Search

Massive Machine-Type Communication (mMTC) is proposed by ITU to provide a large scale of connectivity services for billions of machine-type communications devices (MTCDs) via cellular networks. However, MTCDs are generally energy-constrained, security capability limited and short-packet transmission dominated. It has great challenges for massive MTCDs to perform short-packet transmission simultaneously while guaranteeing the confidentiality and energy efficiency of the information transmission. In this paper, we investigate the energy-efficient secure short-packet transmission of Non-Orthogonal Multiple Access (NOMA) assisted mMTC networks, in which MTCDs aim to transmit secrecy messages to the destination base station via trusted relays with a passive eavesdropper present. To realize secure, reliable and energy-efficient transmission, we maximize the secrecy energy efficiency (SEE) by implementing joint relay and power level selection. Furthermore, we formulate a decentralized stateless Q-learning-based multi-agent reinforcement learning (MARL) algorithm for the dynamic and complex mMTC systems. The simulation results show that adopting the proposed decentralized MARL algorithm and relaying with NOMA can improve the performance of SEE while reducing information exchange overhead. [ABSTRACT FROM AUTHOR]

The 5th-generation (5G) mobile networks and beyond need to support massive machine-type communications (MTC) devices with limited available radio resources. In this paper, we study the power-domain non-orthogonal multiple access (NOMA) technology to support energy-efficient massive MTC networks, where MTC devices exchange information using sporadic and low-rate short packets. We investigate the subchannel allocation and power control policy to maximize the achievable effective energy efficiency (EE) for uplink NOMA-based massive MTC networks, taking into account of short-packet communication characteristics. We model the subchannel allocation problem as a multi-agent Markov decision process and propose an efficient Q-learning algorithm to solve it. Furthermore, we obtain the optimal transmission power policy by approximating the achievable effective rate of uplink NOMA-based short packet communications. Compared with the existing OFDMA scheme, simulations validate that the proposed scheme can improve the achievable effective EE of massive MTC networks with 5.93%. [ABSTRACT FROM AUTHOR]

• An energy-efficient oriented multi-objective urban block form design workflow is proposed. • The relationship between urban form factors and building energy consumption, as well as solar energy potential, is explored. • Reducing energy demand, increasing energy generation, and improving environmental performance should be considered together in the design of energy-efficient blocks. • BD, OSR, SC, and PAR have significant correlations with the total EUI of the block. • FAR, BD, AF, OSR, SC, and PAR are highly correlated with rooftop PV energy generation. Urban form can significantly affect building energy consumption and solar energy potential, which is essential to sustainable urban development. However, few studies have proposed a comprehensive framework to discuss this. In addition, how to bridge the gap between theory and practice, and how to combine quantitative research results with urban form design is also a matter of concern. Based on this background, this study proposes a multi-objective urban form design optimization framework based on the Grasshopper platform. Three optimization objectives were identified: minimum building energy consumption, maximum solar potential and maximum sunlight hours. Then, taking Jianhu in China as an example, the building types are extracted from the actual urban context to create blocks. The Ladybug Tools plugin is used for performance simulation, and multi-objective optimization is run in Wallacei X. Furthermore, based on the optimization process data, a correlation analysis of urban form factors with building energy consumption and solar energy potential is conducted. Finally, the research findings are integrated, and energy-efficient urban form design strategies are proposed. The research results show that a block form with excellent energy performance in Jianhu has the following characteristics: (i) The open space is often located in the center of the block. High-rise buildings are located on the west side. (ii) The block presents a layout consisting of a low south side and high north side. (iii) The orientation of the block is 15° south by westor due south. (iv) Avoid building types with large shape coefficient such as P-4, C-1, S-3 and C-2. In addition, building density (BD), open space ratio (OSR), shape coefficient (SC) and average perimeter-area ratio (PAR) have significant correlations with the total building energy use intensity of the block. For solar potential, floor area ratio (FAR), BD, the average number of floors (AF), OSR, SC, and PAR are highly correlated with rooftop PV energy generation, and sky view factor (SVF) is significantly correlated with rooftop PV energy generation. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmWave) and ultra-dense networks are two key technologies for the fifth-generation (5G) and beyond communication system. However, the ultra-dense deployment of small base stations (SBSs) might introduce severe interference to users that connect to SBSs. This paper analyzes the performance of 5G communication networks where the SBSs with coordinated beamforming, operating at mmWave frequency band and macro base stations (MBSs) operating at sub-6 GHz coexist. First, by utilizing a stochastic geometry approach, we obtain the cell association probability expressions in terms of different cell association biases, base station density ratios and probabilities of line of sight (LoS) link. Furthermore, we propose a clustering method to choose some SBSs to eliminate intra-cell interference. Then, we put forward an average distance from the Kth SBS to a user to obtain signal-to-interference-ratio (SINR) and rate coverage probability expressions. The simulation results validate the correctness of the expressions, and indicate that the optimal cardinality of coordinated SBSs increases with the density of SBSs. In addition, the relationship between the cluster size K and the average energy efficiency is obtained, which can be used to guide the coordination principle in 5G and beyond communication systems. [ABSTRACT FROM AUTHOR]

Urban building energy model has been the focus of much research in recent years, especially using data-driven techniques, however, the success of which needs to solve the recognized challenges, such as sufficient energy use dataset in spatial and temporal scales and mutual effect between inter-buildings. Using monthly and yearly energy data from 539 residential buildings and 153 public buildings in a county-level city, this study investigated five typical data-driven urban building energy prediction models on the neighborhood scale. The k nearest neighbors (KNN), support vector regression (SVR), and long short-term memory (LSTM) algorithms were selected as data-driven predictive techniques. The Model 1 was a data-driven energy prediction model for individual building, and with LSTM, the best results for Model 1 can be averagely 0.41 of MAPE and averagely 0.57 of R2. The Model 2 applied different percentages (100%, 95%, 90%, 85%, 80%, 75%, 70%, 65%, and 60%) of original energy dataset to predict total energy demand. The results for Model 2 are averagely 0.065 of MAPE and averagely 0.95 of R2, which also proved that reducing the size of dataset did not influence the results. The Model 3 and 4 created building networks with energy data and building morphology, respectively, and integrated them in urban building energy prediction models, The MAPE results are mostly lower than 0.4 and 0.36, respectively, and R2 results are mostly higher than 0.85 and 0.8 for Model 3 and 4, respectively. The Model 5 combined building morphological metrics and yearly energy data, which received 0.093 and 0.194 of MAPE results and 0.975 and 0.99 of R2 for residential and public buildings, respectively. Finally, this study can contribute to provide more solutions to urban building energy prediction while reduce the high data requirements of urban energy models. [ABSTRACT FROM AUTHOR]