Channels and Practical Considerations for Cognitive Radios

Cognitive radio networks (CRNs) rely on sensing of the licensed spectrum of a primary network to dynamically ascertain underutilized portion of the spectrum, thus affording additional communication opportunities. In a CRN, a single homogeneous spectrum access, such as interweave only deprives the secondary users (SUs) of channel access during handoff, particularly at high primary network traffic. Therefore, providing quality-of-service (QoS) to multi-class SUs with diverse delay requirements during handoff becomes a challenging task. In this paper, we have evolved a Markov-based analytical model to ascertain the gain in non-switching spectrum handoff scheme for multi-class SUs employing hybrid interweave-underlay spectrum access strategy. To satisfy the QoS requirements of the delay-sensitive traffic, we have analyzed the impact of hybrid spectrum access scheme for prioritized multi-class SUs traffic. The results show substantial improvement in spectrum utilization, average system throughput and extended data delivery time compared to conventional CRN using interweave only spectrum access. This demonstrates the suitability of the proposed scheme towards meeting QoS requirements of the delay-sensitive SU traffic while improving the overall performance for delay-tolerant SU traffic as well.

Analysis of Efficient Spectrum Handoff in a Multi-Class Hybrid Spectrum Access Cognitive Radio Network Using Markov Modelling.

Orthogonal frequency-division multiplexing (OFDM) is a promising technology for communication systems. This paper investigates the impacts of unknown noise variance on the popular spectrum sensing scheme, i.e., energy detection, for OFDM cognitive radios over multipath fading channels. To study the effects of unknown parameters on the energy detector, a new maximum-likelihood estimation of noise and signal powers employing the cyclic prefix of OFDM is presented in this paper. The mean values and Cram $\acute{\text{e}}$ r–Rao lower bounds of the estimation are obtained. Furthermore, the performances of the energy detector for both hypotheses, i.e., false-alarm rate and detection probability, under the influence of unknown noise variance are validated by both simulation and analytical results. The assessment on the required number of samples for the proposed energy detector is conducted, which indicates that an amount of 40–50% samples can be saved compared to the conventional energy detector.

On the Noise Uncertainty for the Energy Detection of OFDM Signals

In this paper, we employ the preemptive resume priority (PRP) M/M/1 queuing model to analyze the transmission delay of priority-based secondary users (SUs) in the opportunistic spectrum access (OSA)-based cognitive radio networks (CRNs) The SUs in the OSA-based CRNs are with different priority levels The SU with the high priority level can access a channel in preference to the low priority level SU when the channel is available Moreover, to reduce the transmission delay of the interrupted SUs, the interrupted SUs are assigned the higher priority than the newly arrived SUs with the same priority level The expression of the transmission delay for the interrupted SUs is derived based on the PRP M/M/1 queuing model Simulation results show that the queuing model with priority-based SUs can effectively guarantee the quality of service of the high priority level SUs and reduce the overall transmission delay of the interrupted SUs

Analysis on the transmission delay of priority-based secondary users in cognitive radio networks

In this article, we investigate the strategies of access and handoff in the opportunistic spectrum access (OSA) based cognitive cellular networks (CCNs). Then, a three dimension (3D) continuous- time Markov chain (CTMC) is constructed to derive the grade of service (GoS) performance metrics in the OSA-based CCNs. Through the 3D CTMC, both the non-hopping and hopping modes are investigated, respectively. Specifically, for a given primary user (PU) traffic, the range of achievable user equipment (UE) traffic is derived with guarantying the GoS of the UE. Moreover, we study the effective spectrum utilization and influence of imperfect spectrum sensing to the GoS performance, respectively. Furthermore, to verify the validity of the theoretical analysis, simulations are conducted. Finally, some open issues are discussed in this article.

Grade of service of opportunistic spectrum access based cognitive cellular networks

Environmental issues are fundamentally problems of development mode and life style. Meanwhile, the digital economy is an important means of optimizing the economic structure and achieving high-quality economic development, thereby changing the way of production and life, which can improve the aforementioned environmental challenges. Therefore, this research investigates how the digital economy can bring new ideas for reducing pollution in depth. Based on panel data from 285 prefecture-level cities in China, this paper examines the impact of the digital economy on PM2.5. We construct the evaluation system of China’s digital economy development from the three aspects of digital penetration, digital human resources, and digital output. We use the digital economy comprehensive index with digital financial inclusion index as the main component to test the robustness. The results show that the increase of the digital economy reduces PM2.5 emissions in Chinese cities. In addition, we also explore technological innovation as a mediating channel for the digital economy to influence PM2.5 emissions. The digital economy provides a better research environment for technological innovation, conducive to improving cleaner production technology and products. Finally, we find that environmental information disclosure can enhance the impact of the digital economy on PM2.5 emissions.

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The Mediating and Moderating Effects of the Digital Economy on PM2.5: Evidence from China

In this paper, we propose a novel spectrum sensing method for Time Domain Synchronous-Orthogonal Frequency Division Multiplexing (TDS-OFDM) signals in Cognitive Radio (CR) Networks and the key idea is to employ the Pseudo-Noise (PN) sequences embedded in the frame headers to carry out the spectrum sensing. We employ the modulation method of the PN sequence rather than the cyclostationary of PN sequence in TDS-OFDM signals. Firstly, the decision statistic is given. Secondly, the detection threshold for a given probability of false alarm is derived. Moreover, the analysis of the detection probability is presented as well. Finally, we give an upper bound to give a good prediction of the proposed spectrum sensing algorithm. Both theoretical analysis and simulation results demonstrate the advantage of the proposed method over the existing PN autocorrelation (PNAC) method.

Spectrum sensing for TDS-OFDM systems in Cognitive Radio Networks

(1) Background: The main research aim of this paper is to investigate the commonly stocked medicines in Chinese households. Firstly, a large number of questionnaires were collected to uncover the problem: most Chinese families have the habit of stocking their family medicine boxes. However, there is a lack of a standardized, systematic, and scientific list of household medicine stockpiles. As a result, there are major problems in stocking medicines in households: (1) There is little connection between the type and quantity of medicines stocked and real life; (2) The expiration date of medicines leads to misuse and waste of medicines; (3) The existing list of medicines can provide little help. (2) Methods: The preliminary drug stock list was summarized through case studies; the authenticity of the questions and the credibility of the list were verified through interviews; the number of different types of drugs and the relationship between the resident’s perception of the importance of drugs and their frequency of use was determined through questionnaires; the authenticity of the list was verified through interviews with senior doctors. (3) Results: We finally composed a scientific and practical list of common household medicines, developed a practical domestic-medication system for Chinese families, and conducted validation studies, which received the approval of senior doctors. (4) Conclusions: (1) Chinese families need to prepare medicines according to the actual composition of the family; (2) Chinese families need a scientific and systematic list of commonly prepared medicines; and (3) in addition to the types of medicines, it is also necessary to consider the number of individual types of medicines to be stocked.

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Yun Zhang

Papers

Analysis on the transmission delay of priority-based secondary users in cognitive radio networks

Grade of service of opportunistic spectrum access based cognitive cellular networks

The Mediating and Moderating Effects of the Digital Economy on PM2.5: Evidence from China

Spectrum sensing for TDS-OFDM systems in Cognitive Radio Networks

Investigating and Developing a Practical Domestic-Medication System of Public Health for Chinese Family