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In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a...
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... (18) where is the displacement transformed to a plane normal to and centered on antenna boresight, as shown in Fig. 6 ( 19) The pointing angles and subtended angles for each cell are, thus, a function of cell coordinates and dimensions and only, and may hence be rapidly generated on changing HAP height or cell width . Let and be the indices for the curve fits of the form in (1) for an elliptic beam, fitted to optimize directivity at the cell edges and ...
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... We can consider a hexagonal antenna phased array structure, illuminating 7 cells according to the 3GPP/ITU model [23], where each beam has 65° half-power beam width covering a 100 km-radius cell with a maximum gain of about 7.8 dBi [23]. The HAPS antenna radiation pattern mask for a beam can be specified as follows [24]: ...
... We can consider the antenna roll-off factor nH ≈ 6 to meet our directivity and beamwidth requirements, as detailed above. Much larger nH values are also used in [24]. ...
... 2) HAP/Satellite Antenna Pattern: For HAP and satellite, multi-beam antennas instead of uniform planar array antennas are considered, as uniform planar array configuration requires the design of a precoding matrix which is beyond the scope of this paper. It is assumed that each cell is served by one main beam [29], [30]. The following normalized antenna x gain pattern of one beam, x ∈ {h, s}, corresponding to a typical reflector antenna with a circular aperture with a radius of 10 wavelengths, is considered [27] ...
... Hence, the effect of interference power on the network is affected by P interf due to the fact that each potential interferer is modeled as a Bernoulli random variable with a probability of P interf . We also assume that the G2H and the G2S links are interference-free, while the interference on H2A/S2A links is due to the side lobes of HAP/satellite's antenna overlapping with the main lobes [29], [30]. ...
Aerial vehicles (AVs) such as electric vertical take-off and landing (eVTOL) aircraft make aerial passenger transportation a reality in urban environments. However, their communication connectivity is still under research to realize their safe and full-scale operation. This paper envisages a multi-connectivity (MC) enabled aerial network to provide ubiquitous and reliable service to AVs. Vertical heterogeneous networks with direct air-to-ground (DA2G) and air-to-air (A2A) communication, high altitude platforms (HAPs), and low Earth orbit (LEO) satellites are considered. We evaluate the end-to-end (E2E) multi-hop reliability and network availability of the downlink of AVs for remote piloting scenarios, and control/telemetry traffic. Command and control (C2) connectivity service requires ultra-reliable and low-latency communication (URLLC), therefore we analyse E2E reliability and latency under the finite blocklength (FBL) regime. We explore how different MC options satisfy the demanding E2E connectivity requirements taking into account antenna radiation patterns and unreliable backhaul links. Since providing seamless connectivity to AVs is very challenging due to the line-of-sight (LoS) interference and reduced gains of downtilt ground base station (BS) antennas, we use coordinated multi-point (CoMP) among ground BSs to alleviate the inter-cell interference. Furthermore, we solve an optimization problem to select the best MC path under the quality of service (QoS) constraints. We maximize spectral efficiency (SE) to specify the optimum MC path with the minimum number of required links. Based on the simulation results, we find out that even with very efficient interference mitigation, MC is the key enabler for safe remote piloting operations.
... as the submatrixes of G t , which is the channel matrix of the HAPS's selected antennas and assigned users. Similar to [16] and [17], for the HAPS antenna, we use the aperture antenna model, in which the gain of the main lobe is obtained as: ...
... We consider Ap ef f = 1, and the roll-off factor value n is chosen to maximize the gain at the cell border. The side lobes are modelled by a flat level at −40 dB below peak directivity [16], [17]. Furthermore, we set ξ u = 0.99, which is suitable for pedestrian users. ...
Non-terrestrial base stations (NTBSs) must be employed for next-generation wireless networks to provide users with ubiquitous connectivity and a higher data rate. In vertical heterogeneous networks (VHetNets), associating users with either a terrestrial base station (TBS) or a NTBS to maximize the sum-rate of the network while accounting for the resource limitations that exist at the NTBS poses a challenge. Moreover, a practical user association method should be capable of working in a realistic situation in which instantaneous channel state information (CSI) is not available. To solve this problem, we propose a deep Q-learning (DQL) approach in which a satellite is our agent and schedules each user to a TBS or a high-altitude platform station (HAPS) in each time slot using the CSI of the previous time slot. The proposed method achieves nearly identical results as the exhaustive search action selection method. Furthermore, we investigate the effect of imperfect CSI and show our proposed method outperforms the convex optimization user association scheme in the presence of noisy CSI.
... Ideally, each beam with a steep roll-off illuminates its corresponding cell, ensuring that no power is delivered outside the cell boundaries. Unfortunately, due to the imperfect roll-off of practical antenna beams, inter-cell interference (ICI) is introduced, and is worsened by the limitations of the array beamforming technique [8]. Furthermore, as the elevation angle of beams referenced at boresight [9] reduces, the resulting cell footprints broaden, thereby increasing both cell overlap [10] and ICI. ...
Conventional coverage and capacity from a high altitude platform (HAP) over an extended coverage area suffer significantly from inter-cell interference (ICI), antenna beam broadening, and uneven cell loading, which results in poor edge performance. In this paper, we show how a single antenna array on a HAP can be used to mitigate against these and achieve ubiquitous coverage by forming two tiers of a homogeneous contiguous cellular structure. We propose separate algorithms that implement the two-tier architecture with many antenna beams, which are used to form cells, and associate users with an appropriate cell and tier. A user associates with the cell and tier, which offer the best carrier power-to-noise ratio (CNR) and carrier power-to-interference-plus-noise ratio (CINR) respectively. The performance of the architecture, which is evaluated using simulation, is compared with a typical one-tier architecture. The results show that the two-tier architecture achieves over 30% higher user throughput and enhances throughput fairness and edge-of-cell connectivity by centralising as many users as possible within cells compared to the typical one-tier architecture. These benefits are better exploited by ensuring spectrum orthogonality between the two tiers.
... He et al. [19] examined the swing state modeling of the cellular coverage geometry model and the influence of swing on handover. Many studies [11,[20][21][22][23][24][25][26][27][28] on antenna control of HAPS proposed employing antenna control methods to prevent interference between surrounding cells and HAPSs to alleviate the decrease in received signal power caused by HAPS shifting or rotation. Kenji et al. [20] proposed a beamforming method to reduce the impact of the degradation of system capacity caused by handover between two cells. ...
In this paper, we propose a novel Deep Reinforcement Learning Evolution Algorithm (DRLEA) method to control the antenna parameters of the High-Altitude Platform Station (HAPS) mobile to reduce the number of low-throughput users. Considering the random movement of the HAPS caused by the winds, the throughput of the users might decrease. Therefore, we propose a method that can dynamically adjust the antenna parameters based on the throughput of the users in the coverage area to reduce the number of low-throughput users by improving the users’ throughput. Different from other model-based reinforcement learning methods, such as the Deep Q Network (DQN), the proposed method combines the Evolution Algorithm (EA) with Reinforcement Learning (RL) to avoid the sub-optimal solutions in each state. Moreover, we consider non-uniform user distribution scenarios, which are common in the real world, rather than ideal uniform user distribution scenarios. To evaluate the proposed method, we do the simulations under four different real user distribution scenarios and compare the proposed method with the conventional EA and RL methods. The simulation results show that the proposed method effectively reduces the number of low throughput users after the HAPS moves.
... where θ is the angle with respect to antenna boresight, and J 1 (.) is the Bessel function of the first kind and first order. It is assumed that each cell is served by one main beam [16]. ...
... N i is the set of interfering nodes and, h xiy indicates the channel coefficient between the interfering node x i and node y. We assume that the G2H link is interference free, while the interference on H2A links is due to the side lobes of HAP's antenna overlapping the main lobes [16]. ...
Aerial vehicles (AVs) such as electric vertical take-off and landing (eVTOL) make aerial passenger transportation a reality in urban environments. However, their communication connectivity is still under research to realize their safe and full-scale operation, which requires stringent end-to-end (E2E) reliability and delay. In this paper, we evaluate reliability and delay for the downlink communication of AVs, i.e., remote piloting, control/telemetry traffic of AVs. We investigate direct air-to-ground (DA2G) and air-to-air (A2A) communication technologies, along with high altitude platforms (HAPs) to explore the conditions of how multi-connectivity (MC) options satisfy the demanding E2E connectivity requirements under backhaul link bottleneck. Our considered use case is ultra-reliable low-latency communication (URLLC) under the finite blocklength (FBL) regime due to the nature of downlink control communication to AVs. In our numerical study, we find that providing requirements by single connectivity to AVs is very challenging due to the line-of-sight (LoS) interference and reduced gains of downtilt ground base station (BS) antenna. We also find that even with very efficient interference mitigation, existing cellular networks designed for terrestrial users are not capable of meeting the URLLC requirements calling for MC solutions.
... where θ is the angle with respect to antenna boresight, and J 1 (.) is the Bessel function of the first kind and first order. It is assumed that each cell is served by one main beam [16]. ...
... N i is the set of interfering nodes and, h xiy indicates the channel coefficient between the interfering node x i and node y. We assume that the G2H link is interference free, while the interference on H2A links is due to the side lobes of HAP's antenna overlapping the main lobes [16]. ...
Aerial vehicles (AVs) such as electric vertical take-off and landing (eVTOL) make aerial passenger transportation a reality in urban environments. However, their communication connectivity is still under research to realize their safe and full-scale operation, which requires stringent end-to-end (E2E) reliability and delay. In this paper, we evaluate reliability and delay for the downlink communication of AVs, i.e., remote piloting, control/telemetry traffic of AVs. We investigate direct air-to-ground (DA2G) and air-to-air (A2A) communication technologies, along with high altitude platforms (HAPs) to explore the conditions of how multi-connectivity (MC) options satisfy the demanding E2E connectivity requirements under backhaul link bottleneck. Our considered use case is ultra-reliable low-latency communication (URLLC) under the finite blocklength (FBL) regime due to the nature of downlink control communication to AVs. In our numerical study, we find that providing requirements by single connectivity to AVs is very challenging due to the line-of-sight (LoS) interference and reduced gains of downtilt ground base station (BS) antenna. We also find that even with very efficient interference mitigation, existing cellular networks designed for terrestrial users are not capable of meeting the URLLC requirements calling for MC solutions.
... Proper beam pointing with an adequate antenna system and characteristics is necessary due to the imperfect roll-off of practical antenna beams, which introduces ICI that is worsened by beam-forming limitations [8], especially with inadequate beam pointing. This paper provides a framework for analysing HAP coverage extension and highlights the feasibility of delivering contiguous cellular coverage over an extended area using a HAP. ...
... A different set of average ASE is also obtained by evaluating (36) using numerical integration. The parameters in Table 2 and a 30 dB transmit antenna gain [8] at the boresight are used to simplify the integration and validate the derived expression (36). These average ASE values (i.e., lower limit, upper limit, and integral) are plotted against the distance of the cells from the SPP, as shown in Figure 11. ...
Interest in delivering cellular communication using a high-altitude platform (HAP) is increasing partly due to its wide coverage capability. In this paper, we formulate analytical expressions for estimating the area of a HAP beam footprint, average per-user capacity per cell, average spectral efficiency (SE) and average area spectral efficiency (ASE), which are relevant for radio network planning, especially within the context of HAP extended contiguous cellular coverage and capacity. To understand the practical implications, we propose an enhanced and validated recursive HAP antenna beam-pointing algorithm, which forms HAP cells over an extended service area while considering beam broadening and the degree of overlap between neighbouring beams. The performance of the extended contiguous cellular structure resulting from the algorithm is compared with other alternative schemes using the carrier-to-noise ratio (CNR) and carrier-to-interference-plus-noise ratio (CINR). Results show that there is a steep reduction in average ASE at the edge of coverage. The achievable coverage is limited by the minimum acceptable average ASE at the edge, among other factors. In addition, the results highlight that efficient beam management can be achieved using the enhanced and validated algorithm, which significantly improves user CNR, CINR, and coverage area compared with other benchmark schemes. A simulated annealing comparison verifies that such an algorithm is close to optimal.
... They propose that antennas for these kinds of applications should be aperture types with steep roll-off on main lobes and suppressed side lobes. The work of [16] investigates the impact of power roll-off on the performance of a 3G communication system from HAP. The paper shows how the most important factor to consider in designing a 3G system with HAP is the main lobe roll-off and beam shape. ...
Wireless communication technologies are rapidly being adopted and developed by countries all over the world as a strategy for sustaining a digital economy. This has proven very useful for economic recovery from the crises brought about by the COVID-19 pandemic of the year 2020. The latency and coverage area of a wireless network are two major areas that are always seeking improvement. The High Altitude Platform communication technology can provide improvement in speed and coverage area for 4G cellular systems. This work investigated the effect of positioning High Altitude Platforms on the latency and coverage of 4G cellular Systems. A quantitative approach was used in the methodology of this paper. A HAP model showing a single platform flying in a circular trajectory over Base Transceiver Stations BTSs and serving as a relay mobile station was presented. A detailed simulation algorithm for the HAP and results for the simulation were given. Results showed that using the HAP as a relay mobile station in a network can give a latency reduction of up to 58.9%. Also, the altitude of the HAP directly affects the angle of reception which was found to improve the coverage.
... It gives up to about 140 thousand square kilometers [1] High Altitude Platforms are said to be radio stations that are positioned to operate in the stratospheric layer of the atmosphere. The altitude lies between 17km and 22km [7][8][9][10]. The concern of radio Engineers in the channel design is to design a channel model that will depict the signal power level as it propagates in the operating environment. ...
... Where: = Received frequency in GHz, the indicates, the direction of the motion, either moving toward each other or away from each other. Now we can substitute equation (7) into equation (8) to have equation (9) as follows: (9) Equation (9) can further be simplified to (10) the free space model is given by the following equation: ...
In this paper, we investigated the effect of different channel propagation characteristics on the performance of 4G systems from high altitude platforms (HAPs). The use of High-Altitude Platforms for communication purpose in the past focused mostly on the assumption that the platform is quasi stationary. The technical limitation of the assumption was that of ensuring stability in the positioning of the platform in space. The use of antenna steering and other approaches were proposed as a solution to the said problem. In this paper, we proposed a channel model which account for the motion of the platform. This was done by investigating the effect of Doppler shift on the carrier frequency as the signals propagate between the transmitter and receiver while the High-Altitude Platform is in motion. The basic free space model was used and subjected to the frequency variation caused by the continuous random shift due to the motion of the HAPs. The trajectory path greatly affects the system performance. A trajectory of 30km, 100km and 500km radii were simulated. An acute elevation angle was used in the simulation. The proposed model was also compared to two other channel models to illustrate its performance. The results show that the proposed model behave similar to the existing models except at base station ID 35 and 45 where the highest deviation of 20dBm was observed. Other stations that deviated were less than 2dBm.
