While research on communications at frequencies above 6 gigahertz (GHz) has been primarily confined to performance improvement, their potentially harmful impacts on human health are not studied as significantly. Most of the existing studies that paid attention to the health impacts above 6 GHz focused only on the uplink due to closer contact with a transmitter to a human body. In this letter, we present the human electromagnetic field (EMF) exposure in the downlink of Fifth-Generation Wireless Systems (5G). Moreover, we propose a downlink protocol that guarantees the EMF exposure under a threshold while keeping the data rate above the 5G requirements.
Very few prior studies in the literature paid attention to human RF exposure in communications systems @cite_20 @cite_19 - @cite_5 . Propagation characteristics at different mmW bands and their thermal effects were investigated for discussion on health effects of RF exposure in mmW radiation @cite_19 . Emission reduction scheme and models for SAR exposure constraints are studied in recent works @cite_10 @cite_13 . Note that if the BSs have the power control or adaptive beamforming capability according to @cite_6 , the human exposure can be reduced sufficiently. Also, if both mmW and microwave architecture wok combined for the 5G network, the exposure level can be reduced as the mmW architecture will use higher carrier frequency with smaller Inter-site distance (ISD) than the micro-wave structure. However, this paper analyzes the maximum possible exposure that a human user can experience if the antennas do not have the power control or adaptive beamforming capability and if only mmW architecture is present with no interference. In other words, this work analyzes the possibility of any threat possible from a 5G network at the worst possible scenario.
@cite_10 @cite_6 @cite_19 @cite_5 @cite_13 @cite_20
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Wideband fifth generation systems utilizing high carrier frequency and multiple-input multiple-output (MIMO) raise major challenges for the system design. Wave propagation and practical hardware tradeoffs at higher frequency ranges provide new boundary conditions for the implementation. This paper addresses system performance boundaries and the analysis method toward multibeam communications at millimeter wave. We combine analysis from antennas and propagation to the radio frequency (RF) transceiver specifications and beamforming requirements. Realistic propagation model and antenna implementation are used to generate beam-specific path gains and provide a wide variety of user scenarios. Using this approach, system level interdependencies and RF performance boundaries can be verified with different antenna configurations in various propagation environments. As an example, we present MIMO link budget analysis targeting 10 Gbits s for multiple devices in the office scenario at 27 GHz. Interactions between a 60-GHz microstrip patch antenna array designed for off-body communications and the human body are investigated numerically and experimentally. First, the array is characterized in free space and on a homogeneous skin-equivalent phantom in terms of reflection coefficient, radiation pattern, and antenna efficiency. Second, a multiphysics dosimetry technique is proposed and implemented to determine the specific absorption rate (SAR) and incident power density (IPD) from the heating dynamics measured on an experimental phantom using a high-resolution infrared (IR) camera. The SAR and IPD are found by fitting the analytical solution of the bio-heat transfer equation to the measured heating dynamics. The experimental and numerical results are in a very good agreement. They demonstrate that for the considered scenario the impact of the body on the antenna characteristics is almost negligible, and even relatively high radiated powers (up to 550 mW) result in exposure levels that are below international exposure limits. The rapid growth of wireless technology worldwide has prompted interest in the underutilized millimeter-wave band from 30 to 100 GHz. Regulation agencies set limits on the amount of electromagnetic radiation absorbed by users, measuring dosimetric quantities such as specific absorption rate (SAR) to assess compliance. The increased rate of energy deposition in human tissue at high frequencies remains a growing concern as wireless cellular networks begin to incorporate millimeter wave technologies. In this paper, we present a baseband model for SAR-aware wireless communication and a strategy for optimal hybrid precoding in millimeter wave systems with SAR constraints. With the increasing demand for higher data rates and more reliable service capabilities for wireless devices, wireless service providers are facing an unprecedented challenge to overcome a global bandwidth shortage. Early global activities on beyond fourth-generation (B4G) and fifth-generation (5G) wireless communication systems suggest that millimeter-wave (mmWave) frequencies are very promising for future wireless communication networks due to the massive amount of raw bandwidth and potential multigigabit-per-second (Gb s) data rates [1]?[3]. Both industry and academia have begun the exploration of the untapped mmWave frequency spectrum for future broadband mobile communication networks. In April 2014, the Brooklyn 5G Summit [4], sponsored by Nokia and the New York University (NYU) WIRELESS research center, drew global attention to mmWave communications and channel modeling. In July 2014, the IEEE 802.11 next-generation 60-GHz study group was formed to increase the data rates to over 20 Gb s in the unlicensed 60-GHz frequency band while maintaining backward compatibility with the emerging IEEE 802.11ad wireless local area network (WLAN) standard [5].