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With the rapid development of information and communication technology, the communication networks have been more efficient and more energy-intensive. In order to decrease the energy consumption, we propose a distributed switch-off method, based on the user equipments (UEs) locations and minimax algorithm, for the orthogonal frequency division multiplexing access-based cellular networks. For the sake of obtaining a nearly optimal result, the minimax algorithm adopted the full search manner and brought higher complexity meanwhile. In the proposed method, the complexity of the minimax algorithm is decreased by narrowing the search range according to the locations of UEs. Furthermore, in order to improve energy efficiency (EE), the numbers of UEs within cells and the load factor (LF) of base stations (BSs) are jointly considered as the measure factors to switch off the appropriate BSs. Simulation results demonstrate that the proposed method can decrease the complexity with a little sacrifice of EE performance, and the joint consideration of the UEs number and LF can improve the EE effectively.

With the continuous increase of user requirement, the Information and Communication Technology (ICT) has developed rapidly. As a result, both capacity and coverage performances have been improved, and at the same time, the communication networks have been more energy-intensive. In order to improve the energy efficiency of cellular networks, the green communication must be realized in the future networks. In this article, we present a short survey on energy-efficient technology of cellular networks. Moreover, we classify them into three categories based on theirapplication scenarios: energy-efficient architectures, energy-efficient resource management and energy-efficient radio technologies. For the first scenario, the applications of relay, Coordinated Multiple Points (CoMP) and heterogeneous network are discussed in detail. For the second scenario, the switching off scheme will be introduced as an emphasis of this part. And for the third scenario, the Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) will be introduced as the representatives of the Energy-Efficient Radio Technologies. Finally, based on the technologies introduced above, a prospect forecast of the energy-efficient wireless cellular network is presented.

Due to the introduction of wireless relays, the performance of LTE-A system was enhanced. Meanwhile, more energy was expensed and more interference was brought in. This is because the frequency used by relays may be the same or adjacent with the other relays or base stations. And the more stations deployed in a cell, the more energy consumed. In this paper, we proposed a novel green quasi-dynamic frequency resource division method for OFDMA download link. This method is suitable for the situation where the frequency resources are not continuous. And the special idle resources within cell are quasi-dynamically allocated, according to the load situations of base station and relays, to make the frequency division variable. With the uniform division and reasonable allocation based on the distribution of stations, the co-channel and adjacent-channel interference can be decreased effectively. Moreover, if possible, the relay stations with little users' access can be switched off and these users will be served by the adjacent relays, so that the energy consumption can be reduced further and some interference can also be eliminated.

Focusing on the high computational complexity of cooperative selection methods in LTE uplink channels, an improved user selection method is proposed in this paper. The selection method is based on the channel quality and signal-to-noise (SNR) of cooperative user. This method is mainly divided into the following two steps: firstly, the user with poor quality channel condition selects a user with better channel condition as its candidate cooperative user; secondly, the method needs to consider the channel environment between the candidate cooperative user and the base station. Thus, the cooperative user could be selected after those two steps. Simulation results show that the cooperative user selection method can not only reduce the bit error rate (BER), but also improve the capacity of the system. Moreover, the proposed method has not much effect on the success rate of the cooperative user selection process. So the transmission efficiency can be improved and the system performance can be optimized.

The main technology measures of anti-EMP in the civil defense shelter department's power network are limiting and filtering circuits. High voltage and low voltage zinc-oxide (ZnO) lightning arresters are commonly selected for limiters. Filtering includes primary filtering and precise filtering. In primary filtering devices, the low voltage non-power compensation condenser components are commonly changed into star connection and grounding. Before entering the high shielding area, special precise power filters, which are more expensive, are fitted. However, up to now, nobody has researched how to design and calculate the primary filtering devices in detail. We present methods for designing, selecting and calculating primary filtering devices, based on more than ten years' design experience. A table is presented of capacitor groups and capacitor value changes required for the design.