Abstract-With the massive multi-input multi-output (MIMO)antennas technology adopted for the fifth generation (5G) wireless communication systems, a large number of radio frequency (RF) chains have to be employed for RF circuits. However, a large number of RF chains not only increase the cost of RF circuits but also consume additional energy in 5G wireless communication systems. In this paper we investigate energy and cost efficiency optimization solutions for 5G wireless communication systems with a large number of antennas and RF chains. An energy efficiency optimization problem is formulated for 5G wireless communication systems using massive MIMO antennas and millimeter wave technology. Considering the nonconcave feature of the objective function, a suboptimal iterative algorithm, i.e., the energy efficient hybrid precoding (EEHP) algorithm is developed for maximizing the energy efficiency of 5G wireless communication systems. To reduce the cost of RF circuits, the energy efficient hybrid precoding with the minimum number of RF chains (EEHP-MRFC) algorithm is also proposed. . Compared with conventional MIMO antenna technology, massive MIMO can improve more than 10 times spectrum efficiency in wireless communication systems [7]. Moreover, the beamforming gain based on the massive MIMO antenna technology helps to overcome the path loss fading in millimeter wave channels. For MIMO communication systems with traditional radio frequency (RF) chains and baseband processing, one antenna corresponds to one RF chain [8], [9]. In this case, a large number of RF chains has to be employed for massive MIMO communication systems. These RF chains not only consume a large amount of energy in wireless transmission systems but also increase the cost of wireless communication systems [10]. Therefore, it is an important problem to find energy efficient solutions for 5G wireless communication systems with a large number of antennas and RF chains.To improve the performance of multiple antenna transmission systems, hybrid precoding technology combining digital
The orbital angular momentum (OAM) technique provides a new degree of freedom for information transmissions in millimeter wave communications. Considering the spatial distribution characteristics of OAM beams, a new OAM spatial modulation (OAM-SM) millimeter wave communication system is first proposed for future mobile networks. Furthermore, the capacity, average bit error probability and energy efficiency of OAM-SM millimeter wave communication systems are analytically derived for performance analysis. Compared with the conventional multi-input multi-output (MIMO) millimeter wave communication systems, the maximum capacity and energy efficiency of OAM-SM millimeter wave communication systems are improved by 36% and 472.3%, respectively. Moreover, numerical results indicate that the proposed OAM-SM millimeter wave communication systems are more robust to path-loss attenuations than the conventional MIMO millimeter wave communication systems, which makes it suitable for long-range transmissions. Therefore, OAM-SM millimeter wave communication systems provide a great growth space for future mobile networks. Index TermsMillimeter wave communications, orbital angular momentum, spatial modulation, capacity, average bit error probability, energy efficiency.with respect to the transmission SNR is illustrated in Fig. 11. When the transmission SNR is less than 10 dB, the energy efficiency of OAM-SM millimeter wave communication systems increase with the increase of the transmission SNR. When the transmission SNR is larger than or equal to 10 dB, the energy efficiency of OAM-SM millimeter wave communication systems decrease with the increase of the transmission SNR. There exist a maximum energy efficiency of OAM-SM millimeter wave communication systems considering different transmission SNR values. When the transmission SNR is fixed, the energy efficiency of OAM-SM millimeter wave communication systems is always larger than the energy efficiency of MIMO millimeter wave communication systems. To be specific, compared with the energy efficiency of MIMO millimeter wave communication systems, the maximum energy efficiency of OAM-SM millimeter wave communication system is improved by 472.3%. VI. CONCLUSIONS Exploiting spatial distribution characteristics of OAM beams, a new OAM-SM millimeter wave communication system is first proposed for future mobile networks. Important performance metrics like capacity, ABEP and energy efficiency of OAM-SM millimeter wave communication systems are analytically obtained in closed forms. It is shown analytically that significant performance gains can be achieved by the OAM-SM millimeter wave communication systems over the conventional MIMO millimeter wave communication systems, e.g., the maximum capacity
In practical mobile communication engineering applications, surfaces of antenna array deployment regions are usually uneven. Therefore, massive multi-input-multi-output (MI-MO) communication systems usually transmit wireless signals by irregular antenna arrays. To evaluate the performance of irregular antenna arrays, the matrix correlation coefficient and ergodic received gain are defined for massive MIMO communication systems with mutual coupling effects. Furthermore, the lower bound of the ergodic achievable rate, symbol error rate (SER) and average outage probability are firstly derived for multi-user massive MIMO communication systems using irregular antenna arrays. Asymptotic results are also derived when the number of antennas approaches infinity. Numerical results indicate that there exists a maximum achievable rate when the number of antennas keeps increasing in massive MIMO communication systems using irregular antenna arrays. Moreover, the irregular antenna array outperforms the regular antenna array in the achievable rate of massive MIMO communication systems when the number of antennas is larger than or equal to a given threshold.Index Terms-Massive MIMO, irregular antenna array, mutual coupling, achievable rate.
Recently, the security of Internet of Things (IoT) has been an issue of great concern. Physical layer security methods can help IoT networks achieve information-theoretical secrecy. Nevertheless, utilizing physical security methods, such as artificial noise (AN) may cost extra power, which leads to low secure energy efficiency. In this paper, the hybrid precoding technique is employed to improve the secure energy efficiency of the IoT network. A secure energy efficiency optimization problem is formulated for the IoT network. Due to the nonconvexity of the problem and the feasible domain, the problem is firstly transformed into a tractable suboptimal form. Then a secure hybrid precoding energy efficient (SEEHP) algorithm is proposed to tackle the problem. Numerical results indicate that the proposed SEEHP algorithm achieves higher secure energy efficiency compared with three existing physical layer security algorithms, especially when the number of transmit antennas is large.Index Terms-Internet of Things, physical layer security, hybrid precoding, secure energy efficiency, secrecy capacity
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