Cognitive Internet of Things (CIoT) can improve spectrum utilization by accessing idle 4G/5G spectrum, in order to provide better transmission quality. However, compared with the traditional IoT, ...spectrum sensing may consume much energy, which decreases the transmission power of the CIoT. In this paper, a green CIoT has been proposed to collect the radio frequency (RF) energy of primary user (PU) by using energy harvesting. The frame is divided into sensing slot and transmission slot, and the nodes are divided into two independent groups to perform spectrum sensing and energy harvesting simultaneously in the sensing slot. The energy efficiency of the CIoT is maximized by formulating an optimization problem about sensing time, number of sensing nodes and transmission power, whose suboptimal value is achieved using a joint optimization algorithm. In order to guarantee energy balance, the alternative mechanism of spectrum sensing and energy harvesting is proposed to prolong the life of the CIoT. Simulation results have indicated the existence of the optimal solution and the outstanding performance of the green CIoT.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In recent years, relaying technique and non-orthogonal multiple access (NOMA) are introduced to visible light communication (VLC) system to improve the system performance. Relay-assisted VLC system ...can boost link reliability and extend effective communication coverage compared with the traditional VLC system. Besides, the adoption of NOMA can significantly improve the system throughput, enhance the spectral efficiency and support massive connectivity. A novel relay-assisted VLC system based on NOMA is proposed in this paper. All the source-to-relay and relay-to-destination links in the proposed system use DCO-OFDM scheme to transmit information. The relay terminal serves two destination terminals at the same time. The signals in these two relay-to-destination links are superposed in the power domain based on NOMA. The total throughput with different parameters such as power allocation factors and DC bias is modeled and deduced in this paper. By simulations, the optimal values of DC bias and power allocation factors that maximize the system throughput are obtained. Moreover, the simulation results also show superiority of the NOMA-based VLC system over the OMA-based VLC system.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Smart homes based on the Internet of Things have been rapidly developed. To improve the safety, comfort, and convenience of residents’ lives with minimal cost, daily activity recognition aims to know ...resident’s daily activity in non-invasive manner. The performance of daily activity recognition heavily depends on solving strategy of activity feature. However, the current common employed solving strategy based on statistical information of individual activity does not support well the activity recognition. To improve the common employed solving strategy, an activity feature solving strategy based on TF-IDF is proposed in this paper. The proposed strategy exploits statistical information related to both individual activity and the whole of activities. Two distinct datasets have been commissioned, to mitigate against any possible effect of coupling between dataset and sensor configuration. Finally, a number of machine learning (ML) techniques and deep learning technique have been evaluated to assess their performance for residents activity recognition.
Green and sustainable communications are crucial for cellular devices and the Internet of Things (IoT) devices in the fifth generation (5G) mobile communication system. Wireless-powered communication ...(WPC) provides a successful technical paradigm to support wireless information transmission for mobile devices by using harvested radio-frequency (RF) energy. In the meantime, non-orthogonal multicarrier transmission techniques, typically represented by the generalized frequency-division multiplexing (GFDM), can not only enhance spectrum efficiency but also improve the flexibility of resource allocation due to its fine-granularity sub-block. In this paper, a GFDM-based cooperative relay system model is proposed to improve the quality of experience of the cell-edge user. Specifically, the system is composed of one source node, one destination node (cell-edge user), and one relay node. The source node transmits a signal to the destination node and the relay node. The relay node performs information transmission and power transfer to the destination node by using different GFDM sub-block sets. The destination node combines the signals from the source node and relay node. In order to maximize the information rate at the destination node subject to the minimum harvested energy, a joint sub-block, sub-block power, and subslot allocation-based WPC scheme is proposed. To solve the non-convex optimization problem, an iterative algorithm is proposed and its effectiveness is validated by simulations. The simulation results demonstrate that the GFDM-based WPC scheme outperforms the orthogonal frequency-division multiplexing (OFDM), and the subslot optimization can significantly increase the information rate at the destination node.
Visible light communication (VLC) is a powerful supplement to the fifth generation (5G) mobile communications. In VLC system, the adoption of orthogonal frequency division multiplexing (OFDM) and ...relaying technique can greatly improve system performance. In this paper, we proposed a novel relay-assisted VLC system based on asymmetrically clipped direct current biased optical OFDM (ADO-OFDM) for 5G networks. An amplify-and-forward relay is used in the proposed system to forward the signals from source terminal and transmit its own signals simultaneously. The signals from source terminal are allocated to even subcarriers, while the signals from relay terminal are allocated to odd subcarriers. Then, these two parts of signals are combined to constitute ADO-OFDM signals. The signals on odd subcarriers don't interfere with the signals on even subcarriers, while the interference of the signals on even subcarriers to the signals on odd subcarriers can be eliminated by the noise estimation in ADO-OFDM system. Finally, both signals can be recovered at the receiver. We derive the formula of system throughput and investigate the impacts of two power allocation factors on system throughput. Simulation results show that the proposed system makes full use of the relay terminal and improves system throughput. In addition, simulation results also demonstrate that there are optimal power allocation factors to achieve maximum throughput.
Generalized frequency division multiplexing (GFDM) is a promising candidate for 5G waveforms because of its flexibility to meet the requirements of different scenarios and applications. Compared with ...the orthogonal frequency division multiplexing, the lower out-of-band radiation and higher spectrum efficiency make GFDM the qualified waveform solution for cognitive radio (CR). In CR networks, channel estimation is the necessity and premise to guarantee reliable spectrum sensing. Because of the block modulation structure for GFDM, conventional channel estimation algorithm cannot be applied to GFDM directly. Also, the feedback information in channel decoding is not fully utilized by the conventional algorithm. To solve these problems, in this paper, a modified turbo receiver is designed to utilize the feedback information for channel estimation. The modulator for the pilot insertion is also improved to make pilots orthogonal to data subcarriers. Based on the modified turbo receiver, an iterative channel estimation strategy combined with threshold control is proposed to cope with the noise enhancement. The symbols rebuilt for the iterative channel estimation are verified that only the credible symbols can be retained for the next iteration. Simulation results demonstrate that the proposed channel estimation method has the better bit error rate and mean-squared error performances over Rayleigh fading channel compared with the conventional algorithm.
High-efficiency utilization of resources has always been the major concern and design objective in the Internet of Things (IoT). In this paper, an orthogonal frequency division multiplexing-based ...wireless system model for IoT is proposed, where the simultaneous wireless information and power transfer and the non-orthogonal multiple access (NOMA) are jointly used to improve the energy and spectrum utilization. Specifically, terminals can decode information and harvest energy simultaneously in the downlink and transmit signals to the access point (AP) in the uplink. Then, the AP decodes terminals' information based on NOMA. A joint uplink and downlink resource allocation scheme is proposed with the optimization objective to maximize the sum information decoding rate in the uplink under the condition that the target sum information decoding rate in the downlink is guaranteed. To solve the optimization problem, a two-step algorithm is proposed. For the first step, a joint subcarrier and power allocation algorithm is designed to maximize the harvested energy of terminals in the downlink. For the second step, a subslot optimization algorithm is designed to increase the sum information decoding rate in the uplink. Simulation results demonstrate that, compared with the conventional algorithms, the proposed algorithm can not only achieve the maximization of harvested energy but also support higher sum information decoding rate in the uplink.
As one of the candidate waveforms for 5G, generalized frequency division multiplexing (GFDM) is a flexible non-orthogonal multicarrier technique. Similar to orthogonal frequency division ...multiplexing, GFDM communication system suffers from symbol timing offset (STO) and carrier frequency offset (CFO) caused by multipath effect and Doppler shift. In this paper, we design a pseudo noise (PN) based preamble and propose an approach for signal synchronization. The preamble is composed of two identical PN sequences whose autocorrelation and cross-correlation are better than cyclic prefix (CP). STO can be detected by calculating the correlation coefficient between the local PN sequence of receiver and the corresponding preamble part of sliding window. These two adjacent PN sequences can be used to calculate phase offset value by Fourier transform, and then obtain CFO value. Simulation results demonstrate that, compared with conventional CP-based synchronization, the proposed approach has the lower mean square error and symbol error rate at the cost of just a little bit more bandwidth.
Due to the superiority of large coverage, high mobility, high-quality channels, and reusability, high altitude platforms (HAPs) can be exploited as the aerial communication means to provide users in ...disaster areas with long-term and stable data relay services. In this correspondence, a HAP relaying system based on clustered non-orthogonal multiple access (C-NOMA) is designed in which the HAP provides data transfer services for base station (BS) and users who cannot communicate directly. According to the system, a joint HAP flight trajectory optimization and power allocation scheme is proposed, which aims at maximizing the downlink average achievable sum rate of all users while satisfying the information causality. Since the formulated problem is non-convex, we propose an efficient iterative algorithm to derive the approximately optimal solution by alternately optimizing the HAP flight trajectory, and the transmit power of BS and HAP. The numerical simulation results demonstrate that the proposed scheme can not only effectively improve the achievable sum rate, but also significantly enhance the fairness between users compared with the benchmark scheme.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In order to overcome the shortcomings of orthogonal frequency division multiplexing (OFDM) and prolong the battery life of devices in the Internet of Things, a joint subcarrier and subsymbol ...allocation-based simultaneous wireless information and power transfer scheme for multiuser generalized frequency division multiplexing (GFDM) system is proposed in this paper. According to the 2-D time-frequency block structure of GFDM, we investigate the problem to maximize sum information decoding (ID) rate by optimizing subcarrier and subsymbol allocation, power allocation and power splitting ratio under the constraints of total transmit power and harvested energy. To solve the nonconvex problem, an iterative algorithm is developed to obtain its optimal solution. The performances of sum ID rate and harvested energy are simulated and evaluated. Simulation results show that the proposed algorithm converges fast. Moreover, the proposed algorithm can not only allocate the subcarriers, subsymbols, and power based on different channel conditions of users, but also outperform the conventional OFDM in sum ID rate on the premise of satisfying the minimum harvested energy of each user.
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