This paper proposes an internetwork interference coordination method using protected bands in the downlink of a network where high altitude platform station (HAPS) and terrestrial base stations (TBSs) coexist. When HAPS and TBS share the same transmission band, interference between them degrades the throughput for users, especially at cell edges. When the overall system bandwidth is divided into two non-overlapping bands, where HAPS and TBS use each of these bands, internetwork interference is avoided. However, this reduces the transmission bandwidth HAPS and TBS use, degrading the throughput of cell-interior users. To address this problem, the proposed method divides the overall system band into three parts. The first is a shared band used by both HAPS and TBS, and the other two are protected bands prepared exclusively for HAPS and TBS. By lowering the transmission power at the protected band of non-protected base stations, internetwork interference at the protected band of the target base station is mitigated while avoiding bandwidth loss in the conventional methods. We quantitatively demonstrate the improvement in system throughput achieved by the proposed method through computer simulations.

This paper proposes an autonomous decentralized user association method for the networks where the high-altitude platform station (HAPS) and conventional terrestrial base stations (BSs) are operated in the same coverage area. The throughput satisfaction rate of each user is defined as the ratio of the actual throughput to the target throughput. The purpose of the proposed method is to maximize the system-level throughput satisfaction rate, which is defined as a generalized mean of the throughput satisfaction rates of all users in the system coverage. The proposed method achieves optimal user association by iteratively performing an autonomous decentralized process that does not require complex cooperation among HAPS and terrestrial BSs. Computer simulation results show that the proposed method can increase the system-level throughput satisfaction rate compared to the conventional cell range expansion (CRE) method and that this increase is particularly significant when fairness among users in terms of the throughput satisfaction rate is emphasized.

High-altitude platform stations (HAPSs) using broad-band millimeter waves promise to enable the timely provisioning of the required high-speed large-capacity access in various locations including mountainous areas, air, and sea. Since no radio propagation measurements from the stratosphere to the ground have been conducted in the 38 GHz band, it is necessary to clarify the characteristics of radio propagation to realize the HAPS broadband system. In this paper, we report the world's first measurement of 38 GHz radio propagation from the lower stratosphere using a high-altitude aircraft, which was conducted in an environment closely similar to real HAPS operations. We present an evaluation of radio propagation characteristics under various elevation angles and weather conditions, as well as the influence of aircraft turning on radio propagation. Experimental results show that it is possible to apply Recommendations of the International Telecommunication Union Radiocommunication Sector (ITU- R) on attenuation values due to weather conditions for terrestrial radio links and satellite communication links to the stratospheric radio propagation environment under the influence of aircraft turning.

High-altitude platform stations (HAPSs) are promising to actualize extreme coverage extension from the stratosphere whereby mobile communications can be made available in various locations including mountainous areas, air, and sea. In particular, a fixed communications system for HAPS that uses the broadband millimeter-wave band will enable the provision of high-capacity communications infrastructure for many types of use cases such as high-capacity backhaul and industrial communications. However, the propagation delay is longer than that for ground systems, and processing delays caused by the HAPS stations and other devices are cumulative. Therefore, the system design must take these delays into account when implementing a network using HAPS. In this paper, to investigate the delay requirements in a fixed communications system for HAPS, we verify the transmission characteristics between a core network and a set of user equipment according to the insertion delay using a delay generator to emulate the delay caused by the HAPS and other system configurations. Up to now no transmission experiments have been reported that evaluate the impact of network latency on the communications quality in a fixed communications system for HAPS. Experimental results show that in the non-standalone 5th generation device environment used in this experiment, one-way delays of up to approximately 90 ms are acceptable, and that the observed communications performance is sufficient for the length of delay expected in a real-world environment.

Non-terrestrial network (NTN) is an important technique to provide extreme coverage towards 5G advanced and 6G. High-altitude-platform-station (HAPS), as one key factor in NTN, is attracting a lot of attentions. To achieve better resource utilization and performance, a unified design for integrated HAPS-Terrestrial networks is necessary, where the interference among these two systems may be important. Current methods usually consider fixed resource allocation among the two systems without considering the distribution of traffic load and hence have low resource utilization. In practice, the traffic load may change dynamically or semi-statically due to the wide coverage in HAPS, which should be considered in the design of integrated HAPS-terrestrial systems. In this paper, we proposed an interference coordination method based on the distribution of traffic load as well as the deployment of HAPS and terrestrial networks. The evaluation results show that the proposed method achieves higher throughput than existing fixed resource allocation method.

Because communications in the future will be as commonplace as the air around us and as important a lifeline as power and water or even more so, the Fifth Generation (5G) Evolution and Sixth Generation (6G) mobile communications systems aim ultimately to expand coverage so that mobile services are available ubiquitously. Towards that goal, we present a new architecture for 5G Evolution and 6G that integrates non-terrestrial networks (NTNs) with terrestrial networks (TNs). The proposed cooperative NTN and TN architecture is promising as a means for expanding coverage in the future because it enables improved cost efficiency by sharing equipment and conservation of frequency resources through shared frequencies. In addition, by making full use of wireless technologies such as handover, carrier aggregation, and dual connectivity between NTNs and TNs, users can connect to 5G Evolution and 6G networks anywhere without being aware of the connection destination. In this paper, we propose a cooperative architecture that focuses on the link between NTNs and TNs, and a cooperative configuration with a particular focus on high-altitude platform stations (HAPSs). Furthermore, we present a HAPS performance evaluation using a 6G system-level simulator developed as a stepping stone for actualizing HAPS technology.

LED-to-camera communication for smartphones promises to enable low-cost, small-size, and intuitive data access to Internet-of-things (IoT) devices. However, for fast and reliable communication under the rolling shutter effect, the packet losses caused by inter-frame gaps and frame drops must be dealt with. In this paper, we introduce LED-to-camera communication between a commercial smartphone and an IoT device with LED flashlight, where the user can intuitively acquire the desired data transmitted from the IoT device to the smartphone. Specifically, we present IoTorch, a fast and reliable LED-to-camera communication that efficiently prevents the packet losses. IoTorch consists of two core mechanisms: 1) a minimum-repetition one-way reliable transmission focusing on the periodicity of inter-frame gaps and 2) an acknowledgement mechanism to overcome frame drops by using a smartphone's built-in flash focusing on its delay characteristics. Additionally, we propose an optimization method to increase the throughput up to 2.92 kbps (i.e., 2.43 times faster than that of the state-of-the-art method that overcomes the inter-frame gaps). Furthermore, we realize a remote wake-up function by using the smartphone's flash as the data transmission trigger. To demonstrate the benefit of IoTorch, we present a sensor data viewer using Arduino and a smartphone console system on TelosB.

As we are surrounded by countless sensing devices, “intuitive” communication, which allows a user to directly obtain information from a device of interest to the user, is needed. Towards this, we present long-range flicker-free LED(lightemitting diode)-to-camera communication in which flickering can be prevented by the rapid switching of LED colors and information can be acquired from remote LEDs that appear as only a few pixels on a camera screen. In the rolling shutter system (typically used in smartphones), the timing of an exposure varies depending on the in-screen position. Hence, the imaging time interval of the LED deviates from the constant frame cycle owing to hand micromotion during communication. Under this condition, when imaging an LED that switches color rapidly, the color captured in the frame changes depending on the degree of hand micromotion. To solve this problem, we present differential color shift keying (DCSK) as a mechanism for correcting the influence of hand micromotion. Experimental results using multiple smartphone models show that the mechanism using DCSK achieves a communication range exceeding 3 m with a throughput of 60 bps from an LED with a diameter of 10 mm compared to several centimeters achieved by state-of-the-art studies.