A High Altitude Platform Station (HAPS) can facilitate high-speed data communication over wide areas using high-power line-of-sight communication; however, it can significantly interfere with existing systems. Given spectrum sharing with existing systems, the HAPS transmission power must be adjusted to satisfy the interference requirement for incumbent protection. However, excessive transmission power reduction can lead to severe degradation of the HAPS coverage. To solve this problem, we propose a multi-agent Deep Q-learning (DQL)-based transmission power control algorithm to minimize the outage probability of the HAPS downlink while satisfying the interference requirement of an interfered system. In addition, a double DQL (DDQL) is developed to prevent the potential risk of action-value overestimation from the DQL. With a proper state, reward, and training process, all agents cooperatively learn a power control policy for achieving a near-optimal solution. The proposed DQL power control algorithm performs equal or close to the optimal exhaustive search algorithm for varying positions of the interfered system. The proposed DQL and DDQL power control yields the same performance, which indicates that the actional value overestimation does not adversely affect the quality of the learned policy.

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The wireless power transfer (WPT) transmitter (Tx) coil and near field communication (NFC) Tx coil are combined in one transmitter. The coil system consists of an NFC Tx coil and a WPT coil system that includes an A4WP Tx coil and an A4WP receiver (Rx) coil. The WPT coil system uses a magnetic resonance method. A4WP coils are tuned to resonate at 6.78 MHz. The NFC Tx coil is tuned to resonate at 13.56 MHz and positioned between the A4WP Tx and Rx coils. Moving the position of NFC Tx coil near the A4WP Tx coil, interference phenomena among coils are investigated and changes of WPT efficiencies are measured. Optimal placements of the NFC Tx coil that minimise the loss of WPT efficiency are determined based on the analysis data.

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A transmitter (Tx) coil system without ferrite was designed and fabricated for use in wireless power transfer (WPT) based on magnetic induction. The Tx coil system consists of an active coil, which is directly connected to the source, and a parasitic coil, which replaces the ferrite. The effects of the parasitic coil parameters, i.e. size, number of turns, and distance from the active coil, on the WPT performance were investigated in terms of the utility value, which was developed based on the power transmission efficiency and shielding effectiveness. The proposed Tx coil system was fabricated, and its performance was measured. The measured results show that the proposed Tx coil system performs better than a conventional Tx coil in terms of the utility value.