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Recently, as the damage of air pollution due to fine dusts, etc. has been continuously increased, there is a growing need for a low-cost air quality monitoring system to observe air pollution information at public facilities or homes. In this paper, we propose an IoT (Internet of Things)-based atmospheric environment monitoring system which can effectively observe air pollution information without...
Many challenges for efficiently supporting MTC (Machine-Type Communications) in LTE network have been investigated. In particular, access control schemes have been investigated to protect the system from excessive connectivity of MTC devices. Nonetheless, as the number of devices with data to send increases, it is inevitable that the energy consumed by the preamble collision and retransmission increases...
This paper provides a thorough analysis of the key aspects affecting the capacity of LTE networks. We group the analysis to the three major categories namely technology, spectrum and topology aspects. Through the extensive system-level simulations we investigate which of the specified aspects mostly affect the capacity and spectrum efficiency of 4G LTE networks. In addition, based on the performed...
As the conventional QAM has a square constellation, PAPR is high due to the corner signal points. To overcome this, the (3 × 2m)-ary QAM with even m was proposed recently. For odd m, the rectangular constellation has high PAPR and perfect Gray code, while the diamond constellation has low PAPR and imperfect Gray code. In this paper, we propose a scheme assigning quasi-Gray code to the diamond constellation...
In this paper, an LFM-based random access preamble (RAP) for underwater acoustic cellular systems is proposed. After showing that the conventional RAP used in LTE systems is not appropriate for underwater acoustic cellular systems, a suitable RAP, robust to Doppler effect, is proposed to detect the identity of underwater equipment/node (UE) and estimate the time delay between a UE and an underwater...
NB-IoT system focues on indoor coverage, low cost, long battery life, and enabling a large number of connected devices. The NB-IoT system in the inband mode should share the antenna with the LTE system and support mult-PRB to cover many terminals. Also, the number of used antennas should be minimized for price competitiveness. In this paper, the structure and implementation of the NB-IoT base station...
The LTE system that traditionally uses the licensed band have added the new technology, licensed assisted access (LAA), that enables to use 5 GHz unlicensed band with existing licensed band. Coexistence with Wi-Fi is major part of the LAA technology and regulations relating to coexistence has been revised after LAA technology emerged in Europe. Channel occupancy time (COT) is a critical parameter...
Massive connectivity is one of the major goals of 5G mobile communications. NB-IoT systems are emerging as a way to achieve this goal. In this paper, we analyze the interferences between the LTE system and the NB-IoT system when they coexist.
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